PRINCIPLES    OF 
STRATIGRAPHY 


COMPANION  VOLUMES  OF  THIS  WORK 


North  American  Index  Fossils 

(Invertebrates) 

By  AMADEUS  W.  GRABAU,  Professor  of  Palaeontology 
in  Columbia  University,  and  HERVEY  WOODBURN  Sm- 
MER,  Assistant  Professor  of  Palaeontology  in  the  Massa- 
chusetts Institute  of  Technology.  2  vols.  Vol.  I,  1909, 
853  pages  and  1210  text  figures;  Vol.  II,  1910,  909 
pages  and  727  text  figures. 

The  volumes  contain  brief  descriptions  of  the  genera 
and  species  of  North  American  fossils  most  important 
for  the  determination  of  geological  horizons,  and  keys 
for  the  determination  of  the  genera.  They  are  suitable 
for  class  work  in  Palaeontology,  and  as  an  aid  to  the 
worker,  in  determining  his  fossils  and  finding  his  hori- 
zons. Owing  to  the  widely  scattered  condition  of  the 
literature,  a  comprehensive  treatise  like  the  present 
becomes  an  indispensable  adjunct  to  the  geologist's 
equipment.  The  Stratigraphic  Appendices,  the  Glos- 
sary of  Terms,  Directions  for  Collecting  and  Preserving 
Fossils,  and  the  extensive  bibliography  will  also  prove 
of  great  value. 

Large  octavo,  cloth  bound,  $12.00  net,  for  the  two 
volumes. 

In  preparation 

Manual  of  Stratigraphy 

By  PROFESSOR  AMADEUS  W.  GRABAU. 
A  discussion  of  the  geological  formations,  with  espe- 
cial reference  to  North  America  and  Europe.   An  appli- 
cation of  "Principles  of  Stratigraphy." 

A.  G.  SEILER  &  Co.,  1224  Amsterdam  Ave.,  New  York 


PRINCIPLES    OF 
STRATIGRAPHY 


BY 

AMADEUS  W.  GRABAU,  S.M.,  S.D. 

PROFESSOR   OF   PALAEONTOLOGY  IN   COLUMBIA   UNIVERSITY 


NEW  YORK 
A..  G.  SEILER  AND   COMPANY 

1913 


COPYRIGHT,  1913,  BY 
A.  W.  GRABAU 

All  rights  reserved 


ERRATA 

Part  changed  in  italic 

PAGE 

54,  7  lines  from  top,  change  Egglest^on  to  Egleston 

56,  1 6  lines  from  top,  change  Pumpelli  to  Pumpelly 

86,  7  lines  from  top,  change  silvestris  to  sylvestris 

90,  1 6  lines  from  top,  change  primogenius  to  prirm'genius 

97,  reference  96,  change  Tolman,  C.  E.,  to  Tolman,  C.  F. 

224,  26  lines  from  top,  change  Skagar  to  Skager 

236,  17  lines  from  top,  change  Barent  to  Barents 

268,  reference  66,  change  Sorbey  to  Sorby 

294,  23  lines  from  top,  change  Philipps  to  Phi//i£s 

296,  6  lines  from  top,  for  shatter  marks  put  chatter  marks 

299,  reference  23,  change  Philipps  to  Phillips 

310,  10  and  ii  lines  from  bottom,  change  Abyssolyth  to  Abyssoh'th 

377,  14  lines  from  top,  change  Pterigotus  to  Pterygotus 

392,  4  lines  from  top,  change  Woods  Holl  to  Woods  Hole 

474,  15  lines  from  bottom,  change  Cymapolia  to  Cymopolia 

534,  4  lines  from  bottom,  change  Yantzi  to  Yangtse 

543,  5  and  7  lines  from  bottom,  change  Solefluction  to  Solifluction 

554,  7  lines  from  top,  change  Askabad  to  As&kabad 

591,  14  lines  from  bottom,  change  Molasse  to  Mo//asse 

614,  2  lines  from  bottom,  change  Dantzig  to  Dawzig 

639,  reference  45,  change  Philipps  to  Phillips 

684,  1 6  lines  from  bottom,  change  Reed  to  Reeds 

689,  reference  80,  change  Reed  to  Reeds 

743,  3  lines  from  top,  initial  letter  c  to  be  capital  C 

830,  3  lines  from  top,  change  Chonoplain  to  conoplain 

893,  bottom  line,  change  Equador  to  Ecuador 

905,  4  lines  from  bottom,  change  R.  D.  Chamberlin  to  R.  T.  Chamberlin 

941,  8  lines  from  bottom,  change  Dadoxylen  to  Dadoxylon 
1034,  4  lines  from  top,  change  Bothryolepis  to  Bothn'olepis 
1038,  top  line,  change  ^Epyornys  to  .^Epyorms 
1051,  8  lines  from  top,  change  Orinoko  to  Orinoco 
1076,  7  lines  from  bottom,  change  Chili  to  Chile 
1086,  7  lines  from  bottom,  change  Valient  to  Valiant 
1096,  reference  22,  change  Roth,  I.  to  Roth,  /. 
1099,  Foot  note  I,  2  lines  from  bottom,  change  Philips  to  Philips 
1 1 08,  column  headed  Founder,  change  Conybear  to  Conybeare 


271728 


TO 

JOHANNES   WALTHER 

A    LEADER    IN    THE 

FIELDS    OF    KNOWLEDGE 

HEREIN    EXPLORED 


ACKNOWLEDGMENTS. 

To  the  many  among  my  colleagues  and  students  who  have  ren- 
dered assistance  in  the  production  of  this  work  I  zvish  to  tender 
heartiest  acknowledgments.  Of  those  whose  helpful  attitude  aided 
the  early  stages  of  my  labors  1  want  especially  to  mention  Alpheus 
Hyatt  and  Robert  Tracy  Jackson,  leaders  in  American  Paleon- 
tology, and  further,  William  Otis  Crosby,  Nathaniel  Southgate 
Shaler,  William  Morris  Davis  and  Jay  Backus  Woodworth,  masters 
all  of  inorganic  geology,  and  known  as  such  in  both  hemispheres. 
More  recently  my  colleagues  at  Columbia  University,  Professors 
James  F.  Kemp,  Douglas  Wilson  Johnson,  and  especially  Charles 
Peter  Berkey  have  put  me  under  obligations  by  helpful  suggestions 
and  criticisms.  My  graduate  students,  too,  during  the  last  ten  years 
have  aided  me  more  than  many  of  them  perhaps  realise,  for  only  a 
teacher  can  know  the  help  and  inspiration  that  comes  from  daily 
contact  with  eager  and,  above  all,  inquiring  minds,  such  as  our 
splendid  body  of  American  graduate  students  furnishes.  May  these 
pages  recall  to  them  the  many  spirited  discussions,  in  which  they 
usually  bore  their  part  so  zvell. 

To  one  of  them.  Miss  Marjorie  O'Connell,  A.M.,  instructor  in 
Geology  in  Adelphi  College,  Brooklyn,  my  special  thanks  are  due 
for  the  careful  and  critical  attention  given  for  a  period  of  a  full 
year  or  over  to  both  manuscript  and  proof,  and  to  the  verification  of 
the  literary  references,  and  the  endeavor,  by  patient  library  re- 
search, to  make  the  bibliographies  as  serviceable  as  possible.  To 
her  prolonged  search  of  the  literature  for  available  material,  I  also 
owe  many  important  references  which  I  would  otherwise  have 
missed.  And,  finally,  she  has  to  her  credit  the  very  complete  index 
of  this  volume.  One  other  I  may  mention  by  name,  Mr.  George  L. 
Cannon,  of  Denver,  Colorado,  whose  broad  conceptions  of  the  prin- 
ciples of  classification  have  rendered  our  discussions  highly  prof- 
itable. 

Finally,  I  cannot  forbear  to  mention  my  many  foreign  friends 
who,  by  word  of  mouth  or  by  their  writings,  have  led  me  into  paths 
replete  with  interest  and  profitable  adventure.  To  their  willingness 
to  guide  me  in  my  studies  within  their  home-lands,  and  to  discuss 
the  problems  which  interested  us  in  common,  I  owe  many  stimulat- 
ing hours.  Some,  like  Kittl  of  Vienna,  Koken  of  Tubingen,  and 
Holzapfel  of  Strassburg,  have  since  passed  away,  and  I  may  think 
of  them  here  in  sorrow.  To  the  many,  however,  who  still  hold 
high  the  torch  of  learning,  these  pages  bring  a  greeting  from  the 
land  which  has  yet  much  to  learn  from  the  culture,  and  the  devo- 
tion to  Pure  Science,  so  characteristic  of  the  European  leaders  in 
the  Earth  Sciences.  And  he,  to  whom  these  pages  are  inscribed, 
will  know  that  the  days  spent  in  his  inspiriting  companionship  in 
field  and  study  are  among  the  potent  influences  which  helped  to 
shape  the  character  of  this  book. 

vi 


PREFACE 

This  book  is  written  for  the  student  and  for  the  professional 
geologist.  It  aims  to  bring  together  those  facts  and  principles 
which  lie  at  the  foundation  of  all  our  attempts  to  interpret  the  his- 
tory of  the  earth  from  the  records  left  in  the  rocks.  Many  of 
these  facts  have  been  the  common  heritage  of  the  rising  genera- 
tion of  geologists,  but  many  more  have  been  buried  in  the  litera- 
ture of  the  science,  especially  the  works  of  foreign  investigators, 
and  so  have  generally  escaped  the  attention  of  the  student,  though 
familiar  to  the  specialist.  Heretofore  there  has  been  no  satisfac- 
tory comprehensive  treatise  on  lithogenesis  in  the  English  language, 
and  we  have  had  to  rely  upon  books  in  the  foreign  tongue  for  such 
summaries.  It  is  the  hope  of  the  author  that  the  present  work 
may,  in  a  measure,  supply  this  need. 

The  book  was  begun  more  than  fifteen  years  ago,  and  the  ma- 
terial here  incorporated  has  been  collected  and  sifted  during  this 
interval.  From  time  to  time  certain  phases  of  the  work  have  been 
published,  and  these  in  a  revised  form  have  been  included  in  the 
book.  The  first  of  these,  on  Marine  Bionomy,  appeared  in  1899, 
the  latest,  on  Ancient  Deltas,  in  1913.  Much  of  the  material  has, 
however,  not  appeared  in  print  before.  The  principles  and  data 
herein  treated  have  for  years  been  considered  and  discussed  in  a 
course  of  lectures  on  the  "Principles  of  Geology,"  given  jointly 
by  Professor  Berkey  and  myself  at  Columbia  University.  Some 
of  the  problems  which  have  taken  form  during  these  discussions 
have  been  chosen  as  subjects  for  more  extensive  investigations  by 
members  of  the  classes,  and  the  results  of  a  number  of  these  have 
already  appeared  in  print. 

My  own  interest  in  the  problems,  and  especially  the  principles 
of  Orogenesis  and  Geodynamics,  goes  back  to  the  days  when,  as  a 
student,  I  listened  to  the  illuminating  expositions  of  that  versatile 
and  accomplished  exponent  of  rational  geology,  Professor  William 
Otis  Crosby,  at  the  Massachusetts  Institute  of  Technology.  It  was 
at  this  time  also  that  Alpheus  Hyatt  and  the  other  eminent  natural- 
ists who  foregathered  at  the  fortnightly  meetings  of  the  Boston 
Society  of  Natural  History,  discussed  the  problems  of  Biogenesis, 
and  evolved  the  working  principles  which  have  since  guided  the  in- 

vii 


viii  PREFACE 

vestigations  of  the  "Hyatt  School"  of  Palaeontologists.  Later,  at 
Harvard  University,  under  the  leadership  of  the  unforgettable 
Shaler,  and  guided  by  that  keenest  of  analysts,  William  Morris 
Davis,  and  by  the  others  of  that  brilliant  coterie  of  Harvard  Ge- 
ologists and  Palaeontologists — Wolf,  Woodworth,  Jackson,  Ward, 
Daly,  Jaggar,  and  others — the  principles  of  Lithogenesis.  Glypto- 
genesis,  and  Biogenesis  formed  daily  topics  of  discussion,  and 
many  of  that  group  of  eager  students,  who  took  part  in  these  dis-, 
cussions,  here  laid  the  foundations  for  subsequent  achievements  in 
these  fields.  It  was  at  this  time  also  that  we  in  America  first  be- 
came acquainted  with  those  monumental  contributions  to  Litho- 
genesis and  Biogenesis,  that  had  been  and  were  being  made  by  the 
then  Haeckel  Professor  of  Geology  and  Palaeontology  at  Jena,  Dr. 
Johannes  Walther,  now  Professor  of  Geology  and  Palaeontology  at 
Halle.  The  Einleitung  in  die  Geologic  als  historische  IVissenschaft 
had  appeared  only  a  few  years  before,  and  its  influence  in  shaping 
geologic  thought;  especially  among  the  younger  men,  was  just  be- 
ginning to  be  felt.  The  Lithogenesis  der  Gegenwart  presented  such 
a  wealth  of  facts  concerning  the  origin  of  sedimentary  rocks,  that 
attention  began  to  be  diverted  from  the  problems  of  the  igneous 
rocks  which  had  heretofore  almost  exclusively  occupied  petrog- 
raphers,  and  "Sediment-Petrographie,"  or  the  petrography  of  the 
sedimentary  rocks,  attracted  more  and  more  of  the  younger  geolo- 
gists, especially  in  Germany  and  France.  In  the  latter  country  the 
works  of  Cayeux  and  Thoulet  led  the  way,  while  in  Britain  Mackie 
and  Goodchild  applied  the  principles  of  eolian  deposition  to  the  in- 
terpretation of  British  strata,  and  Sorby,  Phillips  and  many  others 
accumulated  a  wealth  of  facts  and  inferences. 

It  was  at  this  period,  too,  that  the  attention  of  geologists  and 
especially  stratigraphers  was  first  seriously  directed  toward  the 
desert  regions  of  the  world  and  the  phenomena  of  extensive  sub- 
aerial  deposition.  Here,  again,  Walther  led  the  way  in  that  classic, 
Die  Denudation  in  der  Wiiste,  followed  in  1900  by  his  epoch-mak- 
ing book,  Das  Gesetz  der  Wilstenbildung,  which,  in  its  revised 
second  edition,  appeared  in  1912.  It  is,  of  course,  true,  that  impor- 
tant studies  of  desert  regions  were  made  earlier,  notably  those  of 
von  Zittel  on  the  Libyan  desert  (1883),  but  the  significance  of  the 
desert  deposits  in  terms  of  stratigraphy  was  first  fully  appreciated 
within  the  last  decade.  That  the  importance  of  the  desert  as  a 
geological  factor  has  become  widely  recognized,  is  shown  by  the 
numerous  recent  studies,  especially  those  on  the  Kalahari  by  Pas- 
sarge,  and  those  on  the  Asiatic  deserts,  by  Sven  Hedin,  Pumpelly, 
Huntington,  and  others. 


PREFACE  ix 

It  is  during  this  same  decade  that  the  Sciences  of  Glyptogenesis 
and  Geomorphology  have  come  into  being,  notably  through  the 
labors  of  Davis  in  America,  and  of  Suess  and  Penck  in  Europe. 
Suess's  Antlits  der  Erde  began  to  appear,  it  is  true,  in  1883,  but  it 
is  only  in  recent  years  that  this  work  has  been  readily  accessible  to 
most  American  students,  through  the  medium  of  the  English  trans- 
lation by  Sollas  and  Sollas  (1904-1909).  Penck's  Morphologic  der 
Erdoberflache  appeared  in  1894,  but  did  not  become  well  known 
in  this  country  until  much  later.  It  was,  however,  Davis's  publica- 
tions in  this  country,  chiefly  during  the  early  nineties  of  the  last 
century,  which  gave  the  great  impetus  to  the  study  of  land  forms, 
and  especially  of  the  influence  of  erosion  on  their  production.  The 
concept  of  the  peneplain,  of  the  cycle  of  erosion,  of  the  sequential 
development  of  rivers  and  erosion  forms  on  the  coastal  plain  and 
on  folded  strata,  and  others  chiefly  due  to  him,  have  become  of 
incalculable  value  to  the  stratigrapher.  The  more  recent  develop- 
ment of  the  idea  of  desert  planation  by  Passarge  and  Davis,  has 
opened  further  promising  fields  to  the  stratigrapher,  who  seeks  to 
interpret  the  record  in  the  strata  by  the  aid  of  modern  results 
achieved  by  universal  processes. 

The  science  of  earth  deformations,  or  Orogenesis,  also  received 
renewed  impetus,  during  the  last  decade,  in  the  work  of  Bailey 
Willis  in  this  country  (Mechanics  of  Appalachian  Structure,  1893), 
and  the  researches  of  the  European  geologists  on  the  deformations 
of  the  Alps  and  other  great  mountain  chains.  True,  this  field  had 
been  opened  up  in  a  masterful  way  by  Heim,  when  in  1878  he 
published  his  Mechanismus  der  Gebirgsbildung,  and  by  Suess  in  his 
earlier  studies,  but  such  work  was  of  the  nature  of  pioneer  investi- 
gations. In  the  Face  of  the  Earth,  too,  emphasis  is  laid  on  de- 
formation as  the  principal  agent  in  the  production  of  the  diversi- 
fied surface  features  of  the  earth. 

In  the  field  of  Correlative  Stratigraphy  the  past  decade  has  like- 
wise seen  striking  advances.  The  publication  of  the  Lethaea  falls 
into  this  period,  and  so  .does  Marr's  comprehensive  little  volume, 
The  Principles  of  Stratigraphical  Geology,  not  to  mention  the  elab- 
orate recent  texts  of  Haug,  Kayser,  and  others,  or  the  numerous 
publications  of  Government  surveys,  and  of  individual  contributors. 
That  questions  of  correlation  have  reached  an  acute  stage  in 
American  Geology  is  manifested  by  such  recent  publications  as  the 
Outlines  of  Geological  History  and  Ulrich's  Revision  of  the  Palcco- 
zoic  Systems,  and  the  numerous  papers  accompanying  or  called 
forth  by  these.  Finally,  Palaeogeography,  as  a  science,  is  of  very 
recent  development,  most  of  the  works  of  importance  having  ap- 


x  PREFACE 

peared  in  the  last  five  years.  In  America  Schuchert  and  Bailey 
Willis  are  the  acknowledged  leaders,  while  in  Europe  many  able 
minds  have  -attacked  the  problems  of  Palaeogeography  from  all 
angles. 

It  is  thus  seen  that  this  book  was  conceived  during  the  period 
of  initial  reconstruction  of  our  attitude  toward  the  problems  of 
geology,  and  that  its  birth  and  growth  to  maturity  fell  into  that 
tumultuous  epoch  when  new  ideas  crowded  in  so  fast  that  the  task 
of  mastering  them  became  one  of  increasing  magnitude  and,  finally, 
of  almost  hopeless  complexity.  To  summarize  and  bring  together 
the  ideas  of  the  past  decade,  and  focus  them  upon  the  point  of  view 
here  essayed,  is  probably  beyond  the  power  of  one  individual. 
Nevertheless,  the  attempt  to  present  the  essentials  of  the  new  ge- 
ology for  the  benefit  of  those  who,  grown  up  with  it,  have  perhaps 
treated  it  with  the  lack  of  consideration  usually  bestowed  on  a  con- 
temporary, as  well  as  for  those  who  will  carry  on  the  work  during 
the  next  decade  or  two,  cannot  but  serve  a  useful  purpose.  May 
this  attempt  be  adjudged  'not  unworthy  of  its  predecessors,  nor 
unfit  to  stand  by  the  side  of  its  contemporaries. 

Scarsdale,  New  York, 
The  first  of  November, 
One  thousand  nine  hundred  and  thirteen. 


TABLE   OF   CONTENTS 


CHAPTER  I. 

PAGE 

GENERAL  INTRODUCTORY  CONSIDERATIONS : i 

The  Earth  as  a  Whole i 

I.  The  Atmosphere i 

II.  The  Hydrosphere 2 

Transgression  and  Regression 3 

The  Terrestrial  Part  of  the  Hydrosphere 4 

III.  The  Lithosphere 5 

The  Mean  Sphere  Level  (6) ;  The  Continental  Block  (7);  Isostacy 
(9);  Thickness  of  the  Earth's  Crust  (10);  Material  of  the 
Earth's  Crust  (12);  Deformation  of  the  Earth's  Crust  (Dias- 

trophism) 6-12 

IV.  The  Pyrosphere 12 

V.  The  Centrosphere 13 

Temperature  of  the  Earth's  Interior  (13);  Increase  of  Density.  .13-15 

VI.  The  Organic  or  Biosphere 16 

Interaction  of  the  Spheres 16 

Sculpturing  Processes 16 

Definition  and  Subdivision  of  Geology 19 

Table  of  Division  of  Geological  Time 22 

Bibliography  1 22 


A.  THE  ATMOSPHERE. 
CHAPTER  II. 

CONSTITUTION,   PHYSICAL   CHARACTERISTICS,   AND   MOVEMENTS   OF   THE 

ATMOSPHERE;  GEOLOGIC  WORK  OF  THE  ATMOSPHERE 24 

Composition  of  the  Atmosphere 24 

Nitrogen;  Oxygen;  Argon;  Carbon  Dioxide;  Water  Vapor  (25) ; 
Absolute  and  Relative  Humidity  (26) ;  Source  of  Water  Vapor 

(27) ;  Impurities 25-27 

Optical  Characters  of  the  Atmosphere 28 

Light;  Diffusion  of  Daylight 28 

xi 


xii  TABLE   OF    CONTENTS 

PAGE 

Temperature  of  the  Atmosphere 29 

Distribution  of  Heat  within  the  Earth's  Atmosphere 30 

Geological  Work  of  Heat  and  Cold— Changes  in  Temperature 

(31);  Insolation  and  Radiation;  Frost  Work 31-34 

Chemical  Work  of  the  Atmosphere 34 

Oxidation  (35) ;  Red  and  Yellow  Colors  of  Soil  due  to  Oxidation 

(36) ;  Oxidation  of  Organic  Compounds 35~37 

Hydration;  Kaolinization  (37);  Dehydration;  Carbonation 
(38);  Laterization  (39);  Influence  of  Temperature  on  Rock 

Decomposition 37~4O 

Movements  of  the  Atmosphere.     Winds 40 

Isobars;  Direction  of  Movements  of  the  Air  (41);  Influence  of 
Continents  on  Winds  (44);  Sea  Breezes;  Land  Breezes;  Mon- 
soons   41-45 

Cyclones  and  Anticyclones  (46) ;  Whirlwinds  and  Tornadoes 46-47 

The  Influence  of  Mountains  on  Winds  (47);  Mountain  and 
Valley  Winds  (50) ;  Velocities  of  Wind 47~5o 

Eolation  or  Mechanical  Work  of  the  Atmosphere 51 

Wind  Erosion  and  Translocation 52 

Corrasion  (52);  Facetted  Pebbles  (54);  Deflation  (55);  Character 
and  Amount  of  Deflational  Denudation  (57);  Distance  of  Eolian 
Transportation  (58);  Volume  of  Dust  Falls  (60);  Sorting  and 
Rounding  of  Sand  Grains  by  Wind 52-61 

Condensation  and  Precipitation  of  Atmospheric  Moisture 62 

Dew,  Frost,  Clouds  and  Fogs;  Rain,  Snow  and  Hail 62-63 

Amount  of  rainfall  (63);  Relation  of  Evaporation  to  Rain- 
fall (65);  Influence  of  Winds  and  Topography  on  Rainfall 
(66) ;  The  Equatorial  Belt  of  Calms  and  Variable  Winds 
(67);  Latitude  and  Precipitation;  Periodicity  of  Rainfall.  .63-71 

Electrical  Phenomena  of  the  Atmosphere 72 

Fulgurites 72 

Climate;  Climatic  Zones,  Present  and  Past 74 

Solar  Climates,  Climatic  Belts  or  Zones 74 

Physical  Climate 75 

I.  Marine  or  Oceanic  Climate;  2.  Coast  or  Littoral  Climate; 
3.  Interior  Continental  Climate;  4.  Desert  Climate;  5. 
Mountain  Climate 75~77 

Climatic  Provinces  (77) ;  Climatic  Types  based  on  Separate  Atmo- 
spheric Factors  and  on  Agents  (78);  Climatic  Zones  of  the  Past 
(78);  Neumayr's  Climatic  Zones  of  the  Jurassic  (79);  Discussion 
of  the  subject  of  Climatic  Zones 77~79 

Rhythm  of  Climatic  Changes  (82) ;  Indication  of  Climatic  Changes 
(83);  Topographic  Evidence  of  Change  of  Climate  (83);  Strati- 
graphic  Evidence  of  Change  of  Climate  (84);  Organic  Evidence 
of  Change  of  Climate  (85);  i.  Plants;  2.  Animals 82-87 

Displacement  of  the  Earth's  Axis  as  a  Cause  of  Climatic  Changes .       90 

Origin  of  the  Atmosphere 92 

Bibliography  II 92 


TABLE    OF    CONTENTS  xiii 

B.  THE  HYDROSPHERE. 
CHAPTER  III. 

PAGE 

MORPHOLOGY  AND  SUBDIVISION  OF  THE  HYDROSPHERE 99 

A.  The  Marine  Division  of  the  Hydrosphere 99 

Regional  Subdivisions  of  the  Sea 99 

I.  Intercontinental  Seas  or  Oceans 100 

Bathymetric  Zones  of  the  Sea  (too) ;  Conformation  of  the  Ocean 
Floor  (101);  Features  and  Extent  of  the  Continental  Shelves 
(103);  Table  Showing  Distribution  Area  and  Depth  of  the  Prin- 
cipal Continental  Shelves  (103);  Subordinate  Features  of  the 
Continental  Shelf  (104);  Features  of  the  Suboceanic  Elevations 
and  Depressions 100-105 

II.  Intracontinental  Seas 106 

A.  Independent  Seas  (107);  i.  The  Mediterraneans  (107);  Inter- 
oceanic   Mediterraneans   (109);    2.   Epicontinental  Seas  (109); 

B.  Dependent  Seas,  Funnel  Seas 107-1 12 

Summary  of  Classification 113 

B.  The  Continental  Division  of  the  Hydrosphere 115 

III.  Continental  Seas  or  Lakes 115 

Classification  of  Lakes  and  Lake  Basins.  .„.»..... 1 16 

Classification  of  Lake  Basins 1 16 

A.  Deformational  or  Tectonic  Basins 118 

B.  Constructional  Basins  (120);  Volcanic  Basins ;  Chemi- 
cal Basins;  Organic  Basins;  Detrital  Basins 120-121 

C.  Destruction^!    Basins    (122);    Volcanic;    Chemical; 
Fluviatile;  Glacial;  Deflation;  Artificial 122-123 

D.  Obstructional  or  Barrier  Basins  (124);  Tectonic;  Vol- 
canic; Chemical;  Ice;  Organic;  Detrital 124-126 

Classification  of  Lakes  as  a  Whole 128 

IV.  Rivers 129 

Simple  or  Monogene  Rivers 130 

I.  Consequent  Streams;  II.  Insequent  Streams;  III.  Over- 
flow Streams;  IV.  Glacial  Streams;  V.  Subterranean 
Streams , .  130-133 

Polygene  Rivers 133 

Relative  Ages  of  Rivers  and  River  Systems 135 

Aging  of  Rivers  by  Accident;  Revival  and  Rejuvenation 

of  Rivers I35~I37 

V.  Underground  Water  (Ground  Water) 138 

Classification  of  Ground  Water  (138);  General  Course  of 
Meteoric  Water  (139);  Porosity  of  .Rocks  (140);  The  Water 
Table;  Depth  and  Quantity  of  Ground  Water 138-141 

Bibliography  III 143 


xiv  TABLE    OF    CONTENTS 

CHAPTER  IV. 

PAGE 

COMPOSITION  AND  PHYSICAL  CHARACTERS  OF  THE  HYDROSPHERE 145 

Composition  of  the  Hydrosphere 145 

I.  Salinity  of  the  Sea 145 

Table  Showing  the  Salinity  of  the  Sea  (146);  Variation  in  the 
Distribution  of  the  Salt  Content  of  the  Oceans  and  Intra- 
continental  Seas  (149) ;  Variation  in  Salinity  in  Bay  of  Danzig 
(151);  Table  Showing  the  Bathymetric  Variations  of  Salinity 

in  the  Sea 146-152 

II.  Composition  of  Lake  Waters 154 

Table  of  Salinity  of  Various  Lakes  (154);  Table  Showing  Ver- 
tical Range  of  Salinity  in  Dead  Sea  (156);  Analyses  of  Types 
of  Lake  Water  (157);  Table  in  Percentage  of  Total  Solids  of 
Composition  of  Various  Types  of  Natural  Waters  (158); 
Composition  of  Saline  Lakes  in  Percentage  of  Total  Solids 
(159);  Table  of  Average  Composition  of  Lake  Waters.  — 154-161 

III.  Composition  of  River  Water 161 

Table  Showing  the  Amounts  in  Permille  of  the  Principal 
Elements  and  Compounds  occurring  in  Various  River  Waters 
(162);  Table  Showing  Salinity  of  other  Rivers  (162);  Table 
of  Total  Solids  carried  in  Solution  in  Tons  per  Year  (164); 
Table  Showing  the  Amounts  of  the  Different  Salts  carried  in 
Solution  in  one  Cubic  Mile  of  Average  River  Water 162-164 

IV.  Composition  of  Spring  Water 165 

Table  of  Composition  of  Rain  Water  near  London  (165); 
Impurities  in  Rain  Water;  Solids  in  Rain  Water  (166); 

Composition  of  Spring  Water  from  the  Sahara 165-167 

Classification  of  Natural  Waters;  Gases  and  Organic  Matter  in 

Natural  Waters 169 

Table  of  Analyses  of  Spring  and  Well  Waters  (170);  Com- 
position of  Dissolved  Air  in  Rain  Water  at  Different  Tem- 
peratures (170);  Gases  in  a  Liter  of  pure  Water 170-171 

Organic  Matter  (172);  Table  of  Organic  Matter  in  Various 

Streams  in  Percentage  of  the  Total  Solids 172-173 

Chemical  Work  of  the  Natural  Waters 174 

Solution;  Cementation;  Hydration;  Oxidation;  Carbonation. .  175-179 

Density  and  Specific  Gravity  of  the  Hydrosphere 179 

Variation  in  Osmotic  Pressure  in  the  Sea  Water 180 

Temperature  of  the  Hydrosphere 181 

Freezing  Point  of  Water;  Heat  Capacity  of  Water 181 

Warming  of  the  Water  Body;  Average  Surface  Tempera- 
ture; Vertical  variation  of  Temperature 182-183 

Temperature  of  the  Sea 184 

Horizontal  and  Vertical  Distribution  of  the  Temperature  in 
the  Three  Great  Oceans  (184);  Temperature  of  the  Mediter- 
raneans and  Epicontinental  Seas  Dependent  on  the  Large 
Oceans  (189);  Temperatures  of  Dependent  Seas  (191); 
Temperatures  of  the  Arctic  Ocean  and  its  Dependencies 
(192);  Mean  Temperatures  of  the  Oceans  and  Intraconti- 
nental  Seas;  Eutectic  Temperatures  (193);  Range  of  Tem- 
perature of  the  Oceans 184-194 


TABLE    OF    CONTENTS  xv 

PAGE 

Temperatures  of  the  Terrestrial  Waters 195 

Temperatures  of  Lakes,  etc.  (195);  Classification  of  Lakes 
According  to  Temperature  (196);  Freezing  of  Lakes  (197); 
Normal  and  Excessive  Temperatures  of  Streams  and  of 
Ground  Water  (199);  Freezing  of  Rivers;  Freezing  of 
Ground  Water  (200) ;  Mechanical  Work  of  Freezing  Ground 
Water  (200) ;  Thermal  Springs  (200) ;  Magmatic  or  Juvenile 

Waters 195-201 

Optics  of  the  Water . 204 

Bibliography  IV 206 

CHAPTER  V. 

MOVEMENTS  OF  THE  HYDROSPHERE  AND  THEIR  GEOLOGICAL  EFFECTS 209 

Waves 209 

Table  Showing  Relationships  Between  Wind  Velocities  and 
Wave  Height  (213);  Table  Showing  Relationship  Between 
Mean  Wave  and  Wind  Velocities  (214);  Relation  Between 
Length  and  Height  of  Wave  (214);  Classification  of  Waves 
(214);  The  Swell  or  Ground  Swell  (215);  Depth  of  Wave 
Activity  (216) ;  Waves  in  Shallow  Water  (217) ;  Destructive 
Work  of  Waves  (220) ;  Rounding  and  Sorting  of  Detritus 

by  Wave  Action 213-226 

Tides 226 

Comparison  of  Tides  and  Waves  (228);  Interference  of 
Tides;  Tidal  Scour  and  Transportation 228-231 

Marine  Currents 231 

Currents  of  the  Oceans  (231);  The  Atlantic  Ocean;  the  Arctic 
Ocean;  the  Pacific  Ocean;  the  Indian  Ocean 231-238 

Currents  in  Mediterraneans  and  Epicontinental  Seas 239 

Marine  Currents  in  Relation  to  Migration  and  Dispersal,  Past 
and  Present  (243);  Depth  of  Current  Action 243-244 

Lake  Currents 244 

River  Currents 244 

Velocities  of  River  Currents  (245);  Erosive  Power  of 
Rivers  (246);  Rate  of  Erosion;  Transporting  Power  of 
River  Currents 245-247 

Table  Showing  Transportation  of  Material  by  Rivers 
(248);  Table  of  Velocities  Required  to  stir  up  Bottom 
Material  (248) ;  Table  Showing  the  Size  of  Rock  Frag- 
ments Moved  by  Different  Velocities  of  Currents 248-249 

Sorting  Power  of  Rivers  (252) ;  Rounding  of  Sand  Grains. .  252-253 

Table  Showing  Coefficient  of  Psephicity  of  Minerals  in 
,                        Air  and  Water  (255) ;  Table  Showing  Rounding  of  Sands 
of    Moray  Firth   (256);    Table    Showing   Rounding  of 
Sands  of  Culbin  Dunes 255-256 

Movement  of  Underground  Waters 257 

The  Underflow  (258) ;  Rate  of  Flow  of  Underground  Water 
(259);  Table  Showing  Permeability  of  Various  Soils  (259); 
Pervious  and  Impervious  Strata  (260) ;  The  Deeper  Zones 
of  Flow 258-260 

Springs 261 


xvi  TABLE    OF    CONTENTS    , 

PAGE 

Water  in  the  Solid  Form 261 

Kinds  of  Movement  of  Solid  Water  (262);  Rate  of  Move- 
ment; Wasting  of  the  Glaciers;  Erosive  Work  of  Ice; 

Transportation  by  Ice 262-265 

Bibliography  V 265 

C.  THE  LITHOSPHERE. 
CHAPTER  VI. 

CLASSIFICATION  OF  THE  ROCKS  OF  THE  EARTH'S  CRUST 269 

Subdivision  of  rocks 269 

I.  The  Endogenetic  Rocks 271 

1.  The  Pyrogenic  or  Igneous  Rocks  (Pyroliths) 274 

Composition  Groups   (274);  Textural  Groups   (275);  Water 

and  Ice  as  Igneous  Rocks  (278);  Metamorphic  Derivatives 

of  Igneous  Rocks 274-279 

2.  The  Atmogenic  or  Atmospheric  Rocks  (Atmoliths) 279 

I.  Snow;  II.  Firn  or  Neve;  III.  Snow  Ice  or  Glacial  Ice. .  279 

3.  The  Hydrogenic  Rocks  (Hydroliths) 280 

4.  The  Biogenic  Rocks  (Bioliths) 280 

Caustobioliths  (281);  Sapropelites,  Humus  and  Humuliths, 

Liptobioliths 281 

Subdivision  of  Hydrogenic  and  Biogenic  Rocks 281 

Textures  of  Amorphous  Hydrogenics  (281);  Textures  of 
Biogenic  Rocks  (281);  Table  of  the  Principal  Types  of 

Hydrogenic  and  Biogenic  Rocks 281-282 

Spherytes,  Granulytes  and  Pulverytes , 283 

Ooliths,  Pisoliths,  Rogensteine,  etc 283 

II.  The  Exogenetic"or  Clastic  Rocks 284 

Textural  Groups  (285) ;  Size  of  Grain  (286) ;  Table  of  Stand- 
ard Sizes  of  Rock  Fragments  (287);  Types  of  Sands  Based  on 

Origin  (288);  Composition  of  Clastic  Rocks 285-290 

i.  The  Pyroclastics  (290);  2.  The  Autoclastics  (291);  3.  The 
Atmoclastics  (292);  4.  The  Anemoclastics  (293);  5.  The  Hy- 

droclastics  (294);  6.  The  Bioclastics 290-296 

Summary  of  "Sedimentary  Rocks " 296 

The  Cosmoclastic  Rocks 297 

Special  Rock  Terms 297 

Rock  Terms  Emphasizing  Composition  (297);  Autoch- 
thonous and  Allochthonous  Deposits 297-298 

Bibliography  VI 298 

CHAPTER  VII. 
STRUCTURAL    OR    TECTONIC    FEATURES    OF    ROCK    MASSES.    ORIGINAL 

STRUCTURES  AND  LITHOGENESIS  OF  THE  PYROGENIC  ROCKS 301 

The  Pyrogenic  Rocks • 301 

Intrusive  Igneous  Bodies 302 

Igneous  Versus  Sedimentary  Contact  (309);  Contacts  of 
subterranean  or  abyssal  masses  (309);  Contacts  of  hypa- 
byssal  or  injected  masses 309-310 


TABLE    OF    CONTENTS  xvii 

PAGE 

Effusive  Igneous  Masses 311 

Features  of  Basal  Contact  of  Lava  Sheets  (311);  Features 
of  Upper  Surfaces  of  Lava  Flows  (313);    i.  Basic  Lavas; 

2.  Acid  Lavas 311-317 

Minor  Structural  Characters   of  Volcanic  Rocks 317 

Flow  Structure;  Stratification  of  Flows;  Columnar  Struc- 
ture; Variation  in  Grain 317-319 

Bibliography  VII 320 


CHAPTER  VIII. 

STRUCTURE  AND  LITHOGENESIS  OF  THE  ATMOGENIC  ROCKS 322 

Snow 322 

Height  of  Snow-line  (322) ;  Altitude  of  Snowfall  and  of  Snow- 
line  (323) ;  Conversion  of  Snow  into  Ice 322-323 

Glaciers  (Kinds  and  Character) 323 

Stratification  of  Ice  (326) ;  Shear  Zones  and  Flow  Struc- 
ture  326-327 

Bibliography  VIII 327 


CHAPTER  IX. 

ORIGINAL  STRUCTURES  AND  LITHOGENESIS  OF  THE  TRUE  AQUEOUS  OR  HY- 

DROGENIC  ROCKS 329 

Oceanic  Precipitates 330 

Chemical  Deposits  of  the  Deep  Sea 330 

Chemical  Lime  and  Magnesia  Deposits 33 1 

Chemical  Precipitation  of  Carbonate  of  Lime  and  Magnesia  in 
the  Ocean  (331);  Table  Showing  Proportion  of  Dolomites  to 
Limestones  in  the  Geological  Series  (333) ;  Oolites  and  Pisolites 

of  Chemical  or  purely  Hydrogenic  Origin 331-336 

Deposits  in  Enclosed  or  Nearly  Enclosed  Basins 338 

Chemical  Limestone  Deposits  of  Lakes  in  Arid  Regions  (338); 

Older  Deposits  of  this  Type 338-341 

Limestone  Deposits  from  Rivers 341 

Deposits  of  Lime  by  Springs  (342);' The  Onyx  Marble 342-344 

Underground  Deposits  of  Lime 345 

Method  of  Deposition  of  Lime  from  Solution 346 

Deposits  of  Marine  Gypsum  and  Salt 347 

Experiments  of  Usiglio  (348) ;  Table  Showing  the  Order  of 

Separation  of  Salts  from  Sea  Water 348-349 

The  Bar  Theory  of  Ochsenius  (350);  The  Bitter  Lakes  of 

Suez  an  Example  (352);  The  Karabugas  Gulf 350-354 

Natural  Salt  Pans  (354);  Evaporation  of  Cut-offs  from  the 

Sea 354-355 

Non-calcareous  Terrestrial  Precipitates 356 

Salt  Lakes  and  Salinas  (356);  The  "Salitrales"  of  Patagonia 356-360 

Deposits  of  Sodium  Sulphate  and  Carbonate 361 


xviii  TABLE    OF    CONTENTS 


Table  Showing  Successive  Crystallization  resulting  from 

the  Evaporation  of  the  Waters  of  Owens  Lake 362 

Borax  and  Borates  (363) ;  Deposits  of  Nitrates  (364) ;  Other  Min- 
erals Deposited  under  Desert  Climates 363-365 

Origin  of  the  Saline  Deposits 365 

Sources  of  Sodium  Chloride  (366);  Marine;  Leaching  of  Salt 
from  Older  Formations  and  its  Segregation  (366);  Sources  of 
Calcium  Sulphate  (368);  Sources  of  Alkaline  Carbonates 
(369);  Sources  of  Boric  Acid  and  Borates  and  of  Nitrates.  .366-370 

Summary 370 

Ancient  Salt  Deposits 37 l 

The  Stassfurt  Salts  (371);  The  Siluric  Salts  of  North  America 

(376) ;  The  Salt  Domes 37i~379 

Bibliography  IX 380 

CHAPTER  X. 
MORPHOLOGY  AND  LITHOGENESIS  OF  THE  TRUE  ORGANIC  OR  BIOGENIC 

ROCKS.     ZOOGENIC  DEPOSITS 384 

Coral  and  Other  Reefs 3$5 

Characters  and  Development  of  Modern  Coral  Reefs 386 

Types  of  Modern  Coral  Reefs 386 

Factors  Limiting  the  Distribution  of  Modern  Coral  Reefs  (389) ; 
Depth  of  Water;  Intensity  of  Light;  Temperature;  Other  Phys- 
ical Conditions 389-392 

Composition  and  Structure  of  the  Reef  (393);  Materials  Com- 
posing the  Reef  (393) ;  Structure  of  Coral  Reefs  (396) ;  Cavernous 
character  of  reefs  (401);  Characters  of  Epicontincntal  reefs.  .393-402 
Theories  of  Origin  of  Types  of  Coral  Reefs  (407);  Subsidence 
Theory  of  Darwin  (408);  Evidence  of  Subsidence  (409);  The 
Spreading  Ring  Theory  of  Murray  (410);  Multiple  Origin  of 

Reefs 407-41 1 

Rate  of  Growth  of  Reef  Organisms 411 

Compacting  Agents  of  the  Coral  Reef 413 

Destruction  of  the  Coral  Reefs  (414);    Formation    of    Coral    and 

other  Organic  Lime-Sand  and  Mud 414 

Fossil  Coral  and  Stromatopora  Reefs 417 

Cambric  and  Pre-Cambric  (417);  Ordovicic 417-418 

Siluric  (418) ;  Niagaran  Reefs  of  Wisconsin  (418) ;  Siluric  Reefs  of 

Gotland  (420);  Upper  Siluric  Reefs  of  North  America 418-422 

Devonic  Coral  Reefs  (423) ;  Lower  Devonic  Reefs  of  Konjepruss, 
Bohemia  (423) ;  The  Onondaga  Reefs  of  New  York  (424) ;  Middle 
Devonic  Reefs  of  Michigan  (426) ;  Devonic  Reefs  of  the  Attawa- 
pishkat  River,  Canada  (430) ;  Middle  Devonic  Reefs  of  the  Eifel 

and  Belgium 423-430 

Mississippi  Reefs  (431);  Mississippi  Reefs  of  Belgium;  Missis- 

sippic  Reefs  of  Great  Britain 43i~432 

Fossil  Reefs  of  Bryozoa  and  other  Organisms 433 

Bryozoan  Reefs  of  the  German  Zechstein  (433) ;  The  Triassic 
Reefs  of  the  Tyrol  (434) ;  The  Jurassic  Reefs  of  Solnhofen  (437) ; 
The  Sponge  Reefs  of  the  Swabian  Jura  (442);  Miocenic  Reefs  of 
the  Austro-Russian  Border  (442);  Pliocenic  Bryozoa  Reefs  of 
Kertch 433~443 


TABLE   OF    CONTENTS  xix 

PAGE 

Bedded  Reefs 444 

Loss  of  Structure  through  Alteration  of  Reef  Limestones 445 

Ball-stone  Reefs 446 

Structures  Formed  by  the  Growth  of  Shell  Colonies 447 

Tepee  Buttes  (447) ;  Other  Examples 447-449 

Bedded  Zoogenic  Deposits 449 

Crinoidal  Limestones" (449) ;  Shell  Limestones  (449) ;  Calcareous 
and  Siliceous  Oozes . : 449-450 

1.  The  Calcareous  Oozes  (450);   Recent  Foraminiferal  Oozes 
(450);   Fossil   Foraminiferal   Oozes  (453);   Zoogenic   Oolites 
(455);  Recent  Pteropod  Oozes;  Fossil  Pteropod  Oozes ;  Ento- 
mostracan  Oozes;  Coccolith  and  Rhabdolith  Oozes 450-456 

2.  The  Siliceous  Oozes  (457);   Radiolarian  Oozes  (457);  The 
Jurassic  Radiolarite  of  the  Alps  (459) ;  Recent  Diatomaceous 
Oozes  (460) ;  Fossil  Diatomaceous  Earths  of  both  Fresh  and 
Salt  Water  Origin 457-461 

Phosphate  Deposits;  Guano 461 

Bibliography  X 461 

CHAPTER  XI. 

CHARACTER  AND  LITHOGENESIS  OF  ORGANIC  OR  BIOGENIC  ROCKS  (CON- 
TINUED).    PHYTOGENIC  DEPOSITS. 467 

Acaustophytoliths '. 467 

Deposits  formed  by  Lime-Secreting  Algae 467 

Modern  Marine  Forms  (467) ;  Order  Cyanophyceae  or  Blue-Green 
Algae  (467);  Phytogenic  Oolites  (467);  Order  Chlorophyceae 
or  Green  Algae  (469) ;  Order  Phaeophyceae  or  Brown  Algae  (470) ; 
Order  Rhodophyceae  or  Floridae;  Red  Algae  (470);  Lime-secret- 
ing Algae  of  Fresh  Water 467-471 

Fossil  Phytoliths  of  Algous  Origin 471 

Fossil   Ooliths  (471);    Rogensteine   of   the   Bunter   Sandstein 

(472);  Alteration  of  Oolites 471-473 

Sphasrocodium    and    Girvanella    Deposits;    Fossil    Nullipores; 

Fossil  Chara 474-475 

Travertine  and  Siliceous  Sinter  formed  by  Algae  in  Hot  Springs . . .     475 

Method  of  Lime  Deposition  by  Plants 475 

Separation  of  Siliceous  Sinter  by  Plants 476 

Vegetal  Deposits  (Caustophytoliths) 478 

Petrographical  Types  of  Vegetal  Deposits 478 

Sapropeliths  (478);  Petroleum  (480);  Sapanthraconyte  or  Cannel 
Coal  (481);   Jet  (482);    Black  Shales  (483);    Sapropelcalcilyths 

Sapropelsilicilyth  and  Sapropel-ferrilyths 480-484 

Recent  Humuliths 485 

Marine  Marshes  (487);  Conversion  of  Salt  Peat  into  Coal 

(493) ;  Mangrove  Marshes 487-494 

Fresh  Water  Swamps  (494);  Lake  Swamps  (495);  Rivers  and 

Estuarine  Swamps 494~497 

Terrestrial  Bogs  (501);  Forest  Moors;  Upland  Bogs  or  High 
Moors;  the  Arctic  Tundras 501-507 


xx  TABLE    OF    CONTENTS 

PAGE 

Peat  in  the  Tropics 509 

Fossil  Humuliths 510 

Lignite;  Brown  coal;  Bituminous  Coal;  Anthracite;  Graph- 
ite  510-511 

Ancient  Moors  (511);  Black  Soil  and  Shales  of  Humulithic 
Origin  (513);  Burial  of  Peat  Deposits  (514);  Liptobioliths .  .511-517 
Allochthonous  Vegetal  Deposits  (518);  Marine  Vegetal  Deposits     518 
Bibliography  XI 519 

CHAPTER  XII. 

ORIGINAL  CHARACTERS^  AND  LITHOGENESIS  OF  THE  EXOGENETIC  ROCKS. 

THE  PYROCLASTICS  AND  THE  AUTOCLASTICS 524 

Pyroclastic  Rocks 524 

Modern  Pyroclastics  (524) ;  Organic  Remains  of  Modern  Pyro- 

clastics  (525);  Older  Pyroclastic  Deposits 524-525 

Autoclastic'JRocks 527 

Classification  of  Autoclastic  Rocks 527 

Fault  Breccias  (528);  Intraformational  Breccias  (529);  Fractur- 
ing and  Piling  up  of  Material;  Distortion  of  Layers  in  Gliding.  .528-530 
Glacial  Deposits   (531);   Character  of  Modern  and  Pleistocenic 
Glacial    Deposits    (531);    Ancient   Glacial   Deposits    (534);   The 
Pre-Cambric  Tillite  of  Canada;   Cambric  Glacial  Deposits;  the 

Permic  Glacial  Deposits '.  .  531-535 

Endolithic  Brecciation 536 

Bibliography  XII 537 


CHAPTER  XIII. 

ORIGINAL  STRUCTURE  AND  LITHOGENESIS  OF  THE  ATMOCLASTIC  AND  ANEMO- 
CLASTIC  ROCKS 540 

A.  Atmoclastic  Rocks 540 

Characteristics  and  Occurrence  of  Modern  Atmoclastic  Forma- 
tions      541 

Texture  of  Atmoclastic  Rocks  (542) ;  Movement  of  Atmoclastic 
Material  (543);  Slow  Movements  of  Rock  and  Soil;  Rock  and 
Soil  Creep;  Solifluction  or  Rock  Flow  (543);  Rock  Slides  and 

Falls  (545);  Rock  Slides  Started  by  Earthquakes 542-546 

Ancient  Examples  of  Rock  Streams  and  Slides  (546);  Mackinac 

Limestone  Breccia 546-547 

Residual  Soils 548 

B.  Anemoclastic  or  Eolian  Deposits.     Anemoliths. 549 

Source  of  Material  of  Eolian  Deposits 549 

Textural  Types  of  Anemoliths;  General  Characteristics  of  Modern 
Eolian  Deposits 551 

Sorting  of  Material  according  to  Size  and  Specific  Gravity; 

Size  of  Grain  in  Eolian  Deposits;  Rounding  of  Sand  Grains; 

Stratification  and  Cross-bedding  of  Eolian  Deposits 552-554 


TABLE    OF    CONTENTS  xxi 


Sand  Dunes,  their  Origin  and  Form 555 

Types  of  Sand  Dimes;  (i)  Strand  Dunes;  (2)  Lake  Shore 
Dunes;  (3)  River  Flood  Plain  and  River  Bottom  Dunes; 

(4)  Inland  or  Desert  Dunes 557~56i 

The  Forms  of  Dunes  (563) ;  Origin  of  Intercalated  Dust  and 
Clay  Layers,  and  of  Clay  Balls  in  Sand  Dunes ;  Peat  and  Lig- 
nite Deposits  in  Sand  Dunes  (564) ;  Transgressive  Relation  of 

Dune  Sands  to  Subjacent  Formations 563-565 

Examples  of  Older  Eolian  Deposits 565 

The  Loess  as  an  Example  of  a  Dust  Deposit;  Fossils  and 
Concretions  in  the  Loess ;  Cenozoic  and  Mesozoic  Loess-like 

Deposits;  Palaeozoic  Loess-like  Deposits 565-569 

Older  Deposits  of  Dune  Types 570 

Volcanic  Dust  Deposits 572 

Special  Indicators  of  Eolation 572 

Calcareous  and  Other  Non-Siliceous  Eolian  Sands  (573);  Recent 
and  Tertiary  Examples  (573);    Older  Examples  (577);    Possible 

Application  to  the  Chalk  Beds  (577) ;  Dunes  of  Gypsum 573~578 

Bibliography  XIII 57« 

CHAPTER  XIV. 

ORIGINAL  STRUCTURE  AND  LITHOGENESIS  OF  THE  CONTINENTAL  HYDRO- 

CLASTICS 582 

River-laid  Clastics  or  Potamoclastics 582 

Alluvial  Fans    (583) ;   Form   and   Extent   of   Modern   Alluvial 

Fans  (583) ;  Basins  Filled  by  River-washed  Waste 583-587 

River  Flood  Plains 588 

Cross-bedding  of  Torrential  Sediments  (590);  Thickness 
and  Composition  of  River  Deposits  (590) ;  Depth  of  Com- 
pound Continental  Deposits  (592);  Chatter  or  Percussion 
Marks  (592) ;  Organic  Remains  in  Torrential  Deposits  (592) ; 
Distance  to  which  Material  may  be  Carried  by  Rivers  (594) ; 
Purity  and  Rounding  of  Fluviatile  Deposits  (594);  Form 
of  River  Pebbles  (595);  Overlap  Relations  of  River  De- 
posits  590-597 

Flood  Plains  of  Glacial  Streams  (597) ;  River  and  Flood  Plain 

Deposits  from  Continental  Ice-sheets 597~598 

i.  Torrential  Moraine  or    Kame    Deposits;    2.  The 
Frontal  or  Apron    Plain;    3.  The  Esker;    4.  Glacial 

Sand  Plains 598-600 

Consolidated  Sand  Plains;  The  Nagelfluh  of  Salzburg.  ...     60 1 
Playasor  Takyrs  and  Salinas  (602);  Preservation  of  Footprints, 
etc.,  in  Subaerial  Deposits  (604) ;  Other  Structural  Characters .  602-605 

Normal  Paludal  and  Lacustrine  Clastic  Deposits 605 

Deltas 607 

Form  and  Rate  of  Growth  of  Deltas  (608) ;  Thickness  or 
Depth  of  Deltas  (609);  Delta  Slopes  (610);  The  Bird-foot 
Delta  of  the  Mississippi  (610);  Structure  and  Composition 
of  the  Delta  (612);  Organisms  of  the  Delta  (615);  Gaseous 
Emanations  of  Deltas  (615) ;  Cementation  of  Delta  Deposits 


xxii  TABLE    OF    CONTENTS 


(616);  Modification  of  the  Delta  Surfaces  (616);  Relation 
of  Delta-building  to  Crustal  Movements  (617);  Effect  of 
Subsidence  (618);  Effect  of  Elevation  (619);  Deltas  Merg- 
ing into  Desert  Deposits 608-619 

Colors  of  Continental  Clastics 620 

Alternation  of  Red  Beds  with  Those  of  Other  Colors;  Ori- 
ginal Red  Color  of  Sediments 623-625 

Examples  of  Older  Continental  Hydroclastics 626 

Cenozoic  or  Tertiary  Examples 626 

Mesozoic  Examples  of  Continental  Hydroclastics 631 

The  Potomac  Formation;  The  Red  Beds  of  North  America; 
Triassic  Red  Beds  of  Eastern  North  America,  and  of 

Europe 631-633 

Palaeozoic  Delta  Deposits 635 

Bibliography  XIV 637 


CHAPTER  XV. 

STRUCTURAL  CHARACTERS  AND  LITHOGENESIS  OF  THE  MARINE  HYDRO- 
CLASTICS       641 

Subdivision  of  the  Areas  of  Marine  Deposition 643 

I.  The  Littoral  District;  2.  The  Bathyal  District;  3.  The 

Deep  Sea  or  Abyssal  District 643 

Murray  and    Renard's    Classification    of    Marine   Deposits 
(643);  Krummers  Classification  of  Marine  Deposits  (644); 

A  New  Classification  of  Marine  Deposits 643-545 

Discussion  of  the  Marine  Clastics 646 

The  Littoral  District  and  Its  Deposits 646 

The  Shore  Zone  (Inter  Co-tidal  Zone;  Littoral  Zone  in  a 

Restricted  Sense) 647 

Facies  of  the  Shore  Zone  (648) ;  i.  Rocky  Cliff  Facies 
(648);  2.  Bouldery  Facies  (648);  3.  Gravel  Facies  (649); 
v  Organic  Remains  in  Pebble  Beds  (650) ;  4.  Sandy  Facies 
(651);  Marine  Arkoses  (652);  Sorting  of  Sands  and  Gravels 
by  Waves  (653);  Organic  Remains  in  Marine  and  Lacus-. 
trine  Sands  (654);  5.  Muddy  Facies  (655);  Flocculation 
and  the  Conditions  of  Mud  Deposition  (655);  Table  Show- 
ing Rate  of  Settlement  of  Solid  Matter  in  Fresh  and  Salt 

Water  (656) ;  6.  Organic  Facies 648-657 

Subaqueous   Solifluction    (657);   Accessory  Features  of   Sub- 
aqueous Gliding 657-660 

The    Permanently    Submerged   or    Neritic    Zone    (Flachsee, 

Shallow  Water  or  Thalassal  Zone) 661 

I.  The  Estuary  (66 1) ;  2.  The  Marginal  Lagoon  or  Barachois 
(665);    3.   The  Epicontinental    Seas  and   Mediterraneans 

(666);  4.  The  Ocean  Littoral  or  the  Neritic  Zone 661-667 

Deposits  of  the  Bathyal  District 668 

Table  Showing  Kinds  and  Distribution  of  Bathyal  De- 
posits (668) ;  .Table  of  Analyses  of  Muds,  of  Terrigenous 
and  of  Volcanic  Origin 668-669 


TABLE    OF    CONTENTS  xxiii 

PAGE 

The  Blue  or  Slate  Colored  Mud;  The  Red  Mud;  The  Green 
Mud;  Green  Sand;  Table  of  Analyses  of  Glauconite  from 

Various  Horizons 668-670 

Deposits  on  Lee  Banks  and  at  the  Edge  of  the  Continental 

Shelf 673 

Abyssal  Deposits 674 

Abyssal  Deposits  of  Pelagic  Origin  (674) ;  Abyssal  Deposits  of 
Terrigenous  Origin  (676);  The  Red  Clay  (676);  Analyses  of 
Deep  Sea  Deposits  (677);  Table  of  Analyses  of  Deep  Sea 
Deposits  (677) ;  Older  Deposits  that  have  been  Considered  of 
Deep  Sea  Origin  (678);  Concretions  of  the  Deep  Sea  (678); 
Cosmic  Deposits  of  the  Deep  Sea  (679) ;  Submarine  Volcanic 

Deposits . 674-679 

Interruptions  of  Marine  Sedimentation 680 

Persistence  and  Variation  in  Thickness  of  Marine  Strata 682 

Comprehensive  Formations 684 

Bibliography  XV 685 


CHAPTER  XVI. 

CHARACTERS  AND  LITHOGENESIS  OF  THE  BIOCLASTIC  ROCKS 691 

Work  of  Herds  of  Animals  in  the  Present  and  the  Past ;  Work  of  Burrow- 
ing Animals;  Destructive  Work  of  Fish  and  Marine  Invertebrates; 
Work  of  Earthworms  and  Lobworms;  Work  of  Ants  and  Termites; 
Comparison  of  Work  of  Earthworms  and  Ants;  Summary  of  Work  of 

Ants  in  Soil  and  Subsoil;  Destructive  Work  of  Plants 691-695 

Bibliography  XVI 695 

CHAPTER  XVII. 

SUMMARY  OF  ORIGINAL  FEATURES  OF  CLASTIC  ROCKS 696 

1.  Stratification;  Definitions  of  Stratum;  Types  of  Stratifica- 
tion  697-700 

2.  Cross  Bedding 7O1 

a.  Delta  Type  (702);  b.  Cross-bedding  of  Torrential  Deposits 
(702);  Cross -bedding  of  Eolian  Deposits  (703);  c.  Comparison 

of  Types  (704) 701-704 

3.  Beach   Cusps   (706);   Fossil   Beach   Cusps   (707);  4.  Wave 
Marks  (708);  5.  Rill  Marks 706-708 

6.  Mud-cracks,  Sun  Cracks  or  Desiccation  Fissures 709 

Playa    Surface    (709);    Permanent    Lake    Surface    (709); 
River  Flood  Plains  (710);  The  Shore  Zone  (710) 709-710 

7.  Clay   Galls    (Thon-gallen)    (711);    8.  Clay   Boulders    (711); 
9.  Rain  Prints  (712);  10.  Ripple  Marks  (712);  n.  Impressions 

of  Animals  and  Plants  in  Transit 711-714 

12.  Application  of  these  Structures  in  Determining  Position  of 
Strata 7*5 

13.  Rounding  and  Sorting  of  Sand  Grains  and  Wearing  of 
Pebbles..  7'5 


xxiv  TABLE    OF    CONTENTS 


14.  Characteristics  of  Inclusions  in  Sand  Grains 7*6 

15.  Organic  Remains 717 

16.  Concretions 718 

Accretions    (719);    Intercretions    (719);   Excretions    (720); 
Incretions  (720) 719-720 

17.  Secretions 721 

Bibliography  XVII 721 


CHAPTER  XVIII. 

OVERLAP  RELATIONS  OF  SEDIMENTARY  FORMATIONS 723 

Progressive  Overlap 723 

A.  Marine  Progressive  Overlap 723 

I.  Rising  Sea-level  or  Positive  Diastrophic  Movement 724 

1.  Transgressive  Movement 725 

a.  Rate  of  Depression  Equals  Rate  of  Supply  (725) ;  Older 
Examples  (728) ;  b.  Rate  of  Depression  Exceeds  Rate  of  Sup- 
ply  725-731 

2.  Regressive  Movements 732 

c.  Rate  of  Depression  is  Exceeded  by  Rate  of  Supply 732 

II.  Stationary  Sea-level 733 

III.  Falling  Sea-level 733 

Characteristics  of  Regressive  Deposits  (734);  Burial  of  Re- 
treatal  Sandstone  by  Subsequent  Transgrossive  Movement .  734-735 
Examples  of   Intercalated   Sandstones  from   the   Palaeozoic  and 

Mesozoic;  Formations  of  North  America 738 

The  Saint  Peter  Sandstone  (738) ;  The  Dakota  Sandstone .  738-739 

B.  Non-marine  Progressive  Overlap 739 

The  Pottsville  Series,  a  typical  Example  of  Non-marine  Progressive 

Overlap 741 

C.  Replacing  Overlap -.  743 

Bibliography  XVIII 744 


CHAPTER  XIX. 

METAMORPHISM  OF  ROCKS 746 

General  Definitions  (746);  The  Forces  Producing  Metamorph- 
ism  (746);  The  Region  of  Metamorphism  (747);  Character- 
istics of  the  Zones  of  Metamorphism  (747);  Kinds  of  Meta- 
morphism   746-748 

Static  Metamorphism  or  Diagenism 750 

I.  Lithification  or  Induration 750 

Lithification  or  Induration  of  Clastic  Rocks  (751);  I.  Welding 
(751);  2.  Cementation  (753);  Quartzites  and  Novaculites  (755); 
Lithification  of  Clastics  Largely  a  Supra-marine  Process.  .  .  .751-755 

II.  Recrystallization 755 

Pressure  Phenomena  due  to  Recrystallization  (Enterolithic 
Structure) 756 


TABLE    OF    CONTENTS  xxv 


III.  Dolomitization  of  Limestones 759 

IV.  Replacement  of  Limestone  by  Silica,  Iron  Oxide,  etc.  (762); 
V.  Desalinification  (763);    VI.  Formation  of   Concretions  (763); 

VII.  Hydration  and  Dehydration .  . 762-765 

Contact  Metamorphism  or  Aethoballism 765 

i.  Pyrometamorphism  (765);  2.  Hydrometamorphism  (766); 

3.  Atmometamorphism  (767);  4.  Biometamorphism  ...765-768 

Dynamic  or  Pressure  Metamorphism,  or  Symphrattism 768 

The  Terms  Slate,  Schist  and  Gneiss  (770);  General  Terms 
for  Metamorphic  Rocks  (771);  Variation  in  Metamorphism 

of  Strata  (772);  Age  of  Metamorphic  Rocks 77o~773 

Bibliography  XIX 773 


CHAPTER  XX. 

DEFORMATION  OF  ROCK  MASSES 776 

Endogenetic  Deformations 777 

i.  Endolithic  Brecciation  (777);  2.  Enterolithic  Structure 

(778);  3.  Contraction  Joints,  Basaltic  Jointing 777~778 

Deformation  Due  to  Extraneous  Causes — Exogenetic  Deformations.  .     779 

A.  Gravitational  Deformation 779 

a.  Structures  due  to  Movements 779 

4.  Intraformational  Brecciation 779 

5.  Subaquatic  Gliding  Deformation 780 

Examples    of   Fossil   Subaqueous   Solifluction    (781)   A. 
Miocenic    Sublacustrine    Glidings    of    Oeningen    (781); 

B.  Jurassic  Deformations  (781);  C.  Triassic  Examples 
(782);  D.  Devonic  Examples  (782);  E.  Ordovicic  Ex- 
amples (783);  F.  A  Cambric  or  Earlier  Example 781-784 

6.  Surface  deformations  Due  to  Creep 785 

b.  Deformations  due  to  Vertical  Pressure  of  Overlying  Rock 
Masses  (785);  7.  Squeezing  Out  of  Layers;  8.  Shaliness;  9. 
Slatiness 785-786 

c.  Of  Complex  Origin  (786);  10.  Pressure  Sutures  and  Sty- 
lolites  (786);   ii.  Cone  in  Cone 786-788 

B.  Tectonic  or  Orogenic  Deformations 789 

d.  Deformations  Resulting  in  Fractures  and  Related  Struc- 
tures       789 

12.  Joints    (789);    Minor   Characters   of   Joints;    Feather 
Fractures;  Dendritic  Markings;  Widening  of  Joints.  .  .  .789-791 

13.  Earthquake  Fissures  (792);  14.  Slaty  Cleavage  (793); 
15.  Fissility    (794);    16,    Schistosity    (794);    17-   Gneissoid 
Structure 792-795 

e.  Deformation  due  to  Folding  and  to  Folding  and  Erosion. .  .     795 
18.  Folding  (795);  a.  Anticlines  (795);  b.  Synclines  (795); 

c.  Isoclines  (796);  d.  Fan  Folds  (798);  e.  Monoclines  (798); 
Anticlinoria  and  Synclinoria  (799);  Geosyncline  and  Fore- 
deep  795-799 

Relation  of  Dip  Strike  and  Outcrop  (800);  Strike  as 
Affected  by  Pitching  Axis  of  Folds  (806);  Folding  as 
Indications  of  Unconformity  (815);  The  trend  of  the 
Appalachian  Folds 800-807 


xxvi  TABLE    OF    CONTENTS 


PAGE 


ig.  Domes  and  Basins 808 

f.  Deformation  due  to  Dislocation  of  Strata.    Faulting 810 

20.  Faults 810 

Features  Shown  in  Section  of  Faults  (812);  Features 
Shown  in  Surface  Appearance  of  Faults,  i.e.  Map  Fea- 
tures of  Faults  (813);  Classification  of  Faults  (813); 
With  Reference  to  Direction;  With  Reference  to  Move- 
ment; With  Reference  to  Cause 812-814 

Terms  Applied  to  Rock  Masses  Formed  by,  or  Bounded 
by  Faults,  but  not  Topographically  Distinguishable 
from  Surrounding  Masses  (815);  Terms  Applied  to  the 
Topographic  Expression  of  Faults 815 

Secondary  Features  due  to  Erosion  (816);  Strati- 
graphic  Significance  of  Faults  (817);  Faults  as  Indica- 
tions of  Unconformity  (819);  Relation  of  Folds,  Faults, 
Cleavage,  Fissility  and  Joints 816-819 

C.  Contact  Deformations 820 

21.  Prismatic  Joints  due  to  Contact  with  Igneous  Masses 
(820) ;  22.  Insolation  joints 820-821 

D.  Struc cures  in  Part  due  to  Deformation  and  in  Part  to  Erosion.     821 

23.  Disconformity  and  Unconformity  (821);  Disconformity 
(Parun conformity,  Paenaccordanz)  (822);  Unconformity 
(Clinunconformity;  Discordanz)  (824) 821-824 

Bibliography  XX 826 

i  j 

CHAPTER  XXI. 
THE  PRINCIPLES  OF  GLYPTOGENESIS  OR  THE  SCULPTURING  OF  THE  EARTH'S 

SURFACE 829 

The  Cycle  of  Erosion 829 

A.  Erosion  Features  in  Undisturbed  Strata 830 

1.  The  Coastal  Plain 830 

Dissection  of  the  Coastal  Plain  (831);  Deposition  in  Dis- 
sected Coastal  Plain;  Effect  of  Dissection  and  Peneplana- 
tion  of  Coastal  Plain  Strata  on  Outcrop 831-833 

Ancient  Coastal  Plains  Showing  Cuesta  Topography 835 

Minor  Erosion  Forms  of  Horizontal  Strata 839 

B.  Erosion  Features  in  Disturbed  Strata 846 

2.  The  Monocline  (840);  3.  Erosion  Features  of  the  Structural 
Dome  (841);  4.  Erosion  Features  of  the  Anticline  (843);  5.  The 
Basin  (846);  6.  The  Syncline  (847);  7.  Erosion  Features  in  Faulted 
Strata  (847);  8.  The  Completion  of  the  Cycle  (847) 840-847 

The  Peneplain  (847);  The  Relation  of  the  Peneplain  to  Sedi- 
mentation; Dissection  of  the  Peneplain;  Age  of  the  Peneplain; 
High-level  Plains  of  Arid  Regions 847-852 

C.  Minor  Erosion  Features 856 

Bibliography  XXI 857 


TABLE    OF    CONTENTS  xxvii 

D.  THE  PYROSPHERE. 
CHAPTER  XXII. 

PAGE 

GENERAL  SUMMARY  OF  PYROSPHERIC  ACTIVITIES 859 

Volcanic  Activities 859 

Types  of  Volcanic  Activities 859 

Subdivision  with  Reference  to  Location 859 

Explosive  Eruption  (860) ;  Terrestrial  Type  (860) ;  The  Cinder 
Cone;  Material  of  the  Cinder  Cone;  The  Forms  of  the  Cinder 
Cones;  Consolidation  of  Cinder  Cone;  Submarine  Explosive 
Eruptions 860-863 

Ext ravasative  Eruptions  (865);  Terrestrial  Type;  Fissure 
Eruption;  The  Lava  Dome;  Acid  Lava  Domes;  The  Spine  of 
Pel<§e 865-870 

Composite  Lava  and  Cinder  Cones  (870);  Submarine  Cones; 
Mud  Volcanoes 870-872 

Dissection  of  Volcanoes  (874) ;  Special  Erosion  Features 874-875 

Formation  of  the  Lava 876 

Bibliography  XXII 878 


E.  THE  CENTROSPHERE  OR  BARYSPHERE. 
CHAPTER  XXIII. 

DlASTROPHISM,  OR  THE  MOVEMENTS  TAKING  PLACE  WlTHIN  THE  EARTH'S 
CRUST  AND  THEIR  CAUSES 880 

Classification  of  Earth  Movements 880 

Classification  of  Seismic  Disturbances  (881);  The  Volcanic  or 
Pyroseismic  Type  of  Earthquake;  The  Tectonic  or  Dislocation 
(Baryseismic)  Earthquake 882 

Surface  Manifestations  of  Baryseismic  Disturbances 883 

Rifting  (883) ;  Filling  of  the  Fissures,  Sandstone  Dikes  (884) ; 
Craterlets  (885);  Fossil  Examples  (886);  Slipping  (887); 
Block  Movement  (887);  Disruptive  Effects  of  Earthquakes 
(888) ;  Effects  of  Earthquakes  on  Topography  (888) 883-888 

Submarine  Earthquakes  and  Seaquakes  (889);  Airquakes  (891); 
Periodicity  of  Earthquakes  (891) 889-891 

Movements  due  to  Displacement  or  Migration  of  the  Poles 
(891);  The  Pendulation  Theory  (892);  Determined  Migrations 
of  the  Poles 891-899 

Earth  Movements  and  Geosynclines  (900) ;  Geosynclines,  the  Sites 
of  Orogenic  Disturbance  (902);  Foreshortening  of  the  Crust  (903); 
Height  of  the  Folds  (903) ;  Character  and  Thickness  of  the  De- 
formed Mass 900-904 

Changes  due  to  Extra-Telluric  Influences 9°6 

Bibliography  XXIII 908 


xxviii  TABLE    OF    CONTENTS 

F.  THE  BIOSPHERE. 
CHAPTER  XXIV. 

PAGE 

SUBDIVISION  OF  THE  BIOSPHERE.    CLASSIFICATION  AND  GENERAL  MORPHO- 
LOGICAL CHARACTERS  OF  ORGANISMS 910 

Plants  and  Animals  as  Indicators  of  the  Age  of  the  Period  in 

Which  They  Occur 911 

Classification  of  Plants  and  Animals 912 

Naming  of  Genera  and  Species  (912);  Pryority  and  Syn- 
onymy (914);  Synonymy  (915);  Manuscript  Names,  List 
Names ;  Nomina  Nuda  (917);  Generic  Names  as  Synonyms, 

912-917 
Types    (918);    Terms   Used   for   Specific   Types    (918);    Generic 

Types 918-920 

Selection  of  the  Genotype  or  Type  Species  of  a  Genus  (920) ; 
Union  of  Genera  into  Group  of  Higher  Taxonomic  Value.  .920-921 
Sub-families;  Families:  Super-families;  Sub-orders;  Orders; 

Groups  of  Higher  Rank;  Faunas  and  Floras 921-922 

Table  I,  Subdivisions  of  the  Plant  Kingdom   (922);  Table 

II,  Subdivisions  of  the  Animal  Kingdom 922-925 

Brief   Summary  of   the   Morphological   Characters  of   the   Phyla  of 
Plants  and  Animals 933 

A.  Plants  (933) ;  Phylum  I,  Protophyta  (933) ;  Phylum  II,  Thallo- 
phyta  (934);  a.  Algae   (935);  b.   Fungi   (937);  c.  Lichens  (937); 
Phylum  III,  Bryophyta  (937);  Phylum  IV,  Pteridophyta  (938); 
Phylum  V,  Spermatophyta  (941) 933~94i 

B.  Animals  (942);  Phylum  I,  Protozoa  (942);  Phylum  II,  Porifera 
(Sponges)   (942);   Phylum  III,   Ccelenterata  (942);   Phylum  IV, 
Molluscoidea    (943);    Phylum   V,    Mollusca    (944);    Phylum   VI, 
Platyhelmintha  and  Phylum  VII,  Vermes  (946);  Phylum  VIII, 
Arthropoda  (947);  Phylum  IX,  Echinodermata  (949);  Phylum  X, 
Protochorda  (950);  Phylum  XI,  Vertebrata  (950);  Pisces  (951); 
Amphibia  (952);  Reptilia  (952);  Aves  (954);  Mammalia  (955).  .942-955 

Bibliography  XXIV 956 


CHAPTER  XXV. 

BIOGENETIC  RELATIONS  OF  PLANTS  AND  ANIMALS 958 

The  Conception  of  Species 958 

The  Mutations  of  Waagen 960 

Mutation  Theory  of  De  Vries 962 

Orthogenesis  and  the  Concept  of  Species 963 

Acceleration  and    Retardation    in    Development    (Tachygenesis 

and  Bradygenesis) 964 

Illustrations  of  Orthogenetic  Development   (964);  Origin 
and  Development  of  Characters  the  Important  Question; 

Rectigradations  and  Allometrons 964-970 

Nomenclature  of  Stages  in  Development 970 

Ontogenetic   Stages   and    Morphic   Stages    (970);    Simple 
Organisms  (970) ;  Colonial  Forms 97O~973 


TABLE   OF    CONTENTS  xxix 

PAGE 

Intracolonial  Acceleration  and  Retardation   (973);  Atavism  or 

Reversion 973~974 

Parallelism  and  Convergence  in  Development  (Homceogenesis) . .     976 
Bibliography  XXV 979 

CHAPTER  XXVI. 

PHYSICAL    CHARACTERISTICS    OF    THE    INHABITABLE    EARTH.    BIONOMIC 

CHARACTERS  OF  THE  ENVIRONMENT 982 

I.  The  Littoral  District 983 

A.  Marine  (983);   B.  Fresh  Water  (987);   C.  Terrestrial 

(988) 983-988 

II.  The  Pelagic  District 988 

A.  Marine   (988);  B.  Fresh  Water  (988);  C.  Terrestrial 

(989) 988-989 

III.  The  Abyssal  Life  District 990 

A.  Marine;  B.  Fresh  Water  and  C.  Terrestrial 990 

Bibliography  XXVI 990 

CHAPTER  XXVII. 

BIONOMIC  CLASSIFICATION- OF  PLANTS  AND  ANIMALS 991 

Subdivisions  (991);  Primary  Divisions;  Secondary  Divisions....     991 

A.  Haloplankton 992 

I.  Holoplankton  (992);  2.  Meroplankton  (993);  3.  Pseudo- 
plankton  (994);  4.  Epiplankton  (994);  B.  Halonekton  (996); 

C.  Halobenthos  (996) 992-996 

D.  Limnoplankton    (997);    E.    Limnonekton    (Helionekton, 
Potamonekton) ;     F.    Limnobenthos    (Heliobenthos,    Pota- 

mobenthos) 997-998 

G.  Atmoplankton ;  H.  Atmonekton;  I.  Atmobenthos 998 

Bibliography  XXVII 999 

CHAPTER  XXVIII. 

BIONOMIC  CHARACTERISTICS  OF  PLANTS  AND  ANIMALS 1000 

A.  Bionomic  Characters  of  Plants 1000 

Protophyta  (1000);  Thallophyta  (1001);  (Alga,  Fungi,  Lichens); 

Bryophyta  and  Pteridophyta  (1003) 1000-1003 

Spermatophyta 1004 

Ecology  and  Ecological  Adaptations  of  Spermatophytes 1005 

I.  Hydrophytes    and    Hemihydrophy tes ;    2.    Xerophytes; 

3.    Bog    Xerophytes;    4.    Tropophytes;    5.    Hygrophytes; 

6.  Sciophytes;  7.  Halophytes;  8.  Calcicole  and  Calcifuge 

Plants 1006 

B.  Bionomic  Characteristics  of  Animals 1007 

I.  Protozoa  (1007);  (Foraminifera;  Radiolaria) ',  II.  Porifera  (1008); 
III.  Ccelenterata  (1009)  (Hydrozoa;  Anthozoa);  IV.  Molluscoidea 
(1014)  (Bryozoa;  Brachiopoda) ;  V.  Mollusca  (1015);  (Pelecypoda; 
Scaphapoda  and  Amphineura;  Gastropoda;  Pteropoda;  Cephalo- 
poda)  1007-1023 


xxx  TABLE    OF    CONTENTS 


VI.  Platyhelmintha;  VII.  Vermes. 1023 

VIII.  Arthropoda   (1025);  Crustacea   (1025);   (Trilobita;  Phyllo- 
poda;  Copepoda;  Ostracoda;  Cirrepedia;  Phyllocarida;  Schizopoda; 
Stomatopoda;  Sympoda;  Decapoda;  Arthrostraca);  Acerata  (1028); 
(Merostomata;  Arachnida;   Pantapoda);    Myriopoda  and  Insecta 
(1030) 1025-1030 

IX.  Echinodermata  (1031);  Cystoidea  and  Blastoidea;  Crinoidea; 
Asteroidea;  Ophiuroidea;  Eckinoidea;  Holothuroidea 1031-1033 

X.  Protochordata i°33 

XI.  Vertebrata     (1033);     Osiracoderma     (1033);    Pisces     (1034); 
Amphibia    (1035);    Reptilia    (1036);     Aves    (1037);     Mammalia 
(1038) 1033-1038 

Bibliography  XXVIII 1038 


CHAPTER  XXIX. 

CHOROLOGY  OR  THE  PRINCIPLES  OF  THE  GEOGRAPHICAL  DISTRIBUTION  OF 

PLANTS  AND  ANIMALS 1040 

Dispersal  and  Migration  (1041);  Barriers  to  Migration  and  Dis- 
persal (1042) ;  Faunal  Groups 1041-1044 

Factors  Governing  Dispersal  and  Migration 1044 

Inorganic  Factors;  the  Medium 1044 

Composition  of  Medium  (1044);  Stenohalinity  and  Eury- 
halinity;  Quantity  of  Air  (1045);  Volume  of  Water  (1047), 

1044-1047 

Climate 1047 

Climate  and  Temperature  (1047);  Currents  (1048);  Topog- 
raphy (1051) 1047-1051 

The  Organic  Factors 1052 

Biogeographical  Provinces 1053 

Marine  Provinces  (1055);  Former  Marine  Geographic  Prov- 
inces (1057);    Present  and  Former  Biogeographic  Provinces 
of  the  Land  (1058) ;  Fresh  Water  Biotic  Provinces  (1059) .  1055-1059 
Relicts  (1062);  Relict  Faunas  and  Lakes  (1062);  Marine  Relicts, 

Bipolar  Faunas  (1065);  Terrestrial  Relicts  (1066) 1062-1066 

Dwarf  Faunas  and  Micro-Faunas 1066 

Bibliography  XXIX. . .  .  .* 1069 


CHAPTER  XXX. 

FOSSILS,  THEIR  CHARACTER  AND  MODE  OF  PRESERVATION 1073 

Definition  and  Limitation  of  the  Term  Fossil 1073 

Fossilization 1075 

Types  of  Fossil 1076 

I.  Actual  Remains 1076 

Preservation  of  Soft  Tissues  (1076);  Preservation  of  Hard 

Structures  and  of  Petrified  Remains 1078 

Petrifaction  of  Non-mineral  Substances  (1080);   a.  Re- 
placement of   Soft  Animal  Tissue;    b.  Petrification  of 

Plants 1080 


TABLE    OF    CONTENTS  x*xi 


Petrifaction  of  Mineral  Structures  (1082);  a.  Protozoa 
(1082);  b.  Sponges  and  Hydrozoans  (1082);  c.  Silicifica- 
tion  of  Corals  (1083);  d.  The  Brachiopod  Shell  (1083); 
e.  Shells  of  Molluscs  (1084);  f.  Crustaceans  Merostomes, 
Insects,  etc.  (1086);  g.  Echinoderms  (1086);  h.  Verte- 
brates (1088) 1082-1088 

Excessive  silicification 1089 

Molds  and  Casts 1089 

2.  Tracks,  Trails  and  Burrows  of  Animals 1090 

3.  Artificial  Structures 1093 

4.  Coprolites 1093 

Mechanical  Deformation  of  Fossils 1094 

Index  Fossils 1094 

Bibliography  XXX 1095 

G.   PRINCIPLES  OF  CLASSIFICATION  AND  CORRELATION  OF 
GEOLOGICAL  FORMATIONS. 

CHAPTER  XXXI. 

NOMENCLATURE  AND  CLASSIFICATION  OF  GEOLOGIC  FORMATIONS 1097 

Development  of  Classifications 1097 

Selection  of  the  Type  Section 1 100 

Time  Scale  and  Formation  Scale 1 102 

Subdivision  of  Time  and  Formation  Scales  (1103);  I.  Inter- 
national Geological  Congress  (1104);  II.  Dana's  System 

(1106);  III.  United  States  Geological  Survey 1103-1106 

Unification  of  Terminology  (i  107) ;  Local  Stages  and  Substages  1 107 
Principles  Governing  the  Naming  of  Formations  (1109);  Selection 

of  Names  for  Systems,  Series  and  Stages  (Groups) 1109-1 1 1 1 

Mapping  (1112);  Mapping  on  Formational  Basis  (1112);  Mapping 
on  Faunal  Basis  (1113);    Mapping  of  Discontinuous  Formations 

(1113) , 1112-1113 

Types  of  Geological  Maps  (1115);  Formation  and  System 
Maps  (1115);  Intermediate  Maps  (1115);  Notation  of  Forma- 
tions on  Map  (1116);  Legend  (1116) 1115-1116 

Continuous  and  Discontinuous  Mapping 1117 

Sections;  Types  of  Sections 1117 

The  Length  of  Geological  Time 1 1 18 

Bibliography  XXXI 1119 

CHAPTER  XXXII. 

CORRELATION,  ITS  CRITERIA  AND  PRINCIPLES.     PAL^EOGEQGRAPHY 1121 

Correlation 1121 

History  of  Development  of  Methods  of  Correlation 1121 

Chronological  Equivalency;  Contemporaneous  and  Homo- 
taxial  Formations  (1124);     Contemporaneity     of     Faunas 

(1125);  Prenuncial  Faunas;  Colonies 1124-1126 

Standard  or  Type  Section  (i  127) ;  A  Double  Standard .  1 127-1 129      * 


xxxii  TABLE    OF    CONTENTS 

PAOK 

Methods  of  Correlation 1 129 

i.    Superposition    (1129);    2.    Stratigraphic    Continuity 
(1131);  3.  Lithic  Character  (1132);  4.  Organic  Contents 

(i  133) 1 129-1 133 

a.  Index  Fossils  (i  133) ;  b.  Grade  of  Index  Fossil  (i  134) ; 
c.  Correlation  by  Equivalent  Stages  in  Development 
(1135);  d.  Correlation  by  Faunas  and  Floras.  Repre- 
sentative Species  (1136) 1133-1136 

5.  Correlation  by  Unconformities  and  Disconformities 
(1137);    6.     Correlation    by    Regional    Metamorphism 

(H39);  7-  Correlation  by  Diastrophism 1139-1141 

Palaeogeography  and  Palaeogeographic  Maps 1 144 

Types    of    Palaeogeographic    Maps    (1145);    Construction    of 

Palasogeographic  Maps 1 145-1 146 

Bibliography  XXXII 1 148 

Index 1151 


PRINCIPLES  OF   STRATIGRAPHY 

CHAPTER    I. 
GENERAL  INTRODUCTORY   CONSIDERATIONS. 

STRATIGRAPHY  in  its  broadest  sense  may  be  defined  as  the  inor- 
ganic side  of  Historical  Geology,  or  the  development  through  the 
successive  geologic  ages  of  the  earth's  rocky  framework  or  litho- 
spliere.  Its  relation  to  other  branches  of  geologic  science  may  be 
made  clear  by  a  few  brief  considerations  regarding  the  earth  as  a 
whole,  and  a  short  survey  of  the  science  of  geology  and  its  subdi- 
visions. 

THE    EARTH    AS    A   WHOLE. 

The  earth  as  a  whole  may  be  viewed  as  a  central  mass  or  sphere 
of  unknown  material  surrounded  by  a  number  of  envelopes.  For 
convenience  sake  in  discussion,  these  envelopes  may  be  considered 
as  continuous  shells  or  hollow  spheres,  the  outer  ones  more  or  less 
intimately  interwoven  with  the  upper  part  of  the  rocky  crust.  They 
may  be  grouped  into  the  inorganic  and  the  organic  spheres.  Begin- 
ning with  the  outermost  of  the  inorganic,  the  following  are  recog- 
nized:  I.  Atmosphere  or  sphere  of  gas  and  vapor;  II.  Hydro- 
sphere or  sphere  of  water;  III.  Lithosphere  or  the  rock  sphere  or 
solid  part  of  the  earth.  Below  the  known  crust  of  the  earth  is  the 
zone  of  volcanic  activities  and  the  seat  of  lava  formation.  This  is 
called  the  Pyrosphere,  IV,  and  it  merges  upward  into  the  litho- 
sphere  (III)  and  downward  into  the  Centra-  or  Barysphere,  V, 
which  occupies  the  unknown  center  of  the  earth  and  the  nature 
of  which  is  in  doubt.  Permeating  more  or  less  all  of  these  spheres, 
except  the  last  two,  is  the  organic  or  Biosphere,  VI,  the  living  en- 
velope of  the  earth.  A  brief  summary  of  each  may  first  be  given. 

I.  THE  ATMOSPHERE.  This  consists  of  a  mechanical  mix- 
ture of  nitrogen  about  79  parts,  and  of  oxygen  about  21  parts  (by 
volume),  with  small  quantities  of  carbon  dioxide  (about  0.03  part  of 
the  whole)  and  some  of  the  rarer  elements.  Besides  this  it  nearly 
always  contains  a  variable  amount  of  aqueous  vapor  together  with 
other  impurities,  such  as  dust,  organic  matter,  etc.  Its  weight  at 


2  PRINCIPLES   OF   STRATIGRAPHY 

sea- level  is  about  15  pounds  ( 14.7  pounds)*  per  square  inch,  or  about 
a  ton  per  square  foot,  and  this  is  spoken  of  as  the  normal  at- 
mospheric pressure  or  one  atmosphere.  It  becomes  more  tenuous 
upward ;  above  50  miles  from  the  earth's  surface  it  becomes  so  ex- 
cessively thin  that  it  is  incapable  of  producing  measurable  pres- 
sure, or  of  deflecting  perceptible  amounts  of  sunlight.  CDavis- 
6:/j.)f  Above  100  miles  it  practically  ceases  to  exist  so  far  as  ob- 
servations have  been  made,  though  it  is  supposed  that  it  might  ex- 
tend in  an  excessively  attenuated  state  to  the  limit  of  the  earth's 
gravitative  control,  which  is  at  about  620,000  miles  from  the  sur- 
face of  the  lithosphere.  (Chamberlin  and  Salisbury-4,  i:d.) 

II.  THE  HYDROSPHERE.  This  is  a  fairly  continuous  en- 
velope, concentrated  chiefly  in  the  larger  depressions  of  the  litho- 
sphere, where  it  constitutes  the  oceans,  but  also  permeating  the 
upper  part  of  the  earth's  crust  as  a  more  or  less  continuous  layer. 
The  surficial  extent  of  the  sea  water  on  the  earth  is  estimated  at 
361.1  million  square  kilometers,  while  the  total  land  surface  is  esti- 
mated at  148.8  million  square  kilometers.  This  makes  a  ratio  of 
land  surface  to  sea  surface  of  i :  2.43  or  29.2%  land  and  70.8% 
sea  (Kriimmel-17,  i  :#),:£  or  in  round  numbers  the  sea  surface  is 
2.5  times  that  of  the  land.  When  taken  in  hemispheres,  the 
northern  one  has  60.7%  water  and  the  southern  80.9% 
(17,  i:/j).  The  greatest  known  depth,  that  of  the  Xero  deep, 
opposite  the  island  of  Guam  in  the  Ladrone  Islands  east  of  the 
Philippines,  is  9,636  meters  (5,269.13  fathoms  or  31,615  feeti. 
The  area  of  the  ocean  bottom  below  4,000  meters  comprises  about 
185  million  square  kilometers,  that  below  5,000  meters  of  depth  72 
million  square  kilometers  or  about  half  the  area  of  the  dry  land 
(i/5th  of  the  sea  surface)  ;  that  below  6,000  meters  about  5.4 
million  square  kilometers  or  about  the  area  of  European  Russia. 
Among  the  greater  deeps,  which  are  more  circumscribed,  we  have 
that  of  the  Marian  depression  opposite  the  Marian  or  Ladrone 
Islands  (in  which  the  Xero  deep  occurs)  with  an  area  of  49,000 
square  kilometers  (equal  in  area  to  Sardinia  and  Sicily)  below 
7,000  meters  and  about  22.500  square  kilometers  below  8,000 

*  I-°333  kgm.  per  sq.  cm.,  or  the  weight  at  sea-level  of  a  column  of  mercury 
760  mm.  (29.921  inches)  high. 

t  The  Arabic  figure  refers  to  the  number  of  the  article  in  the  bibliography 
at  the  end  of  the  chapter,  the  italicized  number  refers  to  the  page. 

%  Penck  in  Scobel's  Geographisches  Handbuch  makes  the  surface  area  of  the 
water  366  million  square  kilometers,  and  that  of  the  land  144  million  square 
kilometers,  including  the  Antarctic  continent,  which  has  an  estimated  area  of 
8  to  9  million  square  miles,  giving  in  percentages  71.8%  water  and  28.2rc 
land,  a  ratio  approximately  of  2.5  :  i. 


THE   EARTH   AS   A    WHOLE  3 

meters.  In  the  southern  Pacific  the  Tonga  deep  has  an  area  of 
123.000  square  kilorreters  below  7,000  meters,  and  63,000  square 
kilometers  below  8,000  meters,  while  the  Kermadec  deep  to  the 
south  of  it  has  137,000  square  kilometers  below  7,000  meters,  and 
78,000  square  kilometers  below  8,000  meters.  The  maximum 
depths  of  these  two  depressions  are  9427  and  9,413  meters,  re- 
spectively. (Krummel-i7, 1:6*5.)  The  total  area  of  the  oceanic  de- 
pressions below  6,000  meters  is  given  by  Penck  as  10.6  million 
square  kilometers,  and  by  Krummel  as  5.4  million  square  kilo- 
meters. Taking  .the  area  of  the  seas  as  a  whole  at  361,100,000 
square  kilometers,  and  evening  out  the  irregularities  of  the  bot- 
tom, so  as  to  obtain  a  mean  depth,  we  find  this  to  be  approximately 
3,680  meters  or  2,012  fathoms  (see  further  under  lithosphere). 
Various  estimates  as  to  the  volume  of  the  sea  water  as  a  whole 
have  been  made.  The  most  recent  of  these,  given  by  Krummel, 
places  it  at  1,330  million  cubic  kilometers.  The  weight  of  the  sea 
water  may  be  calculated  from  this  by  taking  its  average  density, 
increased  in  the  deeper  portions  by  pressure,  as  1.04,  the  result 
being  1.3832  X  10  18  metric  tons  or  in  round  numbers  138  X  io18 
metric  tons.* 

Transgressions  and  Regressions.  Two  types  of  alternation  of 
the  level  of  the  hydrosphere  are  recognized :  the  local  and  the  uni- 
versal. The  former  is  due  to  slight  up  or  down  warpings  or  fault- 
ings  of  parts  of  a  continent  with  resulting  local  retreat  or  advance 
of  the  sea.  The  effects  of  such  a  change  will  be  noticed  only  locally 
and  will  at  best  be  of  slight  amount.  An  example  of  this  is  shown 
in  the  periodic  rising  and  sinking  of  the  land  in  the  Gulf  of  Naples 
as  recorded  in  the  ruins  of  the  temple  of  Jupiter  Serapis,  near 
Pozzuoli  (Lyell-i8,  ii  Chapter  XXX)  ;  or,  in  the  Scandinavian 
region,  where,  during  the  last  century,  an  area  of  300,000  square 
kilometers  rose  on  the  average  0.7  meter,  making  a  total  elevated 
mass  of  210  cubic  kilometers. 

The  second  type  of  change  is  one  that  affects  the  entire  surface 
of  the  ocean,  and  is  best  explained  by  a  bulging  up  or  a  sinking  down 
of  the  sea  bottom,  the  result  of  which  will  be  a  universal  rise  of 
the  sea-level  and  transgression  over,  or  fall  and  retreat  from  the 
edge  of  the  land.  For  these  latter  movements  Suess  (27,  \i\68o\ 
28,  11:534)  nas  proposed  the  term:  "Eustatfc  Movements."  The 
sinking  of  the  sea  bottom  and  consequent  lowering  of  the  level  and 
withdrawal  of  the  water  from  the  land  constitute  negative  eustatic 
movements,  while  elevation  or  bowing  up  of  the  sea  bottom  with 

*The  metric  ton  contains  1,000  kilograms,  equivalent  to  2,204.6  pounds 
avoirdupois. 


4  PRINCIPLES    OF    STRATIGRAPHY 

accompanying  rise  and  transgression  cause  positive  eustatic  move- 
ments. A  third  type  of  movement  must  be  considered.  If  we  re- 
gard the  continents  "as  crustal  blocks  of  a  lighter  specific  gravity 
than  the  suboceanic  crustal  blocks,  the  former  being  squeezed 
upward  by  the  downward  pressure  of  the  suboceanic  blocks,  it 
is  conceivable  that  a  single  continental  block  like  that  of  the 
Americas  might  be  squeezed  upward,  while  the  other  conti- 
nental blocks  would  remain  stationary,  and  yet  at  the  same  time 
there  need  be  no  marked  change  in  the  altitude  of  the  suboceanic 
blocks  with  reference  to  the  stationary  continental  blocks.  As  a 
result  there  will  be  a  widespread  emergence,  or  negative  move- 
ment of  the  sea,  so  far  as  the  rising  land  block  is  concerned,  while 
at  the  same  time  the  resultant  displacement  of  the  water  will 
cause  a  transgressive  or  positive  movement  of  the  sea  with  refer- 
ence to  the  stationary  blocks.  Thus  a  retreatal  movement  in  one 
continent  may  be  correlated  with  a  transgressive  one  in  another 
continent.  Such  differential  movements  may  even  affect  different 
parts  of  the  same  continental  block,  if  the  movement  is  an  unequal 
or  tilting  one,  and  this  would  account  for  transgression  of  the  sea 
over  one  section  of  a  continent  at  a  time  when  retreatal  move- 
ments characterized  another  part. 

THE  TERRESTRIAL  PART  OF  THE  HYDROSPHERE.  The  terrestrial 
or  extra-oceanic  part  of  the  hydrosphere  is  chiefly  found  in  the 
ground  water  and  in  the  streams,  lakes  and  ponds  of  the  earth's 
surface.  Since  the  porosity  of  the  rocks  constituting  the  earth's 
surface  region  varies  greatly,  the  quantitative  distribution  of  the 
water  also  varies.  The  ground  water  is  probably  chiefly  confined 
to  the  upper  six  miles  of  the  earth's  crust,  and  here  wre  have  a 
diminishing  porosity  from  5  per  cent,  or  over  at  the  surface  to 
zero  at  the  depth  of  six  miles.  It  has  been  estimated  on  this  basis 
that  the  rock  of  the  earth's  surface  contains  enough  water  to  form 
a  layer  nearly  800  feet  deep  (Chamberlin  and  Salisbury -4:^7), 
but  other  estimates  make  this  layer  much  thicker,  that  of  Slichter 
being  3,000  to  3,500  feet  (25:15).  Van  Hise,  on  the  other  hand, 
has  shown  that  the  amount  is  much  less,  and  is,  according  to  his 
estimate,  sufficient  to  make  a  layer  only  69  meters  or  226  feet 
thick  over  the  continental  area  (30:128-129,  5/0-577).  Kemp  has 
called  attention  to  the  fact  that  in  the  deep  mines  no  water  is  en- 
countered below  a  moderate  depth.  "In  several  important  in- 
stances of  this  class,  as  well  as  in  many  mines  of  smaller  depth, 
it  is  possible  to  impound  all  the  water  within  a  short  distance,  it 
may  be  within  500  feet  of  the  surface.  Below  this  level  the  work- 
ings are  dry,  and  in  not  a  few  cases  dusty."  (15:16.)  He  con- 


THE    EARTH    AS    A    WHOLE  5 

eludes  that  something  like  2,000  feet  appears  to  be  the  limit  to 
which  ground  water  descends,  while  in  some  regions  it  ceases  at  500 
feet.  From  this  it  is  estimated  that  the  amount  of  water  present 
would  produce  a  layer  over  the  surface  of  the  earth  between  50 
and  loo  feet  deep.  Fuller  (7:61,  62,  72)  calculates  the  exact  figure 
at  96  feet,  which  would  be  acceptable  were  it  proven  that  the  data 
on  which  his  calculations  are  based  are  ascertained  with  equal 
exactness. 

III.  THE  LITHOSPHERE.  This  is  the  solid  framework  of 
the  earth.  It  is  a  nearly  perfect  oblate  spheroid  with  a  polar  di- 
ameter of  12,713.5  kilometers  (7,899.7  miles)  and  an  equatorial 
diameter  of  12,756.5  kilometers  (7,926.5  miles),  corresponding  to  a 
meridional  circumference  of  about  40,008  kilometers  (24,860  miles), 
an  equatorial  circumference  of  40,076  kilometers  (24,902  miles), 
and  a  surface  area  of  510  million  square  kilometers  (196,940,700 
square  miles).  As  already  noted,  the  land  surface  is  something 
over  29  per  cent,  of  this,  or  about  148.8  million  square  kilometers. 
The  greatest  elevation  of  the  land  above  sea-level  (Mt.  Everest)  is 
8,840  meters,  which  is  nearly  800  meters  less  than  the  greatest 
known  depth  of  the  sea  (9,636  meters).  Of  the  entire  earth's  sur- 
face not  over  three  million  square  kilometers  of  area  lie  more  than 
4,000  meters,  nor  over  half  a  million  square  kilometers  more  than 
5,000  meters  above  sea-level.  The  following  table  shows  the  per- 
centages of  land  within  successive  strata  of  100  meters  (Penck- 
21/1:145): 

Between  o  and  200  meters,  each  interval  of  100  meters  contains  14.6  % 

of  the  land,  or  a  total  of '; 29 . 2  % 

Between  200  and  500  meters,  each  interval  of  100  meters  contains 

9.0  %  of  the  land,  or  a  total  of 27.0  % 

Between  500  and  1,000  meters,  each  interval  of  100  meters  contains 

3.8  %  of  the  land,  or  a  total  of 19.0  % 

Between  1,000  and  2,000  meters,  each  interval  of  100  meters  contains 

1.7  %  of  the  land,  or  a  total  of 17.0  % 

Between  2,000  and  3,000  meters,  each  interval  of  100  meters  contains 

0.4  %  of  the  land,  or  a  total  of 4.0  % 

Between  3,000  and  4,000  meters,  each  interval  of  100  meters  contains 

o.i  %  of  the  land,  or  a  total  of I  .o  % 

Between  4,000  and  8,840  meters,  each  interval  of  100  meters  contains 

0.04  %  of  the  land,  or  a  total  of 1.9  % 


99-1  % 

It  is  thus  seen  that  more  than  one-half  of  the  earth's  surface  (56 
per  cent.)  lies  below  the  5OO-meter  contour,  and  that  more  than 
half  this  lies  below  the  2oo-meter  contour.  Very  different  values 


6  PRINCIPLES    OF    STRATIGRAPHY 

have  been   reached  by   de  Lapparent,   Heiderich   and   Murray,   as 
shown  in  the  following  table  (Penck-2i,  i  1/50)  : 


Percentage  of 
land  surface 

Below 
o  m. 

From 
o- 

200 

m. 

From 
200- 
500 

m. 

From 
500- 

1,000 

m. 

From 
1,000- 

2,000 

m. 

From 

2,000- 

3,000 
m. 

Above 
3,000 
m. 

de  Lapparent    

1  8  oo 

20  oo 

4.7  o 

Hoo 

Heiderich  
Murray 

0.08 
o  oo 

I3-40 

14.   60 

37-96 
^8  oo 

28.5 
25  8 

17.81 

IQ    8O 

i-95 

I      4-O 

0.30 
o  40 

The  mean  elevation  for  all  continents  is  given  by  Sir  John  Mur- 
ray as  2,250  feet  (686  meters),  and  the  mean  or  average  depth 
of  the  ocean  as  3,840  meters  (2,100  fathoms).  Penck  (21:157; 
22:17),  on  the  other  hand,  finds  the  mean  elevation  of  the  conti- 
nents and  islands  to  be  735  meters  and  the  mean  depth  of  the 
ocean  3,650  meters.  The  mean  depth  of  the  ocean  has  more  re- 
cently been  calculated  as  3,680  meters  (precisely  3,681  meters)  by 
Krummel  (17:144),  who  also  assumes  the  mean  altitude  of  the 
land  at  approximately  700  meters.  More  recently  still  Penck  has 
given  these  figures  as  3,680  meters  and  710  meters,  respectively 
(22:1^5).  With  a  land  area  of  148.8  million  square  kilometers,  the 
volume  of  the  land  mass  above  sea-level  becomes  104.2  million 
cubic  kilometers.  From  these  figures  the  following  ratios  are  de- 
duced :  mean  height  of  land  to  mean  depth  of  sea  =  700 :  3,680  = 
1:5.25;  area  of  land  to  sea=  148.8:361. 2—  i  :2.43 ;  volume  of 
land  to  sea=  1 04.2 -.1,330.0=: i  :i2.8.  Thus  (Krummel-i7,  1:147) 
it  would  take  nearly  13  times  the  volume  of  the  land  rising  above 
sea-level  to  fill  the  sea,  three  times  that  volume  to  fill  the  Atlantic 
Ocean,  2%  times  that  volume  to  fill  the  Indian  Ocean,  and  6l/2 
times  to  fill  the  Pacific  Ocean. 

THE  MEAN  SPHERE  LEVEL.  If  we  regard  the  land  mass  as  a 
whole,  we  may  represent  it  by  a  prismatic  block  (tetragonal)  com- 
posed of  that  portion  which  lies  above  mean  ocean  depth,  plus  that 
portion  rising  above  sea-level,  giving  a  height  of  3,680-1-700= 
4,380  meters,  a  base  of  148.8  million  square  kilometers,  the  present 
area  of  the  land  surface,  and  a  volume  of  651.8  million  cubic  kilo- 


THE    EARTH    AS    A    WHOLE  7 

meters ;  *  while  the  sea  may  be  represented  by  a  prismatic  block 
(tetragonal)  having  twice  that  volume  (1,330.0-1-651.8=2.04).  If, 
then,  we  were  to  flatten  out  all  irregularities  of  the  sea  bottom  by 
cutting  down  the  land  block  sufficiently  to  fill  them,  or,  in  other 
words,  if  we  distribute  the  land  block  of  651.8  million  cubic  kilo- 
meters over  the  entire  surface  of  the  earth,  509,950,000  square 
kilometers,  according  to  Bessel,  it  would  raise  the  mean  level  of 
the  ocean  floor  by  the  quotient  of  651.8-^509.9=1.278  kilo- 
meters. The  level  of  the  earth's  crust  would  therefore  be 
—  3,681-1-1,278=  — 2,403  meters,  or  approximately  — 2,400 
meters  (  —  1,313  fathoms)  below  the  present  sea-level.  This  is 
called  the  mean  sphere  level  (mittlere  Krustenniveau) ,  which  Penck 
originally  placed  at  — 2,500  meters  ( — 1,367  fathoms),  but  more 
recently  at  2,400  meters  (22:125).  Mill  (19:183),  using  the  fig- 
ures of  Sir  John  Murray  for  height  of  land  and  depth  of  ocean 
cited  above,  finds  the  mean  sphere  level  to  be  — 2,560  meters  or 
— 1,400  fathoms,  while  Romieux  (24:994)  from  the  same  data 
finds  it  to  be  approximately  — 2,360  meters  ( — 1,290  fathoms). 
For  the  whole  earth,  222  million  square  kilometers  lie  above  this 
mean  sphere  level  and  288  million  square  kilometers  below  it.  If 
we  assume  a  smooth  lithosphere,  the  surface  of  which  would  cor- 
respond to  the  mean  sphere  level,  and  the  available  sea  water 
(1,330  million  cubic  kilometers)  were  uniformly  spread  over  this 
surface,  we  would  have  an  approximate  but  uniform  depth  of  2,600 
meters  (1,422  fathoms)  for  the  universal  ocean  (1,330.0-1-509.0— 
2.608  kilometers).  The  oceanic  areas  below  this  depth  of  2,400 
meters  (or  approximately  1,300  fathoms)  constitute  the  abysmal 
areas;  those  above  this  to  the  edge  of  the  continental  shelf  (200- 
meter  or  approximately  100- fathom  line)  the  transitional  areas 
(die  aktischen  Regionen  of  Penck)  and  those  above  this  level 
( — 200  meters  to  -(-8,840  meters)  as  the  continental  area 
(  Penck  ).f 

THE  CONTINENTAL  BLOCK.  The  conception  of  a  continental 
block  was  introduced  by  H.  Wagner  (31  '.749)  for  the  mass  of  land 
(222  million  square  kilometers  in  basal  area)  which  rises  above 
the  mean  crustal  level.  This  he  divides  into:  I.  The  continental 
slope  (Kontinentalabhang),  between  the  median  sphere  level  and  the 

*  If  we  represent  the  continental  mass  as  a  prismatic  block  with  a  square 
base  of  148,800,000  square  kilometers  of  area,  a  side  of  12,198.36  kilometers, 
and  a  height  of  4,380  kilometers,  on  the  scale  of  i/j, 000,000,  we  would  have  a 
block  of  square  base  12.2  meters  on  the  side,  and  4.38  mm.  in  height  and  nearly 
one-fifth  of  this  or  0.83  mm.  would  represent  the  part  above  sea-level. 

f  In  the  original  classification  by  Dr.  Hugh  Robert  Mill,  the  line  between  the 
transitional  and  the  continental  areas  was  drawn  at  sea-level. 


8 


PRINCIPLES    OF    STRATIGRAPHY 


edge  of  the  continental  shelf,  i.  e.,  between  —  200  and  —  2,400 
meters  depth.  2.  The  continental  platform  (Kontinentaltafel) ,  be- 
tween —200  meters  below  and  -{-1,000  meters  above  sea-level; 
and  3.  The  culminating  land  region  (Kulminationsgebiet)  from 
1,000  meters  to  8,840  meters  above  sea-level.  The  abysmal  regions 
are  divided  into  (a)  the  deep  sea  platform  (Tiefseetafel),  between 
the  median  sphere  level  ( — 2,400  meters)  and  — 5,000  meters 
depth ;  and  (b)  the  depressed  region  (Depressionsgebiet) ,  below 


Land 
•^Median  Height  of  Land 


Sea.  Let/el 


Meter 


Mean,  J/>/iere  Lei/eJ 

Mean  Depth  of  S 


MOO 
4009 
MOO 


Million  square  kilometers. 

FIG.  i.     Hypsographic  curve,  showing  subdivisions  of  the  heights  of  the  land 
and  of  the  depths  of  the  sea.     (After  Krummel  ) 

—  5,ooo  meters.  A  more  satisfactory  dividing  line  is  placed  by 
Krummel  at  5,500  meters.  (Fig.  I.)  The  continental  block  has 
roughly  the  form  of  a  star  surrounding  the  north  pole,  and  ex- 
tending its  rays  southward.  (Penck-22:/^i.)  Two  principal 
divisions  of  these  rays  are  recognizable,  the  Old  World  and  the 
New  World,  of  which  the  first  is  divided  into  three  continents, 
Eurasia,  Africa,  and  Australia,  and  the  other  into  two :  North 
America  and  South  America.  The  divisions  are  brought  about  by 
deep  indentations  from  the  sea,  constituting  the  mediterraneans. 
Besides  the  five  continents  mentioned,  there  is  the  continent  of 
Antarctica,  still  little  known,  but  larger  than  Australia  in  area. 
The  two  main  divisions  of  the  continental  block  are  separated  by 
the  "arctic  mediterranean." 


THE   EARTH    AS    A    WHOLE  9 

In  some  respects,  as  has  already  been  stated,  it  might  serve  our 
purpose  better  to  consider  the  main  land  groups  as  three  separate 
continental  blocks,  namely;  the  Old  World  block,  comprising  the 
continents  of  Eurasia,  Africa  and  Australia ;  the  New  World  block 
or  the  two  Americas,  and  the  Antarctic  block.  On  the  basis  of 
such  division  we  may  consider  that  we  have  four  great  oceans 
separating  these  blocks  one  from  another,  namely,  the  Atlantic,  the 
Pacific  and  the  Arctic  *  separating  the  Old  and  the  New  World 
blocks,  and  the  Indian  Ocean  separating  the  Old  World  from  the 
Antarctic  block.  These  oceans  would  then  be  the  intercontinental 
divisions  of  the  sea,  while  the  divisions  of  these  masses  into  conti- 
nents, as  ordinarily  understood,  would  be  accomplished  by  mediter- 
raneans, which  may  then  be  regarded  as  w^racontinental  in  char- 
acter. 

Isostasy.     Carrying  out  this  idea,  we  have  to  consider  the  sea 


FIG.  2.  Diagram  illustrating  the  relationships  between  the  denser  suboceanic 
crustal  blocks  A  and  D  and  the  light  or  terrestrial  crustal  blocks 
B,  C,  when  in  static  equilibrium.  (After  Penck.) 

as  divided  into  four  great  blocks  corresponding  to  the  four  oceans, 
including  the  Arctic.  If  we  divide  the  crust  into  continental  and 
suboceanic  masses  or  crustal  blocks,  we  must  consider  that  these 
masses  are  in  static  equilibrium,  due  to  the  greater  density  of  the 
material  of  the  suboceanic  masses,  as  shown  by  pendulum  experi- 
ments. Penck  (22  -.125-126)  illustrates  these  relations  by  compar- 
ing these  masses  with  boards  of  equal  thickness,  but  of  different 
weights  floating  upon  water.  Those  of  heavier  wood  will  sink 
deeper  than  those  of  lighter  wood,  and  may  be  taken  to  represent 
the  suboceanic  masses.  This  static  equilibrium  of  the  blocks  of  the 
earth's  crust  constitutes  the  phenomenon  of  isostasy,  and  indicates 

*  It  must,  on  the  other  hand,  be  considered  that  the  Arctic  Ocean  has  the 
character  of  a  mediterranean,  in  that  its  abyssal  portion  is  everywhere  separated 
from  that  of  the  sea  as  a  whole.  In  fact,  at  the  present  time,  not  only  is  the 
2,4oo-meter  line  continuous  within  the  Arctic,  but  this  is  equally  true  of  the 
i,ooo-meter  line,  the  depths  between  North  America,  Greenland,  Iceland,  and 
Northern  Europe  not  going  below  this.  That  the  Arctic  Ocean  is  one  independent 
depressed  earth  block  similar  to  those  forming  the  three  great  oceans  can  hardly 
be  doubted.  The  peculiarities  which  differentiate  it  from  the  other  oceans  are 
due  largely  to  its  location  at  the  earth's  axis,  and  to  its  extensive  covering  of  ice. 


TO 


PRINCIPLES    OF    STRATIGRAPHY 


that  these  differences  are  of  fundamental  value,  and  that  hence  the 
great  relief  features  of  the  earth's  surface  have  been  persistent 
since  the  earliest  time  (Fig.  2).  Where  the  isostatic  equilibrium  is 
disturbed  by  erosion  of  the  higher  less  dense  masses,  and  by  the 
transference  of  the  product  to  the  denser  block,  a  compensatory 
deep-seated  transference  of  material  by  flow  must  occur,  from  the 
denser  to  the  lighter,  which  is  accompanied  by  a  sinking  of  the 
upper  part  and  surface  of  the  denser  block  and  a  corresponding 
rise  above  the  level  of  compensation  of  the  upper  part  and  surface 
of  the  less  dense  block.  (Hayford-i3  :/pp.) 

'THICKNESS  OF  THE  EARTH'S  CRUST.  In  considering  the  top  of 
the  lithosphere  as  representing  the  surfaces  of  a  series  of  elevated 
and  depressed  crustal  blocks,  we  naturally  assume  that  the  thick- 

SURF4CE 


SEA  LEVEL 
OCEAN    BOTTOM 


y 


COLUM-M    A 


DEPTH 


DEPTH     Of  COMPENSATION 


FIG.  3.    Diagram  illustrating  the  conception  of  isostatic  equilibrium  and  its 
adjustment  with  change  in  surface.     (After  Hayford.) 


ness  of  the  crust  is  measured  by  the  height  of  these  blocks.  Since 
they  are  considered  to  be  in  a  state  of  isostasy,  it  follows  that,  if 
these  masses  were  divided  into  prismatic  columns  of  equal  basal 
area,  the  pressure  due  to  gravity  at  the  bases  of  these  columns 
would  be  the  same.  The  depth  at  which  this  state  of  equilibrium 
is  found  is  the  depth  of  compensation.  From  calculations  made  by 
the  Coast  and  Geodetic  Survey  on  numerous  observations  scattered 
over  the  United  States,  the  conclusion  has  been  drawn  that  the 
most  probable  depth  of  compensation  is  76  miles,  and  that  it  is 
practically  certain  that  it  is  not  less  than  62  nor  more  than  87  miles. 
(Hayford-i2  177- 7$;  13:^00.)  This  assumes  a  uniform  position  of 
the  level  of  compensation  with  reference  to  depth.  In  Fig.  3, 
adapted  from  Hayford,  columns  A  and  B  have  been  assumed  to 
contain  equal  masses.  There  is  complete  isostatic  equilibrium  and 


THE    EARTH    AS    A    WHOLE  11 

the  pressures  at  the  bases  of  the  two  columns  are  equal.  But,  since 
the  heights  of  the  columns  are  unequal,  it  follows  that  their  densi- 
ties must  also  be  unequal,  the  shorter  column,  B,  having  the  greater 
density.  If  the  mass  is  unequal  in  the  two  columns,  isostatic  com- 
pensation is  incomplete.  At  any  plane,  as  x,  above  the  level  of 
compensation,  the  pressure  of  the  two  columns  will  not  be  the 
same,  since  the  mass  above  this  point  differs.  The  mass  of  column 
A  will  be  greater  than  that  of  column  B,  and  hence  the  pressure  of' 
A  at  x  will  be  greater  than  that  of  B.  If  now,  through  erosion, 
material  from  the  higher  column  A  is  transferred  to  the  lower  col- 
umn B,  the  height  of  the  two  columns  will  be  changed,  and  hence 
the  pressure  at  their  bases  will  not  be  the  same,  but  greater  in  B 
than  in  A.  So  long  as  A  remains  higher  than  B,  any  plain,  as  y, 
cutting  A  and  B  near  the  top,  will  leave  A  heavier  than  B.  If, 
then,  the  weight  of  B  becomes  greater  than  A  at  the  base,  owing  to 
the  loading  of  B,  while  at  y  it  is  still  less  than  A,  owing  to  its  lesser 
mass,  it  follows  that  at  some  intermediate  point,  as  at  x,  it  will  be 
uniform.  This  is  the  "neutral  level,"  which,  however,  rises  as  the 
load  on  B  increases  and  as  A  is  lowered  by  erosion.  Below  the 
neutral  level  x  there  will  be  an  excess  of  pressure  in  the  column 
B  over  that  of  column  A,  and  this  excess  of  pressure  will  increase 
as  the  neutral  level  rises,  through  continued  erosion  and  deposition. 
When  the  pressure  becomes  greater  than  the  natural  resistance  of 
the  material  can  balance,  a  transference  or  flow  of  the  material  from 
B  to  A  will  take  place  below  the  neutral  level.  This  transfer  of 
material  will  be  accompanied  by  an  elevation  of  the  upper  part  and 
surface  of  A,  and  a  sinking  of  the  upper  part  and  surface  of  B, 
unless  there  is  a  compensatory  change  in  volume  of  material. 
Chemical  changes  in  the  mass  relieved  by  erosion  may  cause  further 
expansion  in  volume,  and  consequent  further  rise  of  the  surface,  but 
lowering  of  temperature  throughout  the  entire  block,  due  to  the 
lowering  of  the  surface  by  erosion  and  the  invasion  of  surface  tem- 
peratures into  regions  originally  below  the  surface  and  therefore 
of  much  higher  temperatures,  will  cause  a  slow,  but  continued 
shrinking  of  the  mass.  Hayford  assumes  an  approximate  shrink- 
ing from  this  cause  of  the  crustal  column  of  76  miles,  to  the  amount 
of  30  feet  for  every  1,000  feet  eroded  (13:^04).  In  like  man- 
ner, blanketing  of  the  mass  by  deposition  will  cause  a  rise  in  tem- 
perature and  consequent  expansion  and  increase  in  volume.  If  the 
changes  due  to  variations  in  the  temperature  overbalance  those  due 
to  the  causes  with  opposite  effects,  as  may  be  the  case  in  the  course 
of  a  long  time,  the  regions  of  erosion  may  subside,  as  in  the  event 
of  the  submergence  of  a  peneplain,  while  regions  of  former  deposi- 


12  PRINCIPLES    OF    STRATIGRAPHY 

tion  may  rise.  It  thus  appears  that  the  adjustments  within  the 
earth's  crust  and  the  forces  responsible  for  the  geological  changes 
recognizable  on  the  surface  of  the  earth  are  confined  to  the  upper 
76  miles  of  the  earth's  mass,  or  about  1/53  of  the  radius.  This  we 
may,  therefore,  regard  as  the  crust  of  the  earth,  bearing  in  mind, 
however,  that  there  is  no  marked  line  of  separation  between  the 
crust  and  the  subcrustal  part.  It  is  within  this  crust,  and  chiefly 
within  its  upper  part',  that  we  find  the  seat  of  vulcanism;  that  the 
minor  disturbances  recorded  as  earthquakes,  etc.,  occur;  that  the 
ground  water  circulates,  and  that  the  crushing  and  flowage  of  rocks 
take  place,  and  it  is  by  changes  in  the  crust  as  thus  defined  that 
the  rise  and  fall  of  land  masses  and  sea  bottoms  take  place.  It  is 
of  course  possible  that  the  source  of  some  of  our  basic  volcanic 
rocks  is  deeper  than  75  miles.  Thus  the  density  increase  in  the  earth 
cited  below  suggests  that  basalts  are  derived  from  depths  of  105  to 
137  miles. 

MATERIAL  OF  THE  EARTH'S  CRUST.  Only  the  material  of  the 
lighter  blocks  of  the  earth's  crust,  i.  e.,  those  constituting  the  con- 
tinental masses,  is  open  to  observation,  and  constitutes  the  "rocks 
of  the  earth's  crust."  The  average  specific  gravity  of  this  material 
is  2.2  to  3  (average  2.6),  while  that  of  the  earth  as  a  whole  is 
about  5.6.  This  difference  is  accounted  for  by  assuming  that  the 
material  constituting  the  interior  of  the  earth  (centrosphere)  has 
a  higher  specific  gravity  than  the  earth  as  a  whole.  It  is  clear  that 
if  the  continental  and  suboceanic  crustal  blocks  are  in  the  condition 
of  static  equilibrium,  the  latter  must  consist  of  heavier  or  denser 
material  than  that  of  the  known  surface. 

DEFORMATION  OF  THE  EARTH'S  CRUST.  (Diastrophism.)  The 
larger  deformations  of  the  earth's  crust  consist  in  the  sinking  of 
the  suboceanic  crustal  blocks,  or  the  rise  of  the  continental  blocks, 
or  vice  versa.  These  are  designated  epeiro genie  (continent-mak- 
ing) movements.  Minor  diastrophic  changes  result  from  local 
warpings,  either  up  or  down,  from  faultings,  or  foldings  of  the 
strata.  These  are  designated  as  orogenic  (mountain-making) 
movements,  resulting  in  the  formation  of  mountains.  Local  rising 
of  the  land,  even  though  unaccompanied  by  visible  foldings,  must  be 
considered  as  bowing  or  folding  on  a  large  scale,  and  it  often  pre- 
cedes the  formation  of  folded  mountains,  as  shown  by  the  suc- 
cessive elevations  of  the  Appalachian  Old  Land  (recorded  in  the 
successive  continental  fans),  which  preceded  the  folding  of  the 
strata  at  the  end  of  Palaeozoic  time. 

IV.  THE  PYROSPHERE.  This  is  an  indefinite  region  in  the 
lower  part  of  the  earth's  crust,  or  below  it,  and  designated  as  dis- 


THE    EARTH    AS    A   WHOLE  13 

tinct  because  it  is  the  zone  of  fusion  and  of  the  formation  of  vol- 
canic matter.  Its  existence  is  revealed  by  the  manifestation  of  vol- 
canic phenomena,  and  it  passes  insensibly  on  the  one  hand  into  the 
Lithosphere  and  on  the  other  into  the  Centrosphere,  of  which  it 
may  indeed  be  a  part.  Its  depth  varies  for  different  rocks,  and  it 
cannot  be  regarded  as  constituting  a  continuous  sphere,  as  do  the 
others  so  far  discussed.  Its  consideration  as  a  distinct  sphere  is 
rather  more  for  the  sake  of  convenience  of  discussion. 

V.  THE  CENTROSPHERE.  So  far  as  actual  observation  is 
concerned,  the  greater  part  of  the  geosphere  is  unknown  to  us.  Be- 
yond the  relatively  insignificant  thickness  represented  by  the  known 
part  of  the  earth's  crust  or  lithosphere  open  to  observation,  and  the 
inferred  pyrosphere,  there  is  the  vast  mass  of  the  earth's  interior, 
forever  withdrawn  from  direct  observation  and  approachable  only 
in  an  indirect  manner.  This  is  the  centrosphere  which  may  be  the 
ultimate  storehouse  of  the  earth's  internal  heat.  The  following 
diagram  (Fig.  4),  adapted  from  Crosby,*  will  serve  to  illustrate  the 
relation  between  the  known  and  the  unknown  parts  of  the  earth. 
The  diagram  represents  a  sector  of  the  earth,  two  degrees  or  about 
140  miles  broad.  It  is  drawn  to  a  radius  of  75  inches,  or  a  scale  of 
53  j/3  miles  to  the  inch.  Assuming  the  crust  to  have  a  thickness  of  75 
miles,  and  the  greatest  depth  of  the  atmosphere  at  100  miles,  these 
would  be  represented  by  i^  and  ij^  inches,  respectively.  The 
extreme  depth  of  the  ocean  is  taken  as  31,600  feet  (o.n  inches), 
the  mean  depth  as  12,000  feet  (0.043  inches),  the  mean  height  of 
land  as  2,300  feet  (0.009  inches)  and  the  greatest  height  of  land 
as  29,000  feet  (0.03  inches).  The  length  of  radius  on  this  scale 
being  75  inches,  it  follows  that  the  two  radii  will  meet  at  that 
distance  from  the  surface  of  the  water  line,  i.  e.,  the  distance 
to  the  center  of  the  earth  on  this  scale  is  6l/4  feet  from  the  line 
representing  sea-level.  This  shows  well  the  relative  insignificance 
of  the  surface  features  as  compared  with  the  size  of  the  earth  as  a 
whole. 

TEMPERATURE  OF  THE  EARTH'S  INTERIOR.  (Giinther-10,  1:328.) 
From  observations  in  deep  mines,  artesian  wells,  etc.,  it  appears 
that  there  is  an  increase  in  temperature  downward,  this  being  about 
1°  Fahrenheit  for  every  53  feet  vertical  descent,  or,  in  round  num- 
bers, 100°  per  mile.  (2.5°  to  3°  C.  per  100  meters,  or  about  one 
degree  for  every  40  meters.)  Considerable  variation  is,  however, 
shown  in  different  mines  or  wells.  Thus  the  Sperenberg  bore  hole 
in  North  Germany  (south  of  Berlin),  which  went  to  a  depth  of 

*  Collections  of  Dynamic  and  Structural  Geology  in  the  Museum  of  the  Bos- 
ton Society  of  Natural  History. 


PRINCIPLES    OF    STRATIGRAPHY 


1,273  meters  (3,492  feet),  showed  a  rate  of  increase  of  i°  F.  in 
51.5  feet  depth;  the  bore  at  Schladebach,  Saxony  (west  of  Leipzig), 
extending  to  a  depth  of  1,748  meters  (5,630  feet),  showed  a  rate  of 
increase  of  i°  F.  in  67.1  feet,  while  the  Calumet  and  Hecla  mine 


HEIGHT  OF  ATMOSPHERE, 
too 


FIG.  4.  Diagram  illustrating  the  relation  of  the  superficial  features  of  the 
earth  to  the  entire  mass.  Scale  i  inch  =  53  1-3  miles.  Drawn 
to  radius  of  75  inches  (=4,000  miles). 

. 

of  Northern  Michigan,  with  a  depth  of  4,939  feet,  showed  a  rate  of 
increase  of  i°  F.  in  103  feet  depth,  though  between  3,324  feet  and 
4,837  feet  the  rate  of  increase  was  as  high  as  i°  F.  in  93.4  feet. 
Other  bores  and  mines  show  intermediate  values.*  In  the  Witwa- 

*  The  deepest  well  yet  completed  is  at  Paruschowitz,  Province  of  Silesia, 
which  reached  a  depth  of  2,003  meters  (6,571.5  feet). 


THE    EARTH    AS    A    WHOLE  15 

tersrand  mines,  South  Africa,  the  general  rate  of  increase  was  i°  F. 
for  250  feet,  the  temperature  at  1,000  feet  being  68.75°  F.,  and  at 
8,000  feet  102.35°  (32:^0).  These  observations,  however,  are  re- 
stricted to  the  thin  outer  layer  or  shell  of  the  earth's  crust,  which 
does  not  exceed  1/4000  of  the  earth's  radius,  and  hence  we  are 
scarcely  justified  in  extending  this  rate  over  the  whole  interior  of 
the  earth.  If  continued  at  the  known  rate,  enormous  temperatures 
would  be  met  with  at  a  depth  of  only  a  few  miles.  With  a  regular 
increase  of  one  degree  F.  in  60  feet,  we  would  get  at  the  center  of 
the  earth  a  temperature  of  348,000°  F.,  while  at  the  regular  rate  of 
increase  of  one  degree  F.  in  100  feet,  we  would  get  a  temperature 
of  209,000°  F.  at  the  center.  (4:571.)  On  the  other  hand,  we 
may,  with  Crosby  (5:9),  consider  it  as  more  likely  that  the  in- 
crease in  temperature  is  at  a  constantly  diminishing  rate,  so  that  the 
interior  temperatures  do  not  exceed  those  with  which  we  are  ac- 
quainted on  the  surface. 

INCREASE  OF  DENSITY.  As  already  noted,  the  density  of  the 
earth  as  a  whole  is  5.6,  while  the  median  density  of  the  known 
rocks  of  the  earth's  crust  or  lithosphere  is  only  2.6.  Assuming  a 
regular  and  steady  increase  in  density,  Helmert  (14:475)  has  cal- 
culated that  the  density  of  the  center  of  the  earth  is  11.2.  From 
this  it  is  possible  to  calculate  the  depth  at  which  any  given  density 
of  rocktf  should  prevail,  according  to  the  formula: 


h= 


where  0  is  the  given  density,  h  is  the  depth  sought,  and  r  the  radius 
of  the  earth  (r  (equatorial)  =3,959  miles  or  6,375  kilometers). 
(21,  1:442.)  According  to  this  formula  (21,  i:^/j),  andesites  and 
trachytes  with  a  specific  gravity  of  2.7 — 2.8  would  be  derived  from  a 
depth  of  73  to  117  kilometers,  basalts  with  a  specific  gravity  of 
2.9 — 3,  from  a  depth  of  169  to  221  kilometers.  According  to  this 
calculation,  rock-melting  temperatures  (1,200°  C.)  must  exist  at 
a  depth  of  73  kilometers,  which  would  require  a  rate  of  increase  of 
i°  C.  in  61  meters.  That  the  rocks  at  the  depth  at  which  the  tem- 
perature of  1,200°  C.  exists  are  not  in  a  molten  condition,  is  due 
to  the  fact  that  they  are  under  the  weight  of  the  superincumbent 
rock  mass,  and  that  pressure  raises  the  fusing  point.  Thus,  ac- 
cording to  the  experiments  of  Carl  Barus,  as  summarized  by  Clar- 
ence King  (16:7),  basalt,  which  will  melt  at  the  earth's  sur- 
face at  a  temperature  of  1,170°  C.,  will  require  a  temperature  of 
76,000°  C.  (136,800°  F.)  to  fuse  it  at  the  center  of  the  earth.  This 


16  PRINCIPLES    OF    STRATIGRAPHY 

raising  of  the  fusing  point  by  increased  pressure  has  led  to  the  as- 
sumption that,  in  spite  of  the  great  heat,  the  earth's  interior  is  a  solid 
mass.  Dana  and  Crosby  suggested  that  the  earth  might  be  re- 
garded as  a  mass  of  solid  iron  from  the  center  to  within  500  miles 
of  the  surface;  others,  however,  still  hold  to  the  fluid  theory  of  the 
earth's  interior,  more  or  less  universally  accepted  at  the  beginning 
of  the  last  century,  while  still  others  hold  to  the  theory  of  a  gase- 
ous interior  (i:jp5;  9  '.58;  10:554;  33)  with  a  zone  of  liquid  mat- 
ter transitional  to  the  solid  crust. 

VI.  THE  ORGANIC  OR  BIOSPHERE.  This  is  the  sphere 
of  living  matter  which  permeates  the  atmo-  and  hydrospheres,  and 
to  some  extent  the  upper  strata  of  the  lithosphere.  Its  two  main 
divisions,  the  plants  and  the  animals,  are  familiar.  The  first  forms 
a  nearly  continuous  mantle  over  the  land  and  the  shallower  ocean 
bottoms,  and  may  be  spoken  of  as  the  phytosphere;  while  the  sec- 
ond forms  a  less  continuous,  though  more  universally  present  animal 
sphere  or  shell,  which  may  be  designated  the  zoo  sphere. 


INTERACTION  OF  THE  SPHERES. 

Of  the  known  spheres,  the  lithosphere  is  the  most  stable,  and  the 
one  retaining  in  a  more  or  less  permanent  form  the  impressions  re- 
ceived through  the  mutual  interaction  of  the  spheres  upon  each 
other.  The  cycle  of  change,  as  it  affects  the  lithosphere,  has  been 
divided  (11:12)  into:  I.  Lithogenesis,  or  the  origin  and  develop- 
ment of  the  rocks;  2.  Orogenesis,  or  their  deformation  (diastro- 
phism,  including  epeirogenic  elevations),  and  3.  Glyptogenesis,  or 
the  sculpturing  of  the  lithosphere.  In  lithogenesis  all  the  other 
spheres  participate.  Deformation  or  orogenesis  may  be  referred 
especially  to  the  influence  of  the  centrosphere  and  to  gravitative 
forces;  while  glyptogenesis  is  largely  accomplished  by  the  at- 
mosphere and  hydrosphere,  with  minor  contributions  of  the  bio- 
sphere and  pyrosphere. 


Sculpturing  Processes. 

It  will  be  convenient  to  treat  the  sculpturing  processes  while 
discussing  the  characteristics  of  the  spheres  most  actively  engaged 
therein,  leaving  the  larger  aspects  of  the  subject,  i.  e.,  the  land 
forms  due  to  sculpture,  until  we  have  considered  in  detail  the 
processes  of  lithogtnesis  and  orogenesis. 

In  its  broadest  aspects  the  sculpturing  processes  may   be   di- 


INTERACTION    OF   THE    SPHERES  17 

vided  into  the  three  phases :  Erosion,  Transportation,  and  Deposi- 
tion. Erosion  consists  of  ClastattOH*  or  the  breaking  up  of  the  rock 
masses  in  situ ;  and  Ablation,  or  the  separation  of  material  from  the 
main  mass.  The  first  process  is  accomplished  to  a  large  extent 
by  atmospheric  forces  and  hence  is  called  weathering.  It  affects 
only  the  upper  zone  of  the  earth's  crust,  which  is  termed  the 
zone  or  belt  of  weathering,  while  the  zone  beneath  it  is  termed  the 
belt  of  cementation.  The  processes  of  erosion  may  be  tabulated  as 
follows:  (8;  34:573.) 

EROSION. 

I.  CLASTATION  (breaking  up  of  rock  material). 

A.  PHYSICAL  OR  DISINTEGRATION. 

1.  Atmospheric    (generally   included   under   weather- 

ing). 

a.  Insolation  and  radiation. 

b.  Frost  shattering. 

c.  Electrical  (lightning)  shattering,  etc. 

2.  Hydrospheric,  wave  shattering,  etc. 

3.  Pyrospheric,  shattering  by  volcanic  explosion. 

4.  Centrospheric,  shattering  by  earthquakes. 

5.  Biospheric,   shattering  by  growing  organisms,   by 

man,  etc. 

B.  CHEMICAL  OR  DECOMPOSITION. 

1.  Atmospheric   (weathering  in  the  narrower  sense; 

oxidation,  hydration,  carbonation,  etc.). 

2.  Hydrospheric  (hydration,  oxidation,  etc.). 

3.  Pyrospheric   (decomposition  through  the  activities 

of  eruptive  masses;  of  fumaroles,  etc.). 

4.  Biospheric   (decomposition  under  influence  of  liv- 

ing matter,  probably  rare.) 

II.  ABLATION   (separating  off,  or  removal  of  material). 

A.  MECHANICAL. 

i.  Denudation,   removal  of   weathered  or  loose  ma- 
terial, i.  e.,  mantle  rock. 

a.  by  wind  =  deflation. 

b.  by  streams  =  fluvial  ablation. 

c.  by  glaciers  =  exaration. 

d.  by  waves,  shore  currents,  etc. 

e.  by  organisms. 

*  From  Gr.  KXewrds  =  broken,  and  ation. 


i8  PRINCIPLES    OF    STRATIGRAPHY 

2.  Corrasion,  a  filing  process. 

a.  by  wind  =  eolian  corrasion. 

b.  by  running  water=river  corrasion. 

c.  by  ice  =  glacial  corrasion. 

d.  by  waves  =  abrasion. 

e.  by  organisms=  gnawing,  etc. 

3.  Quarrying   (closely  related  to  physical  clastation). 

a.  by  wind  (rare)  undermining  (decapitation  of 

erosion  monuments),  etc. 

b.  by    running    water  =  undermining    (recession 

of  Niagara). 

c.  by  ice=plucking,  sapping. 

d.  by  waves  =  tunneling  and  undermining. 

e.  by    organisms,    plant-wedging,    plucking,    etc., 

man's  work. 
B.  CHEMICAL. 

4.  Corrosion. 

a.  by  air — or  evaporation  (snow,  ice). 

b.  by  water  (aqueous  corrosion) — or  solution. 

c.  by  heat — igneous  corrosion  or  melting. 

d.  by  organisms. 

TRANSPORTATION. 

I.  MECHANICAL. 

A.  IN  SUSPENSION  (in,  and  moving  with  the  mass). 

1.  Atmospheric — by  wind:  eolian  transport. 

2.  Hydro  spheric. 

a.  by  waves,  ocean  and  lake  currents,  tidal  cur- 

rent, undertow,  etc. 

b.  by  rivers  (fluviatile  transport). 

c.  by  ice,  englacial  till ;  ground  moraine,  etc. 

d.  carried  by  floating  host — such  as : 

(1)  floating  dead  organisms    (stones   held  by 
floating  trees,  etc.). 

(2)  icebergs,  shore  ice,  etc. 

(3)  rafts,  ships,  etc. 

3.  Pyrospheric — suspended  in  molten  lava. 

4.  Biospheric — transported     by    animals     either     ex- 

ternally or  internally. 

B.  BASALLY,  by  shoving,  rolling,  sliding,  etc. 

i.  Atmospheric — rolling   by    wind,    as    sand    of    sand 
dune,  etc. 


INTERACTION    OF    THE    SPHERES  19 

2.  Hydrospheric — 

a.  by  water  currents. 

b.  by  ice,  terminal  moraines,  etc. 

c.  by  snowslides,  etc. 

3.  Centra  spheric — purely  under  the  influence  of  gravi- 

tation. 

4.  Biospheric — by  man,   and  more   rarely   other  ani- 

mals. 
II.  CHEMICAL:     In  solution. 

1.  Atmospheric — dissolved    in    air,    as    water-vapor, 

gases,  etc. 

2.  Hydrospheric — dissolved  in  water,  e.  g.}  salt. 

3.  Pyrospheric — in  igneous  solution. 

4.  Biospheric — as  body  constituents,  etc. 


DEPOSITION. 

A.  MECHANICAL. 

1.  Atmospheric — by  wind,  etc.     Atmoclastic  and  ane- 

moclastic  deposits. 

2.  Hydrospheric — by  water.     Hydroclastic  deposits. 

3.  Pyrospheric — by   igneous   action.      Pyroclastic   de- 

posits. 

4.  Biospheric — by  animals,  including  man.     Bioclastic 

deposits. 

B.  CHEMICAL. 

1.  Atmospheric — atmogenic  deposits — snow,  etc. 

2.  Hydrospheric — hydrogenic   deposits,   salt,  gypsum, 

etc. 

3.  Pyrospheric — pyrogenic  or  igneous  deposits. 

4.  Biospheric — biogenic  deposits   (coral  rock),  etc. 


DEFINITION  AND  SUBDIVISIONS  OF  GEOLOGY. 

Geology  is  the  science  of  the  entire  earth.  The  common  im- 
pression of  the  layman,  that  geology  is  the  study  of  the  lithosphere 
alone,  is  a  misconception,  based  on  the  fact  that  the  geologist  con- 
cerns himself  largely  with  the  crust  of  the  earth,  since  here  he  finds 
the  record  of  the  history  he  seeks  to  read.  According  to  the  division 
of  the  earth  as  a  whole  into  a  series  of  spheres,  as  already  set  forth, 
we  may  divide  the  science  of  geology  as  a  whole  into  the  following 
branches : 


20  PRINCIPLES    OF   STRATIGRAPHY 

Inorganic 
Atmology  (Meteorology) 

t  Oceanography  (Oceanology) 
Hydrology \  Limnology 

I  Potamology 


Geology  • 


Lithology  (Petrology,  Geology  in  the  narrow  sense) 


Pyrogeology  (Vulcanology) 
Organic 

r  Zoology  (including  palseozoology) 
Biology |  Phytology  (Botany)  including  palaso- 

<•     botany 

Since  no  direct  study  of  the  Centrosphere  is  possible,  no  corre- 
sponding science  has  been  developed.  (See,  however,  Chapter 
XXIII.) 

Each  branch  or  science  may  again  be  treated  under  the  follow- 
ing headings  :  dynamics,  structure,  and  history  or  genetics.  Dynami- 
cal geology  in  the  broadest  sense  deals  with  the  physical  and  chemi- 
cal forces  and  their  working.  In  the  narrow  sense,  dynamical 
geology  is  dynamical  lithology,  or  the  working  of  the  physical  and 
chemical  forces  in  and  upon  the  earth's  crust.  Dynamical  biology  is 
designated  physiology.  Hydrology  and  atmology  (meteorology)  are 
largely  a  treatment  from  the  dynamic  point  of  view  of  the  water 
and  the  atmosphere,  respectively,  dealing  especially  with  the  move- 
ments of  these.  Volcanic  manifestations  illustrate  the  dynamics  of 
the  pyrosphere,  or  p^ro  dynamics,  while  earthquakes  illustrate  the 
dynamics  of  the  centrosphere,  or  rather  their  effect  upon  the  litho- 
sphere.  The  interaction  of  the  spheres  upon  one  another  must  here 
be  considered  as  developing  the  exogenous  dynamic  forces.  Thus 
the  action  of  the  atmosphere,  hydrosphere,  biosphere,  and  pyro- 
sphere upon  the  lithosphere  furnishes  the  exogenous  dynamic  prod- 
ucts which  are  manifested  chiefly  in  the  clastic  rocks ;  while  the  en- 
dogenous dynamic  forces  reside  within  the  material  of  the  earth's 
crust,  and  are  manifested  in  chemical  combinations,  in  crystalliza- 
tion, etc. 

From  the  point  of  view  of  structure,  structural  lithology  (struc- 
tural geology  in  the  narrower  sense)  deals  with  the  composition 
and  arrangement  of  the  material  of  the  earth's  crust,  and  comprises : 
i,  elements;  2,  minerals  (mineralogy)  ;  3,  rocks  (petrology,  petrog- 
raphy, lithology  in  the  narrower  sense)  ;  4,  large  structural  fea- 
tures (geotectology  or  the  study  of  the  architecture  of  the  earth's 
crust)  ;  5,  the  surface  features  (lithomorphology,  physical  geogra- 
phy). Structural  biology  comprises  the  study  of:  i,  the  cell  (cytol- 
ogy) ;  2,  the  tissues  (histology)  ;  3,  the  larger  structures  (anatomy)  ; 


SUBDIVISIONS    OF    GEOLOGY  21 

4,  the  form  (biomorphology),  etc.  Structural  hydrology  comprises 
the  study  of  composition  (hydrochemistry),  classification  according 
to  form  (hydromorphology),  such  as  oceans,  lakes,  rivers,  etc.,  each 
of  which  has  developed  a  special  science  to  which  are  applied  the 
names  oceanography  (oceanology,  thalassography),  the  hydrology 
of  oceans;  limnology,  the  hydrology  of  the  lakes;  and  potamology, 
or  the  hydrology  of  the  rivers.  Structural  atmology-or  meteorology 
considers  the  composition  of  the  atmosphere,  its  density,  etc.  The 
composition  and  structure  of  the  Pyrosphere  is  only  indirectly  as- 
certainable,  while  those  of  the  Centrosphere  fall  into  the  realm  of 
speculation. 

The  historic  or  genetic  aspect  of  these  sciences  likewise  affords 
an  interesting  series  of  parallels.  Thus  historical  or  genetic  lithol- 
ogy,  or  the  science  of  lithogenesis  in  its  broadest  sense,  deals  with 
the  origin  not  only  of  the  rocks  as  such,  but  also  of  the  structures 
they  exhibit,  and  must  necessarily  take  account  of  the  conditions 
under  which  they  were  formed.  The  study  of  the  genesis  of  the 
stratified  rocks  is  stratigraphy,  which,  however,  is  closely  bound  up 
with  the  other  branches  of  the  earth  science,  and  cannot  be  made 
independent  of  them.  Historical  biology  or  the  science  of  bio- 
genesis is  the  science  of  organic  evolution.  It  may  be  considered 
from  the  botanical  side  (phylogenesis),  or  from  the  zoological  side 
(zoo genesis),  with  reference  to  the  individual  (ontogenesis)  or 
to  the  race  (phylogenesis).  Palaeontology,  or  the  science  of  the 
past  life  of  the  earth,  traces  the  phylogeny  back  through  the  suc- 
cessive geologic  periods,  and  is,  therefore,  the  complement  of 
neobiology,  or  the  science  of  modern  life,  and  further  demonstrates 
the  intimate  relationship  between  the  organic  and  the  inorganic 
sciences.  Hydrogenesis,  atmogenesis,  and  pyrogenesis  are  branches 
of  historical  geologic  science  as  yet  little  developed. 

While  stratigraphy  is  thus  more  especially  the  science  of  the 
genesis  of  the  stratified  series  of  rocks,  it  necessarily  includes  and 
is  based  upon  the  study  of  the  rocks  themselves,  of  their  arrange- 
ment or  structures,  and  of  the  morphology  of  the  earth's  surface 
during  their  formation.  Thus  it  comprises  the  subject  of  Palce- 
ogeography,  or  the  geography  of  former  times,  and  it  furthermore 
takes  careful  account  of  the  physical  conditions  of  the  land  and  sea 
as  indicated  by  the  organic  remains  entombed  in  the  strata.  Nor 
can  it  leave  out  of  consideration  the  various  diastrophic  movements 
and  their  results,  during  all  the  geologic  periods ;  while  igneous 
activities,  in  so  far  as  they  affected  the  strata  of  the  earth's  crust, 
also  belong  to  the  field  of  legitimate  inquiry  for  the  stratigrapher. 
In  other  words,  stratigraphy  is  the  science  of  the  evolution  of  the 


22  PRINCIPLES    OF    STRATIGRAPHY 

lithosphere  since  the  formation  of  the  Archaean  rocks.    The  follow- 
ing table  gives  the  larger  divisions  of  this  evolutionary  history : 

TABLE  or  THE  DIVISIONS  OF  GEOLOGICAL  TIME. 

-~              .         ,-\                  j.-  f  Recent  or  Holocenic 

Psychozoic  or  Quaternary  time 1  Heist 

Pliocenic 

~  ™    , .  Miocenic 

Cenozoic  or  Tertiary  time ~r 

Ohgocemc 

Eocenic 
Cretacic 

Mesozoic  or  Secondary  time .  .  , .    C°manchlc 

Jurassic 

Triassic 

Permic 

Carbonic 

Mississippic 


Palaeozoic  or  Transition  time , 


Devonic 


Siluric 
Ordovicic 
Cambric 

Proterozoic    (Eozoic)    or    Primary   time    (in  j  Keweenawic 
part)  Algonkian I  Huronic 

Azoic  (Archaeozoic)  or  Primary  time  (in  part)  j  Keewatic 
Archaean 1  Laurentic 

BIBLIOGRAPHY  I. 

1.  ARRHENIUS,   SVANTE.     1900.     Geol.  Foren.  Forhandl.     Vol.  XXII. 

2.  BARUS,    CARL.     1891.     The  Contraction  of  Molten  Rock.     American 

Journal  of  Science,  3rd  ser.,  Vol.  XLII,  pp.  498-499. 

3.  BARUS,   CARL.     1892.     The  Relation  of  Melting  to  Pressure  in  Case  of 

Igneous  Rock  Fusion.     Ibid.     Vol.  XLIII,  pp.  56-57. 

4.  CHAMBERLIN,  THOMAS  C.,  and  SALISBURY,  ROLLIN  D.     1906. 

Geology,  Vol.  I. 

5.  CROSBY,   WILLIAM   OTIS.     1892.     Dynamical   Geology  and   Petrog- 

raphy. 

6.  DAVIS,  WILLIAM  MORRIS.     1899.     Elementary  Meteorology. 

7.  FULLER,    MYRON    L.     1906.     Water    Supply    and    Irrigation    Paper, 

No.  1 60. 

8.  GREGORY,  J.  W.     1911.     The  Terms  Denudation,  Erosion,  Corrosion, 

and  Corrasion.     Geographical  Magazine,  Feb.  1911,  pp.  189-195. 

9.  GUNTHER,  SIEGMUND.     1891.     Lehrbuch  der  Physicalischen  Geog- 

raphic.    Stuttgart. 


BIBLIOGRAPHY    I  23 

10.  GtiNTHER,     SIEGMUND.     1897.     Handbuch     der     Geophysik.     2nd 

edit.     Stuttgart.     2  volumes. 

11.  HAUG,  EMILE.     1907.     Traite"  de  Geologic.     T.I. 

12.  HAYFORD,  JOHN  F.     1909.     The  Figure  of  the  Earth  and  Isostasy 

(and  Supplementary  Investigation).     U.  S.  Coast  and  Geodetic  Survey. 

13.  HAYFORD,  JOHN  F.     1911.     Vice-presidential  address  before  section  D 

of  A.  A.  A.  S.     The  Relation  of  Isostasy  to  Geodesy,  Geophysics,  and 
Geology.     Science,  N.  S.,  Vol.  XXXIII,  Feb.  10,  pp.  199-208. 
14..    HELMERT,  F.  R.    1884.    Theorien  der  hoheren  Geodesie.  Leipzig,  Vol.  II. 

15.  KEMP,  JAMES  FURMAN.     1901.     The  Role  of  the  Igneous  Rocks  in  * 

the  Formation  of  Veins.  American  Institute  of  Mining  Engineers. 
Richmond  Meeting. 

16.  KING,  CLARENCE.     1893.     The  Age  of  the  Earth.     American  Journal  v 

of  Science,  3rd  ser.,  Vol.  XLV,  pp.  1-20. 

17.  KRUMMEL,   OTTO.     1907.     Handbuch  der  Ozeanographie.      Band    i, 

2nd  edit. 

1 8.  LYELL,    CHARLES.     1875.     Principles    of    Geology.     Twelfth    edition, 

Vol.  II. 

19.  MILL,    HUGH   ROBERT.     1890.     The   Vertical   Relief   of   the   Globe.  v 

Scottish  Geographic  Magazine.     Vol.  VI,  pp.  182-187,  with  map. 

20.  MURRAY,  JOHN.     1888.     On  the  Height  of  the  Land  and  the  Depth  of  v 

the  Ocean.     Scottish  Geographic  Magazine.     Vol.  IV,  p.  I  et  seq. 

21.  PENCK,  ALBRECHT.     1894.     Morphologic  der  Erdoberflache,  Vol.  I. 

22.  PENCK,  ALBRECHT.     1908.     Die  Erdoberflache  in  Scobel's  Geographi- 

sches  Handbuch. 

23.  PENCK,  A.,  and  SUPAN,  A.     1889.     Mittheilung  liber  Murray's  "Die 

Mittlere  Hohe  des  Landes  und  die  Mittlere  Tiefe  des  Meeres."  Peter- 
mann's  Mittheilungen,  Bd.  XXXV,  pp.  17-21. 

24.  ROMIEUX,   A.     1890.     Relations  entre  la   deformation   actuelle   de  la 

croute  terrestre  et  les  densities  moyennes  des  terres  et  des  Mers.  Comptes 
Rendus  des  Seances  de  1'  academie  des  Sciences.  Paris,  T.  CXI. 

25.  SLIGHTER,  CHARLES  S.     1902.     Water  Supply  and  Irrigation  Paper, 

No.  67.     U.  S.  G.  S. 

26.  STAPFF,  F.  M.     1894.     Ueber  die  Zunahme  der  Dichtigkeit  der  Erde 

nach  ihrem  Innern.     Gerland's  Beitrage  zur  Geophysik,  Vol.  II. 

27.  SUESS,  EDUARD.     1888.     Das  Antlitz  der  Erde,  Bd.  II. 

28.  SUESS,  EDUARD.     1906-     The  Face  of  the  Earth,  Vol.  II. 

29.  TUMLIRZ,  O.     1892.     Die  Dichte  der  Erde,  berechnet  aus  der  Schwer- 

rebeschleunigung  und  der  Abplattung.  Sitzungsberichte  K.  Acad.  d. 
Wiss.  Wien.  Math.  Nat.  Klasse.  CI,  Abh,  Ha,  pp.  1528-1536. 

30.  VAN    HISE,    CHARLES    R.     1904.     A    Treatise    on    Metamorphism. 

United  States  Geological  Survey,  Monograph,  Vol.  XLVII. 

31.  WAGNER,    HERMANN.     1894.     Areal    und    Mittlere    Erhebung    der 

Landflachen  sowie  der  Erdkruste.  In  Gerland's  Beitrage  zu  Geophysik 
Bd.  II. 

32.  WATSON,  THOMAS  L.     1911.     Underground  Temperatures.     Science, 

N.  S.,  Vol.  XXXIII,  pp.  828-831. 

33.  WOODWARD,  R.  S.     1889.    Mathematical  Theories  of  the  Earth.     Pro- 

ceedings of  the  American  Association  for  the  Advancement  of  Science, 
pp.  59-63;  American  Journal  of  Science,  3rd  ser.  Vol.  XXXVIII,  pp. 
337  et  seq. 

34.  WALTHER,  JOHANNES.     1893-4.     Einleitung  in  die  Geologie  als  histor- 

ische  Wissenschaft. 


A.  THE  ATMOSPHERE. 


CHAPTER   II. 

CONSTITUTION,  PHYSICAL  CHARACTERISTICS  AND  MOVEMENTS 
OF  THE  ATMOSPHERE;  GEOLOGIC  WORK  OF  THE  ATMOS- 
PHERE. 

COMPOSITION  OF  THE  ATMOSPHERE. 

As  already  noted,  the  atmosphere  consists  of  a  mechanical  mix- 
ture of  oxygen  and  nitrogen  with  some  argon,  the  proportion  in 
pure  dry  air  being: 

By  weight.     By  volume. 

Oxygen 23.024  20.94! 

Nitrogen 75-539 

Argon 1-437 

100.000    100.000 

Air  is  always  impure,  water  vapor  and  carbon  dioxide,  as  well  as 
various  organic  and  inorganic  impurities  being  generally  present  in 
variable  quantities.  The  average  volumetric  composition  of  the 
gases  of  the  atmosphere  in  parts  per  10,000  is  as  follows  (29:860)  : 

Oxygen 2,065  •  94°  Ozone 0.015 

Nitrogen 7,711 .600  Aqueous  vapor 140.000 

Argon  (about) 79.000  Nitric  acid 0.080 

Carbon  dioxide 3 . 360  Ammonia o .  005 

In  addition  to  this  there  is  often  found  free  hydrogen,  up  to  one 
part  in  5,000  by  volume  (Gautier),  methane,  benzine  and  its  homo- 
logues,  etc.  Other  compounds  are  formaldehyde  (2  to  6  gr.  per 
loo  cu.  meters),  and  sulphur  compounds,  especially  H2S,  which  be- 
comes oxidized  to  SO2.  Sulphur  dioxide  is  also  derived  from  vol- 
canoes and  the  combustion  of  coal,  and  has  been  found  at  Lille 
(France)  to  the  extent  of  1.8  cu.  cm.  of  SO2  in  i  cu.  meter  of  air. 
It  is  returned  to  the  ground  as  H2SO4  in  rain  water.  So  universally 

24 


COMPOSITION    OF    THE    ATMOSPHERE  25 

are  water  vapor  and  CO2  present,  that  we  can  speak  of  a  triple  at- 
mosphere, one  an  intimate  mixture  of  oxygen  and  nitrogen,  and 
the  other  two  of  water  vapor  and  CO2,  respectively,  diffused  through 
the  pure  air  atmosphere. 

NITROGEN  is  the  inactive  element,  though  animals  and  plants  ap- 
propriate it  through  the  formation  of  nitrogenous  compounds. 

OXYGEN,  the  active  element  of  the  atmosphere,  is  consumed  by 
all  animals  and  taken  either  directly  from  the  air,  or,  in  the  case  of 
water-living  animals,  from  the  water  in  which  it  is  dissolved.  De- 
caying organic  matter  consumes  oxygen,  and  so  do  some  minerals 
during  the  process  of  oxidation.  Oxygen  is  supplied  to  the  air  by 
the  growth  of  plant  life,  which  breaks  up  CO2,  using  the  carbon 
and  setting  part  of  the  oxygen  free.  Volcanic  vents  also  supply 
oxygen,  while  another  source  of  supply  is  found  in  the  deoxidation 
of  minerals.  Thus  the  quantity  of  oxygen  withdrawn  from  the  air 
is  balanced  by  that  supplied,  so  that  the  relative  amount  remains 
practically  constant. 

ARGON,  first  separated  from  the  nitrogen  of  the  air  in  1895,  is 
like  that  element  exceedingly  inert,  its  power  of  combining  with 
other  elements  being  even  less  than  that  of  nitrogen.  It  forms  about 
0.94  per  cent,  by  volume,  or  1.44  per  cent,  by  weight,  of  the  at- 
mosphere. Other  previously  unknown  gases  in  the  atmosphere  are : 
helium,  i  to  2  parts  per  million ;  neon,  i  to  2  parts  per  hundred 
thousand;  krypton,  I  part  in  20  millions;  xenon,  i  part  in  170  mil- 
lions. These  are  as  inert  as  argon. 

CARBON  DIOXIDE  (CO2).  This  is  a  relatively  constant  constitu- 
ent of  the  air,  making  about  0.03  per  cent,  by  volume,  or  three  parts 
in  10,000  of  the  entire  atmosphere.  It  is  supplied  to  the  atmosphere 
by  the  burning  or  decay  of  organic  matter,  by  the  respiration  of  ani- 
mals, as  well  as  by  volcanic  emanations  and  other  agents.  Artifi- 
cial consumption  of  coal  and  other  burnables  furnishes  a  large  sup- 
ply of  CO2  to  the  atmosphere,  a  ton  of  bituminous  coal  (75  per  cent, 
of  carbon)  furnishing  about  2^4  tons  of  CO2  ( Salisbury-83  15 15) . 
Since  the  amount  of  CO2  in  the  air  remains  relatively  constant,  a 
quantity  equal  to  that  supplied  [estimated  at  several  billion  tons  a 
year  (Salisbury)]  must  be  removed  from  the  air.  The  chief  agents 
active  in  abstracting  CO2  from  the  air  are  chlorophyll-forming 
plants,  which,  as  already  remarked,  find  in  it  the  source  of  carbon 
for  their  tissues.  Carbonization  of  mineral  matter,  or  the  com- 
bination of  the  CO2  with  other  elements,  is  another  cause  of  the 
reduction  of  the  amount  of  CO2  in  the  air. 

WATER  VAPOR.  The  water  vapor  of  the  atmosphere  varies  with 
temperature  and  other  local  conditions,  and  with  the  amou^-  sup- 


26  PRINCIPLES    OF    STRATIGRAPHY 

plied.  It  is  precipitated  in  the  form  of  dew,  rain,  snow,  frost, 
etc.,  and  is  constantly  returned  to  the  atmosphere  by  evaporation. 
In  damp  countries  near  the  equator  the  amount  of  water  vapor  in 
the  air  may  be  3  or  even  4  per  cent,  by  volume  of  the  whole  air. 
Thus  at  Batavia  (Java),  where  the  vapor  pressure  is  21  mm.,  the 
amount  of  water  in  the  air  is  2.8  per  cent,  by  volume.  The  com- 
position of  the  air  here  is:  N  76.8%,  O  20.4%,  H2O  2.8%  and 
a  few  hundredths  of  a  per  cent,  of  CO2.  At  Allahabad  (Persia) 
during  the  rainy  season,  4  per  cent,  of  water  vapor  by  volume  has 
been  found  in  the  air  (calculated  from  the  vapor  pressure,  which 
was  30.7  mm.).  In  central  Europe,  even  in  summer,  with  a  vapor 
pressure  of  about  10  mm.,  the  volume  of  water  in  the  air  amounts 
to  only  1.3  per  cent.  (Hann-4o:7^.) 

Absolute  and  Relative  Humidity.  Expressed  in  weight  of  wa- 
ter, the  amount  which  one  cubic  foot  of  air  can  hold  is  as  follows : 
one-half  grain  of  water  at  o°  F.,  5  grains  at  60°  F.,  and  II  grains 
at  80°  F.  At  60°  the  amount  which  the  air  of  a  room  4Ox4<Dx  15 
ft.  can  hold  is  nearly  20  pounds,  or  almost  enough  to  fill  a  common 
water  pail.  The  amount  of  moisture  which  the  air  contains  is  its 
absolute  humidity.  The  percentage  of  moisture  which  the  air  con- 
tains at  a  given  temperature,  of  that  which  it  would  contain  at  that 
temperature  if  it  were  saturated,  is  its  relative  humidity,  which  is 
50  when  the  air  contains  only  half  the  amount  which  it  could  con- 
tain at  saturation  at  that  temperature.  In  the  latter  state  the  hu- 
midity is  100.  The  average  relative  humidity  of  the  air  on  the  land 
is  perhaps  60  per  cent.,  and  over  the  ocean  about  85  per  cent.  Be- 
low 65  per  cent,  the  air  becomes  dry.  In  semiarid  regions  it  ranges 
around  45  per  cent.,  and  in  desert  regions  it  ranges  around  25  or  30 
per  cent. 

At  Ghadames  (Hann-4O:/5/),  western  Tripoli,  the  relative  hu- 
midity for  July  is  27  per  cent,  and  for  August  33  per  cent.  The 
oasis  of  Kufra,  in  the  heart  of  the  Libyan  desert,  has  a  relative 
humidity  of  27  per  cent,  in  August,  33  per  cent,  in  September,  and 
17  per  cent,  for  the  3  P.M.  August  mean.  The  oasis  of  Kauar,  in 
the  heart  of  the  Sahara,  has  a  mean  relative  humidity  of  27  per 
cent,  in  August.  In  the  Punjab  district  of  India,  the  relative  mean 
humidity  in  May  is  31  per  cent,  at  Lahore,  while  at  Agra,  in  the 
northwest  province,  it  is  36  per  cent.  It  must,  of  course,  be  borne 
in  mind  that  the  observations  made  in  the  inhabitable  portions  of 
the  desert  regions,  i.  e.,  the  oases,  give  a  much  higher  relative 
humidity  than  occurs  in  the  open  desert  itself. 

In  the  semiarid  regions  of  southwestern  United  States,  the  fol- 
lowing humidities  occur: 


COMPOSITION    OF    THE    ATMOSPHERE 


27 


Mean 

Mean 

annual 

monthly 

Place 

relative 

minimum 

Month 

humidity 

humidity 

Yuma,  Arizona  

42.0% 

74  7% 

June 

Santa  Fe,  New  Mexico  

44.8% 

28.7% 

June 

Pueblo,  Colorado 

46   2% 

VI  6% 

April 

)eath  Valley,  California,  a  typical  American  desert,  showed  a  mean 
relative  humidity  of  23  per  cent,  for  the  five  months  from  May  to 
September  in  1891.  In  regions  of  summer  rain  the  relative  humidity 
is  high,  even  far  inland.  Thus  at  Dorpat,  Baltic  Provinces  of  Rus- 
sia, the  mean  relative  humidity  in  summer  is  73  per  cent. ;  at  Yeni- 
seisk, Central  Siberia,  it  is  70  per  cent. 

Source  of  Water  Vapor.  Evaporation  is  the  chief  source  of  the 
water  vapor  of  the  air.  All  exposed  moist  surfaces  furnish  water 
vapor  to  the  atmosphere,  the  conversion  of  water  into  vapor  con- 
stituting evaporation.  Evaporation  is,  of  course,  most  marked  over 
large  water  surfaces,  such  as  the  oceans,  the  ultimate  source  of  the 
water  vapor,  and  over  lakes,  ponds,  etc.  It  is  estimated  that  the 
average  amount  of  evaporation  from  the  surface  of  the  earth 
amounts  to  a  layer  30  or  40  inches  deep  each  year.  (Some  esti- 
mates make  it  60  inches.)  At  this  rate,  if  the  water  were  not  re- 
turned to  the  sea,  the  oceans  would  be  dried  up  in  from  3,000  to 
4,000  years,  while  the  lakes  of  the  earth  would  probably.be  ex- 
hausted in  a  single  year.  The  water  evaporatipn  from  the  surface 
of  the  Mediterranean  and  Black  Seas  is  estimated  as  more  than 
226  cubic  miles  per  annum.  Evaporation  may  be  going  on  from  an 
approximately  dry  land  surface,  the  moisture  being  drawn  from 
beneath  the  surface.  By  such  processes  mineral  matter  held  in 
solution  within  the  pores  of  the  rock  is  drawn  to  the  surface,  and 
there  left  on  evaporation.  Such  is  the  origin  of  the  brown  desert 
varnish  on  rock  surfaces,  and-  the  efflorescence  of  salt  and  alum 
found  on  many  rocks.  Snow  and  ice  also  evaporate,  at  a  tempera- 
ture below  the  melting  point,  for  snow  and  ice  slowly  disappear, 
even  in  temperatures  below  32°  F. 

Other  sources  of  water  vapor  are  animal  and  plant  respiration, 
and  volcanic  ejections,  the  latter  often  adding  an  appreciable 
amount. 

IMPURITIES.  The  impurities  of  the  atmosphere  are  in  large 
part  inorganic  particles  or  dust.  Organic  matter,  such  as  spores  of 
plants,  bacteria,  etc.,  also  abounds,  but  the  dust  is  by  far  the  most 


28  PRINCIPLES    OF    STRATIGRAPHY 

prevalent.  In  dust  storms  the  amount  is,  of  course,  extreme,  but 
ordinary  air  sometimes  carries  a  surprising  amount.  Thus,  in  Eng- 
land, during  the  fogs  of  February,  1891,  the  amount  of  dust  de- 
posited on  the  previously  washed  glass  roofs  of  the  plant  house  at 
Kew  was  30  grams  to  20  square  yards,  while  at  Chelsea  40  grams 
were  deposited  over  the  same  area.  This  represents  22  pounds  to 
the  acre,  or  six  tons  to  the  square  mile.  Of  this  amount,  uncon- 
sumed  carbon  (soot)  formed  42.5  and  39  per  cent.,  respectively, 
and  41.5  and  33.5  per  cent,  was  other  mineral  matter,  including 
some  metallic  iron.  (Hann-4o:/7;  Russell-8i.) 


OPTICAL  CHARACTERS  OF  THE  ATMOSPHERE. 

LIGHT.  The  three  chief  effects  produced  by  the  energy  of  the 
sun's  rays  are  optical,  thermal,  and  chemical.'  We  may  thus  speak 
of  light  rays,  heat  rays,  and  chemical  or  actinic  rays,  bearing  in 
mind  that  the  difference  of  effect  does  not  lie  in  the  differences  of 
the  rays,  but  in  the  nature  of  the  surface  on  which  they  fall. 

The  rays  of  the  most  importance  to  vegetal  life  are  the  luminous 
or  light  rays,  i.  e.,  the  components  of  radiation  near  the  red  end  of 
the  visible  spectrum,  rather  than  at  the  blue  and  violet  end.  Experi- 
ments with  monochromatic  light  on  Mimosa  pudica  have  shown 
that  the  plant  thrives  best  in  red  light  and  least  in  blue.  "The  red 
and  the  yellow  rays  are  the  most  active  in  promoting  the  respira- 
tion and  the  transpiration  of  the  leaves  and  the  assimilation  of  car- 
bonic acid/'  (C.  Flammarion,  quoted  by  Hann~4o:jd.) 

Diffusion  of  daylight.  The  sunlight  on  penetrating  our  atmo- 
sphere is  scattered  or  diffused  by  the  particles  of  dust  in  the  air, 
and  thus  the  illumination  of  the  whole  atmosphere  on  the  sunny 
side  of  the  earth  is  produced.  If  it  were  not  for  the  dust,  it  is 
probable  that  the  sky  would  be  black,  the  stars  visible  by  day,  and 
darkness  prevail  in  all  shady  places,  while  those  exposed  to  the  sun 
would  be  illumined  with  dazzling  brilliancy.  The  color  of  the  sky 
and  the  sunset  and  sunrise  tints  are  largely  due  to  the  presence  of 
the  dust.  The  very  brilliant  sunset  effects  of  the  autumn  and  winter 
of  1883  were  due  to  the  large  amount  of  volcanic  dust  in  all  parts 
of  the  upper  air,  derived  from  the  explosion  of  the  volcano  Kraka- 
toa  (between  Sumatra  and  Java)  from  May  to  August,  1883.  (See 
the  illustrations  in  Hann  (39),  opposite  page  50.) 

Diffused  sunlight  is  of  the  greatest  importance  to  plant  life.  It 
is  the  diffused  light  which  pours  over  all  portions  of  the  plant 
equally,  which  benefits  the  plant  as  a  whole  by  benefiting  all  its  parts. 


TEMPERATURE  OF  THE  ATMOSPHERE     29 

Plants  need  less   light  as  the  temperature  rises,   and  more   as   it 
falls. 

TEMPERATURE  OF  THE  ATMOSPHERE. 

The  chief  source  of  atmospheric  heat  is  the  sun,  while  of  much 
less  significance  is  the  internal  heat  of  the  earth.  Other  local 
causes,  such  as  friction  in  landslides,  etc.,  volcanic  activities,  fires, 
organic  decay,  etc.,  and  movements  of  the  atmosphere  itself,  locally 
warm  the  air,  but  these  are  generally  of  almost  negligible  signifi- 
cance. 

The  amount  of  heat  received  by  the  earth  from  the  sun  each 
year  would,  if  equally  distributed,  melt  a  layer  of  ice  about  141  feet 
thick  over  the  entire  surface  of  the  earth,  or  evaporate  a  layer  of 
water  18  feet  deep;  yet  the  amount  received  is  less  than  1/2,000,- 
000,000  of  the  heat  given  off  by  the  sun.  The  space  outside  of  our 
atmosphere  is  believed  to  have  a  temperature  of  — 273°  C. 
( — 459°  F.),  which  would  be  the  winter  temperature  (coldest 
month)  of  the  polar  regions  of  the  earth  if  there  were  no  at- 
mosphere. The  winter  temperature  of  the  equator  would  be  about 
-(-56°  C.  (4-164.8°  F.).  The  estimated  summer  temperature  at 
the  poles  under  the  same  condition  would  be  +82°  C.  (4-211.6°  F.), 
while  that  at  the  equator  at  the  same  time  would  be  only  4~67°  C. 
(4-184.6  F.),  since  the  polar  regions,  owing  to  their  continuous  day 
in  summer,  would  receive  a  greater  amount  of  total  heat.  The 
minimum  observed  temperature  is  —  60°  C.  and  the  maximum 
4~  80°  C.  The  chief  agents  in  retaining  the  sun's  heat  within  the 
earth's  atmosphere  are  the  carbon  dioxide  and  the  water  vapor, 
which  act  as  thermal  blankets.  It  has  been  estimated  by  Arrhenius 
(2)  that  if  the  amount  of  CO2  in  the  atmosphere  were  in- 
creased 2.5  to  3  times  its  present  value,  the  temperature  in  the 
arctic  regions  must  rise  8°  to  9°  C.  and  produce  a  climate  as  mild 
as  that  of  Eocenic  time,  so  that  magnolias  would  again  grow  in 
Greenland.  On  the  other  hand,  if  the  CO2  were  decreased  to  an 
amount  ranging  from  0.62  to  0.55  of  its  present  value,  a  fall  of 
from  4°  to  5°  C.  would  result  and  glacial  conditions  would  again 
overspread  the  northern  parts  of  the  continents.  These  estimates 
have  been  seriously  questioned,  but  the  general  fact  that  both  CO2 
and  water  vapor  act  as  thermal  blankets  is  established.  Chamber- 
lin  (13,  14,  15)  has  discussed  in  detail  the  bearing  of  these  facts 
on  former  continental  glaciation,  his  argument  being  that  the  ab- 
straction of  the  CO2  from  the  atmosphere  during  the  periods  of  ex- 
tensive vegetal  growth,  i.  e.,  the  periods  of  coal  formation,  tended 


30  PRINCIPLES    OF    STRATIGRAPHY 

to  refrigerate  the  climate.  The  amount  of  CO2  taken  from  the  air 
in  the  known  geologic  periods  and  locked  up  in  the  coals  and  lime- 
stones of  the  earth  has  been  variously  estimated  at  from  20,000  to 
200,000  times  the  present  atmospheric  content,  or  even  more.  An- 
other factor  favoring  the  consumption  of  CO2  is  the  extensive  sub- 
terranean decomposition  of  the  rocks  following  a  period  of  elevation 
with  its  attendant  fissuring  of  the  rock  and  the  deepening  of  the 
zone  of  circulation  of  surface  waters.  These,  supplied  with  CO2  at 
the  surface,  are  active  in  the  carbonation  of  the  decomposing  rocks. 
The  solution  of  limestones  and  other  carbonates  is  a  further  source 
of  abstraction  of  CO2  from  the  atmosphere,  since  the  original  mono- 
carbonates  are  changed  to  bicarbonates  in  the  process  of  solution,  the 
second  molecule  of  CO2  being  derived  from  the  atmosphere.  This 
is,  however,  a  temporary  abstraction,  for  on  the  redeposition  of  the 
limestone,  either  by  chemical  or  organic  agencies,  the  second  mole- 
cule of  CO2  is  set  free  again.  Hence  periods  of  extensive  limestone 
deposition  must  be  periods  of  extensive  supply  of  CO2  to  the  atmos- 
phere, and  this  would  have  the  effect  of  ameliorating  the  climate. 
It  is  important  to  note  that  extensive  coal  formation  is  dependent  on 
the  great  expanse  of  land  areas,  while  extensive  limestone  formation 
depends  on  the  expanse  of  the  sea.  Extension  of  the  land  is  accom- 
panied further  by  an  extension  of  the  deep-seated  circulation,  and  by 
decomposition  and  carbonation  of  the  crystalline  rocks,  as  well  as  by 
periods  of  solution  of  the  carbonates.  The  two  periods  of  great 
land  expansion,  followed  by  well-authenticated  glacial  periods,  are 
the  close  of  the  Palaeozoic  and  that  of  the  Cenozoic.  Other  periods 
are  the  pre-Cambric,  the  close  of  the  Siluric  and  the  opening  of  the 
Devonic,  the  close  of  the  Jurassic  and  opening  of  the  Comanchic, 
and  the  end  of  the  Cretacic.  Periods  of  marine  extension,  on  the 
other  hand,  with  the  formation  of  much  limestone  and  the  accom- 
panying1 setting  free  of  CO2,  were  the  middle  and  early  upper 
Ordovicic,  the  early  Siluric  (Niagaran),  the  Mississippic,  the  upper 
Jurassic,  the  mid-Cretacic,  and  in  some  regions  the  Eocenic  and 
Oligocenic.  Much  evidence  exists  that  these  periods  of  extensive 
limestone  formation  were  periods  of  mild  and  equable  climates,  very 
nearly  uniform  for  all  latitudes. 

Distribution  of  Heat  Within  the  Earth's  Atmosphere.  The  sun's 
heat  is  distributed  through  the  atmosphere  by  radiation,  conduction, 
and  convection.  The  heat  which  the  earth  receives  from  the  sun  is 
returned  to  the  atmosphere  by  radiation.  These  non-luminous  heat 
waves  are  much  more  readily  absorbed  by  the  air  than  the  luminous 
ones  which  reach  it  from  the  sun.  The  atmosphere  in  contact  with 
the  land  is  further  heated  by  conduction,  provided  the  surface  of  the 


TEMPERATURE  OF  THE  ATMOSPHERE     31 

land  is  warmer  than  the  air,  and  this  warmer  air  will  be  distributed 
by  the  setting  in  of  convection  currents.  The  heated  air  expands 
and  rises,  while  the  heavier,  colder  air  from  above  sinks  down  to 
take  the  place  of  that  which  has  risen,  pushing  upward  and  out- 
ward, at  the  same  time,  the  lighter  air  which  still  remains.  Vertical 
and  horizontal  convection  currents  thus  come  into  existence,  and 
distribute  the  heated  air  in  the  atmosphere.  The  surface  of  the  land 
is  heated  four  or  five  times  as  fast  as  the  surface  of  the  water,  due 
partly  to  the  greater  specific  heat  of  the  latter,  the  more  ready  ab- 
sorption of  heat  by  the  land  and  its  reflection  by  the  water.  The 
land  radiates  its  heat  more  readily  than  the  water,  in  which  convec- 
tion currents  tend  to  distribute  it,  while  at  the  same  time  the  heat 
of  the  sun's  rays  penetrates  more  deeply  into  it  than  into  the  land, 
and  a  given  amount  of  heat  is  distributed  through  a  thicker  layer  of 
water  than  of  land.  All  this  shows  that  the  temperature  of  the  air 
over  the  land  is  heated  more  highly  than  that  over  the  water,  and 
conversely  it  is  cooled  more  quickly  than  that  over  the  water.  Hence 
continental  climates  show  greater  annual  extremes  than  those  of  the 
sea.  As  an  example,  two  points  in  62°  N.  latitude  are  given,  one  at 
Thorshaven  on  the  Faroe  Islands,  where  the  mean  annual  range  is 
7.9°  C.  (+3.0°  C.  in  March,  +10.9°  C.  in  July)  the  other  at  Ya- 
kutsk, Siberia,  where  the  range  is  61.6°  ( — 42.8°  C.  in  January, 
+  18.8°  C.  in  July). 

GEOLOGICAL  WORK  OF  HEAT  AND  COLD — CHANGES  IN  TEMPERATURE. 

This  may  be  grouped  under  the  heads  of  (a)  insolation,  or  the 
exposure  to  the  influence  of  the  sun's  rays  by  day;  (b)  radiation, 
or  the  loss  of  heat  at  night  through  cooling;  and  (c)  congelation,  or 
the  work  of  frost. 

Insolation  and  Radiation.  Heating  in  general  causes  expansion 
of  rock  masses  and  decreasing  density,  while  cooling  causes  contrac- 
tion and  an  increase  of  density.  Even  water  follows  this  rule  down 
to  a  temperature  of  +4°  C.,  when  it  reaches  its  maximum  density, 
after  which  it  expands.  Naked  rock  surfaces  may  be  highly  heated 
by  exposure  to  the  sun  during  the  day,  especially  in  the  rarefied  air 
of  high  altitudes.  This  heating  will  affect  the  outer  part  only, 
owing  to  the  poor  conductivity  of  rock,  and  the  resulting  expansion 
will  cause  a  surface  layer  to  scale  off  from  the  cooler,  less  expanded 
mass  below.  On  cooling  at  night,  the  outer  layer  loses  its  heat  most 
rapidly,  and  the  accompanying  contraction  causes  the  rock  to  break. 
Where  changes  of  temperature  are  great  and  regular,  as  on  exposed 
mountain  summits,  the  surface  may  be  characterized  by  scaling-off 


32  PRINCIPLES    OF    STRATIGRAPHY 

layers,  as  in  Mt.  Starr-King,  California,  or  Mt.  Monadnock,  New 
Hampshire;  or  by  breaking  off  of  fragments  of  all  sizes,  which 
cover  the  mountain. top  to  the  frequent  exclusion  of  solid  ledges,  as 
on  Pike's  Peak,  Colorado;  Mt.  Adams,  New  Hampshire;  Sugar 
Loaf  Mountain,  Brazil ;  Ben  Nevis,  Scotland ;  and  most  mountain 
summits.  Such  fragments,  supplemented  by  those  broken  off  by 
frost  action,  accumulate  at  the  foot  of  every  cliff  and  on  every 
steep  slope,  forming  the  talus,  the  surface  angle  of  which  varies 
with  the  coarseness  of  the  material.  (See  Chapter  XIII.) 

The  best  illustration  of  such  disruption  of  rocks  is  seen  in 
desert  regions,  where  changes  of  temperature  are  very  great.  Liv- 
ingston has  described  the  disruption,  with  ringing  sound,  of  the  basalt 
masses  in  South  Africa.  Other  examples  are  cited  from  Brazil  and 
the  Atacama  desert  of  Chile,  where  the  temperature  in  winter  ranges 
from  —12°  C.  at  7  A.M.  to  +37°  C.  at  n  A.M.,  and  the  summer 
temperature  from  +5°  C.  to  +55°  C.  From  tropical  west  Africa 
Pechuel-Loesche  has  recorded  temperature  ranges  of  60°  to  84°  C. 
( Walther-iO4  -.28  et  seq. ;  also  103  :55<5-557  and  literature  there 
cited.)  Walther  has  found  this  shattering  of  rocks  through  insola- 
tion in  limestone,  flint,  sandstone,  porphyry,  granite,  gneiss,  quartz, 
and  other  rocks.  The  crack  penetrates  gradually  into  the  depths  of 
the  rock,  so  that  half-broken  pebbles  are  not  infrequently  found. 
Such  cracks  are  visible  in  rocks  of  all  sizes,  from  fragments  as  large 
as  a  nut  to  blocks  of  the  dimensions  of  a  house.  In  limestone  and 
granites,  Walther  often  found  peripheral  cracks  which  permitted  the 
separation  of  concentric  shells,  varying  in  thickness  from  that  of  a 
sheet  of  paper  in  some  limestones  to  shells  10  cm.  thick  in  some 
granites.  In  Brazil  the  range  of  temperature  is  considerably  more 
than  100°  F.,  while  in  the  northern  United  States  it  is  150°  F. 
( — 30°  to  +125°)  in  half  a  year,  with  a  diurnal  variation  often 
amounting  to  half  that.  (Shaler.) 

Changes  of  temperature  in  like  manner  affect  the  individual 
mineral  constituents  of  the  rock,  as  well  as  their  association  in  the 
rock.  Since  each  mineral  has  its  normal  coefficient  of  expansion  and 
contraction  under  a  given  influence  of  heat  or  cold,  it  follows  that 
irregular  stresses  and  strains  are  set  up  within  a  rock  mass  of  rela- 
tively coarse-grained  minerals  such  as  a  granite,  and  that  this  must 
lead  to  a  slipping  back  and  forth  of  the  minerals  upon  each  other 
with  ultimate  disruption  or  disintegration  of  the  mass  as  a  whole. 
Walther  regards  the  difference  of  color  of  these  minerals  as  of 
especial  significance  (103:556),  and  Branner  (10)  has  also  called 
attention  to  the  fact  that  coarse  texture  likewise  favors  this  type  of 
disintegration.  This  is  well  shown  in  coarse  granites  of  sub-arid 


WORK    OF   THE   ATMOSPHERE  33 

regions  such  as  Pike's  Peak,  the  granite  countries  along  the  Colo- 
rado River  in  Arizona,  the  peaks  of  Mount  Sinai,  and  many  other 
mountain  tops  where  taluses  or  screes  of  crystalline  sand,  made  up 
of  dissociated  minerals  of  the  granite,  characterize  the  exposed 
mountain  sides  and  fill  up  all  the  hollows.  The  feldspar  of  this 
sand  is  generally  fresh  and  unclouded,  the  original  crystals  being 
scarcely  altered.  Such  sands,  reconsolidated  with  little  assortment, 
give  rise  to  peculiar  arkoses  in  which  the  fresh  feldspar  crystals 
form  the  most  striking  feature,  and  may  even  cause  the  rock  to  be  at 
first  mistaken  for  an  unaltered  granite.  Examples  of  this  kind  are 
found  in  certain  parts  of  the  Torridon  sandstone  (pre-Cambric)  of 
the  west  of  Scotland,  and  in  other  rocks.  Granite  bosses,  wherever 
exposed,  are  generally  marked  by  rounded  surfaces,  intersected  per- 
haps by  joint  cracks  into  which  the  disintegration  products  have 
been  washed,  and  which  alone  support  vegetation,  the  granite  sur- 
face being  bare.  Granite  boulders  exposed  to  the  same  forces  will 
crumble  into  heaps  of  crystalline  sand.  Since  the  corners  and 
angles  of  rock  fragments  are  their  most  exposed  portions,  the  first 
being  attacked  from  three  sides,  it  follows  that  disintegrating  blocks 
will  soon  assume  a  rounded  outline.  Concentric  exfoliation  of  the 
disintegrated  outer  portions  of  such  rock  masses  is  observable,  the 
rock  becoming  a  boulder  formed  in  situ  and  often  embedded  in  a 
mass  of  disintegrated  and  partly  decomposed  residual  sand  and  soil. 
Branner,,  discussing  the  effect  of  these  temperature  changes  on  the 
rocks  of  Brazil,  remarks :  "The  unequal  contraction  and  ex- 
pansion of  the  minerals  composing  the  rock  tend  to  disintegrate  the 
entire  mass,  while  the  even  annual  and  diurnal  changes  and  the 
approximately  even  penetration  of  these  changes  cause  the  rock 
to  exfoliate  or  to  spall  off  in  layers  of  even  thickness,  like  the  coats 
of  an  onion,  while  the  crevices  opened  in  the  rocks  admit  acids  and 
gases  and  set  up  a  train  of  reactions  that  sooner  or  later  disinte- 
grate and  decompose  the  entire  rock  mass."  (10:281.) 

The  individual  minerals  themselves  may  likewise  be  affected  by 
this  change  in  temperature.,  since  there  is  differential  expansion 
along  the  different  crystal  axes.  A  cleavable  mineral  like  feldspar 
may  thus  become  potentially  shattered,  innumerable  fine  rifts  form- 
ing along  the  cleavage  planes,  which,  though  insufficient  to  cause 
the  mineral  to  crumble,  yet  admit  air  and  moisture  and  permit 
chemical  decomposition  within  the  crystal.  In  moist  climates  this  is 
seen  in  the  clouding  of  a  feldspar  crystal  along  the  fine  cleavage 
lines  as  seen  in  a  thin  section  under  the  microscope. 

Disintegration,  as  here  described,  is  always  associated  with  a 
greater  or  less  amount  of  chemical  alteration,  such  as  oxidation, 


34  PRINCIPLES    OF    STRATIGRAPHY 

hydration,  etc.,  according  to  the  state  of  the  atmosphere.  Where 
Jittle  moisture  exists  in  the  air,  as  in  arid  regions,  the  chief  process 
by  which  the  destruction  of  rock  masses  is  effected  is  disintegration, 
supplemented,  of  course,  by  the  mechanical  work  of  the  wind. 

Branner  (10:281)  has  observed  that  the  mica  of  Brazilian 
gneisses  is  an  element  of  weakness,  tending,  both  on  account  of  its 
low  conductivity  and  its  form,  to  develop  crevices  along  which  the 
rocks  exfoliate  more  readily. 

Frost  Work.  Water,  on  freezing,  expands  one-tenth  of  its  vol- 
ume, and  so  becomes  a  powerful  agent  in  destroying  rock  masses. 
The  expansion  of  water  in  fissures  on  freezing  is  capable  of  prying 
off  huge  masses  of  rock,  and  in  some  cases  much  of  the  talus  at  the 
foot  of  the  cliff  is  to  be  referred  to  frost  action.  Rock  surfaces  may 
by  radiation  cool  below  the  freezing  point  (o°  C.  or  32°  F.),  so 
that  moisture  coming  in  contact  with  them  freezes  at  once.  This  is 
often  seen  in  high  altitudes  where  moisture-laden  winds  strike  a  cold 
rock  wall  or  cairn,  with  the  result  that  the  moisture  is  precipitated 
as  ice.  An  interesting,  case  of  freezing  in  contact  with  cold  rocks 
has  been  observed  on  the  coast  of  Newfoundland,  where  the  lime- 
stone cools  more  rapidly  at  the  beginning  of  the  winter  than  the  sea- 
water,  which  penetrates  all  the  fissures  at  high  tide,  freezing  there 
in  contact  with  the  cold  rock  and  shattering  the  mass  during  the  re- 
treat of  the  tide.  The  constant  repetition  of  this  phenomenon  re- 
sults in  covering  the  beach  with  freshly  broken,  angular  fragments. 
(Thoulet,  Walther-i03i55p.) 

The  creep  of  the  soil  on  sloping  surfaces  has  also  been  referred 
to  frost  action,  the  water  in  the  soil  freezing  and  converting  the 
mass  into  an  "earth  glacier"  (Kerr~54:j^5).  The  creeping  down- 
hill of  this  mass  results  in  the  bending  over  of  the  ends  of  the  ver- 
tical or  steeply  inclined  strata. 


CHEMICAL  WORK  OF  THE  ATMOSPHERE. 

The  chemical  activities  of  the  atmosphere  penetrate  the  upper 
layers  of  the  lithosphere  to  the  level  of  the  ground  water.  This 
averages  perhaps  from  30  to  50  meters  below  the  surface,  though  in 
many  regions  it  is  at  the  surface,  while  again,  in  arid  regions  it  may 
be  so  much  as  1,000  meters  or  more  beneath  the  surface.  The  belt 
thus  produced,  between  the  average  level  of  the  ground  water  and 
the  surface,  is  the  belt  of  deniorphism,  or  in  general  the  Belt  of 
Weathering.  It  is  here  that  the  chemical  work  of  the  atmosphere 
is  most  marked  in  destroying  the  rocks,  this  work  consisting,  so  far 


WORK    OF    THE    ATMOSPHERE  35 

as  the  atmosphere  is  concerned,  in  oxidation,  hydration,  and  car- 
bonation.  Solution,  which  also  goes  on  actively  here,  is  to  be  re- 
garded as  the  work  of  the  ground  water,  rather  than  that  of  atmo- 
spheric moisture.  The  two  agents  are,  however,  so  intimately  re- 
lated that  it  is  impossible  to  draw  a  sharp  line  between  them  and 
their  respective  accomplishments. 

Carbonation  of  silicates  is  on  the  whole  the  most  characteristic 
reaction.  This  takes  place  on  a  vast  scale,  producing  carbonates 
from  the  silicates,  and  setting  free,  thereby,  silica  or  colloidal  silicic 
acid.  Hydration  is  the  most  extensive  single  reaction  in  this  belt, 
while  oxidation  is  very  pronounced,  owing  to  the  free  access  of 
oxygen  to  the  pores,  from  the  absence  of  water.  Solution  removes 
many  of  the  products  of  decomposition  from  this  belt  of  weathering, 
and  carries  it  away  over  ground  or  under  ground.  As  a  result  of 
this,  the  volume  of  rock  in  the  belt  of  weathering  becomes  greatly 
reduced,  the  resultant  material  in  the  end  occupying  only  a  small 
fraction  of  the  volume  it  once  had. 

OXIDATION.  "The  oxygen  is  chiefly  utilized  in  the  oxidation  of 
iron,  surphur,  and  organic  material.  In  the  upper  part  of  the  belt 
[of  weathering],  where  oxygen  is  abundant,  large  amounts  of  hema- 
tite and  limonite  may  be  produced  by  the  oxidation  of  the  ferrous 
particles,  but  for  the  greater  part  of  the  belt  of  cementation,  where 
oxygen  is  somewhat  deficient,  the  ferrous  oxide  is  oxidized  only  to 
the  form  of  magnetite,  since  this  requires,  per  unit  of  iron,  only  two- 
thirds  as  much  oxygen  as  to  produce  hematite  and  limonite."  (Van 
Hise-ioordod.)  Magnetite  may  be  directly  oxidized,  into  hematite, 
involving  an  increase  in  volume  of  2.5  per  cent.  •  Hydration  may 
occur  simultaneously,  changing  the  mineral  to  limonite  with  a  cor- 
responding increase  in  volume  of  64  per  cent.  Iron  carbonates,  are 
oxidized  to  ferric  oxide,  with  a  corresponding  decrease  in  volume, 
owing  to  loss  of  CO2.  This  is  49  per  cent.,  if  hematite  is  the  result, 
but  only  18  per  cent.,  if  the  carbonate  is  changed  to  limonite.  Sul- 
phides are  oxidized  to  sulphites  and  sulphates.  Sulphurous  and  sul- 
phuric acids  are  formed,  which  may  enter  into  various  combinations. 
Sulphuretted^  hydrogen  is  a  common 'result  of  the  oxidation  of  iron 
pyrites,  and,  from  the  further  oxidation  of  this,  pure  sulphur  may 
be  precipitated. 

Some  of  the  changes  occurring  may  be  expressed  in  the  follow- 
ing formula  (for  others  see  Van  Hise-ioo :.?//)  :  FeS2-|-6O=: 
FeSO4  -|-  SO...  If  the  water  is  present,  we  may  have : 

FeS,+3O+H2O=FeSO4-fH2S. 
The  ferrous  sulphate  may  be  removed  in  solution  or  may  fur- 


36  PRINCIPLES    OF    STRATIGRAPHY 


ther  be  oxidized  into  hydrated  sesquioxide  of  iron  or  limonite  and 
sulphuric  acid,  thus  : 


.  In  each  of  these  reactions  heat  is  liberated.  Where  H2S  is 
liberated,  this  may  be  further  oxidized,  especially  in  the  presence  of 
bacteria,  and  sulphur  may  result  thus  :  H2S-|-O=H2O-|-S.  The 
sulphur  may  later  be  oxidized  to  sulphuric  acid. 

The  change  from  sulphides  to  oxides  without  hydration  involves 
a  diminution  in  volume.  A  change  to  magnetite  means  a  decrease  in 
volume  of  24  to  39  per  cent.,  oxidation  and  hydration  of  pyrite,  how- 
ever, result  in  a  total  increase  in  volume  of  3  per  cent.,  while  the 
increase  in  the  case  of  pyrrhotite  is  25  per  cent. 

Red  and  Yellow  Colors  of  Soil  Due  to  Oxidation.  Within  the 
zone  of  active  flock  weathering,  the  iron  compounds  are  transformed 
to  ferric  oxide  or  hydrate,  if-  the  amount  of  oxygen  is  sufficient. 
These  iron  compounds  will  impart  their  characteristic  color  to  the 
soil,  which  will  be  yellow  or  red,  according  to  the  simultaneous 
occurrence  or  non-occurrence  of  hydration.  Dehydration  of  ferric 
hydrates  may  likewise  change  the  color  of  yellow  soil  to  red,  as  is 
shown  in  brick-making,  when  the  yellow  clay  on  burning  changes  to 
a  red  brick.  Crosby  has  attributed  the  contrast  of  the  color  of  soils 
of  high  and  low  latitudes  to  the  process  of  dehydration  of  the  latter, 
partly  due  to  the  greater  heat  of  the  southern  latitudes  and  partly  to 
the  greater  age  of  the  products  of  decomposition.  He  calls  at- 
tention to  the  /act  that  the  red  color  is  mostly  a  superficial  feature, 
varying  usually  from  two  to  five  feet  in  depth,  and  rarely  exceeding 
ten  feet.  The  color  is  "usually  reddest  at,  or  near,  the  surface, 
changing  downward  gradually,  more  rarely  abruptly,  through  vari- 
ous shades  of  orange  to  yellow  ;  while  occasional  complete  sections 
show  the  yellow  changing  through  paler  tints  to  gray  or  the  color 
of  the  underlying  hard  rocks."  (Crosby-2o  ://.)  Russell  has 
shown  that  the  grains  of  the  rock  are  encrusted  by  a  ferruginous 
clay  which  contains  both,  ferric  oxide  and  alumina. 

In  Nicaragua,  east  of  the  continental  divide,  the  -  red  color  is 
from  3  to  10  meters  deep.  (Hayes-45  :/,?#,  I29-}  Tne  abundant 
vegetation  here  causes  a  transpiration  of  the  moisture  so  that  the 
soil  is  not  saturated  with  water..  On  the*  western  side  of  Nicaragua 
the  color  of  the  clay  soil  is  blue,  the  iron  being  in  the  ferrous  form. 
Here  dry  seasons  alternate  with  wet  ones,  and  the  deeply  cracked 
soil  of  the  dry  season  is  filled  with  the  remains  of  vegetation,  which 
thus  become  a  powerful  reducing  agent  within  the  zone  of  weather- 
ing. 


CHEMICAL    WORK   OF   THE    ATMOSPHERE        37 

The  red  color  of  desert  sands  has  frequently  been  remarked 
upon.  It  is  due  to  a  coating  of  iron  oxide  over  the  rounded  quartz 
grains.  Phillips  (76)  has  determined  the  total  amount  of  iron 
oxide  of  the  coating  of  the  sands  in  the  Nefud  desert  of  Arabia  to 
be  0.21  per  cent,  while  the -sand  itself,  after  the  solution  of  the 
coating,  still  contained  0.28  per  cent,  of  .iron  oxide,  0.88  per  cent,  of 
clay  and  98.53  per  cent,  of  silica.  Walther  holds  that  the  iron  of 
the  crust  was  also  originally  in  the  sand  and  has  found  its  way  to 
the  surface  of  the  grain  under  the  intense  heating  of  these  grains 
from  exposure  to  the  sun.  Similar  conditions  are  rather  wide- 
spread within  the  arid  belt  of  the  earth,  and  such  coating  of  quartz 
sand  grains  may  be  considered  as  typical  of  desert  sands,  whether 
of  recent  origin  or  preserved  in  older  formations. 

Oxidation  of  Organic  Compounds.  (Van  Hise-ioo:^<5i.)  In 
the  presence  of  water  and  bacteria,  cellulose  and  other  organic  sub- 
stances are  oxidized  with  the  production  of  a  number  of  organic 
acids,  such  as  humic,  ulmic,  crenic,  etc.  (See  Chapter  IV.)  Fur- 
ther oxidation  of  these  acids  results  in  the  production  of  carbon 
dioxide  and  water.  The  artificial  oxidation  of  carbon  in  the  form  of 
coal  and  other  combustibles  has  become  a  factor  of  great  impor- 
tance. It  is  estimated  that  at  the  present  time  1 ,000,000,000  metric 
tons  of  coal  are  oxidized  each  year,  and  this,  with  an  average  of 
80  per  cent,  of  carbon,  would  produce  a  total  of  2,933,333,000 
metric  tons  of  CO2  to  be  passed  into  the  atmosphere  each  year. 
This  is  0.1233  per  cent,  of  the  total  amount  of  CO2  at  present  in 
the  atmosphere.  Continuing  this  rate  of  consumption  of  coal  for 
812  years,  the  amount  of  CO2  in  the  atmosphere  would  be  doubled. 
(Van  Hise-ioo  '.464.)  The  oxidation  of  nitrogen  to  ammonium 
nitrites  and  nitrates  takes  place  in  the  presence  of  water  and  with 
the  aid  of  bacteria.  It  is  most  marked  in  the  tropics,  where  the 
nitrates  of  the  soil  sometimes  amount  to  30  per  cent,  of  the 
mass. 

HYDRATION.  The  chemical  union  of  water  with  minerals  is 
hydration,  and  the  results  are  hydroxides.  So  far  as  hydration  of 
minerals  by  atmospheric  moisture  is  concerned,  the  process  is  a 
superficial  one,  but  within  the  belt  of  weathering  of  the  lithosphere 
it  is  a  very  extensive  process  due  to  the  percolation  of  the  ground 
water.  It  will  be  further  considered  under  that  heading.  A  com- 
paratively low  temperature  favors  hydration  of  minerals,  a  temper- 
ature above  1 10°  C.  at  ordinary  conditions  of  pressure  will  stay  the 
process  or  even  reverse  it,  dehydration  being  the  result. 

KAOLIN IZATION.  The  ordinary  effect  of  the  atmospheric  mois- 
ture on  the  rocks  is  the  attack  upon  the  feldspars  producing  kaolin 


38  PRINCIPLES    OF    STRATIGRAPHY 

or  clay.  This  commonly  takes  place  in  the  presence  of  CO2,  the 
formula  for  the  alteration  of  orthoclase  into  kaolin  and  quartz  being 
(Van  Hise-i 00:389)  : 

2KAlSi3O8+2H2O+CO2=H4Al2Si2O9+4SiO2+K2CO3. 

The  change  to  kaolin  is  accompanied  by  a  volume  decrease  of 
54.44  per  cent. ;  the  change  to  kaolin  and  quartz,  as  in  the  above 
reaction,  by  a  decrease  of  12.57  Per  cent-  The  change  by  hy- 
dration  of  hematite  to  limonite  is  accompanied  by  an  increase  in 
volume  of  60.72  per  cent.,  and  may  be  expressed  by  the  formula : 
2Fe2O3  -j-  3H2O  =  2Fe2O3.3H2O.  Hydration  under  the  atmos- 
phere often  goes  on  so  rapidly  as  to  suggest  slaking  of  quicklime. 
This  has  been  observed  by  Merrill  in  the  granitic  rocks  of  the  Dis- 
trict of  Columbia  (66  :i88),  and  by  Derby  in  the  sedimentary  rocks 
of  railway  cuttings  in  Brazil  (Branner-6).  In  both  cases  the 
rocks  exposed  at  the  surface  soon  break  into  powder,  al- 
though in  fresh  exposures  they  may  be  so  strong  as  to  require 
blasting. 

DEHYDRATION.  The  loss  of  combined  water  or  dehydration  is  a 
phenomenon  of  regions  of  high  temperature  and  low  humidity.  It 
probably  occurs  on  the  largest  scale  in  regions  of  alternating  wet 
and  dry  climate  combined  with  high  temperature.  Such  dehydra- 
tion tends  to  change  the  limonite  or  gothite  of  the  soil  to  hematite, 
with  a  corresponding  change  in  color  from  ochery  to  red.  Crosby, 
Dana,  and  Russell  have  attributed  the  red  color  of  the  soil  of  south- 
ern regions  to  this  process  of  dehydration  under  the  influence  of  high 
temperature  and,  to  some  extent,  under  that  of  age.  Partial  dehy- 
dration of  such  compounds  as  the  zeolites,  colloidal  silicic  acid, 
aluminum  hydroxide,  etc.,  may  take  place  on  a  considerable  scale  in 
regions  of  high  temperature  and  little  moisture. 

CARBONATION.  The  atmosphere  furnishes  much  of  the  CO2 
which  combines  with  the  bases  to  form  carbonates,  either  directly  or 
indirectly  through  the  mediation  of  plants.  Like  oxidation,  it  is 
thus  a  superficial  phenomenon.  As  we  have  seen,  the  oxidation 
(decay)  of  the  vegetable  matter  on  the  surface  of  the  earth  liber- 
ates much  CO2,  which  may  be  taken  up  by  the  waters  entering  the 
soil  and  used  for  carbonation.  The  air,  as  already  noted,  contains 
about  3.4  parts  by  volume  in  10,000  (4.5  by  weight).  Rain  water 
contains  from  0.22  to  0.45  per  cent.  (Merrill-66  :/7p)  of  the  vol- 
ume of  the  water  or  0.00044  to  0.00089  Per  cent-  by  weight.  In  the 
pore  spaces  of  soils  much  more  CO2  exists,  as  shown  by  the  follow- 
ing table  by  Boussingault  and  Lewy  copied  from  Merrill  (66:77$)  : 


CHEMICAL   WORK   OF    THE    ATMOSPHERE        39 

CO2  in  10,000  parts 

by  weight. 

Air  from  sandy  subsoil  in  forest 38 

Air  from  loamy  subsoil  in  forest 124 

Air  from  surface  soil  of  forest 130 

Air  from  surface  soil  of  vineyard 146 

Air  from  pasture  soil 270 

Air  from  soil  rich  in  humus 543 

The  union  which  goes  on  continually  of  the  CO2  with  the  min- 
erals of  the  Belt  of  Weathering  in  the  earth's  crust  is  rather  an 
accompaniment  of  the  processes  set  going  by  the  ground  water,  than 
a  direct  activity  of  the  atmosphere.  The  use  of  CO2  in  solution 
of  limestones  likewise  belongs  there.  On  liberation  in  the  process 
of  decarbonation,  the  CO2  commonly  returns  to  the  atmosphere. 

LATERIZATION.  Laterite  (Meigen-64;  Clarke-i7)  is  the  prod- 
uct of  rock  decay  in  pluvial  tropical  regions,  and  is  especially 
characterized  by  the  high  content  of  iron  oxide.  Its  color  is  mostly 
a  deep  red,  the  iron  being  often  so  abundant  as  to  form  concretions 
of  brown  or  red  iron  ore.  The  depth  to  which  the  laterite  extends 
may  be  very  great,  being  over  300  feet  in  Brazil.  Its  areal  extent 
is  likewise  great ;  thus,  according  to  the  estimates  of  von  Tillo,  it 
covers  49%  of  the  surface  of  Africa,  16%  of  Asia  and  43%  of 
South  America. 

Typical  laterite  is  characterized  by  the  formation,  during  the 
process  of  decomposition,  of  a  considerable  amount  of  hydrous  oxide 
of  aluminum,  chiefly  in  the  form  of  Hydrargillite  (A12O3.3H2O), 
whereas  the  ordinary  products  of  rock  decay  in  moist  temperate 
climates  are  the  hydrous  silicates  of  aluminum,  kaolinite  (H4A12- 
Si2O9),  or  its  ferric  equivalent,  nontronite  (H4Fe2Si2O9).  Often 
the  laterite  still  shows  the  form  or  structure  of  the  gneisses  or  other 
crystalline  rocks  from  which  it  is  derived. 

The  diminution  or  total  disappearance  of  the  silicic  acid  in  com- 
bination with  bases  is  one  of  the  characteristic  features  of  lateriza- 
tion.  Thus  the  laterization  of  a  dolerite  near  Bombay,  India,  in- 
volves a  loss  of  SiO2  from  50.4%  in  the  fresh  to  0.7%  in  the 
weathered,  while  at  the  same  time  there  is  a  proportional  increase 
in  the  A12O3  from  2.2.2%  in  the  fresh  to  50.5%  in  the  weathered 
rock,  and  an  increase  in  Fe2O3  from  9.9%  to  23.4%.  In  the 
kaolinization  of  an  English  dolerite  in  South  Staffordshire,  the 
change  from  the  fresh  to  the  altered  rock  includes  a  change  in  SiO2 
from  49.3%  to  47.0%,  in  A12O3  from  17.4%  to  18.5%,  of  Fe2O3 
from  2.7%  (+8.3%  FeO)  to  14.6%,  and  so  forth.  Laterization 


40  PRINCIPLES    OF    STRATIGRAPHY 

must  be  regarded  as  a  further  step  in  the  decomposition  of  rocks, 
the  silica  being  separated  out  and  deposited  elsewhere  as  agate 
or  chalcedony.  The-alkalies  likewise  are  carried  away  and  the  sep- 
aration and  redeposition  of  the  iron,  if  present,  also  take  place  at 
an  early  moment. 

While  in  the  temperate  climates  the  abundance  of  humus  brings 
about  the  reactions  which  result  in  the  kaolinization  of  the  feld- 
spars, the  absence  of  this  humus  tends  to  subject  the  feldspars  to 
the  attack  of  non-acidulated  waters,  which  under  the  influence  of 
tropical  heat  produce  a  hydrolytic  separation  of  the  silicates  with 
the  formation  of  aluminum  hydrate  and  alkali  silicate,  which  sepa- 
rates further  into  alkali  hydroxide  and  free  silica. 

Influence  of  Temperature  on  Rock  Decomposition. 

The  influence  of  temperature  on  the  decomposition  of  rocks  is 
well  shown  by  the  fact  that  beneath  the  ever-moist  moss  cushions 
of  Finland  and  the  northern  Urals,  the  granite  shows  undecom- 
posed  surfaces,  solution  being  the  only  process  active  here,  (von 
Richthofen^Srptf.)  This  is  due  to  the  prevailing  high  degree  of 
cold.  The  same  thing  is  seen  on  the  Kerguelen  and  the  Crozet  is- 
lands in  the  South  Indian  Ocean,  where  the  cold  humid  climate  has 
produced  but  little  soil,  whereas  in  tropical  regions,  as  in  the  Samoan 
Islands,  a  deep  brilliant  red  soil,  the  terra  rossa,  is  produced.  The 
soil  of  the  Samoan  Islands  is  deep  and  rich  and  is  produced  by  the 
decomposition  of  a  basaltic  rock  similar  to  that  of  the  Kerguelen 
Islands,  which  there,  however,  is  unaffected.  (Russell— 80.) 

MOVEMENTS    OF   THE    ATMOSPHERE. 

WINDS.  The  movements  of  the  atmosphere  are  inaugurated 
by  the  inequalities  in  atmospheric  pressure  and  are  controlled  to  a 
large  extent  by  the  rotation  of  the  earth.  The  normal  atmospheric 
pressure  at  sea-level,  or  one  atmosphere,  is  sufficient  to  balance  the 
weight  of  a  column  of  mercury  in  the  barometer  30  inches,  or  760 
millimeters,  high.  As  the  pressure  decreases  the  mercury  falls,  as  it 
increases  the  mercury  rises.  At  an  elevation  of  5,910  feet  above  sea- 
level  the  mercury  stands  at  24  inches,  at  10,550  feet  at  20  inches,  and 
at  16,000  feet  above  sea-level  it  stands  at  16  inches.  (Davis- 
26:13.)  When  air  is  heated  it  expands  and  so  becomes  lighter, 
and  the  same  is  true  when  air  becomes  saturated  with  moisture. 
Though  temperature  and  humidity  are  causes  of  varying  pressure, 
high  temperature  and  high  humidity,  producing  areas  of  low  pres- 
sure, and  conversely  low  temperature  and  humidity,  producing  areas 


MOVEMENTS    OF    THE    ATMOSPHERE  41 

of  high  pressure,  the  distribution  of  these  over  the  earth's  surface 
depends  on  a  variety  of  factors,  and  is  not  coincident  with  regions 
of  corresponding  temperature  and  humidity.  Areas  of  high  pres- 
sure may  also  be  produced  by  the  crowding  of  warm  rising  air 
against  the  cooler  upper  layers,  as  is  the  case  in  the  higher  atmos- 
phere of  the  equatorial  belt. 

ISOBARS.  If  the  points  of  equal  atmospheric  pressure,  due  to 
unequal  heating,  at  a  given  time  were  united  into  a  series  of  con- 
tinuous surfaces,  they  would  form  a  series  of  superposed  planes 
warped  and  dented  into  domes  and  ridges,  and  basins  and  troughs, 
in  a  more  or  .less  conformable  manner.  So  far  as  the  layers  are 
affected  by  the  heating,  those  representing  the  highest  pressure 
would  lie  below,  and  the  successive  surfaces  upward  would  repre- 
sent a  regularly  decreasing  pressure.  The  elevations  in  these  sur- 
faces cover  the  areas  of  high  pressure  on  the  earth's  surface,  and 
these  elevations,  when  localized,  would  be  dome-like.  The  depres- 
sions similarly  cover  the  areas  of  low  pressure.  Since  pressures 
both  higher  and  lower  than  30  (30  inches  of  mercury)  are  found  at 
sea-level,  this  surface  must  be  regarded  as  a  horizontal  plane  cutting 
the  warped  isobaric  surfaces.  The  resulting  lines  of  intersection  are 
the  isobars,  and  it  will  be  observed  that,  where  the  sea-level  cuts  a 
local  area  of  low  pressure,  i.  e.,  a  depressed  area  in  the  isobaric  sur- 
faces, the  resulting  isobars  will  be  irregular  closed  curves  of  decreas- 
ing value  toward  the  center,  and  crowded  in  proportion  to  the  steep- 
ness of  the  slope  or  gradient,  whereas  a  local  high  pressure  area 
(a  convex  surface)  will  show  closed  curves  of  increasing  value 
toward  the  center.  Over  much  of  the  earth's  surface  the  isobars 
are  long,  more  or  less  parallel  lines  conforming  in  a  general  way 
to  the  direction  of  the  parallels  of  latitude.  The  winds  are  the 
movements  of  the  atmosphere  from  the  regions  of  high  to  those  of 
low  barometric  pressure,  at  the  same  level.  This  may  be  regarded 
as  a  movement  down  the  isobaric  slopes,  and  most  readily  and 
strongly  down  the  steepest  gradient. 

DIRECTIONS  OF  MOVEMENT  OF  THE  AIR.  Since  the  lower  air  of 
the  equatorial  regions  is  heated  more  than  that  of  the  polar  regions 
by  the  direct  action  of  the  sun  (insolation),  it  must  expand  most 
at  the  equator  and,  rising,  produce  a  belt  of  low  pressure  around 
the  globe.  Into  this  will  flow  the  winds  from  the  region  of  greater 
pressure  to  north  and  south,  along  the  bottom  of  the  atmosphere, 
while  at  the  same  time  the  rising  air  crowds  against  the  higher 
layers  of  the  equatorial  atmosphere  which  are  not  heated,  and  so 
produces  a  surface  of  high  pressure  in  the  upper  part  of  the  equa- 
torial belt,  with  a  poleward  gradient  down  which  the  air  will  move. 


42  PRINCIPLES    OF    STRATIGRAPHY 

Thus  a  poleward  movement  of  the  upper  air  and  an  equatorial 
movement  of  the  lower  air  are  established,  with  a  rising  of  the  air  at 
the  equator  and  a  descent  in  the  polar  regions.  (Fig.  5.)  This  is  the 
fundamental  type  of  circulation  of  the  atmosphere.  This  simple  type 
of  circulation  is  greatly  modified,  however,  at  any  rate  so  far  as  the 
lower  part  of  the  atmosphere  is  concerned,  by  various  factors,  chief 
among  which  may  be  counted  the  rotation  of  the  earth,  the  distribu- 
tion of  land  and  sea,  the  lateral  pressure  exerted  by  the  expanding 
warm  air  of  the  equatorial  region,  and  the  crowding  from  the 
descent  of  the  air  in  high  latitudes,  the  subsidiary  motions  set  going 


FIG.  5.  Diagrammatic  section 
of  the  earth  and  the  en- 
closing atmosphere,  illus- 
trating the  fundamental 
type  of  circulation  in  the 
lower  atmosphere,  estab- 
lished by  unequal  heating, 
as  a  result  of  differences 
in  latitude.  (After  Salis- 
bury—Physiography. ) 


FIG.  6.  Diagram  showing  the  general 
movements  which  would  take  place 
in  the  lower  air  if  there  were  no 
rotation.  (After  Salisbury.) 


by  the  aspiratory  action  of  the  larger  currents,  etc.  Considering 
that  in  each  hemisphere  there  is,  on  the  equatorial  side,  a  rising 
mass  of  air,  which  turns  poleward,  while  on  the  poleward  side  an 
equivalent  current  descends,  and  then  flows  equatorward,  we  have 
an  intermediate  area  around  which  this  circulation  takes  place,  and 
these  areas  are  belts  of  high  pressure.  Their  location  is  approxi- 
mately in  latitudes  30°  N.  and  S.,  a  location  determined  in  part 
by  the  rotation  of  the  earth.  The  center  of  this  high  pressure  belt 
in  the  northern  hemisphere  is  in  30°  N.  lat.,  or  a  little  less  in  Jan- 
uary, with  great  expansion  of  the  belt  northward  on  the  land.  In 
July  this  center  shifts  north  to  about  lat.  35°  and  the  belt  is  inter- 
rupted on  land.  The  reverse  is  true  for  the  southern  hemisphere, 
where  the  summer  conditions  exist  in  January,  with  the  center  of 


MOVEMENTS    OF    THE    ATMOSPHERE 


43 


the  high  pressure  belt  in  about  lat.  35°  S.,  while  in  July  the  center 
shifts  to  30°  or  less.  (Fig.  7.)  The  shifting  of  the  center  of  high 
pressure  is,  therefore,  in  harmony  with  the  apparent  motion  of  the 
sun. 

The  general  distribution  of  pressure  areas  is  somewhat  as  fol- 
lows:  i,  an  equatorial  belt  of  low  pressure;  2,  two  belts  of  high 
pressure  in  about  latitudes  30°  N.  and  30°  S.,  respectively;  and  3, 
two  high  latitude  areas  of  low  pressure.  In  general  there  should 
thus  be  a  horizontal  movement  of  air  in  the  lower  part  of  the  atmos- 
phere from  the  extra-tropical  belts  of  high  pressure,  both  poleward 


FIG.  7.  Diagram  illustrating 
the  seasonal  shifting  of 
the  wind  zones.  (After 
Davis.) 


FIG.  8.  Generalized  diagram  illustrating 
the  deflection  of  the  winds  at  the 
bottom  of  the  atmosphere,  due  to 
rotation  of  the  earth.  (After  Salis- 
bury.) 


and  equatorward.  (Fig.  6.)  This  motion  is  modified  by  the  rota- 
tion of  the  earth,  which  causes  a  deflection  of  all  currents  to  the 
right  in  the  northern  hemisphere  and  to  the  left  in  the  southern. 
(Salisbury-83 :  doj,  Fig.  8.)  As  a  result,  the  poleward  winds  in 
each  hemisphere  are  turned  toward  the  east,  and  so  become  westerly 
winds,  or  southwest  winds,  in  the  northern  hemisphere,  and  north- 
west winds  in  the  southern  hemisphere.  The  winds  blowing  equa- 
torward will  be  deflected  to  the  west,  and  so  become  easterly  winds, 
northeast  winds  in  the  northern  and  southeast  in  the  southern  hemi- 
sphere. These  are  the  most  constant  winds  and  are  known  as  the 
trade  winds.  Where  these  currents  meet  at  the  equator,  we  have 
the  zone  of  equatorial  calms,  characterized  chiefly  by  rising  air 


44  PRINCIPLES    OF    STRATIGRAPHY 

currents.  The  center  of  this  zone  shifts  with  the  sun,  but  remains 
near  the  equator.  The  prevailing  winds  or  planetary  ivinds  thus 
produced  belong  strictly  to  the  lower  part  of  the  atmosphere.  This 
is  especially  true  of  the  trade  winds,  which  appear  to  be  confined 
to  the  lower  10,000  feet,  as  shown  by  observations  on  the  Peak  of 
Teneriffe  in  the  Canary  Islands  (lat.  28°).  The  westerly  winds  of 
the  higher  latitudes,  however,  coincide  with  the  general  movement 
of  the  upper  air,  which,  being  poleward,  is  deflected  to  the  east. 
Thus,  as  shown  by  the  movement  of  the  upper  clouds,  the  direction 
of  the  upper  winds  is  toward  the  east,  and  so  a  circumpolar  whirl 
is  instituted. 

Influence  of  Continents  on  Winds. 

Sea-Breezes.  The  chief  disturbing  factor  of  the  planetary  winds 
is  the  unequal  heating  of  the  atmosphere  over  the  land  and  the 
water,  as  explained  on  p.  31,  which,  in  fact,  is  itself  a  cause  of 
local  winds.  As  the  land,  after  the  rising  of  the  sun,  is  more  quickly 
warmed  in  summer  than  the  water,  the  air  above  the  land  expands 
upward,  crowding  against  the  upper  air  and  so  producing  a  seaward 
barometric  gradient  down  which  the  air  will  flow.  The  resulting 
pressure  over  the  sea  and  the  relief  of  pressure  over  the  land  will 
cause  a  lower  return  current,  the  sea-breezt,  to  flow  landward.  The 
velocity  increases  from  the  morning  (8  or  9  A.M.)  to  the  afternoon, 
reaching  its  maximum  at  the  time  of  greatest  air  temperature.  At  first 
the  sea-breeze  blows,  in  general,  at  right  angles  to  the  coast,  but 
as  the  air  is  drawn  from  greater  distances  off-shore,  it  comes  under 
the  influence  of  the  deflective  force  of  the  earth's  rotation  and  is 
turned  to  the  right  in  the  northern  hemisphere  and  to  the  left  in  the 
southern  hemisphere.  Thus  a  sea-breeze  on  the  eastern  coast  will 
change  to  a  southeast  wind  in  the  northern  and  a  northeast  wind  in 
the  southern  hemisphere,  while  a  sea-breeze  on  the  western  coast 
changes  to  a  northwest  and  a  southwest  wind  in  the  northern  and 
southern  hemispheres  respectively.  Where  the  sea-breeze  has  the 
direction  of  the  prevailing  winds  it  often  increases  in  the  afternoon 
to  the  velocity  of  a  gale.  At  Valparaiso  "pebbles  are  torn  up 
from  the  walks  and  whirled  about  the  street"  and  business  and 
shipping  are  interrupted.  (Maury-63.)  At  evening  the  calm 
suddenly  succeeds  the  uproar.  Measurements  on  the  Massachu- 
setts coast  have  shown  the  velocity  of  the  sea-breeze  to  be  at  first 
from  5  to  13  km.  per  hour,  reaching  its  greatest  velocity  of  16  to 
30  km.  late  in  the  afternoon.  At  Boston  the  average  velocity  is 
23  km.  per  hour  at  3  P.  M.  on  sea-breeze  days.  The  height  of  the 


MOVEMENTS    OF    THE   ATMOSPHERE 


45 


sea-breeze  at  Coney  Island,  New  York,  was  found  to  be  150  meters 
in  August,  with  a  distinct  seaward  motion  of  the  air  at  200  meters. 
At  Toulon,  in  the  middle  of  October,  1893,  it  was  found  to  be  400 
meters,  with  a  distinct  off-shore  current  at  600  meters.  On  the 
coast  of  California  its  height  is  about  2,500  meters. 

Land-Breezes.  These  are  generally  much  weaker  than  sea- 
breezes.  They  result  from  the  more  rapid  cooling  of  the  land  at 
night,  involving  a  decrease  in  the  pressure  of  the  higher  air  and  an 
inflow  of  warm  air  from  the  sea.  This  lowers  the  surface  pressure 
over  the  sea  and  increases  that  over  the  land,  with  the  result  that  a 
surface  current  flows  seaward  from  the  land.  As  the  land  winds 
increase  in  length  they  will  fall  under  the  deflective  action  of  the 


r*    r 


FIG.  9.    The  isobars  of  India  for  Jan-    FIG.  10.    Wind  directions  in  India  in 
uary.         (After      Bartholomew;  winter.      (After    Koppen;    from 

from  Salisbury.)  Salisbury.) 

earth's  rotation,  and  the  breeze  on  the  east  coast  will  become  a 
northwest  wind  on  the  northern  and  a  southwest  wind  on  the  south- 
ern coast,  while  the  land-breezes  on  the  west  coast  will  become 
southeast  and  northeast  winds,  respectively.  The  .large  lakes  in  like 
manner  influence  the  formation  of  land-  and  lake-breezes,  though 
not  to  the  extent  that  oceans  do. 

Monsoons.  These  are  the  seasonal  winds,  brought  about  by  the 
heating  of  the  land  during  the  summer  and  the  cooling  during  the 
winter.  These  winds  may  be  regarded  as  sea-  and  land-breezes  act- 
ing continuously  for  nearly  half  a  year  each,  and  hence  attaining 
great  velocity.  In  the  middle  and  higher  latitudes  of  the  northern 
hemisphere  these,  seasonal  winds  may  even  entirely  overcome  the 
prevailing  or  planetary  circulation,  at  least  so  far  as  the  lower 
atmosphere  is  concerned,  and  may  further  exert  a  powerful  influ- 
ence on  ocean  currents. 


PRINCIPLES  OF  STRATIGRAPHY 


A  glance  at  a  chart  of  isobaric  lines  for  January  shows  that 
Eurasia  is  a  center  of  high  pressure,  and  hence  of  air  depression. 
The  Indian  Ocean  us  an  area  of  low  pressure  and  hence  strong  con- 
tinental winds  flow  southward,  and  by  the  rotation  of  the  earth  are 
deflected  to  the  west.  Hence,  over  India  we  have  northeast  conti- 
nental winds  which  harmonize  with  the  trade  winds  and  augment 
their  effectiveness.  In  summer,  on  the  other  hand,  Eurasia  is  a 
center  of  low  pressure,  centering  in  July  over  northwestern  India, 
and  hence  the  direction  of  the  winds  is  a  northward  one,  deflected 
to  the  northeast  by  the  rotation  of  the  earth.  This  is  diametrically 
opposed  to  the  direction  of  the  northeast  trade  winds,  which  become 


FIG.  IT.  Isobars  of  India  for  August 
(After  Bartholomew;  from  Sal- 
isbury.) 


FIG.  12.  Winds  of  India  in  midsum- 
mer. (After  Koppen;  from  Sal- 
isbury.) 


displaced  by  this  more  powerful  southwest  monsoon.  The  influ- 
ence of  these  changes  on  the  ocean  currents  will  be  noted  later. 
Spain,  which  lies  in  the  zone  of  westerly  winds,  furnishes  another 
illustration  of  the  importance  of  seasonal  winds  or  monsoons.  In 
winter  the  central  plateau  is  characterized  by  low  temperature  and 
high  pressure,  and  the  winds  blow  outward,  while  in  summer  the 
reverse  is  true,  the  winds  blowing  toward  the  center.  The  impor- 
tance of  such  winds  in  affecting  the  relative  humidity  of  the  climate 
and  corresponding  sedimentary  deposits  must  not  be  overlooked. 

CYCLONES  AND  ANTICYCLONES. 

An  area  of  high  barometric  pressure  produces  an  anticyclonic 
movement  of  the  air,  which  passes  out  in  all  directions  from  it.  In 
the  northern  hemisphere  these  winds  are.  deflected  to  the  right, 
making  a  clockwise  circulation,  while  in  the  southern  hemisphere 
deflection  to  the  left  produces  a  counter-clockwise  circulation.  Con- 
versely, the  low  pressure  areas  are  characterized  by  a  cyclonic  cir- 


MOVEMENTS    OF    THE    ATMOSPHERE  47 

culation,  the  winds  flowing  inward.  In  the  northern  hemisphere 
the  course  of  the  winds  is  counter-clockwise,  the  deflection  being 
again  to  the  right,  while  in  the  southern  hemisphere  the  direction 
of  the  circulation  is  clockwise,  the  deflection  being  to  the  left. 

WHIRLWINDS  AND  TORNADOES. 

These  are  due  to  ascending  air  currents  of  a  localized  character 
caused  by  excessive  heating  of  the  air  at  one  place.  In  desert  re- 
gions these  whirls  often  reach  a  height  of  1,000  feet  or  more,  as 
shown  by  the  whirling  columns  of  dust.  Rains  of  exceptionally 
heavy  character,  called  cloudbursts,  often  result  from  the  expan- 
sion of  the  air  above  and  the  consequent  cooling.  Tornadoes  are 
whirlwinds  of  unusual  strength  and  very  small  diameter.  The  air 
pressure  at  the  center  of  the  tornado  is  sometimes  a  fourth  less  than 
that  of  the  surrounding  region,  while  the  velocity  of  the  winds  has 
been  estimated  at  from  400  to  500  miles  per  hour.  Tornadoes  are 
thus  of  exceptionally  destructive  character. 

THE  INFLUENCE  OF  MOUNTAINS  ON  WINDS.  The  air  move- 
ments are  locally  modified  to  a  considerable  extent  by  mountains, 
which  give  them  special  characters,  significant  in  their  influence  on 
climate.  As  an  example,  the  foehn  of  Switzerland  may  be  men- 
tioned. (Hann-4O:j^5.)  This  is  a  warm  dry  wind  which  blows 
down  from  the  crest  of  the  Alps  with  great  violence  from  a  south- 
easterly, southerly,  or,  less  frequently,  a  southwesterly  direction,  ac- 
cording to  the  trend  of  the  valleys.  The  main  valleys  which  trend 
southeast  and  northwest  or  south  and  north  on  the  northern  side 
of  the  central  chain  of  the  Alps  are  the  most  exposed  to  the  foehn, 
while  east  and  west  valleys  are  seldom  or  never  visited  by  it.  The 
greatest  frequency  of  these  winds  is  between  Geneva  and  Salzburg, 
where  in  the  valleys  the  velocity  of  the  wind,  the  rise  in  temper- 
ature, and  the  dryness  are  the  greatest.  In  the  upper  portions  of 
the  valleys  of  the  Rhine,  the  Linth,  the  Reuss,  and  the  lower  Rhone, 
the  foehn  sometimes  attains  the  velocity  of  a  gale.  As  it  recedes 
from  the  mountains  its  violence  decreases,  and  over  the  main  part  of 
the  Swiss  highland  and  the  Jura,  and  along  the  northern  frontier  of 
Switzerland,  it  causes  only  a  slight  rise  in  temperature  and  corre- 
sponding decrease  in  humidity.  These  winds  are  most  frequent  in 
spring,  when  the  snow  disappears  before  their  hot  breath,  and  least 
so  in  summer.  T^n  years'  observations  at  Innsbruck  give  the  aver- 
age number  of  foehn  wind  days  for  spring  17,  summer  5,  autumn 
II. i,  and  winter  9.5 ;  a  total  of  42.6  for  the  year. 

While  (40:349)  the  foehn  is  blowing  north  of  the  Alps,  there 


48 


PRINCIPLES    OF    STRATIGRAPHY 


is  a  calm  on  their  southern  side,  with  little  if  any  increase  in  tem- 
perature, and  with  high  humidity.  In  most  cases  also,  a  few  hours 
after  the  foehn  has  begun  to  blow,  rain  and  snow  begin  to  fall  on 
the  southern  slopes  and  the  summits  of  the  Alps,  the  precipitation 
being  often  extraordinarily  heavy;  exceptional  precipitation  on  the 
south  often  coinciding  with  extreme  violence  of  the  foehn  on  the 
north.  The  following  table,  copied  from  Hann,  shows  the  average 
weather  conditions  which  prevailed  simultaneously  at  Milan,  on  the 
southern  side,  at  Bludenz,  Austria,  in  a  tributary  alpine  valley  of  the 
Rhine,  and  at  Stuttgart  in  the  northern  plains,  during  twenty  winter 
days  on  which  there  were  foehn  winds.  (40:550.) 


Temperature    • 

Relative  humidity 

in  degrees  C. 

in  per  cent. 

Station 

Weather 

A.M. 

P.M. 

Eve. 

A.M. 

P.M. 

Eve. 

Milan 

3-2 

5-i 

3-9 

96 

93 

96 

Rain  on  1  6  days. 

Variable 

winds. 

Bludenz 

ii   i 

14.   O 

ii   ^ 

2Q 

22 

28 

S   E   5-8  foehn 

Stuttgart  

i   4 

8  8 

c  o 

84 

72 

81 

Rain  on  lodays 

Variable 

winds. 

The  high  temperature  of  the  wind  and  its  dryness  do  not  exist 
on  the  alpine  summits,  but  are  acquired  during  the  descent  on  the 
northern  side.  They  are  not  imported  from  the  region  to  the  south 
of  the  Alps.  This  is  shown  by  the  observations  on  the  weather 
along  the  St.  Gotthard  Pass  during  the  foehn  of  January  3i-Feb- 
ruary  I,  1869,  as  shown  in  the  following  table.  (Hann~4o:j5O.) 


Station 

Altitude 
(meters) 

Temperature, 
degrees  C. 

Relative 
humidity, 
per  cent. 

Wind 

Bellinzona  

22Q 

+   1  o 

80 

N.  (rain) 

San  Vittore 

26Q 

+    2    q 

85 

S  and  S  W 

Airolo    .          

1,172 

-4-    O  Q 

N  and  S 

St   Gotthard 

2   IOO 

—  4    5 

S      2-1 

Andermatt.  .  .            . 

1,448 

4-25 

S  W     2 

Altdorf  

454 

4-14.  5 

28 

S    (Foehn). 

MOVEMENTS    OF   THE    ATMOSPHERE  49 

The  foehn  winds  are  explained  by  the  development  of  south- 
erly winds  which  flow  toward  a  region  of  low  pressure  in  western 
Europe,  because  of  the  advance  of  barometric  depressions  or  storm 
centers  from  the  Atlantic.  The  air  of  the  Alpine  valleys  is  likewise 
drawn  toward  this  region,  and  to  replace  it  the  air  rushes  in  from 
the  summits,  the  wall  of  the  Alps  preventing  any  direct  supply,  and 
keeping  the  air  calm  on  the  south  side  of  the  Alps.  Air  carried  up 
and  expanding  is  cooled  at  the  rate  of  i°  C.  for  every  100  meters, 
this  loss  of  heat  being  the  thermal  equivalent  of  the  work  done  by 
the  air  in  increasing  its  volume  against  the  pressure  of  the  sur- 
rounding air.  Conversely,  air  drawn  down  from  a  region  of  less  to 
one  of  greater  pressure  will  be  compressed,  and  at  the  same  time 
warmed  at  the  rate  of  i°  C.  for  every  100  meters  (or  more  ex- 
actly 0.99°  C.  for  every  100  m.).  Since  the  average  rate  of  de- 
crease of  temperature  with  increase  in  altitude  is  in  winter  0.45°  C. 
for  every  100  meters,  the  air  coming  down  from  the  mountains 
increases  in  temperature  0.54°  C.  in  every  100  meters.  This  would 
give  13.5°  C.  for  a  descent  of  2,500  meters.  The  increase  in  tem- 
perature readily  explains  the  fall  in  relative  humidity,  since  the 
capacity  of  the  air  for  moisture  is  greatly  increased  with  but  slight 
actual  additions.  Foehn  winds  of  less  magnitude  sometimes  occur 
on  the  south  side  of  the  Alps  when  the  conditions  are  reversed. 
Similar  winds  have  been  recorded  from  the  western  coast  of  Green- 
land, where  a  warm,  dry  easterly  or  southeasterly  wind  blows  across 
the  ice-covered  interior  of  Greenland  and  down  onto  the  fiords  of 
the  western  coast,  raising  the  temperature  on  the  average  12°  to 
20°  C.  above  the  mean  in  winter,  and  about  11°  in  spring  and 
autumn.  Iceland,  New  Zealand,  Japan,  and  other  countries  have 
foehn  winds,  and  the  chinook  wind,  which  blows  eastward  from  the 
Rocky  Mountains  of  North  America  in  Wyoming,  Montana,  Al- 
berta, and  the  Saskatchewan  country,  has  a  similar  origin.  The 
siroccos  of  Sicily  (Palermo),  the  Algerian  coast,  the  north  coast  "of 
Spain,  etc.,  are  other  examples  of  foehn  winds,  but  the  sirocco  of 
Italy  and  the  Dalmatian  coast  is  a  damp,  muggy  south  or  southeast 
wind  in  striking  contrast  with  the  cold,  dry  northerly  winds  of 
that  region.  These  winds,  the  bora,  rushing  down  from  the  high 
plateau  of  the  Istrian  and  Dalmatian  coasts  and  then  down  the 
southerly  slope  of  the  Caucasus  to  the  Black  Sea  (at  Novors- 
siisk,  Russia),  are  ice-cold  blasts  which  apparently  are  not  warmed 
by  their  descent.  This  is  only  apparent,  however,  since  the  initial 
temperature  of  these  winds'  is  so  low  that,  in  spite  of  the  increase 
during  the  descent,  they  reach  the  warm  coast  of  the  Adriatic  or 
the  Black  Sea  as  a  cold  blast.  The  bora  occurs  only  where  the 


50  PRINCIPLES    OF    STRATIGRAPHY 

back  country  is  very  cold  as  compared  with  the  coast.  The  mistral, 
a  stormy  northwest  wind  blowing  from  the  Cevennes  in  southern 
France,  has  a  similar  origin,  descending  from  the  cold  central  plateau 
to  the  warm  Mediterranean  coast. 

Mountain  and  Valley  Winds.  Where  the  general  air  movements 
are  not  too  strong,  a  regular  daily  alternation  of  winds  is  observ- 
able in  mountain  regions,  blowing  up  the  valleys  by  day  and  down 
by  night.  Though  not  confined  to  valleys  on  the  mountain  sides, 
they  attain  their  best  development  there.  In  the  Himalayas,  the 
winds  blow  up  the  valleys  from  9  A.  M.  to  9  P.  M.  and  down  the 
remainder  of  the  night.  Where  the  valleys  open  out  into  the  plains, 
the  winds  often  blow  with  great  violence,  particularly  in  winter. 
The  upward  flow  during  the  day  is  explained  by  the  increase  of 
pressure  at  points  distant  from  the  slope,  owing  to  the  warming  and 
rising  of  the  air  beneath  these  points  and  the  expansion  of  the  air 
at  the  same  level  on  the  mountain  slope.  This  causes  a  movement 
of  the  air  toward  the  mountain  which  must  result  in  an  upward 
flow  of  the  current  on  the  mountain  side.  At  night  the  cool  wind 
naturally  flows  down  the  slope,  attaining  its  greatest  velocity  where 
it  leaves  narrow,  cool  valleys  and  enters  broader,  well-warmed  ones. 

VELOCITIES  OF  WIND.  The  velocity  of  the  wind  current  varies 
enormously,  from  the  frightful  rate  of  400  or  500  miles  per  hour 
obtaining  in  some  tornadoes,  to  the  gentle  zephyr  breeze  of  a  frac- 
tion of  a  mile  per  hour.  The  average  velocity  for  the  winds*  of  the 
United  States  has  been  estimated  at  about  9.5  miles  per  hour  (4.25 
meters  per  second),  and  for  Europe  10.3  miles  per  hour  (4.60 
meters  per  second).  It  is  greater  over  the  sea  than  over  the  land, 
where  friction  retards  it,  and  greater  in  the  upper  air  than  at  the 
earth's  surface.  The  average  velocity  of  the  wind  is  also  greatest 
in  about  latitude  50°.  The  following  wind  scale  gives  the  velocities 
of  the  various  types  of  wind  according  to  Hann  (40)  : 


Number 

Name 

Velocity 

Meters  per  second 

Miles  per  hour 

o 

i 

2 

3 

Calm. 
Light  air. 
Light  breeze. 
Gentle  breeze. 

i-7 
3-i 

4.8 

4.0 
7.0 
10.5 

*  For  comparison  see  velocities  of  streams  given  on  p.  245. 


MOVEMENTS    OF    THE    ATMOSPHERE 


Velocity 

Number 

Name 

Meters  per  second 

Miles  per  hour 

4 

Moderate  breeze, 

6-7 

15.0 

5 

Fresh  breeze. 

8.8 

20.0 

6 

Strong  breeze. 

10.7 

24.0 

7 

Moderate  gale. 

12.9 

29.0 

8 

Fresh  gale. 

15-4 

34-5 

9 

Strong  gale. 

18.0 

40.0    . 

10 

Whole  gale. 

21.0 

47.0 

ii 

Storm. 

30.0 

67.0 

12 

^  Hurricane. 

50.0 

112.  0 

The  following  table  by  Mohn  (67 : 121)  gives  the  range  in 
velocities  and  also  the  corresponding  pressure.  The  values  are 
somewhat  different  from  those  in  the  table  by  Hann. 


Type  of  wind 

Velocity  in 
meters 
per  second 

Pressure  in  kilo- 
grams per 
square  meter 

o.     Calm 

o      to    o  5 

o        to    o  15 

i.     Light  

O    5  to     4.   O 

o  15  to    i  87 

2.     Moderate  

4        to     7 

I  87  to    5.96 

3.     Fresh 

7      to  1  1 

5Q6  to  1  5    27 

4.     Strong  

ii      to  1  7 

1C    27  to  1,4.    T,^ 

5.     Storm 

17      to  28 

1A.    1^  to  Q6.    4. 

6.     Hurricane    . 

above  28 

above  OS  4. 

EOLATION    OR    MECHANICAL    WORK    OF    THE 
ATMOSPHERE. 


The  mechanical  work  of  the  wind  is  expressed  by  the  term  eola- 
tion, which  is  the  process  of  the  earth  sculpture  by  wind,  the  scour- 
ing by  wind-driven  sand,  dust,  and  other  substances,  and  the 
transportation  and  deposition  of  rock  material  by  wind.  It  may  be 
summarized  as  wind  erosion  or  corrosion,  as  wind  transportation  or 
deflation,  and  as  eolian  sedimentation.  The  last  will  be  especially 
dealt  with  in  Chapter  XIII. 


52  PRINCIPLES    OF    STRATIGRAPHY 


WIND  EROSION   AND  TRANSLOCATION. 

Walther  (102,  104)  has  repeatedly  insisted  upon  the  importance 
of  distinguishing  the  twofold  process  of  denudation  performed  by 
the  wind,  namely,  corrasion,  or  the  abrasive  proces-s,  and  deflation, 
or  the  process  of  denuding  by  removal  of  mineral  particles  loosened 
by  weathering.  The  latter  is  by  far  the  more  effective  process,  and 
applies  not  only  to  the  immediate  products  of  weathering,  but  to 
all  the  loose  material  of  the  earth's  surface,  fine  enough  to  be  sub- 
ject to  wind  transportation. 

CORRASION.  Wind  corrasion  is  accomplished  by  means  of  the 
material  carried  by  the  wind.  Sand  grains  are  tlje  commonest  and 
most  effective  agent  in  this  respect,  though  blown  snow  crystals  have 
a  similar  though  less  violent  effect.  Wind-corraded  rocks  usually 
have  a  smooth  and  highly  polished  surface,  which,  however,  is  fre- 
quently irregular,  with  the  harder  minerals  or  bands  projecting,  or 
with  cavities  due  to  corrasion  of  the  soft  parts.  Hard  limestones 
often  have  their  otherwise  obscure  bedding  emphasized  by  the  wear- 
ing of  the  softer  layers;  while  hard  fossils  or  concretions  will  ap- 
pear in  relief  by  the  filing  away  of  the  surrounding  softer  rock.  In 
the  Libyan  desert  the  blocks  of  Tertiary  Operculina  limestone  are 
corraded  by  the  wind  in  such  a  manner  that  the  somewhat  harder 
Foraminifera  are  filed  out  in  relief,  each  resting  on  a  pyramid  or  a 
needle  of  limestone,  the  latter  often  2  cm.  long,  and  sometimes 
giving  the  rock  the  aspect  of  a  pincushion  stuck  full  of  long  pins. 
(Waltrfer-io6:  414.)  On  the  Libyan  limestone  plateau,  where  the 
surface  is  formed  by  an  exceptionally  hard  siliceous  lower  Eocenic 
limestone  bed,  wind-carved  furrows  have  been  discovered,  which 
extend  in  a  N.N.W. — S.S.E.  direction  and  vary  in  depth  up  to  a 
meter.  These  were  carved  by  the  sand-laden  winds  which  for  thou- 
sands of  years  swept  across  this  surface,  with  little  or  no  variation 
of  direction.  (Walther-io6:  413,  and  Martonne-62,  pi.  XXXIII, 
b.)  Similar  furrows,  a  foot  or  more  wide,  but  shallow,  occur  in 
the  surface  of  the  late  Siluric  Anderdon  limestone  of  western  On- 
tario, and  probably  represent  wind  erosion  under  desert  conditions 
during  Lower  Devonic  time.  They  are  covered  with  Middle  De- 
vonic  sands,  both  siliceous  and  calcareous,  about  12  feet  thick,  ap- 
parently free  from  fossils,  and  probably  representing  the  somewhat 
reworked  calcareous  sands  drifted  across  the  old  limestone  plateau. 
These  lower  beds,  chiefly  brown  dolomitic  rocks,  fill  the  fissures 
above  referred  to.  (Grabau  and  Sherzer— 36:  44.)  The  yardangs 
of  Central  Asia  (47)  are  groove-like  hollows,  sculptured  out  of  ar- 


WIND    CORRASION 


53 


gillaceous   rock   surfaces,    and    separated    by   more   or   less    fluted 
ridges.     (Fig.  13.) 

Such  structures  in  an  early  stage  are  also  found  in  the  region 
near  Biggs,  Oregon.  What  may  be  a  similar  structure  is  seen  in 
the  contact  of  the  Upper  Cambric  Olenus  limestones  with  the  high- 
est bed  of  the  Ceratopyge  limestone  in  central  Sweden,  the  lower 


FIG.  13.     Diagrammatic  section  of  yardangs  of  Central  Asia,  the  deeper  de- 
pressions filled  by  sand.     (After  Sven  Hedin.) 

limestone  surface  being  grooved  irregularly,  sometimes  for  a  depth 
o*f  a  few  centimeters,  and  the  succeeding  limestone  filling  the 
crevices.  Other  eolian  erosion  features  are  seen  in  the  Bad  Land 
topography  of  western  North  America,  the  remarkable  sandstone 
pillars  of  the  Bastei,  in  Saxony,  the  equally  remarkable  stone  pillars 


. 


FIG.  14.     Erosion    columns    in    sandstone.      The    result    of    eolian    erosion. 
Monument  Park,  Colorado.     (After  Hayden.) 

of  Tertiary  sandstone,  capped  by  harder  iron-cemented  layers,  found 
in  Monument  Park,  Colorado,  and  the  similar  erosion  pillars  or 
gour  (singular  gar  a)  of  Egypt.  In  part  these  are  probably  due  to 
deflation  of  material  previously  disintegrated.  (Fig.  14.) 

The  natural  sand-blast  in  the  San  Bernardino  Pass,  in  southern 
California,  is  so  powerful  that  the  modern  telegraph  poles  of  the 
Southern  Pacific  Railway  are  greatly  damaged  and  have  to  be  pro- 


54  PRINCIPLES    OF    STRATIGRAPHY 

tected  by  piles  of  rock  and  supplementary  pieces  placed  on  the  wind- 
ward side  of  the  affected  poles.  The  telegraph  wires  of  the  Trans- 
Caspian  Railway  -between  Aidin  and  Bala-ischem  had  to  be  renewed 
after  eleven  years,  because  their  diameter  had  been  diminished  one- 
half  by  the  sand-blast  corrasion.  (Walther-iO4:  52.)  Even  dust 
from  the  city  streets  blown  against  the  tombstones  of  cemeteries 
will  in  time  efface  their  inscriptions.  ( Eggleston-28  :  654-658. ) 

Facetted  Pebbles.  A  highly  significant  and  interesting  result  of 
sand  corrasion  on  loose  stones  is  the  facetted  pebble  or  windkanter. 
This  generally  has  three  or  more  faces  ground  flat,  by  the  sand 
blown  over  it  at  different  times,  and  these  faces  meet  in  sharp 
angles.  These  angles  do  not  represent  the  direction  of  the  wind 
at  the  time  of  cutting,  but  rather  the  more  or  less  accidental  meeting 
of  faces  cut  at  different  times.  Walther  (106)  describes  "Ein- 
kanter,"  Irregular  "Windkanter,"  "Dreikanter,"  and  "Parallel- 
kanter"  from  the  Libyan  desert,  all  formed  by  wind  blowing  in  one 
direction  only.  The  einkanter  are  arranged  with  the  ridge  at  right 
angles  to  the  wind  direction,  the  single  wind-cut  face  being  nor- 
mal to  and  inclined  toward  that  direction.  This  Walther  regards 
as  the  normal  type.  The  polyfacetted  condition  is  brought  about 
by  the  fact  that  the  sand-laden  wind-currents  along  the  bottom  of 
the  atmosphere  wind  in  and  out  among  the  pebbles  strewn  over  the 
surface,  cutting  one  here  and  another  there,  and  so  producing  faces 
and  angles  which  have  no  definite  orientation.  In  some  cases  the 
undermining  of  a  pebble  on  which  one  face  has  been  cut  and  its  sub- 
sequent rolling  over,  expose  a  new  surface  to  the  wind.  (Davis- 
24.)  Of  between  300  and  400  specimens  observed  by  Wade  (101) 
in  the  eastern  desert  of  Egypt,  78  per  cent,  were  set  at  right  angles 
to  the  direction  of  the  wind.  He  found  the  ridge  to  be  more  gener- 
ally a  curved  one,  and  the  face  presented  to  the  wind  not  a  plane  sur- 
face, but  a  gently  curved  one.  Measurements  taken  on  over  fifty 
specimens  showed  that  this  surface  makes  an  angle  with  the  vertical, 
which  varies  between  40°  and  50°,  most  usually  approximating 
45°.  Wade  determined  to  his  own  satisfaction  that  the  air  currents 
were  driven  upward,  carrying  the  sand  against  the  pebble  face. 
Undermining  and  consequent  change  of  position  of  the  pebble  were 
found  to  be  the  cause  of  the  cutting  of  the  several  facets,  as  postu- 
lated by  Davis. 

The  presence  of  these  pebbles  in  undisturbed  condition  in  older 
formations  is  a  reliable  indication  of  the  subaerial  origin  of  the 
deposit.  Davis  (24)  has  used  them  to  prove  the  undisturbed  sub- 
aerial  character  of  the  apron  plains  of  Cape  Cod.  They  have  also 
been  found  in  the  pre-Cambric  Torridon  sandstone  of  Scotland,  the 


DEFLATION 


55 


basal  Cambric  sands  of  Sweden,  the  Rothliegende  of  Germany,  the 
Buntersandstein  of  Thuringia  and  elsewhere. 

DEFLATION.  This  is  by  far  the  most  important  work  of  the  wind, 
and  its  geological  significance  can  scarcely  be  overestimated.  The 
lifting  of  the  material  from  the  surface  is  largely  the  work  of 
eddies  and  irregularities  of  movement  of  the  wind,  including  many 
conflicting  cross-currents.  (Langley-57;  58.)  The  most  important 
are,  of  course,  the  whirling  eddies  of  whirlwinds  and  tornadoes,  but 
many  minor  currents,  due,  in  part,  at  least  to  the  irregularities  of 
the  surface  are  active  in  lifting  the  dust  and  fine  sand.  The  ordi- 
nary convection  currents  of  the  atmosphere  carry  this  finer  material 
up  to  great  heights.  The  force  (Free-33  :  35)  which  moves  the  par- 
ticle is  due  to  the  direct  impact  of  the  wind  plus  the  friction  along 
its  surface.  The  force  of  the  direct  impact  varies  with  the  velocity 
of  the  wind,  and  for  a  given  velocity  with  the  cross-section  of  the 
particle  in  the  plane  perpendicular  to  the  direction  of  the  wind,  as 
well  as  with  the  orientation  of  the  particle,  and  it  is  of  course  most 
efficient  when  a  smooth  plane  is  opposed  to  the  wind.  The  resistance 
of  the  particle  varies  with  its  mass,  i.  e.,  its  size  and  specific  gravity, 
and  to  some  extent  its  form.  In  general  the  velocity  of  the  wind 
necessary  to  carry  a  spherical  particle  of  given  specific  gravity 
varies  as  the  square  of  the  radius,  and  conversely  the  radius  of  a 
particle  which  can  be  supported  by  wind  varies  as  the  square  root 
of  the  velocity.  Thoulet  (94;  95)  found  that  a  uniform  upward 
current  of  air  will  keep  suspended  quartz  grains,  the  size  of  which 
varied  with  the  velocity  as  follows : 


Velocity  in  meters  per  second 

Diameter  of 
quartz  grain 
in  mm. 

o.  so.  . 

0.04 

I    OO                                                                                                                                  . 

o  08 

2.OO  

o.  16 

•*   OO 

o  25 

4.  ^O 

o.  ^5 

S.oo.  . 

0.41 

6  oo 

O.4Q 

7.OO.  . 

0.57 

8  oo 

O.6S 

Q.OO 

0.73 

10  .  oo  

0.81 

1  1  .  OO 

0.89 

12.  OO  "                                     

0.97 

11.  OO. 

i  .05 

56         .         PRINCIPLES    OF    STRATIGRAPHY 

From  this  Free  deduced  the  formula  V  —  Kr,  where  K  is  a  con- 
stant for  the  conditions  of  experiment  and  r  the  radius  of  the 
particle. 

From  numerous  measurements  Udden  concluded  that  the  "aver- 
age largest  size  of  quartz  particles  that  can  be  sustained  in  the  air 
by  ordinary  strong  winds  is  about  o.i  mm.  in  diameter"  (Udden- 
97),  but  the  largest  particle  that  can  be  transported  (not  held  in 
suspension)  is  nearer  2  mm.  in  diameter,  while  gravel  the  size  of 
peas  may  in  rare  cases  be  carried  along  by  the  wind.  This,  how- 
ever, represents  the  limit  of  ordinary  deflation.  (Walther-iO4: 
97.)  Much  larger  fragments,  nevertheless,  are  rolled  along  by  the 
wind,  and  sometimes  even  lifted  and  carried  for  some  distance. 
Stones  as  large  as  a  man's  fist  have  been  observed  blown  along  by 
wind  in  the  deserts  of  Sahara  (Rohlfs),  and  Gobi  (Przhevalsky), 
and  Pumpelli  saw  stones  2  inches  across  blown  by  a  storm  in  Tur- 
kestan. (Pumpelli-77  :joj.)  A  wind-blown  pebble  2  cm.  in  di- 
ameter was  collected  from  the  snows  of  Ben  Nevis  after  a  severe 
storm.  (Murray  and  Renard-69  :  590,  also  Theobold-93  :  534- 
535.)  A  remarkable  case  is  reported  by  St.  Meunier  (66a  :  440;  73  : 
247-248)  of  a  "rain"  of  limestone  pebbles,  whose  diameter  ranged 
from  25  to  35  mm.,  which  fell  on  June  6,  1891,  in  the  Department  of 
Aube,  France.  These  pebbles  are  believed  to  have  been  transported 
150  km.  Other  pebble  falls  are  recorded  by  various  observers.  Or- 
ganisms, often  of  some  size,  are  also  known  among  the  remark- 
able "solid"  rains.  Thus  a  fall  of  lichens  was  reported  from  Persia 
by  De  Candolle.  Falls  of  small  live  fish  have  been  reported  from 
Madras,  India,  and  were  also  observed  at  Singapore,  in  the  Malay 
peninsula;  at  Winter  Park,  Florida,  in  June,  1893;  and  at  Tillers 
Ferry,  South  Carolina,  in  1901.  A  turtle  6  inches  by  8  inches,  and  a 
stone  fragment  y2  inch  by  ^4  inch,  both  incased  in  ice,  fell  at  Vicks- 
burg,  Mississippi,  on  May  n,  1894.  (Abbe  cited  by  Free-33-) 

Sokolow  gives  the  following  table  of  quartz  sand  grains  moved 
by  varying  wind  velocities,  as  derived  from  his  experiments 


Strength  of  wind  in  meters  Maximum  diameter  of 

per  second.  sand  grains  per  mm. 

4-5—  6.7  ......................................  0.25 

6.7—8.4  ......................................  0.5 

9.8  —  11.4  ......................................  i.o 

11.4—13.0  .....................  .  ................  1.5 

These  results  are  only  approximate.     Sokolow  holds  that  eolian 
deposits  with  grains  above  4  to  5  mm.  in  diameter  are  not  known. 

' 


DEFLATION  57 

Character  and  Amount  of  Deflational  Denudation.  On  the  sea- 
shore and  in  the  deserts  all  the  dust  and  fine  sand  grains  are  blown 
away,  leaving  only  the  coarser  sands  and  the  rock  fragments.  The 
latter  are  characteristic  of  the  stony  desert,  the  Hamada  type,  which 
is  found  in  many  deserts  the  world  over.  The  pebbles  are  generally 
smooth  from  wind  wear,  and  may  resemble  water-laid  deposits. 
That  some  pavements  of  this  kind  are  due  to  water  work  is  be- 
lieved to  be  the  case  by  some  observers  ( Free-33 :  j^,  and  works 
cited  there).  Not  infrequently  the  surface  of  the  pebbles  is  covered 
with  the  brown  desert  varnish,  indicating  that  corrasion  has  come  to 
an  end  for  the  time  being.  The  desert  varnish  is  a  brown  to  black, 
often  highly  polished  coating  of  iron  oxide  or  hydrate,  or  of  man- 
ganese oxide,  which  covers  the  stones  and  ledges  of  arid  regions. 
The  amount  of  the  coating,  which  is  seldom  more  than  a  small 
fraction  of  a  millimeter  thick,  increases  with  the  increase  in  aridity. 
Often  it  is  developed  only  on  the  upper,  exposed  side  of  the  stones 
of  the  Hamada,  the  under  surfaces  remaining  uncoated.  Chem- 
ically, the  material  forming  the  rind  is  a  mixture  varying  from  pure 
iron  oxide  to  nearly  pure  manganese  oxide,  with  all  intermediate 
combinations.  The  formation  of  the  rind  begins  with  the  absorp- 
tion of  moisture  by  the  porous  rock  and  the  formation  of  various 
compounds,  through  the  substances  present  in  the  rock  or  derived 
from  without.  The  solutions  formed  are  drawn  to  the  surface  by 
capillarity,  and  under  the  intense  heat  of  the  desert  they  evaporate, 
leaving  the  coating  of  oxide  upon  the  surface.  What  appears  to  be 
a  case  of  desert  varnish  in  Palaeozoic  rocks  is  found  in  a  layer  of 
pebbles  at  the  base  of  the  Siluric  iron  ore  deposit  of  Wisconsin. 
These  rest  upon  an  eroded  surface  of  Ordovicic  shale,  and  are  suc- 
ceeded by  the  iron  ore. 

A  marked  characteristic  of  many  desert  surfaces  is  the  wealth  of 
fossil  organisms  which  are  left  behind  after  the  disintegration  and 
deflation  of  the  rock  mass  originally  containing  them.  Even  if  the 
original  rock  is  only  sparingly  fossiliferous,  a  long-continued  defla- 
tion will  result  in  the  concentration  of  a  considerable  number  of 
specimens  on  the  desert  surfaces.  (Walther-iO4:  j#.) 

Extensive  eolian  erosion,  referable  almost  entirely  to  deflation 
of  materials  loosened  by  other  agencies,  is  shown  in  the  plateau 
country  of  western  North  America.  The  Jurassic  sandstone  of 
Utah  shows  this  especially  well,  numerous  isolated  remnants  or 
buttes  testifying  to  the  great  extent  of  this  work.  The  buttes  them- 
selves often  show  striking  features,  as  in  the  case  of  Casa  Colorado 
and  Looking  Glass  Rock  in  Dry  Valley,  Utah.  In  the  latter  a  large 
alcove  or  cavern  has  been  hollowed  out  by  the  wind,  a  feature  not 


58  PRINCIPLES    OF    STRATIGRAPHY 

uncommon  in  these  sandstones  where  some  parts  are  very  friable. 
(Cross-2i  :  pi.  4,  fig.  2.)  Hollows  of  this  type  are  very  common  in 
sandstones,  especially  Vhere  concretionary  segregation  of  this  iron 
oxide  has  left  some  of  the  sands  in  an  unconsolidated  condition. 
(See  Chapter  XVII.)  Deflational  erosion  of  rocks  in  moist  tem- 
perate regions  is  shown  by  the  classical  example  of  the  Heidelberg 
Schloss.  The  western  tower  of  this  castle,  built  in  1533  and  partly 
blown  up  in  1689,  shows  a  narrow  passageway,  through  which  the 
wind  blows  with  considerable  force.  The  wall  of  this  passage  is 
built  of  heavy  sandstone  blocks,  some  of  which  have  been  hollowed 
out  for  a  depth  of  10  cm.,  entirely  by  the  blowing  away  of  the 
disintegrated  sand  grains,  the  situation  being  such  as  to  exclude 
corrasion. 

Eolian  erosion  over  wide  areas  is  well  shown  in  the  Kalahari 
Desert  of  South  Africa,  where,  according  to  Passarge,  extensive 
plains  have  been  produced  by  this  agent,  the  amount  of  deflational 
work  being  often  indicated  by  the  butte-like  "Inselberge"  still  ris- 
ing above  the  plain  as  unconsumed  remnants.  (Bornhardt-8  :J7.) 
A  similar  origin  has  been  advocated  for  a  part  at  least  of  the  desert 
plains  or  "bolsons"  of  southwestern  United  States.  (Hill-5o; 
Keyes-56.)  That  some  of  the  extensive  depressions  of  the  earth's 
crust  occupied  by  deserts  owe  their  character  to  deflational  work  of 
the  wind  seems  quite  certain.  In  the  Inselberg-landscape  of  South 
Africa  the  country  rock  is  a  crystalline  rock,  mostly  biotite  gneiss, 
biotite  muscovite  gneiss,  garnet  gneiss,  and  amphibolite.  The  resid- 
ual peaks  are  harder  rocks,  chiefly  pegmatite  dikes  and  other  rocks 
high  in  quartz.  The  individual  Inselberge  are  separated  by  dis- 
tances varying  up  to  25  km.  and  over;  the  differences  in  height  of 
various  parts  of  this  plain  are 'not  great,  80  meters  having  been 
found  in  a  distance  of  over  150  km.  Sometimes  the  floor  of  the 
plain  seems  as  smooth  as  a  table  top,  the  minor  depressions  being 
filled  in  by  eolian  deposits.  Near  the  Inselberge,  sometimes  at  their 
very  bases,  are  heavy  masses  of  talus,  consisting  of  the  products  of 
recent  rock  decay,  inaugurated  probably  by  a  change  in  climate  to 
a  more  pluvial  one.  (Hecker-46.) 

Distance  of  Eolian  Transportation.  Only  the  finest  dust  par- 
ticles remain  more  or  less  permanently  suspended  in  the  air,  or  until 
washed  out  by  rains.  Most  of  the  wind-borne  particles  travel  by 
means  of  leaps  and  bounds  of  varying  magnitude..  The  length 
of  the  leap  depends  upon  the  size  and  shape  of  the  particles,  the  wind 
velocity,  and  to  some  extent  on  the  topography  of  the  country. 
From  a  number  of  analyses  of  wind-transported  material  Udden  has 
constructed  the  following  table  of  approximate  maximum  distances 


EOLIAN    TRANSPORTATION 


59 


over  which  quartz  particles  of  different  dimensions  may  be  lifted  by 
moderately  strong  winds  in  single  leaps.     (Udden~99:  65.) 

Gravel  (diameter  from  8-1  mm.)* A  few.feet. 

Coarse  and  medium  sand  (diameter  i-J^  mm.  1-0.25) Several  rods. 

Fine  sand  (diameter  i/4-1/^  mm.  0.25 — 0.125) Less  than  a  mile. 

Very  fine  sand  (diameter  i^-Vio  mm-  0.125-0.0625) A  few  miles. 

Coarse  dust  (diameter  I/LQ  -1/32  mm.  0.0625-0.03125) 200  miles. 

Medium  dust  (diameter  %2~%4  mm-  0.03125-0.015625)..  .  1,000  miles. 

Fine  dust  (diameter  %4  mm.  0.015625  and  less) Around  the  globe. 

These  theoretical  distances  are  probably  never  realized,  owing  to 
the  complex  character  of  the  wind  currents  and  other  factors. 

Dust  storms  may  often  cover  extensive  areas  and  be  the  means  of 
distant  transportation  of  materials.  Udden  (98:196)  records 
storms  extending  300  and  400  miles  in  their  longest  observed  direc- 
tion. A  Chinese  dust  storm  is  known  to  have  existed  simultane- 
ously from  Hankow  to  Chin-kiang,  or  over  a  distance  of  more  than 
450  miles,  and  for  an  unknown  distance  beyond  in  either  direction. 
(Guppy-38.)  On  February  6  and  7,  1895,  dust  fell  in  Mis- 
souri which  must  have  come  from  western  Kansas  and  Nebraska, 
since  all  the  intervening  country  was  covered  with  snow  and  ice. 
On  April  2,  1892,  a  yellow  dust  carried  from  the  interior  of  China 
fell  on  the  deck  of  a  ship  95  miles  west  by  south  of  Nagasaki,  at 
least  1,000  miles  from  its  source;  and  dust  storms  from  Australia 
have  sometimes  reached  New  Zealand,  having  been  transported 
some  1,500  miles.  Dust  believed  to  have  been  brought  from  the 
Sahara  has  been  observed  in  northern  Germany,  and  in  England, 
some  2,000  miles  distant.  This  is  the  so-called  sirocco  or  trade- 
wind  dust,  which,  however,  has  little  or  no  relation  to  the  true  si- 
rocco. Volcanic  dust  carried  to  the  upper  air  is  likewise  trans- 
ported over  great  distances.  Thus  the  dust  formed  by  the  eruption 
of  Krakatoa  in  1883  was  projected  so  high  into  the  air  that,  caught 
by  the  currents  of  the  upper  air,  it  was  carried  around  the  world 
repeatedly  before  settling.  Some  of  this  dust  is  said  to  have  com- 
pleted the  circuit  of  the  earth  in  15  days.  (Chamberlin  and  Salis- 
bury-i6  :<?/.)  This  dust  settled  slowly  all  over  the  world  and 
became  incorporated  in  all  contemporaneous  deposits.  Beds  of  vol- 
canic dust  in  places  30  feet  thick  are  known  in  Kansas  and  Ne- 
braska, hundreds  of  miles  distant  from  volcanoes  which  could  have 
supplied  the  material.  ( Salisbury-82. )  The  following  summary  of 
volcanic  dust  transport  is  taken  from  Free  (33:149-150)  :  "Vol- 
canic dust  from  Iceland  has  several  times  fallen  in  Scandinavia,  in 

*  See  table  of  sizes  of  sand  grains,  etc.,  in  Chapter  VI,  page  287. 


60  PRINCIPLES    OF    STRATIGRAPHY 

northern  Great  Britain,  and  in  Holland.  Dust  from  Tomboro  fell 
on  Sumatra,  a  thousand  miles  away.  Krakatoa  ashes  fell  inches 
deep  at  distances  of 'nearly  1,000  miles  from  the  volcano,  and  small 
quantities  fell  even  in  Holland.  Dust  from  Colima  in  Mexico  fell 
in  February  and  March,  1903,  at  points  over  200  miles  north  and 
east  of  the  volcano,  and  the  ash  from  Santa  Maria  in  Guatemala  in 
October,  1902,  covered  all  the  northern  part  of  that  country  and 
most  of  the  states  of  Tabasco,  Veracruz,  and  Oaxaca  in  southern 
Mexico.  At  Tapachula,  40  miles  away,  the  ashes  were  19.5  centi- 
meters thick. 

"Ash  from  Coseguina  in  Nicaragua  in  1835  covered  an  area  of 
1,500,000  square  miles  and  even  reached  Jamaica,  more  than  750 
miles  away.  The  dust  from  the  eruption  of  Cotopaxi  in  Equador 
in  1877  fell  at  Guayaquil,  150  miles  away,  to  the  amount  of  315 
kilograms  on  every  square  kilometer  during  the  first  thirty  hours 
of  the  fall.  Once  209  kilograms  fell  in  twelve  hours.  The  dust 
ejected  by  this  same  volcano  in  1888  amounted  to  more  than  2,000,- 
ooo  tons.  On  this  occasion  the  dust  cloud  traveled  85  miles  in  six 
hours.  At  the  eruption  of  Tarawera  in  New  Zealand  in  1886, 
1,960,000,000  cubic  yards  of  dust  were  discharged  in  five  or  six  hours 
and  covered  a  land  area  of  over  6,000  square  miles.  Much  more 
dust  fell  into  the  sea.  Dust  from  the  eruptions  of  La  Soufriere  and 
Pelee  in  1902  fell  plentifully  all  over  the  West  Indies  and  especially 
at  Barbados,  130  miles  from  Pelee  and  225  from  La  Soufriere. 
Dust  from  the  eruption  of  Pelee  in  1812  is  said  to  have  reached  the 
Azores.  Dust  from  Vesuvius  has  been  observed  in  Greece,  in 
France,  and  in  Austria." 

Volume  of  Dust  Falls.  In  1863  a  rain  of  dust  occurred  on  the 
Canary  Islands,  the  volume  of  which  was  estimated  at  3,944,000 
cubic  meters.  (Fritsch-34: 212.)  Free  (33:9$)  reduces  this  to 
5,900,000,000  kgm.  or  6,500,000  tons.  The  dust  fall  in  Eng- 
land on  February  22,  1903,  is  said  to  have  furnished  9,100,000,000 
kilograms  or  10,000,000  tons  of  material,  but  the  data  are  not  wholly 
reliable.  The  great  dust  storm  of  March  9-12,  1901,  however, 
brought  to  Europe  1,782,200,000  kilograms  or  1,960,420  tons  of  dust, 
while  North  Africa  received  1,500,000,000  kilograms  or  1,650,000 
tons.  This  dust  deposit  thus  covered  at  least  300,000  square  miles 
of  land  surface,  and  170,000  square  miles  of  ocean,  and,  accord- 
ing to  Walther,  traveled  in  part  at  least  a  distance  of  4,000  kilo- 
meters or  2,500  miles.  Altogether  3,282,200,000  kilograms  or 
3, "6 1 0,420  tons  of  dust  fell.  For  the  European  area  (437,500  square 
kilometers  or  168,437  square  miles),  the  fall  averaged  a  layer  of 
dust  0.239  mm.  thick.  Assuming  the  usual  dust  falls  together  with 


EOLIAN    TRANSPORTATION  61 

the  exceptional  ones  to  average  this  amount  for  every  period  of  five 
years,  we  would  get  a  deposit  4.78  mm.  thick  in  a  century,  while  dur- 
ing the  three  thousand  odd  years  during  which  such  storms  have 
been  recorded,  the  total  amount  would  be  143.4  mm.  or  over  $l/2 
inches  of  material  brought  from  the  desert.  Dust  fogs  are  charac- 
teristic of  the  Red  Sea  at  certain  seasons  and  are  known  on  parts 
of  the  Atlantic  reached  by  the  winds  from  the  desert.  If  dust-laden 
winds  reach  a  district  of  more  rainfall,  or  if  their  velocity  is  dimin- 
ished, they  will  be  relieved  of  their  burden,  and  the  dust  will  settle. 
This  occurs  in  the  steppe  surrounding  the  desert,  where  the  further 
transport  of  the  material  is  in  large  measure  prevented  by  the  grassy 
vegetation.  Thus  the  surface  of  the  steppe  is  gradually  built  up  by 
deposits  of  fine  material  derived  often  from  great  distances.  Skele- 
tons of  terrestrial  animals  may  readily  be  buried  where  accumulation 
is  rapid,  while  along  the  water  courses  leaves  and  shells  of  fresh 
water  or  land  molluscs  may  become  entombed.  The  loess,  discussed 
more  at  length  below,  is  believed  to  be  an  accumulation  of  this  sort, 
and  older  deposits  of  this  type  are  coming  to  be  more  generally 
recognized. 

Sorting  and  Rounding  of  Sand  Grains  by  Wind.  The  sands 
picked  up  by  the  winds  on  the  shores  ordinarily  travel  only  at  a 
slow  and  probably  constantly  diminishing  rate  inland.  But  the 
finer  dust  particles  are  blown  away  rapidly.  If  the  sand  consists  of 
or  contains  minerals  which  are  readily  ground  into  dust,  this  dust 
will  be  blown  away  and  the  destructible  minerals  are  thus  removed 
from  the  dune  sand.  It  is  due  to  this  destruction  of  other  minerals 
that  the  dune  sand  of  some  coasts  consists  almost  entirely  of  pure 
quartz  grains. 

During  this  movement,  these  dry  sand  particles  are  not  only  ac- 
tively engaged  in  abrading  whatever  rocks  or  other  objects  are  in 
their  path,  but  they  themselves  are  well  rounded  through  mutual 
attrition.  So  perfect  is  this  rounding  of  the  grains  in  some  wind- 
blown sands  that  even  the  lens  will  reveal  no  irregularities.  (Wal- 
ther-iO3 :  795.)  Since  particles  o.i  mm.  or  less  in  diameter  are  not 
reduced  by  mutual  attrition  in  water,  it  follows  that  rounded  grains 
below  this  size  must  in  general  be  'regarded  as  wind-worn  grains. 
(The  relative  efficacy  of  wind  and  water  as  agents  of  rounding  will 
be  discussed  in  Chapter  V.)  The  glassy  character  is,  moreover, 
dimmed  by  this  attrition,  and  the  surface  of  the  grains  takes  on  the 
character  of  ground  glass.  Such  sands  may  later  be  worked  over 
by  the  waves  of  a  transgressing  sea  or  lake,  and  so  become  well- 
stratified  waterlaid  deposits  with  remains  of  aquatic  organisms.  Not 
infrequently  shells  are  driven  far  up  on  the  shore  by  the  winds, 


62  PRINCIPLES    OF    STRATIGRAPHY 

and  become  buried  in  the  sand  dunes.  (See,  further,  Chapter 
XIII.)  Wind  is  a  better  sorter  than  water,  hence  pure  quartz  sands 
will  be  more  commonly  formed  from  crystalline  rocks  in  arid 
regions.  When  the  rock  destroyed  is  a  marine  or  other  sandstone, 
the  resulting  sand  requires  comparatively  little  purification. 

The  sands  of  the  Libyan  desert  are  believed  to  have  been  de- 
rived from  the  destruction  of  the  Nubian  sandstone  to  the  south, 
whence  they  were  transported  by  wind  to  their  present  position  on 
the  Cretacic  limestone  plateaus  of  the  desert.  Grains  of  lime  rock 
from  the  underlying  foraminiferal  limestones  are  noted  in  this  sand, 
but  otherwise  it  is  pure  quartz  and  well  assorted  as  to  size. 


CONDENSATION  AND  PRECIPITATION  OF  AT- 
MOSPHERIC MOISTURE.* 

The  moisture  of  the  atmosphere  is  condensed  and  precipitated  in 
the  form  of  frost  or  of  clouds  and  fogs,  rain,  snow,  or  hail.  Air  is 
brought  to  the  point  of  condensation  of  its  moisture  by  being  car- 
ried to  regions  of  lower  temperature,  i.  e.,  up  the  sides  of  mountains 
or  to  higher  latitudes,  by  the  influx  of  a  cooler  wind,  by  radiation, 
and  by  expansion.  Convection  currents  will  carry  the  air  upward 
to  cooler  regions,  or  to  regions  where  it  can  expand.  Such  cur- 
rents are  characteristic  of  the  tropical  belt  of  calms  where  precipi- 
tation occurs  almost  daily. 

DEW.  When  the  temperature  of  the  air  is  lowered  to  such  a 
point  that,  with  a  given  absolute  humidity,  the  relative  humidity 
rises  to  100,  the  next  step  in  cooling  will  cause  the  precipitation  or 
condensation  of  some  of  the  moisture.  The  temperature  at  which 
this  takes  place  in  any  given  case  is  the  dew  point.  According  to  the 
absolute  amount  of  water  in  the  air,  the  dew  point  will  vary  in  tem- 
perature, being  high  when  there  is  a  large  amount  of  water  in  the 
air,  and  low  when  the  amount  is  small.  Radiation  on  clear  nights 
may  reduce  the  temperature  of  the  rocks  and  vegetation  to  such  an 
extent  below  that  of  the  air,  that  moisture  will  condense  in  the  form 
of  dew,  if  the  condensation  temperature  is  above  32°  F.  (o°  C), 
or  in  the  form  of  ice  particles  if  the  temperature  is  below  that  point. 
Moisture  thus  condensed  has  been  observed  by  the  author  to  cover 
the  rocks  and  vegetation  of  the  summits  of  the  White  Mountains 
with  ice  crystals  in  early  August,  these  crystals,  six  inches  long,  jut- 
ting out  into  the  teeth  of  the  moisture-laden  wind  from  the  vertical 


*  For  composition  of  rain  water  see  Chapter  IV. 


ATMOSPHERIC    MOISTURE  63 

surface  of  the  rock  cairn.  Similar  crystals  18  inches  long  have  been 
reported  from  these  summits. 

FROST.  Frost  results  from  a  condensation  of  the  atmospheric 
moisture  at  a  temperature  below  the  freezing  point,  in  contact  with 
cold  objects.  It  has  the  same  relation  to  dew  that  snow  has  to  rain. 
The  atmospheric  moisture  freezing  in  the  finer  rock  crevices  becomes 
a  powerful  agent  in  causing  rock  disruption.  The  freezing  of  water 
in  these  fissures  likewise  acts  as  a  powerful  wedging  agent  (see, 
further,  Chapter  IV.) 

CLOUDS  AND  FOGS.  Clouds  are  the  condensed  atmospheric  vapor 
remaining  suspended  in  the  air,  and  fogs  are  clouds  resting  upon 
the  surface  of  the  earth.  When  condensation  takes  place  above  the 
freezing  point,  the  clouds  and  fogs  will  consist  of  water  particles ; 
if  below  that  point,  they  will  be  ice  particles,  constituting  air  frost. 
Clouds  form  an  effective  thermal  blanket,  preventing  radiation  and 
the  cooling  of  rock  surfaces.  In  regions  of  much  cloudiness,  shat- 
tering of  rocks  by  insolation  is  reduced  to  a  minimum.  The  diame- 
ter of  the  droplets  of  water  in  clouds  and  fogs  has  been  estimated 
at  0.0085  mm.,  and  it  is  owing  to  this  small  size  that  they  remain 
suspended.  The  types  of  forms  which  clouds  assume  are :  cumulus, 
thick  clouds  with  horizontal  base  and  more  or  less  dome-shaped  up- 
per surface ;  stratus,  horizontal  sheets  of  lifted  fog ;  nimbus,  or  rain 
clouds,  of  thick  layers  of  dark  clouds  with  ragged  edges ;  and  cirrus, 
high,  thin,  feathery,  or  fibrous  clouds,  often  consisting  of  particles 
of  snow  or  ice.  Intermediate  types  are  also  recognized. 

RAIN,  SNOW,  AND  HAIL.  The  moisture  of  the  atmosphere  is 
precipitated  as  rain,  snow,  or  hail,  when  the  particles  become  heavy 
enough  to  fall.  If  they  begin  as  frozen  particles  of  snow  in  the 
upper  air,  they  may  melt  on  passing  through  a  stratum  of  warmer 
lower  air  and  so  change  to  rain,  or,  if  the  air  is  dry,  even  evaporate. 
Thus  snow  may  fall  on  the  mountain  top  and  rain  in  the  valley, 
or  no  precipitation  occur  in  the  valley,  while  rain  "or  even  snow 
falls  on  the  summits.  When  water  falling  as  rain  passes  through 
a  colder  stratum  of  air,  it  may  freeze,  and  hail  will  result.  Hail 
also  results  from  the  enlargement  of  snow  crystals  which  pass 
through  a  very  moist  atmosphere  and  so  surround  themselves  with 
layers  of  ice. 

Amount  of  Rainfall.  Sir  John  Murray  (68)  estimates  the  total 
annual  rainfall  of  the  globe  at  29,350  cubic  miles.  Of  this  amount 
2,243  cubic  miles  of  rain  falls  on  the  inland  drainage  areas  of  the 
globe,  such  as  the  Caspian,  the  Sahara,  and  similar  districts.  Of 
this  the  Sahara  alone  gets  728.9  cubic  miles,  or  an  average  of 
31,106,860  cubic  feet  per  square  mile  of  area,  while  the  Kalahari 


64  PRINCIPLES    OF    STRATIGRAPHY 

desert  gets  14.4  cubic  miles,  making  an  average  of  34,261,500  cubic 
feet  per  square  mile. .  The  inland  drainage  areas  of  Eurasia  aver- 
age 25,125,040  cubic  feet  and  those  of  Australia  only  23,986,540 
cubic  feet  per  square  mile.  The  total  of  these  inland  drainage  areas 
comprises  about  11,486,350  square  miles,  giving  an  average  of 
28,729,760  cubic  feet  of  rain  per  square  mile  of  area.  None  of  the 
water  falling  there  reaches  the  sea.  Most  or  all  of  this  amount  is 
returned  to  the  atmosphere  and  often  more,  as  shown  by  the  shrink- 
age of  inland  lake  basins  such  as  Great  Salt  Lake  of  Utah.  When 
the  annual  rainfall  is  under  10  inches,  desert  conditions  will  prevail, 
and  a  "rainless"  condition  is  assumed  to  exist.  Thus  the  average 
precipitation  along  the  Mexican  boundary  of  the  lower  Colorado 
district  is  about  8  inches;  on  the  Yuma  and  Colorado  deserts  it  is 
only  2  or  3  inches.  The  total  area  of  land  thus  affected  at  the 
present  time  is  about  12,200,000  square  miles,  and  corresponds  very 
closely  in  extent  and  position  to  the  inland  drainage  areas  of  the 
world.  These  areas  are  distributed  as  follows : 


Continent 

Area  in  square 
miles  with  less 
than  10  inches  of 
rainfall 

Percentage  of 
total  area  of 
continent 

Australia  and  Tasmania  

I  1  06  2^0 

-7Q     8 

Asia  

5,  802,  2^O 

^6  ^ 

Africa 

•2  221  OOO 

28  2 

North  America  

I  4.72  4.OO 

17   O 

South  America  »  

Wl,O*,O 

A    7 

Europe 

J7.Q   ISO 

37 

Antarctica  

Total  

1221s?  ^OO 

21  2%  total  land 

area  * 

The  highest  rainfall  is  recorded  in  Asia,  where  437,500  square 
miles,  or  2.7  per  cent,  of  its  total  area,  receive  over  75  inches  an- 
nually (averaging  113  inches),  and  in  South  America,  where  1,444,- 
ooo  square  miles,  or  20.5  per  cent,  of  its  total  area,  receives  100 
inches  or  over.  The  distribution  of  areas  receiving  over  75  inches 
of  rainfall  annually  is  as  follows : 


*  Taking  the  total  area  of  the  land  (see  ante)  as  148.8  million  square   kilo- 
meters or  57,460,777  square  miles- 


QUANTITY   OF   RAINFALL  65 

Square  miles. 
Asia — 

Mean  of    85  inches 46,450 

Mean  of    90  inches 92,900 

Mean  of  100  inches 7,75° 

Mean  of  120  inches 58,100 

Mean  of  170  inches 232,300 

Africa — 

Mean  of  100  inches 201,300 

Mean  of  1 10  inches 209,050 

Java,  mean  of  1 10  inches 54,200* 

Sumatra,  mean  of  130  inches 185,800* 

Celebes,  mean  of  120  inches 77,400* 

Borneo,  mean  of  100  inches 290,350* 

Philippines,  mean  of  90  inches 123,900* 

Formosa,  mean  of  85  inches 15,500* 

Japan,  mean  of  80  inches 46,450 

North  America — 

Mean  of    85  inches 92,900 

Mean  of    90  inches 69,700 

South  America — 

Mean  of  100  inches 185,800 

Mean  of  120  inches 1,122,700 

Mean  of  130  inches I35,5°o 


Total  area  over  75  inches  of  rainfall  annually 2,810,550 

The  rainfall  of  Europe  does  not  exceed  75  inches,  nor  does  that 
of  Australia  and  Tasmania.  The  rainfall  of  the  Antarctic  ranges 
from  25  to  50  inches,  that  of  Greenland  from  10  to  50,  and  that  of 
Iceland  from  25  to  75  inches. 

Relation  of  Evaporation  to  Rainfall.  Measurements  of  rainfall 
and  evaporation  made  in  Russia  have  shown  a  steady  decrease  of 
the  former  from  the  coast  to  the  interior,  and  a  corresponding 
rapid  increase  of  the  evaporation.  Thus  at  Kiev  the  rainfall  is  53 
cm.,  while  the  evaporation  is  48  cm.  At  Astrakhan  the  precipita- 
tion is  1 6,  and  at  Petro-Alexandrovsk  it  is  only  6  cm.,  while  the  cor- 
responding evaporation  at  the  two  points  is  74  cm.  and  232  cm.,  re- 
spectively. The  following  table  (p.  66),  compiled  by  Murray, 
shows  the  annual  rainfall  and  annual  discharge  for  33  rivers  in  dif- 
ferent parts  of  the  world,  the  difference  between  these  representing 
the  mean  annual  amount  evaporated.  Over  the  total  area  of  the 
drainage  basins  of  these  rivers,  comprising  13,272,000  square  miles, 
the  annual  evaporation  amounts  to  about  8,000  cubic  miles  of  water. 

*  Total  area  of  the  islands. 


66 


PRINCIPLES    OF    STRATIGRAPHY 


Position 
of 
mouth 
of 
river 

£ 

River 

Drainage 
area 
in 
square 
miles 

Annual 
rainfall 
in  . 
cubic 
miles 

Mean 
annual 
discharge 
in  cubic 
miles 

Mean 
ratio 

5o°-6o°  N 

Rhine 

1,2,600 

IO-5OO 

IO.  IOO 

2    Od.Q 

Oder                      .... 

51,100 

14.700 

2  .  5OO 

5    SO'* 

Niemen  

36,450 

10.355 

3.783 

2    7^7 

Vistula 

65,800 

10.008 

5   657 

T    co8 

40°-50°  N. 

St.  Lawrence  

565,200 

338.967 

87.^12 

T.    004 

Danube 

^2O,^OO 

108  7^6 

67       SI  I 

2    7/16 

Po 

27,100 

2^.887 

11.  122 

I    7Q4 

Volga   

592,300 

152.384 

4^.7^6 

T.    4.84 

Seine 

2^,25O 

10.266 

5  460 

I    877 

Rhone                    

34,850 

22  .439 

14.066 

I    724 

Dnieper 

107,4.  co 

56    ^84 

22    105 

2    527 

Loire                             .  . 

42,600 

18.210 

7  810 

2    112 

Dniester  

30,950 

8.792 

^.274 

2    685 

™°-4.o°  N 

Yang-tse-kiang 

680,100 

408  872 

12  S    OA^ 

^421 

Hoang-ho  

Nile 

387,150 

I  20^  CKO 

117.711 

892    I  20 

28.591 

24    ^4 

4-159 

^6  008 

2o°-3o0  N. 

Pei-ho  
Mississippi        

65,000 
1,285,300 

22.354 

673  .  064 

1.650 
I25.6o^ 

13.551 
5  446 

Rio  Grande 

2^2  1OO 

11^   655 

12    676 

8  966 

Indus                            .  . 

•;  60,050 

104.416 

26    032 

4  886 

* 

Ganges 

cg8  450 

cj.8  70  1 

4^   26^ 

1  6  169 

I0°-20°  N 

Magdalena                  .  . 

Q2.QOO 

116  746 

50   451 

I  064 

Irawadi                    .... 

l8l,Q5O 

180.849 

82    200 

2    256 

Kistna  

Godavery                    .  . 

8l,300 
1^4,8^0 

61.025 
05  024 

14.766 
16  841 

4.137 

5  7o8 

o°-io°  N. 

Orinoco    .      .        

42Q.7OO 

60^  .  1Q7 

122.242 

4-  Q^6 

Eouator 

Amazon 

2  22Q  QOO 

2  811  8^0 

527   051 

8    OOQ 

o°-io°  S. 

San  Francisco  
Congo  

212,900 
1,540,800 

218.459 
1,213.044 

22.197 
419.291 

9,842 

1.211 

20°-30°  S. 

Orange 

267  I  SO 

50  oi  i 

21    875 

2    ^7 

10°-40°  S. 

Olifant  .              

14,^00 

2  .472 

o  670 

1   &1Q 

De  la  Plata 

QQ4.  QOO 

QO4.       687 

I  88  740 

6    OQI 

Uruguav  .  . 

151  ,000 

i^d  800 

^2    1^6 

4  O7^ 

Total    

n,  272,000 

10,186.460 

2,182  485 

Influence  of  Winds  and  Topography  on  Rainfall.  Winds 
blowing  from  higher  to  lower  latitudes,  i.  c.,  from  cooler  to  warmer 
regions,  have  their  capacity  for  moisture  increased  and  hence  be- 
come drying  winds.  This  is  illustrated  by  the  trade  winds,  which 
take  up  moisture  from  the  oceans  and  the  lowlands  over  which 
they  blow.  The  Sahara,  parts  of  Asia,  and  large  parts  of  Aus- 


DISTRIBUTION    OF    RAINFALL  67 

tralia,  South  Africa,  and  southern  South  America  present  such 
lowlands  in  the  trade-wind  zones,  and  hence  are  deserts.  Indeed 
most  of  the  great  deserts  of  the  modern  world  lie  in  the  belts  of 
lowland  country  swept  by  the  trades  outside  the  poleward  limit  of 
the  equatorial  rain  belt,  or  roughly  between  latitudes  20°  and  30°. 
On  the  leeward  western  coasts  of  Australia,  South  America,  and 
South  Africa,  these  deserts  extend  directly  to  the  edge  of  the  sea. 
If  these  winds  are  forced  to  rise  to  greater  altitudes,  as  is  the  case 
when  a  mountain  range  stretches  across  their  path,  they  are  cooled, 
and  the  moisture  is  condensed  and  may  fall  as  rain  or  snow.  Thus 
the  windward  sides  of  these  mountains  will  be  characterized  by 
heavy  rainfall,  as  illustrated  by  the  eastern  slope  of  the  Andes 
Mountains.  The  southeastern  trades  of  this  region  first  lose  a  part 
of  their  moisture  over  the  comparatively  low  Sierras  of  the  east 
coast,  where  the  rainfall  is  over  80  inches  a  year.  Then,  as  they 
sweep  over  the  Brazilian  plains,  the  rainfall  is  less  (between  40  and 
80  inches  per  annum),  to  be  increased  again  to  over  80  inches  as 
they  rise  in  the  Andes.  After  crossing  the  Andes,  they  descend,  and 
being  warmed  both  by  compression  during  the  descent  (see  page 
49,  foehn),  and  by  contact  with  the  warm  surface  of  the  lower 
region,  they  become  drying  winds,  with  the  result  that  the  nar- 
row Pacific  coastal  strip,  to  leeward  of  the  Andes,  is  a  pronounced 
desert  from  near  the  equator  to  about  latitude  30°  S.  Cold  ocean 
waters  and  prevailing  southerly  (drying)  winds  along  shore  further 
contribute  to  this  result.  The  leeward  sides  of  the  mountains  in  the 
path  of  the  trade  winds  are  thus  a  region  of  little  precipitation,  dry 
savannas  or  deserts  occurring,  while  the  windward  sides  support  a 
luxuriant  vegetation.  If  the  eastern  coast  mountains  were  higher, 
the  winds  after  passing  over  them  would  become  drying  winds,  and 
the  plains  of  Brazil  would  be  arid,  rainfall  becoming  abundant  again 
only  as  the  winds  rose  over  the  Andes.  Corresponding  to  such  a 
distribution  of  rainfall,  one  would  expect  densely  wooded  areas  on 
the  eastern  side  and  heavy  torrent-laid  deposits  on  the  western  bor- 
ders of  the  two  mountain  chains,  with  semiarid  or  desert  conditions 
between  them.  The  latter  might  be  characterized  either  by  eolian 
erosion,  or  by  deposition  of  wind-transported  material,  or  by  both. 
Some  of  the  lofty  islands  of  the  Hawaiian  group  which  lie  in  the 
northeast  trade  wind  belt  furnish  other  good  examples  of  rainy 
windward  and  dry  lee  slopes,  the  latter  in  some  cases  being  of  a 
desert  character. 

The  equatorial  belt  of  calms  and  variable  winds,  i.  e.,  the  dol- 
drums, is  a  region  of  exceptionally  abundant  rainfall,  being  one  of 
the  rainiest  regions  of  the  world,  its  average  being  about  100  inches 


68  PRINCIPLES    OF    STRATIGRAPHY 

per  year.  The  cause  of  this  rainfall  is  the  rising  and  expansion  of 
the  air  warmed  near  the  surface,  and  the  consequent  cooling-  and 
condensation  of  its  moisture.  These  precipitations  are  almost  daily 
accompanied  by  thunderstorms,  especially  in  the  afternoon  and  even- 
ing. The  belt  shifts  north  and  south  with  the  position  of  the  sun. 
Two  maxima  occur,  one  in  April  and  one  in  November,  lagging 
thus  somewhat  behind  the  vertical  sun,  the  April  maximum  being 
the  principal  one.  The  minima  between  these  are  seldom  rainless. 
This  constitutes  the  equatorial  type  of  rainfall.  The  tropical  belt 
of  calms,  situated  in  about  latitude  30°,  but  likewise  shifting  with 
the  position  of  the  sun,  is  a  region  of  descending  and  hence  com- 
pressing winds,  which  thus  become  warmed  and  have  a  drying  ef- 
fect. 

From  the  shifting  nature  of  the  tropical  rain  belt  with  the  change 
in  position  of  the  sun,  the  regions  near  its  margin  (or  more  than 
10°  to  12°  from  the  equator)  are  subject  to  regular  alternations  of 
one  wet  and  one  dry  season,  the  two  rainy  seasons  having  become 
merged,  owing  to  the  short  interval  between  the  periods  of  vertical 
sun  in  summer.  This  is  followed  by  a  single  dry  winter  season. 
During  this  period  the  trade  winds  produce  their  drying  effect, 
which  continues  until  the  equatorial  rain  belt  again  encroaches.  This 
type  of  alternating  abundant  rainfall  and  draught  is  called  the 
tropical  type.  The  dry  (winter)  season  lasts  eight  months  in 
typical  cases ;  the  lowlands  become  parched  and  vegetation  withers 
away,  whereas  during  the  shorter  wet  season  grass  and  flowers  will 
grow  in  abundance  and  all  life  take  on  new  activity.  The  Soudan, 
between  the  Sahara  and  the  equatorial  forest  of  Africa,  partakes 
alternately  of  the  character  of  each ;  vegetation  grows  actively  when 
the  doldrums  are  over  it  (May  to  August),  but  when  the  trade 
winds  blow  the  ground  is  dry  and  parched  (December  to  March). 
The  llanos  of  Venezuela  have  a  dry  season  when  the  trade  winds 
blow,  i.  e.,  during  the  northern  winter,  and  an  abundant  rainfall 
from  May  to  October.  The  reverse  is  the  case  in  the  canipos  of 
Brazil,  situated  south  of  the  equator,  where  the  rain  falls  from 
October  to  April,  while  the  remainder  of  the  year  is  dry.  The 
overflow  of  the  Nile  results  from  the  abundant  rainfall  in  the  Abys- 
sinian Mountains  when  the  equatorial  rain  belt  migrates  northward. 

In  the  monsoon  belts  the  rains  follow  the  vertical  sun,  and  there 
is  thus  a  simple  annual  period  similar  to  that  of  the  tropical  type. 
In  summer  the  warm  air  flows  inland  from  the  sea,  bringing  much 
moisture,  which  is  condensed  and  precipitated  as  the  winds  are 
forced  to  rise  over  mountains  or  highland  plateaus.  The  heaviest 
precipitation  in  India  is  in  the  Khasi  Hills  (Assam)  at  the  head  of 


CAUSES    OF   RAINFALL  69 

the  Bay  of  Bengal,  and  at  an  altitude  of  4,455  feet.  Here  the  mean 
annual  rainfall  is  between  400  and  500  inches.  Along  the  southern 
base  of  the  Himalayas  it  is  60  to  100  inches,  on  the  bold  western 
coast  80  to  1 20  inches  and  over,  and  on  the  mountains  of  Burma 
160  inches.  (See  map  of  Indian  winds,  Figs.  10  and  12.)  The  pre- 
vailing direction  of  the  rain-bringing  monsoon  of  India  is  from 
the  southwest,  that  of  the  Pacific  coast  of  Asia  from  the  southeast. 
In  general,  the  eastern  coasts  in  the  tropics  are  the  rainiest,  though 
there  are  notable  exceptions  to  this  rule. 

The  westerly  winds  of  both  hemispheres  (southwesterly  in  the 
northern  and  northwesterly  in  the  southern),  which  blow  poleward 
above  the  latitudes  of  30°,  have  a  corresponding  effect  on  the  rain- 
fall, the  precipitation  occurring  on  the  westerly  side  of  the  mountain 
ranges,  while  corresponding  dryness  prevails  on  the  eastern.  In 
general,  bold  west  coasts  on  the  polar  side  of  latitude  40°  are  very 
rainy,  the  precipitation  being  100  inches  or  more  a  year  in  the  most 
favorable  situations.  The  interior  of  the  continents,  on  the  other 
hand,  especially  when  well  enclosed  by  mountains,  or  open  only  to 
the  cool  ocean  winds  which  become  warmed  as  they  proceed,  have 
only  a  slight  rainfall  of  from  10  to  20  inches  or  less.  The  eastern 
coasts  are  drier  than  the  western,  but  wetter  than  the  interiors  of 
the  continents.  The  maximum  rainfall  occurs  in  winter  over  the 
oceans,  islands,  and  west  coasts  of  the  continents,  this  being  the 
season  of  strong  westerly  winds,  when  cyclonic  storms  are  most 
numerous  and  best  developed.  The  cold  lands,  too,  have  a  chilling 
effect  on  the  inflowing  damp  air.  In  the  interior  of  the  continents 
high  pressure  prevails  and  the  winds  flow  outward,  while  their 
low  temperature  at  the  start  makes  them  drying  winds  as  they  pro- 
ceed outward  to  warmer  regions.  This  season  is,  therefore,  the 
driest  for  the  interior  of  the  continents. 

The  greater  part  of  the  United  States  lies  within  this  zone  of 
prevailing  westerlies,  the  direction  for  almost  all  the  country  being 
from  the  southwest.  In  winter  these  winds  from  the  Pacific  yield 
their  moisture  on  reaching  the  cool  lands,  this  occurring  even  at 
low  altitudes,  as  a  result  of  which  the  lowlands  of  California  have 
a  wet  season.  This  condition  also  exists  in  summer  in  Washington 
and  Alaska,  while  southern  California  has  its  dry  season.  Rising 
over  the  mountains  back  of  the  coast,  the  winds  yield  more  mois- 
ture, so  that  all  the  regions  west  of  the  crest  of  the  coast  ranges  are 
well  supplied  with  rain  and  snow  in  winter.  Beyond  this  range,  and 
beyond  the  Sierras  and  Cascade  Mountains  further  north,  the  winds 
descend  and  become  warmer  and  drier,  and  here  lie  the  semiarid 
lands  of  eastern  Oregon  and  Washington,  and  the  Great  Basin  with 


70  PRINCIPLES    OF    STRATIGRAPHY 

Great  Salt  Lake,  the  shrunken  remnant  of  Lake  Bonneville.  In 
southern  California  the  Mohave  and  Colorado  deserts  lie  just  east 
of  the  Coast  Range.  In  the. higher  parts  of  the  Rocky  Mountains 
these  winds  again  yield  some  moisture,  but  beyond  these  ridges 
they  once  more  become  drying  winds,  with  corresponding  semi- 
aridity  of  the  climate.  The  winds  would  continue  so,  and  arid  con- 
ditions would  prevail  throughout  the  entire  interior  of  the  conti- 
nent, were  it  not  for  the  aperiodic  cyclonic  winds  which,  passing 
over  the  country  from  east  to  west,  cause  moist  air  to  flow  from 
the  Gulf  northward  to  cooler  latitudes. 

If  the  south  winds  from  the  Gulf  were  shut  out  by  a  mountain 
range,  the  region  to  the  northeast  of  it  would  likewise  be  of  an  arid 
nature.  Such  conditions  seem  to  have  existed  in  Triassic  time  in 
North  America  and  western  Europe.  In  North  America  the  newly 
formed  Appalachian  ranges  shut  in  the  land  on  the  Atlantic  side, 
and  their  westward  continuation  in  Arkansas,  Oklahoma,  and  Texas 
formed  a  barrier  against  the  winds  from  the  south.  Continuing 
through  the  region  of  the  present  Basin  ranges,  as  the  Palseo-Cor- 
dilleran  Mountains,  they  formed  the  western  arm  of  the  system 
which  embraced  interior  North  America.  To  the  south  and  west 
extended  the  Triassic  sea  with  its  marine  limestone  accumulations. 
Rising  over  the  Palseo-Cordillerans  in  the  southern  region  (Arizona, 
New  Mexico),  these  winds  became  drying  winds,  as  a  result  of 
which  semiarid  continental  deposits  were  formed  on  the  leeward 
side  of  these  mountains.  These  are  now  found  as  extensive  red 
sandstone  deposits,  partly  of  torrential,  but  perhaps  more  largely 
of  eolian  character,  extending  from  Texas  to  Montana  and  Canada. 
They  are  heaviest  in  the  Arizona  region  and  extend  eastward  and 
northward  into  Colorado  and  Dakota,  dipping  under  the  Cretacic 
deposits  of  the  Great  Plains.  They  come  to  an  end  before  reach- 
ing the  Mississippi  Valley,  where  Cretacic  beds  rest  disconformably 
upon  Permic.  Over  the  whole  eastern  half  of  North  America,  west 
of  the  newly  made  Appalachian  Mountains,  no  Triassic  deposits  are 
known,  and  erosion  rather  than  deposition  seems  to  have  been  ac- 
tive. This  erosion  probably  was  in  part  eolian,  similar  to  that  known 
in  the  Kalahari  desert,  but  near  the  mountains  precipitation  was 
again  abundant,  so  that  river  erosion  characterized  the  mountain 
regions.  Much  of  the  drainage  from  these  mountains  must  have  es- 
caped toward  the  northwest,  where  an  arm  of  the  sea  entered  during 
part  of  Triassic  and  later  Jurassic  time.  Some  of  the  continental  de- 
posits formed  over  the  crystalline  region  of  Canada  and  northern 
United  States  may  have  subsequently  been  reworked  into  the  con- 


PERIODICITY    OF    RAINFALL  71 

tinental  Kootanay  and  Cretacic  deposits,  especially  the  widespread 
Dakota  sandstone.  As  the  west-winds  descended  on  the  eastern  side 
of  the  new  Appalachians,  they  again  produced  semiarid  conditions, 
which  favored  the  deposition  of  the  continental  Newark  and  Con- 
necticut Valley  sandstones  and  their  extensions  north  and  south, 
formations  which  to-day  are  represented  only  by  fragments  of  what 
must  have  been  formerly  a  very  extensive  piedmont  deposit.  South- 
ward the  condition  seems  to  have  been  one  of  less  aridity,  possibly 
because  the  mountains  were  lower,  or  south  winds  from  the  Atlantic 
acted  as  modifiers,  for  here  we  find  plant  beds  and  coal  deposits  as- 
sociated with  the  upper  part  of  the  formation.  These  same  south- 
westerlies  were  also  responsible  for  the  extensive  continental  de- 
posits of  the  Trias  of  western  Europe.  A  mountain  chain,  the  Ar- 
morican,  extended  northwestward  from  central  France  through 
Brittany,  southern  England  and  Ireland,  thus  lying  directly  in  the 
path  of  the  southwesterly  winds.  A  second  chain,  the  Variscian,  ex- 
tended eastward  through  southern  Germany,  around  the  Bohemian 
Mass  on  the  north,  and  thence  to  the  present  Carpathians.  These 
chains  thus  completely  enclosed  northern  Europe  on  the  south,  and 
to  the  north  of  them  were  formed  the  extensive  New  Red  sandstone 
deposits  of  England  and  the  Bunter  Sandstein  with  its  desert  fea- 
tures in  Germany. 

Latitude  and  Precipitation.  Rain  and  snow  decrease  progres- 
sively from  the  equator  polewards,  the  precipitation  being  compara- 
tively slight,  owing  to  the  smaller  capacity  of  the  air  for  water- 
vapor  at  the  prevailing  low  temperature,  and  to  the  absence  of  local 
convectional  storms.  The  western  coast  of  Norway  is  an  exception, 
since  the  rainfall  is  here  much  heavier.  The  precipitation  is  mostly 
in  the  form  of  snow,  though  rain  falls  in  summer  sometimes  prob- 
ably at  all  points.  The  snow  of  the  polar  regions  is  fine  and  dry; 
flakes  are  not  formed  at  low  temperatures,  but  the  atmosphere  is 
full  of  fine,  glittering  ice  needles,  which  gradually  descend  to  the 

§^arth  even  on  clear  days. 
Periodicity  of  Rainfall.     In  a  number  of  places,  as  for  example 
ndia,  observations  have  shown  an  apparent  fluctuation  in  rainfall 
nd  temperature  for  a  period  of  eleven  years,  corresponding  to  the 
un-spot   period   or  the   periodicity   of   the   earth's   magnetic   phe- 
nomena.    A  thirty-five-year  period  of  Oscillation  has  also  been  dis- 
covered  and  elaborated   by   Professor   Bruckner    (12)    (Bruckner 
cycle).    The  cycle  varies  from  20  to  50  years,  but  35  is  the  average. 
The  fluctuations  of  the  rainfall  between  the  dry  and  wet  periods  are 
most  marked  in  the  interior  of  the  continents. 


72  PRINCIPLES    OF    STRATIGRAPHY 

ELECTRICAL  PHENOMENA  OF  THE  ATMOSPHERE. 

By  thunderstorms,  or  other  electrical  discharges  in  the  atmos- 
phere, some  of  its  oxygen  is  probably  converted  into  the  allotropic 
modification  ozone.  Hydrogen  dioxide  and  oxides  of  nitrogen  are 
further  formed,  the  latter  yielding,  with  the  moisture  of  the  air, 
nitric  and  nitrous  acids,  which,  when  brought  to  the  earth  by  rains, 
become  agents  of  corrosion  of  the  rocks.  Both  ozone  and  hydrogen 
dioxide  are  powerful  oxidizing  agents,  and  will  transform  organic 
matter  suspended  in  the  air  into  carbon  dioxide,  water,  and  probably 
ammonium  nitrate. 

Lightning  may  further  act  as  a  disrupter  of  rock  masses.  In 
Fetlar,  one  of  the  Shetland  Islands,  a  solid  mass  of  rock  105  feet 
long,  10  feet  broad,  and  in  some  places  more  than  4  feet  high,  was 
in  an  instant  torn  from  its  bed  by  lightning  and  broken  into  three 
large  and  several  small  fragments.  "One  of  these,  28  feet  long, 
17  feet  broad,  and  5  feet  in  thickness,  was  hurled  across  a  high 
point  of  rock  to  a  distance  of  50  yards.  Another  broken  mass, 
about  40  feet  long,  was  thrown  still  farther,  but  in  the  same  direc- 
tion, and  quite  into  the  sea.  There  were  also  many  lesser  fragments 
scattered  up  and  down."  ( Hibbard-49 :  j#p. ) 

FULGURITES.  When  the  electric  spark  strikes  loose  sand  or  rock, 
a  coating  of  fused  vitreous  material  may  be  formed,  or  a  mass  of 
vitreous  drops  or  bubbles.  More  generally,  slender  tubes  of  fused 
material  mark  the  path  of  the  electric  spark,  especially  in  loose 
sand.  These  tubes,  known  as  fulgurites  *  consist  of  fused  grains, 
and  range  up  to  2^/2  inches  in  diameter.  They  descend  vertically 
or  obliquely  into  the  rock  or  sand,  occasionally  branch,  and  dimin- 
ish in  size  to  a  point.  The  summit  of  Little  Ararat,  which  is  ex- 
posed to  frequent  thunderstorms,  is  riddled  with  fulgurites,  which 
here  occur  in  a  porous  andesite  and  consist  of  irregular  tubes  hav- 
ing an  average  diameter  of  3  centimeters,  and  being  lined  with  a 
blackish-green  glass.  Humboldt  obtained  these  fulgurites  from 
trachyte  peaks  in  Mexico,  and  found  that  in  two  cases  at  least  the 
fused  mass  overflowed  from  the  tubes  onto  the  surrounding  sur- 
face. Other  cases  of  lightning-fused  rocks  have  been  reported  in 
hornblende  schist  of  Mont  Blanc  (De  Saussure)  ;  in  mica  schist 
and  limestones  from  the  Pyrenees  (Ramond;  Arago)  ;  in  basalt  of 
Mount  Thielson,  Oregon,  and  Mount  Shasta,  California  (Diller)  ; 
in  glaucophane  schist  of  Monte  Viso  (J.  Eccles)  ;  in  gneiss  of  Lake 

*  For  extended  bibliography  including  the  cases  cited,  see  the  article  by 
Barrows  (5)  1910. 


ELECTRICAL    PHENOMENA  73 

Champlain  (Hallock),  etc.  Fulgurites  in  sand  have  been  frequently 
described.  These  have  been  found  in  the  sands  of  the  Libyan  desert 
(Giimbel),  as  well  as  in  the  sand  and  soil  of  moist  climates.  In 
Silesia,  near  Olkusz,  26  tubes  were  found  in  an  area  of  200  by  100 
feet,  most  of  them  associated  in  groups.  In  Cumberland,  England, 
near  Drigg,  fulgurites  of  exceptional  size  were  found.  Three  of 
these  tubes  were  found  in  a  sand  hillock  within  an  area  of  fifteen 
square  yards.  One  of  them  was  traced  perpendicularly  to  a  depth  of 
40  feet,  the  basal  part  being  much  contorted  and  branched,  owing  to 
the  presence  of  many  small  pebbles  in  the  soil.  The  maximum 
diameter  of  this  tube  was  2^2  inches. 

The  finer  structure  of  the  glass  lining  of  the  tube  has  been  espe- 
cially investigated  by  Julien  (53).  He  finds  that  the  bubbles  which 
occur  in  such  large  numbers  in  the  clear  amorphous  glass  of  the 
tube  contain  no  water,  these  bubbles  probably  being  formed  by  the 
expansion  of  heated  air.  The  vesicles  are  elongated,  and  their 
longer  axes  disposed  radially.  All  sand  grains  within  a  radius  of 
a  few  millimeters  were  suddenly  and  completely  fused.  The  inner 
wall  is  practically  free  from  bubbles,  and  is  a  clear,  shining  glass, 
streaked  and  spotted  with  black  and  brown,  according  to  the  abun- 
dance of  iron-bearing  minerals.  Externally  the  form  is  very  rough, 
corrugated  longitudinally  and  coated  with  partially  fused  sand 
grains.  The  outline  is  an  irregularly  branching  one,  due  to  the 
forking  of  the  electric  spark.  The  thickness  of  the  wall  varies  from 
o.i  cm.  or  less  to  0.5  cm.  or  more,  and  the  vesicles  from  less  than 
0.002  mm.  to  1.2  mm.  or  over.  The  cross  section  is  often  nearly 
circular ;  at  other  times  it  is  irregular.  Sometimes  the  round  hole  is 
merely  lined  by  a  network  of  fused  materials. 

Of  exceptional  interest  is  a  fulgurite  described  by  Barrows  (5) 
from  the  Raritan  sands  of  New  Jersey.  It  was  found  in  a  mass  of 
sand  fifty  feet  thick,  resting  on  the  South  Amboy  fire  clay,  and  oc- 
curred 15  to  20  feet  above  the  clay  or  from  45  to  55  feet  from  the 
surface  formed  by  the  Pensauken  outwash  gravels  of  Pleistocenic 
age.  The  fulgurite  ran  at  a  low  angle  to  the  horizontal  for  about 
15  feet  parallel  to  the  face  of  the  bank.  The  length  was  about  19 
feet,  including  branches,  and  the  diameter  of  the  tube  varied  from 
3.2  cm.  to  0.3  cm.  The  position  of  this  tube  suggests  that  it  was 
formed  after  part  of  the  sand  had  been  deposited  and  before  the 
laying  down  of  the  upper  part  of  the  sand.  If  this  is  the  case,  these 
sands  would  have  to  be  regarded  as  dune  sands,  since  fulgurites  will 
form  only  in  comparatively  dry  media.  This  interpretation  is  not 
inconsistent  with  the  character  of  the  formation  as  a  whole,  which 
is  of  continental  rather  than  of  marine  origin.  Of  course  the  tube 


A 


74  PRINCIPLES    OF    STRATIGRAPHY 

may  have  resulted  from  a  discharge  entering  the  bank  of  sand  since 
digging  has  exposed  it,  but  it  is  difficult  to  understand  why  the  dis- 
charge should  run  parallel  to  the  face  of  the  cliff. 

It  is  obvious  that  fulgurites  found  in  the  older  formations  may 
have  such  relationships  that  they  must  be  regarded  as  contemporane- 
ous in  age  with  the  formation,  in  which  case  they  would  form  valu- 
able evidence  for  the  continental  origin  of  such  formations. 

CLIMATE.    CLIMATIC  ZONES,  PRESENT  AND  PAST. 

Climate  is  the  average  or  sum  total  of  weather  conditions  normal 
to  a  given  region,  while  weather  is  only  a  single  occurrence  or  event 
in  that  series  of  conditions,  and  of  short  duration.  Climate  may  be 
classified  as  solar  and  physical,  the  latter  comprising  continental, 
marine,  and  mountain  climates. 

SOLAR  CLIMATES.     CLIMATIC   BELTS  OR  ZONES. 

If  the  earth  had  a  homogeneous  land  surface  and  no  atmosphere, 
solar  climate  alone  would  prevail,  the  distribution  of  heat  being 
solely  according  to  latitude.  Five  zones  of  solar  climate  are  recog- 
nized: the  torrid  or  tropical,  limited  by  the  tropics  of  Cancer  and 
Capricorn  and  divided  by  the  equator,  the  two  temperate  zones,  lim- 
ited poleward  by  the  arctic  and  antarctic  circles,  and  the  two  frigid 
or  polar  zones  centering  at  the  poles.  The  torrid  or  tropical  zone 
has  the  least  annual  variation  in  insolation,  and  may  be  called  the 
zone  of  perpetual  summer,  while  the  polar  zones  have  the  greatest 
variation  between  summer  and  winter,  and  may  be  called  the  winter 
zones,  summer  being  so  short  and  cool  that  it  may  be  neglected.  The 
intermediate  zones  have  about  an  equal  distribution  of  seasons, 
summer  in  the  northern  corresponding  to  winter  in  the  southern 
hemisphere.  A  somewhat  different  delimitation  of  the  zones  has 
been  proposed  by  Supan,  who  suggests  that  the  hot  belt  be  limited  by 
the  two  mean  annual  isotherms  of  +  68°  F.  (-f-  20°  C.)  (the  ap- 
proximate polar  limit  of  the  trade-wind  belts,  and  the  polar  limit  of 
palms),  and  the  polar  limits  of  the  temperate  zones,  by  the  two 
isotherms  of  -f-  50°  F.  (+  10°  C.)  for  the  warmest  month  (the  ap- 
proximate northern  limit  of  the  cereals  and  forest  trees).  This 
limit  in  the  north  is  very  near  the  northern  boundary  of  the  conti- 
nent of  North  America  and  Eurasia,  while  in  the  south  it  passes 
through  the  southern  extremity  of  South  America.  Africa  lies  al- 
most wholly  within  the  hot  belt,  and  so  does  the  greater  part  of 
South  and  all  of  Central  America.  The  smaller  size  of  the  north 


CLIMATE  75 

polar  climatic  cap  is  due  to  the  expansion  of  the  land  in  that 
hemisphere.  The  greatest  expanse  of  land  lies  in  the  north  tem- 
perate zone. 

PHYSICAL  CLIMATE. 

This  is  the  climate  produced  through  modification  of  the  solar 
climate  by  the  physical  characters  of  the  earth's  surface.  The  prin- 
cipal kinds  to  be  considered  are:  i,  The  marine  or  oceanic;  2,  the 
coast  or  littoral ;  3,  the  continental  or  interior ;  4,  the  desert,  and  5, 
the  mountain  and  plateau  climates.  Each  of  these  has  its  peculiari- 
ties which  in  turn  influence  the  distribution  of  plant  and  animal  life. 
(See  Chapter  XXIX.) 

1.  Marine  or  Oceanic  Climate.     Owing  to  the  slow  changes  of 
temperature  which  the  ocean  water  undergoes,  the  seasonal  tem- 
perature changes  are  comparatively  slight,  while  the  times  of  oc- 
currence of  maxima  and  minima  are  retarded,  a  cool  spring  and 
warm  autumn  resulting.     Relatively  greater  humidity,  cloudiness, 
and  heavier  rainfall   than  is  found  on  the  land,  are  further  charac- 
teristic of  marine  climates ;  and  are  explained  by  the  greater  evap- 
oration over  the  sea.     In  the  winter  within  the  middle  latitudes, 
there  is  excessive  precipitation  over  the,  oceans,  but  the  continental 
interiors  are  relatively  dry.     Air  over  the  water  is  also  purer  and 
in  more  active  motion  than  that  over  the  land. 

2.  Coast  or  Littoral  Climate.     The   coastal   region   shows   the 
transition  from  the"  marine  to  the  interior  continental  type  of  cli- 
mate, and  may  alternately  partake  of  both,  according  to  whether 
the  prevailing  wind  is  from  the  sea  or  from  the  land.     The  wind- 
ward coasts  are  usually  well  supplied  with  rainfall,  especially  in 
the  tropics,  while  the  leeward  coasts,  notably  those  in  the  trade- 
wind   zones,  are  usually  dry;  and  the  deserts  may  extend  clear 
to  the  coast.     This  is  the  condition  on  the  west  coasts  of  South 
America,  Africa  and  Australia.     The  cold  shore  currents  and  the 
prevailing  long-shore  winds  further  prevent  precipitation.     An  ex- 
ception to  this  general  character  of  wet  eastern  and  dry  western 
coasts  in  the  trade-wind  zone  is  seen  in  the  regions  of  the  monsoons. 
Thus  the  west  coast  of  India  is  abundantly  watered  by  the  wet 
southwest  monsoon.     A  peculiarity  of  these  monsoon  countries  is 
the  threefold  division  of  the  climate  such  as  characterizes  India. 
In  the  winter  little  precipitation  occurs,  and  the  temperature  is  low, 
the  monsoons  blowing  offshore.     Then  follows  the  hot  transition 
period,  which  in  turn  is  succeeded  by  the  cooler  and  wet  summer 
season,  when  the  monsoon  blows  onshore.     The  monsoons  of  the 


76 


PRINCIPLES    OF    STRATIGRAPHY 


eastern  coast  of  Asia,  the  most  northerly  of  such,  likewise  produce 
these  results,  the  weather  being  cold,  clear  and  dry  in  winter,  and 
cool,  cloudy  and  damp  in  summer. 

3.  Interior  Continental  Climates.  In  the  interior  of  continents 
climatic  changes  are  for  the  most  part  very  pronounced.  The  an- 
nual temperature  ranges  become  greater  with  increased  distance 
from  the  shore,  the  coldest  and  warmest  months  in  the  northern 
hemisphere  being  January  and  July,  respectively.  There  being  less 
cloudiness  over  the  land,  the  diurnal  changes  are  greater  than  over 
the  sea.  These  ranges  are  well  shown  by  a  comparison  of  the  Janu- 
ary and  July  temperatures  of  coast  and  inland  stations  in  low  and 
high  latitudes. 


January 
temperature 

July-August 
temperature 

C. 

F. 

C. 

F. 

Low  Latitudes: 
Bagdad,  Asia  Minor  (continental) 

Funchal,  Island  of  Madeira  (ma- 
rine)   

+  ii.5° 

'  +53° 
+60° 

+34° 
+22.5° 

+  22° 

+  16° 

_ 

+93° 

+  15-5° 

High  Latitudes: 
Nertschinsk,    E.    Siberia    (conti- 
nental) 

+72.5° 

-32° 
+  7-5° 

Valentia,  southwest  Ireland  (ma- 
rine) 

-25-6° 

+  71-6° 

+45-5° 

+60.8° 

. 

The  mean  range  of  many  observations  in  widely  distributed  sta- 
tions is  8.2°  C.  for  marine,  and  39.0°  C.  for  continental  climates. 
(Hann-4o:  142.) 

The  relative  humidity  of  continental  interiors  is  of  course  much 
lower  than  that  over  the  sea  or  on  the  coast,  but  even  in  arid  regions 
it  may  reach  20  per  cent,  or  30  per  cent.  The  rainfall  decreases  in 
amount  and  frequency  as  we  proceed  inland,  except  where  local 
topographic  features  act  as  modifiers.  The  winds  average  lower 
in  velocity,  and  calms  are  more  frequent  over  the  land  than  over 
the  sea.  Continental  winds  are  sometimes  so  well  developed  as  to 
become  monsoons. 


TYPES    OF    CLIMATE  77 

4.  Desert  Climate.     This  is  characterized  by  excessive  dryness, 
by  great  heat  during  the  day,  with  accompanying  strong  convection 
currents  resulting  in  high  winds,  and  by  relatively  cool,  clear  and 
calm  nights.     The  peculiarities  of  temperature  and  aridity  are  un- 
favorable to  the  growth  of  vegetation,  except  certain  adapted  forms, 
and  the  general  absence  of  plants  further  intensifies  the  climatic 
conditions.     Rains  are  infrequent;  parts  of  the  Sahara  are  known 
to  have  been  without  rains  for  10  or  15  years,  and  when  they  occur 
they  are  apt  to  be  sudden  downpours  of  great  floods  of  water.    Dust 
storms  are  characteristic  of  the  daytime,  when  high  winds  blow,  and 
it  is  then  that  deflation  and  the  mechanical  wear  by  drifting  sands 
are  chiefly  accomplished.     The   rivers  resulting  from  the  sudden 
rainfalls,  or  fed  by  springs  in  the  mountains,  wither  away,  the  water 
sinking  into  the  parched  ground  or  evaporating.     Brackish  sinks 
and  lakes  abound,  and  temporary  playa-lakes  suddenly  come  into 
existence  and  disappear  by  evaporation,  leaving  behind  a  charac- 
teristic, hard,  mud-cracked  surface.    The  plants  protect  themselves 
against  animals  by  thorns,  and  guard  against  excessive  evaporation 
by  a  reduction  in  the  size  of  the  leaves.    The  roots  penetrate  deep 
into  the  dry  soil  and  subdivide  extensively  to  obtain  all  the  available 
moisture. 

5.  Mountain  Climate.    This  is  distinctive  in  all  zones,  and  always 
contrasts  strongly  with  that  of  the  neighboring  lowlands.    There  is 
a  decrease  in  temperature,  pressure  and  absolute  humidity,  and  an 
increase  in  intensity  of  insolation  and  radiation,  and  generally  an  in- 
crease in  the  frequency  and  amount  of  precipitation.    Pressure  is  re- 
duced to  about  one-half  that  at  sea-level,  at  an  altitude  of  about 
16,000  feet,  while  the  zone  of  maximum  rainfall  lies  at  about  6,000 
to  7,000  feet  in  intermediate  latitudes.     Inversions  of  temperature 
characterize  mountains  at  night  and  during  the  colder  months,  the 
cold  air  flowing  down  the  mountain  sides  to  collect  in  the  valleys 
below,  and  being  replaced  by  warmer  air  above.    Thus  the  diurnal 
and  annual  ranges  of  temperature  are  lessened,  mountain  summits 
having  in  this  respect  a  climate  more  nearly  resembling  the  marine. 


CLIMATIC  PROVINCES. 

Detailed  consideration  of  climates  leads  to  the  recognition  of  a 
number  of  climatic  types  for  the  entire  earth,  the  characters  of  these 
types  being  brought  about  by  combinations  of  distinct  climatic  ele- 
ments. Supan  has  established  thirty-five  types  arranged  in  thirty- 
five  provinces  as  follows  (91  '.232)  : 


78  PRINCIPLES    OF    STRATIGRAPHY 

I.  EASTERN  CONTINENTS  AND  ISLAND  REGIONS  with  the  follow- 
ing provinces : 

i  West  European ;  2  East  European ;  3  West  Siberian ;  4  East 
Siberian ;  5  Kamtschatka ;  6  Chinese-Japanese ;  7  Asiatic  highland ; 
8  Aral;  9  Indus;  10  Mediterranean;  n  Sahara;  12  Tropical  Africa; 
13  Kalahari;  14  Cape  (of  Good  Hope);  15  East  Indo-Australian 
monsoon  province;  16  Australian  lake  province;  17  Southwest  Aus- 
tralia; 18  East  Australian;  19  New  Zealand;  20  Polynesia  (trop- 
ical) ;  21  Hawaii. 

II.  AMERICAN  REGIONS  with  the  following  provinces  : 

I  Hudson  Bay ;  2  Northwest  Coast ;  3  California ;  4  Highlands ; 
5  Atlantic ;  6  West  Indian ;  7  Tropical  Cordilleran ;  8  Tropical 
South  America;  9  Peruan;  10  North  Chilean;  n  South  Chilean;  12 
Pampas. 

III.  ARCTIC  REGIONS  with  only  one  province : 
I  Arctic  province. 

IV.  ANTARCTIC  REGIONS  with  only  one  province: 
i  Antarctic  province. 

CLIMATIC  TYPES,  BASED  ON  SEPARATE  ATMOSPHERIC  FACTORS  AND 

ON  AGENTS. 

In  considering  the  principal  atmospheric  factors,  we  may  recog- 
nize several  distinct  types,  which,  however,  vary  with  change  in 
local  conditions.  The  principal  types  based  on  factors  are :  ( i ) 
moist  and  (2)  dry,  (3)  cold  .and  (4)  warm,  (5)  pluvial  and  (6) 
arid.  Based  on  the  agent  influenced  by  these  factors,  we  may  dis- 
tinguish:  (i)  glacial  climates,  when  glacial  conditions  become 
widespread,  and  (2)  interglacial  climates,  when  glaciers  dwindle; 
(3)  fluvial  and  lacustrine  climates,  when  there  is  an  increase  in  pre- 
cipitation and  consequently  a  rise  in  streams  and  an  extension  of 
lakes,  and  (4)  interfluvial  and  interlacustrine,  or  desert  climates, 
when  the  reverse  is  true,  lakes  and  rivers  shrink  and  vegetation  dries 
up.  These  terms  are  useful  in  discussing  the  prevailing  character  of 
ancient  climates. 

CLIMATIC  ZONES  OF  THE  PAST. 

The  existence  of  climatic  zones  in  the  past  was  first  suggested  by 
Jules  Marcou  in  1860,  who  postulated  their  occurrence  in  Jurassic 
time  to  explain  the  "homozooidal  belts"  of  that  period.  The  Aus- 
trian geologist,  Melchior  Neumayr  (70),  attempted  to  prove  this 
theory  by  palseontological  and  geological  evidence,  and  his  conclu- 


CLIMATIC   ZONES  79 

sions  have  been  widely  accepted  in  some  quarters,  and  combated  in 
others. 

NEUM AYR'S  CLIMATIC  ZONES  OF  THE  JURASSIC.  These  from  the 
north  southward  are  as  follows : 

1.  Boreal  Zone.    Characterized  by  the  presence  of  the  ammonite 
genera,   Cardioceras,   Oxynoticcras,   and   Virgatites,  the  belemnite 
Cylindrotcuthis,  and  the  pelecypod  Aucella;  also  by  the  absence  of 
reef-building  corals,   and  of   the  ammonite   genera:     Phylloceras, 
Lvtoceras,    Simoceras,    and    Lissoceras,    and    the    scarcity   of   the 
genera :    Oppelia,  Hecticoceras,  Peltoceras,  and  Aspidoceras.    The 
boundary  between  this  and  the  next  zone  was  placed  at  latitude  45° 
in  the  Pacific,  but  further  north  in  the  Atlantic  and  Europe. 

2.  North  Temperate  Zone.    This  comprised  especially  the  prov- 
inces of  Central  Europe,  and  was  characterized  by  the  rarity  of  the 
ammonite  genera  which  attained  their  maximum  in  the  two  adjoin- 
ing zones;  and  also   by  the  appearance  of  reef  corals,  and  the 
predominance  of  the  ammonite  genera :  Oppelia,  Reineckia,  Pel- 
toceras, and  Aspidoceras.    The  boundary  between  this  and  the  next 
zone  was  placed  at  latitude  32°  N.  in  the  Pacific,  but  oscillated  about 
latitude  40°  N.  in  the  Atlantic  and  in  Eurasia. 

3.  Equatorial  Zone.     This  comprised  in  Europe  the  Mediter- 
ranean province  and  was  characterized  by  the  abundance  of  the  am- 
monite genera  Phylloceras,  Lytoceras,  and  Simoceras,  the  belem- 
nites  Belemnopsis  and  Duvalia,  and  the  brachiopod,  Pygope.    The 
boundary  between  this  and  the  next  zone  was  placed  at  about  lati- 
tude 32°  S. 

4.  South  Temperate  Zone.     This  reproduced  the  characters  of 
the  north  temperate  zone. 

DISCUSSION  OF  THE  SUBJECT  OF  CLIMATIC  ZONES. 

Of  the  zones  mentioned  above,  the  colder  or  boreal  zone  appears 
to  be  well  established,  but  the  differentiation  of  the  warmer  belt 
into  three  distinct  zones  is  less  generally  supported  by  the  evidence. 
In  Europe  the  north  temperate  province  of  Neumayr  represents, 
according  to  Haug  (42),  the  shallow  water  zone  of  the  warm  belt, 
while  the  equatorial  zone  corresponds  in  general  with  the  open  and 
deep  Thetys  sea.  The  distribution  of  the  genera  in  these  provinces 
is  due  more  to  this  difference  in  depth  and  the  corresponding  differ- 
ence in  temperature  than  to  zonal  distinctness.  That  annual 
changes  of  temperature  existed  in  Jurassic  time  is  shown  by  the  de- 
velopment of  annual  growth  rings  in  the  stems  of  Abietinese  of 
that  period  found  on  King  Charles  Land.  (78°  N.  lat.)  (Gotan- 


80  PRINCIPLES    OF    STRATIGRAPHY 

35:44.)  (See,  further,  under  Chapter  XXIX.)  Although  the 
distribution  of  the  genera  of  ammonites,  as  well  as  of  corals,  does 
not  follow  so  rigidly  the  belt-like  arrangement  in  extra-European 
countries  as  held  by  Neumayr,  and  although  much  of  the  distribu- 
tion  js  explainable  by  difference  in  depth,  still  the  probability  of 
differentiation  of  the  earth's  surface  into  climatic  zones  is  not  to  be 
altogether  discarded.  A  part  of  the  anomalous  distribution  of 
ammonites  may  certainly  be  explained  by  floatation  (see  Chapter 
XXVIII),  while  the  deflection  of  the  zonal  boundaries,  due  to  conti- 
nental expansions  or  contractions,  must  also  be  considered.  Finally, 
the  influence  of  ocean  currents  in  modifying  the  temperature  of  the 
water  must  not  be  neglected.  Ortmann  (71:267}  especially  em- 
phasizes the  occurrence  of  reef-building  corals  in  the  Russian  Jura, 
in  a  region  included  in  Neumayr's  boreal  zone,  and  insists  that 
these  indicate  a  tropical  climate,  but  Neumayr  contended  that  such 
occurrence  was  not  sufficient  evidence  against  his  theory. 

That  climatic  zones  existed  during  Mesozoic  times,  if  not  ear- 
lier, is  not  at  all  an  improbable  supposition,  though  it  may  perhaps 
be  questioned  whether  the  differences  between  successive  zones 
were  always  as  great  as  now.  That  the  air  temperature  as  a  whole 
was  higher  at  times  than  now,  probably  through  an  increase  in  the 
carbon  dioxide  content  and  the  consequent  trapping  of  solar  heat, 
is  highly  probable,  and  indeed  seems  far  more  reasonable  than  the 
assumption  of  a  uniform  climate  over  the  entire  earth.  A  universal 
rise  in  temperature  of  the  air  would  permit  a  wider  distribution  of 
those  marine  types  now  restricted  to  the  tropical  water  of  to-day, 
for  the  present  tropical  temperatures  would  extend  to  higher  lati- 
tudes. Even  though  the  tropics  under  such  conditions  would  be 
much  more  highly  heated,  it  is  questionable  if  the  waters  would  be 
too  hot  for  the  existence  of  life.  It  would  only  be  necessary  for 
organisms  living  in  the  tropics  to  descend  to  greater  depths,  so  as 
to  escape  the  excessive  surface  temperatures.  Nor  must  the  pos- 
sibility be  overlooked  that  stenothermal  modern  forms  may  have 
had  eurythermal  ancestors ;  that,  in  other  words,  the  descendants 
of  once  widely  adapted  classes  of  organisms,  capable  of  existing 
under  a  great  range  of 'temperature,  have  now  become  restricted  to 
a  limited  range,  in  the  warmer  waters  of  to-day. 

It  is  a  universally  recognized  fact  that  climatic  conditions  of 
greater  severity  existed  in  the  recent  geologic  past,  so  that  exten- 
sive portions  of  the  northern  continents  became  glaciated.  The 
very  fact  that  these  glaciers  extended  over  only  part  of  the  earth's 
surface  shows  the  existence  of  climatic  zones,  the  limit  of  glacia- 
tion  marking  the  poleward  limit  of  a  milder  belt.  The  southern 


ANCIENT    CLIMATES  81 

limit  of  Pleistocenic  glaciation  in  North  America  was  at  latitude 
37°  3°'  m  the  Mississippi  valley,  while  in  Europe  it  did  not  extend 
below  about  53°,  though  the  Alps  and  other  great  mountain  ranges 
were  heavily  glaciated.  The  high  mountain  areas  of  Asia  (Leb- 
anon, the  Caucasus,  the  Himalayas  and  the  mountains  of  Man- 
churia) were  heavily  glaciated,  these  glaciers  reaching  down  to 
4,500  feet  A.  T.  in  latitude  26°  in  Bengal,  and  to  2,000  or  3,000 
feet  in  the  western  Himalayas.  (Coleman- 19:34$.)  The  Atlas 
Mountains  of  Africa  and  the  lofty  peaks  under  the  equator  all  show 
an  advance  of  the  glaciers  of  several  thousand  feet  lower  than  at 
present.  A  similar  extent  of  glaciation  of  the  southern  hemisphere 
would  not  have  reached  any  of  the  continents,  except  the  southern 
end  of  South  America  and  perhaps  New  Zealand.  The  greater 
expanse  of  ocean,  however,  with  its  more  moderate  climate,  would 
favor  a  less  extent  of  the  Atlantic  ice;  and  it  may  be  questioned  if 
the  ice  sheet  which  is  known  to  have  been  much  more  extensive 
over  the  Antarctic  continent  extended  much  beyond  its  border. 
Patagonia,  it  is  true,  was  widely  glaciated  south  of  latitude  37°, 
the  ice  reaching  the  sea.  This  may  have  been  purely  local,  however. 
In  the  Andes,  further  north,  even  within  the  tropics,  are  old  mo- 
raines, showing  the  extent  of  these  glaciers  800  to  900  meters  below 
their  present  position. 

The  now  incontrovertible  evidence  pointing  to  glacial  periods  at 
various  times  during  the  geologic  history  of  the  earth  from  pre- 
Cambric  time  on,  indicates  not  only  repeated  periods  of  greater  cold 
in  the  earth's  atmosphere,  explainable  by  the  reduction  in  the 
amount  of  CO2,  but  also  the  existence  of  warmer  and  colder  zones, 
as  shown  by  the  limited  extent  of  these  glacial  deposits.  Indeed, 
it  may  be  questioned  if  zonal  arrangement  of  temperature  has  not 
always  been  the  normal  state  of  the  atmosphere,  and  that  the 
changes  have  only  been  toward  a  greater  universal  increase  or  de- 
crease in  temperature,  the  former  permitting  expansion  of  tropical 
types  of  organisms,  the  latter  the  expansion  of  the  cooler  types, 
and  culminating  in  many  cases  in  periods  of  glaciation.  Evidence 
of  early  glaciation  has  now  been  recorded  from  the  Lower  Huronian 
of  Ontario,  Canada  (Coleman-i9),  the  pre-Cambric  (?)  of 
Varanger  Fjord,  Norway  (Reusch,  Strahan~9O,  etc.),  and  Spitz-  / 
bergen  (Gregory-37),  the  basal  Cambric  or  pre-Cambric  of  the  \f 
Yangtse  canyon  of  China  (Willis-io8),  of  South  Australia  (How- 
chin,  David-23,  etc.),  and  Tasmania;  of  South  Africa  (Griqua- 
town  series,  Rogers-79)  and  less  definitely  from  North  America 
and  North  Asia.  The  extent  in  the  southern  hemisphere  was  north- 
ward to  29°  in  South  Africa,  and  to  32°  or  33°  in  South  Australia, 


82  PRINCIPLES    OF    STRATIGRAPHY 

the  movement  being  northward  and  the  ice  reaching  sea-level.  The 
evidence  of  Permo-Carbonic  glaciation  is  even  more  firmly  estab- 
lished. This  has  been  recognized  in  India,  Australia  and  Tasmania, 
South  Africa  (Dwyka  conglomerate  and  tillite)  and  South  Amer- 
ica. In  India  the  indications  of  glacial  occupancy  have  been  traced 
.from  lat.  16°  or  17°  to  lat.  34°  or  35°,  and  in  Australia  from  lat. 
20°  30'  to  lat.  43°  S.  In  the  eastern  Urals  of  Russia  a  Permic 
boulder  conglomerate  suggests  glacial  origin  (Karpinsky)  and  a 
conglomerate  of  similar  age  in  England  has  been  regarded  by  Ram- 
say as  glacial,  though  this  has  been  disputed  by  others.  In  Prince 
Edward  Island  (F.  Bain~3),  Colorado  (Cross),  and  eastern  Mas- 
sachusetts (Shaler)  conglomerates  of  this  age  occur,  which  sug- 
gest a  glacial  origin.  In  the  Antarctic  region  glacial  deposits  of 
this  age  have  recently  been  found  in  the  Falkland  Islands  (Halle- 
41*64). 

It  is  a  remarkable  fact  that  a  center  of  Permic  glaciation  in  the 
Old  World  seems  to  have  been  near  the  tropics,  perhaps  in  the  In- 
dian Ocean  (the  old  Gondwana  land),  for  the  movement  in  South 
Africa  seems  to  have  been  southward,  and  in  India  northward,  the 
movement  in  both  cases  being  away  from  the  equator.  The  evi- 
dence of  transported  rocks  in  eastern  Massachusetts  is,  however, 
from  the  north  and  similar  in  extent  to  that  of  the  Pleistocenic 
glacial  transportation.  So  far  as  the  evidence  goes,  a  general  re- 
frigeration of  the  climate  of  world-wide  extent  may  have  occurred, 
and  the  development  of  an  ice  sheet  in  the  tropics  may  be  in  part 
due  to  the  great  elevation  of  the  land  of  that  time  and  in  part  to 
the  nature  of  supply  of  moisture  to  feed  the  ice  sheet.  (Philippi- 
75.)  For  another  suggested  explanation,  see  Chapter  XXIII. 

RHYTHM  OF  CLIMATIC  CHANGES. 

The  course  of  climatic  changes  during  geologic  time  passes  from 
a  rhythmically  pulsating  state,  a  climatic  "strophe,"  to  one  of  rela- 
tive torpidity,  the  climatic  "interstrophe."  ( Huntington-5 1 1362.) 
The  pulsations  of  the  strophe  comprise  a  series  of  accentuations  of 
certain  climatic  characters,  such  as  glacial,-  fluvial,  vegetal  (when 
plant  life  spreads  widely),  or  pluvial  (when  much  rain  falls).  Each 
accentuation  forms  an  arsis  of  the  climatic  strophe,  the  time  of  such 
accentuation  being  an  arsial  epoch.  The  thesis,  or  thesial  epoch  of 
the  strophe,  is  the  depression  between  the  accented  epochs,  as  in 
the  case  of  interglacial  or  intern1  uvial  epochs,  intervegetal  or  inter- 
pluvial  epochs.  The  growth  in  strength  of  the  arses  and  theses  of 
the  strophe  is  a  gradual  one  to  the  point  when  the  acme  is  reached, 


CLIMATIC   CHANGES  83 

after  which  a  diminution  will  set  in.  The  interval  between  two 
thesial  epochs  constitutes  a  short  or  strophic  cycle,  while  the  in- 
terval from  the  center  of  one  interstrophe  to  that  of  another  consti- 
tutes a  grand  or  climatic  cycle.  (See  diagram,  Fig.  15.) 


INDICATION  OF  CLIMATIC  CHANGES. 

TOPOGRAPHIC  EVIDENCE  OF  CHANGE  IN  CLIMATE.  Since  the 
angle  of  slope  assumed  by  waste  under  arid  conditions  is  much 
steeper  than  that  assumed  under  pluvial  climates  (see  posted  Chap- 
ter XIV)  and  the  material  of  the  former  is  much  coarser  than  that 
of  the  latter,  it  follows  that  traces  of  such  conditions  in  a  region 
now  well  watered  suggest  a  former  greater  aridity.  This  is  seen  in 
alluvial  fans  of  great  radius  and  steepness  of  slope,  such  as  those 
of  the  region  near  San  Bernardino  with  radii  of  ten,  twelve,  or 

ARSIS          INTER.  STROPHE  — f  STROPHE  ">, 


^^yN/v/V/YVv^-^^--. 


'HESIS 

I CYCLE 


FIG.  15.     Diagram  illustrating  progress  of  changes  of  climate  during  geologic 
time.     (After  Huntington.) 

fourteen  miles,  and  an  elevation,  at  the  head,  of  four,  six,  or  seven 
hundred  feet  above  the  frontal  margin.  Such  fans  are  characteris- 
tic of  arid  mountain  regions,  and  their  essential  features  will  be 
recognizable  in  the  topography  of  a  region  become  more  moist.  The 
clogging  by  waste  of  deep-cut  valleys,  formed  during  a  moist  cli- 
matic period,  as  well  as  the  formation  of  fans  on  the  much  dis- 
sected mountain  slopes,  is  evidence  of  change  from  moist  to  dry 
climate.  In  the  same  manner  the  dissection  of  steeply  graded  val- 
ley floors  and  waste  slopes  shows  a  change  from  dry  to  moist  cli- 
mate, provided  these  features  do  not  indicate  increased  elevation 
of  the  region.  In  lakes  of  a  dry  region  the  water  would  be  low  and 
their  shores  lined  by  alluvial  fans,  against  which,  on  the  change  of 
the  climate  to  moister  conditions,  the  waters  of  the  expanded  lake 
would  come  to  lie.  This  was  the  case  in  Lake  Bonneville,  the  wa- 
ters of  which  rested  against  the  alluvial  fans  of  the  pre-Bonneville 
dry  period.  The  present  dry  period  is  again  characterized  by  the 
formation  of  such  alluvial  fans.  The  outlets  of  these  lakes  are  fur- 
ther marked  by  the  features  of  topographic  youth.  Evidences  of 


84  PRINCIPLES    OF    STRATIGRAPHY 

former  extensive  sand  dunes  now  covered  over  by  vegetation  must 
further  be  regarded  as  indicative  of  a  change  of  climate. 

STRATIGRAPIIIC  EVIDENCE  OF  CHANGE  OF  CLIMATE.  A  careful 
consideration  of  the  lithic  characters  of  the  strata  of  a  given  region 
may  furnish  evidence  of  changes  of  climate  in  the  successive  geo- 
logic epochs.  Thus  ancient  alluvial  fans  and  delta  deposits  inter- 
calated between  marine  sediments  are  not  only  evidence  of  eleva- 
tion followed  by  subsidence,  but  may  also  indicate  a  change  in  cli- 
matic conditions.  This  is  especially  the  case  when  such  alluvial 
fans  are  characterized  by  coarse  waste,  or  by  red  color.  The  red 
color  of  such  continental  deposits  as  the  Longwood  shale  of  the 
late  Siluric,  the  Catskill  and  Old  Red  sandstones  of  the  Devonic, 
the  Mauch  Chunk  of  the  Mississippic,  and  the  Newark  and  Red  beds 
of  the  Trias,  have  been  regarded  as  indicating  more  or  less  arid  con- 
ditions during  the  formation  of  those  deposits.  Huntington  (51) 
has  described  the  alternations  of  red  and  green  strata  exposed  in 
the  uplifted  and  dissected  bottom  of  the  Pleistocenic  lake  Seyistan 
in  eastern  Persia.  The  red  or  pink  strata  are  thick  beds  of  clays, 
silts,  and  fine  brown  sands  of  a  very  continuous  and  uniform  char- 
acter, traceable  for  miles,  even  though  varying  in  minor  details. 
They  show  evidence  of  exposure  to  the  air,  under  conditions  which 
prevented  extensive  development  of  vegetation.  The  white  or 
greenish  layers,  on  the  other  hand,  are  solid  beds  of  clay,  lined  above 
and  below  by  somewhat  more  sandy  films.  These  green  clays  were 
deposited  during  the  periods  of  expansion  of  the  lake,  while  the  red 
beds  indicate  exposure  to  a  dry  climate  followed  by  oxidation  dur- 
ing periods  of  retreat,  when  arid  conditions  prevailed.  There  are 
here  indicated  ten  epochs  of  expansion  of  the  lake  (the  arsial 
epochs)  and  ten  of  contraction  (the  thesial  epochs).  The  Moen- 
copie  beds  of  Utah  and  Arizona  (Permic)  show  a  similar  alterna- 
tion of  red  and  greenish  beds  and  indicate  a  similar  pulsation  of  the 
climate  of  the  Permic. 

Arid  conditions  are  also  shown  by  the  arkose  character  of  many 
rocks,  as,  for  example,  the  Torridon  sandstone  of  western  Scotland, 
where  the  feldspar  crystals  are  scarcely  weathered,  and  the  Newark 
sandstone  beneath  the  Palisades  of  the  Hudson.  Arid  conditions 
are  further  indicated  by  the  occurrence  of  beds  of  salt  and  gypsum, 
and  the  same  thing  is  shown  by  extensive  deposits  of  wind-blown, 
cross-bedded  sands  such  as  are  found  in  the  White  River  beds  (Ju- 
rassic) of  Arizona.  The  extensive  development  of  coal  swamps  and 
marshes  may  indicate  a  change  to  cooler  and  moister  climate,  while 
tillites,  coarse  boulder  conglomerates  and  striated  rock  and  boul- 
der surfaces  indicate  glacial  conditions. 


CLIMATIC    CHANGES  85 

ORGANIC  EVIDENCE  OF  CHANGE  OF  CLIMATE.  This  is  in  many 
respects  the  most  reliable,  since  organisms  are  the  most  sensitive 
indicators  of  climatic  conditions. 

i.  Plants.  Coal  swamp  vegetation,  as  indicative  of  cooler  and 
moister  climates,  has  already  been  referred  to.  The  various  types 
of  swamp  vegetation  preserved  in  the  peats  of  different  coun- 
tries, serve  as  an  excellent  index  to  the  gradual  change  of  climatic 
conditions  since  the  last  glacial  period.  Thus  for  Germany  it  has 
been  ascertained  that  the  first  floral  mantle  following  the  retreat  of 
the  ice  was  of  the  tundra  type  without  any  true  arboreal  growths 
whatever.  In  many  places  a  lower  horizon,  with  the  mountain  or 
arctic  dryas,  Dryas  octopetala,  and  the  arctic  dwarf  willow,  Salix 
polaris,  and  a  higher  one,  with  Salix  phylicifolia  and  S.  rcticulata, 
besides  Dryas  octopetala,  can  be  determined.  Aquatic  plants  are 
rare  in  this  period,  but  several  species  of  Potamogeton  occur  regu- 
larly in  the  upper  beds,  together  with  Myriophyllum  spicatwn,  Hip- 
puris  vulgaris  and  Batrachimn  aquatile  confervoides.  During  the 
Dryas  period,  even  in  the  earliest  epoch,  the  climate  could  not  have 
been  an  arctic  one  in  North  Germany,  for  the  aquatic  plants  require 
a  July  temperature  of  approximately  6°  C,  and  need  4  to  5  months 
with  a  temperature  of  at  least  3°  C.  in  order  that  their  seeds  may 
ripen.  The  rapid  amelioration  of  the  climate  during  the  Dryas 
period  is  shown  by  the  presence  of  Phragmites  communis  in  the 
upper  layers  formed  during  this  period,  followed  by  heavy  deposits 
of  decayed  vegetation,  indicating  a  rapid  increase  in  the  plant  and 
animal  life  of  the  waters.  With  this  appears  the  first  arboreal  vege- 
tation with  birches  and  pines. 

The  two  epochs  of  arctic  floras,  i.  e.,  the  earlier  colder  one  with 
Salix  polaris  and  the  later  milder  one  with  Salix  reticulata,  are  rec- 
ognized in  many  regions  in  Scania  and  elsewhere  in  southern 
Sweden.  In  Finland  the  arctic  Dryas  flora  (Dryas,  Salix  polaris, 
Betula  nana,  Batrachium  confervoides)  and  the  moss  Sphccro- 
cephalus  turyidus,  characteristic  of  the  modern  arctic  region,  to- 
gether with  the  arctic  beetle  Pterostichus  vermiculosus,  occur  in  a 
sandy  deposit  between  Lake  Ladoga  and  the  Gulf  of  Finland,  in- 
dicating a  climate,  during  the  period  of  the  melting  of  the  ice,  com- 
parable to  that  now  found  in  northern  Russia  and  the  neighbor- 
hood of  the  polar  sea.  The  Salix  polaris  flora  has  also  been  found 
in  Norway  and  Denmark,  this  arctic  flora  everywhere  forming  the 
first  or  tundra  type  of  flora  to  appear  during  the  period  of  melting 
of  the  glaciers.  Gunnar  Andersson  lays  especial  stress  on  the  oc- 
currence of  an  aquatic  flora  with  these  arctic  plants,  which,  though 
consisting  of  few  species,  is  nevertheless  rich  in  numbers.  He  con- 


86  PRINCIPLES    OF    STRATIGRAPHY 

eludes  that  "already  in^a  period  immediately  after  the  melting  of  the 
ice  ...  the  vegetation  period  was  four  months  [in  length]  and 
the  July  temperature  about  -f-  6°  C.  This  increased;  during  the 
period  of  the  tundras,  to  a  season  of  five  months'  vegetation  and 
a  July  temperature  of  +  9°  C."  ( Andersson-i :  xxv.)  The  arctic 
flora  of  these  countries  was  followed  by  forests  in  which  three  trees, 
the  pine  (Pinus  silvestris),  the  birch  (Betula  odorata),  and  the 
asp  or  poplar  (Populus  tremula)  became  the  dominant  types.  The 
July  temperature  at  this  time  averaged  probably  10°  to  12°  C. 
These  first  forest  trees  were,  however,  not  uniformly  distributed. 
Thus  in  the  western  regions  the  pines  were  absent,  the  birch  and 
poplar  alone  predominating.  This  corresponds  to  the  distribution 
of  the  trees  in  the  present  arctic  region  where  Betula  odorata  forms 
the  dominant  forest  tree  around  the  fjords  of  South  Greenland,  in 
Iceland,  the  whole  of  Scandinavia  and  the  peninsula  of  Kola  to  the 
White  Sea.  This  may  be  explained  by  the  greater  humidity  of  this 
region.  In  Finland  and  North  Germany  the  birch  and  pine  oc- 
curred together  in  the  first  post-glacial  forests,  which  represented 
the  drier,  more  continental  type  of  arctic  forest,  such  as  is  found 
to-day  in  the  remainder  of  the  arctic  regions,  where  forests,  consist- 
ing primarily  of  pines  (Pinus),  spruces  (Picea)  and  larches 
(Larix),  abut  against  the  treeless  arctic  plains. 

With  the  increase  in  temperature,  the  coniferous  woods  were  re- 
placed by  those  requiring  a  higher  summer  temperature,  such  as 
small  leaf  lindens  (Telia  europcca),  hazel  (Corylus  avellana}, 
maple  (Acer  platanoides) ,  elm  (Ulnius  montana),  etc.  Finally, 
the  oak  (Quercus  pedunculata)  made  its  appearance,  and  displaced 
the  pines  almost  entirely.  Gunnar  Andersson  and  others  have  fur- 
nished evidence  from  the  former  distribution  of  the  hazel,  oak, 
linden  and  several  aquatic  plants,  to  the  effect  that  the  increase  in 
warmth  culminated  in  a  period  of  higher  temperature  than  the  pres- 
ent over  the  whole  of  western  Scandinavia,  and  less  markedly  over 
North  Germany.  In  northern  Sweden  the  temperature  during  the 
warmer  period  averaged  2.5°  C.  higher  than  now,  though  the  win- 
ter temperature  could  not  have  been  higher  than  the  present,  for 
plants  requiring  a  warmer  winter  apparently  did  not  extend  fur- 
ther north  than  they  do  now.  In  the  central  parts  of  southern 
Norway,  Holmboe  finds  that  the  border  line  of  the  fir  was  once 
about  300  meters  higher  than  at  present.  In  general,  the  appear- 
ance of  the  spruce  (Picea  excelsa)  in  the  northern  and  the  beech 
(Fagus  silvatica)  in  the  southern  part  of  the  glaciated' region  seems 
to  indicate  a  gradual  deterioration  of  the  climate  of  Europe  since 
the  maximum  of  post-glacial  temperature. 


CLIMATIC   CHANGES  87 

A  similar  succession  of  floras  seems  to  have  occurred  in  North 
America,  but  the  evidence  has  not  been  fully  gathered.  Over  the 
great  plains  of  Canada,  between  the  international  boundary  and 
the  forest  region  which  stretches  northwestward  through  Manitoba 
and  Saskatchewan  and  westward  across  Alberta,  the  climate  on  the 
melting  of  the  glaciers  was  probably  much  like  that  of  the  barren 
lands  farther  north  at  the  present  time,  where  the  mean  summer 
temperature  is  below  10°  C.,  with  permanently  frozen  subsoil  and 
consequently  a  complete  absence  of  trees.  As  the  climate  became 
warmer  on  the  disappearance  of  the  ice,  it  also  became  drier,  so  that 
forests  were  unable  to  grow  and  Sphagnum  swamps  unable  to  form. 

Evidence  of  a  warmer  climate  preceding  the  present  has  been 
obtained  from  the  Atlantic  coast,  where  the  Talbot  formation  of 
Maryland  and  Virginia,  believed  to  be  post-glacial  in  age,  holds  a 
flora  which  is  more  characteristic  of  southern  portions  of  the  same 
region.  Thus  the  bald  cypress  (Tax odium  distichum),  found  fossil 
as  far  north  as  Long  Branch,  New  Jersey,  has  its  present  northern 
limit  in  southern  Delaware  and  on  the  eastern  shore  of  Maryland ; 
the  loblolly  pine  (Pinus  tceda),  also  found  at  Long  Branch,  does 
not  extend  north  of  southern  New  Jersey  at  the  present  time,  with 
its  maximum  development  west  of  the  Mississippi;  the  tupelo 
(Nyssa  biflora),  found  fossil  in  New  Jersey,  ranges  to-day  from 
North  Carolina  to  Louisiana. 

2.  Animals.  Marine  and  fresh-wrater  mollusca  are  among  the  best 
available  indicators  of  climatic  changes,  so  far  as  species  are  con- 
cerned, which  are  still  existing,  and  the  geographic  range  of  which  is 
known.  In  the  marine  species  it  must,  however,  always  be  borne  in 
mind  that  bathymetric  distribution  may  counteract  the  influences  of 
climate  and  that  hence  the  evidence  must  be  carefully  scrutinized. 
Even  better  indications  of  change  of  climate  are  furnished  by  the 
distribution  of  land  animals,  especially  insects  and  mammals,  though 
this  evidence  is  generally  less  readily  available.  Examples  showing 
changes  of  fauna,  most  probably  due  to  change  of  climate,  have 
been  obtained  in  numerous  late  glacial  and  post-glacial  deposits. 
A  highly  significant  section  of  these  deposits  has  been  studied  by 
Jensen  and  Harder  on  the  west  coast  of  Greenland  in  the  Orpiksuit 
fjord,  Disko  Island  (about  lat.  70°  N.).  In  the  lowest  clays  occurs 
a  fossil  fauna  with  Balanus  hameri,  indicating  a  period  during 
which  the  climate  was  not  high  arctic,  but  rather  resembled  that 
of  the  present  time.  This  is  followed  by  a  series  of  clay  beds 
averaging  10  meters  in  thickness,  with  a  rich  fauna,  among  which 
Mya  truncata  cf.  ovata  and  Yoldia  arctica  must  be  noted,  indicating 
that  the  climate  gradually  refrigerated  until  high  arctic  conditions 


88  PRINCIPLES    OF    STRATIGRAPHY 

existed.  This  period  seems  to  have  been  characterized  by  subsi- 
dence. A  period  of  elevation  followed,  with  an  increase  in  warmth, 
which  reached  its  maximum  when  the  land  stood  approximately  10 
meters  higher  than  at  present.  This  is  shown  by  the  boreal  mol- 
luscs Zirphcca  crispata  and  Anomia  ephippium,  together  with  Mytilus 
edulis,  Tellina  baltica,  Littorina  rudis,  and  L.  palliata,  mostly  forms 
now  common  on  the  New  England  coast.  With  still  greater  eleva- 
tion the  climate  again  cooled,  until  it  resembled  that  of  the  present 
time,  the  maximum  elevation  being  50  meters  above  the  present  sea- 
level.  The  first  two  formations  probably  were  deposited  during 
glacial  time,  while  the  succeeding  deposits  represent  post-glacial  time. 
The  warm-water  fauna  has  a  wide  distribution  in  the  arctic,  espe- 
cially recognizable  by  the  shells  of  Mytilus  edulis,  and  often  by 
Cyprina  islandica  and  Littorina  littorea.  Some  of  the  arctic  locali- 
ties where  this  fauna  has  been  found  fossil  are  the  Franz  Josef 
fjord,  East  Greenland,  Spitzbergen,  King  Charles  Land  and  Franz 
Josef  Land.  It  has  not  yet  been  found  in  arctic  North  America. 

Another  fauna,  found  in  parts  of  the  arctic  where  it  is  now  ex- 
tinct, and  indicating  warmer  conditions  than  now,  is  the  Purpura 
fauna,  with  P.  lapillus,  Pecten  islandicus,  Zirphcea  crispata,  Cy- 
amium  minutum  and  Skenea  planorbis.  This  has  been  found  in 
northwestern  Iceland,  in  a  formation  resting  in  some  cases  directly 
upon  the  peat  beds  with  remains  of  the  arctic  birch,  Betula  odorata. 

In  North  Germany  a  climate  similar  to  the  arctic  one  is  indicated 
by  late  glacial  or  early  post-glacial  deposits,  carrying  the  molluscs, 
Vertigo  paracedentata,  Succinea  schumacheri,  Planorbis  arcticus, 
P.  stroemi,  Sphcerium  duplicatum  and  Anodonta  mutabilis.  Arctic 
conditions  in  Denmark  and  Sweden,  while  the  ice  still  occupied  a 
part  of  the  land,  are  indicated  by  deposits  containing  at  the  base  a 
fauna  with  the  arctic  molluscs,  Yoldia  arctica,  Tellina  torelli,  and 
T.  loveni,  which  at  present  are  restricted  to  seas  where  the  tem- 
perature in  the  depths  at  which  the  species  live  scarcely  rises  above 
2.5°  C.  and  frequently  remains  below  o°,  even  in  the  warmest 
months  of  the  year.  This  corresponded  to  the  time  of  the  Salix 
polaris  flora  in  Denmark.  Higher  up,  together  with  a  flora  in  which 
the  birches  predominate,  occurs  Anodonta  cygnea,  which  has  been 
held  to  indicate  a  July  temperature  of  13°  to  15°  C.  Still  higher 
follows  the  fauna  with  Zirphcea  crispa,  Mytilus  edulis,  Cyprina 
islandica,  etc. 

In  northern  New  England  and  eastern  Canada,  the  glacial  till 
is  followed  by  the  lower  Leda  clays,  the  fauna  of  which  (Leda  sp., 
Saxicava  rugosa,  etc.)  indicates  a  climate  like  that  of  southern 
Labrador.  These  are  followed  by  the  upper  Leda  clays  and  sands 


CLIMATIC    CHANGES  89 

with  Macoma  fusca,  which  indicate  a  climate  like  that  of  the  pres- 
ent St.  Lawrence  valley.  The  occurrence  of  relict  colonies  of 
Ostrea  virginiana  var.  borealis  and  Venus  mercenaria  at  various 
places  in  the  maritime  provinces,  and  in  shell  heaps  along  the  New 
England  coast  as  far  as  Casco  Bay,  Maine,  indicates  a  period  of 
warmer  climate  than  the  present,  since  these  species  are  now  limited 
in  their  northward  migration  by  Cape  Cod.  The  extinction  of  this, 
and  the  character  of  the  present  fauna  indicate  a  return  to  cooler 
conditions.  Warmer  water  conditions  inland  are  also  indicated  by 
the  occurrence  of  Unios  and  other  fresh-water  molluscs  in  the 
gravels  of  Goat  Island  and  the  banks  near  the  Falls  of  Niagara, 
some  of  which  (Unio  clavus,  U.  occidens,  and  U.  solidus  and  the 
Margaritana)  live  to-day  only  in  tributaries  of  the  Mississippi  to  the 
south.  Evidence  of  change  of  climate  during  Pliocenic  times  in 
Japan  is  indicated  by  the  succession  of  molluscan  faunas  (Yoko- 
yama-no).  From  beds  regarded  as  of  middle  Pliocenic  age,  a 
molluscan  and  brachiopod  fauna  of  decidedly  boreal  character  has 
been  obtained.  In  the  Upper  Pliocenic  near  Tokyo  was  obtained 
a  molluscan  fauna  less  boreal  in  character,  though  indicating  still 
colder  conditions  than  exist  at  the  present  time.  Still  higher  beds, 
referred  to  the  Pleistocenic  (Diluvial),  contain  a  molluscan  and 
coral  fauna,  many  species  of  which  are  now  found  only  in  much 
more  southern  localities,  the  China  Sea,  the  Philippines,  and  the 
tropical  portions  of  the  Pacific  and  Indian  oceans.  If  the  identifica- 
tions of  these  formations  as  Pliocenic  and  Pleistocenic,  respectively, 
are  correct,  the  remarkable  conclusion  would  have  to  be  drawn  that 
Japan  actually  had  a  warmer  climate  than  to-day,  while  Europe  and 
America  were  suffering  glacial  conditions.  In  order  to  bring  Japan 
into  harmony  with  the  western  world,  we  would  have  to  assume 
that  the  deposits  called  Pliocenic  on  the  basis  of  numerical  pre- 
ponderance of  living  species  are  actually  later  in  age,  i.  e.,  are  all 
Pleistocenic.  Such  an  assumption  is  not  unwarranted. 

The  Pliocenic  or  Crag  faunas  of  England  show  a  progressive 
refrigeration  of  the  climate.  The  mollusca  of  the  lowest  of  these, 
the  Coralline  Crag,  still  bears  the  stamp  of  a  more  genial  climate 
than  the  present,  in  spite  of  the  admixture  of  a  few  boreal  types.  In 
the  next  division,  the  Red  Crag,  the  number  of  boreal  species  in- 
creases so  as  to  form  10%,  while  the  succeeding  Norwich  Crag 
has  a  still  greater  percentage  of  northern  forms.  Finally,  the  high- 
est, the  Chillesford  and  Wegbourne  Crags,  have  a  really  boreal  or 
arctic  molluscan  fauna,  including  Tellina  baltica,  Saxicava  arctica, 
Mya  arenaria,  M.  truncata,  Cyprina  islandica,  Astarte  compressa, 
A.  sulcata,  A.  borealis,  Turritella  terebra,  Trophon  antiquus,  Pur- 


go  PRINCIPLES    OF    STRATIGRAPHY 

pura  lapillus,  Littorina  littorea,  Buccinum  undatum,  etc.,  most  of 
which  still  exist  in  arctic  and  subarctic  regions. 

The  mammals  of  North  America  have  furnished  some  evidence 
of  the  change  in  climate  (Hay-43).  Along  the  cold  margin  of  the 
ice  sheet  ranged  the  northern  Rangifer,  Bodtheriinn  and  Symbos, 
as  shown  by  their  remains.  The  giant  beaver  Casteroides  lived  with 
the  now  extinct  horses,  tapirs,  mastodons,  elephants,  mylodon,  and 
magalonyx  in  the  southern  States  and  continued  there  during  the 
Pleistocenic  period.  It  moved  northward  after  the  melting  of  the 
ice.  The  peccaries,  apparently  always  lovers  of  a  mild  if  not  warm 
climate,  now  range  from  Arkansas  to  Patagonia.  In  the  Pliocenic 
a  species  lived  in  Texas,  while  after  the  melting  of  the  ice  repre- 
sentatives of  the  family  moved  northward,  their  remains  having 
been  found  in  three  localities  upon  the  Wisconsin  drift  sheet,  viz. : 
northern  Indiana;  near  Columbus,  Ohio,  and  at  Rochester,  New 
York.  The  hairy  mammoth,  Elephas  primogenius,  seems  to  have 
always  lived  near  the  margin  of  the  ice  sheet,  but  the  Columbian 
elephant,  E.  colmnbi,  was  a  denizen  of  warmer  climates,  yet  its 
remains  have  also  been  found  in  deposits  overlying  the  Wisconsin 
drift.  The  same  is  true  of  the  mastodon,  M.  americanus,  a  denizen 
of  mild  climates,  which  has  not  only  left  its  remains  over  the  south- 
ern States,  but  which  roamed  northward  during  the  warm  post- 
glacial period.  The  mammals  also  indicate  a  period  of  warmer  cli- 
mate, during  which  they  ranged  farther  north  than  at  present,  which 
is  a  period  of  somewhat  lower  temperatures.  This  reduction,  while 
fatal  to  many  forms,  was  the  cause  of  the  survivors  moving  south- 
ward again. 

DISPLACEMENT  OF  THE  EARTH'S  Axis  AS  A  CAUSE  OF 
CLIMATIC  CHANGES. 

That  a  change  in  the  position  of  the  earth's  axis  would  bring 
about  a  change  in  climate,  cannot  be  questioned,  and  this  explanation 
has  been  suggested  for  the  glacial  conditions  in  Pleistocenic  time. 
Davis  (25)  has  outlined  the  climatic  consequences  of  displacing  the 
poles  in  such  a  way  that  the  north  pole  would  be  located  at  Iceland, 
in  latitude  70°  N.  on  the  meridian  of  20°  W.,  the  following  being 
some  of  the  effects :  "First,  a  rearrangement  of  shore  lines  in  con- 
sequence of  the  adoption  of  new  locations  of  polar  flattening  and 
equatorial  bulging.  .  .  .  Second,  alteration  in  the  paths  of  ocean 
currents,  of  which  one  of  the  most  important  would  be  the  dimi- 
nution of  the  volume  of  warm  water  transferred  from  the  southern 
to  the  northern  hemisphere  by  the  oblique  cross-equator  current  of 


CAUSES    OF    CLIMATIC   CHANGES  91 

the  Atlantic,  and  thus  the  great  loss  of  importance  in  the  extension 
of  the  Gulf  Stream  into  the  North  Frigid  zone.  Third,  a  change 
in  the  location  of  the  wind  and  rain  belts,  their  boundaries  being 
shifted  twenty  degrees  southward,  in  the  meridian  of  Iceland,  the 
same  amount  northward  on  the  opposite  meridian  which  passes 
somewhat  east  of  New  Zealand,  and  remaining  essentially  un- 
changed at  the  halfway  points,  which  are  located  near  the  meridians 
of  Ceylon  and  the  Galapagos." 

Such  rearrangement  of  wind  and  rain  belts  "would  tend  not  only 
to  glaciate  northwestern  Europe  and  northeastern  America,  but 
would  also  place  arid  trade-wind  climates  on  the  northern  side  of 
the  belt  now  occupied  by  the  equatorial  rains  of  Africa  and  South 
America,  and  at  the  same  time  place  the  equatorial  rains  on  the 
northern  margin  of  the  arid  land  areas  now  found  in  the  southern 
parts  of  these  continents.  On  the  adoption  of  the  present  location 
of  the  poles,  the  change  would  be  reversed."  The  northern  side  of 
the  equatorial  rain  belt  in  Africa  and  South  America  should  then 
be  found  to  possess  topographic  records  of  a  wet  climate  recently 
succeeding  a  dry  climate,  and  the  features  of  the  region  south  of 
the  same  belt  should  indicate  a  dry  climate  following  a  wet  climate. 

Professor  Simroth,  of  Leipzig,  in  his  book,  Die  Pendulations 
Theorie,  1907  (86)  has  tried  to  explain  some  peculiar  distributions 
of  organisms  in  the  present  period  by  oscillations  of  the  poles  along 
the  meridian  of  10°  E.  latitude  (170°  W.  lat).  With  an  oscilla- 
tion of  20°  back  and  forth  this  would  bring  the  north  pole  at  one 
time  near  Behring  Strait,  and  at  the  other  extreme  in  the  Arctic 
Ocean,  west  of  the  northern  end  of  Norway.  If  the  former  posi- 
tion was  held  in  Pliocenic  times,  the  Pacific  side  would  be  cool  and 
gradually  become  warmer,  with  the  change  of  the  pole  to  the  oppo- 
site position ;  while  on  the  Atlantic  side  the  change  would  be  from 
warmer  to  cooler  conditions  terminated  by  glacial  climates.  Such 
conditions  seem  actually  to  have  occurred,  as  shown  by  the  gradual 
change  from  a  warmer  climate  than  at  present  at  the  beginning  of 
Pliocenic  time  in  Europe,  to  the  glacial  conditions  in  Pleistocenic 
time,  and  by  a  gradual  increase  in  warmth  on  the  Pacific  side  as 
shown  by  the  Pliocenic  deposits  of  Japan,  until  in  the  Pleisto- 
cenic the  sun  shone  in  the  region  of  Noma  (35°  N.  lat.),  "with 
about  the  same  intensity  as  it  now  shines  at  least  on  the  Ryukyus 
or  the  Bonin  Islands."  (Lat.  27°  N.)  This  explanation  has 
found  its  most  recent  advocate  in  the  brilliant  palaeontologist  of  the 
Imperial  University  of  Tokyo,  Professor  Matajiro  Yokoyama  (Yo- 
koyama-no://<5).  Investigating  this  problem,  G.  H.  Darwin  (22) 
came  to  the  conclusion  that,  if  the  earth  is  quite  rigid,  the  pole  may 


92  PRINCIPLES    OF    STRATIGRAPHY 

have  moved  about  3°  from  its  original  position.  If,  however,  the 
earth  is  plastic,  as  seems  to  be  the  case  to  a  certain  degree,  so  that  it 
could  readjust  itself  to  the  form  of  equilibrium,  then  there  is  a  pos- 
sibility of  a  cumulative  effect,  and  the  pole  may  have  wandered  10° 
or  15°  from  its  original  position.  This  subject  is  more  fully  dis- 
cussed in  Chapter  XXIII. 

ORIGIN  OF  THE  ATMOSPHERE. 

According  to  the  nebular  hypothesis  of  earth  origin,  the  atmos- 
phere is  merely  the  residuum  of  uncombined  gases  which  were  left 
behind  when  the  globe  assumed  its  solid  form.  To  this  are  added 
various  supplies,  chief  among  which  is  the  carbon  dioxide  from 
volcanic  eruptions,  the  decay  of  organic  matter,  and  the  burning  of 
coal.  The  Planetesimal  hypothesis  of  Chamberlin,  on  the  other 
hand,  considering  the  earth  as  made  up  of  aggregations  of  small 
solid  bodies  coming  from  space,  derives  the  atmosphere  from  the 
small  quantities  of  entangled  or  occluded  atmospheric  matter 
brought  by  these  planetesimals.  The  pressure  of  the  accumulating 
cold  matter  eventually  produced  sufficient  internal  heat  to  expel 
these  gases.  If  the  conception  of  an  internal  gaseous  centrosphere 
can  be  entertained,  the  possibilities  of  addition  to  the  atmosphere 
are  greatly  enhanced. 

BIBLIOGRAPHY   II. 

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Maximum  der  letzten  Eiszeit.  Papers  by  Gunnar  Andersson  (summary 
also  for  North  Italy,  Greece),  F.  Wahnschaffe  (Germany),  G.  van  Baren 
(Netherlands),  A.  Rutot  (Belgium),  G.  W.  Lamplugh  (Great  Britain), 
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J.  B.  Tyrrell,  R.  W.  Brock,  R.  G.  McConnell  (Canada),  Ad.  S.  Jensen, 
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(Egypt),  M.  Blanckenhorn  (Syria,  Palestine  and  Egypt),  Sven  Hedin 
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Lendenfeld  (Australia  and  New  Zealand),  C.  Skottsberg  (Patagonia  and 
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93 


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B.  THE  HYDROSPHERE. 

CHAPTER  III. 
MORPHOLOGY  AND   SUBDIVISIONS  OF  THE   HYDROSPHERE. 

The  hydrosphere  consists  of  the  oceans  and  their  prolongations 
into  the  land  blocks,  the  lakes,  the  rivers,  and  the  ground  water. 
The  oceans  and  their  extensions  into  the  land  blocks  constitute  the 
marine  portion  of  the  hydrosphere;  the  lakes,  rivers,  and  ground 
waters  constitute  the  non-marine  or  continental  portion.  In  the 
present  chapter  their  morphological  characteristics  will  be  discussed, 
and  an  attempt  will  be  made  to  outline  a  natural  classification  of  the 
various  subdivisions,  based  primarily  on  origin. 

A.    THE  MARINE  DIVISION  OF  THE  HYDROSPHERE. 

REGIONAL  SUBDIVISIONS  OF  THE  SEA.  The  classifica- 
tion of  oceans  and  minor  subdivisions  of  the  sea  has  attracted  the 
interest  of  geographers  from  the  earliest  times.  Many  and  varying 
systems  of  classification  have  been  proposed,  based  on  size,  form, 
position  with  reference  to  the  land,  composition,  origin,  etc.  Otto 
Krummel  (23  :^p)  has  published  a  very  comprehensive  system  of 
the  seas,  in  which  he  recognizes  as  primary  divisions:  (i)  The 
independent,  and,  (2)  the  dependent  types;  the  former  comprising 
the  oceans,  the  latter  the  mediterraneans — subdivided  into  (a)  inter- 
continental, and  (b)  intracontinental  mediterraneans — and  the  mar- 
ginal seas.  Added  to  these  are:  (3)  the  gulfs  or  bays,  and  (4)  the 
straits.  Two  other  subdivisions  are  made  on  the  basis  of  ingression 
of  the  sea  into  existing  depressions,  with  the  subsidence  of  the  land, 
forming  ingression  seas,  gulfs,  or  straits ;  or,  on  the  partial  breaking 
down  of  the  surface  and  sinking  of  fault  blocks,  permitting  the  sea 
to  enter  the  land  and  forming  tectonic  seas,  gulfs,  or  straits. 

In  a  natural  subdivision  of  the  sea  into  basins,  its  relation  to  the 
continental  blocks  must  be  considered  of  primary  importance,  since 

99 


ioo  PRINCIPLES    OF    STRATIGRAPHY 

it  is  on  this  relationship  that  the  other  characteristics  are,  in  a  large 
measure,  dependent.  As  shown  in  the  introductory  chapter,  the 
most  natural  view  to  take  of  the  land  mass  as  a  whole  is  that  it 
constitutes  three  continental  blocks — the  American;  the  Old  World, 
comprising  Europe,  Asia,  Africa,  and  Australia ;  and  the  Antarctic. 
These  three  great  blocks  are  separated  one  from  the  other  by  the 
great  divisions  of  the  sea,  the  oceans,  which,  therefore,  have  an 
intercontinental  location.  These  continental  blocks  and  dividing 
oceans  have  certainly  been  distinct  since  the  Mesozoic,  and  it  is 
probable  that  they  have  been  distinct  since  much  earlier,  possibly 
Palaeozoic,  time.  It  is,  of  course,  true  that  America  has  at  different 
times  been  united  with  Europe  or  with  Asia  on  the  north,  and 
with  Antarctica  on  the  south,  either  by  land  bridges  or  by  shallow 
submarine  banks.  But  this  does  not,  therefore,  destroy  the  essen- 
tial independence  of  the  three  great  blocks.  If,  then,  we  regard 
the  oceans  as  the  intercontinental  bodies  of  sea  water,  and  consider 
America  and  the  Old  World  as  distinct  blocks,  we  have  the  follow- 
ing four: 

I.     INTERCONTINENTAL  SEAS  OR  OCEANS. 

1.  Pacific — between  all  three  blocks,  with  a  superficial  area  *  of  166 

million  square  kilometers. 

2.  Atlantic — between  all  three  blocks,  with  a  superficial  area  *  of  82 

million  square  kilometers. 

3.  Indian — between  Old  World  and  Antarctica,  with  a  superficial 

area  of  73  million  square  kilometers. 

4.  Arctic — between  Old  and  New  World,  with  a  superficial  area  of 

about  14  million  square  kilometers. * 

If,  on  the  other  hand,  we  consider,  with  Wagner,  Penck,  and 
others,  the  Old  and  New  World  together  as  one  block,  we  must  take 
the  Arctic  Sea  from  the  list  of  oceans  and  place  it  as  an  intra- 
continental  body  among  the  mediterraneans. 

BATHYMETRIC  ZONES  OF  THE  SEA.  A  strip  of  shallow  sea  sur- 
rounds each  of  the  four  great  oceans  and  constitutes  the  belt  of 
transition  from  the  sea  to  the  land.  This  is  the  littoral  belt,  the 
width  of  which  corresponds  to  the  width  of  the  continental  shelf. 
Similarly,  a  littoral  belt  outlines  each  group  of  oceanic  islands, 
though  this  is  generally  very  narrow.  The  depth  of  the  littoral  belt 
does  not,  perhaps,  greatly  exceed  200  meters  (roughly,  ioo  fathoms), 
and  it  corresponds  very  closely  with  the  depth  to  which  sunlight 

*  Exclusive  of  marginal  bodies. 


THE   OCEANS  101 

ordinarily  penetrates.  The  littoral  belt  is,  therefore,  the  submerged" 
edge  of  the  continental  area,  and  most  of  it  forms  the  margins  of 
the  great  oceans.  The  remainder  of  the  oceans  constitutes  the 
abysmal  or  abyssal  area,  in  the  discussion  of  which  we  may  include 
the  steep  transitional  slopes  between  —200  meters  and  —2,400  me- 
ters (see  ante}.  The  upper  zone  of  the  ocean  as  a  whole,  irrespec- 
tive of  the  position  of  the  sea  floor,  forms  the  pelagic  district,  of 
especial  importance  in  marine  bionomy,  under  which  heading  it  and 
the  abyssopelagic  zone  will  be  more  fully  considered.  (See  Chap- 
ter XXVI.) 

CONFORMATION  OF  THE  OCEAN  FLOOR.    The  ocean  floor  is  char- 
acterized by  elevations  and  depressions,  often  of  great  extent  and 

Andes 


FIG.  16.     (a)  Diagrammatic  cross-section  of  the  Pacific  Ocean  near  lat.  20°  S., 
showing  two  fore-deeps,  the  Tonga  and  the  Atacama. 
(b)  A  similar  section  across  the  South  Atlantic  and  Indian  oceans 
near  lat.  24°  S.    The  Mid-Atlantic  Rise  is  shown  in  section  in  the 
Atlantic.      (After  Haug.) 

diversity.  (Fig.  16.)  The  following  terminology  has  been  de- 
veloped for  these  irregularities  by  the  International  Commission  for 
submarine  nomenclature 


/.     Grand  or  Major  Features,  or  Those  of  Wide  Extent. 

1.  Continental  Shelf  (G.  Schclf,  Fr.  socle  or  plateau  continental). 

The  submerged  border  of  the  continents  to  the  loo-fathom  or 
2oo-meter  line,  where  the  descent  is  abrupt. 

2.  Sub-oceanic  Depressions. 

a.  Basin  (G.  Becken,  Fr.  bassin).     Approaching  a  circular 

form. 

b.  Trough  (G.  Mulde,  Fr.  valid  e).    Elongated  and  broad  de- 

pressions with  gradually  sloping  sides. 

c.  Trench  (G.  Graben,  Fr.  ravin}.    Long  but  narrow  depres- 

sions along  the  continental  border,  with  steep  sides,  of 
which  the  continental  is  higher  than  the  marine. 


102  PRINCIPLES    OF   STRATIGRAPHY 

d.  Prolongations  of  the  basins  or  trough,  comprising: 

(1)  Embayment   (G.  Bucht,  Fr.  golfe).     Semicircular 

to  triangular  indentations  of  the  land  or  of  sub- 
marine elevations. 

(2)  Gully  (G.  Rinne,  Fr.  chenal).    Elongated  indenta- 

tions of  like  character. 

3.  Sub-oceanic  elevations,  either  independent,  or  submarine  pro- 

longations of  the  land. 

a.  Rise  (G.  Schwellen,  Fr.  seuil).     With  very  gradually  as- 

cending sides. 

b.  Ridge  (G.  Riicken,  Fr.  crete).    Prolonged  elevations  with 

steep  sides. 

c.  Plateau  (G.  Plateau,  Fr.  plateau).    Elevations  with  steep 

sides  and  longitudinal  and  transverse  dimensions  of  sim- 
ilar extent. 

4.  Deep    (G.   Tief,   Fr.   fosse).     Abrupt  depressions   of  the  sea 

floor,  e.  g.,  Nero  deep. 

5.  Height  (G.  Hoh,  Fr.  haut).     Abrupt  elevations,  generally  on 

rises,  ridges,  or  plateaus. 


//.     Minor  Features,  or  Those  of  Limited  Extent. 

1.  Elevations. 

a.  Ridge   (G.  Riicken,   Fr.   crcte).     Long  ridges   of  minor 

character,  generally  with  an  irregular  surface,  rising  and 
falling. 

b.  Submarine  hill  or  peak. 

(1)  Dome  (G.  Kuppe,  Fr.  dome).     Small,  steep-sided 

elevations  in  depths  "of  more  than  200  meters. 

(2)  Bank  (G.  Bank,  Fr.  bane).    Elevations  above  200 

meters  but  below  1 1  meters,  e.  g.,  Porcupine  Bank 
west  of  Ireland ;  Grand  Bank  south  of  Newfound- 
land. 

(3)  Reef  or  Shoal   (G.  Riff,  Fr.  recif  or  haut  fond). 

Elevations  to  within  n  meters  or  less  of  the 
surface. 

2.  Depressions. 

a.  Caldron   (G.  Kessel,  Fr.  caldeira).     Steep-sided  depres- 

sions of  slight  extent. 

b.  Furrow  (G.  Furche,  Fr.  sillon).     Canal-like  depressions 

in  the  continental  shelf,  and  more  or  less  transverse  to  it, 
e.  g.}  Ganges  furrow. 


THE    OCEANS 


103 


Features  and  Extent  of  the  Continental  Shelves. 

Among  the  more  prominent  parts  of  the  continental  shelves  we 
may  mention  the  following  (Krummel-23  :uj)  : 


Table  showing  distribution  area  and  depth  of  the  principal 
continental  shelves. 


Name  and  location 

Area  in  sq.  km. 

Depth 

I.  Atlantic  Ocean: 
I.  America 

145,000 

150-200  m. 

Florida-Texas  shelf 

185  ooo 

mostly  less  than 

Campeche  shelf,  Central  America  

170,000 

50  m. 

do. 

Guiana  shelf  South  America 

485  ooo 

do. 

South  Brazil  shelf 

770,000 

do. 

Patagonia  shelf  

060,000 

50-100  m. 

2.  Africa 
Agulhas  shelf,  South  Africa  

75,000 

mostly  over 

3.  Europe 
British   shelf,    including    North   Sea   to 
Cape  Skagen,  Denmark,  and  south  to 
Biarritz   Bay  of  Biscay 

i  050  ooo 

100  m. 
mostly  under 

II.  Arctic  Ocean: 
Norwegian  shelf  

Q  l.OOO 

loom. 
200-300  m. 

Iceland-Faroe  shelf 

IIS  OOO 

200—300  m. 

Barent  shelf. 

810,000 

200-300  m. 

North  Siberian  shelf  (Nova  Zembla  to 
155°  W  Long  ) 

I  ^O  OOO 

one-half  under 

III.  Indian  Ocean: 
I.  Africa 
Zambesi  shelf,  mouth  of  Zambesi  River  .  . 

2.  Asia 
Bombay  shelf,  India 

55,000 
2^0  ooo 

50  m. 

mostly  under 
50  m. 

50-100  m. 

Birma  shelf,  India  

200,000 

mostly  under 

3.  Australia 
Northwest  Australian  shelf  (N.  W.  Cape 
to  Melville  Island)  

500,000 

loo  m. 
50-100  m. 

South  Australian  shelf 

320,000 

50-100  m. 

IO4 


PRINCIPLES    OF    STRATIGRAPHY 


Table  showing   distribution  area  and  depth   of  the  principal 
continental  shelves — Continued. 


Name  and  location 

Area  in  sq.  km. 

Depth 

IV.  Pacific  Ocean: 
i.  Australian  coast 
Tasmania  shelf  

1  60  ooo 

50—100  m 

Queensland  shelf 

IQO  OOO 

mostly  under 

Arafura  shelf,  North  Australia  

Q-JQ  OOO 

100  m. 
50-100  m. 

2.  Austral-Asian  coast 
Borneo-  Java  shelf  

i  850  ooo 

50—100  m. 

3.  Asiatic  coast 
Tonkin-Hong  Kong  shelf  (facing  South 
China  Sea)  

4-7  c  OOO 

mostly  under 

Tung  hai  shelf  (from  Straits  of  Formosa 
to  Straits  of  Korea)  

a  I  E;  OOO 

loom. 

do. 

Okhotsk-Sachalin  shelf 

7  T  e  OOO 

50—100  m 

Behring  shelf  

I   T2O  OOO 

one-half  under 

50  m. 

Along  the  East  Pacific  {West  American)  border  the  continental 
shelf  is  extremely  narrow ;  no  specially  defined  portion  of  any  size 
being  recognizable. 

Subordinate  Features  of  the  Continental  Shelf.  These  are  the 
minor  elevations  and  depressions  of  which  the  banks  and  furrows 
are  the  most  important.  Of  the  former,  the  banks  at  the  mouth 
of  the  English  and  St.  George's  channels  are  characteristic,  the 
largest  of  these,  the  Labadie-Cockburn  bank,  having  a  length  of  280 
kilometers.  These  banks  are  submarine  continuations  of  the  old 
folds  of  southern  Ireland,  and  on  their  surfaces  are  often  found 
the  shells  of  shore  Mollusca,  which  do  not  live  in  the  depth  of  water 
now  covering  the  banks,  showing  a  comparatively  recent  subsidence. 
On  the  other  parts  of  the  British  shelf  we  have  the  great  Dogger 
Bank  in  the  North  Sea.  Bones  of  mammoth,  rhinoceros,  bison, 
urochs,  and  wild  horse  are  not  infrequently  brought  up  from  this 
bank,  this,  together  with  other  facts,  indicating  depression,  prob- 
ably in  glacial  time,  of  a  former  land  area.  The  Silver  Pit  furrow 
in  this  bank  has  been  regarded  by  Jukes-Brown  as  the  ancient  con- 
tinuation of  the  Rhine. 

Examples  of  banks  and  furrows  on  the  American  coast  are  the 
Newfoundland  banks,  Great  Bahama  banks,  Campeche  bank,  etc., 
and  the  St.  Lawrence  and  Hudson  furrows. 


THE   OCEANS 


105 


Features  of  the  Sub-Oceanic  Elevations  and  Depressions. 

Among  the  great  sub-oceanic  elevations  the  most  extensive  is  the 
Mid-Atlantic  Rise  (Supan-38,  plate  12),  which  extends  from  Ice- 
land, over  the  Azores,  southward  to  Tristan  da  Cunha,  a  distance  of 
14,000  kilometers  and  an  area  of  10  million  square  kilometers.  It 
is  bounded  by  the  4,ooo-meter  line,  and  its  width  in  the  South  At- 
lantic is  approximately  indicated  by  the  longitudes  of  Ascension  and 
St.  Helena  islands.  From  the  temperatures  found  in  the  depres- 
sions on  either  side,  and  especially  from  the  high  temperature  of  the 
south  African  trough,  it  is  thought  that  the  axis  of  this  rise  nowhere 


Guam 


MedinilJa 


FIG.  17.  Two  cross-sections  of  the  Marian  Trench,  a  fore-deep  in  the 
western  Pacific.  The  upper  is  east  from  Guam,  and  passes 
through  the  Nero  Deep,  9,636  meters.  The  lower  is  east  from 
Medinilla,  and  passes  through  lesser  deeps,  north  of  the  preced- 
ing, and  also  shows  a  "ridge"  east  of  the  trench.  (After  Kriim- 
mel.) 


falls  below  3,000  meters.  North  of  the  equator  it  is  less  continuous 
than  south  of  it.  With  its  branches  it  divides  the  Atlantic  Ocean 
bottom  into  a  number  of  great  depressions:  a  North  American 
basin  of  13  million  square  kilometers  area,  a  Brazilian  and  an  Ar- 
gentine basin  with  a  combined  area  of  16  million  square  kilometers, 
a  North  African  basin  of  9  million  square  kilometers  area,  and  a 
West  African  trough  of  n  million  square  kilometers  area.  This 
great  Mid- Atlantic  swell  does  not  join  the  Antarctic  continent,  but 
between  30°  and  40°  S.  lat.  it  has  two  branches — a  northwestern 
one,  the  Rio  Grande  rise,  nearly  separating  the  Argentine  and  Brazil 
basins,  and  a  western  one,  the  Whales  rise,  which  extends  from 
Tristan  da  Cunha  island  /to  the  South  African  continent,  and  ef- 


io6  PRINCIPLES  £>F    STRATIGRAPHY 

fectively  cuts  off  the  South  African  trough  from  the  Antarctic  cold 
waters.  In  the  Pacific,  west  of  South  America,  is  the  great  Easter 
Island  rise,  with  an-  area  exceeding  that  of  Africa.  The  South 
Indian  Ocean  shows  two  great  swells  or  rises :  the  Kerguelen  rise, 
from  Antarctica  and  Australia,  and  the  Crozet  swell,  or  rise,  ex- 
tending southward  from  Africa.  As  examples  of  trenches,  or 
Graben,  may  be  mentioned  the  Marian  trench  with  the  Nero  deep, 
and  the  Japan  trench  with  the  Tuscarora  deep.  They  are  regarded 
as  submarine  fault  or  rift  valleys,  just  as  are  those  upon  the  land 
(e.  g.,  Rhine  Graben).  The  two  cross-sections  of  the  Marian  trench 
here  reproduced  show  their  general  characteristics  (Fig.  17). 
Ridges  are  illustrated  by  the  Wyville-Thomson  ridge,  between 
North  Britain  and  the  Faroe  Islands,  and  the  Faroe  Island  ridge, 
which  separates  the  deep  Arctic  waters  of  the  East  Greenland  Sea 
from  the  North  Atlantic.  The  Wyville-Thomson  ridge  has  its 
lowest  point  within  576  meters  of  the  sea-level,  and  shows  a  num- 
ber of  notches  of  the  wind-gap  type,  which  suggest  that  it  is  a  part 
of  an  old  land  ridge.  The  floor  of  the  Faroe-Shetland  gully,  which 
terminates  in  this  ridge,  has  a  fairly  uniform  depression  of  1,170 
to  1,189  meters.  As  an  example  of  a  plateau  may  be  mentioned  the 
Blake  Plateau,  a  nearly  flat  submerged  tableland  averaging  700  to 
800  meters  below  sea-level,  and  bounded  on  the  west  by  the  steep 
slope  rising  to  the  Florida-Carolina  shelf,  and  on  the  east  by  the 
equally  steep  slope  descending  to  the  North  American  basin.  From 
this  basin  rises  the  small  isolated  Bermuda  plateau,  while  the  Pacific 
has  in  its  central  part  the  equally  steep-sided  Hawaiian  plateau, 
both  of  which  are  well  shown  on  Supan's  map,  above  cited.  The 
Pourtales  plateau,  south  of  Florida,  with  a  depth  of  90  to  300 
fathoms  (165  to  549  meters),  is  an  example  of  a  small  plateau  bor- 
dering the  continent. 

II.     INTRACONTINENTAL  SEAS. 

The  continental  blocks  are  divided  into  continents  by  arms  of 
the  sea  penetrating  deep  into  the  land,  or  indented  by  shallow  or 
deep  marginal  seas  more  or  less  land-locked  or  enclosed  by  islands. 
These  are  the  intracontinental  seas,  among  which  two  types  can  be 
distinguished :  the  independent,*  and  dependent.  Independent 
seas  are  more  or  less  distinct  from  the  oceans,  lying  in  depres- 
sions which  are  independent  of  the  main  ocean  basins,  and  sepa- 
rated from  them  by  a  rim,  which  may  be  largely  submerged  or 
may  rise  above  sea-level,  leaving  only  a  slight  superficial  connection 

*  Not  in  the  sense  of  Kriimmel.     See  ante. 


INTRACONTINENTAL   SEAS  107 

with  the  ocean.  These  seas  would  become  wholly  independent  if 
the  surface  of  the  ocean  were  lowered  sufficiently,  or,  at  the  most, 
would  remain  connected  with  the  oceans  only  by  very  narrow  chan- 
nels. Dependent  seas  are  merely  arms  of  the  ocean  extending 
into  the  land,  without  marginal  rim,  becoming  progressively  nar- 
rower and  shallower  the  further  they  penetrate  into  the  land. 
Seas  of  this  type  would  merely  become  shorter  on  the  lowering  of 
the  sea-level,  but  would  always  maintain  their  open  connection  with 
the  oceans. 

In  each  of  these  groups  we  may  further  distinguish  a  subordi- 
nate group  in  which  an  abyssal  area  is  present,  and  another  in  which 
it  is  absent.  Independent  intracontinental  seas  with  an  abyssal  area 
are  called  mediterraneans  (Mittelmeere) ,  while  the  shallow  type, 
without  the  abyssal  area,  constitutes  the  true  epicontinental  sea.* 
Each  of  these  types  may  further  be  divided  into  marginal  seas,  i.  e., 
those  largely  enclosed  by  islands  rising  from  a  submerged  rim,  and 
land-locked  seas,  or  those  largely  surrounded  by  the  mainland. 

A.    Independent  Seas. 

i.  The  Mediterraneans.  The  land-locked  mediterraneans  are  the 
most  typical  of  this  kind,  and  by  some  they  are  regarded  as  the  only 
true  mediterraneans.  Examples  of  these  are  the  Roman  mediter- 
ranean (the  Mediterranean  of  geographers ;  in  reality,  a  double  one, 
the  western  descending  to  3,151  meters  off  the  coast  of  Sardinia, 
and  the  eastern  to  4,404  meters  south  of  Greece)  ;  the  Black  Sea, 
an  extreme  type  with  a  maximum  depression  of  2,244  meters  ;  the 
Red  Sea,  2,271  meters ;  and  the  Mexican  mediterranean,  or  Gulf  of 
Mexico,  3,809  meters.  An  intermediate  type  between  the  land-locked 
and  the  marginal  is  seen  in  the  Caribbean  Sea,  partly  enclosed  by 
islands,  and  in  the  group  of  Austral-Asian  mediterraneans.!  This 
group  comprises  a  number  of  distinct  mediterraneans,  each  one  of 
which,  considered  separately,  would  be  classed  as  of  the  marginal 
type.  The  chief  of  these  are:  the  South  China  Sea,  with  a  maxi- 
mum depth  of  4,226  meters;  the  Celebes  Sea,  5,112  meters;  and  the 
Banda  Sea,  5,226  meters.  An  example  of  an  abnormal  marginal 
mediterranean  is  found  in  the  Tung-Hai,  or  East  China  Sea.  This 
descends  regularly  from  the  shore  to  below  the  2OO-meter  line, 

*  This  term  was  proposed  by  Professor  Chamberlin,  and  made  to  include  the 
littoral  zone  of  the  open  ocean,  which  by  no  stretch  of  meanings  can  be  classed 
as  a  distinct  sea.  The  present  restriction  of  the  term  was  proposed  by  the 
author  in  1907  (18). 

t  Classed  by  Krummel  as  a  typical  intercontinental  mediterranean. 


io8  PRINCIPLES    OF    STRATIGRAPHY 

and  then  rises  abruptly  in  the  chain  of  Lu-Tschu  Islands,  which 
bound  it  on  the  southeast.  Its  littoral  belt  occupies  more  than  two- 
thirds  the  width  of  the  sea  on  the  west  or  continental  side,  but  is 
extremely  narrow  on  the  east  or  oceanic  side,  where  the  islands 
rise  abruptly.  The  maximum  depth  within  the  chain  is  914  meters. 
Typical  marginal  mediterraneans  are  found  in  the  Japan  Sea,  3,731 
meters;  in  Okhotsk  Sea,  3,370  meters;  and  in  Behring  Sea,  5,369 
meters — all  on  the  east  coast  of  Asia.  The  last  of  these  is  an  ex- 
ample of  a  mediterranean  in  which  the  rim  is  in  large  part  sub- 
merged, only  islands  bounding  it  on  the  south,  east,  and  north.  An 
example  of  a  still  more  extreme  marginal  mediterranean  is  .the  Coral 
Sea,  east  of  Australia,  the  deepest  part  of  which  descends  to  4,663 
meters,  but  of  which  the  southeastern  margin  is  largely  composed 
of  submerged  reefs  and  shoals  with  deep  channels  between.  From 
this  a  further  step  takes  us  to  the  oceanic  deeps,  already  mentioned, 
as  the  extremes  in  one  direction,  while  the  land-locked  type  leads 
through  the  Black  Sea  type  of  nearly  cut-off  bodies  to  the  com- 
pletely enclosed  deep  continental  seas  or  lakes,  such  as  the  Cas- 
pian. A  subordinate  type  is  found  in  the  Adriatic,  which  is  a  de- 
pendent, not  of  an  ocean,  but  of  the  Roman  mediterranean.  Only  a 
small  part  of  its  bottom  falls  below  the  2OO-meter  line,  its  greatest 
depth  being  1,589  meters.  It  is  thus  transitional  to  the  epicontinen- 
tal  seas. 

It  is  noteworthy  that  marginal  mediterraneans,  so  characteristic 
of  the  western  or  Asiatic  border  of  the  Pacific,  are  wanting  on  the 
eastern  or  American  border.  On  the  west  Atlantic  (east  American) 
coast  we  have  the  Caribbean  and  Mexican  mediterraneans  already 
mentioned,  and  between  them  the  smaller  Yucatan  basin,  which  de- 
scends to  6,269  meters  south  of  Grand  Cayman  Island.  The  ridge 
between  this  and  the  Caribbean  lies  between  Pedro  and  Rosalind 
banks  and  has  a  maximum  depth  of  nearly  1,300  meters.  The  Wind- 
ward Canal  between  Haiti  and  Cuba  has  a  maximum  depth  of  1,284 
meters  and  the  Mona  passage  between  Porto  Rico  and  Haiti,  one  of 
the  entrances  to  the  Caribbean,  only  583  meters,  though  the  main 
entrance,  the  Anegada  Straits,  between  the  Virgin  Islands  and  Som- 
brero in  the  Lesser  Antilles,  is  less  than  2,000  meters,  while  the 
greatest  depth  of  the  Caribbean  is  5,201  meters.  The  Florida  Canal, 
the  exit  from  the  Mexican  mediterranean,  has  a  maximum  depth  of 
803  meters.  On  the  northern  Atlantic  we  have  Baffin  Bay  (5,249 
meters),  which,  though  also  open  to  the  Arctic  Ocean,  has  its 
broader  connection  with  the  North  Atlantic.  On  the  East  Atlantic 
coast  no  mediterraneans  except  the  Roman,  with  its  dependents  the 
Adriatic  and  Black  seas,  occur, '  but  epicontinental  seas  abound. 


INTRACONTINENTAL    SEAS  109 

The  Indian  Ocean  has  only  the  Red  Sea  as  a  contributory  land- 
locked marginal  mediterranean,  in  addition  to  which  there  is  a  very 
open  and  incomplete  marginal  mediterranean,  the  Burma  or  Anda- 
man Sea,  between  the  Malay  peninsula  and  the  Andaman  and  Nico- 
bar  Island  groups.  The  maximum  recorded  depth  here  is  4,177 
meters,  but  much  of  its  deeper  part  lies  between  2,000  and  3,000 
meters  below  sea-level.  Whether  or  not  mediterraneans  exist  off  the 
southern  borders  of  the  three  great  oceans  is  at  present  unknown. 
The  Arctic  Ocean  has  only  one  large  marginal  mediterranean,  but 
several  epicontinental  seas.  The  mediterranean  type  is  represented 
by  the  East  Greenland  Sea,  lying  between  Greenland  and  Scandi- 
navia, and  Iceland  and  Spitzbergen.  This  has  a  maximum  known 
depth  of  4,846  meters  between  North  Greenland  and  Spitzbergen,  its 
connection  with  the  Arctic  being  by  channels  2,000  meters  deep. 
The  deepest  part  of  its  submerged  southern  border  is  550  meters 
in  Denmark  Straits,  but  much  of  this  border  is  shallow.  (Fig.  18.) 
Interoceanic  mediterraneans.  The  East  Greenland  Sea  and  Baf- 
fin Bay  are  interoceanic  mediterraneans,  i.  e.,  lying  between  the 
Atlantic  and  the  Arctic,  one  belonging  to  each.  Behring  Sea  is  an 
interoceanic  mediterranean  which  lies  between  the  Arctic  and  the 
Pacific,  but  belongs  to  the  latter.  The  Austral-Asian  group  is  inter- 
oceanic between  the  Pacific  and  the  Indian  oceans,  while  the  Red 
Sea  has  been  artificially  made  interoceanic  between  the  Indian  and 
Atlantic  systems  by  the  building  of  the  Suez  Canal,  and  the  Carib- 
bean mediterranean  will  soon  be  placed  in  this  class  also. 

In  general,  mediterraneans  may  be  considered  in  the  light  of  mi- 
nute oceans,  with  the  essential  bathymetric  zones  found  in  these, 
i.  e.,  abyssal,  littoral,  and  pelagic.  The  characteristic  independent 
ocean  currents  are,  however,  wanting,  though  parts  or  branches  of 
these  currents  may  occur,  as,  for  example,  the  Gulf  Stream  in  the 
Central  American  mediterraneans,  and  the  branch  streams  entering 
the  Roman  mediterranean. 

2.  Epicontinental  Seas.  These  are  the  shallow  independent  seas, 
the  greatest  depth  of  which  does  not  pass  much  below  200  fathoms, 
or,  if  so,  in  only  a  few  isolated  spots.  These  have,  therefore,  only 
a  littoral  and  a  pelagic  zone,  the  abyssal  being  absent.  Both  land- 
locked and  marginal  epicontinental  seas  occur;  the  former,  when 
situated  in  a  region  of  normal  pluvial  climate,  generally  falling  in 
percentage  of  salinity  below  that  of  the  open  sea,  owing  to  the 
abundant  influx  of  fresh  water.  Examples  of  the  land-locked  epi- 
continental seas  are  Hudson  Bay  in  North  America,  and  the  Baltic 
with  its  branches,  the  Bothnian  and  the  Finnish  gulfs,  in  Europe. 
Both  of  these  are  tributary  to  the  Atlantic  system.  Hudson  Bay 


no 


PRINCIPLES    OF    STRATIGRAPHY 


has  a  maximum  depth  of  228  meters  in  one  spot,  but  otherwise  is 
less  than  200  meters  deep;  while  the  maximum  depth  of  the  Baltic 
is  249  meters  east  of  Gotland,  that  of  the  Bothnian  Gulf  294  meters 


FIG.  18.  Bathymetric  chart  of  the  Arctic  Ocean.  The  deepest  shade  (solid) 
shows  depths  below  3,000  meters;  the  next  (cross-hatching)  be- 
tween 3,000 -and  1,000  meters;  the  next  lighter  (horizontal  lining) 
shows  depths  between  1,000  and  200  meters,  while  the  white 
color  shows  everything  above  the  2OO-meter  line,  including  the 
lands.  The  character  of  East  Greenland  mediterraneans  and  the 
location  of  the  Wyville-Thomson  Faroe-Iceland  and  Denmark- 
Strait  ridges  is  recognizable.  The  dotted  circle  is  the  Arctic  circle. 
(After  Nansen  and  Haug.) 

opposite  Hernosand,  Sweden,  and  that  of  the  Finnish  Gulf  124 
meters  near  its  mouth.  In  each  case  these  maxima  lie  in  small 
depressions  below  the  main  floor  of  the  water  body.  The  deeper 
portions  of  the  main  floor  of  the  Baltic  average  150  to  170  meters, 


INTRACONTINENTAL    SEAS  in 

while  much  of  the  depth  is  less  than  TOO  meters.  In  the  Bothnian 
Gulf  the  deeper  parts  lie  between  100  and  160  meters,  while  the 
greater  part  has  a  depth  of  less  than  90  meters.  Finally,  the  Finnish 
Gulf,  with  the  exception  noted,  does  not  reach  the  loo-meter  line, 
while  much  of  it  has  a  depth  of  less  than  50  meters.  The  Persian 
Gulf,  with  a  maximum  depth  of  90  meters,  is  the  only  land-locked 
epicontinental  sea  tributary  to  the  Indian  Ocean,  but  several  other 
Eurasian  epicontinental  seas  of  the  land-locked  type  are  tributary  to 
the  Arctic  Ocean.  The  larger  of  these  are  the  White  Sea,  with  a 
maximum  depth  of  329  meters,  but  mostly  above  200  meters,  and 
the  Gulf  of  Obi  in  Siberia.  In  the  Pacific  the  only  land-locked  epi- 
continental sea  is  the  Huang-hai  or  Yellow  Sea,  of  China.  This  sea 
has  a  rather  broad  opening  into  the  East  Chinese  Sea  and  its  margin 
does  not  rise  perceptibly  above  the  general  level  of  its  floor,  which 
is  from  80  to  90  meters  below  sea-level.  Still  there  are  a  few  de- 
pressions of  a  little  more  than  100  meters,  the  maximum  being  106 
meters,  opposite  the  southern  end  of  the  Korean  peninsula.  The 
Gulf  of  Carpentaria  in  North  Australia  is  another  epicontinental  sea 
partly  land-locked,  but  with  ,a  broad  opening  toward  the  north.  The 
average  depth  is  from  50  to  60  meters,  and  this  continues  north- 
ward in  the  shallow  Arafura  Sea  between  Australia  and  New 
Guinea.  Among  the  islands  which  separate  this  sea  from  the 
Banda  mediterranean  on  the  northwest  are  several  deep  holes,  some 
of  them  descending  below  the  2,ooo-meter  line. 

On  the  eastern  shore  of  the  Pacific,  Cook  Inlet  in  Alaska  and 
Georgia  Straits  in  British  Columbia  are  examples  of  land-locked 
epicontinental  seas  of  very  small  size.  The  latter  has  a  hole  316 
meters  deep  opposite  Vancouver,  but  is  generally  quite  shallow,  as 
is  also  Cook  Inlet.  Another  small  water  body  of  this  type  is  San 
Francisco  Bay,  while  marginal  epicontinental  seas  of  small  size  also 
occur  on  the  coast  of  British  Columbia  and  Alaska.  An  aberrant 
type  of  the  marginal  epicontinental  sea  is  found  in  the  Rann  of 
Cutch,  Bombay,  west  coast  of  India.  This  is  very  shallow,  and  as 
it  lies  within  the  belt  of  great  evaporation,  it  has  practically  been 
converted  into  a  salina  or  salt  pan. 

In  the  Arctic  Ocean  system  are  several  epicontinental  seas  of 
the  marginal  type,  besides  the  land-locked  types  already  mentioned 
(White  Sea  and  Gulf  of  Obi).  Melville  Sound  in  Arctic  North 
America  is  probably  to  be  classed  here,  though  its  central  area 
descends  below  the  2OO-meter  line.  The  Kara  Sea,  behind  Nova 
Zembla,  is  another  but  more  open  marginal  sea,  though  in  its  west- 
ern end  a  hole  730  meters  deep  is  recorded.  The  largest  sea  of  this 
class  connected  with  the  Arctic  Ocean  is  the  East  Spitzbergen,  or 


ii2  PRINCIPLES    OF    STRATIGRAPHY 

Barents  Sea,  lying  between  Spitzbergen  on  the  west,  Nova  Zembla 
on  the  east,  the  North  European  coast  on  the  south,  and  nearly 
closed  on  the  north  by  the  island  group  of  Franz  Josef  Land.  It 
has  some  depths  as  great  as  370  meters,  but  is  shallow  for  the  most 
part,  so  that  it  is  best  classed  as  an  epicontinental  sea. 

The  North  Sea  and  the  Irish  Sea  are  examples  of  marginal 
epicontinental  seas  on  the  North  Atlantic  border.  The  former  is 
for  the  most  part  less  than  100  meters  deep,  but  has  some  depths  as 
great  as  187  meters  off  the  Orkneys,  while  the  latter  has  a  maximum 
depth  of  124  meters,  much  of  its  bottom  lying  between  50  and  100 
meters.  The  English  Channel  is  an  extreme  case,  approaching  the 
dependent  type;  still  it  has  a  few  deep  holes  descending  to  a 
maximum  of  172  meters  north  of  the  Channel  Isles.  Its  opening 
into  the  great  North  Sea'  at  Dover  Straits  gives  it,  however,  a 
peculiarity  not  possessed  by  other  marginal  bodies  of  this  kind.  In 
the  South  Pacific  the  Tasmanian  Sea,  between  Australia  and  Tas- 
mania, may  be  classed  as  a  shallow,  flat-bottomed,  rather  open  epi- 
continental sea  of  the  marginal  type.  Its  greatest  reported  depth 
is  88  meters.  , 

B.     Dependent  Seas — Funnel  Seas. 

A  typical  example  of  a  dependent  sea  is  found  in  the  Gulf  of 
California,  between  the  Peninsula  of  Lower  California  and  Mexico. 
The  floor  of  this  water  body  descends  from  zero  at  the  head  to 
2,600  meters  below  sea-level  at  the  mouth,  the  descent  being  a 
regular  one.  At  the  same  time  the  channel  widens  so  that  the  form 
is  that  of  a  narrow  funnel  split  lengthwise.  This  Funnel  Sea 
(Trichter  See,  mare  tuyau),  as  it  may  be  called,  will  never  become 
distinct,  no  matter  how  much  the  surface  of  the, ocean  is  lowered; 
it  will  simply  be  shortened  until,  when  the  level  has  been  lowered 
2,600  meters,  it  becomes  extinct.  In  form  it  resembles  a  broad 
river  valley;  indeed,  if  it  were  shorter  and  shallower  it  might  be 
regarded  as  the  estuary  of  the  Colorado  River,  which  enters  its 
head. 

An  example  of  a  broader  funnel  sea  is  found  in  the  Bay  of 
Biscay,  which  descends  to  near  5,000  meters  at  the  mouth.  Here  a 
few  deeper  depressions  may  occur  inside  of  the  mouth,  but  the  form 
is  in  all  essentials  that  of  a  funnel  sea. 

The  Bay  of  Fundy  on  the  Atlantic  is  a  shallow  funnel  sea,  not 
descending  below  200  meters  at  the  mouth.  It  may  be  regarded  as 
the  littoral  type  of  the  narrow  funnel  seas,  just  as  the  Californian 
Sea  may  be  regarded  as  the  littoral-abyssal  type  of  the  same  class. 


INTRACONTINENTAL    SEAS  113 

Of  the  broader,  or  Biscayan  type,  on  the  east  Pacific  border,  only 
the  Gulf  of  Panama  need  be  mentioned  as  of  sufficient  size  and 
importance.  This  descends  to  3,665  meters.  On  the  Atlantic  bor- 
der, besides  the  Biscayan,  may  be  noted  the  Gulf  of  Guinea  (to 
4,000  meters),  off  the  African  coast.  Of  a  special  type  is  the  Gulf 
of  Cadiz  (3,000  to  4,000  meters),  as  the  funnel  sea  between  Spain 
and  Morocco  is  called.  This  has  all  the  characters  of  a  typical 
funnel  sea  of  the  Biscayan  type,  but  opens  by  the  Straits  of  Gibral- 
tar into  the  Roman  Mediterranean,  making  it  more  truly  a  funnel 
than  Biscay.  Of  a  similar  type,  though  in  form  related  to  the 
Californian  Sea,  is  the  Gulf  of  Oman,  connecting  the  Persian  Gulf 
with  the  Indian  Ocean  (3,292  meters)  and  the  Gulf  of  Aden,  the 
continuation  of  the  Red  Sea  (to  3,584  meters). 

An  extreme  case  of  the  Fundy  type  is  seen  in  the  estuary  of  the 
Rio  de  la  Plata,  which  has  a  depth  of  only  26  meters  at  the  mouth. 
Neither  the  Arctic  nor  the  West  Pacific  furnishes  examples  of 
dependent  seas. 

Examples  of  subordinate  funnel  seas,  situated  on  a  mediter- 
ranean instead  of  an  ocean,  are  found  in  the  Golfe  di  Taranto, 
southern  Italy,  and  the  .Golfe  du  Lion,  southern  France.  Both 
descend  approximately  to  2,000  meters  at  the  mouth.  Of  the  same 
character  is  the  Gulf  of  Sidra  on  the  north  coast  of  Africa.  All 
of  these  are  of  the  Biscayan  type.  The  Gulf  of  Suez  at  the  head 
of  the  Red  Sea  may  be  taken  as  an  example  of  a  subordinate  funnel 
sea  of  the  Fundy  type,  though  its  channel  is  rather  narrow  and 
tortuous.  The  Gulf  of  Akabah,  on  the  other  hand,  forming  the 
east  branch  of  the  head  of  the  Red  Sea,  is  a  subordinate  mediter- 
ranean of  the  land-locked  type. 

An  example  of  a  complex  funnel  sea,  approaching  in  some  of  its 
characters  a  mediterranean  of  the  marginal  type,  is  seen  in  the  Gulf 
of  St.  Lawrence — the  mouth  of  the  river  of  that  name.  This 
descends  regularly  to  572  meters,  but  rises  again  from  Cabot  Straits 
outward  to  410  meters  before  falling  off  to  deep  water.  It  has  two 
arms,  one  from  north  of  Anticosti,  the  other  separating  Labrador 
and  Newfoundland.  A  continuous  deep  channel  is  said  to  exist, 
however,  and  the  valley  is  explained  as  a  Tertiary  erosion  valley. 

SUMMARY  OF  CLASSIFICATION. 

The  classification  of  seas  may  be  summarized  as  follows : 
I.    Intercontinental  seas  or  oceans. 

Zones:   Pelagic,  littoral,  abyssal. 
Examples:    Pacific,  Atlantic,  Indian,  Arctic. 


114  PRINCIPLES    OF    STRATIGRAPHY 

II.     Intracontinental  seas. 

A.  INDEPENDENT  SEAS. 

1.  MEDITERRANEANS. 

Zones:  Pelagic,  littoral,  abyssal. 

a.  LAND-LOCKED. 

Atlantic  system:  Roman,  Black,  Mexican. 
Indian  system:  Red  Sea. 
Subordinate:  Adriatic,  Akabah. 

b.  MARGINAL. 

Pacific  system:  Australasian  group,  East 
China  Sea,  Japan  Sea,  Okhotsk  Sea, 
Behring  Sea. 

Atlantic  system:    Caribbean. 

Indian  system:  Andaman. 

Arctic  system:  East  Greenland  Sea. 

2.  EPICONTINENTAL  SEAS. 

Zones:    Pelagic,  littoral. 

a.  LAND-LOCKED. 

Pacific  system:  Yellow  Sea. 

Atlantic   system:    Hudson    Bay,    Baltic 

group. 

Indian  system:   Persian  Gulf. 
Arctic  system:   White  Sea,  Sea  of  Obi. 

b.  MARGINAL. 

Pacific  system:  Tasmanian  Sea,  Carpen- 
taria Gulf. 

Atlantic  system:  North  Sea,  Irish  Sea, 
English  Channel. 

Arctic  system:  East  Spitzbergen  Sea. 
Kara  Sea,  Melville  Sound. 

B.  DEPENDENT  SEAS.    Funnel  seas. 

i.  CALIFORNIAN  TYPE. 

Zones:   Pelagic,  littoral,  abyssal. 

a.  CLOSED  HEAD. 

Pacific  system:  Calif ornian  Gulf. 
Atlantic  system:  Gulf  of  St.  Lawrence. 

b.  OPEN  HEAD. 

Indian  system:  Gulf  of  Aden,  Gulf  of 
Oman. 


CONTINENTAL    SEAS  115 

2.  BISCAYAN  TYPE. 

Zones:  Pelagic,  littoral,  abyssal. 

a.  CLOSED  HEAD. 

Atlantic  system:  Bay  of  Biscay,  Gulf  of 

Guinea. 
Subordinate:  Gulf  of  Taranto,  Gulf  of 

Lyons,  Gulf  of  Sidra. 

b.  OPEN  HEAD. 

Atlantic  system:  Gulf  of  Cadiz. 

3.  FUNDYAN   TYPE. 

Zones:    Pelagic,  littoral. 

a.  CLOSED  HEAD. 

Atlantic  system:   Bay  of  Fundy,  Rio  de 
la  Plata. 

b.  OPEN  HEAD. 

Indian  system  (Subordinate)  :    Gulf  of 
Suez.      (Head  artificially  opened.) 


B.    THE  CONTINENTAL  DIVISION  OF  THE 
HYDROSPHERE. 

III.     CONTINENTAL  SEAS  OR  LAKES. 

Inland  seas  or  lakes,  i.  e.,  water  bodies  entirely  enclosed  by 
land,  may  be  classed  as  continental.  They  are  either  salt  or  fresh, 
depending  on  their  location  within  the  arid  or  the  pluvial  belts  and 
on  the  relative  amount  of  evaporation  and  precipitation.  Salt  lakes 
lying  near  the  sea  often  have  their  surface  below  that  of  the  ocean, 
as  in  the  case  of  the  Caspian  Sea,  the  surface  of  which  lies  26 
meters  below  the  level  of  the  Black  Sea,  less  than  500  kilometers 
distant;  while  the  Dead  Sea  is  394  meters  below  the  level  of  the 
Roman  mediterranean,  which  is  only  75  kilometers  distant.  The 
Sea  of  Aral,  however,  another  salt  sea  in  the  same  belt,  is  48 
meters  above  the  Black  Sea,  with  a  maximum  depth  of  66  meters; 
while  Balchash  Sea,  in  the  Great  Steppe  farther  east,  has  an  eleva- 
tion of  274  meters,  with  a  depth  of  25  meters.  In  the  region 
bounded  by  the  Caspian,  the  Black,  and  the  Mediterranean 
(Roman),  are  several  small  salt  lakes  varying  from  940  meters  to 
1,925  meters  in  elevation.  In  North  America,  Great  Salt  Lake  has 
an  elevation  of  1,283  meters  above  the  sea. 

Fresh-water  lakes  all  have  their  surfaces  above  or  just  at  sea- 
level,  though  some  of  them  have  their  bottoms  far  below  sea-level. 


ii6  PRINCIPLES    OF    STRATIGRAPHY 

Such  is  the  case  with  Lake  Baikal  in  Siberia,  which  has  an  eleva- 
tion of  520  meters  and  a  depth  of  1,430  meters,  its  floor,  therefore, 
descending  910  meters  below  sea-level. 

Among  the*  great  American  lakes,  Ontario  descends  150  meters 
below  sea-level,  Huron  52  meters,  Michigan  88  meters,  and  Superior 
114  meters.  The  American  Great  Lakes  drain  their  surplus  waters 
through  the  St.  Lawrence  system  into  the  Atlantic,  and  Lake  Baikal 
through  the  Angara  River  into  the  Arctic.  Lake  Tanganyika,  of 
East  Africa,  780  meters  above  sea-level,  has  only  an  interrupted 
outward  drainage,  the  removal  of  surplus  water  being  by  evapora- 
tion ;  but  Lake  Nyassa,  480  meters  above  sea-level,  drains  by  the 
Schire  and  the  Zambesi  into  the  Indian  Ocean.  This  lake  has  a 
maximum  known  depth  of  786  meters  (430  fathoms),  its  floor  thus 
descending  300  meters  below  sea-level.  Its  length  is  about  350 
miles  and  its  average  width  about  40  miles.  Lake  Tanganyika  also 
passes  below  sea-level  in  its  deeper  portion.  On  the  American 
continent,  Lake  Tahoe  in  the  Sierras,  with  a  depth  of  1,654  feet, 
is  second  only  to  Crater  Lake,  Oregon,  which  has  a  depth  of  1,975 
feet.  Lake  Superior  has  a  maximum  depth  of  only  1,008  feet,  while 
Lake  Maggiore  (1,004  feet)  and  Lake  Como  (1,354  feet),  on  the 
south  side  of  the  Alps,  compare  favorably  with  the  American  lakes 
in  depth. 

CLASSIFICATION'  OF  LAKES  AND  LAKE  BASINS.  A  genetic  classi- 
fication of  lake  basins  differs  from  a  classification  of  lakes  as  a 
whole  because  it  deals  only  with  the  depression  in  which  the  lake 
is  situated.  Depressions  of  exactly  similar  characters,  but  without 
water,  may  exist,  and  would  have  to  be  taken  account  of  in  the 
classification  of  basins.  Such  "dry  lakes"  are,  however,  of  no  sig- 
nificance to  the  limnographer  or  to  the  bionomist.  Again,  the 
character  of  the  water,  whether  salt  or  fresh,  is  largely  a  matter  of 
climate,  and  has  no  relation  to  the  lake  basin.  This  is  also  true  of 
the  outlet  or  effluent,  for  if  the  number  of  affluents  is  small  and 
evaporation  lowers  the  lake  sufficiently,  it  will  lose  its  outlet,  just  as 
it  may  through  a  rise  of  the  rim  or  other  tectonic  change.  Such 
excess  of  evaporation  generally  brings  about  the  salinifying  of  the 
water  by  the  concentration  of  the  mineral  solute.  (Davis-7;  also 
Salisbury-33.) 

Classification  of  Lake  Basins. 

In  a  natural  classification  of  lake  basins  the  agent  active  in 
their  production  is  of  first  importance,  and  lake  basins  may,  there- 
fore, be  classified  in  the  first  place  as  A.  Lakes  of  Deformation,  or 


CLASSIFICATION    OF   LAKE    BASINS  117 

Tectonic  Lakes,  B.  Lakes  of  Construction,  C.  Lakes  of  Destruction, 
and  D.  Lakes  of  Obstruction.  The  further  subdivision  is  as  fol- 
lows: 

A.  DEFORMATIONAL  OR  TECTONIC  BASINS. 

1.  Fault  basins. 

2.  Folded  basins. 

3.  Warp  basins. 

4.  Complex  basins,  great  basins. 

B.  CONSTRUCTIONAL  BASINS. 

1.  Volcanic:   a.  Crater  lakes;  b.  depressions  in  lava  flows. 

2.  Chemical :    Hot  spring  and  geyser  basins. 

3.  Organic :   a.  Vegetal  or  swamp ;  b.  coral  reef  lagoon. 

4.  Detrital :    (Reconstructional). 

a.  Marine :    ( i )    Coastal  plain  depressions. 

b.  Lacustrine. 

c.  Fluviatile  :    (i)  River  flood  plain  lakes  (oxbows)  ; 

(2)   delta  lakes;  (3)  fan  lakes. 

d.  Glacial:  (i)  Morainal  kettle  lakes ;  (2)  drift  sheet 

kettle  lakes. 

e.  Atmospheric:      (i)    Land-slip  basins;    (2)    dune 

lakes. 

f .  Artificial :    Human  constructions,  etc.,  e.  g.,  built- 

up  reservoirs. 

C     DESTRUCTIONAL  BASINS. 

1.  Volcanic:    Pit  craters,  volcanic  subsidence  hollows. 

2.  Chemical : 

a.  Solution  hollows  and  sink-holes. 

b.  Disintegration  hollows. 

3.  Fluviatile : 

a.  Waterfall  lakes. 

b.  Pot-hole  lakes. 

4.  Glacial :   Ice  excavated  rock  tarns. 

5.  Deflation  lakes,  or  wind  excavated  hollows. 

6.  Artificial    excavations :      Man-made    excavations ;    mud 

wallows. 

D.     OBSTRUCTIONAL  BASINS.     Formed  by  damming  a  pre- 
existing valley. 
I.     Tectonic  barrier  basins. 

a.  Warp  barrier. 

b.  Fold  barrier. 


n8  PRINCIPLES    OF    STRATIGRAPHY 

2.  Volcanic  barriers 

a.  Volcanoes. 

b.  Lava  flows. 

3.  Chemical :  Tufa  barrier  basin. 

4.  Ice  barrier  basin. 

5.  Organically  built  barrier. 

a.  Coral  reef  barrier. 

b.  Vegetal  growths. 

6.  Detrital  barrier  basin. 

a.  Marine  and  lacustrine  (barrier  beach). 

b.  Fluviatile,  or  river-built :  Fan-delta  barriers ;  mar- 

ginal barriers  (drift-wood  barriers,  etc.). 

c.  Glacial,  or  ice-built :   Drift  and  morainal  barriers. 

d.  Atmospherically  built. 

(1)  Land-slip  barrier. 

(2)  Dune  barrier. 

e.  Artificial   (built  by  organisms  from  foreign  sub- 

stances). 

(1)  Beaver  dams. 

(2)  Man-made  dams. 

While  pure  types  of  these  basins  probably  exist,  the  majority 
of  lake  basins  are  of  a  more  complex  order,  falling  under  more 
than  one  class. 


A.     Deformational  or  tectonic  basins. 

These  are  due  to  faulting,  folding,  or  warping,  so  as  to  produce 
a  closed  depression,  i.  Fault  basins  are  not  uncommon,  the  best 
examples  being  Albert  and  Summer  Lakes  of  Oregon  (Fig.  19), 
and  perhaps  Lakes  Tanganyika  and  Nyassa  of  Africa  (Fig.  20). 
2.  Lakes  due  only  to  folding  or  the  formation  of  mountain  troughs 
are  rare,  but  those  in  which  iolding  takes  a  part  are  not  uncommon 
in  young  mountain  regions.  Here  belong,  in  part  at  least,  Lake 
Baikal  of  Asia,  Lake  Nicaragua,  and  the  western  end  of  Lake  Supe- 
rior in  Central  and  North  America,  respectively.  3.  Basins  due 
wholly  to  warping  are  unknown,  but  Lake  Ontario  is  a  warped  river 
valley  which  is  partly  closed  by  drift  deposits.  4.  Great  basins  are 
produced  when  mountains  arise  all  around  a  less  disturbed  area  by 
combined  folding,  faulting,  and  warping,  and  thus  leave  this  area 
surrounded  by  a  rim,  and  in  condition  to  become  a  lake.  The  size 
of  this  lake,  when  below  the  maximum  possible  for  the  lowest 


DEFORMATIONAL   LAKE    BASINS 


119 


outlet,  is  determined  by  the  relation  between  rainfall  and  evapora- 
tion. A  typical  example  is  found  in  the  extinct  Lake  Bonneville 
(Gilbert-i5),  which  extended  along  the  western  base  of  the 
Wasatch  range  for  300  miles.  Its  surface  covered  19,750  square 
miles  at  the  highest  stage,  and  its  hydrographic  basin  had  an  area 


-~-^~^-  ^  ::LV-  S";-Ji  ^fif^-j3^^^=r    ^ — * 


FIG.  19.     Sketch  of  Albert  Lake,  Oregon,  a  fault-basin  lake.     (After  Russell.) 

of  52,000  square  miles.  By  evaporation  it  has  now  been  reduced 
to  a  body  of  salt  water  which  in  1850  was  1,750  square  miles  in 
area,  with  a  maximum  depth  of  36  feet — the  Great  Salt  Lake  of 
Utah.  Another  example  in  the  same  region  is  the  extinct  Lake 
Lahontan,  which  lay  in  what  is  now  northwestern  Nevada,  with  an 
arm  extending  into  California,  and  with  a  length  of  260  miles, 


FIG.  20.     Section  through  Lakes  Tanganyika  and  Rukwa,  from  northeast  to 
southwest.    Vertical  scale  exaggerated  five  times.     (After  Moore.) 

and  enclosed  an  island  126  miles  long  and  50  miles  broad.  Most 
of  the  valleys  occupied  by  the  arms  of  this  lake  are  deserts  now, 
but  some  contain  small  lakes  of  more  or  less  saline  or  alkaline 
waters,  but  not  of  concentrated  brines.  (Russell— 31.)  What  ap- 
pears to  have  been  an  enormous  inland  sea  or  lake  of  this  type, 
but  beginning  as  a  cut-off  from  the  sea,  occupied,  according  to 


120  PRINCIPLES    OF    STRATIGRAPHY 

Walther  (4574-79),  the  greater  part  of  Germany  during  the 
Middle  Zechstein  period  (Permic),  extending  from  the  Urals  on 
the  east  to  the  Armorican  chain  in  Franee,  Belgium,  South  Eng- 
land and  Ireland  on  the  west,  and  bounded  on  the  south  by  the 
Bohemian  mass,  and  the  mountain  chain  (Vindelician)  correspond- 
ing to  the  present  Danube  plain.  In  this  sea  the  great  salt  deposits 
of  North  Germany  were  laid  down  from  the  complete  evaporation 
of  the  waters.  Fault  depressions  accompanying  earthquakes  also 
belong  to  this  class. 

B.     Constructional  basins. 

1.  Volcanic    (pyrogenic)    basins.       These    include    a.    crater 
lakes,  where  water  is  enclosed  by  the  built-up  rim  of  the  crater,  and 
b.  depressions  in  a  lava  sheet  produced  at  cooling  and  occupied  by 
water.     Examples  of  the  former  are  Crater  Lake  of  Oregon   (in 
part  a  broken-down  cone),  the  Soda  Lakes  of  Nevada,  and  Lakes 
Albano   and   Nemi,   near   Rome,   and   Agnano   and   Averno,   near 
Naples.    Other  lakes  of  this  type  occur  in  the  Auvergne  district  of 
France,    about    Auckland,    New    Zealand,    and    in    other    volcanic 
regions.     (Davis-7:j#o.)*    Sometimes  these  lakes  are  hot,  or  con- 
tain gases  fatal  to  animal  life.    In  the  Caucasus  a  lake  of  this  class 
(Elbruz)  lies  at  an  elevation  of  18,500  feet  above  the  sea.    Lakes  in 
depressions  in  lava  flows  are  probably  not  common,  and  when  they 
are  found  they  are  mostly  small. 

2.  Chemical    (hydrogenic)    basins.       This   class   is   limited   to 
small  ponds,  or  basins  built  by  tufas   in  hot   spring  and  geyser 
regions.     The  small  tufa  basins  in  mammoth  Hot  Springs  of  the 
Yellowstone  region  are  typical  examples.     Examples  of  large  size 
are  so  far  unknown.     (See  Fig.  67,  page  343.) 

3.  Organic  (biogenic}   basins,     a.     Basins  built  by  the  growth 
of  vegetation  in  moist  climates  are  not  an  uncommon  feature  in 
the  peat  bog  regions  of  northern  countries,  though  the  larger  ones 
of  this  class  may  be  in  part  of  the  barrier  type,   the  vegetable 
growth  merely  damming  back  waters  in  a  preexisting  valley.     A 
more  perfect  example  of  a  phytogenetic  or  vegetal  basin  is  seen  in 
Lake  Drummond  in  the  Dismal   Swamp  of  Virginia  and   North 
Carolina.   (41.)     This  lake  was  originally  22  feet  above  sea-level 
and  16  feet  deep.     It  is  completely  surrounded  and  enclosed  by  a 
mass  of  peat  and  vegetable  material  with  a  maximum  thickness  of 
20  feet.     At  present  the  lake  is  only  6  feet  deep  and  only  about  16 

*  Pavis  places  them  among  obstruction  lakes. 


CONSTRUCTIONAL   LAKE   BASINS  121 

feet  above  sea-level,  owing  to  artificial  drainage.  The  lake  decreases 
to  a  few  inches  in  the  woods  surrounding  it.  Although  originally 
believed  to  have  started  in  a  depression  in  the  underlying  stratum, 
it  is  now  entirely  enclosed  by,  and  owes  its  continuance  to,  a  rim  of 
vegetal  material,  and  so  is  typical  of  this  class.  Lakes  and  ponds 
of  this  type  due  wholly  to  the  growth  of  vegetation,  abound  in  the 
tundra  of  Alaska,  where  they  occur  even  on  hillsides,  which  other- 
wise would  be  freely  drained.  (Russell-3O  :/<?#.)  b.  Lake  basins 
of  animal  or  zoogenic  origin  are  less  common,  but  are  represented 
by  coral  island  lagoons,  when  their  connection  with  the  sea  ceases 
or  is  reduced  to  a  minimum.  An  elevation  of  the  coral  island  or 
atoll  would  result  in  complete  separation  of  the  basin  from  the 
ocean,  and  a  freshening  of  the  water.  Lakes  apparently  of  this 
type  have  been  reported  from  the  coral  islands  of  the  Pacific. 

4.  Detrital  (clastic)  basins.  These  are  built  up  by  detrital 
material,  which,  though  it  is  the  product  of  rock  destruction  else- 
where, nevertheless  produces  constructional  basins  similar  to  the 
volcanic  and  the  chemical,  the  material  for  the  building  of  which  is 
obtained  from  within  the  earth,  and  to  the  organic,  the  material  for 
which  is  obtained  from  the  air  or  the  water.  They  may  also  be 
called  reconstructional,  since  the  material  of  old  land  forms  is 
reconstructed  into  the  new. 

a.  Marine  detrital  basins  are  depressions  on  the  subcoastal 
plain,  due  to  irregularity  of  arrangement  of  material.  On  emergence 
these  will  carry  shallow  lakes.  Such  are  the  lakes  on  the  coastal 
plain  of  Buenos  Ayres.  (Davis-7  :j/^.)  b.  Lacustrine  detrital  basins 
are  those  left  in  the  irregular  detrital  deposits  on  the  floors  of  large 
extinct  lakes.  Here  belong  many  lakes  remaining  in  the  Great 
Basins,  such  as  the  successors  of  Lake  Lahontan  and  Lake  Bonne- 
ville  and  others,  c.  Fluviatile  detrital  basins  comprise  (i)  those 
formed  on  river  flood  plains  by  irregular  deposition,  though  these 
are  always  complicated  by  erosion,  as  in  the  case  of  oxbow  lakes ; 
(2)  those  formed  by  irregular  deposition  of  deltas;  and  (3)  those 
formed  by  irregular  deposition  on  alluvial  fans.  Lake  Pontchar- 
train,  near  the  mouth  of  the  Mississippi,  is  of  the  delta-lake  type. 
It  has  a  surface  of  twenty  by  forty  miles,  but  a  depth  of  only  27 
feet.  Others  are  found  on  the  Mississippi  delta,  the  deltas  of  the 
Rhine,  and  elsewhere.  (Davis-7.)  Oxbows  and  other  flood-plain 
lakes  occur  on  most  large  rivers,  while  delta-fan  basins,  though 
small,  are  not  uncommon.  A  combination  of  flood  plain  and  delta 
basin  is  seen  in  the  lakes  of  the  great  alluvial  plains  of  China, 
d.  Morainal  and  drift  kettle  holes  are  common  in  the  region  affected 
by  the  PJeistocenic  ice  sheet.  They  are  mostly  small,  though  often 


122  PRINCIPLES    OF    STRATIGRAPHY 

proportionately  deep  for  their  size.  Though  mostly  due  to  irregu- 
larity of  deposition,  many  owe  their  chief  characteis  to  the  caving- 
in  of  the  sand  upon  the  melting  of  an  included  ice  block,  e^  Land- 
slip basins  are  rare  and  small,  forming  in  irregularities  or  depres- 
sions in  the  land-slide  surface.  e2.  Hollows  between  dunes  are  com- 
mon, but  these,  as  a  rule,  hold  no  water,  owing  to  the  porousness  of 
the  sands.  Examples  of  lakes  held  up  by  sand  dunes  are,  however, 
abundant  in  Cherry  county  and  elsewhere  in  the  sand-dune  region 
of  Nebraska,  f.  Finally,  artificial  structures,  such  as  built-up  (not 
excavated  or  dammed)  reservoirs,  belong  here. 

C.     Destructional  basins. 

1.  Volcanic  destructional.    Of  this  type  the  most  characteristic 
are  the  pit  craters,  or  the  more  or  less  circular  hollows  produced 
by  volcanic  explosions,  without  the  building  up  of  a  crater,  or  by 
subsidence.    The  Maare  of  the  Eifel  and  elsewhere  in  Germany  are 
typical  examples,  the  largest  of  this  type  being  the  Laacher  See, 
near  Coblenz,  with  a  diameter  of  a  mile  and  a  half  and  a  depth  of 
about  200  feet.    Other  examples  are  found  in  the  Auvergne.    Where 
the  surrounding  region  is  strewn  with  the  pyroclastic  ejectamenta, 
the  basin  may  be  regarded  as  due  to  explosion,  as  in  the  case  of  the 
Maare  of  the  Eifel  in  general.     In  other  cases  subsidence  after  the 
removal  of  rock  matter  below  may  be  the  cause  of  the  depression. 
Lake  Balaton   (Flatten  See)   in  Hungary  is  regarded  as  of  this 
type.     It  is  50  miles  long,  3  to  10  miles  wide  and  40  feet  deep. 

2.  Chemical  basins  of  the  destructional  type  include  (a)  solu- 
tion  basins,   where   limestone   or   gypsum   has   been   removed   by 
solution;  some  of  the  lakes  in  Florida  may  have  originated  in  this 
way.    Sink-holes,  due  to  caving-in  of  the  surface  over  caverns,  also 
belong  here.    These  are  common  in  limestone  regions.    Lakes  due  to 
solution  of  underground  salt  deposits  and  to  the  caving-in  of  the 
surface  are  also  of  this  type.     An  example  of  a  recently  formed 
lake  of  this  class  is  the  intensely  saline  Lake  Illyes  or  Medve  Lake, 
near  Szovata,  Hungary.     Temporary  solution  lakes  on  glacier  sur- 
faces must  also  be  included  in  this  group,     (b)  Decomposition  and 
disintegration  hollows.     These  are  of  little  significance,  since  they 
can  be  cleared  out  only  by  wind,  ice,  or  other  agency. 

3.  Fluviatile  destructional  basins  are  never  of  great  size,  for 
rivers  cannot  excavate  large  hollows,  their  chief  work  resulting  in 
free  drainage  channels.     Pot-holes,  however,  and  the  depressions 
gouged  out  by  retreating  waterfalls,  are  rock  basins  of  this  type. 
Pot-holes  are  mostly  small,  though  exceptional  cases  have  a  diameter 


DESTRUCTIONAL   LAKE    BASINS  123 

of  20  feet  and  a  depth  of  40  feet.  Waterfall  hollows  also  are 
limited  in  size.  At  Niagara  a  hollow  nearly  200  feet  deep,  over 
three  miles  in  length,  and  a  thousand  feet  or  more  broad  has  been 
gouged  out  by  the  Horseshoe  Falls.  When  Niagara  goes  dry,  this 
will  remain  as  a  lake.  A  typical  example  of  an  existing  lake  of 
this  type  is  Lake  Thaxter  of  the  St.  Croix  Dalles  region  in  Minne- 
sota. Along  the  course  of  most  rivers  are  deeper  reaches  which 
represent  stronger  scour,  and  these  may  be  converted  into  lakes. 
This  is  the  case  in  some  of  the  branches  of  the  Nile,  where,  during 
the  dry  season,  these  pools  contain  water.  In  old  river  courses 
like  that  of  the  Oxus,  an  affluent  of  the  Caspian,  and  the  old  course 
of  the  Huang-ho,  such  lakes  are  sometimes  a  characteristic  feature. 

4.  Glacial  rock  basins.    When  a  glacier  gouges  out  the  floor  of 
its  valley  above  the  mouth,  so  as  to  leave  the  frontal  rim  actually 
higher  than  some  other  parts  of  the  basin,  the  conditions  for  the 
formation  of  a  destructional  lake  basin  are-  furnished.     Such  lakes 
are  common  in  areas  of  recent  glaciation  and  many  of  the  lakes 
in  the  region  of  the  Pleistocenic  ice  sheet  invasion  owe  their  exist- 
ence partly  to  this  cause.     The  Finger  Lakes  of  New  York  are 
believed  to  be  in  part  glacial  rock-basins,  and  in  part  due  to  ob- 
struction. 

5.  Deflation  basins.     These  result  from  the  removal,  by  wind, 
of  sand  and  dust  from  a  disintegrating  surface,  in  such  manner  as  to 
leave  a  complete  rock  rim  surrounding  the  area  of  removal.    This 
area  will  be  deepened  to  the  extent  determined  by  the  power  of  the 
wind  to  remove  disintegrated  material.    Desert  basins,  in  so  far  as 
they  are  not  tectonic  depressions,  owe  their  character  to  this  agent, 
since  no  other  force  (excepting  man)  can  remove  soil  or  sand  from 
the  enclosed  basin.     Playa  lakes  may  occupy  temporarily  the  lower 
depressions  of  these  basins.     Hollows  excavated  by  wind  carrying 
sand,  though  insignificant,  should  nevertheless  be  mentioned. 

6.  Artificial  excavations.    These  are  included  for  completeness 
sake,  but  need  no  further  comment.     Mud  wallows,  on  the  other 
hand,  may  be  briefly  discussed.     In  desert  areas  where  elephants 
and  other  large  creatures  wallow  about  in  pools,  they  produce  hol- 
lows several  meters  deep.    Rains  washing  down  the  sandy  sides  of 
these  hollows  widen  the  area  affected.    Thus  if  the  hollow  left  after 
the  filling  is  still  i  meter  deep  its  diameter  may  be  25  in.    Continued 
wallowing  will  result  in  the  formation  of  a  depression  5  meters 
deep  and  120  to  150  meters  in  diameter,  such  as  are  found  in  abun- 
dance at  the  present  time  in  the  drier  districts.    Their  formation  by 
animal  erosion  is  often  observed  in  the  Kalahari  and  other  deserts. 

Where  salty  marl  surfaces  are  covered  by  sand,  these  retain 


124  PRINCIPLES    OF    STRATIGRAPHY 

the  moisture  to  which  the  buried  salt  surface  is  relatively  impervi- 
ous. Efflorescences  of  salt  on  the  surface  attract  herds  of  animals 
who  stamp  the  soil  jnto  powder,  which  then  is  carried  away  by 
wind.  Water  may  gather  in  the  resulting  shallow  depression,  and 
this  will  attract  more  animals,  and  by  their  trampling  of  the  soil 
and  the  deflation  of  the  material  large  hollows  are  formed,  which 
will  be  permanent  lakes  when  the  ground  water  level  is  reached. 
Such  lakelets  abound  in  the  northern  Kalahari.  Where  the  surface 
of  the  Kalahari  is  formed  by  a  porous  limestone  with  efflorescence 
of  salt,  it  is  broken  up  by  the  hoofs  of  animals  and  blown  away  by 
wind.  As  water  accumulates  in  the  shallow  depressions,  the  ani- 
mals coming  to  drink  trample  the  rock  into  fragments.  The  finest 
particles  are  separated  out  by  the  water  and  settle  as  a  layer  of  fine 
mud  which,  on  the  drying  of  the  pool  curls  up,  is  powdered  by  the 
hoofs  of  the  animals  and  blown  away  by  the  wind. 

In  a  region  where,  through  increasing  aridity,  vegetation  dies 
out,  the  roots  are  grubbed  after  by  animals,  which  thus  begin  the 
formation  of  a  hollow,  later  subject  to  enlargement. 


D.     Obstructional  or  barrier  basins. 

These  in  all  cases  arise  by  an  obstruction  or  dam  placed  across 
a  valley  which,  but  for  this  obstruction,  would  have  free  drainage. 
The  principal  types  are  the  following.  (Davis-7.)* 

1.  Tectonic  barrier  basins.    These  are  brought  about  by  warp- 
ing, by  folding,  or  by  faulting.     Warp  barrier  basins  are  produced 
by  the  deformation  of  an  entire  valley  area  by  warping  so  as  to 
reduce  it  from  its  continuous  slope  to  a  depression.     Lake  Ontario 
owes  its  existence  in  part  to  such  warping,  which  has  carried  the 
upper  part  of  the  ancient  river  valley  below  sea-level,  leaving  the 
lower    part    considerably    above    it.       (Grabau- 17:49.)       Valleys 
dammed  by  folding  are  not  uncommon  in  the  Alps.     Laggo  Mag- 
giore,  Lake  Lucerne  and  others  have  been  classed  here. 

2.  Volcanic  barrier  basins.    These  are  formed  by  the  growth  of 
volcanoes  so  as  to  cut  off  a  preexisting  valley,  or  by  the  damming 
of  such  a  valley  by  a  lava  flow.     Lake  Kivu  in  the  great  rift  valley 
of   Africa   is   a   good   example   of   the   first   type.     Formerly   this 
drained  northward  into  the  Albert  Edward  Nyanza  and  the  Albert 
Nyanza,   with   the   valleys   of   which   its   own   is   continuous.       A 
group  of  modern  volcanoes,  the  Mfumbiro  Mountains,  dammed  it 

*  Davis  includes  as  obstructional  many  of  those  here  classed  as  constructional, 
especially  the  detrital  section. 


OBSTRUCTIONAL    LAKE    BASINS 


125 


on  the  north  and  raised  its  level  2,000  feet,  until  it  began  to  over- 
flow southward  across  the  gneiss  rim  into  Lake  Tanganyika.  The1 
watershed  on  the  north  has  been  raised  by  these  (in  part)  still  active 
volcanoes  to  something  over  7,000  feet,  while  individual  peaks  of 
the  barrier  rise  to  great  altitudes,  the  peak  of  Karisimbi  reaching 
14,000  feet  and  being  often  snow-capped.  (Moore-26:#/.) 
(Fig.  21.)  The  valley  of  Lake  Kivu  is  of  tectonic  origin.  The 
extinct  Tertiary  Lake  Florissant  of  Colorado  was  due  to  a  lava 
dam.  Lakes  of  this  type  are  usually  long  lived.  Navahoe  Lake  of 
Utah  is  held  by  a  flow  of  scoriaceous  lava. 

3.     Chemical  (Hydrogenic)  or  tufa  barrier  basins  are  probably 
always  of  small  size.    Some  of  the  smaller  lakes  of  the  Yellowstone 


FIG.  21.  Sketch  of  Lake  Kivu  and  the  Mfumbiro  Mountains  of  Africa.  The 
lake  lies  in  the  great  rift  valley  of  Africa,  and  is  dammed  by 
volcanoes  of.  recent  origin.  (After  Moore.) 


region  appear  to  owe  their  existence,  in  part  at  least,  to  damming  of 
valleys  by  hot  springs  or  geyser  deposits.  The  Plitvicer  seas  of 
Croatia  are  small  lakes  in  a  Karst  valley  dammed  by  tufa  deposits. 
The  same  may  be  true  of  Lac  de  Brenets  of  the  French  Jura,  which 
has  a  depth  of  31.5  meters.  (Penck-28:  288.) 

4.  Ice  barrier  basins.  Of  these  the  Merjelen  See  in  Switzer- 
land is  the  best  known  existing  example.  An  example  of  one  now 
extinct  is  seen  in  Glen  Roy  (Agassiz-i  :jj)  in  the  Highlands  of 
Scotland.  Here  only  the  old  wave-cut  shore-lines  remain  in  the 
"Parallel  Roads,"  marking  the  successive  changes  in  level  of  the 
lake  which  was  held  up  by  the  glacier  occupying  the  valley  to  which 
Glen  Roy  is  tributary.  Ice  barrier  lakes  were  abundant  toward 
the  close  of  the  Pleistocenic  ice  age,  when  the  continental  glacier 
blocked  northward  draining  valleys  and  converted  them  into  tern- 


126  PRINCIPLES    OF    STRATIGRAPHY 

porary  lakes.  Examples  of  these  are  Lake  Agassiz  (Upham-4o) 
on  the  Minnesota-Canadian  border;  Lake  Passaic  (Salisbury-33) 
of  eastern  New  Jersey;  Lakes  Bouve  (Grabau-i6),  Charles  (Clapp- 
3),  Nashua  (Crosby-4),  etc.,  in  eastern  Massachusetts;  and  Lake 
Shaler  (Wilson-46)  in  the  Cape  Cod  region;  and  the  glacial 
Genesee  and  other  lakes  of  New  York  (Fairchild-i3).  Additional 
examples  are  found  in  Scotland,  Scandinavia,  the  north  of  Ger- 
many, etc.  Ice-barrier  lakes  are  as  a  rule  very  short-lived. 

5.  Organic  barriers.     The  growth  of  vegetal  material  at  the 
mouth  of  a  river  may  serve  directly  to  choke  drainage  and   so 
transform  the  district  into  a  lake,  and  indirectly  it  will  serve  this 
purpose  by  inviting  deposition  of  fine  detritus  where  the  current  is 
checked.    The  growth  of  coral  reefs  may  also  form  a  barrier  across 
an  indentation  of  the  shore,  which  may  then  be  transformed  into 
a  lake.     According  to  Davis   (7),  the  lakes  of  the  Everglades  in 
southern  Florida  are  examples  of  this  type. 

6.  Detrital  barrier  basins.     These  are  perhaps  the  most  com- 
mon barrier  basins,  and  to  them  by  far  the  largest  part  of  the 
barrier  lakes  now  existing  belong. 

(a)  Barrier  beach   basins.     A  barrier  beach  may  cut  of!  a 
valley  or  embayment  from  the  ocean  or  from  other  lakes  and  so 
convert  it  into  a  separate  lake  basin.     So  long  as  the  free  connec- 
tion with  the  parent  body  is  maintained,  so  that  water  flows  into 
the  new  basin  from  the  sea  or  lake  to  which  it  belongs,  it  cannot 
be  considered  distinct,  but  only  as  an  arm  of  the  parent  body.     In 
some  cases  the  opening  remaining  is  so  small  as  practically  to  pro- 
hibit the  entrance  of  the  water  from  the  parent  body.    This  seems 
to  be  largely  the  case  in  the  Frische  Haff  and  the  Kurische  Haff 
on   the   Prussian   coast    (2)  ;   and   to   a   large    extent   also   in   the 
Black  Sea.     Occasionally  the  cut-off  from  the  sea  becomes  brackish 
or  fresh,  as  in  the  case  of  some  ponds  along  the  Massachusetts 
coast,  and  those  of  the  coast  of  Pomerania,  while  in  others  exces- 
sive evaporation  may  cause  the  extinction  of  the  lake,  unless  the 
barrier  is  broken,  as  in  the  salt  lakes  of  Bessarabia  on  the  north- 
west coast  of  the  Black  Sea. 

(b)  Fan  delta  basins.     These  are  formed  by  the  damming  of  a 
valley  by  the  dry  delta  or  fan  of  a  tributary.     Lake  Pangkong  in 
the  Himalayas,  back  of  Kashmir,  represents  this  type.     Its  drain- 
age is  now  entirely  by  seepage,  the  water  being  slightly  brackish. 
Another  example  is  Tulare  Lake,  a  shallow  sheet  of  water  with 
indefinite  marshy  shores,  situated  along  the  San  Joaquin  River  in 
the  Valley  of  California.    The  upper  tributaries  of  this  stream  have 
been  ponded  back  by  the  alluvial  fan  of  King  River,  which  rises 


OBSTRUCTIONAL    LAKE    BASINS  127 

in  the  Sierra  Nevada  range.  Lakes  Brienz  and  Thun  are  divided 
by  a  delta  or  fan  on  which  Interlaken  stands,  and  other  examples 
are  found  in  the  Alps,  in  the  Mississippi  region,  and  elsewhere. 
Marginal  lakes  also  come  into  existence  when  the  main  stream 
aggrades  its  valley,  thus  damming  the  tributaries.  The  lakes  along 
the  Red  River  of  Louisiana  have  been  regarded  as  due  to  this 
process,  but  organic  accumulations  or  "rafts"  played  an  extensive 
part  in  the  ponding  of  the  tributaries.  (Veatch-44.)  These 
organic  accumulations  are  to  be  regarded  as  detrital  material,  just 
as  are  the  inorganic  materials  swept  together. 

(c)  Moraine   and    drift-barrier   basins.      These   are    numerous 
in  all  glaciated  regions,  but  are  generally  accompanied  by   some 
deepening  of  the  basin  through  glacial  scour.     This  is  the  condition 
of  many  of  the  Alpine  lakes  and  it  is  also  the  condition  of  the 
Finger  Lakes  of  New  York.     A  typical  example  of  a  drift  barrier 
lake  now  extinct  is  found  in  the  Upper  Genesee  valley  from  Por- 
tageville  southward.     This  was  dammed  by  drift  at  Portageville, 
and  the  resulting  lake  overflowed  southward  for  a  time,  until  a 
gorge  was  cut  through  the  rock  to  drain  the  waters  northward. 
The  drainage  here  was  originally  southward,  but  was  inverted  by 
depression  of  the  land  on  the  north.     Slight  glacial  overdeepening 
also  occurred.     (Fairchild-13  ;  Grabau-iQ.)     Drift  damming  accom- 
panied by  warping  is  shown  in  the  Great  Lakes  of  North  America. 
It  must  be  clearly  understood  that  only  lakes   formed  in  valleys 
dammed  by  drift  or  moraines  belong  to  this  class.     Lakes  formed 
in  depressions  in  the  drift  itself,  i.  e.,  kettle  lakes,  are  construc- 
tional, not  obstructional.     Morainal  lakes  are  generally  short-lived, 
although  those  blocked  by  great  drift  sheets  may  fairly  be  called 
permanent. 

(d)  A tmo clastic  barriers  are  either  land-slip  barriers  or  dune 
sand  barriers,     (i)   Land-slip  barriers  originate  when  a  landslide 
dams   a   mountain   valley.     They  are   mostly   short-lived,    for   the 
drainage  across  the  barrier  will  result  in  their   rapid  extinction. 
Lake    St.    Laurent,    10   kilometers    long,    in    the    Oisans,    western 
Alps,  was  created  by  a  land  slip  in  1181.     It  existed  about  40  years, 
during  which  period  the  farmers  of  the  valley  became  fishermen, 
and  it  was  destroyed  by  the  breaking  of  the  drift  dam.     (Reclus- 
29:5^.)     In  September,  1893,  a  great  landslide,  lasting  three  days 
and  bringing  down  800,000,000  'tons  of   rock,   dammed  the  deep 
valley  of  one  of  the  upper  branches  of  the  Ganges  in  the  Himalayas, 
150  miles  above  the  city  of  Hardwar,  which  lies  at  the  mouth  of 
the  valley.     The  dam  made  was  nearly  1,000  feet  deep  and  the 


128  PRINCIPLES    OF    STRATIGRAPHY 

lake  behind  it  grew  to  a  length  of  four  miles  before  it  overflowed, 
a  year  after  the  slide.  "The  flood  occurred  at  midnight,  August 
26-27,  1894.  In  four  hours  about  400,000,000  cubic  yards  of  water 
were  discharged,  cutting  down  the  dam  nearly  400  feet,  flooding 
the  valley  to  a  depth  of  from  100  to  170  feet,  and  rushing  forward 
with  a  velocity  of  20  miles  an  hour.  .  .  .  Every  vestige  of  habita- 
tion was  destroyed  in  villages  along  the  Ganges  above  Hardwar. 
But  so  well  was  the  notice  of  danger  given  that  only  one  man  lost 
his  life,  and  that  because  he  would  not  heed  the  warning."  (Davis- 
11:182,  183.)  (2)  Dune  sand  barriers  may  give  rise  to  marshes 
and  small  ponds,  and  more  rarely  to  lakes  of  some  size.  These 
will,  however,  rarely  be  deep,  for  seepage  will  keep  down  the 
level. 

(e)  Detrital  dams  built  by  organisms.  Dams  built  by  organisms 
of  detritus  are  typically  represented  by  beaver  dams,  and  by  the 
artificial  dams  built  by  man.  Neither  of  these  requires  more  than 
a  passing  notice. 


Classification  of  Lakes  as  a  Whole. 

From  a  bionomic  and  stratigraphic  point  of  view,  lakes  must  be 
classified  irrespective  of  the  origin  of  the  basin  in  which  they  are 
held.  The  most  natural  division  from  such  a  viewpoint  should  be 
based  on  the  -character  of  the  water,  for,  since  this  is  the  medium 
in  which  life  exists  or  sediments  are  deposited,  its  composition 
exercises  a  more  or  less  controlling  influence.  Waters  may  be 
classed  as  fresh,  salt  or  alkaline.  Fresh  waters  do  not  on  the  aver- 
age carry  much  over  0.2  part  per  thousand  of  dissolved  mineral 
matter,  of  which  only  about  2  per  cent,  is  sodium  chloride.  (See 
tables  in  Chapter  IV.)  With  an  increase  in  the  percentage  of 
sodium  chloride,  the  water  becomes  brackish  and  then  salt.  Alkaline 
waters  contain  a  large  percentage  of  alkali  carbonates.  Lakes  may 
next  be  divided  into  deep  lakes,  i.  e.,  those  in  which  an  abyssal  as 
well  as  a  littoral  region  is  distinguishable,  and  shallow  lakes,  those 
in  which  the  abyssal  district  is  wanting.  The  shallow  lakes  include 
permanent  and  temporary  ones,  the  latter  sometimes  being  ex- 
tremely shallow,  as  in  the  case  of  playa  lakes,  which  may  not 
exceed  six  inches  in  depth.  The*  presence  or  absence  of  an  outlet 
or  effluent  is  also  of  significance,  and  its  permanent  or  intermittent 
character,  when  marked,  must  be  considered.  These  features  may 
be  tabulated  as  follows: 


RIVERS  129 

Classification  of  Continental  Seas  or  Lakes. 

A.  Saline  (without  effluent). 

1.  Deep,  with  pelagic,  littoral,  and  abyssal  zones.      (Cas- 

pian, Dead  Sea.) 

2.  Shallow,  with  pelagic  and  littoral  zones.     (Aral,  Great 

Salt  Lake.) 

B.  Alkaline  (without  effluent). 

1.  Deep. 

2.  Shallow,  with  pelagic  and  littoral  zones.     (Albert  and 

Summer  Lakes,  Oregon;  Mono  Lake,  California,  etc.) 

C.  Fresh. 

1.  Without  effluent  or  with  only  temporary  one. 

a.  Deep,   with   pelagic,   littoral,   and   abyssal   zones. 

(Tanganyika.) 

b.  Shallow,  with  pelagic  and  littoral  zones.     (Eifeler 

Maare;    Silver    Lake,    Oregon;    Eagle    Lake, 
California;  many  ponds.) 

2.  With  effluent. 

a.  Deep,   with   pelagic,   littoral,   and   abyssal   zones. 

(Lake  Superior,  Lake   Nyassa,  Lake  Geneva, 
Lake  Baikal.) 

b.  Shallow,  with  pelagic  and  littoral  zones.     (Lake 

Erie;   most   of   the   fresh   water   lakes   of   the 
world.) 


IV.     RIVERS. 

In  the  genetic  classification  of  rivers  we  must  recognize  at  the 
outset  that  we  are  dealing  with  two  distinct  things,  the  rivers  them- 
selves and  their  drainage  basins.  Either  may  be  simple  or  compli- 
cated. A  simple  type  of  river  may  be  conceived  of  as  existing  in 
a  complicated  drainage  basin  (see  antecedent,  superimposed  con- 
sequents, and  consequents  on  a  peneplain  surface)  ;  or  the  reverse 
may  be  conceived  of,  a  complicated  (polygene)  river  existing  in  a 
drainage  basin  of  simple  structure,  as  on  a  coastal  plain.  Consid- 
ering rivers  alone,  we  may  class  them  with  reference  to  their 
development  as  simple  or  monogene  and  complicated  or  polygene; 
and  with  reference  to  their  relation  to  the  structure  of  the  region 
as  antecedent,  or  existing  before  the  structure,  and  postcedent, 
coming  into  existence  after  the  structure.  Most  rivers  belong  to 
the  latter  class.  Rivers  generally,  by  growth,  capture  and  the  acci- 


130  PRINCIPLES    OF    STRATIGRAPHY 

dents  brought  about  by  outside  agencies,  become  polygenetic,  i.  e., 
become  a  union  of  originally  separate  rivers,  but  all  of  them  begin 
as  simple  types. 

Simple  or  Monogene  Rivers. 

Five  simple  or  monogene  types  can  be  recognized.  I.  Conse- 
quent streams,  II.  Insequent  streams.  III.  Overflow  streams,  IV. 
Glacial  streams,  V.  Subterranean  streams. 

I.  Consequent  Streams.  These  are  the  streams  which  come 
into  existence  upon  a  new  land  surface.  Such  a  land  surface  may 
be  young  or  rejuvenated,  but  so  far  as  the  river  is  concerned,  it  is 
a  new  land.  The  mode  of  origin  may  be  A.  by  origination  (de 
novo),  B.  by  extension,  and  C.  by  inheritance.  In  all  cases  the 
consequent  is  distinguished  from  the  insequent  type  by  the  fact 
that  -it  starts  upon  a  sloping  land  surface  and  cuts  primarily 
downward  rather  than  headward,  although  this  latter  also  occurs. 
From  the  other  types  it  is  distinguished  by  not  having  primarily  a 
stored  supply  at  its  head,  as  in  the  overflow  river  from  a  lake,  or 
in  the  stream  supplied  by  the  melting  of  a  glacier.  Its  supply  of 
water  is  derived  from  the  run-off  and  the  ground  water. 

A.  Ne^vly  originated  consequents  may  be  classed  as  principal 
and  as  tributary,  the  former  entering  the  sea  or  receiving  basin 
direct,  the  others  being  tributary  to  other  consequents,  which  may 
,or  may  not  be  principal  ones.  Calling  the  principal  type  the  conse- 
quent of  the  first  order,  its  consequent  branches  would  be  those  of 
the  second  order,  their  consequent  branches  would  represent  the 
third  order,  and  so  forth.  These  streams  may  next  be  divided 
according  to  the  type  of  land  they  come  into  existence  on,  the  three 
types  being:  I.  Constructional  surface  consequents,  2.  Destruc- 
tional  surface  consequents,  and  3.  Deformational  surface  conse- 
quents. The  consequents  arising  on  constructional  surfaces  may 
be  divided  into  (a)  coastal  plain  consequents,  or  those  originating 
on  a  newly  emerged  coastal  plain,  elevated  by  purely  epeirogenic 
movements  of  the  land"  or  by  negative  eustatic  movements  of  the  sea, 
or  by  the  drainage  of  an  elevated  water  basin;  (b)  fan  delta  conse- 
quents, or  those  originating  on  dry  deltas  of  other  streams  or  on 
landslides;  (c)  moraine  and  till  surface  consequents,  or  those  com- 
ing into  existence  on  a  sloping  surface  of  deposition  of  glacial 
detritus;  and  (d)  lava  and  volcanic  cone  consequents,  or  those  orig- 
inating on  the  slopes  of  volcanoes  or  on  lava  flows.  Consequents 
arising  on  a  surface  of  destruction,  upon  simple  elevation,  are  almost 
wholly  represented  by  peneplain  consequents,  i.  e.,  those  developing 


CLASSIFICATION    OF   RIVERS  131 

on  an  uplifted,  slightly  tilted  peneplain  or  plain  of  subaerial  denuda- 
tion. Streams  originating  on  a  newly  ice-scoured  surface  may  be 
noted  as  of  this  class,  but  of  minor  importance.  If  surfaces  of  purely 
marine  denudation  are  of  sufficient  extent  to  have  streams  originate 
on  them  on  elevation,  these  would  also  be  classed  here.  Finally, 
consequents  arising  on  a  surface  of  deformation  include  several 
types :  those  formed  on  a  simple  dome,  those  formed  on  a  series  of 
anticlines  and  synclines,  and  those  formed  on  tilted  fault  blocks. 
In  the  first  case  we  have  radial  consequents  of  the  nth  +'i  order 
tributary  to  another  consequent  of  the  nth  order  which  may  be  the 
first  (principal  consequent)  or  any  higher  order.  In  rare  cases 
domes  of  deformation  rise  directly  out  of  the  sea,  when  the  radial 
consequents  are  of  the  first  order,  n  being  zero.  In  the  anticlinal 
and  synclinal  folds  we  have  transverse  consequents  flowing  down 
the  limbs  of  the  anticline,  and  longitudinal  consequents  flowing  in 
the  synclines.  The  first  belong  to  the  nth  +  i  order,  the  second  to 
the  nth.  In  exceptional  cases  a  transverse  consequent  may  flow  into 
the  sea,  the  shore  of  which  may  be  formed  by  an  anticline,  or  the 
syncline  may  be  filled  by  an  arm  of  the  sea  or  by  a  lake.  Conse- 
quents flowing  down  the  back  slopes  of  inclined  fault  blocks  are  in 
all  essentials  like  those  flowing  down  the  limbs  of  anticlines. 

B.  Extended  consequents  are  streams  of  an  older  type  which 
become  extended  across  the  newly  emerged  coastal  plain.     These 
streams  do  not  differ  from  those  originating  on  the  coastal  plain, 
except  in  their  greater  volume  of  water  and  hence  greater  erosive 
power.    They  will,  therefore,  cut  deeper  than  the  others,  becoming 
the  master  streams  of  their  respective  regions,  and  directing  to  a 
large  extent  the   further   development   of   their   drainage   system. 
Streams  extended  across  a  dry  delta  may  also  be  classed  here,  as 
are  those  extended  across  a  plain  of  glacial  deposition.     In  so  far 
as  the  older  part  of  the  stream  is  concerned  it  may  be  simple  or 
complex,  monogene  or  polygene. 

C.  Inherited  consequents.     These  are  consequents  which  are 
superimposed  upon  a  complex  terrane  by  learning  to  flow  upon  a 
coastal  plain  which  once  covered  the  complex  rocks,  and  which 
directed  the  course  of  the  river,  though  long  since  removed  by 
erosion.     Superimposed  consequents  are  believed  to  be  illustrated 
by  the  lower  courses  of  the  Housatonic  and  Connecticut  rivers  in 
southern  New  England.    The  coastal  plain  strata  which  apparently 
once  extended  over  this  area  have  been  entirely  removed  by  erosion. 
(Dodge-i2.)     The  coastal  plain  strata  may  be  replaced  by  layers  of 
volcanic  ash  (Gunnison  River),  by  drift,  by  river,  or  eolian  deposits, 
or,  in  exceptional  cases,  by  glacial  ice. 


132  PRINCIPLES    OF    STRATIGRAPHY 

II.  Insequent  Streams.    These  are  essentially  distinct  from  the 
preceding  type  in  that  they  originate  upon  the  side  of  a  preexisting 
valley  of  erosion  or  dislocation,  and  in  that  their  chief  mode  of 
development  is  by  headward  gnawing  instead  of  downward  cutting. 
Nevertheless,  there  are  times  when   it  might  be  difficult  to  dis- 
tinguish this  type   from  a   consequent   originating  on   an   erosion 
surface,  or  one  flowing  down  the  back-slope  of  a  fault  block.     For 
the  question  would  arise,  when  is  the  erosion  slope  steep  enough 
to  support  insequents  instead   of  tributary  consequents?     In  the 
case  of  the  fault  block,  we  may  consider  that  the  streams  on  the 
back  slope  are  consequents  and  those  on  the  fault  scarps  are  inse- 
quents.    Of  course  this  merely  emphasizes  the  fact  that  in  any 
natural  classification  of  inorganic,  as  well  as  of  organic  things,  sharp 
lines  do  not  exist,  but  the  classes  are  connected  by  gradations. 

Most  insequent  streams  are  classifiable  into  a.  erosion-bluff  and 
b.  fault-scarp  insequents.  The  former  comprise  ( i )  wave-cut  cliffs 
(marine  and  lacustrine),  (2)  river-cut  cliffs,  (3)  ice-cut  cliffs,  (4) 
wind-cut  cliffs,  and  (5)  artificially-cut  cliffs,  while  the  second 
includes  scarps  due  to  faulting  and  to  local  subsidences,  such  as 
kettle-holes  in  moraines,  etc.,  sink-holes  over  caverns  and  others. 
A  third  but  rare  type  c.  forms  on  the  margins  of  pit  or  explosion 
craters,  while  a  fourth  type  d.  is  seen  in  embankment  insequents, 
where  cliffs  of  construction  or  artificial  embankments  are  gullied. 
This  type  approaches  the  consequent  type  developed  on  dry  river 
deltas  or  alluvial  fans,  since  it  develops  on  a  constructional  surface. 

Simple  subsequent  streams.  Insequent  streams,  near  the  head 
of  a  coastal  plain,  may  open  out  a  lowland  parallel  to  the  strike  of 
the  strata  on  an  underlying  softer  substratum.  Such  enlarged 
insequents  have  been  termed  subsequents,  and  in  a  young  region 
these  may  be  of  simple  type.  In  most  cases,  however,  subsequents 
become  compound  through  capture.  Axial  subsequents  open  up 
longitudinal  valleys  on  the  crests  or  axes  of  anticlines,  and  by 
sliding  downward  occupy  the  monoclinal  valleys.  (See  chapter 
XXI.) 

Obsequent  streams.  These  are  insequents  peculiar  on  account 
of  their  location  on  the  inface  of  a  cuesta,  as  a  result  of  which 
their  course  is  in  an  opposite  direction  from  that  of  the  consequents. 
Rivers  on  the  fault  face  of  tilted  blocks  would  also  come  under  this 
category. 

III.  Overflow  Streams.     These  are  the  spillways  from  stand- 
ing water  bodies  and  as  such  include  all  effluents  of  lakes.     Such 
effluents  may  be  terminal,  carrying  the  waters  of  the  lake  directly 
to  the  sea  or  into  a  trunk  stream  which  flows  into  the  sea  without 


CLASSIFICATION    OF   RIVERS  133 

further  laking;  or  inter  lacustrine,  spilling  over  from  one  lake  into 
another.  The  St.  Lawrence  River  is  a  good  example  of  the  former 
type,  and  the  Niagara  of  the  latter.  Overflow  streams  are  charac- 
terized by  little  or  no  sediment,  this  being  all  left  behind  in  the 
lake.  They  may,  however,  pick  up  sediment  on  the  way  from  their 
bed  and  banks,  or  from  tributaries,  and  so  obtain  tools  for  erosion. 
Niagara  is  a  good  example  of  such  a  stream,  free  from  sediment  in 
its  upper  part  and  accomplishing  its  erosion  work  by  undermining 
at  the  cataract  and  drilling  on  the  floor. 

IV.  Glacial  Streams.    These  have  their  water  supplied  by  the 
melting  ice  mass,  which  also  furnishes  detrital  material.     Hence 
these  streams  are  distinct  from  all  others.     Streams  originating  on 
the  ice,  i.  e.,  superglacial  streams,  have  the  consequent  habit,  and 
might  be  classed  as  an  extreme  type  of  that  group.     But  sub- 
glacial  streams  are  unlike  all  others.     Their  peculiar  position  under 
the  ice  cover  and  subject  to  hydrostatic  pressure,  often  forces  them 
to  flow  across  obstacles  no  normal  river  could  surmount,  or  actually 
to  flow  for  a  part  of  their  course  uphill.     Such  abnormal  courses 
of  ancient  subglacial  streams  are  indicated  by  the  position  of  the 
eskers    which    they    have   built.     In    many    characters,    subglacial 
streams  approach  subterranean  streams. 

V.  Subterranean  Streams.    These  are  often  of  great  extent  and 
diversity,  following  enlarged  joints  in  limestone  strata,  and  forming 
caverns  along  their  paths,  which  are  subsequently  more  or   less 
filled  up  again  by  stalactic  deposits.     Underground  drainage  may 
develop  to  the  complete  absorption  of  surface  drainage,  giving  the 
peculiar  Karst  type  of  landscape  so  characteristic  of  the  west  side 
of   the  Balkan  peninsula,  and  also   seen  in  the   Barren   lands   of 
Kentucky  and  Tennessee,  in  the  plateau  of  the  Cevennes  in  southern 
France,  in  the  German  Jura,  and  in  many  other  regions.     (Cvijic-5; 
Neumayr-27  .-500-5/0.) 

Polygene  Rivers. 

Under  this  heading  may  be  grouped  the  three  types  denomi- 
nated by  Davis:  i.  compound  rivers,  2.  composite  rivers,  and  3. 
complex  rivers.  (Davis-8:/#j;  9:10^.)  Davis  defines  a  compound 
river  as  one  "which  is  of  different  ages  in  its  different  parts,"  and 
cites  as  examples  "certain  rivers  of  North  Carolina  which  have  old 
headwaters  rising  in  the  mountains  and  young  lower  courses  tra- 
versing the  coastal  plain."  These  are  the  extended  consequents  of 
our  classification.  The  term  should  be  made  to  cover  streams 
which  by  capture  have  enlarged  their  drainage  basin  at  the  expense 


134 


PRINCIPLES    OF    STRATIGRAPHY 


of  other  streams  Extended  consequents,  by  reason  of  their  greater 
water  supply,  are  apt  to  become  compound  or  at  least  their  principal 
branches  will  be  affected  in  this  manner.  This  is  especially  the  case 
with  the  subsequent  type  of  stream.  The  present  Moselle  of 
western  Europe  i&  an  example  of  a  compound  river,  having  ac- 
quired by  capture  some  of  the  headwaters  of  the  Meuse.  (Davis, 
10:229-230.)  (Figs.  22,  23.) 

A  composite  stream  is  defined  by  Davis  as  one  including  in  its 
basin,  drainage  areas  of  different  structure.    In  so  far  as  the  differ- 


Hypothetical    sketch    map  of    the 

Meuse      and      Moselle  rivers, 

France,  before  capture.  (After 
Davis.) 


FIG.  23.     Map  of  the  Meuse  and  the  I 
selle  after  capture.     (Davis. 


ence  in  structure  affects  the  stream,  causing  it  to  modify  its  course, 
this  definition  may  stand.  We  must,  however,  bear  in  mind  that  we 
are  dealing  with  two  distinct  things,  the  river  and  the  drainage 
basin.  A  simple  consequent  on  a  destructional  surface  (peneplain) 
or  a  superimposed  consequent  on  a  much  folded  older  terrane  may 
flow  across  regions  of  different  structure -in  different  parts,  i.  e., 
have  a  composite  drainage  basin  and  yet  be  of  simple  character. 

The  third  type  of  polygene  river  is  the  complex.  This  is  defined 
by  Davis  as  a  river  which  "has  entered  a  second  or  later  cycle  of 
development."  Rivers  inherited  by  an  uplifted  peneplain  from  the 
previous  cycle  are  typical  examples  of  this  class.  They  will  differ 
from  simple  consequents  upon  a  peneplain  in  that  they  have  ac- 


AGE    OF    RIVERS  135 

quired  a  meandering  course,  while  the  peneplain  was  low,  and  this 
will  be  in  a  large  measure  retained,  so  that  the  inherited  stream  will 
be  characterized  by  deeply  incised  meanders,  whereas  the  new  con- 
sequent will  generally  be  straight.  A  more  pronounced  complexity 
is  produced  when  by  warping,  partial  damming  and  division  a  river 
enters  locally  on  a  new  cycle,  while  other  parts  remain  compara- 
tively unchanged.  An  example  of  such  a  river  is  the  Genesee,  which 
at  present  occupies  the  valleys  of  two  formerly  distinct  streams  of 
diverse  origin.  This  is  really  the  case  with  the  St.  Lawrence  drain- 
age system  as  a  whole,  the  affluents  of  the  lakes,  which  belong  to 
this  system,  having  a  varied  history,  as  already  noted  in  the  case 
of  the  Genesee. 

RELATIVE  AGES  OF  RIVERS  AND  RIVER  SYSTEMS.  In  discussing 
the  relative  ages  of  rivers  and  river  systems,  we  must  distinguish 
between  the  age  of  the  river  or  river  system  and  the  age  of  the  dis- 
trict it  inhabits.  Thus  a  young  stream  may  exist  in  a  young  country, 
as  in  the  case  of  new  streams  on  a  young  coastal  plain,  or  it  may 
exist  in  a  mature  or  old  country.  The  age  -of  the  land  must  be 
considered  distinct  from  the  age  of  the  river.  (Johnson-2i.) 
Only  the  latter  will  be  considered  here.  Streams  are  classed  as 
young,  mature  and  old,  according  to  the  degree  of  their  develop- 
ment. No  conception  of  actual  time  is  involved,  for  of  two  rivers 
born  at  the  same  time  one  may  reach  maturity  while  the  other  is  still 
very  youthful.  Young  rivers  are  characterized  by  rapids  and  falls, 
and  by  steep-sided,  narrow  gorges.  Lakes  may  further  interrupt 
the  course  of  the  drainage.  A  river  is  mature  when  it  has  destroyed 
its  lakes  and  falls,  and  reduced  its  valley  sides  to  graded  slopes,  and 
broadened  its  floor  so  that  it  may  swing  upon  it  in  great  meanders. 
A  mature  river  is  able  to  carry  away  all  the  load  that  it  receives, 
but  generally  has  no  power  to  do  further  erosion.  A  river  system 
is  mature  when  all  the  branches  have  become  mature,  but  generally 
youthful  branches  are  found  long  after  the  trunk  stream  has  become 
mature.  Old  rivers  are  those  which  move  sluggishly  along  across 
a  flat,  much-encumbered  valley  bottom.  Their  grade  is  so  low  that 
they  cannot  carry  away  the  rock  waste,  and  so  they  aggrade  their 
beds,  or  stagger  about  in  them  by  avoidance  of  the  debris.  In  a 
river  system  the  main  stream  may  grow  old,  while  its  branches  are 
still  mature  or  even  youthful. 

Aging  of  Rivers  by  Accident.  Rivers  may  grow  old  rapidly 
through  various  accidents.  Among  these  are  mutilation,  sudden 
overloading,  and  drowning.  The  first  of  these  produces  perma- 
nent senescence,  and  may  be  compared  to  the  permanent  aging  of 
an  animal  body  through  a  severe  illness  or  accident.  The  second  is 


136  PRINCIPLES    OF    STRATIGRAPHY 

only  temporary,  for  as  soon  as  the  supply  ceases  the  river  will  re- 
vive and  begin  active  cutting  again.  This  may  be  compared  to  a 
temporary  depression  or  weakening  from  overwork,  which  pro- 
duces temporarily  a  weariness  akin  to  that  of  old  age,  but  from 
which  recovery  is  usually  certain,  on  cessation  of  the  excess  of 
work.  The  third'may  be  of  long  duration  with  ultimate  revival,  or 
it  may  lead  to  extinction.  It  may  be  compared  with  a  serious  ill- 
ness, from  which  recovery  is  doubtful. 

1.  Mutilation.     When  a  river  has  its  headwaters  or  branches 
cut  off  by  capture  or  diversion,  it  quickly  begins  to  age.     From  a 
youthful,  cutting  or  degrading  stream  it  changes  to  a  mature  one, 
where  graded  conditions  are  maintained.    By  further  reduction,  old 
age  is  reached,  when  the  river  begins  to  aggrade  its  valley,  by  drop- 
ping what  debris  is  brought  to  it.    The  river  Bar,  an  affluent  of  the 
Meuse,  is  such  an  old  river,  aged  by  mutilation,   which  resulted 
in  the  loss  of  its  headwaters.     It  now  staggers  through  a  debris- 
clogged   valley,   which   is   out   of   proportion   to   its   present    size. 
The  Meuse  itself  may  be  considered  at  least  a  submature  river, 
just  able  to  maintain  its  course,   which  in  this  case   means   cut- 
ting through  the  rising  ground,  which  is  equivalent  to   carrying 
away  all  the  debris  brought  to  it  without  cutting,  in  a  stationary 
region. 

2.  Sudden  overloading  of  a  mature  or  submarine  river  may  also 
produce  the  phenomena  of  old  age,  by  causing  the  river  to  aggrade 
its  floor.    This  may  occur  while  the  river  valley  is  still  a  long  way 
from  entering  upon  the  state  of  old  age.    The  gravel  terraces  of  the 
Allegheny,  Monongahela  and  other  Pennsylvania  rivers,  which  rise 
about  200  feet  above  the  present  stream  channel,  have  been  ex- 
plained as  remnants  of  high  flood-plains  due  to  aggrading  of  the 
valleys  by  the  overloaded  Allegheny  in  early  glacial  time.     The 
debris  was  largely  supplied  to  the  river  by  the  melting  ice.     Even 
the  tributary  streams  were  forced  to  aggrade  their  valleys  from  the 
mouth  upward.    Since  then  the  rivers  have  cut  down  again  through 
this  old  flood  plain,  leaving  the  terraces  on  either  side  to  mark  its 
former  elevation.      (Shaw,  35.)      Similar  examples  are   found  in 
New  England  rivers. 

3.  Drowning  of  rivers  also  brings  on  the  phenomena  of  old  age. 
This  drowning  may  be  due  to  overflow  of  a  lake  to  which  the  river 
is  affluent,  or  to  subsidence  of  the  coast  or  to  other  causes.     Ex- 
amples of  drowned  coastal  rivers  are  the  Hudson,  the  lower  St. 
Lawrence,  and  numerous  other  rivers  of  the  North  Atlantic  coast. 
No  erosion  is  accomplished  by  these  rivers ;  they  have  no  apprecia- 
ble current  of  their  own,  the  movements  of  the  water  being  regu- 


REVIVAL   OF   RIVERS  137 

lated  by  the  tides,  and  they  deposit  all  the  debris  furnished  to  them. 
They  are  justly  called  old  rivers,  though  their  old  age  is  premature, 
and  they  may  be  situated  in  young  valleys.  Partial  drowning  re- 
sults when,  through  damming  by  drift,  a  portion  of  a  river  valley  is 
converted  into  a  lake,  as  was  the  case  in  the  upper  Genesee  River. 
(Fairchild-i3.) 

Revival  and  Rejuvenation  of  Rivers.  Rivers  which  have  be- 
come prematurely  old,  or  which  have  grown  old  in  the  normal  cycle 
of  development,  may  be  revived  or  rejuvenated  by  an  uplift  of  the 
land  or  by  a  removal  of  the  cause  of  senescence.  The  overloaded 
stream  is  most  easily  revived  by  the  removal  of  the  cause  of  senes- 
cence, i.  e.,  the  excessive  supply  of  material.  This  is  better  spoken 
of  as  a  recovery.  Drowned  coastal  rivers  may  be  revived  by  eleva- 
tion until  they  have  again  reached  the  condition  prior  to  drowning. 
If  further  elevation  occurs  they  will  become  rejuvenated  and  enter 
upon  a  new  cycle  of  erosion  as  youthful  streams.  Partly  or  wholly 
drowned  rivers,  through  damming  by  drift  or  otherwise,  may  be  re- 
vived by  removal  of  the  dam,  or,  what  is  more  often  the  case, 
by  the  cutting  of  a  new  outlet.  This  will  result  in  a  complex  stream, 
in  which  the  outlet  portion  is  youthful,  while  the  rest  is  mature  or 
older.  The  narrow  gorges  with  rapids  and  waterfalls  connecting 
the  present  upper  and  lower  Genesee  valleys  are  examples  of 
young  connecting  portions  interpolated  between  revived  mature 
portions. 

Rivers  which  in  the  course  of  their  normal  development  have 
reached  a  state  of  old  age,  may  be  rejuvenated  by  a  favorable 
change  of  the  environment,  through  an  uplift  of  the  land,  or  a  low- 
ering of  the  base-level  of  erosion,  i.  e.,  the  local  level  to  which  ero- 
sion proceeds;  or  by  an  infusion  of  new  life,  in  the  case  of  certain 
rivers,  through  a  change  in  climatic  conditions,  which  will  greatly 
increase  the  amount  of  water,  and  hence  the  power  of  work  of  the 
stream.  The  Great  Falls  of  the  Missouri  in  eastern  Montana  occur 
in  a  rejuvenated  valley,  i.  e.,  a  valley  now  in  its  second  or  later 
cycle  (nth  -f-  i  cycle,  where  n  may  be  the  first  or  any  later  cycle). 
(Davis.)  The  rivers  of  the  Piedmont  district  of  Virginia,  and  all 
rivers  which  incised  themselves  into  uplifted  peneplains  which 
they  had  helped  to  make,  are  examples  of  rejuvenated  rivers,  now 
in  their  nth  -f-  i  cycle.  These  rivers  are  generally  characterized  by 
well-entrenched  meanders,  which  differ  strikingly  from  the  crooked 
curves  of  young  streams.  Such  meanders  are  shown  by  the  Seine  in 
the  Normandy  upland,  the  Moselle  and  the  Rhine  in  the  old  Rhine 
uplands  of  western  Germany,  the  Susquehanna  in  the  old  Appa- 
lachian upland,  and  by  many  other  streams. 


138  PRINCIPLES    OF    STRATIGRAPHY 

V.  UNDERGROUND  WATER  (GROUND  WATER). 

Ground  water  is  that  part  of  the  hydrosphere  enclosed  within 
the  pores  of  the  rock  of  the  earth's  crust,  and  either  circulating  by 
slow  movements  within  the  crust,  or  remaining  stagnant  within  its 
pores. 

Classification  of  Ground  Waters. 

According  to  the  mode  of  origin,  ground  water  may  be  divided 
into  three  types. 

A.  Meteoric  or  Pluvial  Waters,  or  those  derived  from  rain  or 
snow  and  penetrating  into  the  crust  from  above.     These  form  the 
vadose  circulation. 

B.  Connate   Waters,  or  those  buried  originally  with  the  sedi- 
ments in  which  they  occur,  and  varying  according  to  their  derivation 
from  fresh  to  marine  waters.     This  is  the  fossil  water,  and  to  be 
conserved  must  remain  stagnant  within  the  pores  of  the  rock. 

C.  Magmatic  or  Juvenile  Waters,  or  those  given  off  by  cooling 
magmas  and  in  a  sense  generated  anew  by  the  combining  of  gases 
from  the  igneous  mass. 

Some  observers,  notably  Van  Hise  and  his  followers,  would  re- 
gard all  ground  water  as  of  meteoric  origin,  and  consider  the  high 
temperature  and  mineral  content  of  such  waters,  originally  cool  and 
nearly  pure,  as  due  to  a  descent  into  regions  of  high  temperature 
within  the  depths  of  the  earth,  or  their  coming  in  contact  with 
heated  igneous  masses,  and  the  consequent  impartation  of  heat  and 
thermal  solvent  power,  so  that  both  their  temperature  and  mineral 
content  are  acquired  properties.  Other  workers  in  this  field,  notably 
Eduard  Suess  and  J.  F.  Kemp,  have  insisted  on  the  magmatic  ori- 
gin of  many  if  not  most  of  the  heated  and  mineral-laden  waters, 
the  temperature  and  mineral  content  of  which  are,  therefore,  pri- 
mary or  a  part  of  their  original  character.  It  is  this  class  of  waters 
which  is  believed  to  be  responsible  for  most  of  the  ore  deposits 
within  the  older  rocks,  and  to  such  an  origin  may  perhaps  also  be 
traced  most  of  the  hot  and  mineral  springs  of  the  present  day.  Re- 
cent experiments  at  Kilauea  have  resulted  in  the  actual  condensation 
of  water  from  gases  given  off  by  the  lavas. 

The  term  connate  waters  was  proposed  by  Lane  (24:50^),  who 
calls  attention  to  a  class  of  waters  which  has  been  much  neglected. 
Walther,  more  than  any  other  writer,  has  insisted  on  the  signifi- 
cance of  fossil  sea  waters  as  an  important  source  of  salts  concen- 
trated from  them  by  surface  agencies  under  arid  climatic  conditions. 


GROUND    WATER  139 

The  amount  of  such  water  preserved  in  the  rocks  depends,  of 
course,  on  the  volume  of  the  pore  space  (see  below,  p.  140), 
which  may  be  as  high  as  60%  of  the  volume  of  the  sediment,  though 
of  course  it  is  much  less  in  the  majority  of  clastic  deposits. 

Lane  has  called  attention  to  the  role  played  by  connate  waters  in 
preventing  the  downward  passage  of  the  meteoric  waters,  which 
will  tend  in  a  measure  to  dilute  some  of  these  stagnant  waters. 
While  the  meteoric  waters  circulate  freely  in  the  upper  zone  of 
the  earth's  crust  (the  belt  of  weathering),  the  zone  of  permanent 
ground  water  is  one  of  more  or  less  stagnation,  and  one  in  which 
deposition  of  the  mineral  matter  of  these  waters  in  the  pores  of  the 
rock  will  take  place.  We  have,  therefore,  beneath  the  zone  of 
weathering  and  free  circulation,  one  of  cementation,  and  thus  a 
barrier  to  the  further  downward  progress  of  the  meteoric  waters 
is  formed.  This  at  the  same  time  forms  a  barrier  against  the  es- 
cape of  the  imprisoned  connate  waters,  which  will  thus  be  con- 
served until  erosion  of  the  rocks  sets  them  free  once  more.  Lane 
was  led  by  such  considerations,  and  by  the  study  of  the  composition 
of  the  deep-seated  waters,  to  conclude  that  a  large  part  of  the 
ground  water  attributed  by  Van  Hise  and  others  to  a  meteoric  ori- 
gin was  in  reality  connate,  i.  e.,  the  imprisoned  water  of  former 
oceans. 

General  Course  of  Meteoric  Waters. 

Rain  falling  upon  the  land  is  disposed  of  in  several  ways.  A 
part  of  it  runs  off  down  the  slopes  (the  run-off),  a  part  sinks  into 
the  ground  (the  absorp),  and  a  part  evaporates,  returning  to  the  air 
(the  evaporate).  The  part  that  sinks  into  the  ground  becomes  the 
ground  water,  while  the  run-off  starts  the  development  of  surface 
drainage.  The  quantitative  relation  between  run-off,  evaporate  and 
absorp  depends  upon  (i)  the  character  of  the  surface,  i.  e.,  its 
topography  or  slope,  porosity  of  material,  state  of  saturation, 
amount  of  vegetable  covering,  etc.,  (2)  the  rate  of  rainfall  or  melt- 
ing of  snow,  and  (3)  the  subsequent  dryness  of  the  atmosphere, 
and  perhaps  other  local  features.  Very  porous  soil  holding  little 
water  will  greedily  absorb  the  rain  if  it  falls  not  too  heavily.  In 
this  latter  case  much  will  run  off,  as  the  rate  of  absorption  cannot 
keep  pace  with  the  rate  of  supply.  In  a  very  dry  atmosphere  much 
will  evaporate  before  it  has  time  to  sink  in,  while  much  more  will 
be  evaporated  from  the  upper  layers  of  the  soil  before  it  has  de- 
scended far,  or  will  be  taken  up  by  vegetation  to  be  ultimately  re- 
turned to  the  air. 


140  PRINCIPLES    OF    STRATIGRAPHY 

Porosity  of  Rocks. 

The  porosity  of  a  rock  or  soil  mass  is  determined  by  the  frac- 
tional part  of  the  mass  occupied  by  open  spaces  or  voids.  (Slichter- 
37:/d.)  If  a  cubic  foot  of  sandstone  holds,  on  saturation,  one- 
quarter  of  a  cubic  foot  of  water,  the  porosity  of  the  sandstone  is  25 
per  cent.  The  following  table  of  tests  made  by  Dr.  E.  R.  Buckley, 
State  Geologist  of  Wisconsin,  shows  the  variation  in  the  porosity  of 
various  building  stories  of  that  state: 


Kind  of  rock,  and  locality 


Average  porosity 

of  two  specimens 

per  cent. 


Granite  from  Montello,  Wis 

Granite  from  Berlin,  Wis 

Niagara  limestone  from  Marblehead,  Wis 

Sandstone,  Ableman,  Wis ; 

Niagara  limestone,  Wauwatosa,  Wis ._ 

Lower  Magnesian  limestone,  Bridgeport,  Wis 

Sandstone,  Ashland,  Wis 

Sandstone,  Dunville,  Wis 


0.237 

0.384 

0.770 

5.600 

6.400 

13.190 

20.700 

28.260 


The  porosity  of  quartz  sand  usually  varies  between  30  and  40 
per  cent.,  and  that  of  clay  loams  between  40  and  50  per  cent.,  de- 
pending on  the  variety  of  size  of  grains  in  the  mixture,  and  on  the 
manner  of  packing  the  particles.  (Slichter,  34,  p.  17.)  The  pore 
space  of  fresh,  strong  granite  varies  from  0.2  to  0.5  per  cent.,  the 
absorption  of  water  being  0.08  to  0.20  per  cent,  by  weight.  Ordi- 
nary compact  limestone  varies  from  2.5  to  12.5  per  cent,  (absorp- 
tion i  to  5  per  cent,  by  weight  of  water),  although  the  more  porous 
limestone  can  absorb  10  per  cent,  by  weight  of  water,  corresponding 
to  a  pore  space  of  25.0  per  cent.  The  more  compact  types  of  lime- 
stones, however,  fall  as  low  as  0.55  per  cent,  of  pore  space.  Sand- 
stones generally  have  a  pore  space  ranging  from  5  to  28  per  cent. 
Chalk  has  been  credited  with  the  ability  to  absorb  20  per  cent,  by 
weight  of  water  corresponding  to  a  pore  space  of  about  41  per  cent. 
(Van  Hise-43  :  125.)  The  pore  space  of  an  organic  limestone  from 
the^Gulf  of  Naples  was  over  35  per  cent.  (Walther),  while  recent 
sediments  of  the  Mississippi  delta  contained,  according  to  Hilgard, 
a  pore  space  ranging  from  23  to  61  per  cent.  The  actual  size  of  the 
grains  is  of  less  importance  in  influencing  the  porosity  of  the  mass 
than  the  variation  in  size  within  the  same  mass,  or  the  arrangement 


GROUND    WATER  141 

• 

or  mode,  of  packing.  Thus,  if  a  quantity  of  shot  be  poured  into  a 
glass,  and  the  quantity  of  water  required  to  fill  the  pores  be 
measured,  it  will  be  found  that  the  porosity  varies  greatly  if  different 
methods  be  used  in  filling  the  glass,  each  producing  a  different 
arrangement,  but  that  the  same  values  may  be  obtained  with  small 
shot  as  with  large.  (Slichter-37  :<?/.)  Slichter  has  determined  that 
the  minimum  porosity  of  a  mass  of  spheres,  packed'in  the  most  com- 
pact manner,  is  25.95  Per  cent-  of  the  whole  space  occupied  by  the 
spheres,  while  the  maximum  porosity  is  47.64  per  cent,  of  the  whole 
mass.  ( Slichter-38 ^95. ) 

The  pores  between  the  grains  are  both  larger  in  diameter  and 
shorter  in  length  for  a  packing  of  spheres  having  a  large  porosity 
than  they  are  for  a  packing  of  low  porosity.  As  already  noted, 
slight  variations  in  the  shape  of  the  grains  make  little  difference  in 
the  porosity  of  the  mass,  but  variations  in  size  within  the  mass 
make  a  great  difference.  Thus  a  mass  of  sand  of  uniform-sized 
grains  will  have  a  greater  porosity  than  one  in  which  the  grains 
vary  greatly.  Many  rocks  of  originally  great  porosity  have  suffered 
a  considerable  reduction  in  this  respect  by  the  filling  of  the  pores 
by  secondarily  introduced  mineral  matter. 

The  Water  Table. 

The  level  beneath  which  the  soil  is  completely  saturated  is  called 
the  level  of  groundwater,  or  the  water  table  or  water  plane.  This 
is  also  the  summit  plane  of  the  true  groundwater,  that  between  it 
and  the  surface  of  the  lithosphere  constituting  the  subsurface  water. 
This  latter  plays  an  important  part  in  the  influence  it  has  on  the  soil 
and  on  plant  growth. 

The  depth  of  the  water  table  varies  greatly  both  regionally  and 
seasonally.  Where  the  rainfall  is  heavy  it  usually  lies  only  a  few 
feet  below  the  surface,  but  in  arid  regions  its  depth  may  be  several 
hundred  feet.  In  general  the  surface  of  the  water  table  corre- 
sponds to  the  surface  of  the  land,  but  the  irregularities  are  less  pro- 
nounced (Fig.  24.)  Where  the  water  table  lies  deep,  it  can  be 
reached  only  by  deep  wells,  and  springs  are  wanting.  Where  it  co- 
incides with  the  surface  of  the  ground,  the  region  is  a  swamp  or 
marsh. 

Depth  and  Quantity  of  Ground  Water. 

According  to  Van  Hise  (42:595;  43:16*9),  at  a  depth  of  about 
6  miles  (about  10,000  meters)  below  the  surface,  the  rock  pressure 


142 


PRINCIPLES    OF    STRATIGRAPHY 


is  so  enormous  as  to  close  effectively  all  cavities  and  pores.  This 
is  the  limit  of  the  zone  of  rock  fracture,  the  zone  below  it  being 
that  of  rock  flowage.  This  is,  then,  the  depth  to  which  ground 
water  can  penetrate,  though  by  far  the  largest  quantity  exists  con- 
siderably above  this.  More  recently  the  experiments  of  Adams  and 
King  have  shown  that  pore  spaces  may  exist  at  greater  depths,  even 
down  to  eleven 'miles.  (Kemp-22.) 

Slichter,  assuming  that  the  geologic  limit  of  the  existence  of 
ground  water  is  at  an  average  depth  of  six  miles  below  the  surface 
of  the  land,  and  five  miles  below  the  floor  of  the  sea,  estimates  the 
entire  amount  of  ground  water  to  be  about  565,000  million  million 
cubic  yards,  or  about  430,000  million  million  cubic  meters.  This  is 
nearly  one-third  the  amount  of  the  water  of  the  sea  as  a  whole.  Ac- 


River 


Flood  plain 


FIG.  24.    Diagrammatic  section   illustrating  the  position  of  the  water  table. 
(After  Slichter.) 

cording  to  these  estimates  the  total  amount  of  ground  water  is  suffi- 
cient to  cover  the  entire  surface  of  the  earth  to  a  uniform  depth  of 
from  3,000  to  3,500  feet.  (Slichter-37.)  These  estimates  are 
based  on  the  selection  of  an  average  pore  space  for  all  rocks  of 
10  per  cent.,  which  Slichter  himself  regards  as  too  large  rather 
than  too  small. 

It  has,  however,  been  shown  by  Kemp  that,  according  to  the  ex- 
perience in  deep  mines,  ground  water  of  meteoric  origin  is  limited 
to  the  upper  1,000  feet  of  the  earth's  crust.  This  makes  the  total 
amount  of  ground  water  much  less  than  that  given  by  the  estimates 
above  cited.  Kemp  concludes  that  this  ground  water  is  sufficient 
to  cover  the  earth's  surface  with  a  layer  of  water  from  only  50  to 
loo  feet  deep.  Fuller  subsequently  made  more  close  calculations, 
concluding  therefrom  that  the  layer  of  water  would  be  96  feet  deep. 
(Fuller-i4:5p-7^.)  See  the  preliminary  discussion  on  pp.  4  and  5 
and  further  under  thermal  springs,  their  possible  relation  to  mag- 
matic  waters,  etc.  (pp.  200-203).  Finally  movements  of  ground 
water,  pp.  257-261. 


THE    HYDROSPHERE  143 

BIBLIOGRAPHY  III. 
(See  also  references  under  Chapters  II  and  IV.) 

1.  AGASSIZ,  LOUIS.     1876.     The  Parallel  Roads  of  Glen  Roy.     Geological 

Sketches.     2nd  series,  pp.  32-76. 

2.  BERENDT,  G.     1869.      Geologie  des  kurischen  Haffes,  Erlauterung  zu 

Section  2,  3,  4,  der  geologischen  Karte  von  Preussen,  Konigsberg. 

3.  CLAPP,  F.  C.     1902.     Geological  History  of  the  Charles  River  in  Massa- 

chusetts.    American  Geologist,  Vol.  XXIX,  pp.  218-233. 

4.  CROSBY,  WILLIAM  OTIS.     1899.     Geological  History  of  the  Nashua 

Valley    during    the    Tertiary    and    Quaternary    Periods..     Technology 
Quarterly,  Vol.  XII,  No.  4,  pp.  288-324,  4  plates. 

5.  CVIJIC,  J.     1893.     Das  Kartsphanomen.     Geographische  Abhandlungen, 

Vol.  Ill,  Wien. 

6.  DANA,  JAMES  D.     1872.     Corals  and  Coral  Islands. 

7.  DAVIS,  WILLIAM  MORRIS.     1882.     On  the  Classification  of  Lake  Ba- 

sins.    Proceedings   of   the   Boston   Society   of   Natural    History,    Vol. 

xxi,  pp.  315-381. 

8.  DAVIS,  W.  M.     1889.     The  Rivers  and  Valleys  of  Pennsylvania.     Nation- 

al Geographic  Magazine,  Washington,  Vol.  I,  pp.  183-253. 

9.  DAVIS,  W.  M.     1890.     The  Rivers  of  Northern  New  Jersey  with  Notes 

on  the  Classification  of  Rivers  in  General.     Ibid.,  Vol.  II,  pp.  81-110. 

10.  DAVIS,  W.  M.     1896.     The  Seine,  the  Meuse,  and  the  Moselle.     Ibid., 

Vol.  VII,  pp.  189-238. 

11.  DAVIS,  W.  M.     1899.     Physical  Geography.     Boston,  Ginn  and  Com- 

pany. 

12.  DODGE,     R.     E.,    and    others.     1902.     Physiography.     United    States 

Geological  Survey,  New  York  City  Folio.     No.  83. 

13.  FAIRCHILD,    H.    L.     1899.     Glacial   Genesee   Lakes.     Bulletin   of   the 

Geological  Society  of  America,  Vol.  X,  pp.  27-68. 

14.  FULLER,  MYRON  L.     1906.     Total  Amount  of  Free  Water  in  the  Earth's 

Crust.     Water  Supply  and  Irrigation  Paper,  No.  160.     United  States 
Geological  Survey. 

15.  GILBERT,   G.   K.     1890.     Lake   Bonneville.     United   States  Geological 

Survey  Monograph,  Vol.  I. 

16.  GRABAU,    AMADEUS    WILLIAM.     1900.     Lake    Bouve,    an    Extinct 

Glacial  Lake  in  the  Boston  Basin.     Occasional  Papers  of  the  Boston 
Society  of  Natural  History,  Vol.  IV,  Pt.  Ill,  pp.  564-600,  map. 

17.  GRABAU,  A.  W.     1901.     Geology  and  Palaeontology  of  Niagara  Falls  and 

Vicinity.     Bulletin  of  the  New  York  State  Museum  of  Natural  History, 
No.  45,  Vol.  IX. 

1 8.  GRABAU,    A.    W.     1907.     The    Geographical    Classification   of    Marine 

Life  Districts.     Science,  N.  S.     Vol.  XXV,  NO.  631,  p.  185.     Feb.  i, 
1907. 

19.  GRABAU,  A.  W.     1908.     Preglacial  Drainage  in  Central  Western  New 

York.     Science,  N.  S.,  Vol.  XXVIII,  No.  720,  pp.  527-534. 

20.  HAGUE,  ARNOLD.     1912.     Origin  of  Thermal  Waters  of  Yellowstone. 

Bulletin  of  the  Geological  Society  of  America,  Vol.  XXII,  No.  i,  pp. 

IO2-I22. 

21.  JOHNSON,   DOUGLAS  W.     1905.     Youth,   Maturity  and  Old  Age  of 

Topographic  Forms.     American  Geographical  Society,  Bulletin  XXXVII, 
pp.  648-653;  3  figs. 


i44  PRINCIPLES    OF    STRATIGRAPHY 

22.  KEMP,  JAMES  F.     1913.     The  Ground  Waters.     Transactions  of  the 

American  Institute  of  Mining  Engineers,  pp.  603-624. 

23.  KRUMMEL,  OTTO.     1907.     Handbuch  der  Ozeanographie,  Band  I. 

24.  LANE,  ALFRED  C.     1909.     Mine  Waters  and  Their  Field  Assay.     Bulle- 

tin of  the  Geological  Society  of  America,  Vol.  XIX,  pp.  501-512. 

25.  LINCOLN,   F.    C.     1907.     Magmatic   Emanations.     Economic   Geology. 

Vol.  II,  pp.  258-274. 

26.  MOO^-E,  J.  E.  S.     1903.     The  Tanganyika  Problem.     London. 

27.  NEUMAYR,  MELCHIOR.     1895.     Erdgeschichte,  Vol.  I.     Leipzig  und 

Wien. 

28.  PENCK,  ALBRECHT.     1894.     Morphologic  der  Erdoberflache.     Vol.  I. 

29.  RECLUS,  JEAN  JACQUES  ELISEE.     1867.     La  Terre,  Vol.  I. 

30.  RUSSELL,  ISRAEL  COOK.     1885.     Geological  History  of  Lake  Lahon- 

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31.  RUSSELL,  I.  C.     1890.     Notes  on  the  Surface  Geology  of  Alaska.     Bul- 

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33.  SALISBURY,   ROLLIN   D.     1907.     Physiography.     New  York,    Henry 

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34.  SALISBURY,  R.  D.,  and  others.     1902.     The  Glacial  Geology  of  New  Jer- 

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CHAPTER    IV. 

COMPOSITION    AND    PHYSICAL    CHARACTERS    OF    THE    HYDRO- 
SPHERE. 

COMPOSITION    OF   THE    HYDROSPHERE. 

The  hydrosphere  is  never  pure  H2O,  but  always  includes  dis- 
solved salts  and  gases.  The  former  are  most  abundant  in  sea  wa- 
ter and  in  the  waters  of  salt  lakes,  the  latter  in  some  underground 
waters.  The  composition  of  the  larger  divisions  of  the  hydrosphere, 
the  oceans  and  the  intracontinental  seas,  the  lakes,  rivers  and 
ground  water,  will  be  considered  in  turn.  The  totality  of  dissolved 
salts  constitutes  the  salinity  of  the  water,  though  in  the  open  sea 
less  than  80  per  cent,  of  this  is  common  salt  (NaCl).  The  totality 
of  mineral  matter  is  determined  in  parts  (by  weight)  per  1,000 
parts  of  water,  or  the  number  of  grams  in  1,000  grams  (i  liter)  of 
water.  This  amount  is  expressed  as  so  many  permille  (°/00)  of 
salts.  Thus  a  salinity  of  35  permille  exists  when  each  1,000  grams 
(or  approximately  each  liter)  of  sea  water  contain  35  grams  of 
salts,  as  in  average  ocean  water.  (For  details  and  corrections  of 
method  see  Krummel-2o:  221-222.) 


I.  SALINITY  OF  THE  SEA. 

The  salinity  of  the  sea  as  a  whole  has  been  calculated  at  34.49 
permille,  but  that  of.  individual  divisions  varies  greatly.  The  fol- 
lowing table  adapted  from  Krummel  gives  the  mean  surface  salinity 
for  the  principal  divisions,  to  which  is  added  the  mean  salinity  of 
the  entire  volume.  (Krummel-2o :  333,  361.) 

The  seven  important  elements  which  form  most  of  the  salts  con- 
tained in  solution  in  the  sea  water  are:  Chlorine  (Cl),  Bromine 
(Br),  Sulphur  (S),  Potassium  (K),  Sodium  (Na),  Calcium  (Ca), 
and  Magnesium  (Mg). 


146 


PRINCIPLES    OF    STRATIGRAPHY 
Table  Showing  the  Salinity  of  the  Sea. 


Surface 
salinity 
in 
permille 

Mean 
total 
temperature 
C.  degrees 

Volume 
salinity 
in 
permille 

A.     OCEANS. 
I      Atlantic  Ocean  

35.  37 

4.02 

2      Indian  Ocean 

74  8l 

3  82 

3      Pacific  Ocean                                   .    . 

74  QI 

^   7^ 

Average  for  the  three  large  oceans 
(or  3  5  per  cent   by  weight) 

7C    O3 

3  83 

4      Arctic  Ocean                   

25.  50  (?) 

—  0.66 

34  80 

B.     MEDITERRANEANS. 
a.     Land  Locked. 

e      Roman  mediterranean 

74    85 

13    35 

^6  10 

6.     Red  Sea  mediterranean  
7      Mexican  mediterranean.  ...          .  "1 

38.80 

22.69 

39.00 

8.     Yucatan  mediterranean  r 

35-95 

6.60 

35.30 

9.     Caribbean  mediterranean  J 
10      Black  Sea  mediterranean  

18.30 

22.04 

b.     Marginal. 
1  1      Austral-  Asian  group  . 

33.87 

6.9O 

34.00 

12.     Andamanian  mediterranean  

31  .50 

IO.O9 

33.00 

13.     East  Chinese  mediterranean  

32.10 

9.29 

34.00 

14      Japanese  mediterranean  

34.  10 

0.90 

34.00 

15.     Okhotsk  mediterranean  
1  6      Behring  Sea  mediterranean 

30.90 
30.30 

1.50 
2  .OO 

33-50 
32.00 

C.    EPICONTINENTAL  SEAS. 
a.     Land  Locked. 

17      Hudson  Bay  .  .    .  .            

26.00  (?) 

1.  00  (?) 

30.00  (?) 

18.     Baltic  Sea  

7.80 

3.91 

10.00 

19      Persian  Gulf 

36.70 

24.00 

37.00 

20.     Sea  of  Azov  

b.     Marginal. 
21      British  group 

10.50-10.70 

34  80 

0.77 

10.50-10.70 
35.00 

22.     North  Sea  

34.2O 

7.72 

35.00 

23      Tasmanian  Sea 

35.  SO 

12    5O 

35-  5O 

D.     FUNNEL  SEAS. 
24      Californian  funnel  sea      .          

35    5O 

9.  12 

35.50 

25.     Laurentian  funnel  sea  

3O.  5O 

2.18 

33-00 

COMPOSITION    OF    SEA    WATER 


147 


From  a  total  of  77  very  complete  analyses  of  samples  of  ocean 
water  obtained  by  the  Challenger  Expedition,  Dittmar  (2: 189,  204; 
Krummel-2O : 219)  has  calculated  the  following  average  composi- 
tion of*  the  salt  content  of  the  sea.  The  calculations  are  in  percent- 
ages of  the  total  solids,  in  grams  per  thousand  grams  of  sea  water 
(permille)  and  in  British  tons  per  cubic  mile  of  sea  water.  The 
total  of  the  solids  is  taken  at  35  permille,  or  3.5  per  cent,  by  weight 
of  the  sea  water.  The  earliest  calculations  of  Forchhammer  (7), 


+J 

I 

& 

3 

•a  g^ 

^    C    w 

§,s  • 

! 

I 

a 

-8  2  6 

rt    M  g 

VH     j-j     W)       . 

sl 

1 

O 

4J 

c    . 

£'~  §! 

ri  . 

"3 

£ 

D    tn 

'1  s°  ^  ^ 

•«  .y  <3 

* 

& 

I1 

i1*1 

S  *§  « 

i    Sodium  chloride  (NaCl)  

c8  5 

2    17 

77  7c8 

117,434,000 

2.  Magnesium  chloride  (MgCl2)  . 

O"  •  O 

95-3 

/ 

2.18 

/  /  •  /  O 

10.878 

3.807 

16,428,000 

3.  Magnesium  sulphate  (MgSO) 

120.4 

2.65 

4-737 

1.658 

7,154,000 

4.  Calcium  sulphate  (CaSO4)  .  .  . 

136.1 

2.97 

3.600 

1.260 

5,437,000 

5.  Potassium  sulphate  (K2SO  )  .  . 

174.  i 

2    4.6^ 

o  86^ 

7  727  OOO 

6.  Calcium  carbonate  (CaCO,)f. 

/  rr  • 
100.  0 

2.72 

*    .  i|.V^^ 

0-345 

*f"O 

0.123 

O  >  /     w  I  v-'v/vy 

521,000 

7.  Magnesium  bromide  (MgBr2)  . 

184-3 

0.217 

0.076 

328,000 

Total  

IOO.OOO 

35  .000 

151,025,000 

based  on  more  than  150  analyses  of  sea  water,  gave :  NaCl  78.32% 
of  the  total  solids,  or  a  salinity  of  26.862  permille;  MgCL,  9.44%, 
or  3.239  permille;  MgSO4,  6.4.0%,  or  2.196  permille  ;  CaSO4,  3.94%, 
or  1.350  permille.  The  K  is  calculated  as  KC1,  1.69%  of  the 
total  solids,  or  a  salinity  of  0.582  permille,  no  K2SO4,  MgBr2 
or  CaCO3  being  given.  A  residue  of  0.21%  or  0.070  permille 
is  left,  making  a  total  of  100%  solids,  or  a  salinity  of  34.299 
permille. 

Calculated  in  percentages-  of  ions,  we  have  (Tolman-39)  : 

*  One  British  ton  equals  2,240  pounds  avoirdupois;  one  metric  ton  equals 
i, ooo  kilograms,  or  2,204.6  pounds  avoirdupois.  One  cubic  mile  of  sea  water 
(density  1.026)  weighs  4,315,000,000  tons. 

f  Including  all  traces  of  other  salts,. 


148  PRINCIPLES    OF    STRATIGRAPHY 

Per  cent.  Grams  per  liter.* 

Cl 55-292  19 . 68 

Br o.i  88  0.07 

SO4 7.692  2.74 

CO3 o .  207  o .  08  ' 

Na 30-593  10-89 

K 1.105  0.40 

Mg.., 3-725  i-33 

Ca i  .197  0.43 


99-999  35-62 


Besides  the  predominating  seven  elements  in  the  sea,  there  are 
traces  of  numerous  others,  the  quantity  of  which,  precipitated  as  salts 
in  the  evaporation,  are  figured  in  the  above  table  of  Dittmar  with  the 
calcium  carbonate.  The  following  additional  elements  have  been  de- 
tected (for  details  see  Krummel--2O : 216,  218)  :  Aluminium  (Al), 
Arsenic  (As),  Barium  (Ba),  Boron  (B),  Caesium  (Ce),  Cobalt 
(Co),  Copper  (Cu),  Fluorine  (F),  Gold  (Au),  Iodine  (I),  Iron 
(Fe),  Lead  (Pb),  Lithium  (Li),  Manganese  (Mn),  Nickel  (Ni), 
Phosphorus  (P),  Rubidium  (R),  Silicon  (Si),  Silver  (Ag), 
Strontium  (Sr),  Zinc  (Zn),  together  with  dissolved  Oxygen  (O), 
Nitrogen  (N),  and  Carbon  dioxide  (CO2),%the  latter  estimated  at 
1 8  times  the  amount  contained  in  the  atmosphere.  (Chamberlin 
and  Salisbury-3  :  5^5) . 

The  weight  of  the  sea  water,  as  a  whole,  being  taken  at 
138  X  IOIG  metric  tons  (Chapter  I,  p.  3),  and  the  average  per- 
centage of  salts  by  weight  as  3.5,  we  obtain  for  the  total  amount  of 
salt  in  the  sea  the  product  of  4.84  X  iolc  metric  tons.  The  volume 
of  salt,  resulting  from  a  complete  evaporation  of  the  oceans,  would 
depend  on  the  average  specific  gravity  of  the  salt,  which  may  be 

4.84 
taken  at  2.22.    This  would  give  us X  io36  or  2.18  X  io16  cubic 

meters,  or  21.8  million  cubic  kilometers,  a  quantity  sufficient,  if 
spread  over  a  level  sea  bottom  of  361  million  square  kilometers,  to 
make  a  layer  more  than  60  meters  thick.  Of  this  47.5  meters  would 
represent  sodium  chloride  or  common  salt,  5.8  meters  magnesium 
chloride,  3.9  meters  would  represent  magnesium  sulphate,  2.2 
meters  calcium  sulphate,  and  0.6  meter  the  remaining  salts.  The 
total  quantity  of  salts  forms  a  mass  three  times  as  great  as  the  con- 
tinent of  Europe,  or  a  little  more  than  half  the  volume  of  land  in 
Asia,  which  has  41.6  million  cubic  kilometers. 

*  With  the  average  salinity  taken  as  35.6  permille. 


COMPOSITION    OF    SEA    WATER  149 

Variation  in  the  Distribution  of  the  Salt  Content  of  the  Oceans  and 
Intracontinental  Seas. 

The  distribution  of  salts  in  the  surface  layers  of  the  oceans 
varies  with  the  degrees  of  latitude.  Thus,  for  the  Atlantic  it  is 
32.80  permille  between  70°  and  65°  N.  lat.  (Schott-36:  -?//).  It  in- 
creases to  37.00  permille  between  30°  and  20°  N.  lat.,  and  decreases 
to  35.07  permille  at  the  equator.  Then  it  increases  again  to  36.52 
permille  between  20°  and  25°  S.  lat.,  after  which  it  decreases  to 
33  permille  at  70°  S.  lat.  There  are  thus  two  maxima  in  the  At- 
lantic. In  the  Pacific  we  have  a  salinity  of  31.72  permille  at  60° 
N.  lat.,  increasing  to  35.42  permille  between  30°  and  25°  N.  lat., 
and  decreasing  again  to  34:36  permille  at  10°  north  of  the  equator. 
Then  it  increases  to  its  second  maximum  of  36.18  permille  between 
15°  and  20°  S.  lat.,  after  which  it  decreases  again  to  33.00  permille 
at  70°  S.  lat.  In  the  Indian  Ocean  the  first  maximum  of  35.37  per- 
mille lies  near  the  equator,  and  the  second  between  25°  and  30°  S. 
lat.  (35.88  permille).  The  minimum  of  34.55  permille  between  these 
two  lies  about  10°  south  of  the  equator.  Southward  the  decrease  is 
similar  to  that  in  the  other  oceans,  to  33  permille  at  70°  S.  lat. ;  but 
northward  from  the  equator  the  change  is  oscillatory.  (Kriim- 
mel-2o:  334.)  The  causes  of  this  variation  are  to  be  sought  chiefly 
in  the  varying  rate  of  evaporation  from  the  surface  of  the  ocean, 
and  the  consequent  increase  in  salinity.  Evaporation  is  a  func- 
tion of  the  temperature,  wind  velocity  and  relative  humidity. 
( Schott-36 :  218. )  Opposing  factors  are  the  amount  of  precipi- 
tation, and  the  addition  of  fresh  water  by  streams,  melting  ice- 
bergs, etc.  Displacement  of  waters  of  a  certain  salinity  through 
currents  also  must  be  considered.  The  following  table  gives  the  re- 
sults of  Marzelles'  experiments  in  this  direction  ( Schott-36 :  218)  : 

I.  Average  evaporation  in  24  hours  with  varying  temperatures 
without  considering  wind  velocity  or  humidity. 

At    i°  C 0.80  mm.     At  19°  C ...1.52  mm. 

At  11°  C 0.97  mm.     At  27°  C 2.96  mm. 

II.  Evaporation  in  24  hours  with  the  temperature  of  the  air 
about  20°  C.  and  varying  wind  velocity. 

With  velocity  of    0.3  meter  per  second 1.21  mm. 

With  velocity  of    4.2  meters  per  second i .  90  mm. 

With  velocity  of    7.5  meters  per  second 2.97  mm. 

With  velocity  of  10.3  meters  per  second 4.01  mm. 


150  PRINCIPLES    OF    STRATIGRAPHY 

III.  Evaporation  in  24  hours  with  varying  humidity  and  a  tem- 
perature of  the  air  of  20°  C. 

Relative  humidity  81-85  % I  •  23 

Relative  humidity  71-75  % i .  44 

Relative  humidity  61-65  % 2  •  °6 

Relative  Jiumidity  5 1-55  % 2 . 66 

Relative  humidity  41-45  % 2.97 

Experiments  by  Schott  have  given  the  following  results  in  con- 
centration of  normal  sea  water  through  evaporation  at  a  tempera- 
ture of  the  air  ranging  around  25°  C.  and  an  average  velocity  of  the 
wind  of  7.5  meters  per  second.  The  measurements  were  made  on 
the  Atlantic  from  the  5th  to  the  8th  of  September,  1892,  at  8  o'clock 
each  morning,  on  10  liters  of  sea  water,  in  a  vessel  giving  600 
square  centimeters  surface,  and  fully  exposed  to  the  wind. 

Salinity  Height  of  water 

Date  (8  A.  M.)  permille  column  in  cm.    Volume  c.  c. 

Sept.  5 36.3  16.5  10.000 

Sept.  6 38.5  16.2 

Sept.  7 40.3  15.9 

Sept.  8 42.1  15.6  9.360 

Thus  in  three  days  the  decrease  in  volume  was  about  6  per  cent., 
while  the  increase  in  salinity  was  nearly  6  permille. 

B at hy metric  Variation.  Besides  the  regional  variation,  there  is 
a  bathymetric  variation  in  the  different  water  bodies.  In  rare  cases 
is  the  salinity  uniform  throughout  (homalinc);  it  is  commonly  vari- 
able (heterohaline).  A  decreasing  salinity  downward  constitutes  an 
anohaline  arrangement  (ah)  ;  an  increasing  one  is  a  katohaline 
(kh)  condition.  A  decreasing  followed  by  an  increasing  salinity 
downward  constitutes  a  dichohaline  (dh)  condition,  while  the  re- 
verse, an  increasing  followed  by  a  decreasing  salinity  downward, 
constitutes  a  mesohaline  condition  (nih),  the  most  saline  layers  being 
in  the  middle.  (Krummel,  20:554.)  These  relations  may  be  sum- 
marized graphically  as  follows : 

Decreasing  Increasing 

salinity  salinity 

Homohaline    J 

C  Anohaline      ,/  &'  ff 

Katohaline    .  .   \  cu  C 

Heterohaline  i  T\»  t_  t_  V*  f>  3 

Dichohaline /  ^  & 

[  Mesohaline \  &  ™ 


COMPOSITION    OF    SEA    WATER  151 

The  following  table  copied  from  Krummel  shows  the  variation 
in  salinity  with  depth,  and  the  seasonal  variations  in  the  Bay  of 
Danzig  on  the  southern  border  of  the  Baltic.  (20 :  J5J.) 


Variation  in  Salinity.  Bay  of  Danzig,  1902-1906. 


Depth  in  meters.  .  .  . 

0 

10 

20 

30 

40 

50 

75 

105 

February  

7.  1O 

7.  11 

7-  ^i 

7-  ^4 

7.  12 

7.16 

7.86 

II    17 

May 

7    I  ^ 

7    1^ 

7    10 

7    2Q 

7   ^ 

7    ^.^i 

8   04 

II    72 

August  

7    22 

7.2^ 

7.21 

7.20 

7.26 

7   11 

7   QQ 

1  1    QQ 

November  

7.2A 

7.21 

7.2^ 

7.21 

7.26 

7.27 

Q.  17 

II    74 

Average  

7.22 

7.22 

7.24 

7.26 

7.29 

7-32 

8.49 

11.66 

In  the  Arctic  Ocean  the  variation  in  the  salt  content  has  been 
found  by  the  Fram  to  average  as  follows  ( Krummel-20 : 


Depth  in  meters: 

o 

40 

250 

45° 

1,000  .  . 

2,000 


3,000 


Parts  per  1,000 

by  weight 

21 .00 

33-26 

34-97 
35-02 

35-07 
35-oS 
35-12 


The  increase  is  rapid  at  first  owing  to  the  fact  that  the  surface 
strata  are  diluted  by  river  waters  and  melting  ice.  A  slight  irregu- 
larity is  shown  by  the  fact  that  at  one  locality  the  salt  content  was 
35.19  at  2,500  meters'  depth.  In  the  East  Greenland  Mediterranean 
Sea,  between  Spitzbergen  and  the  Faroe  Islands,  the  bottom  layers, 
below  800  or  1,000  meters  in  depth,  have  a  homohaline  character, 
the  salinity  being  34.91  permille.  A  homothermal  character  of 
-  1.2°  C.  also  prevails.  Along  the  Norwegian  coast  the  upper  lay- 
ers, of  200  to  300  meters,  have  a  uniform  salinity  of  something  over 
35.2  permille,  south  of  70°  north  latitude,  while  north  of  that  it 
decreases. 

The  following  table  gives  some  of  the  variations  in  salinity  in  the 
Atlantic  Ocean  (Krummel-2o:  338*341)  : 


152  PRINCIPLES    OF    STRATIGRAPHY 

Table  Showing  Bat hy metric  Variations  of  Salinity  in  the  Sea. 


Depth  in 
meters 

Parts  by  weight  in  1,000  parts  of  sea  water  (permille) 

Bay  of 
Biscay 

43°  7' 
N.  Lat. 

19°  43' 
W.  Long. 

Azores 

S.  W. 
Cape 
Verde 
Islands 

South 
Atlantic 

23°  33' 
S.  Lat. 
20°  51' 
W.  Long. 

Off  Cape 
of 
Good 
Hope 
35°  52' 
S.  Lat, 
13°  8' 
E.  Long. 

o 

100 
2OO 
500 
600 
692 
800 
900 
1,000 
I,2OO 
1,500 
2,OOO 

3,000 
4,000 

4,777 
4,957 
5,045 
5,900 

6,035 

35-78 

35-90 

35-90 

36.40 
35-70 

36.77 
36.60 

35-43 
34-55 

35-50 

35-72 
35-6o 

35-75 

34-50 

35-45 

35-40 

^s  10 

35-6o 

34-33 
34-43 

34-73 

34-36 

35-53 

35.65 

35-40 

34-58 
34-60 

35-51 

35-34 
35-08 

35-10 
35-oo 

35-00 

f  35-12 
to. 
I  35-69 

» 

34-77 

34-72 

T.A     67 



34-90 

35-8i 

In  the  Indian  Ocean  (35°  S.  lat.,  74°  E.  long.)  the  salinity  de- 
creases from  35.3  at  the  surface  to  34.38  at  900  meters,  increasing 
again  to  34.45  at  1,500  meters  and  34.65  at  the  bottom.  It  is  thus  a 
strictly  dichohaline  arrangement.  A  similar  condition  exists  in  the 
South  Pacific,  where  a  minimum  of  34.2  to  34.3  is  found  at  a  depth 
of  730  meters. 

The  salinity  of  the  Roman  Mediterranean  may  be  taken  as  an 
example  of  the  conditions  in  the  nearly  landlocked  types.  In  this 
the  increase  in  salinity  of  the  surface  waters  is  from  the  west  east- 
ward. At  the  Straits  of  Gibraltar,  where  the  Atlantic  water  enters, 
the  salinity  is  36.35  permille;  at  Cape  Gata,  Spain,  it  is  37.83  ~per- 


SALINITY    OF    SEA    WATER  153 

inille;  between  Greece  and  Barca  (Africa)  38.46  permille,  and  about 
halfway  between  the  islands  of  Rhodes  and  Cyprus  (long.  30°  18' 
E.,  lat.  35°  49'  N.)  it  is  39.40  permille.  The  salinity  varies  strongly 
with  depth.  Thus  at  the  Straits  of  Gibraltar  the  following  changes 
occur : 

Surface 36 . 35  permille  The  denser  water  flows  out  as  an 

25m 36 .  56  permille       undercurrent  and  affects  the  salinity 

50  m 37 .00  permille       of  the  deeper  strata  of  the  Gulf  of 

100  m 38-07  pcrniille       Cadiz  for  a  long  distance  out.     The 

200  m 38 . 30  permille       density  of  38.46  found  at  400  meters 

400  m 38.46  permille       depth   in    the    Gibraltar    Straits    is 

found  between   Malta  and   Pantel- 

leria  at  a  depth  of  200  meters  and  south  of  Greece  at  the  surface. 
In  the  eastern  region  (Cyprus  district)  the  surface  salinity  was 
found  in  the  summer  to  be  from  0.2  to  0.4  permille  greater  than 
at  the  bottom  (2,000  to  2,950  meters).  This  change  occurs  in  the 
upper  100  meters,  and  is  believed  to  be  due  to  the  rapid  evapora- 
tion on  the  surface.  The  seasonal  change  in  the  salinity  of  surface 
waters,  due  to  the  influx  of  fresh  water  through  the  streams,  is 
well  shown  in  the  Adriatic,  where  in  the  spring  the  salinity  sinks  to 
18  or  even  16  permille  in  the  neighborhood  of  the  land,  while  in 
the  winter  the  salinity  is  38  permille  even  at  the  mouths  of  streams. 
This  freshening  of  the  surface  waters  extends,  however,  to  the 
depth  of  only  about  one  meter.  Throughout  the  year  salt  water 
ascends  the  streams  along  their  bottoms ;  in  the  Natissa  River  at  the 
head  of  the  Adriatic,  it  ascends  as  far  as  Aquileja,  10  kilometers 
from  the  coast.  (Krummel-20 :  555.) 

The  Sea  of  Marmora,  between  the  Black  and  Roman  mediter- 
raneans, has  a  surface  layer,  of  n  meters  or  more,  of  low  salinity 
(22  to  25  permille),  followed  by  a  rapid  increase  to  a  depth  of 
25  meters  where  the  salinity  is  28.5  permille.  Beyond  this  follows 
a  slow  increase  to  a  depth  of  200  to  300  meters,  where  the  salinity 
is  38.1  permille,  increasing  later  to  38.4  permille,  after  which  it 
remains  constant  to  the  bottom  (1,400  meters). 

The  surface  stratum  of  low  salinity  is  again  seen  in  the  Black 
Sea,  where,  according  to  Wrangell  and  Spindler,  the  upper  40  or  45 
meters  have  a  homohaline  character  of  18.3  permille.  Downward  this 
slowly  increases  to  19.7  at  90  m.,  to  21.4  at  180  m.,  22.0  at  350  m., 
and  22.4  to  22.5  from  900  m.  to  2,000  m.  The  Sea  of  Azov  is  an  epi- 
continental  sea,  being  very  shallow,  and,  as  a  result,  it  is  usually 
homohaline,  with  10.5  to  10.7  (more  rarely  ii.o)  permille.  In  the 


154  PRINCIPLES    OF    STRATIGRAPHY 

northeast,  where  fresh-water  streams  enter  the  basin,  the  salinity 
may  be  as  low  as  7  permille.  In  the  Straits  of  Kertch,  connecting 
the  Azov  and  Black  seas,  the  upper  5  meters  of  10  permille  salinity 
flow  outward,  while  the  remainder  (2  to  3  meters)  represents  the 
inflowing  water  from  the  Black  Sea,  with  16  to  17  permille,  the 
isohaline  surfaces  lying  higher  in  the  east  than  in  the  west.  In  the 
Red  Se#  the  salinity  decreases  on  the  surface  from  40.43  in  the 
north  to  37.77  in  the  south.  In  the  northern  section  the  salinity 
increases  downward  from  40.43  to  40.55  permille  at  the  bottom  (547 
meters),  and  in  the  southern,  from  37.77  to  40.41  permille  at  the 
bottom  (1,120  meters).  In  the  greatest  depth  (2,160  meters)  near 
the  middle,  the  salinity  is  40.68  permille. 

II.  COMPOSITION  OF  LAKE  WATERS. 

The  composition  of  the  waters  of  enclosed  basins  varies  greatly, 
as  does  also  the  absolute  salinity,  which  is  much  greater  than  that  of 
the  ocean  in  many  cases,  and  less  in  still  more  numerous  cases. 

The  following  table  (Russell-29,  table  C;  Clarke-4)  gives  the 
salinity  of  the  surface  layers  of  a  number  of  enclosed  waters  in 
permillages.*  For  comparison  it  should  be  remembered  that  the 
permillage  of  average  ocean  water  is  35.— 

Table  of  Salinity  of  Various  Lakes. 

A.     Saline  and  Alkaline. 

Permille. 

1.  Tinetz  Lake,  a  residue  lake  of  the  Caspian 289 . ooo 

2.  Karaboghas  (Karabugas)  Gulf 285 .  ooo 

3.  Elton  Lake,  Russiaf. .' 270 . 627 

4.  Indevsk  Lake 261 . 530 

5.  Bogdo  Lake,  Russia 256.750 

6.  Illyes  Lake,  Hungary 233 . 747 

7.  Great  Salt  Lake,  Utah  (1892) 230.355 

8.  Owen's  Lake,  Cal.,  1905  (triple  alkali) 213 . 700 

9..     Urmiah  Lake,  Persia 205 . 500 

10.  Black  Lake,  Hungary 195 . 300 

11.  Dead  Sea  (maximum) I92- 153 

12.  Great  Salt  Lake,  Utah  (1889) 167 . 160 

3.  Lake  Domoshakovo,  Siberia 145.500 

14.  Great  Salt  Lake,  Utah  (1877) i37-9°o 

15.  Soda  Lake,  near  Ragtown,  Nevada  (triple  alkali). .  H3-644 

16.  Goodenough  Lake,  British  Col.  (alkali  carbonate) 103.470 

17.  Sevier  Lake,  Utah 86 . 403 

18.  Borax  Lake,  Cal.  (alkali,  carbonate-chloride) 76 . 560 

*  Equivalent  to  grams  per  liter  of  water, 
t  Average  of  3  analyses. 


COMPOSITION    OF   LAKE    WATERS  155 

Table  of  Salinity  of  Various  Lakes — Continued. 

A.  Saline  and  Alkaline. — Continued 

Permille. 

19.  Owen's  Lake,  Cal.  1876  (sp.  gr.  1.051) 60.507 

20.  Mono  Lake,  Cal.  (triple  alkali) . .  49 . 630 

21.  Albert  Lake,  Oregon,  1890  (alkali) 39 . 172 

22.  Albert  Lake,  Oregon,  1883  (sp.  gr.  1.02317) 27.357 

23.  Van  Lake 22 . 600 

24.  Caspian  Sea*  (1878) 12 .940 

25.  Lake  Koko-Nor,  Tibet 1 1 . 100 

26.  Aral  Sea 10 . 842 

27.  Lake  Biljo,  Siberia 8 . 800 

28.  Chichen  Kanab  (Little  Sea),  Yucatan 4-446 

29.  Natron  Lake,  near  Thebes,  Egypt  (alkali,  carbonate-chloride).  .  .  4.407 

30.  Winnemucca  Lake,  Nevada  (alkali,  carbonate-chloride) 3 . 603 

31.  Issyk-Kul,  Siberia 3 . 574 

32.  Pyramid  Lake,  Nevada  (alkali,  carbonate-chloride) 3.486 

33.  Walker  Lake,  Nevada  (triple  alkali) 2 . 562 

34.  Palic  Lake,  Hungary 2-2I5 

35.  Humboldt  Lake,t  Nevada  (alkali,  carbonate-chloride) 0.929 

36.  Laacher  See,  Germany  (alkaline  sodium  carbonate) 0.213 

B.     Fresh  Water  Lakes. 

37.  Lake  Erie  at  Buffalo^ o .  134 

38.  Lake  Michigan* o.  1 16 

39.  Lake  Huron  f o.  105 

40.  Croton  Reservoir,  New  York o .  084 

41 .  Lake  Baikal,  Siberia o .  069 

42.  Lake  Champlain* 0.067 

43.  Lake  Superior* o .  058 

As  will  be  seen  by  a  comparison  inter  se  of  the  analyses  made  in 
1876  and  1905  of  the  waters  of  Owen's  Lake,  California,  a  lake  of 
triple  alkaline  waters,  and  those  of  the  Great  Salt  Lake,  Utah,  made 
in  1877,  1889  and  1892,  a  difference  of  salinity,  amounting  in  the 
case  of  Owen's  Lake  to  153.2  permille,  and  in  that  of  Great  Salt 
Lake  to  116.7  permille,  obtained  between  the  extreme  dates.  This 
shows  the  variation  in  concentration  of  the  smaller  salt  lakes.  In 
both  cases  it  is  seen  that  the  concentration  has  been  a  progressive 
bne  in  time.  For  Great  Salt  Lake,  successive  analyses  show  the 
following  concentration,  which,  with  the  exception  of  the  first, 

shows  a  regular  progression. 

» 

*  Average  of  5  analyses.  » 

t  Average  of  4  analyses. 
|  Average  of  6  analyses. 


156 


PRINCIPLES    OF    STRATIGRAPHY 


Permille. 

1869 149-94 

1877 137.90 

1879 156.71 


Permille. 

1885 167.16 

1889 I95-58 

1892 230.36 


Elton  Lake,  Russia,  gave  in  April  a  salinity  of  255.6  permille; 
in  August  264.980  permille,  and  in  October  291.300  permille,  the 
specific  gravity  in  the  last  case  being  1.273. 

The  vertical  range  in  salinity  is  well  shown  by  a  number  of 
analyses  of  the  waters  of  the  Dead  Sea,  which  are  here  tabulated. 
(Terreild,  in  Clarke,  4.) 

Table  Showing  Vertical  Range  in  Salinity  in  the  Dead  Sea. 


Depth 

Salinity 
permille 

Specific 
gravity 

a    Surface,  Ras  Dale      

25.700 

i  .0216 

b.  Surface,  north  end  ". 

IQ2.  I  S3 

I  .  1647 

c    At  20  meters   5  miles  east  of  Wady  Mrabba 

2O7    OQO 

d.  At  42  meters,  near  Ras  Mersed  

242  6^0 

e.  At  depth  of  120  meters  (393  ft.),  5  miles  east  of 
Ras  Feschkah 

24C    7-10 

i  2225 

f.    At  200  meters  (656  ft.),  same  locality  as  e.  ... 
g.  At  300  meters,  same  locality  as  c  

251.  ioo 

2  SO  -08O 

i  .  2300 

The  salinity  of  the  River  Jordan,  flowing  into  the  Dead  Sea,  is 
only  i. 6 1  permille.  Its  carbonates  and  gypsum  are  precipitated 
when  it  enters  the  lake,  and  its  contribution  consists  almost  entirely 
of  chlorides,  derived  from  the  Cretacic  salt-  and  gypsum-bearing 
strata  of  the  region.  Soda  Lake,  Nevada,  at  one  foot  below  the  sur- 
face, where  the  specific  gravity  was  i.ioi,  gave  a  salinity  of  113.644 
permille,  a  large  part  being  carbonate  and  sulphate  of  sodium.  At  a 
depth  of  ioo  feet  the  salinity  was  113.651  permille. 

The  waters  of  salt  and  alkaline  lakes  may  be  divided  into  several 
fairly  well-defined  groups  (Clarke-4:  134-138}.  Among  the  salt 
lakes  we  have  first  a  group  of  normal  chloride  waters,  characterized 
mainly  by  sodium  chloride,  and  having  a  close  resemblance  to 
oceanic  water.  They  may  represent  remnants  of  the  ocean  water, 
or  the  salts  may  be  due  to  leaching  of  ancient  marine  deposits  carry- 
ing oceanic  salt.  The  analyses  of  the  waters  of  Great  Salt  Lake 
(Aj)  and  of  Illyes  Lake,  Hungary  (A2)  may  be  taken  as  examples. 
The  second  group  is  that  of  Natural  Bitterns  derived  from  the  pre- 


COMPOSITION    OF   LAKE    WATERS  157 

ceding,  but  having  its  magnesium  salts  concentrated  from  prolonged 
evaporation,  sodium  chloride  having  crystallized  out.  The  Dead 
Sea  (Bj)  and  Elton  Lake,  Russia  (B2),  are  examples.  The  third 
group  is  characterized  by  sulphate  waters,  there  being,  however,  no 
distinct  line  of  demarcation  between  this  and  the  last  group.  Sevier 
Lake,  Utah  (Q),  and  Lake  Domoshakovo,  Siberia  (C2),  show  ex- 
tremes. A  somewhat  different  group  comprises  the  sulphate- 
chloride  waters  of  the  Caspian  and  the  Aral  Sea  (DJ,  which  show 
a  falling  off  of  the  alkaline  metals  and  an  increase  in  calcium  and 
magnesium,  while  the  sulphates  approach  the  chlorides.  The  bit- 
terns of  this  type  differ  from  the  natural  or  normal  bitterns 
(B±,  B2)  in  the  proportion  of  sulphates.  This  is  shown  in  the  analy- 
ses of  the  waters  of  the  Karabugas  Gulf  (D2)  and  of  Issyk-Kul 
Lake  (D3),  Siberia.  An  extreme  case  representing  a  subgroup  is 
shown  in  Lake  Chichen-Kanab,  Yucatan  (D4). 

The  alkaline  lakes  comprise,  first,  a  group  in  which  the  car- 
bonates are  largely  in  excess  of  all  other  salts,  constituting  the 
typical  carbon  waters.  Goodenough  Lake,  British  Columbia  (Ej), 
and  Palic  Lake,  Banat,  Hungary  (E2),  are  examples.  A  second 
group  of  alkaline  waters  is  the  carbonate-chloride  group,  these  two 
salts  predominating,  while  sulphates  are  present  in  subordinate 
quantity.  Humboldt  Lake,  Nevada  (FJ,  Albert  Lake,  Oregon 
(F2),  and  Pyramid  Lake,  Nevada  (F3),  are  examples  of  this  type. 
"Triple"  waters,  in  which  chlorides,  sulphates  and  carbonates  are 
present  in  notable  quantities,  constitute  the  next  group.  Owens 
Lake,  Cal.  (Gj),  and  Soda  Lake,  Nevada  (G2),  are  examples  of  this 
type.  Finally,  the  waters  of  two  sulphate-chloride  lakes  of  a  mod- 
erate alkaline  character,  Lake  Biljo  (HJ  and  Lake  Koko-Nor  (H2), 
are  included,  and  the  corresponding  constituents  of  the  sea  are  also 
given  (I).  (Clarke-4  : 118-138.) 

Analyses  of  Types  of  Lake  Water. 

i.  Saline  Lakes. 

Ai  Great  Salt  Lake  (1877)  normal  chloride  waters. 
A2  Illeyes  Lake,  Hungary,  normal  chloride  waters. 
BI  Dead  Sea,  natural  bittern. 
B2  Elton  Lake,  Russia,  natural  bittern. 
Ci  Sevier  Lake,  Utah,  sulphate  waters. 
C2  Lake  Domoshakovo,  Siberia,  sulphate  waters. 
DI  Aral  Sea,  sulphate-chloride  waters. 
D2  Karabugas  Gulf,  sulphate-chloride  bittern. 
D3  Issyk-Kul  Lake,  Siberia,  sulphate-chloride  bittern. 
D4  Lake  Chichen  Kanab,  Yucatan,  sulphate-chloride  bittern. 


158 


PRINCIPLES    OF    STRATIGRAPHY 


Analyses  of  Types  of  Lake  Water — Continued. 

2.  Alkaline  Lakes. 

EI  Goodenough  Lake,  British  Columbia,  carbonate  waters. 
E2  Palic  Lake,  Hungary,  carbonate  waters. 
FI  Humboldt  Lake,  Nevada,  carbonate-chloride  waters. 
F2  Albert  Lake,  Oregon,  carbonate-chloride  waters. 
Fa  Pyramid  Lake,  Nevada  (mean  of  four  concordant  analyses), 

carbonate-chloride  waters. 

F4  Borax  Lake,  Lake  Co.,  California,  carbonate-chloride  waters. 
Gi  Owen's  Lake,  California,  " Triple"  waters  (1965). 
G2  Soda  Lake,  Nevada,  " Triple"  waters. 
HI  Lake  Biljo,  Siberia,  alkaline  sulphate-chloride  waters. 
H2  Lake  Koko-Nor,  Tibet,  alkaline  sulphate-chloride  waters. 

For  Comparison 
I    Ocean  water. 


TABLE,  IN  PERCENTAGES,  OF  TOTAL  SOLIDS,  OF 


Normal 
chloride 

Natural 
bittern 

Sulphate 
waters 

Sulphate  chloride 
waters 

A! 

.Ai 

Bi 

B2 

Ci 

C2 

D! 

D2 

D3 

D4 

Cl 

56.21 

60.  18 
tr. 
0.44 
0.04 

65.81 
2.37 
0.31 

tr. 

64.22 

'o  82 
o  04 

52.66 
'io!88 

3.71 
tr. 
63.62 
0.08 
0.07 

35-40 
0.03 
30.98 
0.85 

53.32 
0.06 
17-39 

15.64 
0.03 
55-94 
i  .26 

8.14 

Br 

SO4        

6.89 
0.07 

58.64 

COs 

NOs 

PO4 

* 

O.O2 

Li 

11.65 
I.8S 

4-73 
13.28 

tr. 

II    27 

•  •  

B407  
Na    

33^45 

39-02 

33-33 

30.61 
0-59 

.0.58 
0.74 

tr. 
tr. 

22.62 
0.54 

O.O2 
4.02 
5-50 

o.o4f 

11.51 
1.83 
0.06 

15*83' 

11.76 

1.85 

H.99 
0.43 

K  
Rb 

0.  IO 

17.55 

0.  12 
3-01 

Ca  
Mg  
Si02  
AhOs..    .. 
pe2O3 

O.2O 

3.18 

0.25 
0.03 
0.04 

tr 

0.94 
12.50 

tr. 

13-49 
7.31 

* 

MnzOs  
S.  sulphide 
As2Os      .  .  . 



o  6 

Total  %... 

Salinity 
permille  . 

IOO.OO 

IOO.OO 

IOO.OO 

100.00 

IOO.OO 

IOO.OO 

IOO.OO 

IOO.OO 

100.00 

100.00 

137.90 

233.747 

192.15 

265.00 

86.40 

145.50 

10.84 

285.00 

3-574 

4.446 

The  composition  of  saline  lakes  in  percentage  of  total  solids  is 
given  in  the  following  partial  analyses  of  the  waters  of  Great  Salt 
Lake,  a  normal  chloride  water ;  of  the  Dead  Sea,  a  natural  bittern ; 
and  of  the  Caspian  Sea,  a  sulphate-chloride  water.  The  composi- 


COMPOSITION    OF    LAKE    WATERS 


159 


Composition  of  Saline  (and  Alkaline  Saline)  Lakes,  in  Percentage 

of  Total  Solids. 


* 

Koko-Nor 

Caspian 

Dead 

Great  Salt 

Sodium  chloride  (NaCl) 

64  4 

6-z  QI 

29  oo 

8l    71 

Magnesium  chloride  (MgCU) 

65  oo 

°O*  /O 

6  «U 

Magnesium  sulphate  (MgSO4)  .  . 
Calcium  sulphate  (CaSO4)  

8-7 

23.29 

-zoo 

0.40 

"•Oo 
2.26 
3C7 

Potassium  sulphate  (K^SC^) 

371 

Sodium  sulphate  (Na2SO4)  

16.1 

Calcium  carbonate  (CaCOs)  .... 

4-4 

2.66 

Magnesium  carbonate  (MgCOs)  . 

4.0 

1.46 

Calcium  chloride  (CaCl2)  

4..  6S 

tion,  in  like  manner,  of  a  moderately  alkaline  sulphate-chloride  wa- 
ter is  given  in  the  analysis  of  the  waters  of  Lake  Koko-Nor,  Tibet. 


COMPOSITION  OF  VARIOUS  NATURAL  WATERS. 


Carbonate 
waters 

Carbonate  chloride 
waters 

Triple 
waters 

Sulphate  chlo- 
ride waters 

Ocean 

Ei 

E2 

Fi 

Fs 

F3 

F4 

GI 

G2 

H! 

H2 

I 

7.64 

7.08 
41.41 

0.62 

15-68 

2.92 
41.02 

31.82 

3-27 
21.57 

36.04 

41.04 

32.27 

o  04 

24.82 

36.51 

9.91 

40.05 
0.04 
17.84 
5-55 

55-29 
0.19 
7.69 

0.21 

1.90 

20.67 

5-25 
14.28 

0.13 

22.47 

O   02 

9-93 

24-55 
0.45 

O    II 

10.36 
13.78 

52.33 

6.22 

1.07 

0.07 

o  02 

5.05 
38.10 
1.52 

0.03 
0.14 
38.09 
1.62 

tr. 

O.O2 
O.OI 

o.  14 
}  0.04 

tr. 
36.17 
6.65 

O.O2 
O.O4 
O.O4 
0-33 

35-75 

29-97 
6.54 

0.25 
36.63 

2.01 

0.22 

0.24 

39-33 
1.44 

33-84 

2.  II 

21.83 
0.87 

0.43 
7.28 

0.03 
0.03 

30.60 
1.  08 
0.04 
1.77 
2.90 
0.09 

30.59 
I.  II 

0.66 
3-35 
0.27 

1-35 
1.88 
3-53 

0.62 

0.25 

2.28 

0.95 

0.03 
0.35 

O.OI 
[  O.OI 

I.  2O 
3-72 

o  35 

O.O2 

100.00 

100.00 

IOO.OO 

100.00 

100.00 

100  .  00 

100.00 

100  .  00 

100.00 

100  .  00 

IOO.OO 

103.470 

2.215 

0.929 

39.172 

3.486 

76.560 

213.70 

113.70 

8.80 

II.  10 

35-00 

*  Included  with  SiO2.         t  Including  PO4  and  Fe2O3. 

The  quantitative  composition  of  a  typical  alkaline  lake  is  shown 
by  the  following  analysis  made  in  1883  by  F.  W.  Taylor  of  the 
water  of  Albert  Lake,  Oregon,  a  carbonate  water  (sp.  gr.  1.02317). 
(Russell-29:  454.) 


i6o 


PRINCIPLES    OF    STRATIGRAPHY 


Silica  in  solution  (SiC^) 

Sodium  chloride  (NaCl) 

Potassium  chloride  (KC1) 

Potassium  sulphate  (K2SO4) 
Potassium  carbonate  (K2CO3) .  . 
Magnesium  carbonate  (MgCO3) . 


Total. 


Grams  per  liter 

of  the  water 

0.065 

7.219 

8.455 

o .  92 1 

10.691 

o .  006 

27.357 


The  following  analyses  of  the  waters  of  Pyramid  Lake,  another 
carbonate-chloride  lake,  show  variation  vertically  as  well  as  hori- 
zontally. ( Rtissell-30 :  57,  58. ) 


Probable  combination  in  grams  per  liter 

South  of  Anaho  Isl. 

North  of  Anaho  Isl. 

i  foot 
below 
surface* 

200  feet 
below 
surface** 

i  foot 
below 
surf  ace  f 

350  feet 
below 
surface! 

Silica  (SiO2) 

o  .  0425 
o  .  2632 

0-1374 

2  .  2466 
0.2621 
0.4940 

0.0300 
0.2912 

0.4212 
0.2800 
0.0447 
0.1474 
2.2411 
0.2667 
0.4738 

0  .  0200 
0.2818 
0.0447 
O.I38I 
2.2550 
0.2737 
0.4756 

Magnesium  carbonate  (MgCOa) 
Calcium  carbonate  (CaCO3)  .... 
Potassium  chloride  (KC1)  
Sodium  chloride  (NaCl) 

0.1387 
2.2428 
0.2757 
0.4834 

Sodium  sulphate  (Na2SO4)  
Sodium  carbonate  (Na2COs)  .... 

Total 

3-4458 

3.4618 

3-4949 

3.4889 

Nearly  all  the  fresh  water  entering  Pyramid  Lake,  which  is 
without  outlet,  is  delivered  at  the  southern  end  by  Truckee  River, 
near  the  mouth  of  which  the  water  is  fresh  enough  for  camp  pur- 
poses. At  the  northern  end  of  the  lake  the  water  is  unfit  for  human 
consumption,  but  animals  may  drink  it  without  injury. 

3.  Fresh-water  Lakes.    Water  absolutely  free  from  mineral  mat- 

*  99-23  per  cent,  of  total  solids  accounted  for. 
**  99.19  per  cent,  of  total  solids  accounted  for. 
f  99.94  per  cent,  of  total  solids  accounted  for. 
I  Error  of  0.15  per  cent,  in  excess. 


COMPOSITION    OF    RIVER    WATERS 


161 


ter  does  not  exist  in  nature.  That  of  lakes  and  rivers  suitable  for 
drinking  purposes  (by  man)  always  contains  in  the  neighborhood  of 
o.i  permille  of  mineral  matter,  especially  calcium  carbonate.  Wa- 
ter above  0.15  or  0.2  permille  cannot  be  considered  potable,  espe- 
cially if  the  percentage  of  sodium  chloride  is  high.  (Bibliography 
V-44.)  The  average  composition  of  fresh-water  lakes  is  shown  by 
the  following  analyses  of  the  waters  of  Lake  Baikal,  the  American 
Great  Lakes  and  Lake  Champlain.  (Clarke-4:  61,  81.) 


Table  of  Average  Composition  of  Lake  Waters. 


Lake 
Baikal 

Lake 
Superior 

Lake 
Michigan 

Lake 
Huron 

Lake 
Erie 

Lake 
Cham- 
plain 

CO3  
SO4 

49.85 
6  93 

45.26 
4-  33 

48.82 
5.67 

48.99 
5.64 

45  64 
9.48 

45.8i 
ii  .03 

Cl            

2.44 

1  .69 

2  .OI 

2.  19 

5-4° 

1.78 

NO3  

O.2I 

0.56 

0.22 

0.30 

0.  12 

POi 

O    72 

Ca  

23.42 

25.78 

23.42 

23.  ii 

23.79 

21  .  19 

Mg.. 

3-57 

4.96 

6.94 

6-35 

5.51 

4.21 

Na 

S  85  | 

K   

3.44 

4.96 

3-65 

3.21 

4.84 

8.80 

NH4 

o  08 

SiO2 

2    Ol 

12     T.T, 

Q    22 

10.  14 

5.  14 

5.58 

Fe2O3  
A12O3 

1.46 

0.13 

0.05 

0.07 

0.08  I 

1.60 

Total... 

100.00 

100.00 

100.00 

100.00 

100.00 

IOO.OO 

III.  COMPOSITION  OF  RIVER  WATER. 

The  composition  of  river  water  varies  in  accordance  with  the 
character  of  the  rock,  over  or  in  which  the  river  flows,  and  the  na- 
ture of  the  supply.  Though  different  rivers  show  varying  amounts 
in  the  totality  of  solids,  this  is  never  very  high,  while  at  the  same 
time  the  relative  preponderance  of  the  salts  does  not  change  greatly. 
The  following  table  gives  the  totality  of  solids  in  a  number  of  rivers, 
together  with  the  predominant  element  or  compounds  in  each. 
(Russell-30,  Table  A;  Clarke-4  160-82. ) 


162 


PRINCIPLES    OF    STRATIGRAPHY 


Table  Showing  the  Amounts  in  Permille  of  the  Principal 


Total 

Cal- 
cium 
Ca 

Mag- 
nesium 
Mg 

I. 

2. 

Rio  de  los  Papagayos,  Argentina  
San  Lorenzo  River,  California 

9.18500 
4  68500 

0.73572 
o  23472 

0.03307 
o  11609 

3- 

Pecos  River,  New  Mexico;  average  of  6  analyses  

.     2  .  83400 

o  .  40999 

o  .  10259 

4- 
5. 
6. 

7. 

Arkansas  River,  Rocky  ford,  Colorado  
Salt  River,  at  Mesa,  Arizona;  aver,  of  6,  anal  
Brazos  River,  Waco,  Texas  
Mono  Creek   California;  aver,  of  3  anal 

2  .  I34OO 
I  .  23400 
I  .  06600 
I    O040O 

0.27273 
0.09193 

o.  10170 
o  14889 

0.08024 
0.03319 
0.02175 

8 

Arkansas  River,  Little  Rock  

0.7940O 

0.06034 

o  .  01326 

9- 
10. 

Red  River  of  the  North  below  Assiniboine  
Red  River  of  the  North  at  Fargo,  N.  Dakota  

0.55IOO 
O.39800 

0.07102 
0.07375 

0.04402 

1  1. 

Humboldt  at  Battle  Mt.,  Nevada  

o  .  36150 

0.04890 

o  01240 

12. 

Jordan   Utah  Lake,  Utah 

o  30600 

o  05580 

o  01860 

13- 

14. 

Los  Angeles,  Los  Angeles  (hydrant;  
Rhine  at  Strassburg  

0.24475 

0.23200 

0.01750 
0.05869 

0.02097 
o  .  00142 

\l' 

Genesee  at  Rochester,  New  York  
Rhine  at  Cologne  

o.  19526 
o.  17800 

0.04170 
0.04870 

0.00896 
o  .  00991 

17- 
T« 

Bear  River  at  Evanston,  Wyoming  
Walker    Mason  Valley    Nevada 

0.18450 
o  18000 

0.04320 
o  02280 

0.01250 
o  00380 

IQ. 
2O. 
21. 
22. 
23. 

Mississippi  at  New  Orleans  
Lower  Nile;  average  of  12  monthly  samples  
St.  Lawrence,  Pt.  de  Cascades,  S.  side  
Rio  Grande  del  Norte,  Fort  Craig,  New  Mexico  
Mohawk,  Utica,  New  York  :  

0.16990 
o.  16800 
0.16055 
o.  15760 
o.  15250 

0.03720 
0.03377 
0.03233 
0.01633 
0.03180 

0.00674 
0.00585 
0.00123 
o  .  00690 

24- 
25. 

Hudson,  Hudson,  New  York  
Cumberland,  Nashville,  Tennessee  

o.  14238 
0.13786 

O.O222O 
O.O2987 

0.00465 
0.00280 

26. 
27. 

Passaic,  4  miles  above  Newark,  New  Jersey  
Sacramento  Sacramento   California 

0.13267 
o  11484 

O.OI459 

o  01279 

o  .  00404 

O    OOI2I 

^8 

Maumee   Ohio 

o  10971 

o  02645 

o  00443 

29. 
30. 

Croton,  New  York  City  
Moldau   above  Prague 

0.08433 
o  07400 

o  .  00905 

O    OIOOI 

0.00336 
o  00361 

31- 
32. 

Truckee,  Lake  Tahoe,  Nevada  
James,  Richmond,  Virginia 

0.07300 
o  07246 

0.00930 
o  01284 

0.00300 
o  00377 

33- 

Delaware,  Trenton,  New  Jersey 

o  06795 

o  01104 

o  00435 

34- 

Ottawa  Montreal  Canada 

o  06116 

o  00992 

o  00161 

The  following  table  gives  the  total  salinity  of  a  number  of  addi- 
tional rivers,  as  quoted  by  Penck  (26:509)  and  Clarke  (4). 


Table  Showing  Total  Salinity  of  Other  Rivers. 


35.  Rio  Saladillo,  Argentine 

36.  Cheliff  near  Orleansville,  Africa 

37.  Colorado  River,  Argentine,  South  America. . . 

38.  Thames,  above  London  (average) 

39.  Elbe,  above  Hamburg 

40.  Nile  at  Cairo * 

41.  La  Plata,  near  Buenos  Ayres 

42.  Vistula,  near  Culm 

43.  Dwina,  Russia , 

44.  Danube  at  Budapest  (average) 

45.  Rhone  at  Lyons  (average) 

46.  Rio  Negro,  above  Mercedes,  South  America .  . 

47.  Parana,  5  miles  above  its  entry  into  La  Plata 

48.  La  Plata,  5  miles  above  Buenos  Ayres 


Permille. 
1.213 
0.780 
0.651 
0.289 
0.237 
0.231 
0.206 

0.201 
0.187 
0.187 

0.145 
0.132 
O.098 
O.O9I 


COMPOSITION    OF    RIVER    WATERS 


163 


Elements  and  Compounds  Occurring  in  Various  River  Waters 


Potas- 
sium 
K 

Sodium 
Na 

Carbonic 
acid 
CO, 

Sulphuric 
acid 
SO* 

Chlorine 
Cl 

Other  substances  present 

0.04501 

2.43219 

0.00551 

2.92535 

2.99707 

S 

o  .  06044 

1.07204 

0.14477 

2.20710 

0.77209 

0.02182 

o.  14226 

o  .  04364 

1.23911 

0.63835 

Si02,  A1203,  Fe203 

0.00597 

0.30943 

0.56650 

1.29512 

0.10435 

Si02 

i  .70292 

0.32553 

o.  11858 

0.01430 

0.51305 

SiO2,  A12O3,  Fe2Oa 

0.2/ 

806 

0.24806 

0.22109 

0.35935 

Si02,  Fe203 

trace 

o  .  10893 

0.18875 

0.45863 

0.03614 

SiO2,  A12O3,  Fe2O3 

0.00588 

0.20580 

0.08575 

0.  IOOI2 

o  .  30609 

Si02>  A1203,  Fe20, 

0.00650 

0.05328 

0.17340 

0.12155 

0.04838 

SiO3,  (AlFe)2O3 

0.01485 

0.22348 

0.00346 

0.00394 

(AlFe)203 

O.OIOOO 

0.04670 

0.15440 

0.04770 

0.00750 

SiO2,  A12O3 

o  .  01780 

o  .  06080 

o  .  13060 

o  .  01240 

SiO2 

o  .  02968 

o  .  05635 

o  .  05724 

O    OIO.44 

SiO2,     Al2Os,  FeCOs,      MnCOs,     NH4, 

u  •  **AW|^, 

organic  matter 

0.00153 

0.00503 

0.08373 

0.01888 

O.OOI2O 

SiO2,  A12O3,  Fe2O3,  NOs 

0.00230 

o  .  00440 

o  .  06460 

0.04310 

O.OO24O 

SiO2,  A12O3,  Fe2O3,  organic  matter 

0.00479 

0.08377 

0.02244 

O.OO742 

SiO2,  A12O3,  Fe2O3,  PO< 

o  .  00820 

o  .  09820 

o  .  o  1050 

o  00490 

SiO2 

trace 

0.03180 

0.05760 

0.02840 

0.01310 

Si02 

0.03100 

o  .  03830 

Carbonates  and  sulphates  of  K   Na    Me 

0.01329 

0.00511 

0.00613 

0.02929 

0.0075 

Si02,  Fe203 

0.00115 

0.00513 

0.06836 

0.00831 

0.00242 

Si02 

o  .  00063 

0.03220 

0.01025 

0.04700 

o  .  03604 

Organic  mattef  ,  traces  of  other  minerals 

o  .  00090 

0.00360 

0.05690 

0.01870 

0.00230 

SiO2,  A12O3,  Fe2Os,  organic  matter 

0.00058 

0.00243 

0.07278 

0.01257 

0.00581 

SiO2,  Fe2O3,  A12O3,  H,  organic  matter 

0.00050 

0.01032 

0.05727 

0.00563 

0.00299 

SiO2,  HNO3,  Fe2O3,  Al2Os,  organic  matter 

0.00163 

0.02357 

0.02634 

0.01716 

0.03192 

SiO2,  A12O3,  Fe2O3 

O.002OO 

0.00887 

0.00397 

H3P04,  Si02,  A1203,  FeCOa,  MnCO3,  NaCl, 

Na2S04 

o  .  00309 

0.00162 

0.04438 

0.01401 

0.00250 

SiO2,  Fe2O3,  organic  matter 

0.00154 

0.00298 

0.02248 

0.00441 

0.00213 

SiO2,  Fe2O3,  A12O3,  organic  matter 

0.00384 

0.00756 

0.00243 

0.00843 

0.00793 

Si02,  (AlFe)j,  03(  P04 

0.00330 

0.00730 

0.02870 

0.00540 

0.00230 

Si02 

0.00251 

0.00234 

0.02954 

0.00363 

0.00105 

HNOs,  Si02,  AU03,  Fe203  Mn2O3,  NH4,  or- 

ganic matter 

0.00178 

0.00072 

0.02552 

0.00175 

O.OOI2I 

H3PO4,  SiO2.  A12O3,  Fe2O3,  organic  matter 

0.00139 

0.00239 

0.02255 

0.00194 

0.00076 

SiO2;  traces  of  other  substances 

Table  Showing  Total  Salinity  of  Other  Rivers. — Continued. 

Permille. 

49.  Uruguay,  above  Fray  Bentos 0.066 

50.  Amazon,  between  the  Narrows  and  Santarem o .  059 

51.  Xingu,  South  America o .  045 

52.  Tapajis,  South  America o .  038 

53.  Amazon  at  Obidos o .  037 

In  most  of  the  rivers  calcium  is  in  excess,  probably  in  the  form 
of  the  bicarbonate.  Jn  some  cases,  however,  as  in  the  Jordan  River, 
Utah,  the  calcium  is  chiefly  in  the  form  of  the  sulphate. 

From  the  analyses  of  the  waters  of  twenty  American  rivers 
(United  States  and  Canada),  it  has  been  found  that  the  average 
total  amount  of  solids  carried  in  solution  is  0.15044  permille,  of 
which  0.056416  permille  is  calcium  carbonate  (Russell-^.i/o3). 
Forty-eight  analyses  of  the  waters  of  European  rivers  tabulated  by 
Bischof  give  the  average  total  solids  in  solution  as  0.2127  permille 
with  an  average  of  0.1139  permille  of  CaCO3,  while  forty  analyses 


164  PRINCIPLES    OF    STRATIGRAPHY 

gave  Roth  an  average  total  of  0.2033  permille  and  of  cakium  car- 
bonate 0.009598  permille  (Russell-33 :  79).  For  both  American 
and  European  rivers  the  above  data  give  an  average  of  total  solids 
in  solution  of  0.1888  permille,  of  which  0.088765  permille,  or  47 
per  cent,  of  the  total  solids,  represents  calcium  carbonate. 

The  annual  total  transport  of  mineral  matter  in  solution  was 
compiled  for  a  number  of  rivers  by  Russell  (31  :  79),  and  is  given 
in  the  following  rearranged  and  supplemented 

Table  of  Total  Solids  Carried  in  Solution,  in  Tons  per  Year* 

1.  Mississippi 112,832,170 

2.  Danube 22,521,430 

3.  Nile 16,950,001 

4.  Rhone 8,290,464 

5.  Arkansas 6,828,350 

6.  Rhine 5,816,804 

7.  Thames , 613,930 

8.  Hudson : 438,005 

9.  Croton 66,795 

Total  for  nine  rivers i?4>357>949 

Sir  John  Murray  (22:  76)  has  computed  the  number  of  tons  of 
different  salts  carried  in  solution  in  a  cubic  mile  of  river  water; 
the  average  of  which  for  nineteen  of  the  principal  rivers  of  the 
world  is  given  in  the  following  table  (Russell-33  :8o)  :  f 

Table  Showing  the  Amounts  of  the  Different  Salts  Carried  in  Solu- 
tion in  One  Cubic  Mile  of  Average  River  Water. 

British  tons  in 
Constituents.  one  cubic  mile.J 

Calcium  carbonate  (CaCO3) 326,710 

Magnesium  carbonate  (MgCQa) 1 12,870 

Calcium  phosphate  (Ca3P2O8) 2,913 

Calcium  sulphate  (CaSO4) 34,36i 

Sodium  sulphate  (Na2SO4) 31,805 

Potassium  sulphate  (K2SO4) 20,358 

Sodium  nitrate  (NaNO3) 26,800 

Sodium  chloride  (NaCl) 16,657 

Lithium  chloride  (LiCl) 2,462 

Ammonium  chloride  (NH4C1) 1,030 

Silica  (SiO2) • 74,577 

Ferric  oxide  (Fe2O3) 13,006 

Alumina  (A12O3) 14,315 

Manganese  oxide  (Mn2O3) 5>7°3 

Organic  matter , 79,020 

Total  dissolved  matter 762,587 

*  See  other  tables  cited  by  Clarke~4 : 80- 

|  Acids  and  bases  combined  according  to  the  principles  indicated  by  Bunsen. 

j  One  cubic  mile  of  fresh  water  weighs  about  4,205,650,000  British  tons  of 
2,240  pounds  each. 


COMPOSITION    OF    SPRING    WATER  165 

Murray  has  further  computed  that  the  volume  of  water  flowing 
into  the  sea  in  one.  year,  for  all  the  land  areas  of  the  earth,  totals 
about  6,524  cubic  miles,  which,  with  the  average  composition  given 
above,  results  in  the  grand  total  of  4,975,117,588  British  tons  of 
mineral  matter  carried  in  solution  into  the  sea  annually.  Large  as 
the  amount  is,  when  compared  with  the  total  mineral  matter  in  the 
sea,  it  dwindles  in  proportion.  Of  calcium  carbonate  alone  2,131,- 
455,940  tons  are  carried  into  the  sea  annually,  of  magnesium  car- 
bonate 736,363,880  tons,  or  a  total  of  carbonates  of  2,867,819,820 
tons,  or,  in  round  numbers,  2,868  million  British  tons,  or  2,823  mil- 
lion metric  tons.*  (Krummel  figures  out  only  2,460  million  metric 
tons  of  carbonates,  using  Penck's  estimate  [26:310]  of  4,100  mil- 
lion metric  tons  of  mineral  matter  carried  into  the  sea  annually,  or 
1/6000  of  the  total  amount  of  the  water  flowing  into  the  sea.  The 
percentage  of  carbonates  dissolved  in  river  water  is  taken  as  60.) 
Although  the  percentage  of  carbonates  in  the  sea  may  be  as  low  as 
0.2,  the  absolute  quantity  is  99.4  X  io12  metric  tons,  or  39,000  times 
as  much  as  the  yearly  supply  by  streams,  according  to  Krummers 
estimate.  On  these  same  estimates  it  appears  that  of  sulphates  there 
is  9  million  times  the  amount  by  weight,  while  of  chlorides  there  is 
17  million  times  the  amount  by  weight  brought  into  the  sea  annually 
by  all  the  rivers  of  the  world.  (Krummel-2o:  228.) 


IV.  COMPOSITION  OF  SPRING  WATER. 

Rain  water  is  not  absolutely  pure  H2O,  but  always  contains  im- 
purities gathered  in  its  passage  through  the  lower  strata  of  the 
atmosphere.  An  analysis  of  rain  water  collected  near  London,  Eng- 
land, gave  the  following  composition  : 


Table  of  Composition  of  Rain  Water  near  London. 

Permille. 

Organic  carbon o .  00099 

Organic  nitrogen o .  00022 

Ammonia o .  00050 

Nitrogen  as  nitrates  and  nitrites o .  00007 

Chlorine o .  00630 

Other  impurities 0.03142 


Total 0.03950 

*  One  metric  ton  equals  1,000  kilograms,  equals  2,204.6  pounds  avoirdupois; 
I  British  ton  equals  2,240  pounds  avoirdupois. 


i66 


PRINCIPLES   OF   STRATIGRAPHY 


This  is  39.50  grams  in  one  thousand  liters  of  rain  water.  At 
Troy,  New  York,  the  mean  chlorine  content  of  the  rain  water  for 
one  year  was  found  to  be  0.00164  permille,  or  1.64  grams  per  1,000 
liters. 

At  Lincoln,  New  Zealand,  the  impurities  of  the  rain  water  were 
found  by  Gray  to  average  during  two  years  as  follows : 

Impurities  of  Rain  Water. 

Permille 

Cl 0.00774 

SO3 o . 00201 

N  in  NH3 0.00012 

N  in  nitrates o .  00014 

N  albuminoid o .  00009 

Other  matter 0.01350 


Total  dissolved  matter o .  02360 

The  following  solids,  in  pounds  per  acre  per  annum,  have  been 
determined  as  brought  by  the  rain  in  various  localities.  (Clarke- 
4:46-47.) 

Solids  in  Rain  Water.    (Pounds  per  acre  per  year.) 


Nitrogen 

Ammonia- 
cal 

Nitric 

Total 

Chlorine 

Sodium 
chloride 

Rothamsted,  England* 
Barbados 

2.823 
I  ooq 

0.917 
2.441 

3-740 
1.452 

14.400 
116  980 

24  .  ooo 

British  Guiana  

I  .  151 

2.190 

3.541 

108.613 

From  the  soil  the  rain  water  takes  CO2  and  humus  acids  derived 
from  both  living  and  decaying  vegetation,  and  these,  with  the  acids 
derived  from  the  atmosphere,  will  exercise  a  solvent  power  upon 
the  rocks  through  which  the  water  passes.  Several  of  them  are 
good  solvents  of  silica,  and  the  streams  passing  through  bogs  are 
generally  rich  in  this  constituent.  Thus  the  Ottawa  drains  a  region 
occupied  chiefly  by  crystalline  rocks,  covered  by  extensive  forests 
and  marshes,  and  its  percentage  of  silica  is  33.7  of  the  total  in- 
organic solids.f 

*Average  of  five  years. 

t  For  a  full  discussion  of  the  Geological  action  of  the  Humus  Acids  see  Julien 
(17).  For  a  correlation  between  compositions  of  river  water  and  source  of  the 
water  see  Hanamann  (12). 


COMPOSITION    OF    SPRING   WATERS  167 

The  ordinary  spring  or  vadose  water  will  thus  have  a  certain 
type  of  composition,  though  varying  greatly  within  that  type.  The 
leading  acid  ions  in  its  mineral  content  are  CO2  and  SO3,  and  lime 
and  magnesia  are  the  leading  bases,  except  in  granitic  countries  or 
in  arid  regions.  Lane  thinks  that  the  salinity  is  not  commonly  over 
i  permille,  that  saturation  with  bicarbonates  (0.238  permille  of 
CaCO3)  seems  to  be  a  very  common  goal,  and  that  the  specific  grav- 
ity of  such  waters  is  not  greater  than  i.  Analysis  A  on  page  170 
may  be  taken  as  a  type  of  such  waters. 

Waters  regarded  by  Lane  as  showing  large  proportions  of  bur- 
ied sea  water  were  obtained  from  Sheboygan,  Wisconsin.  These 
have  a  salinity  of  589.2536  grains  per  U.  S.  gallon  (8.782  grams  per 
liter,  or  8.782  permille),  of  which  52.1%  is  NaCl.  Others  have 
been  obtained  from  Bowling  Green,  Ohio,  which  had  a  salinity  of 
3,297.93  grains  per  U.  S.  gallon  (49.154  grams  per  liter,  or  49.154 
permille),  of  which  72.3%  is  NaCl. 

Magmatic  waters  obviously  have  the  greatest  range  of  variabil- 
ity in  composition.  Still  it  would  not  be  proper  to  hold  that  all  wa- 
ters varying  beyond  the  limits  ordinarily  set  for  meteoric  waters  or 
for  connate  waters  are  to  be  regarded  as  of  magmatic  origin.  Such 
an  assumption  would  disregard  the  evident  ability  of  meteoric 
waters  to  take  up  mineral  matter  in  their  passage  through  the  rocks. 
Since  magmatic  waters  are  essentially  thermal,  they  will  be  more 
fully  discussed  under  the  section  dealing  with  the  temperature  of 
the  water.  (See  page  201.)  Analyses  of  spring  waters  from  the 
Algerian  Sahara  gave  the  following  extremes  of  composition  (Rol- 
land  quoted  by  Walther-43  :  57)  : 

Composition  of  Spring  Water  from  the  Sahara. 

Permille 

SiO2 0.012  to  0.068 

NaCl 0.039104.030 

KC1  o .  005  to  o .  307 

CaCO3 o .  076  to  o .  294 

MgCO3 0.005  to  0.052 

Fe2CO3 o .  004  to  o .  013 

CaSO4 0.008  to  1.851 

MgSO4 o.ioo  to  0.916 

Na2SO4 0.025  to  i  -2I4 


Total  amount  of  solids o. 274  to  8 . 745 

In  the  table  on  pp.  170-171  a  number  of  analyses  of  the  waters 
of  springs  and  wells  are  given  to  show  their  variations  and  general 


i68  PRINCIPLES    OF    STRATIGRAPHY 

character.  For  a  more  extensive  tabulation  the  student  is  referred 
to  Clarke's  Data  of  Geochemistry.  As  with  the  waters  of  lakes,  so 
here  a  number  of  divisions  are  made,  but  no  hard-and-fast  line  can 
be  drawn  between  end  members  of  adjoining  groups.  The  follow- 
ing springs  are  given: 

A.  Spring    near    Magnet    Cove,    Arkansas — ordinary     (Car- 
bonate) spring  water. 

B.  Spring   near   Mount   Mica,    Paris,    Maine — ordinary    (sul- 
phate) spring  water. 

C.  Artesian  well,  Cincinnati — chloride  waters. 

D.  Upper  Blue  Lick  Springs,  Kentucky — chloride  waters. 

E.  Utah  hot  springs,  8  miles  north  of  Ogden,  Utah — chloride 
waters. 

F.  The  Kochbrunnen,  Wiesbaden — chloride  waters. 

G.*  Well,  2,667  feet  deep  at  Conneautsville,  Pa. — chloride  wa- 
ters. 

H.*     Boiling  spring,  Savu-Savu,  Fiji — chloride  waters. 

I.f     Congress  Spring,  Saratoga — chloride  waters. 

J.f     Steamboat  Springs,  Nevada — chloride  waters. 

K.     Bitter  Spring  Laa,  Austria — sulphate  waters. 

L.     Cruzy,  Herault,  France — sulphate  waters. 

M.  Pine  Creek  Valley  Spring,  near  Atlin,  British  Columbia — 
carbonate  waters. 

N.     Orange  Spring,  Yellowstone  National  Park — mixed  waters. 

O.     The  Sprudel,  Carlsbad,  Bohemia — mixed  waters. 

P.  Chalybeate  waters,  Mittagong,  New  South  Wales — mixed 
waters. 

Q.  Old  Faithful  Geyser,  Upper  Geyser  Basin — siliceous  wa- 
ters. 

R.     Excelsior  Geyser,  Midway  Basin — siliceous  waters. 

S.     Great  Geyser,  Iceland — siliceous  waters. 

T.     Hot  Spring,  Sulphur  Bank,  Clear  Lake,  Cal. — borate  water. 

U.     Viry,  Seine-et-Oise,  France — phosphate  water. 

V.     Holy  Well,  Zem  Zem,  Mecca — nitrate  water. 

W.  Tuscarora  Sour  Spring,  9  miles  south  of  Brantford,  Can- 
ada— acid  water. 

X.     Solfatara  at  Pozzuoli,  Italy  (volcanic) — acid  water. 

Y.  Hot  Lake,  White  Island,  Bay  of  Plenty,  New  Zealand 
(a  10%  solution  of  HC1) — acid  water. 

*  With  much  calcium.          f  Notable  quantities  of  other  acid  radicles  present. 


COMPOSITION    OF    SPRING   WATERS  169 

CLASSIFICATION  OF  NATURAL  WATERS. 

Clarke  (4:  757)  has  summarized  the  characters  of  natural  wa- 
ters in  the  following  classification : 

I.  Chloride  waters.    Principal  negative  ion  Cl. 

A.  Principal  positive  ion  sodium. 

B.  Principal  positive  ion  calcium. 

C.  Waters  rich  in  magnesium. 

II.  Sulphate  waters.    Principal  negative  ion  SO4. 

A.  Principal  positive  ion  sodium. 

B.  Principal  positive  ion  calcium. 

C.  Principal  positive  ion  magnesium. 

D.  Waters  rich  in  iron  or  aluminum. 

E.  Waters  containing  heavy  metals  such  as  zinc. 

III.  Sulphato-chloride  waters,  with  SO4  and  Cl  both  abundant. 

IV.  Carbonate  waters.    Principal  negative  ion  CO3  or  HCO3. 

A.  Principal  positive  ion  sodium. 

B.  Principal  positive  ion  calcium. 

C.  Chalybeate  waters. 

V.  Sulphato-carbonate  waters  SO4  and  CO3  both  abundant. 

VI.  Chloro-carbonate  waters  Cl  and  CO3  both  abundant. 

VII.  Triple   waters,    containing   chlorides,    sulphates    and   car- 
bonates in  equally  notable  amounts. 

VIII.  Siliceous  waters.    Rich  in  SiO2. 

IX.  Borate  waters.    Principal  negative  radicle  B4O7. 

X.  Nitrate  waters.    Principal  negative  ion  NO3. 

XI.  Phosphate  waters.    Principal  negative  ion  PO4. 

XII.  Acid  waters.    Contain  free  acids. 

A.  Acid  chiefly  sulphuric. 

B.  Acid  chiefly  hydrochloric. 

While  this  emphasizes  the  essential  types,  it  must  be  borne  in 
mind  that  many  waters  are  intermediate  in  character  between  these 
types,  and  their  classification  with  one  or  the  other  may  be  a  matter 
of  opinion. 

GASES  AND  ORGANIC  MATTER  IN  NATURAL  WATERS. 

Besides  the  dissolved  mineral  matter  found  in  the  natural  wa- 
ters of  the  world,  there  exist  various  dissolved  gases  and  a  varying 
proportion  of  organic  matter.  The  relative  quantity  of  different 
gases  varies  according  to  the  temperature,  as  shown  in  the  follow- 
ing table  prepared  by  R.  W.  Bunsen  and  quoted  by  Clarke  (4:  45)  : 


170 


PRINCIPLES    OF    STRATIGRAPHY 

Table  of  Analayses  of 


A 

B 

C 

D 

E 

F 

G 

H 

I 

J 

K 

L 

Cl  
Br,  I,  F... 
S04  
COs  
POi 

1.35 

-3'40 
53.59 

trace 

60^97 
6.22 

55.83 
0.07 
3.12 
2.63 

53.08 
0.53 
6.03 
2.34 

58.79 
trace 
0.94 
0.61 

56.58 
0.04 
0.78 
3.13 
trace 

62.31 
0.54 
0.03 
0.27 

57.91 

'3^38 
trace 
trace 

42.00 
1.15 

0.08 
18.59 
trace 

35.00 

'4^58 
5.08 
0  03 

0.57 

69  ^  87 
4.75 

3.73 

74J6 
0.03 

NOS  
B407 

trace 

8  88 

H2S04free. 

HNOafree. 
HClfree... 
As04  
BOs  .. 

trace 
0  01 

Na  
K.. 

1.08 
0.63 

4.32 
0.21 

33.09 
0.27 

31.47 
0.96 

30.38 
3.76 

32.60 
1.16 

18.35 
1.55 

16.65 
0.93 

27.62 
0.78 

30.35 
3.79 

2.99 
0.35 

4.50 
0.03 

Li  
NH4 

trace 

0.04 
0  07 

0.04 
0  23 

0.08 

0.27 

6  22 

Ca  

Sr 

30.95 

22.37 

3.72 

3.56 

4.90 

4.05 
0  12 

13.86 

18.34 

6.03 
trace 

0.25 

7.63 

0.02 

Ba... 

0.01 

0.09 

Mg  
Mn 

3.45 

2.62 

1.13 

1.57 

0.40 

0.61 

1     «    A. 

2.53 

0.04 

3.41 

0.01 

13.18 

17.45 

Fe"  
Fe'" 

>  0.04 

Fe  
FesOa  

'6'49 

6!66 



0.25 

trace 

'6'03 

trace 


\  0.02 

'oioi 

AhO,  
Al 

0.02 

6  02 

0.54 
0  43 

trace 

0.01 

SiO*  
Cd.Zn  Cu 

5.55 

2.80 

0.08 

0.16 

0.20 

0.76 

0.02 

1.78 

11.41 

0.42 

0.07 

S.As.Sb.Hg 

0.34 



Total  solid. 

100.00 

100.00 

100.00 

100.00 

100.00 

100.00 

100.00 

100.00 

100.00 

100.00 

100.00 

100.00 

Permille 
of  total  . 

0.224 

0.606 

10.589 

11.068 

23.309 

8.241 

309.175 

7.813 

12.022 

2.850 

62.371 

101.000 

The  HNOs  is  found  in  some  waters  not  included  in  this  table.    It  is  listed  here  on  account  of  its  interest  as 

Composition  (in  Percentages  of  Total  Gases)  of  Dissolved  Air  in 
Rain  Water  at  Different  Temperatures. 


0° 

5° 

10° 

15° 

20° 

Nitrogen  (N2)  

63.20 

63  35 

63   4Q 

63  62 

63.60 

Oxygen  (O2) 

33  88 

T.T.   07 

-IA      O5 

T.A    12 

^4.    17 

Carbon  dioxide  (CO2)  .... 

2.92 

2.68 

2.46 

2.26 

2.14 

100.00 

100.00 

100.00 

100.  OO 

100.00 

The  absolute  amounts  of  the  different  gases  vary  more  markedly 
with  different  temperatures.  Thus  a  liter  of  pure  surface  water, 
under  a  normal  barometric  pressure  of  760  mm.,  contains  the  fol- 
lowing absolute  and  percental  amounts  of  dissolved  gases  in  c.  c. 
(Krummel-2o:  ^pj;  Forel-8:p5  gives  somewhat  different  val- 


ues.)* 

*  See  also  Cyrus  F.  Tolman  (39). 


COMPOSITION    OF    SPRING    WATERS 
Spring  and  Well  Waters 


171 


M 

N 

0 

P 

Q 

R 

s 

T 

u 

V 

W 

X 

Y 

0.03 

'i!ai 

67.56 
trace 

10.07 
trace 
32.80 
20.76 

11.52 
0.03 
31.19 
19.15 
0.01 

27.34 
36:58 

31.64 
0.25 
1.30 
8.78 

20.91 
trace 
1.31 
25.01 
trace 

13  52 

'9  6i 

10  16 

16.49 
0.03 
trace 
21.96 

5.11 

Y74 
19.46 
22.41 
6.33 

16.44 

iiioi 

12.78 
24^  62 

22.il 
trace 

0.34 
55:68 

11.69 

io'.ei 

L91 

trace 

1.19 

1.34 

25.61 

69:62 

16.62 

trace 

65  42 

0  24 

0  29 

'ijs 

0.26 
'2:54 

Yes 

3.78 
0.10 

17:50 

32:49 
1.35 

'2:23 
0  01 

7^3 
8.96 

"4:25 

26:  42 
1.93 
0.40 
trace 
0.11 

3L34 
2.43 
0.15 
trace 
0.17 

i^ri 

1.88 
6:28 

24:99 
trace 

'7'88 
trace 

'3'.32 
trace 
trace 

36:38 

12^6 
6.67 

'8^70 

'6:26 
0.44 

'3:76 

trace 
0.57 

0:58 

2.91 

'6:75 
0.59 

'2:36 

25.03 

4.09 

0.65 
0.01 

5.89 

0.04 
trace 

0.17 
trace 

0.08 

trace 

1.21 

2.70 

0.50 
2  17 

0.55 
trace 
3  47 

0.34 
trace 

5.98 

0  02 

15  85 

0  13 

0  21 

0.14 

'L79 

0.13 
'3J2 

trace 
1.34 

0.12 
27!  58 

0.17 
i(L58 

45:64 

0.40 

Y.ei 

"I'M 

L39 

'i:20 

Yie 
12:72 

'0^5 

6:03 

So  32 

trace 

100.00 

100.00 

100.00 

100.00 

100.00 

100.00 

100.00 

100.00 

100.00 

100.00 

100.00 

100.00 

100.00 

7.829 

1.612 

5.431 

0.225 

1.388 

1.336 

1.131 

5.343 

0.490 

3.455 

6.161 

2.477 

158.051 

another  free  acid  in  natural  waters. 


Gases  in  a  Liter  of  Pure  Water. 


Absolute  amounts 
in  c.  c.  per  liter 

Tem- 
pera- 
ture 

Nitro- 
gen 

Oxy- 
gen 

Argon 

Carbon 
dioxide 
(C02) 

Total 

0° 

18.32 

10.26 

0-54 

0.51 

29-63 

30° 

10.46 

5-47 

0.31 

0.20 

16.44 

Percentage  of  total 
absorbed  gases  t 

0° 

61.8 

34-6 

1.8 

i-7 

100.00 

30° 

63-6 

33-3 

19 

I  .2 

100.00 

*  Compare  with  table  of  absorbed  gases  in  rain  water,  p.  1 70. 


172  PRINCIPLES    OF    STRATIGRAPHY 

The  amount  of  dissolved  gases  depends  directly  on  the  pressure 
on  the  water.  Thus  a  lake  lying  in  lowlands  contains  more  dis- 
solved gases  than  a  mountain  lake,  where  the  pressure  is  less.  With 
rising  barometer  and  sinking  temperature  the  upper  strata  of  water 
of  a  lake  will  absorb  more  gases,  while  with  falling  pressure  and 
rising  temperature  gases  will  be  given  off.  Change  in  temperature 
is,  however,  more  important  than  change  in  pressure.  With  a  rise 
from  o°  to  25°  C.  the  power  of  water  for  absorption  of  gases  de- 
creases from  30  to  40%,  while  the  extremes  of  pressure  bring  about 
a  change  in  absorption  of  only  about  6%.  The  surface  waters  of 
lakes  are  generally  saturated  with  atmospheric  gases,  though  the 
presence  of  living  animals  and  plants  and  the  decay  of  organic  mat- 
ter tend  to  disturb  the  normal  balance.  In  the  deeper  strata  of  the 
waters  of  lakes  the  power  to  absorb  gases  is  much  greater,  owing 
to  the  increased  pressure,  but  as  a  matter  of  fact  the  actual  amounts 
correspond  more  nearly  to  those  obtained  in  surface  waters  during 
periods  of  low  temperature.  This  is  due  to  the  fact  that  the  deeper 
waters  depend  for  their  atmospheric  gases  upon  the  amount  fur- 
nished them  by  the  upper  layers,  when  supersaturated,  this  amount 
being  greatest  in  the  cold  period ;  or  upon  the  amount  carried  down 
to  the  deeper  strata  by  surface  waters  acting  as  convection  cur- 
rents, when  the  temperature  of  the  surface  has  sunk  to  that  of 
the  deeper  strata.  In  the  deeper  strata  of  lake  waters  a  deficit  in 
oxygen  and  an  increase  in  CO2  may  further  develop  through  the 
physiological  activities  of  bottom  organisms  or  the  decay  of  organic 
matter.  This  change  is  less  marked  in  surface  waters,  owing  to  the 
balancing  effect  of  chlorophyll-bearing  plants,  which  are  absent  in 
the  deeper  waters.  (See  Chapter  XL) 

From  the  tables  above  given  it  is  clear  that  the  proportion  of 
oxygen  to  nitrogen  is  much  higher  in  the  absorbed  air  of  water 
than  in  the  normal  atmosphere.  The  latter  has  21  parts  of  oxygen 
to  78  parts  of  nitrogen,  the  proportion  being  in  round  numbers  as 
1:4.  In  the  absorbed  air  of  pure  fresh  water  the  proportion  of  O 
to  N  at  o°  is  as  34.6:61.8,  and  at  30°  as  33.3:63.6,  or,  in  round 
numbers,  in  either  case  as  1:2.  In  applying  this  fact,  however,  to 
the  available  oxygen  for  aqueous  plant  and  animal  life,  it  must  be 
borne  in  mind  that,  though  the  proportion  of  oxygen  to  nitrogen 
is  greater  in  water  than  in  air,  the  absolute  amount  of  oxygen  per 
liter  of  the  medium  in  which  the  organism  breathes  is  vastly  greater 
in  air  than  in  water,  being  210  c.  c.  for  each  liter  of  air,  and  only 
10  c.  c.  for  each  liter  of  water. 

ORGANIC  MATTER.  This  is  present  in  solution  in  many  waters, 
especially  those  of  rivers  and  lakes.  Calculated  in  percentages  of 


ORGANIC    MATTER    IN    STREAMS 


173 


total  solids,  we  find  that  it  rises  in  sonic  of  the  tropical  streams  to 
more  than  fifty  per  cent.  The  variation  is  shown  in  the  following 
table  (Clarke-4:^)  : 


Table  of  Organic  Matter  in  Various  Streams  in  Percentages  of  the 

Total  Solids. 


Danube 3.25 

James 4. 14 

Maumee 4 . 55 

Nile 10.36 

Hudson 1 1 . 42 

Rhine 1 1 . 93 

Cumberland 12 .08 

Thames 12.10 

Genesee..  .  12.80 


Amazon 15-03 

Mohawk 15 .34 

Delaware 16 .  oo 

Lough  Neagh,  Ireland. ...    16.40 

Xingu 20  ~63 

Tapajos 24 . 16 

Plata 49-59 

Negro 53.89 

Uruguay 59 . 90 


In  the  tropical  streams  at  the  end  of  the  list  the  high  percentage 
is  due  to  the  contributions  formed  by  tropical  swamps  through  which 
they  flow.  Lough  Neagh,  Ireland,  derives  its  organic  matter  in  part 
from  peat  bogs. 

Among  the  vegetable  acids  present  are  Humic  acid  (C20H10OG), 
Geic  acid  (C20H12O7),*  and  Ulmic  acid  (C20H14O6),*  derived 
from  peat  or  soil  richly  charged  with  decaying  vegetation.  They 
form  various  compounds  or  salts,  such  as  ammonium  humate,  so- 
dium and  potassium  humates,  calcium  humate,  magnesium  humate, 
ferric  humate,  etc.  The  alkaline  salts  are  easily  soluble  in  water,  but 
those  of  the  alkaline  earths  and  metallic  oxides  are  not  soluble  or 
only  with  great  difficulty,  but  these  are  soluble  in  aqueous  alkalies, 
especially  ammonia  and  its  carbonate.  Humic  acid  itself  dissolves  in 
8>333  Parts  of  water  at  6°  C.  and  in  625  parts  at  100°  C.  It  is  in- 
soluble in  water  free  from  nitrogen  or  air.  Among  the  products  of 
higher  oxidation  of  these  acids  are  the  more  soluble  crenic  acid 
(C24H30O19  Wurtz),  or  Quellsaure,  and  apocrenic  acid  (C24H14O13 
Wurtz),  or  Quellsalzsaure.  The  former  occurs  in  the  waters  of 
probably  all  springs,  rivers,  lakes,  etc.,  and  in  rain  water,  rotten 
wood,  peat,  and  tilled  soil,  and  in  bog  ore,  ochre,  etc.  It  is  easily 
soluble  in  water;  its  alkali  salts  (ammonium  crenate,  etc.)  are,  how- 
ever, soluble  to  a  less  degree.  Some  of  the  salts  of  the  alkaline 
earths  (calcium  crenate)  require  much  water,  while  others  (mag- 
nesium crenate)  are  easily  soluble.  The  salts  of  metals  are  insoluble 
(aluminium  crenate,  ferric  crenate)  or  slightly  soluble  (ferrous 
crenate,  manganese  crenate).  Apocrenic  acid  also  occurs  in  the 

*  Formulas  according  to  Mulder,  others  give  different  formulas.     (See  Julien- 


174  PRINCIPLES    OF    STRATIGRAPHY 

waters  of  springs  and  rivers,  and  in  tilled  soil,  peat,  decaying  wood, 
and  bog  ores ;  it  easily  dissolves  in  water.  The  salts  of  the  alkalies 
and  alkaline  earths  are  soluble,  the  latter  to  a  less  degree.  Some 
of  the  apocrenates  of  the  metals  are  soluble,  others  insoluble. 

f  he  solvent  action  of  these  acids  on  siliceous  rocks  is  of  con- 
siderable importance.  Humic  acid  is  said  to  decompose  silicates. 
The  various  humous  acids  absorb  nitrogen  from  the  air  and  form 
azohumic  acids,  which,  in  the  presence  of  alkaline  carbonates,  are 
capable  of  dissolving  silica,  especially  when  it  is  in  the  amorphous 
state,  though  even  quartz  is  corroded.  From  this  it  follows  that  a 
stream  well  supplied  with  these  organic  acids  may  acquire  a  high 
percentage  of  silica  in  solution,  unless  the  solvent  power  is  neu- 
tralized in  some  way.  Since  tropical  streams  carry  the  highest  per 
cent,  of  organic  matter  they  are  likely  to  be  rich  in  dissolved  silica. 
Thus  the  Uruguay  River,  with  59.9%  of  the  total  solids  as  organic 
matter  contains  46.22%  of  the  remainder,  or  18.53%  °f  the  whole, 
of  SiO2,  though  the  total  salinity  (inorganic)  is  only  0.04  permille. 
In  the  St.  Lawrence,  along  the  borders  of  which  "the  granite  of  the 
main  and  islands  is  almost  everywhere  covered  with  peat,  full  of 
stagnant  ponds  of  dark  bog  water"  (Hunt),  SiO2  forms  23%  of  its 
total  dissolved  inorganic  matter,  while  the  Ottawa,  which  "drains 
a  region  occupied  chiefly  by  crystalline  rocks,  covered  by  extensive 
forests  and  marshes"  (Hunt-i6: 126]  Julien-i 7:555),  has  33.7% 
of  its  total  dissolved  inorganic  matter  as  SiO2. 


CHEMICAL  WORK  OF  THE  NATURAL  WATERS. 

The  chemical  work  of  the  natural  waters  is  chiefly  that  of  the 
ground  water,  and  is  primarily  confined  to  that  zone  or  belt  within 
the  earth's  crust  which  is  permanently  occupied  by  this  water,  i.  e., 
that  zone  extending  from  the  level  of  the  ground  water  or  the  water 
table  to  the  greatest  depth  to  which  such  water  extends.  This  belt, 
for  which  Van  Hise  estimates  the  great  depth  of  10,000  or  12,000 
meters,  but  which  others  believe  to  be  much  less  (see  ante),  con- 
stitutes the  belt  of  cementation,  in  contradistinction  to  the  belt  of 
weathering,  which  forms  the  upper  zone  of  the  lithosphere  above 
the  level  of  the  ground  water.  In  this  latter  belt  the  activities 
are  largely  those  of  the  atmosphere,  but  the  ground  water  in  passing 
through  it  also  performs  a  considerable  amount  of  both  chemical 
and  mechanical  work,  of  which  solution  is  the  most  pronounced. 

•  The  chief  chemical  processes  going  on  in  the  belt  of  cementa- 
tion are  solution  and  redeposition,  hydration,  carbonation  and  oxida- 


CHEMICAL   WORK   OF   WATER  175 

tion.  Reduction  or  deoxidation  may  also  go  on  at  times,  and  so 
may  decarbonation  and  silicatiqn.  Solution  is  less  characteristic 
than  in  the  belt  of  weathering,  while  deposition  becomes  of  the 
greatest  significance.  Hydration  and  carbonation  are  important  re- 
actions, but  oxidation  is  confined  to  the  upper  layers. 

SOLUTION.  This  is  most  active  in  the  belt  of  weathering.  Lime- 
stone, gypsum,  and  salt  beds  are  dissolved  by  the  underground 
water,  with  the  production  of  caverns  sometimes  of  very  limited 
duration.  The  rate  of  solution  may  be  estimated  from  the  amount 
of  dissolved  matter  discharged  by  the  springs  of  a  given  region,  and 
some  data  are  available  for  this  determination.  Thus  the  warm 
springs  of  Bath,  England  (mean  temperature  of  120°  F.),  discharge 
annually  a  quantity  of  dissolved  sulphates  of  calcium  and  sodium, 
and  chlorides  of  sodium  and  magnesium,  sufficient  to  make  a  square 
column  of  mineral  matter  9  feet  in  diameter  and  140  feet  high 
(Ramsay,  quoted  by  Geikie-io :  477} .  The  St.  Lawrence  spring  at 
Loueche,  Switzerland,  discharges  every  year  1,620  cubic  meters 
(2,127  cubic  yards)  of  dissolved  sulphate  of  lime,  which  is  equiv- 
alent to  lowering  a  bed  of  gypsum  one  square  kilometer  (0.3861 
square  miles)  in  extent,  more  than  16  decimeters  (upward  of  5 
feet)  in  a  century  (Reclus;  Geikie-io:  477).  It  is  estimated 
that  the  Solnhofen  limestone  is  reduced  I  meter  in  thickness  in 
72,000  years  (Pfaff),  and  that  of  the  Nittany  Valley  I  meter  in  30,- 
ooo  years  (Ewing-6: 51).  T.  Mellard  Reade  has  calculated  that 
throughout  the  entire  globe  there  is  removed  annually  in  solution 
96  tons  (about  86  metric  tons  or  tonneaux)  of  material  per  square 
mile,  divided  as  follows:  Calcium  carbonate,  50  tons  (45  ton- 
neaux)  ;  calcium  sulphate,  20  tons  (18  tonneaux)  ;  sodium  chloride, 
8  tons  (7.2  tonneaux)  ;  silica,  7  tons  (6.3  tonneaux)  ;  alkaline  car- 
bonates, and  sulphates,  6  tons  (5.4  tonneaux) ;  magnesium  car- 
bonate, 4  tons  (3.6  tonneaux) ;  oxide  of  iron,  i  ton  (0.9  tonneaux) 
(quoted  by  Van  Hise-4i :  486). 

The  rate  of  solution  is  strongly  influenced  by  the  temperature  of 
the  solvent.  "At  temperatures  above  100°  C,  and  especially  above 
185°  C.,  the  activity  of  water  may  increase  to  an  amazing  degree." 
(Van  Hise-4i :  79.)  It  thus  follows  that  solvent  action  of  water  is 
greater  at  the  equator  than  in  the  arctic  regions,  where  it  is  prac- 
tically at  a  standstill  when  the  temperature  is  below  o°  C.  Solution 
at  any  temperature  goes  on  until  saturation  is  reached,  which  is 
much  sooner  at  high  than  at  low  temperatures. 

Through  continued  solution  extensive  underground  channels  and 
grottos  are  produced  within  the  upper  zone  of  the  earth's  crust  in 
limestone  regions.  The  presence  of  these  is  marked  on  the  surface 


i ;6  PRINCIPLES    OF    STRATIGRAPHY 

by  sink-holes,  and  sometimes  by  depressions  filled  intermittently 
with  water.  That  all  large  caverns  are  the  result  of  solution  of 
solid  limestone  masses  has  been  seriously  questioned.  Walther 
(42:560)  has  called  attention  to  the  fact  that  large  dome-like  cham- 
bers'are  commonly  found  in  reef-like  masses  of  limestone  and  that 
these  are  covered  with  stalactic  deposits,  showing  that  deposition  and 
not  solution  has  been  active  here  for  a  long  period  of  time.  He  sug- 
gests that  many  of  these  may  be  original  hollows  in  the  reef  masses, 
such  as  are  known  to  occur  in  structures  of  this  type. 

No  minerals  are  wholly  insoluble  in  the  ground  water  solutions, 
even  quartz,  the  most  resistant,  being  at  times  attacked  by  moisture- 
carrying  solvents.  (Hayes-i4.) 


FIG.  25.     Karren  or  lapias  (rascles)  topography  of  the  Sentis  formed  by  solu- 
tion by  surface  streams  on  a  limestone  plateau.     (After  Heim.) 

.  • 


While  solution  is  most  characteristic  of  the  belt  of  weathering,  it 
is,  nevertheless,  not  confined  to  it.  Active  solution  goes  on  in  the 
belt  of  permanent  ground  water,  but  it  is  here  balanced  by  equally 
active  deposition.  Streams  and  rain  water  form  a  rough  solution 
topography  on  limestone  plateaus.  These  are  illustrated  by  the 
Karren  or  lapiaz  of  the  Sentis.  (Fig.  25.) 

CEMENTATION.  This  is  of  equal  importance  with  solution  in  the 
belt  of  cementation,  forming  one  of  the  characteristic  processes  of 
this  belt.  It  is  practically  unknown  in  the  belt  of  weathering.  The 
material  deposited  is  largely  derived  from  the  belt  of  weathering, 
and  the  result  of  such  deposition  is  the  partial  closing  of  the  pore 
spaces  in  the  rock  below  the  level  of  ground  water.  The  expan- 
sion of  the  minerals  on  hydration  further  tends  to  close  up  these 
pores.  The  ultimate  result  of  these  processes  will  be  the  induration 


CHEMICAL  WORK  OF  WATER        177 

or  lithification  of  the  rock  masses.     (See  the  section  on  diagenesis 
of  rock  masses,  Chapter  XIX.) 

Not  only  are  the  pores  in  the  rock  masses  filled,  but  fissures  are 
closed  up  by  the  formation  of  mineral  veins.  Large  cavities,  either 
originally  due  to  some  disturbance,  or  solution-caves,  brought  into 
the  belt  of  cementation  by  a  rise  of  the  ground  water  level,  will  be 
slowly  filled  by  crystallized  mineral  matter.  In  the  lead  and  zinc 
district  of  Missouri  such  caverns  were  slowly  filling  with  crystals  of 
calcite  before  the  last  change  in  ground-water  level.  These  crystals 
have  the  form  of  huge  scalenohedrons,  some  of  them  half  a  meter  or 
more  in  length,  and  they  project  from  the  walls  in  the  manner  of 
crystals  from  the  walls  of  a  geode.  The  ordinary  deposits  of  cav- 
erns, stalactites  and  stalagmites,  characteristic  of  the  zone  of  weath- 
ering, are  wholly  absent  from  these  caverns,  which  were  but  recently 
exposed,  by  the  lowering,  through  pumping,  of  the  ground-water 
level,  from  a  few  meters  to  a  depth  of  45  to  60  meters  (Van  Hise- 


The  temperature  of  the  water  within  the  belt  of  cementation  may 
be  greatly  raised  by  the  presence  of  masses  of  hot  igneous  rock, 
the  time  of  cooling  for  which  is  much  greater  than  that  required 
at  the  surface.  The  juvenile  waters  given  off  by  such  lava  sheets 
are  likewise  in  a  highly  heated  state,  and  so  accomplish  much  solu- 
tion. 

HYDRATION.  This  is  the  chief  reaction  in  the  belt  of  cementa- 
tion, and  is  second  in  importance  only  to  deposition  or  cementation. 
Since  water  is  everywhere  present,  the  minerals  are  constantly  ex- 
posed to  it,  and  hydration  as  well  as  solution  must  result.  It  is  in 
this  belt  that  the  great  group  of  hydrous  silicates  and  oxides,  such 
as  the  hydromicas,  chlorites,  zeolites,  serpentine,  epidote,  limonite, 
and  gibbsite  form  most  abundantly.  Kaolin  and  talc  also  form  here, 
though  they  are  more  characteristic  of  the  belt  of  weathering.  Gyp- 
sum is  altered  to  anhydrite,  in  the  belt  of  weathering,  whereas  hy- 
dration may  change  anhydrite  to  gypsum.  The  change  in  the  proc- 
ess of  hydration  involves  an  increase  in  volume  of  from  30  to  50 
per  cent. 

OXIDATION.  Water  entering  the  soil  commonly  carries  oxygen 
in  solution,  the  amount  varying  with  the  porosity  of  the  soil,  lack  of 
vegetation,  atmospheric  pressure,  etc.  Oxidation  goes  on  through- 
out the  belt  of  weathering,  but  affects  only  the  upper  layers  of  the 
permanently  saturated  belt,  for  the  supply  of  oxygen  is  quickly  ex- 
hausted, and  its  replenishing  is  a  slow  process.  Normally  the  depth 
below  ground-water  level  to  which  oxidation  is  restricted  is  not  more 
than  a  few  meters,  but  in  exceptional  cases  this  may  go  much  far- 


178  PRINCIPLES    OF    STRATIGRAPHY 

ther.  Thus  in  the  Lake  Superior  mining  region  it  has  gone  to  a 
depth  of  100  meters  on  an  extended  scale,  while  in  a  few  exceptional 
cases  the  depth  affected  has  been  500  to  700  meters.  In  the  San 
Juan  district  of  Colorado  it  is  marked  at  a  depth  of  600  meters,  and 
occasionally  is  noted  at  1,000  meters.  In  the  Missouri-Kansas  lead 
and  'zinc  district,  on  the  other  hand,  oxidation  scarcely  extends  be- 
neath the  level  of  ground  water. 

In  the  belt  of  weathering,  and  to  some  extent  in  that  of  cementa- 
tion, hematite  and  limonite  are  the  common  products  of  oxidation  of 
iron  compounds.  Throughout  the  remainder  of  the  belt  where  oxi- 
dation occurs,  magnetite  is  the  common  product  of  oxidation  of  iron, 
since  this  requires  a  smaller  amount  of  oxygen  in  its  production. 
Oxidation  of  the  sulphur  of  pyrite  and  marcasite  produces  a  ferrous 
sulphate  of  ferric  oxide,  and  sulphuric  acid,  in  the  belts  where  oxy- 
gen is  abundant.  In  the  major  part  of  the  belt  of  cementation, 
where  oxygen  is  not  abundant,  magnetite  and  sulphurous  acid  are 
more  likely  to  be  formed. 

The  oxidation  of  organic  matter  produces  carbon  dioxide  and 
water,  which  join  the  circulating  ground- water,  producing  carbon- 
ates in  the  belt  of  cementation.  When  the  oxygen  is  all  exhausted, 
organic  and  other  compounds  may  be  taken  into  solution,  and  so 
give  the  waters  a  reducing  quality.  Waters  which  have  made  long 
underground  journeys  are  especially  likely  to  be  in  this  state.  Oxi- 
dation of  carbonates,  and  the  liberation  of  CO2,  may  cause  a  consid- 
erable decrease  in  volume,  amounting  in  some  instances  to  50  per 
cent.  This  may  counterbalance  the  increase  from  oxidation  of  inor- 
ganic compounds,  which,  in  some  cases,  is  as  much  as  64  per  cent. 
(Van  Hise-4i:<5oS.) 

CARBONATION.  Carbon  dioxide  is  produced  in  abundance  in 
regions  of  luxuriant  vegetation,  through  the  oxidation  of  the  carbon, 
and  hence  the  waters  entering  the  soil  here  will  be  rich  in  CO2,  but 
poor  in  oxygen.  Conversely,  in  regions  of  little  vegetation  carbon 
dioxide  will  be  lacking,  but  oxygen  may  be  carried  in  considerable 
quantity  by  the  water  sinking  into  the  ground.  If  this  water  en- 
counters buried  carbon  in  the  form  of  coal  beds  or  of  other  types, 
the  oxygen  will  be  used  up  and  carbon  dioxide  produced.  The  same 
result  is  caused  by  the  decomposition  of  carbonates  in  the  zone  of 
cementation.  Carbon  dioxide  is  also  produced  in  enormous  quanti- 
ties in  the  zone  beneath  the  ground  water  (the  zone  of  anamorphism, 
see  Chapter  XIX)  by  silication  or  the  union  of  silicic  acid  with  the 
bases  of  the  carbonate  rocks,  and  the  simultaneous  liberation  of  the 
CO2  (Van  Hise-4i). 

The  process  of  carbonation,  or  the  union  of  CO2  with  bases, 


DENSITY    OF   THE    HYDROSPHERE  179 

within  the  belt  of  cementation  is  a  slow  one,  and  much  of  the  CO2 
therefore  remains  unused  and  issues  again  on  the  surface.  The 
mineral  springs  of  the  Auvergne  district  of  France  alone  furnish  an 
amount  of  CO2,  estimated  by  Lecoq  at  7,000,000,000  cubic  meters 
per  year,  and  these  represent  only  a  small  fraction  of  the  carbonated 
waters  of  the  world.  Carbonation,  or  the  production  of  carbonates, 
is,  on  the  whole,  one  of  the  most  important  chemical  reactions  within 
the  zone  permanently  occupied  by  the  ground  water. 


DENSITY  AND  SPECIFIC  GRAVITY  OF 
THE  HYDROSPHERE. 

Pure  water  (distilled)  has  its  greatest  density  at  a  temperature 
of  4°  C.,  and  this  is  taken  as  the  unit  of  measurement,  or  i.  (Its 
salinity  is  o,  and  this  may  be  expressed  by  S',  while  that  of  any 
other  water  is  expressed  by  S.)  The  addition  of  dissolved  substances 
increases  the  density  of  the  water,  which  in  the  case  of  normal  sea 
water  of  35  permille  salinity  (35  gr.  of  salts  in  1000  gr.  of  sea  water) 
at  o°  C.  becomes  1.02812.  This  is  expressed  by  the  following 

S  o°         1.02812 
formula:  ^7— 3    =   -          —  =   1.02812,  where  S  o    represents  the 

o  4-  i 

density  of  the  water  in  question  at  o°  C.  and  S'  4°  that  of  pure  water 
at  4°  C.  For  convenience  sake  we  may  transform  the  above  formula 

(Q  O  v 

-~7 — £  • —  i  J ,  and  express  the  result  by  the  symbol  <TO. 

Thus  for  normal  sea  water  of  35  permille  salinity  <TO  =  28.12,  while, 
if  the  salt  were  NaCl  only,  o-0  would  be  26.67.  If  wholly  MgSO4,  <TO 

(S  t°         \ 
oT~8  —  i  ) 

where  t  =  the  temperature  at  which  the  density  of  the  water  in 
question  is  taken.  For  sea  water  where  o-0  =  28  *,  <r4  =  27.68,  0-15  = 
25.87,  0-15.5  =  25.76  (approx.),  0-26  =  23.24.  15°  is  the  temperature 
for  which  the  hydrometers  used  in  foreign  laboratories  are  usually 
graduated,  while  those  of  English  and  American  use  are  graduated 
for  60°  F.  (15.56°  C.).  Many  of  the  newer  instruments  are  arranged 
for  the  more  usual  temperature  of  laboratories,  which  is  25°  C.  or 
77°  F.  For  the  same  temperatures,  distilled  water  has  the  following 
densities:  o°  C.  (32°  F.)  0.99987,  4°  C.  (39.20°  F.)  i.ooooo,  15°  C. 
(59.00°  F.)  0.99913,  25°  C.  (77°  F.)  0.99707.  (See  the  table  given 
in  Krummel-2o,  232-233.)  When  the  salinity  is  known  <r0  may  be 

*28  instead  of  28.12  is  used,  since  the  tables  of  Knudsen  given  by  Krumme1 


i8o  PRINCIPLES    OF    STRATIGRAPHY 

calculated  from  the  following  formula  devised  by  Martin  Knudsen 
(Krummel-2o,  237),  where   S  represents  the   salinity  in  permille. 

o-0  =  — 0.093  +  0.8149  S — 0.000482  S2  -f-  0.0000068  S3 
According  to  this  formula  the  density  of  the  waters  of  the  Kara- 
bugas  Gulf,  which  has  a  salinity  of  285  permille,  should  be  1.353329 
at  o°  C.  or  O-Q  =  353.329,  though  since  the  salts  are  not  those  of 
normal  sea  water  this  figure  is  not  wholly  correct.  While  the 
maximum  density  of  distilled  water  (i)  is  at  +  4°  C.  (+  3.947°  C.), 
i.  e.,  a  density  when  ve  =  0.00,  that  of  sea  water  of  different  con- 
centration varies  greatly. 

The  temperature  at  which  any  given  water  is  at  its  greatest 
density  may  be  designated  6°.  Substituting  this  in  the  general 

formula  we  have  °0  =    1000  (-— ).   When  the  salinity   is   .35 

\  S  40  / 

permille,  0°  equals  — 3.524°  C.,  and  °0  =  28.22   as  compared  with 
CTO  =  28.12. 

VARIATION  IN  OSMOTIC  PRESSURE  IN  SEA  WATER. 

By  osmotic  pressure  is  meant  that  pressure  which  causes  diffusion 
between  the  solution  of  a  substance  and  its  solute,  or  between  solu- 
tions differing  in  concentration.  It  varies  directly  with  the  concen- 
tration of  the  solution,  and  increases  with  the  temperature.  Thus 
for  Baltic  water  with  a  salinity  of  7.5  °/oo,  at  a  temperature  of 
1 8°  C.  the  osmotic  pressure  is  4.9  atmospheres;  in  water  of  the  Red 
Sea,  with  40  °/oo  salinity  and  a  temperature  of  30°  C.,  it  is  26.7 
atmospheres.  Normal  sea  water  with  a  salinity  of  35  °/oo  has  an 
osmotic  pressure  of  23.12  atmospheres  at  o°  C.  For  water  of  i  °/oo 
salinity  at  o°  C.  the  osmotic  pressure  is  0.66  atmosphere  (Krummel= 
20,  table,  p.  241).  In  general  for  each  increase  of  one  permille  of 
salinity  there  is  an  increase  of  2/3  atmosphere  in  osmotic  pressure, 
equivalent  to  the  pressure  of  a  mercury  column  500  mm.  long. 

Osmosis  may  be  considered  either  as  Exosmosis,  or  that  tendency 
of  the  fluid  within  a  submerged  body  to  pass  into  the  surrounding 
fluid,  and  Endosmosis,  the  tendency  for  the  outer  fluid  to  pass  into 
the  space  occupied  by  the  inner;  or  that  action  of  the  fluid  which 
passes  with  greater  rapidity  into  the  other.  The  effect  on  organisms 
of  the  different  osmotic  pressures  is  very  marked.  Thus  a  frog 
placed  into  sea  water  loses,  by  exosmosis,  which  commences  at  once, 
a  considerable  quantity  of  water,  and  in  a  short  time  its  weight  is 
diminished  by  one-fifth.  On  the  other  hand,  a  salt-water  fish  placed 
suddenly  into  fresh  water  suffers  through  rapid  increase  by  endos- 
mosis  of  the  water  in  its  body,  which  results  in  swelling  and  death. 


TEMPERATURE    OF   WATER  181 

(Regnard-28.'4j7.)  A  direct  passage  of  organisms  from  the  fresh 
waters  to  the  sea  or  the  reverse  is  thus  attended  with  great  dangers 
to  the  organisms,  and  can  be  safely  accomplished  only  through  the 
intracontinental  waters  of  intermediate  salinity. 

TEMPERATURE  OF  THE  HYDROSPHERE. 
FREEZING  POINT  OF  WATER. 

The  freezing  point  of  pure  water  is  o°  C.  or  32°  F.  With  addition 
of  salts  the  freezing  point  is  lowered  as  shown  in  the  following 
table,  condensed  from  Krummel  (20:241). 

Salinity    I  permille,  freezing  point —  o .  055°  C. 

Salinity    5  permille,  freezing  point —  o .  267°  C. 

Salinity  10  permille,  freezing  point . — o. 534°  C. 

Salinity  15  permille,  freezing  point — o. 802°  C.    " 

Salinity  20  permille,  freezing  point —  1 . 074°  C. 

Salinity  25  permille,  freezing  point —  1 . 349°  C. 

Salinity  30  permille,  freezing  point —  i  .627°  C. 

Salinity  35  permille,  freezing  point _  1 .910°  C. 

Salinity  40  permille,  freezing  point —  2 . 196°  C. 

Ordinary  sea  water  of  35  permille  salinity  will  therefore  freeze  at 
a  temperature  of  — 1.9°  C.  or  +28.58°  F.  when  its  density  (o-t)  is 
28.21.  According  to  the  formula  given  by  Krummel,  the  surface 
water  of  the  Black  Sea,  with  a  salinity  of  18.5  permille,  will  freeze 
at  a  temperature  of  — 0.99°  C.  (+30.2°  F.),  that  of  Behring  Sea 
(30  permille)  at  — 1.6°  C.  (+29.12°  F.),  while  the  water  of  the  Baltic 
(7.8  permille)  would  freeze  at  about  —0.4°  C.  (+31.28°  F.)  If  o-0 
is  known  (see  formula  p.  180)  then  the  freezing  point  r  of  water  may 
be  calculated  according  to  the  following  empirical  formula  devised 
by  H.  J.  Hansen  of  Copenhagen  (Krummel-2o:^o). 

r  =  — 0.0086  — 0.064633  <r0  — 0.0001055  o-Q2.* 

According  to  this  formula  the  waters  of  the  Karabugas  Gulf  where 
°"o  =  353.329  would  freeze  at  a  temperature  of  — 36.016°  C  or 
— 32.836°  F.  if  it  were  of  the  composition  of  normal  sea  water. 

HEAT  CAPACITY  OF  WATER. 

The  heat  required  to  raise  a  gram  of  pure  water  from  14.5°  to 
15.5°  C.  is  the  unit  of  measurement  of  the  heat  capacity  or  specific 
heat  of  water,  and  is  called  the  small  calorie  or  gram-calorie.  Saline 
waters  have  a  smaller  heat  capacity  than  pure  water,  i.  e.,  it  takes 
less  heat  to  raise  a  gram  one  degree.  The  following  table  is  given 

*  The  formula  as  printed  in  Krummel  is  incorrect,  the  second  term  of  the 
right-hand  member  is  there  given  as  0.0064633^. 


1 82 


PRINCIPLES    OF    STRATIGRAPHY 


by  Krummel  for  the  heat  capacity  of  waters  of  different  salinity 
at  17.5°  C.  (20:272): 


Salinity  in  permille  

o 

5 

10 

15 

20 

25 

30 

35 

40 

Heat  capacity  

i  .000 

0.982 

0.968 

0.958 

0-951 

0-945 

0-939 

0.932 

0.926 

Warming  of  the  Water  Body.  The  heat  conductivity  of  water 
is  very  low.  It  has  been  calculated  that  a  mass  of  water  5,000 
meters  deep,  and  of  a  uniform  temperature  of  o°  C.,  would,  if  in 
contact  with  a  heat  source  of  30°  C.  at  the  surface,  experience  the 
following  rate  of  warming,  providing  no  other  factor,  such  as  con- 
vection currents,  etc.,  entered  in :  In  100  years  no  appreciable  in- 
crease in  temperature  would  be  found  at  a  depth  of  100  meters ;  in 
1,000  years  not  one  per  cent,  of  the  surface  warmth  is  to  be  found  at 
a  depth  of  300  m.,  while  it  takes  10,000  years  to  carry  this  fraction 
of  the  surface  warmth  to  a  depth  of  1,000  m.,  and  one  million  years 
to  carry  it  to  a  depth  of  4,900  m.  After  1,000  years  the  temperature 
at  a  depth  of  100  m.  will  be  7.3°  C.,  while  at  200  m.  it  will  be  only 
0.6°  C.  The  temperature  of  15°  C.  descends  in  a  half  year  1.3 
meters,  in  a  year  1.85  m.,  in  10  years  5.8  m.  Thus  daily  or  yearly 
variation  of  temperature  is  of  little  significance  for  great  depths  so 
far  as  conductivity  of  water  is  concerned. 

Warming  of  the  water  is,  however,  produced  by  the  absorption 
of  the  sun's  rays,  which  penetrate  to  a  certain  depth,  and  through 
vertical  convection  currents.  The  latter  are  in  part  due  to  the 
evaporation  on  the  surface  and  the  consequent  increase  in  density, 
which  brings  about  a  readjustment  between  the  denser  surface  and 
the  lighter,  deeper  waters.  In  the  tropical  waters  of  the  Indian 
Ocean  the  average  evaporation  during  the  day  is  ^4  to  ^3  mm. 
per  hour,  which,  for  a  surface  layer  of  I  mm.,  with  a  temperature 
of  26°  C.  and  a  salinity  of  35  permille  at  the  beginning,  would  re- 
sult in  an  increase  of  13  to  16  permille  at  the  end  of  the  hour,  or 
an  increase  in  density  from  1.023  to  1.033,  or  I-°37>  which  would 
cause  this  water  to  sink,  carrying  with  it  its  temperature  of  26°.  Of 
course,  the  water  begins  to  sink  long  before  it  has  reached  that 
density,  in  fact,  as  soon  as  it  becomes  slightly  heavier  through  in- 
creased salinity. 

Average  Surface  Temperature.  The  average  temperature  of  the 
surface  of  the  oceans  varies  from  —1.7°  C.  at  the  poles  to  27.4°  C. 
at  5°  N.  latitude,  the  latitude  of  maximal  surface  temperature.  It 
varies  in  the  different  oceans,  where  the  maximum  is  26.83°  C.  in 
the  Atlantic,  27.88°  C.  in  the  Indian,  27.20°  C.  in  the  Pacific.  In  all 


TEMPERATURE  OF  THE  HYDROSPHERE    183 

cases  there  is  an  abrupt  increase  between  45°  and  35°  both  north 
and  south  latitude,  where  the  temperature  is  sometimes  nearly 
doubled  in  going  toward  the  equator.  Of  course,  the  sur- 
face temperature  is  not  divisible  into  a  series  of  regular  zonal  belts, 
but  is  in  reality  quite  irregularly  distributed  owing  to  the  influence 
of  currents,  etc.  Considering  average  surface  temperatures  as  a 
whole,  it  appears  that  the  Pacific  is  the  warmest  of  the  four  oceans, 
its  mean -being  19.1°  C,  whereas  the  mean  of  the  Atlantic  is  only 
16.9°  C.  The  mean  of  the  Indian  Ocean  is  only  17°  C.  in  spite  of  its 
high  maximum  of  27.88°.  The  Pacific  is  the  great  tropical  ocean, 
so  far  as  surface  temperatures  are  concerned,  owing  to  its  great 
expanse  in  the  equatorial  region,  where  the  Atlantic  experiences  its 
greatest  contraction.  Of  the  total  surface  of  the  Pacific  59.5  per 
cent.,  or  about  3/5,  lies  between  30°  N.  and  30°  S.  latitude.  This  is 
well  brought  out  by  the  wide  distribution  of  coral  reefs  in  the  Pacific 
as  compared  with  their  occurrence  in  the  Atlantic  Ocean  ;  these  reef- 
building  coral  polyps  being  confined  to  relatively  shallow  waters. 
A  similar  difference  is  shown  in  the  temperature  of  the  air  over  the 
two  oceans,  as  noted  by  von  Tillo,  who  found  the  temperature  of  the 
air  over  the  Atlantic  2.6°  lower  than  that  over  the  Pacific.  As  will 
be  noted  later,  the  waters  of  the  Atlantic,  taken  as  a  whole,  are 
warmer  than  those  of  the  other  oceans. 

Vertical  Variation  of  Temperature.  As  has  been  noted  above, 
the  heat  conductivity  of  water  is  very  low,  and  were  it  not  for  the 
absorption  of  the  sun's  rays  by  the  deeper  strata  of  water,  and  the 
existence  of  vertical  convection  currents,  there  would  be  little  change 
in  the  temperature  of  the  deeper  waters.  Kriimmel  has  introduced 
terms  to  designate  the  downward  changes  in  temperature,  for  all 
heterothermal  water  bodies,  i.  e.,  those  in  which  the  temperature  is 
not  uniform  throughout,  or  homothermal.  When  the  temperature  of 
the  water  decreases  downward  we  have  the  anothermal  arrange- 
ment which  normally  prevails  in  the  open  ocean  and  in  some  intra- 
continental  seas  of  low  latitudes ;  when,  on  the  other  hand,  it  in- 
creases downward,  we  have  the  katothermal  arrangement,  which  is 
generally  associated  with  a  katohaline  state.  This  condition  exists 
in  the  intracontinental  seas  of  higher  latitudes  during  winter.  A 
dichothermal  arrangement,  with  a  colder  stratum  between  warmer 
upper  and  lower  strata,  is  characteristic  of  such  seas  during  the 
summer  months,  while  the  reverse,  a  mesothermal  arrangement,  with 
warmer  strata  enclosed  between  upper  and  lower  colder  layers,  is 
found  in  polar  waters,  and  may  even  extend  into  the  other  oceans. 

In  the  anothermal  arrangement  of  the  ocean  waters  the  decrease 
is,  in  general,  comparatively  rapid  and  uniform  for  the  first  500 


184 


PRINCIPLES    OF    STRATIGRAPHY 


fathoms  (915  meters)  or  more,  after  which  the  rate  of  decrease 
becomes  a  slower  one.  Thus  the  Challenger  Expedition  found  at 
one  of  its  stations  in  the  South  Atlantic  (35°  59'  S.,  i°  34'  E.)  a 
drop  from  13.4°  to  13.0°  in  the  first  100  fathom's,  i.  e.,  a  decrease  of 
only  0.4°  then  a  rapid  drop  to  about  4.5°  C.  at  400  fathoms,  or  a  de- 
crease of  about  8.5°  in  300  fathoms,  after  which  the  decrease  was 
a  slow  one  again  to  nearly  2°  at  1,500  fathoms,  or  6.5°  in  1,100 
fathoms  (Fig.  26).  In  general,  the  temperature  of  the  deeper 

-      I40C 


io!L 


500 

915 


1000 
1830 


1500F 
2745  HI. 


FIG.  26.  Diagram  illustrating  the  rate  of  decrease  of  temperature  from  the 
surface  to  1,500  fathoms.  Challenger  station,  South  Atlantic, 
35°  58'  S.  i°  34'  E.  (After  Krummel.) 

parts  of  the  oceans  becomes  relatively  uniform  below  1,000  meters, 
so  that  where  the  average  depth  is  4,000  m.  only  the  upper  *4  is 
affected.  The  other  %  °f  the  ocean  are  generally  below  3°  C., 
and  near  the  bottom  the  temperature,  even  in  many  parts  of  the 
tropics,  is  but  little  above  o°  C. 

TEMPERATURE  OF  THE  SEA. 

HORIZONTAL  AND  VERTICAL  DISTRIBUTION  OF  THE  TEMPERATURE 
IN  THE  THREE  GREAT  OCEANS.     Leaving  the  Arctic  Ocean  for  sep- 


TEMPERATURE  OF  THE  HYDROSPHERE    185 

arate  consideration,  we  must  first  note  the  principal  sources  of  the 
hot  and  cold  waters  of  the  three  great  oceans,  and  then  note  their 
distribution.  It  need  scarcely  be  repeated  that  the  chief  source  of 
warm  waters  is  the  sinking  warm  surface  water  of  the  tropical 
regions  of  the  ocean.  The  chief  source  of  the  cold  waters,  especially 
in  the  deeper  parts,  must  be  sought  in  the  antarctic  extensions  of  the 
three  great  oceans,  though  the  cold  waters  of  the  Arctic  Ocean  to 
a  considerable  extent  modify  the  surface  layers  of  the  North  Atlan- 
tic and  North  Pacific. 

The  cooling  of  the  surface  waters  of  the  antarctic  extensions  and 
the  formation  of  ice,  with  the  corresponding  extrusion  of  the  salts, 
greatly  increase  the  density  of  the  water,  which  will  sink  and  carry 
the  low  surface  temperatures  with  it.  The  following  temperatures 
have  been  recorded  for  the  antarctic  extensions  of  the  three  great 
oceans,  showing  in  each  case  a  mesothermal  arrangement.  In  the 
Atlantic  at  61°  S.  latitude  off  the  coast  of  South  America  (63°  W. 
long.)  the  Belgica  found  surface  temperatures  of  +3.2°  C,  which  at 
75  meters  depth  had  fallen  to  —  i°.o  and  at  125  meters  to  the  cool- 
est, — 1.4°  C.  Rising  beyond  this  the  temperature  reached  +0.4°  C. 
at  175  meters,  +1.9°  between  500  and  1,000  meters,  and  then  fell 
again  to  +0.6°  C.  at  the  bottom,  3,690  meters.  At  the  other  side 
of  the  Atlantic,  in  70°  30'  south  latitude,  off  the  South  African 
coast  (94°  W.  long.),  the  same  vessel  found  surface  temperatures  of 

—  1.8°    C.,  which  increased  downward  more  or  less  regularly  to 
+0.3°  at  175  meters,  and  to  +1.7°  C.  at  400  meters,  after  which 
it  decreased  to  the  bottom  (1,750  meters),  where  it  was  -j-o.8°  C. 
In  the  antarctic  extension  of  the  Indian  Ocean  the  Gauss  found  at 
65^°  S.  lat,  8$l/2°  E.  long,  surface  temperatures  of  — 1.80°  C, 
increasing  to  —1-75°  C.  at  75  meters,  and  then  decreasing  again  to 

—  1.90°  C.  between  175  and  200  meters.     This  is  followed  by  an 
increase  to  +0.35°  at  1,000  meters,  and  a  decrease  to  —0.20°  at  the 
bottom  of   2,821    meters.     At  62°    S.   lat.   and    56°    E.    long,   the 
Valdivia  found  surface  temperatures  of  —  1.0°  decreasing  to  —  1.6° 
at  75  meters  depth,  and  rising  again  more  or  less  regularly  to  +1.7° 
C.  at  300  m.    After  this  a  decrease  with  some  irregularity  to  — 0.4° 
C.  at  4,636  meters  occurs.     For  the  Pacific,  the  Belgica  found  at 
61°  S.  lat.  and  63°  W.  long,  surface  temperatures  of  — 1.8°  C,  in- 
creasing downward,  though  with  some  irregularity,  to  -j-i.7°  C.  at 
400  meters,  after  which  a  slow  decrease  followed  to  -f-o.8°  C.  at  the 
bottom,  of  1,750  meters. 

Turning,  now,  to  the  intercontinental  portion  of  the  three  great 
oceans,  we  find  that  the  temperature  distribution  in  the  upper  100 
meters  is  largely  affected  by  the  seasonal  variations,  which  for  the 


i86  PRINCIPLES    OF    STRATIGRAPHY 

surface  are  shown  by  the  isobars  of  February  and  August  on  tem- 
perature maps.  At  a  depth  of  100  meters  the  surface  influence 
is  still  visible  to  some  extent.  The  Indian  and  West  Pacific 
are  strongly  contrasted  with  the  Atlantic.  The  zone  of  tem- 
peratures exceeding  25°  C.  comprises  the  West  Pacific,  west  of 
125°  W.  long,  and  between  18°  N.  and  S.  lat.,  and  continues 
through  the  Banda  and  Flores  seas  into  the  Indian,  extending  north- 
westward to  Ceylon,  and  westward  beyond  the  Maldives  (to  65°  E. 
long).  In  the  Atlantic,  on  the  other  hand,  only  a  small  area  in  the 
Brazilian  current  reaches  this  mean  temperature.  Along  the  whole 
western  border  of  tropical  America,  as  well  as  tropical  Africa,  the 
temperature  of  the  water  does  not  rise  above  20°  C.  at  a  depth  of 
100  meters,  though  higher  temperatures  exist  at  the  surface.  No 
temperatures  of  o°  are  known  at  a  depth  of  100  meters  in  the 
North  Atlantic  or  North  Pacific,  except  at  the  south  end  of  Green- 
land and  in  Denmark  and  Davis  Straits  and  close  to  the  southeast 
coast  of  Kamtchatka,  where  the  cold  currents  enter  from  the  Arc- 
tic. In  Davis  Straits,  near  the  Arctic  circle,  the  surface  tempera- 
ture varies  from  +1.15°  C.  to  +2.6°  C.,  whereas  in  Denmark 
Straits  the  surface  temperature  as  well  as  that  at  100  meters  is 
—0.7°  C.,  but  at  50  meters  it  is  —1.5°  C.,  rising  to  +1.5°  C.  at  150 
m.  and  to  +  3.1  °  C.  at  200  m.  At  a  depth  of  200  meters  the  tempera- 
ture distribution  becomes  greatly  modified,  the  chief  feature  being 
the  distribution  of  the  warmer  portions  of  this  stratum  in  the  three 
great  oceans,  which,  instead  of  lying  in  the  equatorial  region,  are 
now  pushed  to  the  north  and  south  of  the  same,  an  arrangement 
which  becomes  still  more  pronounced  at  a  depth  of  400  meters.  At 
this  depth  the  zone  of  highest  temperature,  over  18°  C.,  lies  in  the 
West  Atlantic  below  the  Florida  stream,  at  about  30°  N.  lat.  Be- 
tween 22°  and  40°  N.  lat.  the  temperature  at  this  depth  is  every- 
where above  17°  C.  in  the  western  half  of  the  North  Atlantic.  In 
the  South  Pacific  a  temperature  of  16°  was  found  only  near  the 
Fiji  Islands  at  this  depth,  14°  or  even  12°  being  the  more  usual 
maximum  temperature.  At  a  depth  of  600  meters  the  area  of 
maximum  temperatures  in  the  North  Atlantic  spreads  eastward 
(between  20°  and  40°  N.  lat.)  and  shows  a  height  of  over  10°,  in- 
creasing in  some  cases  to  16.8°  (northwest  of  the  Bermudas),  while 
under  the  equator  the  temperatures  are  only  5°  or  5.5°.  Maximum 
temperatures  of  over  10°  C.  are  found  besides  in  the  South  Pa- 
cific in  scattered  areas,  and  in  the  Indian  Ocean  at  this  depth.  At 
1 ,000  meters  the  mid  North  Atlantic  is  bounded  by  the  7°  isotherm, 
which  is  deflected  northward  to  the  North  British  coast.  Tempera- 
tures of  8°  occur  in  two  areas,  between  30°  and  40°  N.  lat.  and  40° 


TEMPERATURE  OF  THE  HYDROSPHERE    187 

and  80°  W.  long.,  and  in  an  eastward  broadening  area  in  the  Span- 
ish Sea,  which  nearer  the  land  becomes  9°  or  more  and  in  the  Gulf 
of  Cadiz  11°,  thus  showing  the  influence  of  the  undercurrent  of 
warmer  Mediterranean  waters.  At  2,000  meters  in  the  southwestern 
part  of  the  South  Atlantic,  the  southern  part  of  the  Indian,  and  the 
whole  Pacific,  the  temperature  lies  between  2°  and  3°  C.  It  rises  to 
something  over  3°  in  the  other  parts  of  the  Atlantic,  except  in  the 
southwest  part  of  the  Sargasso  Sea  region  and  in  the  Spanish  Sea 
between  the  tropic  of  Cancer  and  Cape  Finisterre  on  the  north 
coast  of  Spain,  where  it  is  something  over  4°  C.  Temperatures 
above  3°  C.  are  also  found  at  this  depth  in  the  two  northern  exten- 
sions of  the  Indian  Ocean — the  Bay  of  Bengal  and  the  Arabian  Sea, 
the  latter  having  temperatures  as  high  as  5°  or  6°  C. 

At  3,000  m.  the  Pacific  has  a  uniform  temperature  of  1.6°  to  2.2° 
C.,  except  where  depressions  surrounded  by  higher  rims  occur,  as  in 
the  Fiji  *  basin  and  tire  Coral  basin,  where  the  temperatures  rise 
from  2°  to  2.7°  C.  In  the  Indian  Ocean  at  this  depth  great  uni- 
formity of  1.3°  to  1.9°  C.  occurs  with  but  few  exceptions,  notably 
beneath  the  Arabian  and  Bengal  gulfs,  where  it  rises  sometimes  to 
2.9°  C.  In  the  Atlantic  the  temperatures  are  somewhat  higher, 
falling  nowhere  below  2°  C.  north  of  40°  S.  lat.,  and  rising  more 
often  to  2.2°  or  even  2.9°  C.  Only  below  the  eastern  part  of  the 
Guinea  current,  and  the  Sargasso  Sea,  are  the  temperatures  more 
than  3°  C.,  reaching  a  maximum  of  3.7°  C. 

At  4,000  meters  and  lower  the  temperature  of  the  North  Pacific 
is  nearly  uniform  at  1.6°  to  1.7°  C,  even  in  depths  of  6,000 
meters.  The  same  temperature  occurs  in  the  various  depressions 
southwest  of  the  Hawaiian  Islands,  except  in  the  deeps,  like  the 
Tonga  and  Kermadec  deeps,  where  temperatures  as  low  as  1.1°  C. 
have  been  obtained.  Near  the  border  of  the  Antarctic  continent  the 
Belgica  found  temperatures  of  about  0.6°  C.,  while  in  the  Atlantic- 
Indian  Polar  basin,  which  descends  below  5,000  meters,  a  tempera- 
ture of  o°  to  — 0.5°  obtains.  This  cold  bottom  water  flows  north- 
ward in  the  west  Atlantic  trough,  for  in  the  basins  composing  it 
bottom  temperatures  of  0.1°  to  0.4°  are  found.  The  mid-Atlantic 
and  the  Whale  swells,  or  rises,  however,  cut  off  the  east  Atlantic  or 
South  African  trough  from  these  cold  waters  to  the  south,  for, 
although  this  descends  to  depths  of  5,000  to  5,600  meters,  the  lowest 
bottom  temperatures  found  are  +  2.2°  to  +  2.6°  C. 

In  the  Cape  trough  to  the  south  of  the  Whale  ridge  the  tempera- 
ture at  4,800  m.  is  0.9°  C.  This  shows  that  the  Whale  ridge  can- 

*  Some  .lower  temperatures  occur  in  this  basin  also,  suggesting  that  it  is  not 
completely  closed. 


i88 


PRINCIPLES    OF    STRATIGRAPHY 


not  fall  below  3,000  m.,  for  the  temperature  of  2.4°  C.  is  that  of  the 
2,950  m.  depth  (Fig.  27).  The  mid- Atlantic  rise  is  broken  in  the 
equatorial  region  just  west  of  the  great  Romanche  deep  by  cross 
channels  descending  to  5,000  m.  Through  these  channels  the  cold 
wafers  of  the  Brazil  basin  (derived  from  the  Antarctic)  find  access 

Sea    Level 


SOUTH  AFRICAN  TROUGH 

2.91 

vypT/. 

3000  M.  OR  LESS 

ilwHALE  RIDGE; 


CAPE   TROUGH 
E.4--C. 


FIG.  27.     Diagrammatic  section  of  the  Whale    Ridge   in  the   South   Atlantic, 
showing  the  differences  of  temperature  on  opposite  sides. 

to  the  North  African  basin,  but  this  trans-passage  is  a  mild  one,  ow- 
ing, probably,  to  the  narrow  character  of  the  cross  channel,  for  its 
effects  are  no  longer  noticeable  beyond  2 
normal  bottom  temperatures  of  2.2°  to  2.6° 
North  African  basin  are  found. 


0  or  3°  N.  lat.,  where  the 
characteristic  of  the 


s.o. 


N.E. 


(T 


500m 


4000" 


2000m 


FIG.  28.  Diagrammatic  transverse  section  of  the  Wyville-Thomson  Ridge 
in  the  North  Atlantic,  showing  its  effect  as  a  thermal  barrier. 
(After  Prouvot  and  Haug.) 

In  the  North  Atlantic  the  bottom  temperatures  of  2.0°  to  2.6° 
are  preserved  through  the  barring  of  the  cold  waters  of  the  Arctic 
Ocean  by  the  Wyville-Thomson  and  Faroe -Iceland  and  Denmark 
Straits  ridges,  which  completely  divide  the  two  oceans  below  a  depth 
of  550  to  580  meters.  To  the  north  of  these  ridges  the  temperature 
$inks  as  low  as  —1.2°  C.  in  2,222  meters  (Fig.  28). 


TEMPERATURE  OF.  THE  HYDROSPHERE    189 

TEMPERATURES  OF  THE  MEDITERRANEANS  AND  EPICONTINENTAL 
SEAS  DEPENDENT  ON  THE  LARGE  OCEANS.  As  a  general  chracteris- 
tic  of  mediterraneans  may  be  noted  the  deep  homothermal  bottom 
layer,  which,  as  a  rule,  has  a  somewhat  higher  temperature  than 
that  of  the  neighboring  ocean  at  the  same  depth.  Thus  the  Roman 
mediterranean  has  a  temperature  of  12.8°  between  200  m.  and  2,600 
m.,  while  the  layers  above  this  show  a  gradual  increase  to  25.0°  at 
the  surface.  The  temperature  of  the  Atlantic  in  the  Bay  of  Cadiz 
at  1,000  meters  depth  is  normally  not  over  8°,  though  the  outflow  of 
the  warm  mediterranean  bottom  water  raises  it  to  11°,  whereas  in 
depths  of  2,000  m.  the  temperature  of  this  part  of  the  Atlantic  is 
only  a  little  over  4°  C.  The  Sea  of  Marmora  below  a  depth  of  220 
to  350  m.  to  the  bottom  of  1,403  m.  has  a  homothermal  temperature 
of  14.2°,  which  is  the  approximate  winter  temperature  of  the  sur- 
face water  of  the  ^Egean  Sea.  While  thus  the  Marmora  Sea  has 
a  higher  bottom  temperature  than  the  Mediterranean,  the  Black 
Sea  shows  a  much  lower.  Here,  in  summer,  we  have  a  typical  dicho- 
thermic  stratification,  the  minimum  temperature  of  6.3°  in  the  north- 
ern part  lying  at  75  m.,  while  the  bottom  at  131  m.  has  a  temperature 
of  8.3°  C.  In  the  central  area  the  minimum  temperature  is  7.3° 
and  lies  only  45  m.  below  the  surface,  while  between  100  and  2,012 
m.  the  bottom  temperature  rises  from  8.5°  to  9.1°  C.  In  the 
southern  part  the  minimum  temperature  of  6.2°  lies  at  65  m., 
the  bottom  temperature  at  366  m.  having  risen  to  8.9°.  The  South 
China  Sea  shows  a  fall  of  10°  at  200  m.  from  the  surface  tempera- 
ture of  24°  characteristic  of  the  upper  50  m.  At  1,000  m.  the  tem- 
perature is  3.9°,  at  1,500  m.  2.6°,  but  below  i, 600  m.  to  the  bottom 
(3,480  m.)  a  homothermal  temperature  of  2.5°  obtains,  which  is  the 
average  temperature  of  the  Pacific  at  1,500  meters.  That  the 
deeper  strata  of  the  China  Sea  are  uninfluenced  by  the  correspond-  • 
ingly  colder  waters  of  the  Pacific,  which  sink  to  1.6°  at  3,000  m., 
indicates  that  the  submarine  barrier  of  this  sea  is  nowhere  below 
i  ,600  m.  Similar  conditions  are  found  in  the  Celebes  Sea,  where  a 
homothermal  state  exists  below  1,500  m.,  with  a  temperature  of 
3.67°  C.  In  the  Philippine  waters,  on  the  other  hand,  a  homother- 
mal condition  with  10.9°  exists  from  500  m.  to  the  bottom  (1,280 
meters),  and  in  the  neighboring  Sulu  Sea  a  temperature  of  10.3° 
characterizes  the  water  from  730  m.  to  the  bottom  at  4,070  m.  Here, 
then,  a  greater  separation  from  the  Pacific  is  shown.  The  Red  Sea 
offers  some  striking  features  owing  to  its  situation  in  the  tropical 
belt.  It  has  the  highest  bottom  temperatures  of  all  mediterraneans, 
this  being,  according  to  J.  Luksch,  uniformly  at  21.5°  from  700  m. 
to  its  greatest  depth  at  2,200  m.  This  is  associated  with  a  salinity  of 


PRINCIPLES    OF    STRATIGRAPHY 


from  40.5  permille  to  40.7  permille.  The  elevation  of  the  marginal 
rim  in  the  Straits  of  Bab-el-Mandeb,  which  rises  to  within  185  m. 
of  the  surface,  prevents  the  cooler  and  less  saline  waters  of  the 
Indian  Ocean  from  entering.  These  waters  in  the  Arabian  Sea  and 
Gulf  of  Aden  have  a  temperature,  at  800  m.,  of  11°  to  13°.  This 
is  4°  above  the  normal  and  is  due  to  the  outflow  of  the  warm  waters 
of  the  Red  Sea.  At  2,000  m.  the  temperature  of  the  Arabian  Sea  is 
5°  to  6°,  whereas  that  of  the  Red  Sea  at  this  depth  remains  at  21.5° 
(Fig.  29). 

The  three  Central  American  mediterraneans,  the  Mexican,  Yuca- 
tan, and  Caribbean,  show  homothermal  conditions  below  1,700  m., 
from  which  depth  the  temperature  of  4.2°  C.  continues  to  the  great- 
est depth  at  6,269  m.  In  the  corresponding  depths  of  the  Atlantic 
the  temperature  ranges  from  4°  to  2°. 


RED    SEA 


I  Pvel     GUL'r  ofr  ADEN 


Hornotherwal    2,1. 5*C 
....E200M... 


FIG.  29.     Diagrammatic  cross-section  of  the  ridge  dividing  the  Red  Sea  and 
the  Gulf  of  Aden,  to  show  temperature  differences. 

Among  the  epicontinental  seas  the  Baltic  may  serve  as  an  ex- 
ample of  a  special  type  of  low  salinity.  The  surface  temperature 
varies,  of  course,  greatly  with  the  season,  the  minimal  temperature 
ranging  in  the  Danzig  Bay  region  from  1.6°  to  2.8°  C.,  according 
to  the  rigor  of  the  winter.  This  temperature  extends  through  the 
upper  40  to  60  m.,  which  are  also  homohaline.  The  maximum 
density  of  water  of  the  salinity  of  the  Baltic  (7^2  permille)  is 
reached  at  2.4°  C.  Hence  cooler  waters  will  remain  at  the  surface. 
The  freezing  point  of  this  water  is,  moreover,  at  — 0.4°  C.  Down- 
ward the  temperature  increases,  so  that  at  the  bottom  of  the  Danzig 
Bay  temperatures  of  5.68°  and  5.88°  C.  have  been  found  in  Febru- 
ary, while  those  of  August  range  from  3.82°  to  4.90°.  In  the  Alands 
deep,  near  the  mouth  of  the  Bothnian  Gulf,  surface  temperatures 
of  —0.2°  C.  extending  to  a  depth  of  20  meters  were  found  in  Feb- 
ruary, 1903,  and  below  this  an  increase  to  3.07°  at  273  meters.  In 
the  summer  months  the  temperature  of  the  upper  layers,  varying 
in  different  years  from  20  to  45  m.,  ranges  from  15°  to  18°  or  over 


TEMPERATURE  OF  THE  HYDROSPHERE    191 

on  the  surface  and  from  14°  to  nearly  16°  at  the  bottom.  Below 
this  surface  layer  a  sudden  drop  occurs,  a  feature  characteristic  of 
fresh-water  lakes.  Thus  east  of  Bornholm  observations  by  F.  L. 
Ekman  in  July,  1877,  showed  a  surface  temperature  of  15.7°  C. 
slowly  decreasing  to  14°  at  18  meters  depth,  followed  by  a  sudden 
drop  to  8°  at  20  meters,  decreasing  regularly  to  5°  at  25  meters. 
The  salinity  here  was  7.5  permille  down  to  30  meters,  where  it  rose 
to  7.6  permille.  Such  abrupt  changes  are  found  only  in  water 
bodies  of  slight  wave  and  current  activities. 

So  far  as  measurements  have  been  made  in  Hudson  Bay,  a  nearly 
homothermal  condition  seems  to  be  indicated,  with  temperatures 
between  —0.3°  and  —1.7°,  to  a  depth  of  365  m.  The  North  Sea 
is  a  typical  and  well-studied  example  of  a  marginal  epicontinental 
sea.  Southwest  of  the  Dogger  bank  the  strong  wave  activity  and 
tides  produce  a  homothermal  arrangement  which  in  winter  has  a 
temperature  of  5°  to  6°.  Northward  and  eastward  this  decreases  to 
4°  or  even  3°.  After  a  period  of  quiet  days  a  surface  layer  of  less 
salinity  may  form  from  the  influx  of  fresh  waters,  and  with  this  a 
low  temperature  occurs.  Thus,  while  the  salinity  of  the  surface  at 
the  German  station  15  (lat.  55°  2'  N.,  long.  7°  30'  E.)  fell  to  32.5 
permille  on  February  24,  1906,  the  temperature  fell  to  2.89°  ;  both 
salinity  and  temperature-  increased  downward,  being  at  24  meters 
32.18  permille  and  3.20°,  respectively.  A  typical  kathothermal  condi- 
tion for  February  is  shown  by  measurements  off  the  mouth  of  the 
Moray  Firth  (Scottish  station  25,  lat.  58°  n'  N.,  long.  o°  32'  W.) 
on  February  18,  1904,  when  the  temperature  rose  from  6.63°  at  the 
surface  to  6.77°  at  no  m.,  and  the  salinity  from  35.10  permille  to 
35.14  permille  at  the  same  depths.  In  the  summer  the  reverse  is 
true,  the  surface  temperature  (18°)  being  slightly  higher  than  the 
bottom,  7.6°,  at  35  m.,  except  where  after  storms  a  homothermal 
and  homohaline  condition  prevails.  A  sharply  defined  stratification 
may  occur  even  here,  as  shown  by  observations  in  the  open  North 
Sea  in  August,  1905  (lat.  55°  22'  N.,  long.  4°  18'  E.),  when  it 
was  found  that  the  temperature  decreased  slowly  from  15.74°  on  the 
surface  to  15.67°  at  20  meters,  then  fell  to  11.38°  at  25  meters,  and 
to  8.26°  at  30  meters,  and  8.25°  at  43  meters.  On  the  west  side  of 
the  Great  Fisher  bank  the  observations  for  1903  show  a  sudden  drop 
from  12.24°  at  30  m.  to  6.52°  at  40  m.,  with  but  little  decrease  be- 
low this.  Such  a  condition  is  general  north  of  the  Dogger  bank. 

TEMPERATURES  OF  DEPENDENT  SEAS.  In  the  Funnel  seas  with 
closed  head  the  conditions  of  the  ocean  to  which  they  are  dependent 
prevail,  and  this  is  true  of  the  Biscayan  as  well  as  of  the  California 
type.  Where  the  head  is  open,  leading  into  a  mediterranean,  the 


192  PRINCIPLES    OF    STRATIGRAPHY 

generally  warmer  bottom  waters  of  this  sea  will  influence  the  tem- 
peratures of  the  adjoining  funnel  sea.  This  is  shown  in  the  ab- 
normally high  temperatures  of  the  Gulf  of  Cadiz  and  that  of  Aden. 

TEMPERATURES  OF  THE  ARCTIC  OCEAN  AND  ITS  DEPENDENCIES. 
Through  the  entrance  over  the  Wyville-Thomson  ridge  of  the  warm 
waters  of  the  gulf  stream,  the  eastern  part  of  the  Greenland  Sea  has 
a  surface  temperature  of  +6°  to  +7°  m  summer  and  something 
over  +7°  in  winter.  On  reaching  the  latitude  of  Spitzbergen  the 
main  branch,  much  cooled,  sinks  beneath  the  cold  but  less  dense  ice- 
bearing  East  Greenland  stream  and  turning  southwestward  pro- 
duces the  mesothermal  stratification  of  this  part  of  the  waters  as 
far  as  the  ridge  in  Denmark  Straits,  across  which  the  warm  water 
still  is  able  to  pass.  Midway  between  Spitzbergen  and  Greenland 
(78°  13'  N.  lat,  2°  58'  W.  long.)  the  temperature  is  still  3.1°  and 
decreases  more  or  less  regularly  to  —  1.3°  C.  at  the  bottom  (2,690 
m.).  Seven  degrees  farther  south,  near  the  center  of  the  East 
Greenland  Sea  (71  °N.  lat,  5°  9'  W.  long.),  a  thin  surface  layer 
of  warmer  water  has  a  temperature  decreasing  from  -j-4-60  at  the 
surface  to  +2.0°  at  25  meters,  below  which  lies  arctic  water  from 
—  1.6°  at  50  m.  to  —1.9°  at  75  m.,  and  decreasing  to  —1.3°  at 
1,516  meters.  On  the  east  coast  of  Greenland  (74°  38'  N.  lat,  15° 
3'  W.  long.),  in  the  cold  East  Greenland  stream,  the  surface  tem- 
perature of  —  0.95°  decreases  to  —  i-53°  at  50  m.  depth,  and  then 
increases  again  at  the  bottom  (277  m.)  to  -(-0.70°,  showing  the  in- 
fluence of  the  warm  submerged  Gulf  Stream  drift  from  180  m. 
downward.  In  Denmark  Straits  wrest  of  Iceland  and  a  little  below 
the  Arctic  circle  (66°  25'  N.  lat.,  25°  50'  W.  long.)  the  surface 
temperature  of  -f  1.7°  sinks  to  —  1.4°  at  20  m.,  to  —  1.6°  at  30  m., 
and  rises  again  to  —0.8°  at  40  m.,  these  temperatures  representing 
the  East  Greenland  stream.  Then  at  50  meters  the  temperature  sud- 
denly rises  to  +5.3°,  increases  to  +6.3°  between  75  and  100  m.,  and 
then  sinks  again  to  +5-°°  at  300  m.,  then  more  rapidly  to  —0.5° 
at  600  m.,  and  to  —  1.1°  at  650  m.,  the  bottom.  Where  the  water  is 
strongly  and  normally  influenced  by  the  Gulf  Stream  drift  only  an 
anothermal  arrangement  occurs,  as  north  of  the  Faroe  Islands  (63° 
22'  N.  lat.,  5°  29'  W.  long.),  where  the  temperature  sinks  from 
+  10.0°  C.  at  the  surface  to  —  1.2°  at  2,222  fathoms.  The  measure- 
ments above  given  were  made  in  the  summer ;  for  the  winter  months 
the  temperature  in  the  upper  100  meters  is  much  lower,  the  differ- 
ence amounting  at  the  surface,  between  July  and  April,  to  six 
degrees. 

In  general  the  temperature  of  the  East  Greenland  Sea  below 
600  m.  is  down  to  o°,  while  from  800  or  1,000  m.  to  3,800  m.  homo- 


TEMPERATURE  OF  THE  HYDROSPHERE    193 

thermal  conditions  at  —1.2°  to  —1.3°  C.  exist.  In  the  Central 
Polar  Sea,  the  temperatures  of  the  upper  strata  (themselves  of  a 
dichothermic  arrangement)  are  mostly  below  — 1°  C.  and  range 
from  1 60  m.  to  200  m.  in  depth,  where  the  temperatures  sometimes 
are  as  high  as  —0.2°.  A  second  stratum  of  mesothermal  character 
ranges  from  -(-0.2°  to  -(-1.2°  and  lies  between  200  and  800  meters 
in  depth,  while  a  third  deeper,  nearly  homothermal,  one  of  —0.7° 
to  —0.8°  extends  to  depths  of  3,000  and  3,800  meters,  though  the 
actual  temperature  of  — 0.7°  is  not  reached  above  1,400  to  2,000 
meters  depth.  Of  the  other  dependencies  of  the  Arctic  Ocean  the 
shallow  White  Sea  has  winter  temperatures  of  —1.9°  to  — 1.6°, 
which  range  throughout  and  are  associated  with  a  salinity  of  34.85 
permille  and  30.08  permille,  respectively.  In  the  summer  months 
the  temperature  rises  to  over  +  13°  on  the  surface,  but  below  30  m. 
the  temperature  is  under  o°,  while  below  120  m.  it  is  — 1.6°,  as  in 
winter.  This  does  not  hold  for  the  very  shallow  bays,  however, 
where  temperatures  of  8°  to  9°  and  over  are  still  found  at  the  bot- 
tom of  30  to  35  meters. 

MEAN  TEMPERATURES  OF  THE  OCEANS  AND  INTRACONTINENTAL 
SEAS.  The  mean  temperatures  of  the  four  oceans  have  been  de- 
termined to  be  as  follows  (Krummel-2o:^p5),  see,  ante,  p.  146: 
Arctic,"  —0.66°  ;  Pacific,  +3.73°  ;  Indian,  +3.82°  ;  Atlantic,  +4.02°  ; 
mean  of  three  larger  oceans,  -)-3.86°.  This  shows  that,  taken  as  a 
whole,  the  Atlantic  is  warmer  than  the  other  oceans,  this  being  due 
to  the  comparatively  high  bottom  temperatures.  As  already  noted, 
when  surface  temperatures  alone  are  considered  those  of  the  Pacific 
are  higher  than  those  of  the  other  oceans.  Of  the  mediterraneans, 
the  Red  Sea  has  the  highest  (22.69°)  and  the  Japanese  the  lowest 
(0.90°)  mean  temperature.  In  the  latter  only  the  surface  waters 
down  to  100  or  150  m.  are  warm,  the  western  side  being  cooler 
owing  to  the  cold  southward-flowing  current.  The  deeper  waters 
of  the  central  basin  have  a  temperature  of  0.7°  to  0.3°.  Among  the 
epicontinental  seas  the  Persian  Gulf  has,  as  might  be  expected  from 
its  location,  the  highest  mean  temperature  (24°),  while  Hudson  Bay 
has  the  lowest  (1.0°). 

EUTECTIC  TEMPERATURES.  This  term  is  applied  to  the  tempera- 
ture at  which  salts  are  separated  from  cooling  waters  holding  them 
in  solution  by  the  simultaneous  crystallization  of  the  salt  and  water. 
This  temperature  is  always  lower  than  the  temperature  of  freezing 
water,  and  differs  for  the  different  salts  in  the  following  order,  as 
shown  by  Pettersson  (27:501,  see  also  Krummel-2o:5oj)  ;  Na^SO4 
(-0.7°)  ;  KC1  (-n.r ).;  NaCl  (-21.9°)  ;  MgCla  (-33-6°) ;  CaCl2 
(  —  55°).  With  progressive  cooling  the  salts  would  thus  be  sep- 


194 


PRINCIPLES    OF    STRATIGRAPHY 


arated  out  in  the  above  order,  sodium  sulphate  first  and  calcium 
chloride  last.  Owing  to  the  presence  of  the  other  salts  in  sea  water, 
however,  Na2SO4  does  not  separate  out  at  its  eutectic  temperature 
of  —0.7°,  but  only  at  —8.2°.  When  the  entire  mass  is  frozen,  a 
mixture  of  ice  and  salt  crystals  results,  the  so-called  cryohydrate, 
which  may  be  compared  with  graphic  granite  (pegmatite),  the  best 
known  eutectic  among  rocks.  The  following  table  shows  the  results 
of  Ringer's  experiment  in  freezing  1,000  grams  of  sea  water  of 
35.05  permille  salinity  (Krummel-2o:50^)  : 


At  temperature  of  

—5° 

—8.2° 

—10° 

—15° 

—23° 

Liquid  remains,  grams  

420.  5 

281.5 

2^4.0 

186.1 

114.0 

Solid  occurs,  mostly  ice,  in  grams  .... 
Solid  Na2SC>4  in  grams  in  above  solid  . 

570-5 
o.o 

718-5 

o.o 

766.0 

1.84 

813.9 
3.09 

865.1 

3-68 

Temperatures  lower  than  —8.2°  C.  exist  in  the  drift  ice  itself 
near  the  surface  (at  depth  of  40  cm.)  from  October  to  May  in- 
clusive, falling  close  to  —24°  in  January.  At  a  greater  depth  the 
temperature  is  invariably  higher  in  the  cold  months  and  lower  in  the 
warm.  Thus  at  200  cm.  depth  the  January  temperature,  which  at  40 
cm.  was  —23.9°,  was  — 10.6°,  while  the  July  temperature,  which  at 
40  cm.  was  —  0.5°,  was  at  200  cm.  — 1.4°  C.  In  all  cases  the  ice  in 
winter  is  warmer  than  the  air  above  it.  The  water,  however,  retains 
a  nearly  constant  temperature  of  —1.5°  to  —1.7°  C.  From  the  above 
considerations  it  appears  that  sea  ice  is  likely  to  be  richer  in  sul- 
phuric acid  (SO3  -f~  H2O)  than  normal  sea  water,  while  sea  water 
coming  in  contact  with  ice  at  a  temperature  below  —8.2°  C.  will 
have  its  SO3  extracted  and  so  become  poorer  in  this  substance.  On 
the  other  hand,  portions  of  the  ocean  where  the  sea  ice  melts  will 
be  richer  in  SO3  than  normal  sea  water.  The  normal,  according  to 
Dittmar,  is  11.576  parts  of  SO3  to  100  Cl;  according  to  Forchham- 
mer,  it  is  n.88;  and,  according  to  Schmelck,  it  is  11.46.  Pack  ice 
melted  by  Irvine  gave  10.84,  H-97,  and  H-93  for  different  samples, 
two  of  them  higher  than  the  highest  figure  for  normal  sea  "water. 
One  piece  of  ice  melted  by  Hamburg  gave  a  proportion  of  SO3  of 
57.4  or  5  times  as  much  as  normal  sea  water.  This,  however,  had 
only  0.05  permille  of  chlorine. 

RANGE  OF  TEMPERATURE  OF  THE  OCEANS.  The  annual  range  of 
temperature  of  the  waters  is  of  greater  bionomic  significance  than 
the  absolute  temperature  itself.  Sir  John  Murray  has  mapped  these 


TEMPERATURE  OF  THE  HYDROSPHERE    195 

for  the  oceans  (23)  and  from  his  maps  the  following  general  facts 
may  be  taken:  For  tropical  waters,  the  range  is  small  (less  than 
10°  F.  or  5.55°  C.)  in  the  Pacific  between  the  tropics  of  Cancer  and 
Capricorn,  except  off  the  west  coast  of  South  America,  where  the 
range  increases  to  15°  or  even  20°  F.  (11.11°  C.).  In  the  Atlantic 
this  small  range  of  less  than  10°  F.  occupies  about  the  same  position, 
except  off  the  North  African  coast  and  the  Gulf  of  Guinea.  A  sim- 
ilar low  range  occurs  in  the  Indian  and  Australian  waters  between 
20°  N.  and  S.  lat.,  except  in  the  Madagascar  region,  where  a  greater 
range  exists.  Similar  small  ranges,  but  for  low  temperatures,  exist 
in  the  Arctic  Ocean,  except  where  the  Gulf  Stream  carries  warmth 
to  Iceland,  and  in  the  southern  parts  of  the  other  oceans  below  50° 
or  60°  S.  lat.  Ranges  of  20°  or  over  exist  in  the  North  Pacific 
north  of  40°  N.  lat.  and  in  the  North  Atlantic  between  30°  and  55° 
N.  lat.,  likewise  in  the  South  Atlantic  and  Indian  between  30°  and 
50°  S.  lat.,  from  South  America  to  New  Zealand.  The  greatest 
ranges  of  temperature,  more  than  50°  F.,  or  27.78°  C.,  are  found  in 
the  west  Atlantic,  eastward  from  the  New  England  coast,  and  in 
the  western  part  of  the  Philippine  Sea.  Ranges  from  30°  to  40°  F. 
(16.66°  to  22.22°  C.)  are  found  off  the  Rio  de  la  Plata,  and  in  the 
Roman  Mediterranean,  the  Black,  Caspian,  and  Baltic  seas  and  in 
part  of  the  North  Sea,  and  in  the  northern  ends  of  the  Red  Sea  and 
Arabian  Gulf,  as  well  as  the  western  North  Atlantic  and  the  western 
or  Asiatic  Pacific. 

Shifting  of  the  areas  of  great  range  of  temperature  may  be 
brought  about  by  storms  or  by  change  in  currents  or  otherwise,  and 
such  a  shifting  may  be  lateral  or  vertical.  This  results  generally  in 
the  wholesale  destruction,  of  animal  life  adapted  to  a  smaller  range, 
as  illustrated  by  the  enormous  destruction  of  Tile  fish  off  the  New 
England  coast  in  1882,  which  exceeded  in  estimation  the  number  of 
one  billion,  and  covered  the  floor  of  the  ocean  in  this  region  to  a 
depth  estimated  at  six  feet  with  the  bodies  of  dead  Tile  fish.  The 
influence  of  the  changes  in  temperature  on  the  destruction  of  life 
will  be  more  fully  discussed  in  a  subsequent  chapter. 


TEMPERATURES  OF  THE  TERRESTRIAL  WATERS. 

TEMPERATURES  OF  LAKES,  ETC.  Since  lakes  are  mostly  shallow 
the  seasonal  variations  in  temperature  are  more  pronounced  through- 
out than  in  the  oceans  or  mediterraneans.  The  chief  source  of  heat 
is  the  sun,  whose  rays  are  absorbed  to  a  greater  or  less  extent.  Re- 
flection from  the  surface,  however,  greatly  reduces  the  amount 


196  PRINCIPLES    OF    STRATIGRAPHY 

which  would  otherwise  go  to  heat  the  water,  this  reflection  being  in 
some  instances  with  the  sun  near  the  horizon  as  high  as  68%  of 
the  total  radiation  received  (Dufour-5).  The  heat  taken  up  by  the 
water  is  chiefly  absorbed  by  the  upper  layers;  and  absorption  is 
greatest  in  water  containing  much  sediment  in  suspense.  Contact 
with  warm  air  further  warms  the  upper  layers  of  the  water.  Trans- 
portation of  the  superficial  heated  layers  to  cooler  depths  occurs  by 
convection  as  well  as  by  wind  or  by  currents.  Loss  of  heat  from  the 
upper  layers  occurs  through  radiation,  and  through  conduction  or 
contact  of  the  surface  with  cold  air.  Fresh  water  has  its  maximum 
density  at  +4°  C.  (+39.2°  F.)  and  this  may  serve  as  a  dividing 
line  between  warm  and  cold  fresh  water,  the  former  being  above,  the 
latter  below  this  temperature  (Forel-8: 105).  The  densest  layers 
sink,  of  course,  to  the  bottom,  and  so  warm  water  will  show  an  ar- 
rangement of  strata  progressively  cooler  downward,  i.  e.,  an  ano- 
thermal  arrangement.  This  has  been  called  direct  stratification. 
Cold  water,  on  the  other  hand,  i.  e.,  that  below  4°  C.,  will  have  a 
reversed  stratification,  the  warmer  but  denser  layers,  i.  e.,  those  at 
or  near  4°  C.,  lying  at  the  bottom,  and  the  colder  above.  The  tem- 
perature arrangement  will  be  katothermal.  For  saline  lakes,  the 
temperature  corresponding  to  their  maximum  density  must  be 
chosen  as  the  dividing  point. 

Classification  of  Lakes  According  to  Temperature.  From  the 
viewpoint  of  temperature  three  types  of  lakes  may  be  recognized : 
a.  tropical,  where  the  water  is  always  above  the  maximum  density 
temperature  (4°  C.  for  fresh  water)  ;  b.  temperate,  where  it  alter- 
nately rises  above  and  falls  below  this  temperature;  and,  c.  polar, 
where  it  is  always  below  the  maximum  density  temperature.  These 
lakes  are,  however,  not  restricted  to  the  corresponding  geographic 
zones  of  the  earth.  Tropical  lakes  always  have  a  direct  thermal 
stratification,  or  an  anothermal  arrangement.  In  spring  and  sum- 
mer the  stratification  becomes  increasingly  marked,  while  in  fall 
and  winter  it  decreases  until  homothermic  conditions  are  approached 
in  winter.  Examples  of  such  lakes  are  the  great  lakes  of  upper 
Italy,  i.  e.,  Lake  Geneva  (Germ.  Genfer  See,  Fr.  Lac  Leman),  etc. 

Polar  lakes  always  have  a  reversed  thermal  stratification,  or 
katothermal  arrangement,  the  warmest  water  (not  above  4°  C.,  how- 
•  ever)  lying  at  the  bottom.  Here  the  stratification  becomes  most  pro- 
nounced in  fall  and  winter,  decreasing  in  the  spring  and  approaching 
homothermal  conditions  in  summer.  Such  lakes  occur  in  the  polar 
regions  and  in  the  mountains  of  the  temperate  regions. 

Temperate  lakes  assume  a  tropical  habitus  in  summer  and  au- 
tumn, the  stratification  being  pronounced  in  the  former  and  tending 


TEMPERATURE  OF  THE  HYDROSPHERE   197 

to  disappear  in  the  latter,  only  to  appear  in  reversed  order  as  win- 
ter approaches,  when  the  polar  type  of  reversed  stratification  is 
pronounced.  This  will  disappear  again  in  spring  and  give  place  to 
the  tropical  type.  The  minimum  and  maximum  surface  tempera- 
tures of  fresh-water  lakes  are :  for  tropical  lakes  -j-  4°  C.  and 
+  25°  C.  to  +30°  C;  for  polar  lakes  o°  and  +4°  C. ;  and  for 
temperate  lakes  below  +  4°  in  winter,  and  above  +  4°  m  summer, 
seldom  rising,  in  the  deeper  lakes  of  the  temperate  zone,  above  25° 
C.  In  all  cases  the  temperature  of  the  surface  waters  is 'lower  than 
that  of  the  air  immediately  above  it  in  summer,  and  higher  in 
winter.  The  depth  to  which  the  seasonal  variation  penetrates  is 
about  100  meters. 

Differences  of  temperature  also  exist  between  the  littoral  and 
open  lake  or  pelagic  district,  the  former  being  warmer  in  summer 
and  colder  in  winter  than  the  latter.  As  has  already  been  indi- 
cated, the  bottom  temperatures  of  tropical  lakes  are  generally  above 
4°  C.,  though  those  of  subtemperate  ones  may  be  at  times  as  low  as 
4°  C.  Temperate  lakes,  even  those  inclining  toward  either  extreme, 
i.  e.,  subtropical  and  subpolar,  have  a  normal  bottom  temperature  of 
4°,  though  the  former  may  at  times  be  greater  than  4°  and  the  lat- 
ter less.  Polar  lakes  have  a  normal  bottom  temperature  lower  than 
4°  C.,  though  the  subtemperate  ones  may  occasionally  have  as  high 
a  bottom  temperature  as  4°.  Lake  Geneva,  having  a  depth  of  309 
m.  (surface  elevation  375  m.),  is  beyond  the  influence  of  seasonal 
variation  (100  m.),  nevertheless  a  difference  of  from  0.1°  to  0.3° 
between  seasons  has  been  observed  in  the  deepest  layers.  This  is 
regarded  as  chiefly  due  to  the  sinking  down  of  sediment-bearing 
waters  of  higher  ^emperature.  The  actual  temperatures  at  the  bot- 
tom of  this  lake  are  from  -f-  4°  to  +  5°  C.,  while  the  temperature 
of  the  littoral  belt  varies  from  +  15°  to  +  25°  C.  in  summer,  that 
of  the  inflowing  Rhone  being  -f-  10°  to  +  I5°-  In  winter  the  tem- 
perature of  the  littoral  region  sinks  to  +4.5°  or  to  +5-5°  in  dif- 
ferent years;  only  near  the  shore,  in  the  shallow  littoral  region, 
does  the  temperature  fall  below  4°  and  may  fall  to  o°  with  the 
formation  of  ice.  This  results  in  the  formation  of  a  reversed  ther- 
mal stratification,  whereas  that  of  the  littoral  region  is  normal  or 
direct,  as  shown  in  the  accompanying  diagram  (Fig.  30),  copied 
from  Forel.  The  line  along  which  the  densest  water  of  4°  tem- 
perature reaches  the  surface  has  been  called  the  thermal  barrier. 

Freezing  of  Lakes.  Where  reversed  thermal  stratification  ex- 
ists the  temperature  on  the  surface  may  sink  to  o°,  and  ice  will  be 
formed.  This  is  normal  in  polar  lakes,  usual  during  the  colder 
months  in  temperate  lakes,  and  may  occur  in  the  shallow  littoral  belt 


198  PRINCIPLES    OF    STRATIGRAPHY 

of  tropical  lakes,  where  a  thermal  barrier  separates  this  from  the 
littoral  zone,  as  in  the  above  illustration  from  Lake  Geneva.  In 
quiet  lakes,  where  the  surface  water  has  reached  o°,  a  slight  lower- 
ing of  the  temperature,  as  during  a  still,  clear  night,  will  cause  the 
formation  of  a  uniform,  continuous,  though  thin  sheet  of  ice  over 
the  entire  surface,  which,  if  not  melted  -during  the  succeeding  day, 
will  thicken  the  following  night  by  addition  of  ice  on  its  under  side, 
until  a  thick  crust  is  formed.  The  increase  in  thickness  is,  however, 
at  a  diminishing  rate,  owing  to  the  low  conductivity  of  ice. 

In  disturbed  waters  ice  floes  are  formed,  a  method  of  ice  forma- 
tion characterizing  the  sea  and  rivers  as  well.  These  pancake 
masses  (Fr.  glaqons-gateaux,  Ger.  Kuchschollen)  result  from  the 
union  of  the  ice  needles  tossed  about  by  the  waves,  these  needles 
often  forming  suddenly  in  the  super-cooled  mass,  through  agita- 


FIG.  30.  Diagram  representing  thermal  barrier  of  4°  between  the  littoral  and 
pelagic  districts  of  Lake  Geneva  in  winter.  The  barrier  is  in  reality  a 
vertical  sheet.  (After  Forel-8.) 

tion,  or  through  the  dropping  in  of  snowflakes,  analogous  to  the 
formation  of  crystals  in  a  supersaturated  solution  on  agitation  or 
on  dropping  in  of  a  crystal.  The  round  form  of  the  pancake  floes  is 
due  to  the  constant  friction  they  undergo.  The  density  of  ice  is 
about  0.92,  while  that  of  pure  water  at  o°  is  0.9998676  and  that  of 
normal  sea  water  is  1.028.  (Pure  water  at  4°  [or  better  3.947°  ],- 
its  maximum  density,  is  taken  as  I.)  It  is,  therefore,  evident  that 
ice  will  float  on  fresh  as  well  as  on  salt  water  of  the  temperature 
permitting  its  formation.  Owing  to  the  addition  of  ice  fragments 
and  crystals  on  the  margins  of  the  cakes  where  they  are  thrown  by 
the  waves,  the  weight  of  the  mass  will  increase  until  it  sinks  suffi- 
ciently to  be  covered  by  a  thin  stratum  of  water,  which  will  cause 
further  addition  to  the  ice  mass  on  its  surface,  while  at  the  same 
time  it  grows  marginally  as  well  as  on  its  under  side.  The  ice  mass 
eventually  acquires  the  form  of  a  plano-convex  lens,  with  the  con- 
vex side  downward  and  a  thickness  of  a  meter  or  more.  The  ice 
floes  will  freeze  together  when  heaped  up  by  waves  or  currents  or 
when  coming  in  contact  after  the  water  has  quieted  down. 


TEMPERATURE  OF  THE  HYDROSPHERE    199 

As  the  temperature  of  ice  sinks  below  zero,  especially  at  night, 
further  contraction  takes  place,  and  thus  cracks  are  formed  in  the 
ice  sheet,  which  may  extend  for  hundreds  if  not  thousands  of 
meters  in  length  and  cross  each  other  at  various  angles.  Water 
rising  in  these  fissures  freezes,  and  so  prevents  the  closing  of  the 
old  fissures  on  the  expansion  of  the  ice  during  the  day.  A  powerful 
lateral  pressure  is  thus  inaugurated  which,  if  the  whole  lake  is 
frozen,  will  cause  the  ice  to  move  up  on  the  shore,  carrying  ma- 
terials with  it  and  building  a  shore  wall  of  ice-shoved  boulders, 
while  at  the  same  time  it  may  scratch  the  underlying  rock  layers 
and  produce  the  effect  of  glaciation.  Such  boulder  walls  and  ridges 
may  also  be  built  by  the  ice  floes  resulting  from  the  breaking  up 
of  the  ice  in  spring.  These  floes  are  driven  onto  the  shelving  shores 
by  wind  and  carry  stones  up  with  them.  This  action  is  pronounced 
in  northern  lakes  like  those  of  Labrador.  Tyrrell  (40:64  B.)  has 
described  such  ridges  around  Lake  Winnipegasie,  and  Russell  men- 
tions their  occurrence  on  other  Canadian  and  northern  United 
States  lakes,  where  they  are  found  "40  or  50  feet  from  the  water's 
edge,  are  20  feet  high,  and  broad  enough  to  furnish  convenient 
roadways."  (Russell-3i  '.52.)  The  same  lateral  pressure  through 
expansion  of  the  ice  causes  the  buckling  of  the  ice  masses  in  the 
center  of  the  lake.  Only  in  very  shallow  water  bodies  will  the  ice 
extend  to  the  bottom.  Owing  to  the  greater  density  of  water  at 
4°  C.,  this  will  sink  to  and  remain  at  the  bottom,  and  the  slow  con- 
ductivity of  both  water  and  ice  will  prevent  the  reduction  of  the 
bottom  temperature  during  the  cold  season.  It  is  in  this  way  that 
organisms  can  survive  under  the  frozen  surface  of  a  lake. 

NORMAL  AND  EXCESSIVE  TEMPERATURES  OF  STREAMS  AND  OF 
GROUND  WATER.  The  temperature  of  streams  in  a  given  area  varies 
according  to  the  season,  but  also  with  the  volume  of  water  and  with 
its  source,  the  length  of  the  stream,  the  character  of  its  bottom  and 
banks,  etc.,  so  that  different  streams  within  the  same  region  and  at 
the  same  time  may  have  different  temperatures.  Thus  streams  re- 
sulting from  melting  glaciers  will  always  be  cold,  although,  as  they 
proceed  in  their  course,  the  waters  may  be  warmed  to  a  certain  ex- 
tent by  contact  with  the  warm  air.  If  much  sediment  is  carried 
in  suspension  by  a  stream,  its  temperature  will  be  proportionally 
higher.  A  stream  flowing  through  a  lake  will,  after  leaving  the 
lake,  have  in  general  the  temperature  of  the  surface  waters  of  that 
body,  which  alone  are  carried  out.  Underground  effluents  in  like 
manner  have  the  temperature  of  the  layers  of  water  in  which  they 
originate. 

Spring  waters  vary  less  in  temperature,  for  their  sources  are 


200  PRINCIPLES    OF    STRATIGRAPHY 

generally  below  the  influence  of  the  seasonal  variation,  which  in 
temperate  regions  may  extend  to  a  depth  of  50  feet.  The  normal 
temperature  of  spring  water  lies  in  general  between  47°  and  51°  F. 

Freezing  of  Rivers.  Rivers  of  comparatively  gentle  current  will 
freeze  over  after  the  manner  of  lakes,  but  rivers  of  strong  current 
will  freeze  over  only  under  exceptional  circumstances.  In  all  cases 
the  current  continues  under  the  ice. 

Freezing  of  Ground  Water.  The  ground  water  will  sometimes 
freeze  to  an  astonishing  depth.  Thus  in  the  Tundras  of  Alaska  and 
Siberia  the  permanently  frozen  soil  often  extends  to  a  great  depth, 
that  of  Yakutsk,  Siberia,  having  been  given  as  382  feet.  (K.  E.  von 
Baer,  quoted  by  Russell~3i  :/Jo.)  Sands  saturated  with  glacial 
waters  may  freeze  throughout  and  then  behave  like  solid  rock.  In 
this  manner  faulting,  crumpling,  and  other  structures  normal  only  to 
solid  rock  have  been  formed  in  the  otherwise  unconsolidated  glacial 
sands  and  clays  of  the  glacial  period.  (Berkey  &  Hyde-i  :  223- 

#*.) 

Mechanical  work  cf  freezing  ground  water.  ( Salisbury-34 : 
208.)  The  upper  layers  of  the  lithosphere  in  high  latitudes  are 
subject  to  periodic  refrigeration  below  the  freezing  point  of  the 
ground  water.  This  is  especially  true  of  the  soil  layer,  which  may 
be  affected  to  a  depth  varying  considerably  with  the  latitude,  the 
intensity,  and  above  all  the  duration  of  the  period  of  cold.  When 
the  soil  is  frozen,  erosion  is  retarded,  and  where  the  subsoil  is 
permanently  frozen,  as  in  the  northern  regions  of  the  larger  con- 
tinents, the  arboreal  type  of  vegetation  is  absent  as  already  noted. 
The  freezing  of  the  soil  also  disturbs  the  solid  particles  in  it.  Thus 
stones  and  boulders  work  their  way  up  through  the  soil  to  the 
surface,  producing  constantly  recurring  stony  surfaces,  leading 
sometimes  to  the  belief  that  stones  "grow."  Foundation  walls  of 
buildings  which  do  not  extend  below  the  zone  of  freezing  are  like- 
wise disturbed  in  this  manner. 

Moisture  rising  from  the  soil  through  capillary  attraction  may 
freeze  as  it  reaches  the  surface  and  so  form  ice  crystals  which  push 
upward  by  addition  from  below.  These  may  be  two  or  three  inches 
in  length,  and  they  will  raise  leaves,  sticks  and  stones. 

Where  the  soil  is  thin  the  water  may  freeze  in  the  crevices  of 
the  rock  beneath  the  soil  cover,  and  so  shatter  the  rocks.  This  is 
especially  effective  where  moisture  is  abundant,  and  where  there  is 
a  frequent  change  of  temperature  from  above  to  below  the  freezing 
point.  (On  the  depth  of  frost  in  the  Arctic  regions  see  Wood- 
ward-45.) 

Thermal  Springs.     Heated  waters  reaching  the  surface  in  the 


TEMPERATURE  OF  THE  HYDROSPHERE   201 

form  of  hot  springs  either  represent  the  meteoric  waters,  which,  as 
ground  water,  descended  to  sufficient  depth  to  be  heated  to  a  high 
temperature,  or  which  by  contact  with  unexposed  igneous  masses 
became  heated;  or  it  is  juvenile  or  magmatic  water  newly  formed 
and  liberated  from  the  molten  rock.  The  temperatures  of  the  hot 
springs  and  geysers  of  Yellowstone  National  Park  and  of  Iceland 
have  been  regarded  as  due  to  the  contact  with  igneous  masses, 
though  Suess  holds  that  they  are  due  to  the  gaseous  emanations  of 
lava  masses  lying  at  moderate  depths  below  the  surface,  cooling  to 
a  certain  degree  reducing  them  to  the  liquid  state.  Surface  or 
vadose  waters  may  find  access  to  these  newly  formed  or  juvenile 
(magmatic)  waters  and  so  form  a  mixed  product. 

In  non-volcanic  countries  the  water  probably  comes  from  great 
depths.  This  is  believed  to  be  the  case  with  the  Bakewell  Buxton, 
warm  springs  of  England,  which  range  in  temperature  from  60°  to 
82°  F.,  and  the  three  hot  springs  of  Bath,  which  have  a  temperature 
varying  from  104°  to  120°,  and  yield  an  estimated  quantity  of  about 
half  a  million  gallons  daily.  Prestwich  estimates  that  the  water 
rises  from  a  depth  of  about  3,500  feet.  The  Mountain  Home  hot1 
springs  of  Idaho  have  temperatures  ranging  from  103°  to  167°  F., 
and  Russell  estimates  that  the  depth  at  which  this  temperature  would 
be  found  in  that  region  is  about  5,000  feet  below  the  surface.  The 
Hot  Springs  of  Arkansas  have  a  temperature  ranging  from  95° 
upward,  and,  if  not  magmatic,  probably  owe  their  temperature  to 
contact  with  young  igneous  rocks  still  hot. 

In  the  Yellowstone  Park  there  are  more  than  3,000  hot  springs 
and  about  100  geysers.  The  geysers  are  intermittently  eruptive  hot 
springs,  throwing  their  waters  into  the  air  at  intervals,  sometimes  to 
a  height  of  200  feet  or  more.  The  eruption  is  believed,  by  those  who 
hold  to  the  vadose  origin  of  the  waters,  to  be  due  to  the  superheat- 
ing of  a  long  column  of  water  in  a  tube  with  hot  walls.  If  this 
results  in  the  formation  of  steam  in  the  lower  part  of  the  tube  this 
may  lift  the  column,  causing  an  overflow  of  the  water  at  the  top 
and  a  corresponding  relief  of  pressure.  This  permits  a  sudden 
expansion  of  the  superheated  waters  into  steam  on  the  relief  of 
pressure,  and  a  consequent  eruption  of  the  entire  mass.  In  the 
change  of  the  water  to  steam  it  expands  about  1,700  times.  (See 
Hague-n.)  (Fig.  31.) 

MAGMATIC  OR  JUVENILE  WATERS.  The  steam  clouds  accom- 
panying volcanic  eruptions,  and  formerly  regarded  as  due  to  infiltra- 
tion of  surface  or  vadose  waters  into  the  volcanic  regions,  are  now 
held  by  many  geologists  to  be  the  result  of  gaseous  emanations  from 
the  lava  itself  and  their  cooling  and  condensation  into  steam  and 


2O2 


PRINCIPLES    OF    STRATIGRAPHY 


FIG.  31.     The  Giant  Geyser  of  the  Yellowstone.      (After   Hayden.) 

later  water.  Such  waters  are  designated  as  juvenile  or  magmatic 
waters.  Suess  holds  that,  instead  of  volcanoes  being  fed  by  infiltra- 
tions from  the  sea  (directly  or  indirectly),  the  sea  receives  additions 
through  each  eruption.  (38.)  He  believes  that  the  oceans  and  the 
whole  body  of  vadose  water  were  separated  from  the  cooling  litho- 


TEMPERATURE  OF  THE  HYDROSPHERE    203 

sphere,  in  the  form  of  emanations.  Tschermak,  Reyer,  de  Lap- 
parent,  Kemp  and  others  have  actively,  supported  the  view  of  the 
importance  of  such  magmatic  waters,  especially  as  causes  in  ore 
deposition,  a  view  advocated  by  £lie  de  Beaumont  before  1850. 
(Kemp-iQ:  610-618 \  Lincoln-2i  :  258-274.)  Armand  Gautier  (9) 
has  shown  that  when  powdered  igneous  rocks  (granites,  porphyries, 
trachytes,  gneisses,  gabbros,  etc.)  are  raised  to  a  red  heat  in  a 
vacuum  they  give  off  water  and  gases  among  which  hydrogen  and 
carbon  dioxide  predominate.  This  is  'not  water  taken  in  by  the 
rock,  but  water  of  constitution.  The  quantity  of  water  lost  at  red 
heat  varies  from  7  grams  per  kilogram  in  granite  to  nearly  17 
grams  per  kilogram  in  Iherzolite.  With  the  water  is  driven  off 
from  3  to  1 8  times  its  volume  of  gases  which  are  only  -in  small  part 
included  gases,  being  produced  mainly  by  the  action  of  the  ferrous 
salts  in  the  rock  upon  vapor  of  water  at  a  red  heat.  These  gases 
are  similar  to  volcanic  gases,  being  rich  in  free  hydrogen  and  CO2. 
The  great  eruption  of  Etna  in  1865  supplied  11,000  metric  tons  of 
water  a  day  for  200  days,  or  a  total  of  over  2,000,000  tons  for  this 
critical  period.  A  cubic  kilometer  of  granite  would  furnish  at  red 
heat,  from  25  to  30  million  tons  of  water,  one-fourth  of  which  would 
be  sufficient  to  supply  a  volume  like  that  given  out  by  Etna  during 
the  whole  eruption  of  1865.  "De  Laumy  estimates  that  the  princi- 
pal thermal  springs  of  France  discharge  a  total  of  700,000  hecto- 
liters of  water  in  24  hours.  The  water  which  issues  from  a  single 
cubic  kilometer  of  granite  raised  to  a  temperature  of  600°  or  700° 
C.  would  suffice  to  keep  all  these  springs  running  for  a  year  with  a 
flow  of  48,500  liters  a  minute."  ( Gautier-o, :  692. )  Suess  regards 
the  springs  of  Carlsbad,  Bohemia,  as  having  their  source  in  'mag- 
matic  emanations,  and  he  also  places  the  hot  waters  of  Iceland  and 
the  Yellowstone  under  this  category.  In  fact,  if  we  accept  the  con- 
clusions of  Kemp  and  others  that  the  meteoric  water  is  limited  to 
the  upper  2,000  feet  or  less  of  the  earth's  crust,  we  are  forced  to 
regard  most  thermal  springs  as  newly  originated  or  magmatic  waters 
emanating  from  a  not  too  deeply  buried  igneous  mass  which  has  not 
yet  wholly  expired.  "Thermal  springs,"  says  Armand  Gautier, 
"may  be  explained  as  a  kind  of  gentle  distillation  of  crystalline 
rocks  in  a  region  so  hot  that  water  of  constitution  tends  to  escape 
upon  a  slight  increase  in  temperature."  (9-603.)  The  view  is 
also  held  to  some  extent  by  geologists  that  mineral  veins  owe  their 
origin  to  just  such  emanations,  the  magmatic  waters  carrying  with 
them  in  solution  the  mineral  matter  to  be  deposited  in  the  fissures 
penetrated  by  these  waters.  (See  Kemp-i9  for  summary  of  most 
recent  opinions;  also  Schneider~35  and  Hague-n.) 


204  PRINCIPLES    OF    STRATIGRAPHY 

OPTICS  OF  THE  WATER. 

Of  the  greatest  importance  to  organisms  living  in  the  sea  or  in 
fresh  water  is  the  depth  to  which  sunlight  penetrates.  It  is  to  this 
depth  only  that  chlorophyll-generating  plant  life  occurs,  which  in 
turn  determines  the  depth  to  which  animal  life  subsisting  on  it  may 
penetrate.  Thus  the  Characea  exist  in  Lake  Geneva  to  depths  of 
25  m.,  while  Hypnum  lehmanie  has  been  found  as  deep  as  60  m.  (a 
single  case.)  Diatoms  extend  in  summer  to  a  depth  of  20  m.,  in 
winter  to  80  m. 

The  transparency  of  water  varies  greatly.  Thus  in  tropical  seas 
the  animal  and  plant  life  can  easily  be  seen  at  a  depth  of  20  meters 
or  more,  while  45  meters  has  been  recorded  near  the  Philippine 
Islands  as  a  depth  at  which  corals  were  still  visible.  A  white  plate 
submerged  by  von  Kotzebu  in  tropical  waters  of  the  North  Pacific 
was  still  visible  at  50  meters,  while  Wilkes  found  that  the  depth  at 
which  such  an  object  became  invisible  varied  in  the  same  region 
from  31  to  59  meters.  Observations  on  the  Gazelle  showed  that 
the  visibility  depth  of  other  colors  was  less  than  that  of  white,  the 
depth  at  which  yellow  disappeared  being  88%  of  that  at  which  white 
disappeared,  while  for  red  it  was  77%  and  for  green  67%.  Ex- 
periments with  submerged  lights  gave  for  the  Lake  of  Geneva  the 
following  results : 

Depth 
visible. 

1.  Moderator  lamp  with  vegetable  oil  (July  18,  1884)  ..41.3  m. 

2.  Edison  lamp,  7  candle  power  (March  15,  1886)  .  . .  .50.9111. 

3.  Arc  light  (August  8,  1885) 88.0  m. 

tit 
A  small  electric  lamp  of  8  candle  power  was  submerged  in  the 

Black  Sea,  where  the  depth  was  over  2,000  meters.  The  depth  at 
which  the  point  of  light  disappeared  varied  from  3.7  m.  to  40  m., 
that  at  which  the  light  disappeared  entirely  varied  from  43  to 
77  m.,  according  to  the  locality.  Measurements  made  by  expos- 
ing photographic  plates  at  various  depths  showed  that  the  influence 
of  the  light  still  extended  to  500  or  550  m.  depth.  From  various 
measurements  it  appears,  however,  that  in  the  sea  only  the  upper 
300  meters  receive  light  throughout  the  day,  while  at  350  meters 
depth  light  is  present  for  only  8  hours. 

In  fresh  water  the  depths  beyond  which  photographic  plates  are 
no  longer  affected  appear  to  be  much  less.  Thus  in  Lake  Geneva 
F.  A.  Forel  found  that  silver  chloride  plates  were  affected  in  sum- 


OPTICS    OF    THE    WATER  205 

mer  to  depths  of  45  m.  only  after  exposure  for  a  full  day,  while  in 
winter  the  depth  increased  to  no  meters.  Lake  Constance  (Boden- 
see)  gave  a  depth  for  the  same  phenomena  of  30  m.  in  summer  and 
less  than  50  m..  in  winter.  Sensitive  plates  coated  with  silver  bro- 
mide and  exposed  for  a  whole  day  in  the  Lake  of  Zurich  were 
affected  to  a  depth  of  100  meters  in  August,  1881,  and  in  the 
Walensee  to  a  depth  of  140  m.  in  October,  1891.  In  the  Lake  of 
Geneva  after  10  minutes'  exposure  Fol  and  Sarasin  found  in  August 
that  the  plates  were  faintly  affected  at  113  m.  and  not  at  all  at  237 
m.  In  September  very  faint  results  were  shown  at  170  m.  and  in 
March,  1885,  at  192  m.,  while  at  235  m.  no  effect  was  obtained. 
In  the  next  year,  however  (March,  1886),  slight  results  were  ob- 
tained at  240  m.  From  these  facts  Forel  concludes  that  the  limit 
of  light  effect  for  silver  bromide  is  between  200  and  240  meters, 
varying  with  the  season  and  the  water  body,  while  at  the  same 
time  the  depth  varies  for  different  substances  sensitive  to  light. 
(S:i34.) 

The  recent  work  in  the  North  Atlantic  by  the  Michael  Sars  has 
brought  out  some  very  interesting  results.  A  series  of  measure- 
ments of  the  intensity  of  the  light  at  various  depths  was  made,  by 
a  photometer  carrying  panchromatic  plates  and  gelatine  color  filters. 
Near  the  Azores  the  light  strongly  affected  the  plates  at  100  meters' 
depth,  the  red  rays  being  weakest  and  the  blue  and  violet  strongest. 
At  500  meters  the  blue  and  violet  rays  still  made  distinct  impres- 
sions, the  violet  and  ultra  violet  still  affecting  the  plate  at  1,000 
meters.  At  1,700  meters,  however,  not  the  faintest  trace  of  light 
effect  occurred  after  2  hours'  exposure.  Observations  in  several 
latitudes  showed  equal  intensity  of  light  as  follows : 

In  33°  N.  lat.  at  about  800  meters  depth. 
In  50°  N.  lat.  at  about  500  meters  depth. 
In  67°  N.  lat.  at  about  200  meters  depth. 

These  depths  correspond  to  those  which  were  found  to  be  the 
upper  limit  of  the  red  pelagic  crustaceans  (Acanthephyra),  as  well 
as  that  of  certain  black  pelagic  fish  (Gastrostomus,  Cyema)  in  the 
same  latitudes,  so  that  these  organisms  are  found  only  where  during 
the  daytime  the  chemically  effective  rays  from  the  violet  portion 
of  the  spectrum  are  alone  active,  or  at  depths  where  the  red  forms 
are  as  invisible  as  the  black  ones.  It  is  only  at  night  that  they 
rise  into  the  upper  strata  of  the  sea.  (Hjort-i5;  Murray  and 


206  PRINCIPLES    OF    STRATIGRAPHY 

BIBLIOGRAPHY  IV 

See  Also  References  Under  Chapters  III  and  V. 

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Structures  Preserved  in  Unconsolidated  Rocks.  Journal  of  Geology, 
Vol.  XIX,  No.  3,  pp.  223-231. 

2.  CHALLENGER  REPORTS,  PHYSICS  AND  CHEMISTRY,  Vol.  I. 

3.  CHAMBERLIN,  THOMAS  C.,  and  SALISBURY,  ROLLIN  D.     1906. 

Geology,  Vol.  I. 

4.  CLARKE,  FRANK -W.     1908.     Data   of    Geochemistry.     United    States 

Geological  Survey  Bulletin,  No.  330,  Second  Edition,  Bulletin  491,  1911. 

5.  DUFOUR,    LOUIS.     1873.     Bulletin   de  la  Societe  Vaudoise.      Sciences 

Naturelles,  XII,  i.  Lausanne. 

6.  EWING,  A.  L.     1885.     An  Attempt  to  Determine  the  Amount  of  Chemi- 

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American  Journal  of  Science,  3rd  series,  Vol.  XXIX,  pp.  29-31. 

7.  FORCHHAMMER,  GEORG.     1865.     On  the  Composition  of  Sea-Water 

in  the  Different  Parts  of  the  Ocean.  Royal  Society  of  London,  Philosophi- 
cal Transactions,  Vol.  CLV,  No.  4,  pp.  203-262. 

8.  FOREL,  F.  A.     1901.     Handbuch  der  Seenkunde.     Stuttgart. 

9.  GAUTIER,    ARM  AND.     1906.     The   Genesis   of   Thermal   Waters   and 

Their  Connection  with  Vulcanism.  English  Abstract  by  F.  L.  Ransome, 
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10.  GEIKIE,  ARCHIBALD.     1903.     Text  Book  of  Geology,  Fourth  Edition, 

Vol.  I. 

11.  HAGUE,  ARNOLD.     1912.     Origin  of  Thermal  Waters  of  Yellowstone. 

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102-122. 

12.  HAN  AM  ANN,  J.      1894.      Archiv  der  Naturwissenschaftlichen  Landes- 

durchforschung  von  Bohmen,  Prague.  Vol.  IX,  No.  4;  1898,  Vol.  X, 
No.  5. 

13.  HARRISON,  J.  B.,  and  WILLIAMS,  JOHN.     1897.     The  Proportions  of 

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Tropical  Rainwaters.  Journal  of  the  American  Chemical  Society,  Vol. 
XIX,  pp.  1-9. 

14.  HAYES,  C.  W.     1879.     Solution  of  Silica  under  Atmospheric  Conditions. 

Bulletin  of  the  Geological  Society  of  America,  Vol.  VII,  pp.  214-217. 

15.  HJORT,    JOHN.     1911.     The    Michael    Sars    North    Atlantic    Deep-Sea 

Expedition,  1910.     Geographical  Journal  (London)  April  and  May. 

16.  HUNT,  T.  STERRY,   1878.     Chemical  and  Geological  Essays.     Second 

Edition. 

17.  JULIEN,  ALEXIS  A.     1880.     On  the  Geological  Action  of  the  Humus 

Acids.  Proceedings  of  the  American  Association  for  the  Advancement 
of  Science,  Vol.  XXVIII,  pp.  311-410. 

1 8.  KEMP,  JAMES  F.    1908.    Waters  Meteoric  and  Magmatic.     Mining  and 

Scientific  Proceedings,  May  23,  1908. 

19.  KEMP,  J.  F.     1913.     The  Gound  Waters.     Transactions  of  the  American 

Institute  of  Mining  Engineers.  New  York  Meeting,  Feb.,  1913,  pp. 
603-624. 

20.  KRUMMEL,  OTTO.     1907.     Handbuch  der  Ozeanographie.     Band  I. 


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21.  LINCOLN,   F.   C.     1907.     Magmatic  Emanations.     Economic  Geology, 

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22.  MURRAY,  SIR  JOHN.     1887.     On  the  Total  Annual  Rainfall  on  the  Land 

of  the  Globe,  and  the  Relation  of  Rainfall  to  the  Annual  Discharge  of 
Rivers.  Scottish  Geographical  Magazine,  Vol.  Ill,  pp.  65-77. 

23.  MURRAY,  SIR  JOHN.     1899.     On  the  Temperature  of  the  Floor  of  the 

Ocean  and  of  the  Surface  Waters  of  the  Ocean.  Geographical  Journal, 
Vol.  XIV,  pp.  34-51,  3  maps. 

24.  MURRAY,  SIR  JOHN,  and  HJORT,  JOHAN.     1912.     The  Depths  of 

the  Ocean.     Macmillan. 

25.  PALMER,   CHASE.     1911.     The  Geochemical  Interpretation  of  Water 

Analyses.     Bulletin  479  U.  S.  Geological  Survey,  1911,  31  pp. 

26.  PENCK,  ALBRECHT.     1894.     Morphologic  der  Erdoberflache.     Band  I. 

27.  PETTERSSON,  SVEN  OTTO.     1883.     On  the  Properties  of  Water  and 

Ice.  Vega  Expeditionens  Vetenskapliga  lakttagelser,  Band  II,  Stock- 
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28.  REGNARD,  PAUL.     1891      Physique  biologique:  Recherches  experimen- 

tales  sur  les  conditions  physiques  de  la  vie  dans  les  eaux.     Paris. 

29.  RUSSELL,  ISRAEL  COOK.     1882-83.     A  Geological  Reconnaissance  in 

Southern  Oregon.  Fourth  Annual  Report  of  the  LTnited  States  Geo- 
logical Survey. 

30.  RUSSELL,  I.  C.     1885.     Geological  History  of  Lake  Lahontan,  a  Quater- 

nary Lake  of  Northwestern  Nevada.  Monograph  United  States  Geo- 
logical Survey,  No.  XI. 

31.  RUSSELL,  I.  C.     1890.     Notes  on  the  Surface  Geology  of  Alaska,     Bul- 

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Company. 

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34.  SALISBURY,  ROLLIN  D.     1907.     Physiography.     Henry  Holt. 

35.  SCHNEIDER,  KARL.     1913.     Beitrage  zur  Theorie  der  heissen  Quellen. 

Geologische  Rundschau.  Zeitschrift  fur  allgemeine  Geologic,  Band 
IV,  Heft  2,  pp.  65-102. 

36.  SCHOTT,  GERHARD.     1902.     Die  Verteilung  des  Salzgehalts  im  Ober- 

flachenwasser  der  Ozeane.     Petermanns'  Mittheilungen.,  Vol.  XLVIII, 

pp.  217-218. 
37-     SCHOTT,  GERHARD.     1912.     Geographic     des    atlantischen     Ozeans. 

Hamburg,  C.  Boyson. 
38.     SUESS,    EDUARD.     1902.     Ueber   heisse   Quellen,    Verhandlungen   der 

Gesellschaft    Deutscher   Naturforscher   und  Aerzte,  allgemeiner  Theil. 
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Relation  to  the  Carbon  Dioxide  of  the  Atmosphere.     Journal  of  Geology, 

Vol.  VII,  pp.  585-620. 

40.  TYRRELL,  J.  BURR.     1893.     Report  on  Northwestern  Manitoba,  with 

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208  PRINCIPLES    OF    STRATIGRAPHY 

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f        Vol.  I,  pp.  130-132. 


CHAPTER   V. 

MOVEMENTS  OF  THE  HYDROSPHERE  AND  THEIR    GEOLOGICAL 

EFFECTS. 

The  movements  of  the  hydrosphere  are  manifested  in  the  waves, 
the  tides  and  seiches,  the  ocean  and  river  currents,  and  the  move- 
ments of  ground  waters.  The  effects  of  these  movements  upon  the 
lithosphere  are  seen  in  mechanical  erosion  and  the  transportation 
of  eroded  material,  and  to  a  less  degree  in  chemical  solution  and 
decomposition  of  the  rock.  Diminution  or  cessation  of  motion  is 
followed  by  the  deposition  of  the  material  in  suspension.-  Deposi- 
tion of  material  in  solution  at  a  distance  from  the  source  of  origin 
is  a  further  result  of  the  movements  of  water.  The  effect  of  the 
motion  upon  the  biosphere  is  shown  by  the  increase  in  the  supply 
of  oxygen  in  the  water  and  the  transportation  of  food.  The  dis- 
tribution of  organisms  is  also  affected  to  a  considerable  degree  by 
the  currents. 

WAVES. 

These  are  the  undulatory  motions  of  water  produced  by  wind 
blowing  over  its  surface.  In  the  open  sea,  the  motion  of  the  water 
is  an  orbital  one;  the  particles  move  in  curves,  and  only  the  wave 
form  advances.  The  top  of  the  wave  is  its  crest,  the  bottom  the 
trough,  the  lines  of  both  lying  at  right  angles  to  the  direction  of  the 
wind.  The  distance  from  crest  to  crest  is  the  wave  length,  which  in 
stormy  weather  in  the  open  ocean  varies  between  60  and  150  meters 
(200  and  500  feet).  Swells  may  in  some  cases  reach  nearly  twice 
this  length,  however.  The  rapidity  with  which  wave  crests  travel 
is  the  velocity  of  the  wave,  which  varies  from  10  to  15  meters  per 
second  (22  to  33.5  miles  per  hour,  and  may  be  as  high  as  60  miles 
per  hour).  The  time  taken  by  a  crest  to  travel  a  wave  length  is 
the  period  of  the  wave,  which  in  storm  waves  varies  from  6  to  10 
seconds  or  over.  The  vertical  distance  between  the  top  of  the  crest 
and  the  bottom  of  the  trough  is  the  height  of  the  wave,  and  its  mag- 
nitude depends  on  the  strength  of  the  wind.  In  the  open  sea  the 
average  height  of  the  waves  varies  between  2  m.  (6l/2  feet)  and  5 

209 


210  PRINCIPLES    OF    STRATIGRAPHY 

meters  (nearly  i6j/2  feet),  while  storm  waves  may  have  a  height  of 
30  feet  or  over  (10-11.5  meters),  reaching  50  feet  (15+  meters)  in 
exceptional  cases.  On  the  shore  the  breaking  wave  or  the  surf 
may  be  as  high  as  100  feet,  or  even  higher.  In  mediterraneans  the 
waves  are  as  a  rule  smaller  than  in  the  open  ocean.  In  the  Roman 
mediterranean  the  maximum  height  is  probably  not  over  5  meters 
(16.38  feet).  A  height  of  4  meters  is  regarded  as  the  usual  maxi- 
mum for  storm  waves  in  the  North  Sea,  though  a  maximum  height 
of  6  meters,  a  length  of  45  meters,  and  a  period  of  9  seconds  have 
been  reported. 

The  orbits  in  which  the  water  particles  of  a  given  wave  move 
have  a  diameter  corresponding  to  the  height  of  the  wave,  while 
the  time  required  for  the  completion  of  the  circuit  by  the  water 


FIG.  32.  Diagrams  to  illustrate  wave  form,  and  its  change  with  change  in 
size  of  orbit,  strength  of  wind,  etc.  The  heavy  arrows  indicate 
the  wind  direction  and  the  direction  of  wave-form  advance.  The 
smaller  (curved)  arrows  indicate  the  movements  of  the  water  par- 
ticles. (Original.) 

particle  corresponds  to  the  period  of  the  wave.  Thus  when  a  par- 
ticle has  moved  from  the  top  of  the  orbit,  where  it  forms  a  part  of 
the  crest  of  the  wave,  to  the  bottom,  a  trough  has  replaced  the  crest, 
the  crest  has  moved  half  a  wave  length  forward,  or  half  the  wave 
period  has  been  completed,  corresponding  to  half  the  revolution  of 
the  particle  in  its  orbit.  By  the  time  the  entire  orbit  has  been 
completed  the  wave  crest  has  traversed  the  entire  wave  length ;  the 
period  is  completed.  The  length  of  a  wave  period  varies  ordinarily 
for  ocean  waves  from  5.8  to  9.5  seconds,  corresponding  to  an 
orbital  velocity  of  i.i  to  2.3  m.  per  second,  and  may  sometimes 
exceed  4  m.  per  second.  The  orbital  velocity  (v)  is  obtained  from 

the   formula,    v  =   — ,    where    h    is  the  height  of  the  wave   (or 

the  diameter  of  the  orbit)  and  r  the  wave  period.  («•  = 
3.14159265359+;  3.1416  approximately.) 


WAVES  2ii 

The  preceding  diagrams  represent  these  movements  and  the 
resultant  waves.  (Fig.  32.)  They  show  clearly  the  relation  be- 
tween the  wave  height  and  amplitude  of  the  orbits,  and  that,  with 
the  same  wave  length,  the  increase  in  the  size  of  the  orbit  brings 
about  a  corresponding  increase  in  the  height  of  the  wave.  At  the 
same  time  it  will  be  noted  that  the  crest  becomes  sharper,  the  slopes 
being  steeper  and  the  angle  more  acute.  If  the  velocity  of  the 
moving  particle  remains  the  same  with  an  increase  in  the  size  of  the 
orbit,  the  period  must  lengthen,  because  the  particles  have  a  longer 
path  to  travel  before  they  return  to  their  starting  point.  If,  on  the 
other  hand,  the  period  remains  the  same,  or  is  shortened,  giving 
the  same  or  greater  velocity  for  the  wave  progress,  the  orbital 
velocity  of  the  particles  must  increase.  This  is  also  true  when  the 
wave  increases  in  height  by  an  increase  in  the  size  of  the  orbit,  as 
is  the  case  near  shore.  With  the  same  size  of  orbit  an  increase  in 
the  wave  length  brings  about  a  reduction  in  the  sharpness  of  the 
crest.  The  change  in  wave  length  is  brought  about  by  a  relative 
change  in  the  spacing  of  particles  whose  position  in  the  orbit  differs 
by  a  uniform  degree.  Thus  if,  as  in  Fig.  32b,  we  have  particles 
selected  from  the  wave  surface  revolving  in  immediately  adjoining 
orbits,  of  the  size  indicated  and  spaced  so  that  they  are  just  45° 
apart,  we  have  the  wave  length  AB,  and  the  form  given  in  the 
dotted  line.  This  means  that  the  velocity  of  the  wind  is  such  that  it 
not  only  produces  the  orbit  shown,  but  also  reaches  and  sets  in 
motion  the  second  particle  at  the  moment  the  first  particle  has  com- 
pleted y$  of  its  revolution.  If,  now,  the  velocity  of  the  wind  in- 
creases, so  that,  when  it  reaches  the  next  particle,  the  first  one  has 
completed  only  1/16  of  its  revolution,  the  wave  length  with  the 
same  size  orbit  would  become  twice  as  great  and  correspondingly 
flatter.  But  increased  velocity  of  wind  means  an  increase  in  the 
size  of  the  orbit,  which  in  turn  means  an  increase  in  the  height  of 
the  wave,  and  a  sharpening  of  the  crest.  As  the  wave  length  in- 
creases the  period  would  lengthen  correspondingly,  since  the  dis- 
tance to  travel  increases,  unless  the  wave  velocity  also  increases, 
which  means  a  great  augmentation  of  the  orbital  velocity  of  the 
moving  particles.  The  period  does  increase  in  length,  but  not  in 
proportion  to  the  increase  in  wave  length.  (See  formula  i,  page 
212.)  Thus  a  wave  with  a  length  of  500  feet  may  have  a  period 
of  10  seconds,  which  corresponds  to  a  wave  velocity  of  about  34 
miles  per  hour.  On  increasing  to  1,500  feet,  the  period  will  increase 
to  between  17  and  18  seconds,  corresponding  to  a  wave  velocity  of 
about  56  miles  per  hour.  If  the  wave  velocity  had  remained  the 
same,  the  period  would  have  been  30  seconds.  The  disproportional 


212  PRINCIPLES    OF    STRATIGRAPHY 

increase  in  the  length  of  the  period,  therefore,  means  an  increase  in 
the  orbital  velocity,  which,  if  the  wave  height  also  increases,  must 
increase  still  further.* 

Wave  velocity  (Davis-i7 : 123}  does  not  depend  so  much  on 
the  orbital  velocity  as  on  the  rate  at  which  the  crest  position  is 
assumed  by  successive  parts  of  the  water,  and  this  rate  depends 
chiefly  on  the  depth  to  which  orbital  oscillations  are  felt  in  the 
water  body,  so  that  the  progress  of  the  wave  increases  with  the 
increase  in  the  depth  affected. 

*  The  following  f ormula?  copied  from  Krummel  (42 : 0)  serve  to  show  the 
relationship  which  exists  between  height  and  length  of  wave,  its  period,  orbital 
and  translatory  velocity  in  deep  water.  In  all  these: 

r     =   radius  of  orbit  of  water  particles. 

h    =   half  the  wave  height,  i.  e.,  its  height  above  mean  surface. 

H  =   entire  wave  height  (bottom  of  trough  to  top  of  crest). 

v    =   orbital  velocity  of  water  particles  in  meters  per  second 

Z    =   depth  of  water  (in  meters)  from  mean  surface. 

\    =   wave  length  in  meters. 

c     =  translatory  velocity  or  wave  velocity  (meters  per  second) 

T     =  wave  period  in  seconds. 

if    =  3.1416. 

g    =  velocity  of  a  free  falling  body  at  the  end  of  the  first  second  (9.81  m.). 

I      The  relation  between  the  period  of  the  wave  T  and  the  wave  length  X 

.    /   2   7T 

is  T  -  V  T 

TI     The  relation  between  the  wave  velocity  c  and  the  period  r  is 

2  IT 

T     =     C 

g 

III  The  relation  between  wave    velocity    c    and    wave    length    X    is 

e,t-/~£-\: 
y  TT 

IV  The  relation  between  wave  velocity  and  size  (radius)  of  the  orbit  r  is 

c  =    \/g  r 

V  The  relation  between  wave  period  r    and  the  radius  of  the  orbit  r  is 


=  27r  v  ~g 

VI  The  relation  between  velocity  c  and  period  r  is 

"    27T 

VII  Given  velocity  or  period  the  wave  length  is  therefore 

x==^:c2orJLT2 

g  2    7T 

VIII  The  orbital  velocity  v  is  found  according  to  the  formula 

h 
v 


WAVES 


213 


The  height  of  the  waves  increases  until  the  resistance  awak- 
ened by  the  orbital  motion  throughout  the  mass  of  water  affected, 
balances  the  wind  work  on  the  surface.  As  increase  in  length 
depends  on  the  increase  in  the  spacing  of  particles,  i.  e.,  the  in- 
crease in  rapidity  with  which  adjoining  particles  are  affected,  it  is 
seen  that  the  wave  length  may  increase  even  after  the  height  no 
longer  increases.  Thus  while  the  height  of  hurricane  waves  or 
great  "seas"  is  seldom  over  thirty  or  forty  feet  and  their  length 
perhaps  500  feet,  the  latter  may  increase  to  1,500  feet,  or  three 
times,  while  the  height  does  not,  or  but  rarely,  reach  50  feet.  The 
velocity  of  such  waves  varies  from  20  to  60  miles  an  hour,  and  their 
period  from  10  to  20  seconds. 

The  height  of  the  waves  depends  not  only  on  the  strength  of 
the  wind  causing  them,  but  also  on  the  size  of  the  water  body, 
especially  the  diameter  of  the  surface  along  the  path  of  the  wind. 
Wind  velocity  is  greater  over  the  open  sea  than  along  the  coast  or 
inland,  and  this,  together  with  their  smaller  size,  makes  the  waves 
of  inland  lakes  less  pronounced  than  those  of  the  sea,  and  hence 
lake  shores  suffer  less  erosion  than  the  sea-coast.  In  a  small  water 
body  the  wave  height  is  proportional  to  the  square  root  of  its  diam- 
eter (Stevenson,  Th.-68  '.358) .  As  soon  as  the  wave  height  ex- 
ceeds 0.8  m.,  it  may  be  determine^  according  to  the  following  for- 
mula (modified  from  Stevenson),  when  H  is  the  wave  height  in 
meters,  d  the  diameter  of  the  water  body  in  kilometers  (Penck- 
$2:466): 

H  =  H~3+  0.8 -H~d 

In  the  ocean  the  waves  rise  quickly  to  a  height  of  5  meters,  but 
also  decrease  rapidly,  as  soon  as  the  wind  producing  them  ceases. 
The  maximum  height  of  waves  in  the  open  ocean,  with  a  given 
wind  velocity,  is  shown  in  the  following  approximate  table,  ab- 
stracted from  Krummel  (42:75). 


Table  shoiving  relationships  between  wind  velocities 
and  zvave  height. 


Wind    velocity    in 
meters  per  second 
(w). 

i 

2 

3 

4 

5 

10 

15 

20 

25 

30 

40 

Maximum  height 
of  waves  in  me- 
ters (Hm). 

O.I 

0-3 

0.5 

0.8 

I.O 

3-5 

6-7 

10.9 

13-3 

15-0 

17.0 

214 


PRINCIPLES    OF    STRATIGRAPHY 


With  increase  in  the  strength  of  the  wind,  the  length  of  the 
waves  increases  more  rapidly  than  their  height ;  the  former  may 
increase  threefold  before  the  latter  is  doubled.  Lieutenant  Paris 
noted,  east  of  the  Cape  of  Good  Hope,  that  during  strong  westerly 
storms,  extending  over  four  days  with  remarkable  uniformity,  the 
height  of  the  waves  rose  only  from  6  to  7  meters,  while  the  length 
increase  threefold  before  the  latter  is  doubled.  Lieutenant  Paris 


i.  e.,  —    changed  from  18.84  to  33.57. 
H 


This  increase  in  length 


means  an  increase  in  the  velocity  of  the  wave,  which  may  rise  to 
exceed  that  of  the  wind  itself.  The  following  table  shows  the 
mean  velocity  of  the  waves  compared  with  that  of  the  wind  in  the 
several  oceanic  bodies  (Krummel-42  :8o)  : 

Table  showing  relationships  between  mean  wave  and  wind  velocities. 

Mean  Mean 

velocity   of  velocity   of 

wind  in  waves  in 

meters  per  meters  per 

second  second 

Atlantic  Trade  Wind 5.9  11.2 

South  Atlantic  West  Wind 10.9  14.0 

Indian  Ocean  West  Wind 12 . 5  15.0 

Indian  Ocean  Trade  Wind .  .  .• 7.0  12.6 

Chinese  Sea 11.3  11.4 

West  Pacific  Region 8.2  12.4 

Relation  between  Length  and  Height  of  Wave.     This  may  be 

expressed  by  the  formula     —    and    varies    greatly  according  to 

H 

the  age  of  the  waves.  In  young  waves  it  may  be  10  or  less,  i.  e., 
if  the  height  of  the  waves  is  I  meter  its  length  would  be  10  meters 


As  the  wave  grows  the  quotient   —    increases  until  it 

H 


or  less. 

is  50  or  over.     The  following  classification  of  waves  was  made  by 
Paris  ( Krummel-42  -.83  ): 

Classification  of  waves. 


Type  of 

Waves 

Very 
High  Sea 

High 
Sea 

Rough 
Sea 

Moder- 
ate Sea 

High 
Swell 

Ordinary 
Swell 

77  Mean  

19.  i 

21  .O 

21.6 

38.7 

20    T. 

-72    S 

rl 
"  Maximum  

22.  S 

21.  O 

30.  o 

80.0 

48.6 

6-5  3 

"   Minimum 

IS   4- 

IS    O 

1^  1 

21    6 

18  4. 

1C     -I 

WAVES  215 

We  have  seen  that  the  higher  the  wave  with  a  given  length,  the 
sharper  the  crest,  or,  what  amounts  to  the  same  thing,  the  increase 
of  length  without  or  with  but  moderate  increase  of  height  flattens 
the  crest,  and  this  flattening  lessens  the  destructiveness  of  the 
waves  in  the  open  sea.  In  sharp-crested  waves  the  crest  water 
"tends  to  roll  forward  faster  than  the  front  is  built  up,  and  this 
tendency  is  increased  by  the  forward  brushing  of  the  wind.  Sharp 
waves  of  moderate  height  break  in  'white  caps';  great  seas  gain 
curling  or  combing  crests,  which  capsize  small  boats  and  break 
with  dangerous  force  on  the  decks  of  large  vessels."  (Davis- 


The  Swell  or  Ground  Swell.  "Waves  spread  rapidly  from  the 
gales  in  which  they  are  formed.  As  they  advance  they  decrease 
in  height,  but  retain  length,  velocity  and  period  unchanged.  Their 
long,  flat  undulation  is  called  'swell.'  [German,  Diinung;  French, 
houle.]  It  may  swing  for  thousands  of  miles  across  the  ocean, 
fading  as  it  goes.  The  glassy  water  of  calm  weather  in  the  equa- 
torial 'doldrums'  is  always  slowly  heaving  and  sinking  with  passing 
swells."  (Davis-i"7:  124-5.}  The  swell  or  ground  swell  of  great 
hurricanes  may  break  with  destructive  force  on  a  coast  a  thousand 
miles  or  more  distant.  Davis  states  that  "landing  in  the  harbor 
of  St.  Helena  is  sometimes  impossible  on  account  of  surf  from 
swell  that  originates  in  winter  gales  in  the  North  Atlantic,  thou- 
sands of  miles  away."  (126.) 

Swells  are  much  longer  than  true  waves.  The  longest  were 
measured  by  the  French  Admiral  Mottez  in  the  Atlantic,  just  north 
of  the  equator,  and  had  a  length  of  824  meters  (2,703.5  feet),  a 
period  of  23  seconds,  or  a  velocity  of  35.8  m.  (117.5  ^eet  Per  sec~ 
ond). 

On  the  coast  of  Ascension  Island,  Buchanan  (6:234)  observed 
in  March,  1886,  a  rhythmic  breaking  of  the  swell  at  intervals  of 
16  seconds,  this  being  the  period  (T)  of  the  swell  wave.  These 
great  "rollers"  represented  waves  originating  south  of  Newfound- 
land, and  their  length  after  traveling  this  great  distance  is  deter- 
mined from  their  period  to  be  400  meters.  At  Bournemouth,  on 
the  south  coast  of  England,  Dr.  Cornish  (10)  found  the  mean 
period  of  continuous  series  of  139  breakers  to  be  19.35  seconds,  cor- 
responding to  a  wave  length  of  585  meters.  Breakers  with  periods 
of  15  to  17  seconds  are  common  at  certain  seasons  of  the  year  on 
the  Channel  and  the  Atlantic  coast  of  England  and  Ireland,  where 
they  are  known  as  "Death  Waves"  and  regarded  as  indications  of 
coming  storms.  The  origin  of  these  waves  is  in  the  Gulf  Stream 


2l6 


PRINCIPLES    OF    STRATIGRAPHY 


region,  where  their  period  is  probably  not  over  8  to  1 1  seconds,  and 
their  length  from  100  to  200  meters. 

Depth  of  Wave  Activity.  The  orbital  radius  of  wave  particles 
in  the  open  sea  decreases  downward  in  geometrical  progression,  so 
that  for  each  descent  in  depth  equal  to  1/9  of  the  wave  length  the 
diameter  of  the  orbit  decreases  by  one-half.  (Krummel-42 :  6.) 
Thus: 


For  depths  equal  to 

the  following  frac- 

tions of  the  wave 

length,  X  

o 

1/9 

2/9 

3/9 

4/9 

5/9 

8/9 

9/9 

The  diameter  of  the 

orbit  (2  p)  is  equal 

to    the    following 

fraction  of  the  wave 

height  (2h)    ...    . 

i 

1/2 

i/4 

1/8 

1/16 

1/32 

1/256 

1/512 

be 


At  twice  the  depth  of  the  wave  length  the  orbital  diameter  will 
part  of  the  wave  height  at  the  surface.    A  wave  of  90 


,144 


meters  in  length  and  3  m.  high  (a  not  uncommon  size  in  the  open 
ocean,  during  strong  winds)  will  show  the  following  decrease  of 
the  orbits  in  which  the  particles  move. 


Depth 

o. 

lorn. 

20  m. 

50  m. 

100  m. 

200  m. 

Approximate  size  of 
orbit  (2  p)    . 

^  m. 

1.5  m. 

0.75  m. 

91.5  mm. 

2.79  mm. 

.002725  mm. 

Thus  with  a  wave  length  of  1,500  ft.  and  a  height  of  50  ft.  the  orbital 
motion,  which  at  the  surface  is  50  ft.,  will  at  a  depth  of  1500  ft. 
be  50/512  ft.  or  1.17  inches,  while  at  a  depth  of  3,000  ft.  (500  fathoms) 
it  is  50/262,144  ft.  or  0.0023  of  an  inch,  or  0.058  millimeter  or 
practically  nothing.  At  100  fathoms,  a  wave  600  feet  in  length  on 
the  surface  and  with  a  height  of  30  ft.  (i.  e.  an  orbital  diameter 
(2p)  of  30  ft.)  will  be  represented  by  orbital  movements  of  0.7  inch  in 
diameter. 


WAVES  217 

The  radius  of  the  orbit  p  may  be  calculated  according  to  the  follow- 
ing formula  of  Bertin  (quoted  by  Krummel-42 :6) 


O  7 

he         "  A    or  log  —   =  —  2  TT  m  — 
h  A 

where  h  is  the  half  height  of  the  waves  (radius  of  orbit  on  surface) ; 
e  the  basis  of  the  natural  logarithms  (2.718);  z  the  depth  of  water 
in  meters  from  the  mean  surface,  A.  the  wave  length  and  m  the 
modulus  of  the  common  system  of  logarithms  (0.4342944819)^11^6 
TT  =  3.1416. 

Waves  in  Shallow  Water.  "When  waves  run  into  shoaling 
water  their  period  remains  unchanged,  their  height  increases,  and 
their  velocity  and  length  decrease.  The  height  increases  because  the 
wave  energy  at  any  given  point  is  spent  upon  a  lessening  depth  of 
water.  The  velocity  decreases  because  the  forward  propagation 


FIG.  33.  Diagrams  showing  the  change  in  the  orbit  described  by  the  moving 
particles  of  the  waves  as  they  approach  the  shore,  and  their  direc- 
tion of  movement.  (After  Davis.) 

of  wave  disturbance  is  slower  in  shallow  than  in  deep  water.  The 
wave  length  decreases  because  the  forward  waves  are  more  re- 
tarded than  the  following  waves.  The  period  is  unchanged  because, 
at  any  given  point,  one  wave  is  as  much  delayed  in  arrival  as 
another. 

"On  a  steep-sloping  beach  the  waves  may  wash  up  and  down 
without  breaking;  then  the  orbit  is  a  narrow  ellipse,  much  inclined 
forward ;  directly  on  the  beach  the  orbit  is  practically  a  line  coinci- 
dent with  the  slope  of  the  beach;  and  here  the  water  rises  as  it 
advances  and  falls  as  it  recedes.  This  relation  of  rise  and  fall  to 
forward  and  backward  motion  is  not  found  where  the  orbit  is  an 
oval.  If  the  orbit  is  a  vertical  ellipse,  rise  goes  with  the  last  half 
of  recession  and  the  first  half  of  advance;  fall  goes  with  the  last 
half  of  advance  and  the  first  half  of  recession."  This  is  illustrated 
by  the  "square  frames"  fitted  to  different  forms  of  orbit  in  the 
above  diagrams  (Fig.  33)  given  by  Davis. 

"On  a  gradually  shoaling  bottom,  swell  changes  to  surf  or  break- 
ers close  to  shore.  The  height  of  the  wave  increases,  its  front 


218  PRINCIPLES    OF    STRATIGRAPHY 

becomes  steeper  than  its  back,  its  crest  curls  forward  and  at  last 
plunges  into  the  trough  ahead  of  it,  splashing  and  surging  up  the 
beach.  Just  at  the  time  of  breaking,  the  water  may  be  seen  ascend- 
ing in  the  concave  front  of  the  wave  and  curling  forward  at  the 
crest.  Breaking  is  therefore  the  result  of  normal  orbital  move- 
ment at  a  place  where  the  water  is  so  shallow  that  there  is  not 
enough  of  it  to  build  up  the  front  of  the  wave."  Davis  thinks  that 
this  is  a  more  effective  cause  than  the  "drag"  of  the  waves  on  the 
bottom  in  shallow  water,  and  their  consequent  retardation. 

In  general  the  critical  point  at  which  breaking  of  waves  occurs 
is  found  where  the  depth  is  equal  to  the  height  of  the  wave,  or  the 
diameter  of  the  orbit  in  which  the  water  particles  move.  This  is, 
however,  complicated  by  the  ground  swell  over  submerged  banks, 
such  as  the  Dogger  bank,  the  Newfoundland  banks,  the  Agulhas 
banks,  etc.,  where  the  shoaling  of  the  water  results  in  the  breaking 
of  waves  over  water  several  times  deeper  than  the  height  of  the 
visible  waves.  Thus  waves  have  been  known  to  break  in  water 
25  to  30  meters  deep,  on  the  north  coast  ©f  Spain,  in  48  meters 
near  Terceira,  in  the  Azores;  46-57  meters  off  Punta  Robanal, 
North  Spain,  and  at  84  meters  on  the  Syrian  coast.  During  heavy 
tidal  runs  at  Faira  Island,  north  of  the  Orkneys,  heavy  surf  was 
found,  according  to  Stevenson,  in  water  70  meters  deep,  and  Airy 
mentions  surf  on  the  outer  margin  of  the  "Grounds"  at  the  mouth 
of  the  English  Channel  where  the  water  was  180  to  200  meters  deep 
(100  fathoms).  Again  heavier  and  shorter  seas  have  been  observed 
over  the  Wyville  Thomson  ridge  between  Faroe  and  Scotland 
than  on  either  side  of  it,  although  the  ridge  culminates  at  a  depth  of 
300  to  500  meters  below  the  surface  of  the  ocean. 

On  the  Banks  of  Newfoundland  the  water  is  often  stirred  to 
the  bottom,  although  the  depth  is  50  meters  and  over.  Heavy  waves 
breaking  on  the  decks  of  the  vessels  in  water  20  to  25  meters  deep 
often  leave  there  sand  stirred  up  from  the  bottom.  The  stirring  up 
of  the  bottom  is  also  shown  by  the  fact  that  the  remains  of  Mya 
truncata,  which  lives  buried  at  a  depth  of  20  to  25  cm.  in  the  sandy 
bottom,  are  found  in  the  stomachs  of  bottom-feeding  fish,  which 
could  have  obtained  them  only  after  they  were  dug  up  by  the 
waves. 

The  sand  and  mud  of  the  bottom  of  the  North  Sea  is  kept  in 
constant  motion  by  the  waves  and  the  tides,  so  that  no  seaweeds 
can  become  attached,  except  on  the  rocky  cliffs  of  the  coast.  Meas-> 
urements  made  in  Lake  Ontario  showed  that  stirring  of  the  sand 
at  the  bottom  by  storm  waves  does  not  extend  down  to  20  feet. 
Four  empty  boxes  were  anchored  in  the  sloping  sand  bed  of  the 


WAVES  219 

lake  bottom  "at  equal  distances  over  a  length  of  650  yards,  in 
depths  .of  6  feet,  12  feet,  18  feet  and  20  feet.  After  storms  it  was 
found  that  the  first  box  in  the  shallow  water  became  filled  with 
sand;  the  box  in  12  feet  of  water  half-full;  in  the  one  at  18  feet 
there  was  very  little  sand ;  and  at  20  feet  there  was  no  sand  in  the 
box."  (Wheeler-73:  jo.) 

In  the  open  Atlantic  ripple  marks  have  been  found  at  a  depth 
of  200  meters,  but  in  the  English  Channel  they  occur  only  down  to 
depths  of  40  meters,  and  to  depths  of  50  meters  in  the  Roman 
mediterranean.  Off  the  Florida  coast,  too,  Agassiz  has  noted  dis- 
turbances to  a  depth  of  200  meters. 

Destructive  wave  work,  however,  does  not  extend  to  such  depths, 
especially  in  the  more  protected  water  bodies.  Thus  submarine  con- 
structions in  the  Mediterranean  scarcely  suffer  damage  from  storms 
at  a  depth  of  5  meters,  and  the  coarse  sand  at  the  bottom  of  the 
Bay  of  Biscay  in  less  than  10  fathoms  of  water  is  scarcely  dis- 
turbed. (Delesse-2i.)  A  great  oceanic  swell  may,  on  reaching 
a  coast,  break  more  than  once.  The  first  surf  line  will  occur  at 
about  the  point  where  the  shoaling  water  becomes  equal  in  depth  to 
the  wave  height.  If  this  is  far  from  shore  the  water  mass,  after 
breaking,  will  roll  forward  as  a  wave  of  diminished  height,  and 
this  will  break  again  where  the  further  shoaling  demands  it,  and 
this  may  be  repeated  several  times.  The  resultant  piling  up  of 
the  waters  on  the  coast  will  induce  a  strong  seaward-tending  bot- 
tom current  or  undertow,  which  will  carry  the  less  heavy  substances 
out  along  the  bottom. 

The  height  to  which  a  breaking  wave  may  be  thrown,  or  the 
height  of  the  surf,  is  sometimes  surprising.  Lighthouses  and  even 
rock  cliffs  have  been  destroyed  at  a  height  of  100  feet  above  sea- 
level.  The  lighthouse  of  Unst,  the  northernmost  of  the  Shetland 
Islands,  which  stands  nearly  60  meters  above  sea-level,  repeatedly 
has  had  its  windows  broken  by  the  high-dashing  surf.  "During 
northeasterly  gales  the  windows  of  the  Dunnet  Head  lighthouse  [on 
the  north  coast  of  Caithness  in  Scotland],  at  a  height  of  upwards 
of  300  feet  above  high-water  mark,  are  said  to  be  sometimes  broken 
by  stones  swept  up  the  cliffs  by  sheets  of  sea  water,  which  then 
deluge  the  building."  (Geikie-26 :  561.) 

The  surf  from  the  ground  swell  alone  will,  "even  when  no  wind 
is  blowing,  often  cover  the  cliffs  of  North  Scotland  with  sheets  of 
water  and  foam  up  to  heights  of  100  or  even  nearly  200  feet." 
(  Geikie-26 :5<5/.) 

As  the  waves  advance  on  the  shore,  they  tend  to  become  more 
and  more  nearly  parallel  to  the  shore  line,  mainly  as  a  result  of  the 


220 


PRINCIPLES    OF    STRATIGRAPHY 


differential  decrease  in  velocity.  Where  the  shore  projects  into 
headlands  or  points,  the  energy  from  a  considerable  crest  line  is 
C9ncentrated,  resulting  in  intensive  destructional  work.  In  bays, 
on  the  other  hand,  the  energy  of  a  small  portion  of  the  crest  line  is 
stretched,  as  it  were,  over  a  broad  area,  and  hence  becomes  rela- 
tively weak.  This  is  shown  in  Fig.  34,  copied  from  Davis,  where 
the  energy  of  the  crest  line  D  F  is  concentrated  on  d  f,  whereas 
at  A  C  only  the  energy  of  the  short  portion  of  the  crest  lying 
between  a  c  is  felt.  The  bay  head  thus  becomes  a  place  of  relative 
safety  for  vessels  and  a  region  of  slight  erosion. 


FIG.  34.  Map  showing  concentration  of  energy  from  a  considerable  crest 
line  upon  a  narrow  headland  and  its  diffusion  in  the  bay  or 
harbor.  (After  Davis.) 

An  on-shore  wind  produces  a  shoreward  "drift"  of  the  water 
aside  from  the  movement  due  to  waves.  The  "undertow"  is  the 
return  current  flowing  outward  at  the  bottom.  This  is,  of  course, 
greatly  increased  during  strong  wave  action.  When  the  wave 
strikes  the  shore  obliquely,  a  movement  parallel  to  the  shore  is  inau- 
gurated, and  this  is  the  longshore  or  littoral  current,  the  chief 
agent  in  the  transportation  of  material  along  the  shore. 

Destructive  Work  of  the  Waves.  Wherever  the  waves  beat 
upon  a  shore,  erosional  work  of  some  kind  is  going  on.  If  the 
shore  is  sandy,  the  waves  may  only  stir  up  the  sand,  which  will  then 
be  carried  seaward  by  the  undertow,  or  along  the  coast  by  the 


WAVE    EROSION  221 

longshore  currents.  The  actual  impact  of  the  waves  upon  a  sandy 
or  rocky  shore  produces  comparatively  little  effect.  By  compress- 
ing the  air  in  the  caves  or  joint  cracks,  completely  closed  by  the 
water,  or  by  hydraulic  pressure,  the  waves  may  succeed  in  ulti- 
mately shattering  the  rocks  or  loosening  large  masses.  The  most 
effective  wave  erosion  work  is,  however,  accomplished  by  hurling 
pebbles  and  even  boulders  or  ice  blocks  against  the  cliffs,  and  so 
undermining  them  and  by  removing  the  pieces  broken  off  by  this 
process,  by  frost  action  or  otherwise. 

The  force  of  the  waves  in  great  storms  is  often  surprising. 
Measurements  with  a  dynamometer  made  by  Stevenson  on  the 
north  coast  of  Scotland  gave  a  force  of  impact  equal  to  about 
3,000  kgm.  per  square  meter  in  summer  (611  Ib.  per  square  foot), 
and  more  than  10,000  kgm.  per  square  meter  in  winter  (2,086  Ib. 
per  square  foot),  while  in  exceptional  storms  the  force  may  exceed 
30,000  kgm.  per  square  meter.  "The  greatest  result  yet  obtained 
at  Skerryvore  was  during  the  heavy  westerly  gale  of  2Qth  of  March, 
1845,  when  a  pressure  of  6,083  Ibs.  per  square  foot  was  registered. 
The  next  highest  is  5,323  Ibs."  (Stevenson-67 1^5.)  At  Cher- 
bourg, on  the  coast  of  France,  and  at  Algiers,  on  the  north  coast  of 
Africa,  similar  measurements  gave  a  force  3,000  to  3,500  kgm.  to 
the  square  meter,  while  at  Civitavecchia,  on  the  west  coast  of  Italy, 
a  force  of  16,000  kgm.  per  square  meter  has  been  obtained. 

Observations  on  the  transporting  powers  of  waves  are  also  avail- 
able. Rock  masses  weighing  100  tons  have  been  known  to  be 
moved  by  the  great  waves  of  winter  storms  on  the  north  British 
coast.  Many  times  blocks  weighing  five  tons  or  over  have  been 
torn  from  the  ledges  or  from  foundations  and  dragged  many  yards 
by  the  waves.  At  Plymouth,  during  a  severe  storm  in  November, 
1824,  granite  blocks  up  to  14,000  pounds  were  broken  from  the 
harbor  embankment,  and  pushed  uphill  in  some  cases  for  60  yards. 

"On  more  than  one  occasion  at  Plymouth  during  the  construc- 
tion of  the  breakwater  large  blocks  of  stone,  some  of  them  weigh- 
ing 7  to  9  tons,  were  removed  from  the  sea  slope  of  the  break- 
water at  the  level  of  the  low  water,  carried  over  the  top  a  distance 
of  138  feet,  and  piled  up  on  the  inside.  In  one  night  200,000  tons 
[British]  of  stones  were  thus  removed;  and  on  another  occasion 
9,000  tons."  (Wheeler-73:/#.)  At  the  Peterhead  breakwater 
waves  30  feet  in  height  and  500  to  600  feet  long  have  on  three 
occasions  displaced  blocks  weighing  over  40  tons  each  at  levels 
from  17  to  36  feet  below  tide,  and  at  Cherbourg  over  200  blocks 
weighing  each  about  4  tons  were  lifted  over  the  top  of  the  break- 
water, while  blocks  weighing  over  12  tons  were  turned  upside  down. 


222  PRINCIPLES    OF    STRATIGRAPHY 

Murchison  and  Stevenson  noted  in  the  Bound  Skerries,  the 
eastern  ramparts  of  the  Shetland  Islands,  a  gneiss  block  weighing 
jy2  tons  at  a  height  of  about  7  meters  above  sea-level,  which  shortly 
before,  during  a  southerly  storm,  had  been  dragged  over  a  ragged 
surface  from  a  position  22  meters  nearer  the  sea,  and  at  the  same 
elevation,  by  the  waves  which  broke  over  these  cliffs.  The  path 
along  which  the  boulder  was  dragged  was  clearly  marked  by  the 
splinters  left  by  the  way,  and  the  block  itself  showed  the  marks 
of  the  concussions  during  passage.  Blocks  from  6  to  13  tons  in 
weight  were  elsewhere  seen  to  have  been  transported  inland  at  a 
height  of  20  m.  above  the  sea.  The  most  noteworthy  case  on 
record  is,  however,  that  of  the  dislocation  of  the  breakwater  in  the 
harbor  of  Wick  in  North  Scotland  by  an  unusually  heavy  eastern 
storm  in  December,  1872.  The  depth  of  water  in  the  bay  is  more 
than  10  meters,  while  just  outside  it  is  over  30  meters.  The  break- 
water consisted,  above  the  foundation,  of  three  large  blocks,  weigh- 
ing 80  to  100  tons  each,  across  which  a  huge  concrete  monolith 
weighing  over  800  tons  was  cast  in  situ,  and  firmly  anchored  to  the 
blocks  by  iron  anchors.  The  total  mass  weighed  1,350  tons,  and 
yet  this  mass  was  torn  from  the  foundations  by  the  successive  wave 
impacts,  and  hurled  into  the  inner  harbor  a  distance  of  10  to  15 
meters,  the  monolith  and  the  three  foundation  stones  remaining 
anchored  together  and  being  moved  as  a  single  mass. 

Shingle  has  been  thrown  from  the  beach  to  the  roadway,  18  feet 
above  high  water,  at  Brighton,  England,  by  southwest  gales.  Sir 
John  Coode  found  that  "on  one  occasion  .  .  .  3^4  million  tons  of 
shingle  had  been  torn  down  from  the  Chesil  Bank  and  carried  sea- 
ward by  the  waves ;  and  on  another  occasion  4^2  million  tons  were 
scoured  out,  three-fourths  of  which  was  removed  back  after  the 
gale  ceased."  (Wheeler-73 :  77.)  On  this  same  bank  a  laden 
sloop  of  100  tons  burden  became  stranded  during  a  heavy  gale  in 
1824,  and  was  cast  to  the  top  of  the  bank,  where  it  was  more  than 
30  feet  above  ordinary  high  water.  "At  Hove  [England]  it  was 
calculated  that  27,000  tons  of  shingle  were  removed  from  the  beach 
in  a  heavy  gale  during  one  set  of  spring  tides,  and  that  10,000  tons 
were  drifted  along  the  beach  in  two  tides  on  another  occasion." 
Entire  shingle  banks  may  be  removed  in  a  single  storm.  "In  the 
Solent,  near  Hurst  Castle  [England],  a  shingle  bank  two  miles  long 
and  12  feet  high,  consisting  principally  of  flints  resting  on  a  clay 
base,  was  moved  forward  in  a  northeasterly  direction  40  yards, 
during  a  storm  in  1824."  (Wheeler-73  : 77.) 

Rock  fragments  weighing  from  10  to  150  Ibs.  have  been  rolled 
along  the  shore  of  Barnstable  Bay,  England,  between  Hartland 


WAVE    EROSION  223 

Point,  a  cliff  of  Carbonic  rock,  and  Abbotsham,  12  miles  distant; 
the  boulders  have  been  rolled  "for  a  distance  of  from  10  to  15 
miles  and  piled  up  into  banks  of  from  100  to  150  feet  wide  and  20 
feet  high,  the  top  being  from  6  to  9  feet  above  high  water." 
(Wheeler-73:i;.) 

The  progress  of  wave  erosion  on  a  cliff  of  uniform  exposure 
depends  in  a  large  measure  upon  the  relative  hardness  or  resistance 
of  the  rock  in  question.  Unconsolidated  material  is  readily  re- 
moved, even  in  sheltered  places.  Berkey  (4)  has  estimated  from 
observations  extending  over  a  year  that  the  cutting  back  of  a  cliff  of 
glacial  sand  and  fine  gravel  near  Port  Jefferson,  at  the 'head  of  a 
narrow  enclosed  bay  on  the  north  shore  of  Long  Island,  New 
York,  proceeds  at  the  rate  of  10  feet  per  hundred  years.  On  the 
exposed  outer  shore  of  Cape  Cod,  the  unconsolidated  glacial  sands 
and  older  clays  are  cut  back  at  a  rapid  rate,  as  shown  by  the  neces- 
sity of  repeated  removal  of  the  lighthouses  at  the  three  Nauset 
Lights. 

The  Island  of  Sylt,  on  the  west  coast  of  Schleswig-Holstein,  fur- 
nishes an  instructive  example  of  rapid  erosion.  The  sand  dunes 
which  protected  this  island  from  the  sea  began  to  move  eastward, 
in  the  middle  of  the  eighteenth  century,  and  the  sea  followed.  The 
church  of  the  village  of  Rantum  had  to  be  taken  down,  and  in 
thirty  years  the  sand  hills  had  passed  the  site,  and  the  waves  had 
swallowed  the  foundations  of  the  church.  Fifty  years  later  the 
former  site  of  the  church  was  nearly  300  yards  from  the  shore. 
(Andresen-2.) 

Many  striking  examples  of  the  advance  of  the  sea  on  a  low 
coast  are  recorded  in  the  district  of  the  Landes  on  the  west  coast  of 
France.  This  region  between  the  Gironde  and  the  mouth  of  the 
Adour,  is  believed  by  many  to  be  subsiding,  while  others  hold  the 
advance  of  the  sea  as  due  to  wave  and  current  erosion  entirely. 
The  retreat  of  the  coast  near  the  Garonne  is  estimated  at  not  less 
than  2  meters  per  year ;  the  lighthouse  of  Cordonan,  -formerly  situ- 
ated on  the  coast,  is  at  present  separated  from  the  mainland  by  an 
inlet  7  kilometers  in  width.  On  many  portions  of  the  coast  the 
dunes  are  washed  away  by  the  constant  advance  of  the  sea. 

On  the  south  coast  of  the  North  Sea  subsidence  with  encroach- 
ment of  the  sea  through  erosion  is  abundantly  illustrated.  The 
Zuidersee,  originally  a  marsh,  then  a  coastal  lake,  finally  became  an 
arm  of  the  sea,  and  is  constantly  increasing  in  depth,  being  navi- 
gable to-day  by  much  larger  vessels  than  in  the  former  centuries. 
In  many  places  the  sea  now  covers  sites  of  villages  which  flourished 
thirty  years  ago.  A  structure  built  by  the  Romans  under  Caligula, 


224  PRINCIPLES    OF    STRATIGRAPHY 

which  sank  into  the  sea  anno  860,  was  discovered  in  the  last  cen- 
tury at  a  distance  of  4,710  meters  off  the  west  coast  of  Katwijk,  in 
south  Holland,  while  the  remains  of  another  structure  swallowed 
earlier  by  the  sea  now  lie  at  a  distance  of  a  mile  from  the  coast. 
The  dunes  at  Gravenzande,  north  of  the  Meuse  mouth,  which  in 
1726  had  a  width  of  640  meters,  had  been  entirely  removed  by  the 
sea  near  the  end  of  that  century,  making  an  average  retreat  of  the 
coast  for  this  section  of  10  meters  per  year. 

On  the  west  coast  of  Denmark,  erosion  of  the  coast  proceeds  at 
a  rapid  rate,  accompanied  by  subsidence.  At  Agger,  near  the  west- 
ern end  of  the  Lumfjord,  a  strip  of  coast  141  meters  in  width  dis- 
appeared between  the  years  1815  and  1839,  making  an  annual  re- 
treat of  more  than  5.6  meters.  Even  more  extended  was  the  loss  be- 
tween the  years  1840  and  1857,  during  which  time  the  sea  devoured 
a  strip  157  meters  broad,  the  coast  thus  retreating  at  a  rate  of 
more  than  9.4  meters  per  year.  In  many  places  along  the  coast  of 
the  North  Sea  submarine  forests  are  found,  with  many  stems  still 
erect,  while  numerous  structures  built  in  historic  times  are  now 
beneath  the  water. 

The  cliffs  of  glacial  sand,  gravel  and  boulder  clay  which  form 
the  coast  of  Yorkshire,  England,  for  36  miles  from  Flamborough 
head  to  the  mouth  of  the  Humber  furnish  numerous  examples  of 
rapid  erosion  by  the  sea.  The  process  is  generally  a  removal  of 
the  loose  material  at  the  foot  of  the  cliffs,  by  the  waves,  with  a 
partial  undermining  of  the  cliff,  followed  by  the  slipping  of  a  large 
mass  into  the  sea.  The  cliff  faces  the  opening  of  the  Skagar 
Rack  on  the  opposite  shore  of  the  North  Sea,  400  miles  away,  and 
so  is  exposed  to  the  full  force  of  the  waves  of  this  turbulent  epi- 
continental  sea  during  northeast  gales.  The  ordinary  rise  of  the 
spring  tides  is  16  feet,  the  water  reaching  the  foot  of  the  cliff 
throughout  a  great  part  of  the  length,  in  some  places  rising  2  to  3 
feet  above  the  foot.  At  low  tide  the  beach  is  150  to  300  yards 
wide.  "The  waste  of  the  cliff  has  been  estimated  at  2  miles  since 
the  time  of  the  Romans,  a  mile  of  which  has  gone  since  the  Nor-  ' 
man  Conquest."  (Wheeler-73 : 222.)  Phillips  (54)  and  others 
have  estimated  a  loss  of  2^  yards  annually,  equal  to  30  acres  a 
year  over  the  36  miles  of  coast,  the  average  height  being  taken  at 
40  feet.  On  one  part  of  the  coast  a  recession  of  215  feet  occurred 
in  the  37  years  between  1852  and  1889,  according  to  the  estimates 
of  Captain  Kenny,  while  Captain  Salversen  estimated  the  erosion 
on  12  miles  of  the  coast  to  be  132  feet  in  40  years,  or  a  loss  of  204 
acres.  From  the  record  of  old  maps  it  appears  that  whole  town- 
ships have  been  devoured  by  the  sea,  while  others  have  lost  churches, 


WAVE   EROSION  225 

houses  and  the  greater  part  of  their  land.  "Kilnsea  church  fell  in 
1826-36,  and  the  village  was  removed.  Nearly  the  whole  of  this 
parish  has  been  washed  away  during  the  last  century.  Aldborough 
church  is  far  out  at  sea  and  Thorpe  parish  has  been  reduced  from 
690  to  148  acres.  Of  Ravenser  and  Ravenserodd,  once  a  seaport 
town  at  the  mouth  of  the  Humber,  not  a  vestige  is  left."  ( Wheeler- 
73  :  222.}  Wheeler  has  estimated  that  the  total  quantity  of  material 
falling  from  this  cliff  each  year  is  1,615,680  cubic  yards,  of  which 
969,408  cubic  yards  is  alluvial  matter  carried  away  in  suspension. 
This  occurs  only  for  about  two  hours  before  and  two  hours  after 
high  water  of  spring  tides,  or  about  four  hours  260  tides  a  year. 
Thus  each  tide  would  carry  away  about  3,728  cubic  yards.  (73 : 

-) 

The  progress  of  erosion  of  steep  rocky  coasts  is  strikingly  illus- 


FIG.  35.  Diagrammatic  view  of  the  Island  of  Helgoland  (direction  S.  W. 
by  N.  E.),  showing  the  great  erosion  platform,  especially  in  the 
southwest  side,  where  the  beds  dip  into  the  island.  The  rock 
is  Bunter  Sandstein)  (Triassic)  much  faulted.  (After  Walther.) 

trated  by  the  numerous  sea  stacks  found  on  nearly  every  coast,  and 
so  familiar  from  the  illustrations  in  the  basaltic  cliffs  of  Nova 
Scotia,  the  chalk  cliffs  of  Yorkshire  and  the  Isle  of  Wight  in  Eng- 
land, the  Old  Red  Sandstone  cliffs  of  North  Britain,  the  Zechstein 
cliffs  of  the  Sunderland  coast,  the  Buntsandstein  of  Helgoland,  etc. 
On  these  coasts  the  erosion  is  seen  to  progress  at  an  almost  visible 
rate,  changes  in  outline  being  perceptible  often  from  year  to  year. 
Perhaps  the  most  noted  example  is  the  island  of  Helgoland,  the 
position  of  which,  off  the  mouth  of  the  Elbe,  makes  it  such  an 
important  strategic  possession  for  the  German  Empire  that  they 
obtained  it  in  1890  from  England  by  relinquishing  Zanzibar.  In 
1570  this  island  extended  eastward  across  the  present  dune,  where 
it  formed  the  Wittecliff  of  Muschelkalk,  which  had  the  height  of 
the  present  Helgoland.  Destruction  of  these  limestone  banks  by 
the  Helgolanders  made  it  possible  for  the  great  flood  of  1712  to 
separate  the  entire  mass  of  Muschelkalk  and  chalk  from  the  main 
mass  of  Helgoland.  In  the  nineteenth  century  the  last  remnant  of 
this  mass  was  a  little  island  covered  by  dunes,  which  was  threat- 


226  PRINCIPLES    OF    STRATIGRAPHY 

ened  with  complete  destruction  by  the  great  storm  flood  of  Christ- 
mas, 1894,  and  is  at  present  protected  from  the  waves  by  artificial 
constructions.  (Fig.  35.) 

Rounding  and  Sorting  of  Detritus  by  Wave  Action.  Wave  work 
on  sand  grains  is  limited  to  those  of  larger  size*.  Shaler  (63)  has 
called  attention  to  the  fact  that  between  the  smaller  grains  of  sand 
on  the  beach  a  cushion  of  water  exists,  due  to  capillary  attraction, 
and  that  to  this  the  wet  beach  sand  owes  its  firmness.  It  is  this 
cushion  of  water  which  prevents  the  sand  grains  from  rubbing 
against  each  other,  and  thus  the  finer  grains  remain  angular.  Ex- 
periments by  Daubree  (16:256)  showed  that  granules  o.i  mm.  in 
diameter  will  float  in  feebly  agitated  water,  and  that  hence  grains 
of  this  size  and  less  could  not  be  mechanically  rounded  by  water. 
Destructible  material,  such  as  feldspar  grains,  is  slowly  eliminated 
in  wave-churned  sands.  On  the  shores  of  eastern  Moray  the  sands 
contained  only  10  per  cent,  of  feldspar,  whereas,  at  the  river  mouths 
which  furnished  the  sands,  18  per  cent,  of  feldspar  grains  is  still 
found.  The  rounding,  purity  and  assortment  according  to  size  is 
never  as  great  as  in  the  case  of  wind-blown  sand,  but  probably  in 
most  cases  better  than  river  sands.  (See  the  tables  and  discussion 
on  p.  256.) 

Pure  sands,  i.  e.,  sands  consisting  of  one  mineral — generally 
quartz — are  sometimes  found  on  the  seashore,  though,  as  a  rule, 
other  minerals  are  present.  An  unusually  pure  beach  sand  is  found 
at  West  Palm  Beach,  on  the  Atlantic  coast  of  Florida,  nearly  every- 
thing but  quartz  being  eliminated.  The  grains  are,  however, 
mostly  subangular,  though  the  material  has  been  transported  for 
many  miles  along  shore  from  the  Piedmont  region  to  the  north. 
Shaler  (63)  calls  attention  to  the  fact  that  these  sands,  though  some- 
what rounded,  are  not  much  smaller  than  those  in  the  region  of 
that  coast  about  Cape  Hatteras,  whence  they  come. 

Large  rock  fragments,  on  the  other  hand,  are  rapidly  rounded 
by  the  waves.  At  Cape  Ann,  cubes  of  granites  of  a  kind  which 
forms  excellent  blocks  for  paving  city  streets  are  worn  by  the  surf 
in  the  course  of  a  year  to  spheroidal  forms,  with  an  average  loss  of 
more  than  an  inch  from  their  peripheries  (Shaler-63 : 208),  while 
fragments  of  hard-burned  bricks  are  reduced  to  half  their  size  by 
a  year  of  moderate  beach-wearing. 

TIDES. 

Tides  are  the  periodic  rise  and  fall  of  the  ocean  waters,  due  to 
combined  attraction  of  sun  and  moon,  and  occur  twice  in  every 


TIDES  227 

24  hours  and  52  minutes.  At  flood  tide  the  water  is  high,  at  ebb 
tide,  low.  Twice  each  month,  at  new  moon  and  at  full  moon,  the 
tides  are  exceptionally  high,  owing  to  the  relative  position  of  sun 
and  moon  at  these  times,  when  they  exert  a  combined  influence  of 
the  same  character  upon  the  waters.  Such  tides  are  called  Spring 
Tides.  Twice  a  month  also,  at  the  period  of  first  quarter  and  last 
quarter  of  the  moon,  the  interval  between  high  and  low  water  is  at 
its  lowest,  since  at  such  times  the  moon  and  sun  act  in  contrary 
direction  upon  the  waters,  each  tending  to  neutralize  the  force  of 
attraction  of  the  other.  This  constitutes  the  Neap  Tides. 

In  the  open  ocean  the  rise  is  estimated  to  be  2  or  3  feet,  but 
along  coasts  this  is  generally  greatly  increased.  This  is  especially 
the  case  where  the  water  is  crowded  into  narrowing  bays,  as  illus- 
trated by  the  Bay  of  Fundy,  a  funnel  sea,  with  the  highest  known 
tides  of  the  world.  The  mouth  of  this  bay  is  48  miles  wide  and 
its  depth  at  this  point  from  70  to  no  fathoms.  The  bottom  rises 
at  the  rate  of  4  feet  per  mile  for  145  miles,  when  the  head  of  the 
bay  is  reached.  Near  the  mouth  the  spring  tides  vary  from  12  to 
1 8  feet,  while  at  its  head,  in  Cobequid  Bay,  the  range  is  as  high 
as  53  feet,  that  of  the  neap  tide  being  31  feet.  The  tide  runs  up 
the  Petit-Codiac  River  from  the  head  of  the  bay,  presenting  a  more 
or  less  perpendicular  wall.  This  is  the  tidal  bore  which  is  seen  in  a 
number  of  rivers,  such  as  the  Severn  and  the  Wye  of  England,  the 
Seine  of  France,  the  Hugh  of  India,  and  the  Tsien-Tang  of 
China,  where  it  is  sometimes  25  feet  high  and  very  destructive. 
According  to  the  observations  of  Captain  Moor,  ij4  million  tons 
of  water  rushed  past  a  point  in  the  river  in  a  minute.  Up  river 
the  tides  are  often  felt  for  a  considerable  distance.  Thus  its  influ- 
ence is  felt  up  the  Hudson  as  far  as  Troy,  New  York,  up  the 
Delaware  nearly  to  Trenton,  and  70  miles  up  the  St.  John's  River 
in  New  Brunswick,  where  it  is  felt  at  an  elevation  of  14  feet  above 
mean  sea-level.  The  salt  water  does  not  actually  run  up  the 
rivers  to  the  distances  mentioned,  the  waters  of  the  Hudson,  for 
example,  being  fresh  above  Poughkeepsie.  The  tidal  influence  is 
felt  rather  in  a  backing  up  of  the  river  water,  which  is  of  course 
accompanied  by  a  checking  of  the  current,  a  condition  favoring  the 
deposition  of  material  held  in  suspension. 

Where  tides  pass  through  narrow  channels,  tidal  currents  or 
races  are  produced,  which  are  generally  effective  agents  in  scouring 
the  channels  or  preventing  deposition.  Where  bars  or  other  obstruc- 
tions retard  the  entrance  of  the  tide  into  a  narrow  bay  or  estuary, 
it  may  not  reach  its  full  height  before  the  setting  in  of  ebb  tide, 
and  thus  the  rise  and  fall  will  be  less  than  on  the  unprotected  shore. 


228  PRINCIPLES    OF    STRATIGRAPHY 

The  removal  of  such  a  bar  would  cause  a  greater  rise  and  fall  of 
the  tide  on  the  shores  of  the  bay,  and  so  produce  the  appearance  of 
subsidence  of  the  land.  Johnson  (35;  37)  has  used  this  explana- 
tion to  account  for  many  apparent  indications  of  recent  subsidence 
along  the  Atlantic  and  other  shores. 

Comparison  of  Tides  and  Waves.  Tides  may  be  regarded  as 
huge  waves  sweeping  successively  around  the  earth  from  east  to 
west,  their  theoretical  period  being  a*  little  over  12  hours  and  26 
minutes.  If  lines  were  drawn  connecting  the  points  which  have 
the  same  high  tide  at  the  same  moment,  these  cotidal  lines  would 
mark  the  crests  of  the  tide  waves.  Normally  there  would  be  two 
such  cotidal  crest  lines  on  opposite  sides  of  the  earth,  and  between 
them  would  be  the  cotidal  trough  line.  If  the  earth  were  covered 
by  a  universal  ocean  of  uniform  depth,  the  cotidal  lines  would  be 
great  circles,  and  the  period  of  the  tide  waves  would  be  exactly  12 
hours  and  26  minutes.  The  velocity  at  the  equator  would  be  equal 
to  that  of  the  rotation  of  the  earth,  and  is  approached  by  the  tides 
of  the  deep  and  open  sea.  The  continents,  however,  greatly  inter- 
fere with  this  movement  of  the  tides,  and  this  is  especially  the  case 
in  bays  or  funnel  seas,  where  we  have  not  only  an  increase  in  the 
height  of  the  wave,  but  also  a  change  in  interval  between  high  and 
low  water,  or  between  the  crest  and  trough  of  the  wave.  As  the 
bay  na'rrows,  low  water  occurs  nearer  the  following  than  the 
preceding  high  tide,  the  rise  being  more  rapid  than  the  fall.  In 
some  estuaries  the  duration  of  rise  is  to  the  duration  of  fall  as  one 
is  to  ten  or  twenty.  In  such  cases  we  have  the  production  of  the 
tidal  bore  already  mentioned,  the  water  rushing  up  the  estuary  as  a 
visible  wall  of  water  with  a  speed  of  ten  or  more  miles  per  hour. 

The  tidal  currents  (flood  and  ebb)  likewise-  suffer  a  striking 
change.  In  the  ocean  "the  flood  begins  three  hours  and  six  minutes 
before  high  water,  attains  its  greatest  velocity  at  high  water,  and 
ceases  three  hours  and  six  minutes  later."  (Davis-i?:  J^p.)  Like- 
wise, in  the  ebb  tide,  slack  water  occurs  at  mid-interval  between 
high  and  low  tides.  This  is  illustrated  by  the  tides  in  the  center  of 
the  English  Channel,  where  the  current  flows  up  the  channel  (toward 
Dover)  for  three  hours  before  high  tide,  and  down  the  channel  for 
three  hours  after.  This  phenomenon  is  understood  when  we  com- 
pare the  movement  of  the  waters  of  the  tidal  wave  with  that  of 
the  ordinary  wave.  Rise  and  fall  of  the  tide  is  brought  about  by 
the  vertical  component  of  the  orbital  movement  of  the  water,  while 
the  back  and  forward  currents  are  due  to  the  horizontal  compo- 
nent. The  change  in  the  latter  occurs  at  mid-tide,  which  is  the 
period  of  slack  water. 


TIDES  229 

The  conformation  of  the  coast  line  and  the  relation  of  the  tidal 
wave  to  it  modify  this  interrelation  of  current  and  tide.  Thus  at 
the  mouth  of  the  Elbe,  at  Cuxhaven,  the  reversal  of  the  current 
occurs  i  hour  and  30  minutes  after  low  water,  and  i  hour  and  25 
minutes  after  high  water.  Thus  during  the  first  hour  and  a  half 
of  falling  tide  a  current  still  runs  up  the  Elbe,  and  during  the 
same  interval  of  rising  tide  the  current  still  runs  down.  On  Lon- 
don Bridge  one  may  observe  that  in  the  center  of  the  Thames  the 
current  still  runs  up  stream,  even  after  the  water  has  fallen  2  feet, 
while  at  the  mouth  of  the  Thames,  at  the  Mouse  lightship,  the  re- 
versal of  the  current  occurs  2  hours  after  high  and  low  water. 

At  the  heads  of  small  bays,  and  on  shores  where  the  tide  comes 
on  broadside,  slack  water  agrees  with  high  and  low  tides ;  all  the 
rising  tide  having  a  flood  current,  all  the  falling  tide  an  ebb  current. 
This  is,  however,  not  the  case  when  the  tide  progresses  obliquely 
along  the  shore. 

Interference  of  Tides.  In  bays  or  channels  open  in  two  direc- 
tions, remarkable  interferences  may  occur  by  the  meeting  of  high 
and  low  tides  or  by  cross  tides.  "At  New  York  high  tide  entering 
from  the  harbor  reaches  the  rocky  narrows  of  Hell  Gate  when  a 
low  tide  arrives  through  Long  Island  Sound,  and  six  hours  later  a 
low  tide  from  the  harbor  meets  a  high  tide  from  the  Sound." 
(Davis-i8:#7.)  This  produces  a  rapid  back  and  forth  flowing 
current  or  tidal  race,  which  made  this  passage  a  dangerous  one  to 
vessels  until  the  channel  was  widened  by  blasting  away  the  rocks. 

Even  more  complicated  interferences  occur  in  the  English  Chan- 
nel, especially  near  the  Dover  Straits,  where  the  tides  from  the 
Atlantic  and  the  North  Sea  meet,  with  the  production  of  the  famil- 
iar strong  series  of  currents  and  waves.  In  the  Irish  Sea  the  meet- 
ing of  two  tides  of  equal  height  from  opposite  directions,  and  with 
a  difference  of  phase  of  12  hours,  produces  excessive  tides  (5  to  7 
meters),  but,  owing  to  the  direct  opposition  of  movements  of  the 
two  tidal  streams,  complete  slack  water  results,  as  is  the  case  at 
the  Isle  of  Man.  When,  on  the  other  hand,  the  phase  difference  is 
6  hours,  no  rise  or  fall  of  the  tide  will  occur,  since  a  crest  ap- 
proaching, say,  from  the  right,  balances  a  trough  approaching  from 
the  left.  In  both  the  movement  is  to  the  left,  that  of  the  crest 
being  forward  and  that  of  the  trough  being  backward,  and  so  a 
current  of  double  strength  will  alternately  flow  in  the  one  and  the 
other  direction,  slack  water  being  halfway  between  high  and  low 
water  time. 

Where  the  waters  are  crowded  in  narrow  channels,  as  between 
islands  or  headlands,  the  tidal  stream  likewise  becomes  greatly 


230  PRINCIPLES    OF    STRATIGRAPHY 

strengthened.  Between  the  cliffs  of  the  Pentland  fjord  the  tidal 
stream  known  as  the  Roost  has  a  velocity  of  10  to  n  knots,  and 
even  steamers  which  have  a  speed  of  more  than  n  knots  avoid 
steaming  against  this  stream  when  the  wind  favors  it.  Between  the 
Orkneys  and  the  north  coast  of  Scotland,  tidal  streams  of  8  to  10 
knots  are  normal  during  spring  tides.  In  such  tidal  races  irregu- 
larities of  the  coast  will  produce  whirlpools  such  as  the  one  off 
Mosken  and  Varo,  among  the  Lofoten  Islands,  famous  for  centuries 
as  the  "Maelstrom" ;  or  the  even  more  dangerous  "Saltstrom"  at 
the  mouth  of  the  Saltenfjord  on  the  Norwegian  mainland  oppo- 
site. The  whirlpool  known  since  the  days  of  Homer  as  the 
Charybdis,  in  the  Straits  of  Messina,  and  the  fainter  but  equally 
noted  maelstroms  at  Scilla,  on  the  Italian  coast  of  the  Straits,  owe 
their  peculiarities  to  the  meeting  in  the  narrow  passage  of  the  tides 
from  the  Tyrrhenian  and  Ionian  seas,  which  have  a  phase  differ- 
ence of  6  hours,  and  thus  high  water  approaches  from  one  and  low 
water  from  the  other  side,  the  differences  being  adjusted  by  the 
strong  currents  generated  which  change  in  direction  every  six 
hours.  Owing  to  the  conformation  of  the  borders  and  bottom  of 
the  passage,  strong  whirls  of  water  are  produced,  which  bring  the 
colder  and  more  saline  waters  from  the  deeper  parts  and  with  it 
deep  water  organisms,  such  as  the  larval  form  of  the  eel,  etc. 

Tidal  currents  extend  to  much  greater  depth  than  that  reached 
by  wave  motion.  North  of  the  Dogger  bank,  in  water  73  meters 
deep,  the  maximum  tidal  current  in  the  upper  10  meters  of  water, 
measured  at  intervals  of  six  hours,  was  15.9,  20.4  and  20.1  cm.  per 
second,  and  in  70  meters'  depth  or  3  meters  above  the  bottom,  the 
corresponding  velocities  were  8.9,  13.2  and  10.2  cm.  per  second. 
The  tidal  wave  in  this  case  was  not  over  i  meter  high ;  deep  water 
waves  of  this  height  would  be  imperceptible  at  a  depth  of  70 
meters,  while  the  tidal  stream  still  retained  56,  65  and  51  per  cent, 
respectively,  of  its  surface  velocity. 

Tides  and  tidal  streams  are  not  as  pronounced  in  the  mediter- 
raneans as  in  the  open  sea,  and  this  difference  becomes  emphasized 
when  the  outlet  of  the  mediterranean  is  narrow,  as  in  the  case  of 
the  Straits  of  Gibraltar.  The  Gulf  of  Mexico  (Mexican  mediter- 
ranean), with  a  wider  opening,  still  illustrates  this  phenomenon,  the 
range  of  the  tide  at  Galveston,  Texas,  being  less  than  i  foot. 

Tides  independent  of  the  Atlantic  tides  and  more  nearly  com- 
parable to  the  seiches  in  lake  basins  also  occur.  In  still  more 
enclosed  basins,  as  in  the  Black  Sea,  tides  are  wanting  altogether. 
In  large  lakes  a  periodic  rise  and  fall  of  the  water  of  slight  extent 
has  been  observed  and  compared  with  the  tides.  These  lake  tides 


MARINE    CURRENTS  231 

are  very  small,  that  of  Lake  Michigan,  for  example,  having  an 
interval  of  only  2  inches.  More  irregular  oscillations  of  the  entire 
water  body  of  lakes  are  found  in  the  seiches,  which  are  due  to 
some  disturbance  of  the  water  as  a  whole,  as  in  the  case  of  sudden 
barometric  changes,  .in  storms,  etc.,  and  may  be  compared  to  the 
oscillation  of  the  water  in  a  basin  which  has  been  lifted  on  one  side 
and  suddenly  dropped.  Such  oscillations  will  continue  for  some 
time  after  the  cessation  of  the  disturbing  force. 

Tidal  Scour  and  Transportation.  Wherever  the  tide  passes 
through  a  narrow  channel  so  as  to  produce  a  race,  considerable 
scouring  of  the  bottom  results.  Thus  the  tidal  stream  channels  in 
salt  marshes  are  kept  open  by  this  tidal  scour,  and  not  infrequently 
harbors  are  benefited  by  such  scour.  Transportation  of  sand  and 
mud  by  tidal  currents  is  often  extensive.  Sand  grains  i/ioo  inch 
(about  0.25  mm.)  will  be  moved  in  a  state  of  semisuspension  by 
tidal  currents  of  3  or  4  knots.  The  movement  is,  however,  princi- 
pally a  forward,  backward  movement,  the  sands  carried  away  by 
ebb  tide  being  brought  back  during  flood.  This  is  illustrated  by 
the  case  of  a  vessel  which  sank  at  the  mouth  of  the  Gironde, 
opposite  Verdun,  where  she  rested  on  her  keel  at  the  bottom  of  the 
channel  in  6  fathoms  of  water  at  low  tide.  "At  the  end  of  the  ebb 
tide  the  sand  was  so  scoured  as  to  leave  a  space  under  the  keel  at 
both  ends,  leaving  the  hull  only  supported  in  the  middle;  at  the 
end  of  the  flood  tide  the  vessel  was  again  completely  buried  in  the 
sand,  the  sand  bed  extending- 100  yards  fore  and  aft  of  the  vessel 
and  50  yards  from  each  side."  (Partiot~5o  and  Wheeler-73  :i6.) 

MARINE  CURRENTS.* 

CURRENTS  OF  THE  OCEANS.  Ocean  currents  are  due  to  a  com- 
bination of  causes,  which  may  be  classed  either  as  primary  or  as 
secondary  stream  constituents.  The  primary  causes  are  the  active 
producers  of  the  currents,  and  as  such  may  be  noted  (i)  internal 
or  endogenetic  causes,  existing  within  the  water  itself,  such  as 
local  differences  in  density,  due  to  variation  in  temperature  and 
salinity  under  the  influence  of  varying  sunshine,  evaporation,  rain- 
fall, or  melting  of  snow  and  ice;  (2)  external  or  exogenetic  causes, 
such  as  variation  in  air  pressure,  and  especially  the  winds.  Among 
the  secondary  causes  which  act  chiefly  in  modifying  the  current 
may  be  noted,  I,  friction,  2,  the  rotation  of  the  earth  on  its  axis,f  and 

*  In  this  section  I  have  followed  Krummel  closely. 

f  This  operates  to  deflect  all  moving  particles  on  the  surface  of  the  Northern 
Hemisphere  to  the  right,  and  to  the  left  in  the  Southern. 


232 


PRINCIPLES    OF    STRATIGRAPHY 


3,  the  configuration  of  the  basins.  It  is  this  latter,  i.  e.,  the  presence 
of  continental  masses  .in  the  path  of  the  currents,  which  causes  a 
piling  up  of  the  waters  on  the  coast  against  which  it  is  driven  by 
the  primary  causes,  and  a  potential  depression  of  the  surface  from 
which  it  flows  away.  In  the  one  case,  then,  .the  heaped-up  water 
must  flow  away,  and  in  the  other  compensating  streams  originate, 
drawing  the  water  into  the  space  whence  removal  has  taken  place. 
In  a  symmetrical  ocean  reaching  from  pole  to  pole  and  covering 


80° 


FIG.  36.     Schematic  representation  of  ocean  currents  in  an  ideal  ocean.  (After 
Kriimmel.) 

a  meridional  distance  of  90°,  we  would  have  a  symmetrical  ar- 
rangement of  currents  as  shown  in  the  annexed  diagram  repro- 
duced from  Krummel  (Fig.  36).  On  both  sides 'of  the  equator, 
at  10°  north  and  south  latitudes,  the  equatorial  streams  would  flow 
westward  and  on  approaching  the  western  shores,  bending  respec- 
tively northward  and  southward  and  crossing  eastward  again  in 
50°  north  and  south  latitude,  would  approach  the  equator  again 
along  the  eastern  border  of  the  sea,  thus  constituting  the  principal 
north  and  south  circulation.  Between  the  equatorial  currents  set- 
ting westward  is  an.  eastward-setting  equatorial  counter  current, 


OCEAN    CURRENTS  233 

while  two  polar  currents  also  exist,  each  flowing  westward  and 
forming  a  complete  circulation  with  the  eastward-flowing  northern 
arm  of  the  main  circulation.  The  configurations  of  the  lands  are 
largely  responsible  for  the  course  of  the  currents  in  the  different 
oceans.  Broadly  outlined,  the  currents  of  the  several  oceans  and 
its  main  dependencies  are  as  follows : 

The  Atlantic  Ocean.  The  North  Equatorial  current  is  somewhat 
variable  in  its  position,  its  southern  border  ranging  from  6°  north 
latitude  in  March  to  12°  north  latitude  in  September,  and  with  an 
average  velocity  of  15  to  17  nautical  miles  per  day,  or  from  32  to 
36.5  cm.  per  second,  1.15  to  1.3  km.  per  hour,*  the  maximum 
rising  to  2.4  km.  per  hour  or  over.  The  direction  of  this  current 
is  west-southwest  to  west,  east  of  longitude  35°,  then  turns  due 
west  and  becomes  west-northwest  at  the  Lesser  Antilles. 

The  South  or  principal  Equatorial  current  is  of  a  very  constant 
character,  and  crosses  the  equator  diagonally.  Its  southward  ex- 
tent is  near  15°  south  latitude,  while  its  northern  border  is  already 
i°  north  latitude  in  the  meridian  of  Greenwich  during  the  winter 
and  spring  months.  Its  average  velocity  in  June,  July  and  August  is 
20  to  24  nautical  miles  in  24  hours,  or  from  1.58  to  1.85  km.  or 
more  per  hour,  while  velocities  as  high  as  72  nautical  miles  per  24 
hours  (5.55  kilometers  per  hour)  occur.  The  current  divides  at 
Cape  St.  Roque,  the  eastern  point  of  South  America,  one  arm 
passing  southward  to  become  'the  Brazil  current  and  the  other 
uniting  with  the  North  Equatorial  current  to  produce  the  Guiana 
current,  which  later  becomes  the  Gulf  Stream.  The  velocity  of 
this  northern  arm  near  Cape  St.  Roque  is  not  infrequently  from 
30  to  60  nautical  miles  per  24  hours  (2.3  to  4.6  kilometers  per 
hour).  The  Guiana  stream  is  continued  as  the  Caribbean  stream, 
with  a  velocity  of  24  to  72  nautical  miles  per  day  (1.85  to  5.55 
km.  per  hour).  It  here  becomes  a  veritable  sea  in  motion  rather 
than  a  single  stream.  In  the  Gulf  of  Mexico  it  bends  eastward  and 
leaves  between  Florida  and  Cuba  as  the  warm  Gulf  Stream,  flowing 
at  first  eastward,  then  turning  northward  between  Florida  and  the 
Bahama  banks,  and  then  crosses  the  North  Atlantic  as  the  Gulf 
Stream  or  West-wind  drift.  At  the  Florida  Straits  the  average 
annual  velocity  is  72  nautical  miles  per  day  (5.55  km.  per  hour), 

*  The  nautical  or  geographic  mile  (Seemeile)  as  defined  by  the  United  States 
Coast  Survey  is  "equal  to  one-sixtieth  part  of  the  length  of  a  degree  on  the 
great  circle  of  a  sphere  whose  surface  is  equal  to  the  surface  of  the  earth."  This 
makes  the  value  of  a  nautical  mile  6,080.27  ft.  or  1,853.248  meters.  The  Brit- 
ish admiralty  knot  is  6,080  ft.  The  German  Seemeile,  in  terms  of  which  the 
following  measurements  are  given,  is  equal  to  1.852016  km.  or  6079.55  ft. 


234  PRINCIPLES    OF    STRATIGRAPHY 

but  rises  to  100  or  120  nautical  miles  in  the  colder  and  warmer 
seasons,  i.  e.,  1.5  to  2.5  meters  per  second,  a  velocity  which  com- 
pares favorably  with  that  of  many  great  rivers  in  their  lower 
reaches  during  high  water. 

The  western  border  of  the  Gulf  Stream  follows  pretty  closely 
the  edge  of  the  continental  shelf  and  remains  more  or  less  sharply 
defined.  It  is  often  abruptly  outlined  by  the  rising  of  a  wall  of 
cold  water,  the  temperature  of  which  in  different  seasons  is  from 
10°  to  20°  lower  than  that  of  the  Florida  stream.  This  so-called 
"cold  wall"  is  an  effective  barrier  to  migration,  and  its  displace- 
ment by  strong  winds  brings  about  anomalous  bionomic  results. 
Eastward  the  current  widens  from  30  nautical  miles  in  the  straits 
to  twice  that  at  Cape  Canaveral,  and  becoming  from  120  to  150 
nautical  miles  wide  opposite  Charleston.  It  constantly  increases 
northward.  Southeast  of  New  York  the  average  velocity  has  be- 
come reduced  to  from  30  to  48  nautical  miles  per  day,  though  some- 
times it  rises  to  72  nautical  miles.  The  stream  as  such  cannot 
be  traced  beyond  the  meridian  of  the  eastern  border  of  the  Great 
Newfoundland  banks,  before  reaching  which  it  already  begins  to 
break  up  into  a  series  of  separate  streams  of  varying  temperature. 
The  velocity  of  the  West-wind  drift  becomes  reduced  to  an  average 
of  12  or  15  nautical  miles  in  mid-ocean,  though  as  much  as  4$ 
nautical  miles  per  day  has  been  observed.  The  well-known  mild 
temperatures  of  the  British  Isles,  especially  Ireland,  where  flowers 
bloom  in  January,  though  the  latitude  is  that  of  Labrador,  are  due 
to  the  impingement  against  the  coast  of  a  branch  of  this  warm 
West-wind  drift.  Dividing  on  the  British  co^st,  both  arms  of  this 
branch  enter  the  North  Sea,  one  by  way  of  the  English  Channel 
and  Dover  Straits,  and  the  other  around  the  north  coast,  the  Hebri- 
des and  Orkneys,  while  sending  a  third  arm  along  the  Norwegian 
coast.  A  large  part  of  the  West-wind  drift  or  "Irish  Stream," 
however,  turns  northward  to  Iceland,  passing  to  the  west  of  the 
Faroe  Islands  and  turning  westward  and  southwestward  as  the 
Irminger  current,  running  parallel  to  the  cold  East  Greenland 
current  and  sending  a  branch  around  Cape  Farewell  into  Davis 
Straits.  Throughout  this  course  the  velocity  of  the  current  is  prob- 
ably less  than  21  cm.  per  second.  From  the  west  coast  of  Davis 
Straits  the  cold  southward-flowing  Labrador  current  runs  past  the 
Newfoundland  coast  and  the  eastern  border  of  the  Grand  Banks 
and  disappears  on  reaching  the  Gulf  Stream.  This  disappearance 
has  been  regarded  as  due  to  a  "swallowing"  of  the  cold  water  by 
the  warm,  or  to  a  submergence  of  the  cold  beneath  the  warm,  but 
is  probably  due  rather  to  dispersal  as  suggested  by  Krummel.  Part 


OCEAN    CURRENTS  235 

of  the  cold  water  passes  westward  and  southwestward  into  the 
St.  Lawrence  Gulf  and  Cabot  Straits,  and  bathes  the  eastern  coast 
of  the  United  States  to  Cape  Cod  (Cabot  current).  It  is  probably 
recognizable  in  the  "cold  wall"  bordering  the  Florida  current.  An- 
other part  turns  eastward  and  even  northeastward,  occasionally 
carrying  iceberg  fragments  to  the  North  British  coast. 

The  southern  arm  of  the  West-wind  drift  forms  the  Canary 
current,  which  flows  southward  between  Madeira  and  the  Cape 
Verde  Islands,  to  join  the  North  Equatorial  current.  Flowing  from 
higher  to  lower  latitudes,  it  is  a  relatively  cool  current,  varying  in 
velocity  from  8  to  30  nautical  miles  per  day  (0.62  to  2.3  km.  per 
hour). 

The  Equatorial  Counter  current  of  the  Atlantic  is  especially  well 
developed  off  the  African  coast,  where  it  is  known  as  the  Guinea 
current.  Its  position  varies  with  the  seasons,  but  it  is  always  a 
warm  current.  It  is  not  traceable  over  the  entire  mid-Atlantic, 
being  formed  by  recurring  branches  of  the  two  equatorial  currents. 
In  March  its  western  end  lies  near  25°  west  latitude,  and  in  Sep- 
tember near  40°  west  latitude,  and  in  other  months  it  lies  between 
these.  It  broadens  westward,  gaining  an  average  velocity  of  per- 
haps 1 8  nautical  miles  per  day,  though  velocities  as  high  as  40  or  50 
may  occur,  while  at  Cape  Palmas  a  velocity  of  85  nautical  miles  per 
day  has  been  recorded.  Owing  to  the  conformation  of  the  West 
African  coast,  an  arm  of  the  Guinea  current  is  deflected  northward, 
though  its  main  mass  enters  the  Gulf  of  Guinea.  This  is  especially 
the  case  in  the  summer  months. 

In  the  South  Atlantic  the  principal  warm  stream  is  the  Brazil 
current,  which  follows  the  South  American  coast  to  latitude  49°  or 
50°,  before  reaching  which  it  has  turned  eastward  and  united  with 
the  cold  Cape  Horn  current,  forming  .the  South  Atlantic  connecting 
current,  which  varies  in  velocity  between  6  and  33  nautical  miles 
per  24  hours.  The  northern  part  of  this  connecting  stream  has  a 
higher  temperature  than  the  southern,  as  is  to  be  expected  from 
the  double  origin  of  this  current.  An  arm  of  the  Cape  Horn  cur- 
rent turns  northward  along  the  Patagonian  coast,  forming  the  cold 
Falkland  current,  which  is  always  at  least  3°  to  4°  cooler  than  the 
neighboring  Brazil  current. 

Where  the  cold  West-wind  drift  of  the  South  Atlantic  meets  the 
West  African  coast,  it  turns  northward  and  becomes  the  cold 
Benguelan  current,  with  a  velocity  of  generally  more  than  12,  but 
seldom  more  than  30,  nautical  miles  per  day,  a  velocity  sufficient 
to  deflect  the  red-brown  water  of  the  Congo  northward  and  cause 
the  floating  mangrove  islands  and  tree  trunks  furnished  by  this 


236  PRINCIPLES    OF    STRATIGRAPHY 

stream  to  be  carried  northeastward,  far  out  into  the  Atlantic.  Of 
the  two  great  current  rings  thus  formed  in  the  Atlantic,  that  of  the 
Nprth  Atlantic  turns  clockwise,  that  of  the  South  Atlantic  counter 
clockwise.  The  areas  enclosed  by  them  are  relatively  free  from 
currents,  both  air  and  water,  and  mark  a  region  of  high  air  pressure. 
The  northern  is  filled  with  the  floating  seaweed  forming  the  Sar- 
gasso Sea,  while  the  southern  is  relatively  free  from  accumulated 
drift  material.  Transportation  of  floating  material  (plankton) 
from  one  circle  to  the  other  occurs  sometimes,  but  generally  these 
circles  remain  distinct. 

The  Arctic  Ocean.  In  this  ocean  the  chief  current  is  the 
continuation  of  the  Gulf  or  Atlantic  stream,  which,  after  giving 
off  a  branch  to  the  southeast  into  the  North  Sea  around  the  North 
British  coast,  continues  past  the  Shetland  Islands  along  the  Nor- 
wegian coast  to  beyond  North  Cape,  where  it  splits  into  a  number 
of  minor  streams,  one  of  which,  the  North  Cape  current,  turns  east 
along  the  north  coast  into  the  Barent  Sea,  to  the  south  coast  of 
Nova  Zembla,  with  a  branch  north  to  Franz  Josef  Land.  Another 
arm  continues  northward  to  Spitzbergen,  where  it  can  be  recognized 
beyond  80°  north  latitude.  All  along  its  course,  driftwood  from 
tropical  regions  has  been  observed,  the  most  noted  example  being 
the  bean  of  the  West  Indian  Entada  gigalobium,  one  of  the  com- 
monest drift  materials  of  the  Gulf  Stream,  which  was  found  by 
Otto  Torell  in  latitude  80°  8'  north,  longitude  17°  40'  east,  the 
western  point  of  North  East  Land.  The  cold  currents  most  pro- 
nounced are  the  East  Greenland  current  already  noted  and  its 
branch,  the  East  Iceland  current.  This  meeting  with  the  warm 
water  of  the  Gulf  Stream  extension  produces  a  series  of  compli- 
cated whirls,  which  have  a  decided  influence  on  the  distribution 
of  the  temperature,  the  salinity,  and,  with  these,  the  planktonic  life. 
(See  the  maps  given  by  Helland  Hansen  and  F.  Nansen~3o; 
Krummel-42  :  652.)  Various  other  cold  streams  have  been  charted, 
such  as  the  cold  Bear  Island  stream,  issuing  from  the  Barent 
Straits,  another  issuing  from  Kara  Straits  and  passing  along  the 
south  and  west  coast  of  Nova  Zembla,  one  between  Nova  Zembla 
and  Franz  Josef  Land,  and  one  between  the  latter  and  Spitzber- 
gen, flowing  southward  and  westward.  All  these  are  branches  of  a 
general  southward  drift  of  the  cold  surface  waters  of  relatively  low 
salinity,  which  result  from  the  inpouring  and  excessive  precipitation 
of  fresh  waters,  and  give  the  arctic  waters  in  general  a  higher  level 
than  that  of  the  neighboring  oceans.  On  the  Atlantic  side  the  out- 
lets are  on  the  two  sides  of  Spitzbergen,  especially  between  Spitz- 
bergen and  Greenland.  Another  line  of  outflow  is  from  the  waters 


OCEAN    CURRENTS  237 

of  the  Parry  Archipelago,  eastward  to  Baffin  Bay,  and  south  to 
Davis  Straits,  where  it  becomes  part  of  the  Labrador  current, 
which  is  further  fed  by  recurving  waters  of  the  West  Greenland 
current.  (See  maps,  Krummel-42  :  663.) 

The  Pacific  Ocean.  The  currents  of  this  ocean  conform  more 
nearly  to  the  typical  arrangement  sketched  at  the  beginning  than  do 
those  of  any  other  terrestrial  ocean.  The  North  Equatorial  stream, 
driven  by  the  northeast  trade  winds,  crosses  the  entire  ocean  from 
east  to  west  (S.  87°  W.),  a  distance  of  7,500  nautical  miles,  with  an 
average  velocity  of  14.5  nautical  miles  in  24  hours,  31.08  cm.  per 
second  or  1.12  km.  per  hour,  and  with  a  high  percentage  of  stability. 
The  southern  border  of  this  stream  lies  10°  north  of  the  Equator  in 
summer,  and  5°  in  winter.  East  of  the  Philippines,  the  current 
turns  north,  increasing  its  velocity  to  30  or  even  50  nautical  miles 
per  day.  The  main  body  goes  north  to  form  the  Kuroshiwo  or 
Japan  current,  which,  skirting  Japan,  gives  rise  to  the  North 
Pacific  West-wind  drift  and  bends  southward  again  on  the  West 
American  coast  as  the  California  current.  This  replaces  the  waters 
carried  westward  in  the  North  Equatorial  current  under  the  influ- 
ence of  the  northeast  trade  wind,  and  corresponds  to  the  Canaries 
current  of  the  North  Atlantic.  A  smaller  part  of  the  North  Equa- 
torial stream  bends  off  through  the  Ballingtang  channel  north  of  the 
Philippines  into  the  China  Sea,  where,  especially  in  winter,  during 
the  period  of  the  northeast  monsoon,  it  adds  a  considerable  amount 
to  the  cyclonal  circulation  of  that  mediterranean.  Finally,  large 
parts  of  the  current  become  reversed,  especially  in  summer,  to  form 
part  of  the  Equatorial  Counter  current.  The  South  Equatorial  cur- 
rent is  much  stronger  than  the  northern,  velocities  of  20  nautical 
miles  per  day  being  normal,  velocities  of  40  or  50  not  uncom- 
mon in  all  seasons,  while  occasional  velocities  of  70,  80,  or  even 
more  than  100  nautical  miles  in  24  hours  have  been  recorded.  The 
greatest  velocity  is  in  its  northern  part,  near  or  north  of  the 
Equator,  especially  in  the  eastern  region,  and  here  the  rapid  move- 
ment brings  about  a  welling  up  of  the  colder,  deeper  waters  as 
clearly  indicated  by  the  tongue-like  drawing  out  of  the  isotherms 
west  of  the  Galapagos  Islands  on  the  temperature  chart  of  the 
Pacific.  The  length  of  this  stream  is  about  8,500  nautical  miles; 
its  northern  border  may  reach  to  i°  or  2°  north  of  the  Equator. 
Opposite  the  Molucca  Straits  the  northern  part  of  the  stream  bends 
northward  and,  recurving,  produces  its  part  of  the  Equatorial 
Counter  current.  The  greater  part,  however,  flows  southward  along 
the  Australian  coast,  and  constitutes  the  East  Australian  current. 
This  in  part  disposes  of  the  excess  of  water  driven  against  this 


238  PRINCIPLES    OF    STRATIGRAPHY 

coast  by  the  southeast  trades,  as  the  South  Equatorial  current,  and 
in  part  becomes  a  compensating  current  to  replace  the  eastward- 
flowing  waters  of  the  great  South  Pacific  West-wind  drift.  This 
finally  turns  northward  as  the  Peruvian  current,  with  an  average 
velocity  of  15  nautical  miles  per  day,  which  velocity  is  greatly 
increased  as  it  nears  and  finally  joins  the  South  Equatorial  stream, 
which  has  the  effect  of  an  aspirator.  Cold  waters  well  up  between 
the  Peruvian  current  and  the  South  American  coast,  and  these  were 
formerly  regarded  as  Antarctic  waters  flowing  northward. 

The  Equatorial  Counter  current  crosses  the  entire  Pacific  from 
west  to  east,  being  especially  strong  during  the  northern  summer, 
when  it  occupies  the  zone  between  5°  and  10°  north  latitude, 
though  in  winter  it  shrinks  to  a  narrow  band  between  5°  and  7°. 
With  the  varying  season  the  strength  of  the  current  fluctuates. 
Thus  in  winter  it  is  from  5  to  8  nautical  miles  per  day,  while  in 
summer  it  rises  to  9  or  12  nautical  miles. 

The  Indian  Ocean.  The  currents  of  this  ocean  are  subject  to 
semiannual  variation  induced  by  the  alternate  dominance  of  the 
winter  or  summer  monsoons.  During  the  winter  or  northeast  mon- 
soons the  currents  correspond  in  a  measure  to  those  of  the  Atlantic 
and  Pacific.  Two  westward-flowing  currents  separated  by  an  east- 
ward-flowing counter  current  occur.  The  South  Equatorial  is  the 
most  pronounced,  its  boundaries  being  between  10°  and  27°  south 
latitude,  while  the  counter  current  lies  between  2°  and  5°  south 
latitude.  This  latter  has  a  strength  of  20  to  60  nautical  miles  per 
day.  During  the  northern  summer,  when  the  southwest  monsoon 
prevails,  the  southern  westward-flowing  current  is  broadened  to 
near  5°  south  latitude,  the  counter  current  as  such  has  disap- 
peared, while  the  movement  of  the  waters  north  of  the  equator  is 
eastward. 

Against  Madagascar  the  impinging  South  Equatorial  current 
divides,  a  large  part  passing  southward  as  the  Mozambique  cur- 
rent, and  later  becoming  the  Agulhas  stream,  which  bathes  the  coast 
of  Cape  Colony  in  South  Africa  outside  of  the  continental  shelf, 
where  velocities  ranging  from  50  to  no  nautical  miles  per  day 
have  been  noted.  South  of  the  Cape  of  Good  Hope  the  Agulhas 
current  meets  the  southern  continuation  of  the  cold  West-wind  drift 
of  the  South  Atlantic,  which  causes  it  to  splinter  into  numerous 
fingers,  the  spaces  between  which  are  taken  by  the  cold  fingers  of 
the  eastward-flowing  stream.  In  addition  to  carrying  off  the  waters 
of  the  South  Equatorial  current,  the  Agulhas  stream  further  acts  in 
a  compensatory  manner  to  supply  the  water  carried  eastward  by 
the  strong  west  winds  of  the  southern  latitudes.  This  south  Indian 


OCEAN    CURRENTS  239 

West-wind  drift  is  again  continued  in  part  in  the  northward-flowing 
West  Australian  current,  the  close  analogue  of  the  Benguelan  cur- 
rent of  the  South  Atlantic.  The  velocity  of  this  current  generally 
ranges  from  1 8  to  36  nautical  miles  per  day,  though  sometimes  it  is 
scarcely  perceptible.  The  main  part  of  the  West-wind  drift,  how- 
ever, continues  eastward  past  Cape  Leeuwin  and  along  the  South 
Australian  coast  past  Tasmania  to  the  Pacific,  forming  part  of  the 
great  circumpolar  current  of  the  Antarctic  region.  That  this  great 
eastward  drift  around  the  antarctic  continent  is  a  reality  has  been 
shown  by  many  tests  with  floating  bottles,  one  of  which,  thrown 
overboard  December  16,  1900,  off  the  Patagonian  coast  (long.  60° 
W.),  was  picked  up  June  9,  1904,  on  the  north  coast  of  New 
Zealand  (long.  172°)  having  traveled  in  1,271  days  a  distance  of 
10,700  nautical  miles,  or  nearly  2/3  the  circumference  of  the  earth, 
between  latitude  40°  and  50°  south,  a  distance  equal  to  that  from 
pole  to  pole,  or  an  average  of  Sy2  nautical  miles  per  day.  (Map, 
Krummel-42  '.677.) 

A  characteristic  accompanying  feature  of  the  wind-drift  cur- 
rents is  a  vertical  compensatory  movement,  the  upwelling  of  the 
colder,  deeper  waters  where  the  velocity  of  the  surface  stream  is 
such  that  the  lateral  compensation  is  insufficient.  An  example  of 
this  has  already  been  cited  in  the  tongue  of  deep-green,  colder  wa- 
ter extending  westward  from  the  Galapagos  into  the  blue  warm 
water  of  the  South  Equatorial  current  of  the  Pacific.  A  similar 
phenomenon  occurs  along  the  west  American  coast,  where  the  Cali- 
fornia current  draws  up  the  colder,  deeper  water  on  its  landward 
side.  This  is  likewise  the  case  in  the  Canary  and  Benguelan 
streams,  as  well  as  along  the  west  coast  of  South  America.  The 
upwelling  follows  the  wind,  while  a  compensating  downward  move- 
ment of  the  warmer  water  must  occur  before  the  wind.  This  ex- 
plains the  phenomenon  that  a  persistent  land  breeze  will  cause  the 
upwelling  along  the  coast  of  the  colder  waters,  the  warmer  being 
blown  out  to  sea,  while  a  sea  breeze  brings  the  warmer  surface  wa- 
ters. Thus  it  is  observed  at  the  bathing  beaches  on  the  North  Ger- 
man coast  that  the  north  winds  cause  a  warming,  but  south  winds 
a  distinct  cooling  of  the  water. 

CURRENTS  IN  MEDITERRANEANS  AND  EPICONTINENTAL  SEAS. 
The  currents  of  intracontinental  water  bodies  are  generally  mere 
branches  of  the  main  oceanic  circulation,  and  sometimes  indeed,  as 
in  the  case  of  the  Caribbean  and  Mexican  seas,  are  an  integral  part 
of  it.  The  circulation  of  the  North  Sea  is  a  southward-bending 
branch  from  the  Gulf  Stream,  and  the  main  currents  of  the  East 
Greenland  mediterranean  are  also  a  part  of  this  larger  circulation. 


240  PRINCIPLES    OF    STRATIGRAPHY 

The  currents  of  the  Arabian  Sea  and  the  Bengal  Bay  are  clearly  a 
part  of  the  circulation  of  the  Indian  Ocean,  while  the  circulation 
of  the  China  Sea  is  in  part  a  branch  of  the  North  Equatorial  cur- 
rent of  the  Pacific.  In  general,  the  circulation  of  the  mediter- 
raneans is  a  cyclonal  one,  and  it  becomes  more  individualized  the 
more  the  water  body  is  separated  from  the  ocean's  adjoining. 

The  Roman  Mediterranean,  which  is  connected  with  the  At- 
lantic only  by  the  narrow  Gibraltar  Straits,  nevertheless  receives  a 
small  branch  of  the  northern  West-wind  drift.  This  stream, 
though  subject  to  modification  by  local  winds,  is  recognizable 
throughout,  and  influences  the  migration  of  the  sands  of  the  bot- 
toms and  coasts.  It  passes  eastward  along  the  north  coast  of  Al- 
giers, through  the  narrows  between  Tunis  and  Sicily,  with  a  veloc- 
ity of  5  to  10.5  nautical  miles  per  day,  and  south  of  Malta  toward 
Barca  (Africa),  causing  eddies  in  the  Gulf  of  Sidra,  turning  north- 
ward on  the  Syrian  coast,  and  westward  on  the  south  coast  of  Asia 
Minor,  around  Crete  into  the  Ionian  Sea,  then  north  along  the  Dal- 
matian, and  south  along  the  east  Italian  coasts,  making  a  counter- 
clockwise circulation  in  the  Adriatic.  In  the  Tyrrhenian  Sea  it  con- 
tinues northwestward,  then  west  in  the  Ligurian  and  southwest 
along  the  Spanish  coast,  thus  completing  the  counter-clockwise  cir- 
culation. This  circulation  takes  place  largely  under  the  influence  of 
the  local  winds,  and  is  not  always  constant. 

Both  the  Adriatic  and  ^Egean  seas  have  practically  independent 
circulations  in  a  counter-clockwise  direction,  and  a  similar  circula- 
tion exists  in  the  Black  Sea,  though  a  part  of  the  water  moving 
along  the  west  coast  of  this  body  passes -out  as  a  strong  stream 
through  the  Bosphorus,  the  Sea  of  Marmora,  and  the  Dardanelles 
into  the  ^Egean  Sea.  To  compensate  this  outflow,  a  deeper  lying 
current  enters  from  the  yEgean  and  the  Marmora  Sea.  At  Con- 
stantinople the  outflowing  stream  of  the  Bosphorus  has  a  velocity  of 
123  cm.  per  second  at  the  surface,  and  rapidly  decreases  to  nothing 
at  20  meters'  depth.  At  25  meters'  depth  the  inflowing  stream  is  at 
its  maximum  with  a  velocity  of  73  cm.  per  second  with  moderate 
diminution  downward,  its  strength  at  40  m.  depth  being  still  43  cm. 
per  second.  Makaroff  has  estimated  that  the  outflowing  stream  car- 
ries 10,530  cb.  m.  per  second,  while  the  inflowing  carries  only  5,700 
cb.  m.  per  second.  This  makes  a  yearly  deficit  of  152  cb.  km.,  the 
excess  carried  out  over  the  inflow,  and  this  has  to  be  replaced  by  the 
annual  precipitation  and  afflux  of  water  from  the  drainage  basin. 
A  similar  out-  and  influx  take  place  through  the  Straits  of  Kertch 
between  the  Sea  of  Azov  and  the  Black  Sea.  Just  the- reverse  mo- 
tion is  seen  at  the  mouth  of  the  Roman  Mediterranean  and  that  of 


CURRENTS    IN    MEDITERRANEANS  241 

the  Red  Sea.  Here  the  ocean  waters  are  of  less  salinity  than  those 
of  the  mediterraneans,  and  they  flow  in  on  the  surface,  while  the 
more  saline  waters  from  the  mediterraneans  escape  below  the  sur- 
face to  the  oceans,  influencing  the  salinity  of  the  adjoining  parts  of 
the  sea.  In  the  Straits  of  Bab-el-Mandeb  the  surface  waters  enter 
the  Red  Sea  with  a  velocity  of  2  to  2^4  nautical  miles  per 'hour,  ex- 
tending down  with  diminishing  velocity  to  130  or  140  meters,  below 
which  the  outflowing  stream  ranges  in  velocity  from  i  to  3  nauti- 
cal miles  per  hour. 

An  outflowing  surface  stream,  the  Baltic  Stream,  carries  the 
weakly  saline  waters  of  the  Baltic  through  the  Ore  Sound  and  con- 
tinues along  the  Swedish  coast  of  the  Kattegat,  where  it  is  driven 
by  the  prevailing  west  wind  and  the  rotation  of  the  earth.  Its 
velocity  at  a  distance  of  4  to  6  miles  from  shore  is  24  to  48  nautical 
miles  per  day  in  calm  weather.  Turning  westward  along  the  Nor- 
wegian coast,  it  may  reach  a  velocity  of  80  to  100  nautical  miles  in 
24  hours.  It  normally  flows  against  the  prevailing  wind,  which 
must  reach  great  strength  before  it  is  able  to  reverse  the  current 
even  temporarily.  This  stream  has  its  greatest  strength  in  the 
spring  and  early  summer  months,  when  the  influx  of  fresh  water 
into  the  Baltic  is  at  its  maximum. 

The  currents  of  the  Baltic  and  its  branches  are  largely  dependent 
on  the  wind  and  are  further  complicated  by  the  tidal  currents  and 
the  relative  amount  of  influx  and  evaporation.  In  the  spring  76 
per  cent,  of  all  currents  flows  westward,  owing  to  the  strong  influx 
of  land  waters  and  the  pronounced  east  winds.  In  summer  this 
drops  to  60.5  per  cent.,  when  evaporation  over  the  Baltic  becomes 
strong  and  west  winds  prevail,  while  during  autumn  and  winter  71 
per  cent,  and  69  per  cent,  of  all  currents  of  the  Baltic  flows  west- 
ward. The  strength  of  the  outflowing  streams  may  reach  3  to  4 
nautical  miles  per  hour  in  the  narrows  of  the  western  part,  or  Belt 
Sea.  The  Finnish  Gulf,  which  is  scarcely  separated  from  the  Bal- 
tic, and  has  therefore  much  the  structure  of  a  funnel  sea,  is  charac- 
terized by  a  westward-flowing  surface  stream  of  fresher  water  and 
an  eastward-flowing  compensating  stream  of  greater  salinity  at  some 
depth  below  the  surface.  The  Bothnian  Gulf,  on  the  other  hand, 
has  a  more  independent  circulation  in  the  counter-clockwise  direc- 
tion, and  this  corresponds  to  its  greater  distinctness  from  the  Bal- 
tic. The  current  flows  into  the  gulf  east  of  the  Aland  Islands,  and 
out  on  the  west,  except  when  interfered  with  by  strong  winds. 

The  circulation  of  other  northern  intracontinental  seas,  like  Hud- 
son Bay,  St.  Lawrence  Gulf  and  Kara  Sea,  is  a  cyclonal  one  in  the 
counter-clockwise  direction.  A  similar  circulation  exists  in  the  Red 


242  PRINCIPLES    OF    STRATIGRAPHY 

Sea,  where  the  current  sets  north  on  the  Arabian  and  south  on  the 
African  coast.  Here,  however,  the  strong  monsoons  act  as  modi- 
fiers of  this  general  circulation.  Similar  conditions  exist  in  the  Per- 
sian Gulf,  but  here,  as  in  epicontinental  seas  generally,  the  circula- 
tion is  strongly  modified  by  winds  and  tidal  streams.  The  marginal 
mediterraneans  of  the  West  Pacific  coast  show  the  cyclonic  circu- 
lation in  the  counter-clockwise  direction  characteristic  of  the 
northern  hemisphere,  but  more  or  less  modified  by  the  inflowing  cir- 
culation of  the  North  Pacific  itself.  The  Japan  Sea  may  be  taken 
as  typical.  Here  a  branch  of  the  warm  and  highly  saline  Kuro- 
shiwo  current  enters  through  the  Straits  of  Korea,  and  follows  the 
west  coast  of  Japan  northeastward.  It  sends  branches  out  to  the 
Pacific  through  the  several  straits,  and  then  turns  into  the  Gulf  of 
Tartary,  where  it  unites  with  the  counter  current  from  the  north, 
the  low  temperature  and  salinity  of  which  strongly  influence  the 
Asiatic  coast,  which  it  follows  to  the  east  coast  of  Korea.  The  cir- 
culation within  the  sea  of  Okhotsk,  and  to  a  less  extent  in  Behring 
Sea,  follows  the  same  plan,  though  in  the  latter  the  influence  of  the 
warm  Kuroshiwo  in  summer  causes  marked  modifications  such  as  a 
northward  flowing  warm  surface  stream  in  the  western  half  to 
Behring  Straits. 

The  Australian  group  of  mediterraneans  is  of  especial  interest, 
as  it  lies  on  bath  sides  of  the  equator  and  so  partakes  alternately 
of  both  systems  of  circulation.  At  the  time  of  the  northeast  mon- 
soon the  counter-clockwise  circulation  normal  for  the  northern 
hemisphere  exists  in  the  China  Sea,  the  water  running  W.  S.  W. 
along  the  Chinese  coast  with  a  velocity  of  20  to  40  nautical  miles 
toward  the  coast  of  Anam,  where  it  reaches  velocities  of  50  to 
80  nautical  miles  per  day,  turns  south  and  east,  and  then  to  the 
northeast,  along  the  west  coast  of  Borneo,  Palawan  Island  and  the 
Philippines,  with  velocities  of  15  to  25  nautical  miles  per  day.  The 
currents  of  the  Java,  Flores  and  Banda  seas  flow  prevailingly  east- 
ward with  southward  flowing  branches  through  the  straits  between 
the  small  Sunda  Islands  and  on  both  sides  of  Timor.  The  reverse 
direction  is  taken  by  the  circulation  in  the  time  of  the  southwest 
monsoon.  Along  the  coast  of  Cochin  China,  the  stream  flows 
northeastward,  reaching  a  strength  of  40  to  70  nautical  miles  at 
Cape  Pedaran ;  along  the  Anam  coast  it  flows  north,  and  off  the 
South  Chinese  coast  in  general  eastward.  Along  the  coast  of  Pala- 
wan and  Borneo  the  movement  is  southwestward,  the  circle  being 
closed  by  a  northward  stream  from  the  Natuna  to  the  Condore 
islands.  In  the  Java,  Flores  and  Banda  seas  the  main  direction  of 
the  flow  is  westward.  It  thus  appears  that  the  circulation  in  med- 


CURRENTS   AND    MIGRATION  243 

iterraneans  and  epicontincntal  seas  of  the  northern  hemisphere, 
when  not  a  part  of  the  main  oceanic  circulation,  as  in  the  American 
mediterraneans,  is  normally  a  singly  cyclonic  movement  in  counter- 
clockwise direction,  while  the  movement  of  the  main  oceanic  circu- 
lation of  this  hemisphere  is  clockwise.  Only  in  the  case  of  the  seas 
lying  on  the  Equator  does  a  reversal  of  conditions  occur  when  the 
sun  crosses  to  the  north  of  the  Equator  during  the  northern  summer 
or  the  period  of  southwest  monsoons. 

The  type  of  currents  found  in  funnel  seas  of  the  California!!  type 
is  illustrated  by  that  water  body.  During  the  cooler  months  the 
prevailing  northwest  winds  drive  the  surface  waters  southward, 
while  in  summer  the  monsoon-like  southeast  winds  drive  the  surface 
waters  into  the  gulf.  At  a  depth  of  50  meters  the  stream  flows 
again  southward. 

MARINE  CURRENTS  IN  RELATION  TO  MIGRATION  AND  DISPERSAL, 
PAST  AND  PRESENT.  As  will  be  more  fully  set  forth  in  Chapter 
XXIX,  ocean  currents  are  among  the  important  factors  in  influenc- 
ing migration  of  organisms,  and  they  are  the  chief  cause  of  the  dis- 
persal of  the  plankton  or  floating  matter,  organic  and  inorganic,  of 
the  sea.  The  numerous  records  of  the  wide  dispersal  of  floating 
matter,  such  as  sealed  bottles,  purposely  thrown  into  the  sea,  wrecks 
of  known  date,  tree  trunks  brought  by  tropical  rivers  to  the  sea, 
and  carried  by  the  ocean  currents  to  the  arctic  regions,  and  others 
have  indeed  been  one  of  the  chief  sources  of  our  knowledge  of  the 
direction  of  these  currents.  Taking  our  cue  from  these  dispersals 
in  the  modern  sea,  we  may  look  for  similar  evidence  of  currents 
in  the  past.  In  such  determination  the  dispersal  of  the  holo- 
planktonic  organisms  serves  perhaps  as  the  best  guide.  In  the  early 
Palaeozoic,  the  graptolites  seem  to  furnish  reliable  indications  of  the 
general  course  of  the  currents,  and  they  have  been  so  used  in  the 
construction  of  Palseogeographic  charts.  (Ruedemann-6o:  488', 
Grabau-29;  Map  figs.  /,  2,  7,  8.)  Sometimes  the  direction  of  the 
current  can  be  found  by  the  position  which  the  rhabdosomes  of  the 
graptolites  assumed  in  the  strata,  as  in  the  case  cited  by  Ruedemann 
from  the  Utica  shales  of  Dolgeville,  New  York,  where  not  only  the 
rhabdosomes  of  the  graptolites,  but  also  the  spicules  of  sponges, 
fragments  of  byozoans  and  shells  of  Endoceras  proteifonne  have  a 
parallel  arrangement,  indicating  an  east-northeast  by  south-south- 
west direction  of  the  currents.  "That  the  flow  came  from  N.  78° 
E.  and  ran  toward  S.  78°  W.,  can  be  inferred  from  the  appearance 
of  the  mud-flow  structure,  the  drift  ridges  behind  the  fossils  (En- 
doceras), the  eastward  pointing  of  the  apices  of  the  Endoceras 
shells,  and  often  also  of  the  sicular  ends  of  the  graptolites.  .  .  . 


244  PRINCIPLES    OF    STRATIGRAPHY 

Gastropods  have  been  noticed  with  transversally  arranged  frag- 
ments, which  apparently  were  arrested  by  the  immovable  shell,  on 
the  .east  side,  and  with  a  drift  ridge  of  longitudinally  arranged 
fragments  on  the  west  side."  ( Ruedemann-59 :  380-381.)  Since 
the  general  direction  of  the  great  ocean  currents  seems  to  have  been 
to  the  northeast,  this  indication  of  a  southwestward  flow  estab- 
lishes a  secondary  recurving  current  of  the  type  common  at  the 
present  time. 

DEPTH  OF  CURRENT  ACTION.  The  depth  of  current  action  can 
often  be  ascertained  by  the  scouring  which  it  accomplishes  on  the 
bottom,  sweeping  off  all  fine  sediment,  and  leaving  a  ''hard  bottom." 
T.  M.  Reade  has  recorded  such  bottoms  between  Gran  Canaria  and 
Teneriffe  in  the  Canary  Islands  in  depths  of  2,000  meters.  (T.  M. 
Reade— 56.)  This  is,  however,  to  be  regarded  as  more  properly  the 
work  of  a  tidal  current.  In  the  Florida  straits,  at  depths  of  160  to 
550  meters,  the  bottom  is  kept  clean,  the  fine  mud  being  swept  be- 
yond the  edge  of  the  Pourtales  Plateau,  which  consists  of  recent 
organic  material  consolidated  into  a  hard  breccia.  The  bottom  of 
the  Straits  of  Gibraltar  is  swept  clean  and  smooth  through  the  out- 
ward flowing  bottom  current. 

LAKE  CURRENTS. 

Lakes,  owing  to  their  usually  small  size,  are  not  influenced  in 
the  same  manner  by  the  primary  current-producing  agents  as  are 
the  larger  water  bodies.  It  is  true  that  on  the  large  lakes,  like  those 
of  North  America,  longshore  currents,  due  to  prevailing  winds, 
are  of  considerable  significance,  not  only  in  navigation,  but  in  the 
transportation  of  material  along  the  beach,  and  the  building  of 
bars,  sandspits,  etc.  In  general,  however,  the  movements  of  lake 
waters  induced  by  wind  partake  of  the  nature  of  a  vortical  circu- 
lation. The  wind  blowing  steadily  across  the  surface  of  a  lake 
forces  the  water  to  the  opposite  shore,  where  it  sinks,  while  the  com- 
pensatory streams  behind  the  wind  rise  from  below.  This  produces 
an  under  current  flowing  in  the  opposite  direction  from  that  on  the 
surface,  and  at  a  depth  depending  on  the  temperature,  density,  etc., 
of  the  water  and  the  configuration  of  the  basin.  (Forel-24 :  81-83.) 

RIVER  CURRENTS. 

Rivers  are  currents  of  water  confined  between  banks  of  rock  or 
soil,  and  they  differ  from  currents  in  water  bodies  in  that  typically 
their  movement  is  due  to  gravity  alone.  While  the  whole  mass  of 


RIVER    CURRENTS  245 

water  of  the  river  is  in  motion,  nevertheless  there  is  to  be  found 
in  each  cross-section  of  a  river  a  point  of  maximum  motion.  This 
is  generally  a  short  distance  below  the  surface,  and  in  a  symmetrical 
section,  near  the  center.  This  .fast-moving  portion  of  the  river  is 
especially  designated  the  "current,"  and  its  course  in  a  winding  river 
is  always  more  curving  than  that  of  the  river  itself.  As  a  result, 
it  impinges  alternately  upon  the  right  and  left  bank  of  the  river, 
which  points  become  the  centers  of  maximum  erosion.  The  bank 
against  which  the  current  impinges  will  be  kept  vertical  by  under- 
mining, and  the  river  at  the  same  time  will  be  deepest  at  that  point. 
The  opposite  side  is  shallow,  the  bank  sloping,  and  deposition  rather 
than  erosion  occurs. 

Velocities  of  River  Currents.  The  velocity  of  a  river  depends 
on  a  number  of  factors,  first  among  which  may  be  mentioned  the 
slope  of  the  river  bed,  and  next  the  volume  of  water.  The  width  of 
the  channel  is  also  an  important  factor,  this  varying  from  the  in- 
definite width  of  the  sheet  floods  of  Arizona  and  Mexico  (Mc- 
Gee-45)  to  the  narrow  canyons  of  a  youthful  topography.  The 
slope  may  vary  from  nearly  horizontal  to  vertical;  in  the  one  case, 
a  nearly  stagnant  stream  results;  in  the  other,  the  extreme  of  a 
waterfall  is  produced.  The  most  variable  of  these  factors  is  the 
volume,  and  hence  the  velocity  of  a  given  current  may  change 
greatly  between  low  and  high  water.  Sudden  changes  in  volume 
due  to  sudden  precipitation  of  vast  amounts  of  water,  as  in  semi- 
arid  regions,  may  produce  a  marked  change  in  the  slope  or 
width  of  the  channel,  and  so  affect  the  strength  of  the  current  in 
a  more  permanent  manner.  Within  the  same  stream  velocities  vary 
according  to  slope,  or  width  and  depth  of  the  channel.  Thus  the 
velocity  of  the  Rhine,  during  medium  height  of  water,  has  been 
found  to  be  3.42  m.  per  second  at  the  Bingerloch,  0.63  m.  at  Wert- 
hausen  and  1.5  m.  at  Mannheim,  while  high  water  at  Coblenz  gave 
a  velocity  of  1.88  m.  per  second.  The  Vistula  (Weichsel)  during 
high  water  has  a  velocity  of  1.2  to  1.9  m.  per  second.  The  Neckar 
above  Mannheim  at  medium  water  has  a  velocity  of  0.9  m.,  but  at 
high  water  over  3  m.  The  Danube  at  Vienna  has  a  velocity  of  1.94 
m.  per  second  during  high  water,  while  the  maximum  velocity  of 
the  Mississippi  between  the  mouths  of  the  Ohio  and  the  Arkansas 
is  1.91  m.  and  between  Bayou  la  Fourche  and  the  forking  is  1.76  m. 
per  second.  (  Krummel-42 : 575,  footnote.) 

Perhaps  the  best  example  of  local  changes  due  to  change  in  the 
bed  of  the  river  is  furnished  by  Niagara.  This  river  is  placid  and 
calm  from  its  head  near  Lake  Erie  to  within  a  half  mile  or  more 
of  the  falls,  the  fall  being  14  feet  in  something  over  20  miles,  and 


246  PRINCIPLES    OF    STRATIGRAPHY 

the  current  very  slight.  Then  a  sudden  change  in  the  slope  of  the 
river  bed,  causing  a  descent  of  55  feet  in  less  than  half  a  mile,  trans- 
forms the  river  into  a  rushing  torrent — the  rapids  above  the  falls — 
culminating  in  a  drop  of  160  feet  at  the  cataracts,  over  which  22,- 
400,000  cubic  feet  of  water  fall  per  minute.  Below  the  falls  strong 
currents  and  eddies  continue  for  a  while,  due  to  the  disturbance  of 
the  water  at  the  falls.  Then,  however,  the  river  becomes  relatively 
calm  again  with  moderate  current,  easily  navigable  for  about  two 
miles.  The  channel  is  from  1,200  to  1,300  feet  wide  at  the  top,  and 
the  water  from  160  to  190  feet  deep.  At  Suspension  Bridge  the 
channel  suddenly  contracts  to  700  or  750  feet  at  the  top,  while  the 
water  is  not  over  35  feet  deep.  In  this  narrow  and  shallow  gorge 
the  whirlpool  rapids  are  situated,  the  great  volume  of  water  rushing 
through  it  with  indescribable  force,  far  exceeding  that  of  the  upper 
rapids.  The  descent  at  the  same  time  is  slightly  more  than  50  feet 
in  a  distance  of  about  a  mile,  or  about  half  the  descent  of  the 
upper  rapids.  The  curious  eddy  of  the  whirlpool  is  entirely  due  to 
the  conformation  of  the  channel,  wnich  here  bends  at  right  angles. 
A  second  narrowing  at  Fosters  Flats  again  produces  rapids,  but  be- 
low this  the  river  becomes  relatively  quiet  and  placid  again,  and 
navigable  for  seven  miles  of  its  lower  course. 

Erosive  Power  of  Rivers.  The  erosive  power  of  a  river,  i.  e., 
the  ability  to  overcome  cohesion,  varies  as  the  square  of  its  velocity. 
Pure  water  does  little  or  no  actual  erosion,  this  being  accomplished 
by  the  transported  material.  The  rock  fragments  carried  by  the 
stream  corrode  its  bed,  while  at  the  same  time  they  abrade  each 
other.  In  the  part  of  a  stream  bed  unsupplied  by  new  material 
from  tributaries  it  is  noticeable  that  there  is  a  progressive  diminu- 
tion in  size  of  the  fragments  downstream,  the  reduction  being  pro- 
portional to  the  weight  of  the  rock  in  water  and  the  distance  trav- 
eled. The  following  measurements  made  on  the  river  Mur  show 
the  progressive  reduction  in  average  size  of  the  fragments  in  ac- 
cordance with  distance  (Hochenburger-33 153,  quoted  by  Penck- 
51  -.292}  : 

At  Graz 224  cb.  cm. 

At  Gossendorf (  10  km.  below  Graz) 184  cb.  cm. 

At  Wildon (26  km.  below  Graz) 132  cb.  cm. 

At  Landscha ( .43  km.  below  Graz) 1 17  cb.  cm. 

At  Unterschwarza (56  km.  below  Graz) 81  cb.  cm. 

At  Dippersdorf (71  km.  below  Graz) 60  cb.  cm. 

At  Leitersdorf (83  km.  below  Graz) 50  cb.  cm. 

At  Mauth-Eichdorf .  .  .  .    (101  km.  below  Graz) 33  cb.  cm. 

At  Wernsee (112  km.  below  Graz) 37  cb.  cm. 

At  Unter-Mauthdorf .  .  .    (120  km.  below  Graz) 21  cb.  cm. 


EROSION    BY   RIVERS  247 

The  distance  necessary  for  rock  fragments  to  travel  before  they 
become  completely  destroyed  varies  with  the  character  of  the  rock, 
as  shown  in  the  following  table : 

Rhaetic  sandstone (Average  weight,  40  grams) 15  km. 

Clay  slate (Average  weight,  24  grams) 42  km.    * 

Orthoceras  limestone .  .  (Average  weight,  61  grams) 64  km. 

Granular  limestone ....  (Average  weight,  40  grams) 85  km. 

Granite (Average  weight,  36  grams) 278  km. 

Rate  of  erosion.  From  the  known  area  of  the  hydrographic 
basin  of  a  river,  and  the  measured  amount  of  transportation  of  the 
material  in  the  river,  it  is  possible  to  arrive  at  a  reasonably  accurate 
estimate  of  the  rate  of  erosion  of  the  river  system  in  question. 
Thus  the  Mississippi  system,  with  a  hydrographic  basin  1,244,000 
square  miles  in  area  and  an  annual  discharge  of  sediment  of 
7,471,411,200  cubic  feet  of  sediment,  erodes  at  the  rate  of  one  foot 
in  4,640  years ;  while  the  Ganges  system,  with  a  hydrographic  basin 
of  only  400,000  square  miles  and  an  estimated  annual  discharge  of 
sediment  of  6,368,000,000  cubic  feet,  erodes  its  basin  one  foot  in 
1,751  years.  Other  estimates  make  it  I  meter  in  7,781  years,  or  I 
foot  in  about  2,628  years.  The  greater  efficiency  of  the  Ganges  is 
attributable  in  large  part  to  heavy  rainfall  during  six  months  of  the 
year,  and  to  the  steeper  slopes  of  the  basin. 

Le  Conte  (43:11),  using  the  Mississippi  basin  as  more  typical 
than  the  Ganges  for  the  earth's  surface  as  a  whole,  concludes  that 
the  continent  is  probably  lowered  at  the  rate  of  one  foot  in  5,000 
years. 

Transporting  Poiver  of  River  Currents.  Streams  move  solid 
material  either  by  rolling  it  along  the  bottom  or  by  carrying  it  in 
suspension.  Suspension  of  fine  material  is  favored  by  minor  up- 
ward currents  in  the  main  current,  while  others  carry  it  down  again 
or  against  the  side  of  the  channel.  Suspended  material  is  repeat- 
edly dropped  and  picked  up  again,  the  solid  particles  making  their 
journey  down  the  river  with  many  interruptions.  The  total  amount 
of  material  transported  by  rivers  is  often  very  great.  Thus  the 
Mississippi  River  carries  more  than  400,000,000  tons  of  sediment 
each  year  to  the  Gulf  of  Mexico,  or  more  than  a  million  tons  a  day. 
The  exact  volume,  according  to  the  measurements  of  Humphreys 
and  Abbot  (34:148-150),  is  7,471,411,200  cubic  feet,  a  mass  suffi- 
cient to  cover  an  area  of  one  square  mile  to  a  depth  of  268  feet. 
The  amount  carried  to  the  sea  by  all  the  rivers  of  the  earth  has  been 
estimated  at  perhaps  40  times  this  quantity.  (Salisbury-62 :  122.) 

The  following  table  (Kayser-39:  545)  gives  the  amounts  of  ma- 


248  PRINCIPLES    OF    STRATIGRAPHY 

terial  carried  in  suspension  or  rolled  along  the  bottom  of  some  of 
the  larger  streams  of  the  world,  according  to  the  investigations 
of  Guppy  and  T.  Mellard  Reade. 

Table  showing  the  transportation  of  material  by  rivers. 

TTT  ,      .  Material 

Water  in 

Stream  cu.  meters 

in  cu.  meters 
per  sec. 

per  year 

Amazon 69,580             

Congo 50,970             

Yangtsekiang 21,810  182,000,000 

La  Plata 19,820  44,000,000 

Mississippi 17,500  21 1,500,000 

Danube 8,502  35,540,000 

Ganges 5,762  18,030,000 

Indus 5,649             

Nile 3,680             

Huang-ho 3,285  472,500,000 

Rhine i,974             

Po 1,735  11,480,000 

Pei-ho 220  2,266,000 

Thames 65  528,300 

The  ability  of  a  current  to  transport  material  varies  in  general 
as  the  sixth  power  of  its  velocity.  Thus,  if  the  velocity  is  doubled, 
the  carrying  power  is  increased  64  times.  A  current  having  a 
velocity  of  3  feet  (or  approximately  I  meter)  per  second  (about 
2  miles  per  hour)  will  move  ordinary  rock  fragments  of  the  size  of 
a  hen's  egg  and  weighing  about  3  ounces.  From  the  law  of  varia- 
tion it  follows  that  a  current  of  ten  miles  per  hour  will  carry  rocks 
weighing  one  and  one-half  tons,  while  a  torrent  of  20  miles  per  hour 
will  carry  rock  masses  100  tons  in  weight.  Taking  the  varying  spe- 
cific gravities  of  different  rocks  into  consideration,  the  table  on  page 
249  has  been  constructed  by  T.  E.  Blackwell  (5;  cited  by  Beard- 
more~3:7;  Penck~5i :  281)  to  show  the  size  of  the  various  rock 
masses  transported  by  currents  of  varying  velocity. 

According  to  the  experiments  of  Forbes  (23 :  474)  made  in  a 
shallow  trough,  the  following  velocities  were  required  to  stir  up 
various  sediments  from  the  bottom : 

Table  of  -velocities  required  to  stir  up  bottom  material. 

Moist  brick  clay  at  a  velocity  of 0.077  m.  per  sec. 

Fine  fresh-water  sand  at  a  velocity  of 0.213  m.  per  sec. 

Sea  sand  at  a  velocity  of °-337  m-  Per  sec- 
Gravel,  pea  size,  at  a  velocity  of 0.610  m.  per  sec. 


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249 


250  PRINCIPLES    OF    STRATIGRAPHY 

Recent  experiments  by  Sorby  (66 :  180)  indicate  that  a  current 
of  about  6  inches  per  second  is  sufficient  to  slowly  drift  along 
granules  of  common  sand  having  a  diameter  of  about  a  hun- 
dredth of  an  inch.  No  rippling  of  the  sand  was  produced  until  the 
velocity  was  somewhat  greater.  In  the  bed  of  the  River  Rhine  at 
Breisbach  the  following  measurements  were  made  by  Suchier 
(71 :  jji ;  Penck-5i  :  283}  to  ascertain  the  velocity  at  which  various 
sediments  begin  to  move,  (i)  through  the  influence  of  the  cur- 
rent alone,  and  (2)  after  the  sediments  on  the  bottom  are  stirred 
up: 

A.  With  stream  bed  covered  by  fine  sediment. 

Under  action  of  current  alone,  no  movement  found,  with 

bottom  velocity  at 0.694  m-  Per  sec- 
After  being  stirred  up,  the  movement  of  the  sediment  be- 
gan for  fragments  of  the  size  of  beans,  when  bottom 
velocity  reached 0.897  m-  Per  sec- 
Fragments  of  the  size  of  hazelnuts,  when  bottom  velocity 

reached 0.923  m.  per  sec. 

Fragments  of  the  size  of  walnuts,  when  bottom  velocity 

reached 1.062  m.  per  sec. 

Fragments  of  the  size  of  a  pigeon  egg,   when  bottom 

velocity  reached 1.123  m.  per  sec. 

B.  With  river  bottom  free  from  sediment,  the  smallest  particles 

are    moved    when    the    current    velocity    reaches    at 

bottom 1.180  m.  per  sec. 

Pebbles  of  pea  and  hazelnut  size  move  freely  under  a 

velocity  of 1.247  m.  per  sec. 

With  noticeable  noise  at 1 .300  m.  per  sec. 

Pebbles  of  walnut  size  are  moved  without  stirring  and 
such  of  250  gr.  weight  after  stirring  up,  with  current 

at i  .476  m.  per  sec. 

Pebbles  of  1,000  gr.  wt.  rolled  at 1.589  m.  per  sec. 

C.  General  movements  of  pebbles: 

Up  to  the  size  of  pigeon  eggs,  at i  .623  m.  per  sec. 

Up  to  the  size  of  hens'  eggs,  at 1.71?  m.  per  sec. 

(including  such  of  1,500  gr.) 

Pebbles  of  less  than  2,500  gr.  wt.  are  moved  at 1.800  m.  per  sec. 

All  pebbles  moved  at 2.063  m.  per  sec. 


It  is  evident  that  it  requires  a  much  greater  velocity  to  start  the 
movement  than  is  required  to  keep  it  up.  This  is  shown  by  the  fol- 
lowing comparison : 


TRANSPORTATION    BY    RIVERS  251 

Velocity  re-  Velocity  re- 

Size  of  pebbles  quired  to  move  quired  to  start 

after  stirring  up  motion 

Hazelnut  size , 0.923  m.  per  sec.  1.35  m.  per  sec. 

Walnut  size 1.062  m.  per  sec.  1.39  m.  per  sec. 

Pigeon  egg  size 1.123  m.  per  sec.  1.45  m.  per  sec. 

The  transportation  of  the  coarser  detritus  in  streams  is  chiefly 
by  rolling  along  the  bottom,  more  rarely  by  pushing  along.  The 
entire  river  bed  may  be  in  motion,  forming  a  waste  stream  saturated 
with  water,  which  in  the  case  of  the  Rhine  at  Ragaz  and  the  Birsig 
at  Basel  has  been  found  to  possess  a  depth  of  more  than  three 
meters  (Pestalozzi-53  :vi)  and  of  four  meters  in  the  Danube  at 
Vienna.  This  phenomenon  is,  however,  ordinarily  restricted  to 
mountain  streams  in  flood. 

The  sands  of  the  river  bottoms  generally  assume  the  arrange- 
ment of  a  series  of  low  banks,  alternating  in  position  on  opposite 
sides  of  the  stream.  Opposite  each  low  bank  is  a  deep  channel  with 
steep  sides,  harboring  the  main  current  of  the  river.  These  banks, 
which  in  general  have  a  triangular  outline,  their  bases  against  the 
river  banks,  slowly  wander  downstream,  through  removal  of  the 
sand  on  the  upstream  side,  its  passage  across  the  bank  and  deposi- 
tion against  the  downstream  side.  On  the  middle  Rhine  such  banks 
move  at  the  rate  of  200  to  400  meters  per  year  downstream,  this 
being  increased  to  three  times  that  amount  in  years  of  high  water. 
In  seven  years  a  bank  may  thus  reach  the  former  position  of  the 
one  next  downstream  on  the  same  side.  (Grebenau,  cited  by  Penck- 
51  -.286.)  In  the  regulated  reaches  of  the  Danube  at  Vienna,  the 
sand  banks  have  wandered  in  seven  years  from  700  to  1,000  meters 
downstream.  (Penck~5i  -.286.)  In  the  Loire  the  sand  banks  mi- 
grate at  the  rate  of  1.72  to  3.61  meters  per  day  in  summer  and  2.37 
to  18.65  m-  Per  day  m  winter,  according  to  the  varying  angle  of 
fall  of  the  water,  which  is  from  0.28  permille  to  0.45  permille.  This 
also  shows  the  great  difference  between  the  transport  in  summer 
and  winter,  the  latter  being  the  season  of  floods  and  high  water  gen- 
erally. In  all  cases  the  motion  of  the  waste  matter  is  much  slower 
than  that  of  the  water,  and  the  amount  of  water  passing  a  given 
point  may  be  a  thousand  times  the  amount  of  sediment  carried 
past  that  point  in  the  same  period.  Thus  the  Rhine  above  Germers- 
heim  carries  nearly  7  cu.  cm.  of  waste  for  every  cubic  meter  of  wa- 
ter, while  the  Danube  at  Vienna  carries  on  the  average  13  cu.  cm. 
in  every  cubic  meter  of  water.  That  sands  and  pebbles  can  be  trans- 
ported in  the  course  of  time  to  great  distances  by  river  currents 


252  PRINCIPLES    OF    STRATIGRAPHY 

is  shown  in  the  great  delta  of  the  Huang-ho,  which  extends  for  300 
miles  or  more  from  the  mountains  which  have  furnished  the  sedi- 
ment. The  sands  and  round  quartz  pebble  conglomerate  at  the 
base  of  the  Carbonic  of  North  America  (Pottsville)  have  been 
spread  over  an  area  of  more  than  400  miles  radius.  With  progres- 
sive transport  a  constant  decrease  in  the  size  of  the  fragments  oc- 
curs, owing  to  the  grinding  processes  which  they  undergo.  [See  the 
table  given  above  for  the  reduction  of  the  sediments  of  the  Mur 
River  (p.  246).] 

Sorting  Power  of  Rivers.  When  sands  and  gravel  consist  of  a 
variety  of  material,  a  gradual  assorting  and  elimination  of  the  more 
destructible  matter  will  result  by  river  transportation,  as  well  as 
wave  action.  This  sorting  of  sands  by  rivers  and  by  the  waves 
along  the  shore  is,  however,  always  much  slower  and  generally  less 
complete  than  when  it  is  done  by  the  wind.  The  gravels  of  the 
River  Saale  at  Jena,  derived  from  the  Thuringer  Wald,  consist 
chiefly  of  fragments  of  the  Culm  and  Cambric  formations.  The 
Siluric,  Devonic,  Zechstein  and  Buntsandstein  formations  of  this 
region  are  scarcely  represented  in  the  Saale  gravels  on  account  of 
the  preponderance  of  soft  shales,  sandstones,  limestones  and  dolo- 
mites, which  in  the  course  of  transportation  are  destroyed.  (Keil- 
hack~40 : 15. ) 

Analyses  (Mackie-46:  149)  of  the  sands  of  the  River  Spey  de- 
rived from  the  fundamental  gneiss  of  Scotland  showed  at  Cromdale 
1 8  per  cent,  of  feldspar  and  I  per  cent,  of  mica,  while  further  down 
the  river  at  Orton  the  percentage  of  feldspar  was  only  12.  That 
of  the  River  Findhorn  above  Dulsie  bridge  showed  42  per  cent,  of 
feldspar,  while  between  Forres  bridge  and  the  sea  the  percentage 
was  reduced  to  twenty-one.  This  shows  the  gradual  washing  out 
by  rivers  of  the  feldspar  and  mica.  On  the  seashore,  as  already 
noted,  further  assorting  takes  place.  Thus  the  average  per  cent. 
of  feldspar  in  the  sand  furnished  by  the  four  principal  rivers  of 
Eastern  Moray  (Spey,  Lossie,  Findhorn,  Nairn)  was  10,  whereas 
in  the  rivers  themselves,  near  their  mouths,  the  average  per  cent, 
was  1 8.  Prolonged  sorting  by  either  waves  or  river  currents  may 
thus  produce  nearly  pure  quartz  sand  by  the  removal  of  the  other 
destructible  minerals.  The  distance  traveled  by  river  gravels  is  often 
very  great.  Pebbles  from  the  hills  bordering  the  Red  Sea  have 
been  found  in  the  Nile  Delta,  400  miles  away.  (See  Chapter  XIV.) 
There  are  reasons  for  believing  that  the  well-rounded  quartz  peb- 
bles of  the  Sharon  (Upper  Pottsville)  conglomerate  of  Ohio  and 
western  Pennsylvania  and  the  Olean  of  southern  New  York  have 
traveled  over  400  miles  from  their  original  source. 


EROSION    BY    RIVERS  253 

Rounding  of  Sand  Grains.  (Goodchild-27;  Mackie-47: 500.) 
The  chief  factors  concerned  in  the  rounding  of  sand  grains  by 
attrition  are : 

1.  The  size  of  the  particles. 

2.  Their  specific  gravity. 

3.  Their  hardness. 

4.  The  distance  over  which  they  had  traveled. 

5.  The  agent  by  which  they  had  been  transported. 

The  amount  of  rounding  of  a  particle  varies  directly  as  i,  2  and 
4,  and  indirectly  as  3.  Particles  transported  by  wind  are  more 
rounded  than  those  transported  an  equal  distance  by  water. 

A  cube,  with  the  side  measuring  I  inch,  presents  an  area  of  6 
square  inches,  while  a  sphere  of  one  inch  diameter  presents  a  sur- 
face of  only  3.14159  +  square  inches.  Now,  since  the  surface  area 
of  bodies  of  similar  figure,  but  different  in  size,  varies  as  the  square 
of  their  linear  dimensions,  a  doubling  of  the  linear  dimensions  of 
the  cube  would  increase  its  surface  area  to  24  square  inches.  If 
the  diameter  of  the  sphere  is  doubled,  the  surface  area  becomes 
12.566  +  square  inches.  On  the  other  hand,  reducing  the  cube 
from  a  linear  dimension  of  one  inch  to  one  of  half  an  inch  by  the 
side,  the  area  of  its  surface  is  reduced  from  6  square  inches  to  one 
and  one-half  square  inches.  In  like  manner  the  reduction  of  the 
diameter  of  the  sphere  to  one-half  inch  reduces  its  surface  area  to 
0.78539  square  inch. 

The  volumes  of  bodies  of  similar  figure,  however,  increase  as 
the  cube  of  their  respective  linear  dimensions,  or  decrease  as  the 
cube  root  of  those  dimensions.  Thus,  while  the  sphere  reduced 
from  one  inch  to  one-half  inch  diameter  changes  in  area  from 
3.1416  square  inches  to  0.78539  square  inch,  its  volume  will  change 
from  0.5236  cubic  inch  to  0.06545  cubic  inch.  That  is,  while 
the  superficial  area  is  decreased  to  one-fourth,  the  volume  is  de- 
creased to  one-eighth  its  original  amount.  Since  the  weight  of  an 
object  depends  on  its  volume,  it  follows  that  the  decrease  in  weight 
is  greater  than  the  decrease  in  surficial  area,  and,  since  adhesion 
(surface  tension  or  the  adhesion  between  the  object  and  the  medium 
in  which  it  is  immersed)  is  dependent  on  the  surficial  area  of  the 
object,  it  follows  that  in  the  wearing  down  of  a  sand  grain  the  de- 
crease in  weight  is  always  greater  than  the  decrease  of  surface  ten- 
sion. Thus,  with  the  progressive  wearing  down  of  a  sand  grain,  a 
stage  will  be  reached  when  the  surface  tension  will  balance  the 
gravitational  force,  and  further  wearing  of  the  grain  becomes  im- 
possible in  that  medium.  So,  with  a  given  medium  and  strength 


254  PRINCIPLES    OF    STRATIGRAPHY 

of  current,  grains  below  a  certain  size  will  not  be  rounded.  Since 
the  buoyancy  or  surface  tension  (adhesion  between  water  and  sand) 
of  salt  water  is  greater  than  that  of  fresh  water,  the  smallest 
rounded  grain  of  the  former  should  be  somewhat  larger  than  that 
of  the  latter,  other  things  being  equal.  Again,  since  the  surface 
tension  of  air  is  very  much  less  than  that  of  water,  very  much 
smaller  grains  will  be  rounded  by  wind  than  by  water.  In  other 
words,  wind-blown  sands  of  even  extremely  small  size  will  come  in 
contact  with  each  other  and  with  stationary  objects,  and  so  become 
worn  and  rounded.  The  fact  that  all  grains  below  a  certain  size 
show  angularity,  and  that  the  transition  from  rounded  to  angular 
grains  is  not  a  gentle  but  an  abrupt  one,  is  readily  noticeable  in 
both  modern  sands  and  ancient  sandstones.  Moreover,  grains  of 
materials  of  different  specific  gravity,  but  of  the  same  size,  will 
show  a  greater  rounding  with  higher  specific  gravity.  (Mackie- 
47:  298.}  Ziegler  (75)  noted  from  experiments  that  quartz  par- 
ticles less  than  i  mm.  in  diameter  showed  repulsion  due  to  the 
viscosity  of  the  liquid.  He  concludes  that  it  is  impossible  that 
grains  less  than  0.75  mm.  in  diameter  could  be  well  rounded  under 
water,  but  if  rounded  must  be  wind-worn. 

Since  mineral  particles  have  less  wreight  in  water  than  in  air,  it 
follows  that  particles  of  the  same  size  and  material  will  suffer  more 
erosion  in  air  on  this  account  also. 

Hardness  and  the  distance  over  which  the  material  is  trans- 
ported are  likewise  factors  in  the  rounding  of  grains,  the  amount 
of  rounding  varying  indirectly  as  the  former  and  directly  as  the 
latter.  Mackie  has  reduced  the  variability  of  the  rounding  (R)  of 
particles  to  the  following  formula : 

size  X  the  specific  gravity  X  distance 


Roc 


hardness 


Distance  (d)  traveled  may  be  expressed  by  the  number  of  times 
the  body  turns  on  its  axis.     This  number  of  times  for  a  cube  with 

side  measuring  x  will  be—  -  and  since  the  weight  of  such  a  cube  is 

4X 

expressed  by  x3  X  sp.  gr.  (i.  e.  the  size  or  volume  x  multiplied  by  its 
sp.  gr.)  we  have 

x3  spg.  „ 

_.  4X  x2spg.d  „     x2spg.d 

Roc 2 —  =  -          _or  generally  - 

h  4h  mh 

where  m  varies  with  the  outline  of  the  figure,  being  4  in  a  cube,  and 
3.1416  in  a  sphere,  with  proportional  values  for  other  forms.     Since 


ROUNDING    OF    SAND    GRAINS  255 

sand  grains  weigh  less  in  water  than  in  air,  a  corresponding  correction 
must  be  made  (47),  the  formula  being  according  to  Mackie  for  water: 

Roc  *'(*Pfr-')d 

mh 

On  making  a  comparison  (Mackie— 47:510)  of  the  relative  efficiency 
of  wind  and  water  as  rounding  agents,  we  have  from  the  formulas 

for  wind  Roc  x'  Spg<d  and  for  water  Roc  x"  (sPg--D  d 
mh  mh 

the  following  relationships : 

wind   agency          spg.       .  .  ,    .  2.6$ 

s i   =  -       _  which  for  quartz  = 

water  agency        spg.— 1  i .  65 

or  wind  =  1.6  times  water,  but  since  average  wind  velocities  are 
always  greater  than  average  water  velocities,  it  follows  that  the  result 
attained  by  wind  will  be  much  greater  than  that  given.  Mackie 
has  calculated  that  with  a  wind  velocity  of  8  miles  an  hour,  and  a 
water  velocity  of  2  miles  an  hour,  the  ability  of  the  wind  to  round 
a  given  quartz  particle  (sp.  2.65)  is  nearly  29  times  as  great  as  that 
of  water.  Mackie  concludes  that  "under  the  conditions  stated, 
particles  less  than  one-fifth  the  diameter  of  those  rounded  by  water 
will  be  rounded  to  an  equal  degree  by  wind"  (47:510).  Mackie  has 
calculated  the  values  of  the  coefficient  of  roundability  or  psephicity 
for  various  minerals  a  few  of  which  are  given  (Mackie~4  7:502). 

Table  showing  coefficient  of  psephicity  of  minerals  in  air  and  water. 
In  air  In  water 

Quartz  )— '•  =  0.38  -  =  0.23 

n  n 

=  0.29 
=  0.30 
=  0.39 
=  0.39 
=  o-45 
=  0.70 
=  0.76 
=  0.86 

Examination  of  a  sample  of  sand  from  the  River  Spey  at 
Craigellachie,  Scotland,  at  a  point  where  it  could  not  be  contami- 
nated by  admixture  of  particles  derived  from  the  sandstones 
showed,  according  to  Mackie  (47:506),  no  appreciable  rounding  of 
the  quartz  grains,  "though  they  certainly  did  not  all  of  them  pre- 
sent the  marked  angularity  of  the  quartz  grains  in  most  boulder 
clays."  The  feldspars  also  were  angular,  though  some  of  them,  be- 


Orthoclase        ' 

=  0.40 

Tourmaline      ' 

=  0.43 

Garnet 

=  0.53 

Hornblende     ' 

=  0.57 

Zircon 

=  0.59 

Biotite 

=  1.05 

Chlorite 

=    1.20 

Muscovite        ' 

=    1.30 

PRINCIPLES    OF    STRATIGRAPHY 


ing  kaolinized  in  a  high  degree,  exhibited  considerable  blunting  of 
their  angles.  The  chlorite  flakes  were  generally  rounded,  though 
with  frayed,  irregular  edges,  the  muscovite  and  biotite  were  some- 
what rounded  on  their  prominent  angles,  but  generally  of  irregular 
outline.  The  hornblende  and  garnets  were  angular,  as  was  also  the 
zircon,  though  showing  occasionally  ground-glass  surfaces.  Mackie 
concludes  that  these  sands  had  traveled  not  less  than  70  miles. 

A  specimen  of  sand  from  the  seashore,  midway  between  Lossie- 
mouth  and  Covesea  on  the  south  coast  of  the  Moray  Firth,  gave 
Mackie  the  following  results : 

Table  showing  rounding  of  sands  of  Moray  Firth. 


Mineral  Particles 

No. 
ob- 
served 

Rounded 

Sub- 
angu- 
lar 

Angular 

Average 
round- 
ing* 

Hornblende 

10 

c 

c 

I    c 

Kyanite                  

2 

I 

I 

I    c 

Biotite  

16 

7 

7 

6 

1.8 

Opaque  iron  ore 

-I 

I 

I 

i 

2    O 

Chlorite            

4 

I 

2 

i 

2    O 

Muscovite  

2O 

7 

9 

4 

2  .2 

Quartz** 

18      ' 

6 

i^ 

10 

I    7 

Feldspar**  

26 

8 

13 

5 

2.1 

Average  rounding  represented  by 


A  sample  from  the  sand  dunes  of  Culbin,  in  the  same  region, 
gave  the  following: 

Table  showing  rounding  of  sands  of  Culbin  dunes. 


Mineral  Particles 

No. 
ob- 
served 

Rounded 

Sub- 
angu- 
lar 

Angular 

Average 
round- 
ing 

Staurolite 

2 

2 

I    O 

Kyanite                      .              .... 

2 

i 

i 

I     C 

Garnet  

45 

Ii 

14 

18 

I  .9 

Hornblende                              .    . 

K 

7 

i 

i 

2    4 

Tourmaline  

IT. 

8 

4 

2  .  S 

Opaque  iron  ore 

IO 

7 

T. 

2    7 

Sphene         

q 

8 

r 

2    8 

Zircon 

7 

T.     O 

Feldspar                    

16 

IO 

e: 

I 

2    6 

Quartz  

16 

6 

9 

i 

2.3 

Average  rounding  represented  by 2.27 

*  Obtained  by  counting  3  for  a  round,  2  for  a  subangular,  and  i  for  an  angular 
particle  and  dividing  the  sum  by  the  number  of  particles  in  each  group. 

**  A  proportion  of  these  evidently  derived  from  the  sandstones  of  the  coast. 


MOVEMENTS    OF   GROUND    WATER  257 

Comparing  this  with  the  sea  sands,  it  is  at  once  apparent  that 
the  rounding  is  much  more  pronounced,  though  the  sands  were  car- 
ried only  a  few  miles.  These  sands  have  a  common  origin  and  are 
of  about  the  same  degree  of  fineness. 


MOVEMENT  OF  UNDERGROUND  WATERS. 

The  movement  of  underground  water  depends  on  the  nature  of 
the  material  through  which  it  flows  and  the  space  available  for  this 
flow.  Underground  channels  or  tunnels  may  allow  the  water  to 
flow  as  readily  as  it  does  upon  the  surface.  If  the  channel  is  filled 
completely,  the  water  is  under  hydrostatic  pressure,  and  it  may  be 
forced  up  a  rising  slope.  Such  a  stream  may  act  as  an  aspirator, 
drawing  water  or  air  through  fissures  past  which  it  flows,  and  caus- 
ing currents  to  flow  toward  it  by  suction,  and  even  causing  water 
to  rise  from  a  lower  to  a  higher  level.  This  has  been  regarded  by 
Penck  and  others  as  the  cause  of  the  currents  flowing  from  the 
ocean  into  the  land  at  the  island  of  Cephalonia,  Greece,  the  water 
replacing  that  which  is  drawn  up  by  suction  of  a  strong  under- 
ground stream,  which  completely  fills  its  channel.  For  these  cur- 
rents, which  formerly  drove  the  "sea  mills  of  Cephalonia,"  Crosby 
and  Crosby  (14)  and  Fuller  (25)  have  offered  other  explanations. 
Underground  streams  of  this  kind  are  further  illustrated  by  some 
subglacial  streams,  which,  being  confined  in  a  tunnel-like  tube,  often 
flow  uphill,  as  shown  by  the  eskers  which  mark  their  former  course. 
(Grabau-28.) 

Water  flowing  through  a  porous  soil  has  of  course  a  vastly  lower 
rate  of  motion  under  the  same  gravitational  influence  on  account 
of  friction.  The  rate  of  movement  of  water  through  such  a  porous 
medium  depends  on  the  following  factors : 

1.  Size  of  pores  in  the  water-bearing  medium. 

2.  Porosity  of  material,  i.  e.,  the  relative  abundance  of  pores. 

3.  Pressure  gradient,  or  change  in  pressure  or  head,  per  unit  of 
length,  measured  in  the  direction  of  the  motion. 

4.  Temperature  of  water. 

In  general  the  rate  of  flow  varies  with  the  variation  in  all  of 
these  factors,  the  law  governing  this  rate  of  flow  or  velocity  (v) 

being  expressed  by  the  formula  of  Darcy,  v  =  k  ^,  where  p  is  the 

difference  in  pressure  at  the  ends  of  the  column  of  soil  (measured 
by  height  of  water  column),  //  the  length  of  the  column  and  k  a 
constant  depending  upon  the  determinable  characters  of  the  soil, 


258  PRINCIPLES    OF    STRATIGRAPHY 

especially  the  size  of  the  grains.  The  following  formula  of  Allen 
Hazen  (32:5^7)  takes  more  factors  into  consideration  and  serves 

for- experimental  purposes,  v=c  d2  -  (0.70-1-0.03^),  v  being  the 

velocity  of  the  water  in  meters  per  day  in  a  solid  column  of  the  same 
area  as  that  of  the  sand,  c  a  constant  factor  found  empirically  to 
approximate  1,000;  d  is  the  "effective  size"*  of  sand  grains  in 
mm.,  which  is  such  that  10  per  cent,  of  the  material  is  of  smaller 
grains  and  90  per  cent,  of  larger  grains  than  the  size  given ;  h  is 
the  loss  of  head;  /  is  the  thickness  of  sand  through  which  water 
passes,  and  t  is  the  temperature  on  the  centigrade  scale.  The  loss 
of  head  is  measured  from  points  just  inside  the  ends  of  the  column 
of  sand  or  soil.  (See,  further,  King-4i:5p;  and  Slichter-64  '.322, 
329;  65:79,  22.) 

The  quantity  of  water  transmitted  by  a  column  of  sand  depends 
upon  the  length  of  the  column  and  the  head  of  water,  and  further- 
more varies  with  the  effective  size  of  the  soil  grain,  the  tempera- 
ture of  the  water  and  with  the  porosity  of  the  soil.  The  flow  varies 
as  the  square  of  the  size  "of  the  soil  grain,  and  doubling  the  size  of 
the  grain  will  quadruple  the  flow  of  water.  Thus  the  flow  through  a 
soil  whose  effective  size  of  grain  is  I  mm.  is  10,000  times  the  flow 
through  a  soil  whose  effective  size  of  grain  is  o.oi  mm.  The  flow 
at  70°  F.  is  about  double  that  at  32°  F. 

The  Underflow.  This  is  the  moving  sheet  of  water  beneath  the 
bed  and  banks  of  a  stream  through  the  porous  medium.  This  may 
be  so  concentrated  as  to  produce  a  subterranean  stream,  scores  of 
feet  in  depth  and  miles  in  breadth.  It  naturally  follows  a  line  of 
depression  in  the  surface  of  the  sustaining  impervious  layer — the 
Thalweg — and  the  rapidity  of  flow  will  depend  in  a  very  large 
measure  upon  the  texture  of  the  material  forming  the  river  bed. 
Where  this  is  fine  the  water  will  be  stored,  but  a  considerable  un- 
derflow is  impossible.  Where  the  material  is  coarse  sand  and 
gravel,  however,  as  near  the  mountains,  the  water  will  readily  flow 
through  it.  In  arid  regions,  the  lower  reaches  of  the  surface 
streams  often  disappear  altogether,  by  sinking  into  the  ground. 
They  are  then  continued  by  the  underflow,  and  only  occasionally 
after  a  heavy  storm  are  the  "dry  washes"  filled  again  by  a  rushing 
surface  torrent.  In  general,  the  underflow  follows  the  trend  indi- 
cated by  the  surface  branches,  which  may  extend  as  dry  washes 

*  Determined  by  experiment  to  be  the  mean  diameter  of  the  grains,  or  the 
one  which,  if  all  the  grains  corresponded  to  that  size,  would  give  the  soil  the 
porosity  it  actually  has. 


MOVEMENTS  OF  GROUND  WATER 


259 


across  the  alluvial  fan  built  up  by  the  dropping  of  the  stream-trans- 
ported material. 

Rate  of  Floiv  of  Underground  Water.  The  following  table 
adapted  from  Slichter  (65 :  ^7)  shows  the  theoretical  rate  of  flow 
and  amount  of  transmission  determined  by  experiment  for  various 
kinds  of  soil,  with  a  porosity  of  32  per  cent.,  and  at  the  temperature 
of  50°  F.  and  with  pressure  gradients  of  i  :  i,  and  100  feet  to  I 
mile.* 


Table  showing  permeability  of  various  soils. 


Diam- 

Velocities 
pery 

in  miles 
-ear 

Maximum 

eter  of 
grains 

Pressure 
gradient 
1:1 

Pressure 
gradient  100 
ft.  to  i  mile 

cubic  feet 
per  min. 

Silt  

f  O.OI 

0.0113 

o  .  00026 

o  .  000036 

Very  fine  sand   ... 

10.04 

f  0.05 

0.1807 
0.2823 

o  .  00408 
o  .  00638 

0.000577 
0.000901 

.  ,,:..v^~v;:v-'v/.  : 
Fine  sand  

10.09 
f  o.  10 

0.9147 
I  .  1290 

o  .  02066 

0.02551 

o  .  002920 
o  .  003605 

Medium  sand  .  .  . 

\  O.2O 

(0.25 

4.5180 
7.0580 

O.I02IO 
0.15940 

0.014420 
0.022530 

Coarse  sand  .    . 

10.45 
(0.50 

22.8700 
28.2300 

0.51650 
0.63770 

o  .  073000 
0.090120 

Very  coarse  sand  .  . 

10.95 

I    OO 

101  .9000 

112   9OOO 

2  .  30200 
2    SSI  OO 

0.325300 
o  360500 

or 
Very  fine  gravel 

2    OO 

4  SI    8OOO 

I  O   21  OOO 

I    442000 

Fine  gravel  .  .    . 

/  3-oo 

IOI6.OOOO 

22  .  96000 

3  .  244000 

I5»oo 

2823.OOOO 

63  .  77000 

9.012000 

Note. — The  last  figures  (o)  in  the  higher  numbers  are  approximate. 

Direct   observations   on   the   underflow   of   water   to  the  Loup 
River,  Nebraska,  have  indicated  a  rate  of  one-third  of  a  mile  per 

*  The  number  in  italics  gives  the  value  just  before  the  upper  limit  of  each 
grade  is  reached.     Compare  table,  p.  287,  Chapter  VI.   . 


260 


PRINCIPLES    OF    STRATIGRAPHY 


day,  a  rate  so  high  (120  -(-  miles  per  year,  compare  column  4  of  ta- 
ble) that  the  observations  are  probably  erroneous.  Observations  on 
seepage  of  water  from  canals,  etc.  (Slichter-65 142),  have  given 
rates  of  0.2074,  0.2500,  0.3000,  and  1.0369  miles  per  year,  values 
closely  in  accord  with  those  received  by  experiment. 

Pervious  and  Impervious  Strata.  Strata  which,  from  their  por- 
osity, permit  a  flow  of  water  through  them  are  called  pervious, 
while  those  not  so  constituted  are  impervious.  Quartz  sandstones, 
especially  those  of  uniform  grain,  are  usually  the  most  pervious, 
and  shales  the  most  impervious  of  stratified  rocks.  Limestones  are 
generally  impervious,  owing  to  the  filling  of  their  pores  by  secondary 
deposit,  a  change  much  less  characteristic  of  quartz  sandstones, 
though  also  found  here.  Some  limestones  are,  however,  porous 
enough  to  be  good  water  bearers,  such  as  chalk  and  partly  consoli- 


FIG.  37.  Cross-section  through  South  Dakota  artesian  basin.  Elevations 
above  sea-level.  Vertical  scale  much  exaggerated  over  the  hori- 
zontal. (After  Slichter.) 

dated  shelly  limestone  (coquina,  etc.)  ;  limestones  rendered  porous 
in  the  belt  of  weathering  by  solution ;  and  limestones  rendered 
porous  by  dolomitization  through  replacement  of  some  of  their  cal- 
cite  by  magnesium  carbonate. 

The  Deeper  Zones  of  Flow.  Pervious  strata  confined  between 
impervious  ones  may,  from  their  position,  carry  surface  waters  to 
great  depths  and  constitute  a  deeper  zone  of  flow.  In  thus  being 
confined  between  impervious  layers  it  differs  from  the  surface  zone, 
which  is  bounded  below  by  an  impervious  layer,  but  above  is  not 
confined,  but  formed  merely  by  the  upper  limit  of  ground  water. 
Whereas  the  subsurface  flow  follows  the  slope  of  the  region,  that  of 
the  deeper  zone  depends  on  geologic  structure.  The  deeper  zone 
also  draws  its  supply  from  great  distances  and  is  independent  of  the 
local  drainage  level,  while  that  of  the  subsurface  zone  is  local. 
An  example  of  such  a  pervious  bed  is  the  Dakota  sandstone  of  the 
Front  Range  and  the  Great  Plains,  which  is  capped  by  the  impervi- 


SPRINGS'  261 

ous  Benton  clay  of  the  Cretacic.  The  water  enters  along  the  outcrop 
of  this  formation  more  than  3,000  feet  above  sea-level.  Over  parts 
of  the  Great  Plains  the  Dakota  has  descended  near  to  or  even  below 
sea-level,  while  perhaps  2,000  feet  of  other  strata  are  piled  above 
it.  When  tapped  by  artesian  wells  the  water  will  rise  to  within  2,400 
to  1,500  feet  above  sea-level,  according  to  the  distance  from  the 
mountains.  As  the  surface  over  most  of  the  country  is  lower  than 
this,  the  result  is  the  formation  of  actively  flowing  artesian  wells 
(see  Fig.  37). 

Springs. 

Springs  are  the  escape  of  ground  water  at  the  surface  of  the 
lithosphere.  By  surface  of  the  lithosphere  is  here  meant  any  point 
where  the  lithosphere  is  in  contact  with  a  mass  of  water  or  air; 
thus  we  have  sublacustrine  springs  and  springs  formed  in  subterra- 
nean channels,  in  wells,  etc. 

Springs  commonly  issue  where  the  contact  between  a  pervious 
and  an  impervious  lower  layer  is  exposed  in  section.  In  the  Helder- 
berg  Mountains  the  spring  line  is  at  the  base  of  Siluric  or  Devonic 
limestones,  where  they  rest  upon  impervious  clays  (Brayman),  or 
unconformably  upon  the  Hudson  River  beds.  Along  the  line  of 
contact  between  the  Devonic  Onondaga  limestone,  a  porous  rock, 
and  the  Siluric  Monroe  limestone,  a  compact,  impervious  one  in 
western  New  York,  Canada,  and  Michigan,  occurs  a  line  of  copious 
springs.  The  contact  line  here  is  a  disconformity,  and  the  water 
sometimes  gushes  out  in  great  volume.  The  contact  between  the 
Lockport  dolomite  and  Rochester  shales  along  Niagara  gorge  and 
the  whole  front  of  the  Niagara  escarpment  constitutes  another  such 
spring  line,  and  so  does  the  upper  surface  of  the  Black  Shale 
throughout  the  southern  Appalachians.  Where  the  section  is  made 
only  into  the  pervious  layer,  as  in  a  well,  a  general  seeping  or 
"welling"  of  the  ground  water  takes  place ;  where  the  surface  is  de- 
pressed to  the  ground-water  level,  or  below  it,  a  similar  "welling" 
of  the  ground  water  takes  place.  Swamps  are  formed  in  this  way, 
which  may  be  regarded  as  natural  wells  on  a  large  scale. 

WATER  IN  THE  SOLID  FORM. 

Snow  and  ice  may,  on  the  one  hand,  be  considered  as  water  in 
the  solid  state,  and  so  referred  to  the  hydrosphere ;  or,  on  the  other 
hand,  as  a  rock,  solid  only  at  low  temperatures.  In  the  latter  case 
it  belongs  either  to  the  igneous  or  pyrogenic  rocks  when  due  to 


262  PRINCIPLES    OF    STRATIGRAPHY 

solidification  of  water,  or  to  the  atmogenic  when  precipitated  as  snow 
and  snow  ice.  Ice  is  thus  a  substance  intimately  uniting  the  hydro- 
sphere and  lithosphere,  just  as  water  in  the  form  of  vapor  unites 
tHe  hydrosphere  and  atmosphere.  The  freezing  of  water  has  been 
dealt  with  to  some  extent  under  the  heading  of  temperature  influence 
on  the  hydrosphere.  As  a  rock  it  will  be  dealt  with  in  Chapter  VI 
and  its  larger  structural  features  will  be  taken  up  in  Chapter  VIII. 
Glacial  deposits  naturally  fall  under  the  heading  of  autoclastic  rocks 
and  are  discussed  in  Chapter  XII,  while  deformation  due  to  glacial 
motion  is  considered  in  Chapter  XX.  Finally,  the  results  of  glacial 
sculpture  are  treated  under  the  head  of  glyptogenesis,  or  the  land 
forms  produced  by  the  sculpturing  agents.  In  the  present  chapter  a 
brief  preliminary  summary  of  the  movement  of  water  in  the  solid 
form  and  its  geological  effects  will  be  given. 

Kinds  of  Movement  of  Solid  Water.  Water  in  the  solid  state 
may  become  translocated  either  ( I )  passively  by  transportation,  or, 
(2)  actively  by  movements  due  to  its  own  gravitative  and  internal 
readjustments.  Transportation  may  be  either  by  wind,  as  in  the 
case  of  snowflakes  and  ice  crystals,  or  by  water,  as  icefloes  or  ice- 
bergs. Wind-transported  snowflakes  and  ice  crystals  may  accom- 
plish a  certain  amount  of  geological  work  by  corrasion,  as  noted 
in  Chapter  II,  and  they  may  be  heaped  up  in  dunes  or  deposited  in 
strata,  which  may  be  temporary,  or  may  endure  for  a  long  time,  with 
gradual  metamorphosis  into  crystalline  ice.  One  result  of  wind- 
transported  snow  is  a  special  distribution,  and  consequently  the 
placing  of  sources  of  water  supply  in  positions  which  might  prob- 
ably not  be  accessible  to  them  in  any  other  way.  Water-transported 
ice  blocks  often  act  as  powerful  agents  in  erosion  and  destruction, 
and  they  may  be  responsible  for  groovings  and  markings  on  rock 
surfaces  not  otherwise  explainable.  Extensive  deposits  of  trans- 
ported material  frozen  into  the  ice  block  or  resting  on  its  back 
are  also  sometimes  formed,  as  in  the  case  of  the  Grand  Banks  of 
Newfoundland,  where  the  debris  brought  by  the  icebergs  from  the 
north  is  dropped  upon  their  melting  and  so  embedded  in  and  made 
part  of  contemporaneous  marine  sediments,  boulder  conglomerates 
here  accumulating  beneath  the  zone  of  wave  activity.  The  anomal- 
ous occurrence  of  erratics  or  strayed  rock  masses  in  marine  forma- 
tions is  also  accounted  for  by  floating  icebergs.  Such  ice-rafted 
erratics  have  been  found  in  the  Caney  shale  of  Oklahoma  (Car- 
bonic) (Woodworth-74). 

Ice  masses,  moving  over  the  surface  of  the  land  constitute  the 
glaciers,  which  may  be  either  glacial  streams  or  glacial  sheets. 
Their  motion  is  due  to  a  variety  of  causes,  among  which  partial 


MOVEMENT    OF    GLACIERS  263 

melting  and  refreezing  of  the  ice  crystals  constituting  the  mass  are 
at  least  important  ones.  (See  the  discussion  by  Chamberlin  and 
Salisbury-9:j7j-j<?j.)  Observations  on  glaciers  flowing  in  valleys 
have  shown  that  motion  is  faster  at  the  center  than  at  the  sides, 
and  near  the  top  than  at  the  bottom.  A  current  analogous  to  that 
found  in  water  streams  is  thus  produced,  which  also  meanders  more 
strongly  than  does  the  ice  stream  as  a  whole.  In  broad  glaciers, 
formed  by  the  union  of  a  number  of  branches,  several  lines  of  rapid 
motion  may  exist,  with  lines  of  weaker  movement  between.  Up- 
ward currents  within  the  ice  also  exist,  which  bring  debris  from  the 
bottom  to  the  surface  at  the  sides.  In  this  manner  lateral  moraines 
of  rock  and  soil  are  formed  on  the  surface  of  the  valley  glacier. 
This  morainal  material,  augmented  by  that  falling  from  the  cliffs 
between  which  the  glacier  flows,  is  left  at  the  foot  of  the  ice  with 
much  that  is  carried  along  the  bottom,  there  to  constitute  the  termi- 
nal moraine. 

Rate  of  Movement.  Movement  of  glaciers  is,  as  a  rule,  greater 
in  summer  than  in  winter.  .  Some  of  the  glaciers  of  Greenland 
move  50,  60,  or  even  more  feet  per  day  in  summer  time,  while  a 
case  of  100  feet  per  day  has  been  noted  (Chamberlin  &  Salisbury-9). 
In  this  case  the  movement  in  April  was  only  34  feet.  Such  rapid 
movements  occur  only  where  the  ice  of  large  inland  areas  crowds 
down  into  comparatively  narrow- fjords.  In  Switzerland  the  rate 
of  motion  ranges  from  I  or  2  inches  to  four  feet  or  more  per  day, 
while  the  Muir  glacier  of  Alaska  has  been  found  to  move  7  feet  or 
more  per  day  (Reid).  The  causes  affecting  rate  of  movement 
of  the  ice  are:  I,  thickness  and  volume  of  the  ice  sheet;  2,  slope 
of  the  land  surface ;  3,  slope  or  gradient  of  upper  surface  of  the  ice ; 
4,  character  and  relief  of  the  rock  bed ;  5,  temperature ;  6,  quantity 
of  water  falling  on  or  reaching  the  glacier. 

Wasting  of  the  Glaciers.  Glaciers  waste  away  by  melting  at 
their  surface,  front  and  sides,  and  to  some  extent  at  the  bottom, 
where  heat  is  generated  through  friction  and  compression  as  well  as 
by  the  rise  of  the  earth's  heat  through  conduction  under  cover  of  a 
thick  ice  sheet.  Glaciers  also  waste  away  by  evaporation,  the  ice 
changing  directly  to  the  form  of  vapor.  The  wasting  of  glaciers  on 
the  surface  is  generally  spoken  of  as  ablation. 

Erosive  Work  of  Ice.  The  erosive  work  of  ice  may  be  twofold : 
denudation,  or  the  removal  of  material  formed  through  decomposi- 
tion and  disintegration  of  the  rock  surface,  and  the  active  removal 
of  fresh  rock  material  by  scraping,  plucking,  etc.,  or  glacial  corra- 
sion.  The  general  process  of  erosion  by  ice  has  been  termed  execra- 
tion by  Walther  (from  arare,  to  flow).  This  word  might  be  re- 


264  PRINCIPLES    OF    STRATIGRAPHY 

stricted  to  glacial  denudation,  i.  e.,  the  removal  and  transport  of 
weathered  material.  (See  ante,  Chapter  I.) 

The  first  step  in  glacial  erosion  is  generally  ablation,  or  the 
taking  up  of  the  weathered  material  on  the  surface  of  the  land. 
When  ice  accumulates  through  a  long  period  of  gradual  refrigera- 
tion, punctuated  by  intervals  of  partial  melting,  the  waterlogged 
soil,  the  product  of  pre-glacial  weathering,  is  incorporated  as  an  in- 
tegral part  into  the  base  of  the  glacier  or  ice  sheet  and  carried 
away  with  it  when  movement  begins.  Through  shearing  and 
through  formation  of  ascending  ice  currents  this  material  may  be 
carried  upward,  and,  from  being  subglacial,  becomes  successively 
englacial  and  then  super  glacial.  The  part  remaining  in  the  bottom 
of  the  ice  is  used  as  a  tool  for  the  corrasion  of  the  rock  surface, 
which  soon  is  worn  down  to  the  undecomposed  layers  and  becomes 
smoothed,  polished,  and  marked  by  parallel  striae,  the  direction  of 
which  indicate  the  direction  of  ice  movement.  The  material  held 
in  the  base  of  the  ice  sheet  (the  product  of  denudation  plus  material 
which  may  have  descended  from  the  surface)  is  likewise  polished 
and  striated,  this  in  the  flatter  fragments  of  rock  usually  being  con- 
fined to  two  faces. 

The  heat  generated  by  friction  over  the  rock  surfaces,  aug- 
mented by  the  rising  heat  of  the  earth,  owing  to  the  ice  blanketing, 
may  result  in  melting  the  basal  portion  of  the  ice  sheet,  or  glacier, 
whereupon  a  layer  of  basally  transported  material  or  till  is  deposited 
on  the  previously  eroded  surface,  protecting  it  from  further  erosion. 
If  the  direction  of  motion  of  the  ice  is  subsequently  changed,  it  may 
not  again  remove  this  material,  but  leave  it  to  protect  the  striae 
made  during  the  early  period  of  movement  (Crosby).  That  ice  is 
able  to  move  over  unconsolidated  material  without  actively  eroding  it 
is  shown  by  many  observations  (Fairchild-22).  Glacial  grooves  of 
exceptional  size  are  sometimes  formed,  the  best  known  being  those 
of  Kelley's  Island  in  Lake  Erie.  The  most  effective  work  of  cor- 
rasion by  glaciers  seems  to  occur  somewhere  above  the  lower  end  of 
the  glacier,  so  that  deepening  of  the  valley  above  its  mouth  results. 
Both  glaciers  and  ice  sheets  effect  little  or  no  erosion  at  their  front 
or  margins.  At  the  head  of  the  glacier,  i.  e.,  at  the  Bergschrund, 
plucking  or  pulling  out  of  loose  blocks  occurs,  resulting  in  the 
formation  of  cirques.  Plucking  also  occurs  on  the  lee  side  of  pro- 
jecting rock  masses  which  on  their  stoss  side  are  eroded  by  corra- 
sion, the  result  being  a  rock  mass  with  smooth  upper  surface,  grad- 
ually rising  in  the  direction  of  ice  movement,  and  terminating  in  a 
rough  cliff  downstream.  These  structures  are  known  as  roches  mou- 


TRANSPORTATION    BY    ICE  265 

tonnees.     Combined  erosion  by  glaciers  and  subglacial  streams  is 
called  fluvioglacial  erosion. 

Transportation  by  Ice.  As  already  noted,  much  material  may 
be  transported  by  floating  icebergs  or  floes  and  so  become  incor- 
porated in  marine  sediments.  Land  ice  transports  rock  debris  on  its 
surface  as  superglacial  drift,  within  its  mass  as  englacial  drift,  and 
at  its  bottom  as  subglacial  drift.  In  form  the  superglacial  material 
generally  constitutes  lateral  and  median  moraines.  (See  posted 
Chapter  XII.)  The  englacial  is  likely  to  be  scattered,  and  the  sub- 
glacial  is  often  in  the  form  of  a  more  or  less  continuous  sheet. 
Changes  from  one  position  to  another  are  constantly  effected,  the 
subglacial  rising  by  shearing  and  upward  currents  to  become  en- 
glacial  or  superglacial,  the  englacial  becoming  subglacial  by  basal 
melting  of  the  ice  or  superglacial  by  surface  ablation,  and  the  super- 
glacial  material  becoming  englacial  or  subglacial  through  the  action 
of  descending  currents  or  by  falling  through  fissures  or  crevasses. 
By  melting  on  reaching  the  sea  this  material  may  be  incorporated 
with  marine  sediments,  or  by  advancing  over  forests  and  swamps  it 
may  be  deposited  on  organic  accumulations  (future  coal  beds),  and 
finally,  by  taking  up  material  from  the  bottom  of  the  shallow  sea 
over  which  it  passes,  the  ice  may  incorporate  remains  of  marine 
organisms  in  continental  sediments,  as  in  the  case  of  the  fossils  of 
Tertiary  or  younger  age  included  in  the  drumlins  of  Boston  Harbor 
and  the  moraine  of  Cape  Cod.  (Crosby  and  Ballard-i3,  Crosby-n.) 

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C.  THE  LITHOSPHERE 

CHAPTER  VI. 
CLASSIFICATION   OF   THE   ROCKS   OF   THE   EARTH'S   CRUST. 

As  has  been  outlined  in  the  introductory  chapter,  the  stratig- 
rapher  deals  with  the  genesis  of  the  rocks  of  the  earth's  crust  and 
considers  their  structure  and  composition,  or  the  petrographical 
characters  of  rocks,  chiefly  from  the  point  of  view  of  their  bearing 
on  lithogenesis.  The  dynamic  forces  active  in  the  production  of 
rocks  are  likewise  considered  by  him  in  their  bearing  upon  this 
subject.  Naturally,  those  rocks  which  bear  the  most  satisfactory 
evidence  of  chronological  succession,  i.  e.,  the  stratified  rocks,  re- 
ceive most  attention,  for  it  is  the  business  of  the  stratigrapher  to 
establish  the  events  in  the  history  of  the  earth  in  the  order  of  their 
occurrence. 

SUBDIVISION  OF  ROCKS. 

Numerous  subdivisions  of  rocks  have  been  proposed,  most  of 
them  being  largely  or  entirely  artificial  in  character.  The  most 
familiar  divisions  are:  igneous,  aqueous,  ceolian,  and  organic.  The 
last  three  are  commonly  classed  together  as  stratified  or  sedimentary, 
as  opposed  to  the  unstratified  or  igneous  rocks.  Metamorphic  rocks 
are  generally  grouped  by  themselves,  though  in  the  beginning  they 
were  grouped  with  the  stratified  (6).  The  chief  objection  to  this 
classification  lies  in  the  fact  that,  under  the  aqueous  as  well  as 
under  the  organic  groups,  rocks  of  chemical  and  of  mechanical 
origin  are  included.  Nor  are  all  of  the  rocks  so  classed  truly  sedi- 
mentary or  stratified.  One  of  the  earliest  attempts  at  a  rational 
classification  based  on  origin  was  that  of  Carl  Friedrich  Naumann, 
who,  in  the  second  edition  of  his  Lehrbuch  der  Geogn.osie,  1858 
(21),  recognized  two  classes  in  which  all  rocks  are  included.  These 
are:  I,  The  Protogenous,  or  original;  and  II,  the  Deuterogenous, 
or  derived,  terms  corresponding  essentially  to  the  endogenetic  and 

269 


PRINCIPLES    OF    STRATIGRAPHY 

exogenetic  divisions  used  in  this  book.  Naumann's  terms  have  been 
adopted  in  the  latest  of  French  text-books  by  Hang  (14),  but  in  a 
more  restricted  meaning.  He,  first  of  all,  divides  all  rocks  into  roches 
exogenes,  or  those  formed  on  the  outside  of  the  earth,  i.  e.,  the  sedi- 
mentary rocks ;  and  into  the  roches  endogcnes,  or  those  having  their 
origin  from  within  the  lithosphere,  i.  e.,  the  volcanic  rocks.  The  exo- 
gene  rocks  are  then  divided  into  roches  protogcnes,  comprising  (a) 
the  chemical  and  (b)  the  organic  deposits,  and  roches  deutogcnes,  or 
the  elastics.  The  old  notion  of  a  primary  distinction  between  igne- 
ous and  sedimentary  rocks  still  prevails  in  this  classification,  but 
Haug  recognizes  the  important  distinction  between  elastics  and  non- 
clastic  sediments.  Zirkel  (31),  too,  used  similar  subdivisions  of 
primary  rank  when  he  divided  rocks  into :  A,  Original  crystalline, 
and  B,  Clastic  rocks;  terms  used  by  Naumann  in  the  first  edition 
of  his  Lehrbuck,  1850.  The  term  for  the  first  group  was  not  well 
chosen,  since  it  included  rocks  which  were  not  crystalline,  i.  e.,  ob- 
sidian, etc.  For  this  reason  Zirkel  substituted  the  term  non-clastic 
in  1873.  Both  Naumann  and  Zirkel  included  metamorphic  rocks  in 
their  class  of  Protogene  or  non-clastic  (crystalline)  rocks.  H. 
Rosenbusch  (24),  in  1877,  on  the  other  hand,  included  metamor- 
phic rocks  in  his  class  of  stratified  rocks  (Geschichtete  Gesteine), 
which,  with  the  class  of  massive  rocks  (Massige  Gesteine) — the 
igneous  rocks  of  our  present  classifications — constituted  the  two  ma- 
jor divisions  of  rocks.  In  1898  (25),  however,  he  made  the  three  fol- 
lowing classes:  I,  Eruptive  rocks  (Eruptivgesteine).  These  are 
the  igneous  rocks  of  other  authors  and  they  are  divided  into :  a, 
deep-seated  rocks,  or  Tiefengesteine  (Plutonic  rocks  of  other  classi- 
fications) ;  b,  dike  rocks,  or  Ganggesteine;  and,  c,  effusive  rocks,  or 
Ergussgesteine,  i.  e.,  volcanic  rocks  of  later  classifications.  II, 
Stratified  rocks  (Schichtige  Gesteine).  These  include  clastic  sedi- 
ments and  chemical  precipitates  from  water;  rocks  of  organic 
origin  and  the  porphyroid  rocks.  The  latter,  though  bedded,  are 
clearly  out  of  place  in  this  division,  as  the  author  himself  recognizes, 
since  they  never  were  sediments  nor  are  such  now,  but  are  meta- 
morphic derivatives  of  igneous  rocks.  Siliceous  rocks  of  organic 
(biogenic)  and  those  of  aqueous  (hydrogenic)  origin  are  grouped 
together  by  Rosenbusch  in  this  classification,  and  the  same  is  true 
for  calcareous  rocks.  Coals  and  other  combustibles  are  placed  in 
a  separate  subdivision  or  appendix.  Under  argillaceous  rocks  are 
included  the  phyllites  and  other  more  or  less  altered  or  metamor- 
phosed clay  rocks ;  under  sandstones  he  includes  quartzites,  and 
under  calcareous  rocks  he  places  marbles,  but  other-  metamorphic 
rocks  are  placed  in  the  third  main  division.  Altogether  the  grouping 


ENDOGENETIC   ROCKS  271 

within  this  class  is  as  illogical  and  unsatisfactory  as  it  well  could  be. 
Ill,  Crystalline  slates  (Krystalline  Schiefer),  This  includes  the 
gneisses,  mica  schists,  talc  schists,  chlorite  schists,  amphibole  and 
pyroxene  rocks,  serpentines,  the  metamorphic  calcareous,  mag- 
nesian,  and  iron  rocks,  and  emery.  These,  then,  include  metamorphic 
sedimentaries  as  well  as  metamorphic  igneous  rocks,  and  this  group- 
ing can  be  excused  only  on  the  ground  of  convenience.  Rosenbusch, 
indeed,  tries  to  separate  these  metamorphics  of  diverse  origin  by 
proposing  the  prefix  ortho  for  those  derived  from  igneous,  and  para 
for  those  derived  from  sedimentary  rocks.  To  the  above  three 
groups  is  added  a  fourth,  that  of  the  original  crust  of  the  earth, 
Erste  Erstarrungs  Kruste.  We  owe  to  Johannes  Walther  (30)  the 
first  comprehensive  attempt  at  a  truly  genetic  classification  of  all 
rocks.  One  of  the  essential  features  of  this  system  is  the  recognition 
of  the  fact  that  metamorphic  rocks  belong  with  the  rocks  from 
which  they  are  derived.  He  proposed  four  main  divisions,  namely : 
I,  mechanical  or  clastic;  II,  chemical  precipitates  and  sublimates; 
III,  organic;  and,  IV,  volcanic  rocks,  or  consolidated  lavas. 

This  is  essentially  the  classification  adopted  in  this  book,  except 
that  a  stronger  distinction  is  made  between  the  first  group,  the 
E.voyenctic,  or  clastic,  and  the  others  which  are  classed  as  Endo- 
genetic  (Grabau-9).  The  Endogenetic  are  those  formed  by  agents 
acting  from  within,  i.  e.,  by  agents  intimately  associated  with  the 
rock  mass  forming;  they  produce  rocks  by  solidification,  precipita- 
tion or  extraction  of  the  mineral  matter  from  the  states  of  igneous 
fusion,  aqueous  solution  or  vaporization.  The  Exogenetic  rocks,  on 
the  other  hand,  are  those  formed  by  agents  acting  from  without 
upon  already  existing  rock  matter,  reducing  it  to  a  finer  condition 
either  by  mechanical  or  by  chemical  means,  while  still  leaving  it  in 
a  solid  state.  They  are,  in  fact,  the  clastic  rocks  of  earlier  writers, 
while  the  Endogenetic  rocks  are  the  non-clastic. 


I.     THE  ENDOGENETIC  ROCKS. 

These  are  best  understood  when  we  approach  them  through  a 
consideration  of  the  material  of  the  earth  as  a  whole,  and  the  con- 
ditions under  which  it  appears  to  us.  Aside  from  the  solid  state, 
three  general  conditions  may  be  conceived  of  under  which  :the  ma- 
terial of  the  earth's  crust  may  exist.  These  are:  -r/the  molten  con- 
dition, or  state  of  igneous  fusion  and  solution ;  2,,  the  state  of  solu- 
tion in  water;  and,  3,  the  state  of  vapor  or  incorporation  in  the  air. 
A  molten  magma  is  not  merely  produced  by  a  change  of  condition 


272  PRINCIPLES    OF    STRATIGRAPHY 

from  the  solid  to  the  liquid  state  through  a  rise  in  temperature 
(i.  e.,  snow  or  ice  to  water),  though  this  is  undoubtedly  to  be  re- 
garded as  the  simplest  state  of  fusion.  A  much  more  complex  state, 
however,  exists  in  the  fusion  of  compound  materials  such  as  the 
rock  magmas  consist  of.  These  are  to  be  regarded  as  solutions  of 
the  silicates  one  in  another  or  several  in  one,  under  a  condition  of 
high  temperature.  Solutions  of  salts  in  water  are  not  actually  dif- 
ferent in  kind  from  these  "igneous  solutions,"  though  they  take 
place  at  a  lower  temperature.  Since,  however,  such  a  large  part  of 
the  earth's  surface  consists  of  water  in  the  liquid  state,  it  is  con- 
venient to  consider  solution  in  water  as  distinct  from  igneous  solu- 
tions. This  conception  makes  it  possible  to  identify  the  three  states 
of  the  material  from  which  the  lithosphere  is  to  be  formed,  re- 
spectively, with  the  pyrosphere,  hydrosphere,  and  atmosphere.  By 
a  direct  crystallizing  out  from  the  three  states  (or  precipitation  in 
the  amorphous  state),  we  have  three  groups  of  endogenetic  rocks 
composing  the  lithosphere,  namely:  I,  the  pyrogenic,  or  igneous;  2, 
the  atmogenic,  or  atmospheric;  and,  3,  the  hydrogenic,  or  aqueous 
(in  a  restricted  sense).  By  the  physiological  activities  of  the  organ- 
isms which  constitute  the  biosphere,  the  biogenic  or  truly  organic 
rocks  are  formed  and  these  may  be  divided  into  zoogenic,  or  animal- 
formed,  and  phytogenic,  or  plant-formed.  These  four  types  of 
endogenetic  rocks  may  then  be  tabulated  as  follows : 

1.  Pyrogenic,  or  igneous,  rocks — Pyroliths. 

2.  Atmogenic,  or  atmospheric,  rocks--Atmoliths. 

3.  Hydrogenic,   or   aqueous,   rocks    (in   a   restricted   sense)  — 
Hydroliths. 

4.  Biogenic,  or  organic,  rocks  (in  a  restricted  sense) — Bioliths. 
The  origin  and  interrelations  of  these  types  are  shown  in  the 

following  diagram   (Fig.  38). 

The  first  of  these  groups  comprises  the  Igneous  rocks  of  most 
current  classifications,  the  other  three  are  commonly  included  with 
the  clastic  rocks  as  sedimentaries.  Metamorphic  rocks,  though  gen- 
erally considered  independently  for  convenience  sake,  belong  strictly 
with  the  unaltered  rocks  from  which  they  are  derived,  and  of  which 
they  constitute  modifications.  The  chief  practical  difficulty  in  plac- 
ing them  with  their  unaltered  prototypes  in  a  scheme  is  found  in 
the  impossibility  of  determining  the  precise  types  from  which  they 
have  been  derived  (see  further  below). 

The  further  subdivisions  of  the  Endogenetic  rocks  are  pri- 
marily based  on  chemical  composition,  and  secondarily  on  texture. 
As  a  rule,  composition  is  most  readily  expressed  in  terms  of  the 
minerals  composing  the  rock  if  they  can  be  ascertained,  and  this  is 


ENDOGENETIC    ROCKS 


273 


a  simple  matter  in  all  but  the  pyrogenic  rocks.  In  refined  work 
the  chemical  composition  of  the  latter  is  by  some  subjected  to  a 
recalculation  into  the  minerals  which  satisfy  the  composition  (Cross, 
Iddings,  Pirsson,  etc.-4),  though  this  at  best  seems  an  artificial 
procedure. 

Texture  and  structure  have  been  used  with  rather  indefinite 
limitations.  In  general,  texture  is  the  fine  structure  or  microstruc- 
ture,  concerned  especially  with  minute  arrangement  of  the  compo- 


Fic.  38.     Interrelations  of  the  Endogenetic  Rocks. 

"The  material  of  the  earth  may  be  in  three  states  before  solidification, 
i.  e.,  that  of  fusion,  of  solution  in  water,  and  that  of  vapor.  From  these  states 
by  direct  deposition  (endogenetically)  we  get  the  three  types  of  fundamental 
rocks — the  Igneous,  or  Pyrogenic;  the  Aqueous,  or  Hydrogenic;  and  the 
Atmospheric,  or  Atmogenic  (snow  and  snow-ice).  By  the  physiological  ac- 
tivities of  organisms  we  have  formed  the  Organic,  or  Bio  genie,  rocks,  the 
material  of  which  is  derived  either  from  the  atmosphere  (chiefly  through 
plants — Phytogenic,  though  also  in  a  minor  degree  through  animals,  as  indi- 
cated by  the  heavy  dotted  line)  ;  or  from  the  water  (chiefly  through  animals — 
— Zoogenic,  though  also  in  a  minor  degree  through  plants).  The  lighter 
arrows  show  to  which  states  the  rocks  finally  return,  the  dotted  lines  indicating 
the  less  likely  change.  Biogenic  rocks  are  either  vaporized  or  dissolved,  hence 
the  return  arrows  rise  from  the  center.  Pyro-atmogenic  rocks,  half  way 
between  Pyro-  and  Atmogenic  are  illustrated  by  sublimates,  and  Pyro-hydro- 
genic  rocks,  half  way  between  Pyro-  and  Hydrogenic,  by  pegmatites." 


274  PRINCIPLES    OF    STRATIGRAPHY 

nent  particles,  while  structure  is  the  coarser  arrangement.  It  might 
be  serviceable  to  retain  structure  as  a  general  term,  and  to  speak 
of  the  finer  structure  of  rocks,  i.  e.,  that  which  can  be  seen  in  a 
hand  specimen,  as  texture,  while  the  coarser  structural  features, 
generally,  visible  only  in  the  field,  come  under  the  heading  of 
geotectonics,  or  earth  architecture. 

The  texture  of  Endogenetic  rocks  is  either  crystalline  or  amor- 
phous, each  of  these  having  a  number  of  subordinate  phases,  pecu- 
liar to  one  or  other  of  the  classes  of  endogenetic  rocks.  A  type 
of  texture  or  aggregation  of  a  higher  order  approaching  structure 
may  also  be  observed  at  times  in  the  endogenetic  rocks,  which  give 
them  a  resemblance  to  rocks  of  clastic  origin.  The  three  types  of 
these  aggregates,  spherites,  granulites,  and  pulverites,  will  be  dis- 
cussed at  the  end  of  the  section  on  endogenetic  rocks.  A  brief  de- 
scription of  each  class  follows: 

i.  THE  PYROGENIC  OR  IGNEOUS  ROCKS  (Pyroliths).  These 
rocks  result  from  the  cooling  of  a  molten  magma,  and  are  crystal- 
line or  glassy,  or  of  intermediate  character.  The  following  groups, 
based  on  the  composition  of  the  magma,  are  most  generally  met 
with: 

Composition  Groups. 

I.  Granite  group,  where  the  composition  is  that  of  granite,  which 
when  fully  crystallized  out  would  result  in  the  formation 
of  quartz  and  orthoclase  with  hornblende  and  biotite  or 
muscovite  generally  present. 

II.  Syenitic  group,  where  the  composition  is  that  of  syenite,  re- 
sulting on  crystallization  in  the  formation  of  orthoclase 
and  hornblende,  with  other  accessory  minerals  generally 
present. 

III.  Dioritic  group,  where  the  composition  is  that  of  diorite,  i.  e., 

resulting  in  the  crystallizing  out  of  plagioclase  and  horn- 
blende, frequently  with  some  orthoclase,  biotite,  and  other 
minerals,  and  sometimes  with  sufficient  silica  to  form  free 
quartz. 

IV.  Gabbroitic  group,  with  the  composition  of  gabbro,  which  on 

crystallization  will  yield  pyroxene  and  plagioclase,  with  or 
without  basic  minerals,  as  olivine,  etc. 

V.  Ultra  Basic  group,  the  component  minerals  being  ferromag- 
nesian  silicates,  without  feldspar,  and  in  the  more  basic 
with  olivine. 

The  first  of  these  constitutes  the  acid  group  with  the  percentage 
of  silica  (SiO2)  68  or  over,  the  second  and  third  constitute  the  in- 


PYROGENIC    ROCKS  275 

termediate  group  with  the  percentage  of  silica  (SiO2)  between 
50*  and  68;  while  the  fourth  and  fifth  constitute  the  basic  group, 
with 'the  percentage  of  SiO,  below  50.  That  this  classification  is 
only  approximate  appears  from  the  fact  that  some  gabbros  have  a 
percentage  of  SiO2  approaching  55,  while  some  granites  fall  as 
low  as  62  per  cent.  Each  of  these  groups  may  be  subdivided  ac- 
cording to  texture  as  follows : 


Textural  Groups. 

I.     Crystalline  Division. 

A.  Holo crystalline,   or   Granitic.     Also   called   phaneritic, 

with  the  minerals  all  crystallized  out,  and  the  lead- 
ing minerals  visible  magascopically,  as  in  granite. 
They  may  occasionally  exhibit  a  rude  porphyritic 
structure.  The  crystals  may  be  in  part  idiomorphic 
(automorphic),  each  having  its  own  form,  or  allo- 
trionwrphic  (xenomorphic),  having  their  outline 
determined  by  the  surrounding  crystals,  or  both.  In 
basic  igneous  rocks,  of  either  holo-  or  cryptocrys- 
talline  texture,  an  ophitic  structure  may  occur,  in 
which  the  crystals  of  pyroxene  have  the  character  of 
large  plates,  separated  and  penetrated  by  fine  needles 
and  crystals  of  feldspar.  The  pyroxene  has  crystal- 
lized around  the  feldspar,  as  shown  by  the  fact  that 
the  pyroxene  is  in  optical  continuity  on  both  sides 
of  the  obstruction.  Orbicular  structure  may  also 
occur  in  basic  igneous  rocks,  and  consists  of  an 
abundance  of  spheroidal  aggregates  ranging  in  size 
up  to  that  of  a  walnut  or  over,  and  composed  of 
silicates  with  radial  or  concentric  arrangements.  In 
the  well  known  napoleonite  from  Corsica  they  con- 
sist of  concentric  shells  with  a  radial  structure  and 
composed  of  hornblende  and  feldspar  alternately. 
The  Finnish  granite,  known  as  Rapakiwi,  belongs 
here.  (Harris-i3.) 

B.  Cryptocrystalline,  also  called  aphanitic,  with  a  consid- 

erable proportion  of  the  mineral  constituents  not 
visible  magascopically.  When  larger  crystals  (pheno- 
crysts)  are  scattered  through  the  main  mass  (ground 
mass)  the  rock  is  said  to  be  porphyritic  or  porphyry. 

*  55,  according  to  some. 


276  PRINCIPLES    OF    STRATIGRAPHY 

When  the  ground  mass  predominates,  the  pheno- 
crysts  being  few,  the  rock  is  spoken  of  as  porphy- 
ritic  rhyolite,  trachyte,  etc.  But  if  the  phenocrysts 
abound  then  the  rock  is  called  a  rhyolite  porphyry, 
trachyte  porphyry,  andesite  porphyry,  etc. 

Porphyries  (Cross,  etc.~4)  may,  in  a  general  way, 
be  divided  into  light-colored,  or  leucophyres,  and 
dark-colored,  or  melaphyres,  and,  according  to 
the  character  of  the  phenocrysts,  into  Quartz-leu- 
cophyres,  Feldspar-leucophyres,  Quartz-melaphy- 
res,  Feldspar-melaphyres,  etc.  When  intermediate 
as  to  color  the  names  quartz-porphyry  or  quart- 
zophyres,  feldspar-porphyry  or  feldspar -phyres, 
hornblende  porphyries,  or  hornblendophyres,  etc., 
are  useful. 

Cryptocrystalline  texture  may  be  original  or  second- 
ary through  a  process  of  devitrification  of  lavas  orig- 
inally glassy  or  acrystalline.  They  may  be  divided 
as  follows : 

B-i.  With   Trachytic   texture,  the  ground  mass 
consisting  of  an  aggregate  of  little  rods  of 
feldspar  in  parallel  arrangement.     This  is 
sometimes  visible  to  the  unaided  eye. 
B-2.  With  Felsitic  texture  (lithoidal),  when  the 
ground   mass   is    so   dense   as    to    appear 
acrystalline  except  under  the  microscope, 
where  it  is  seen  to  consist  of  minute  quartz 
and  feldspar  grains  with  some  glass. 
B-3.  Vesicular  and  Ainygdaloidal,  with  a  crypto- 
crystalline  ground  mass,  but  with  numer- 
ous vesicles  or  steam  holes  which  may  be 
filled  with   mineral   matter    (amygdaloidal 
texture). 
II.     Amorphous  Division. 

C.  Acrystalline,  or  glassy,  the  greater  part  of  the  mass  be- 
ing an  amorphous  glass,  without  crystalline  charac- 
ter even  under  the  microscope.  It  may  be  divided 
into: 

C-i.  Vitreous,    or    obsidianic,    when    a    uniform 

glass  as  in  obsidian. 

C-2.  Perlitic  with  spheroidal  structure  due  to  con- 
centric cracks  from  contraction  in  cooling. 
Ex.  Perlite. 


PYROGENIC   ROCKS  277 

€-3.  Vesicular,  or  pumiceous  and  scoriaceous. 
When  rendered  light  and  cellular  by  the 
abundance  of  steam  holes  due  to  expansion 
of  the  steam  during  solidification.  The 
commoner,  rougher  type  constitutes  the 
scoriaceous  texture.  These  vesicles  may 
characterize  the  entire  mass  or  be  limited 
to  layers  or  streaks.  In  the  basic  rocks  the 
scattered  vesicles  may  become  filled  by  min- 
eral matter  either  during  or  subsequent  to 
the  volcanic  period,  and  so  produce  an 
amygdaloidal  structure. 

€-4.  Spherulitic,  micro  spherulitic,  variolitic,  etc. 
Containing  globes  or  spherules  made  up  of 
extremely  delicate  fibers  of  feldspar,  ar- 
ranged radially  and  embedded  in  a  mass 
consisting  chiefly  of  aggregates  of  tridy- 
mite  or  quartz.  In  size  these  spherulites 
may  range  to  several  inches.  Microspheru- 
lites  are  very  minute  Spherulitic  bodies, 
often  occurring  in  great  numbers  in  bands 
or  affecting  the  entire  ground  mass.  The 
large  spherulites  of  older  acid  lavas  are 
often  partly  or  totally  replaced  by  flint  or 
quartz.  In  basic  rocks  a  similar  structure 
is  known  as  variolitic.  Lithophysce  are 
spherulitic  structures  varying  up  to  a  foot 
or  more  in  diameter,  and  consisting  of  con- 
centric shells  separated  by  interspaces. 
(For  illustrations,  see  Iddings-i5;  pis.  xli 
and  xliii.) 

Cryptocrystalline  and  Acrystalline  rocks  may  also  exhibit  a 
banded  texture,  i.  e.,  flow  structure  on  a  small  scale  (see  beyond). 
From  the  combination  of  any  member  of  the  composition  group 
with  members  of  the  texture  group  we  get  the  common  types  of 
pyrogenic  rocks,  as  follows* : 

*  For  a  more  detailed  discussion  of  the  pyrogenic  rocks  the  student  is  referred 
to  the  Hand  Book  of  Rocks,  by  J.  F.  Kemp,  and  to  the  work  of  Cross,  Iddings, 
Pirsson  and  Washington,  on  Quantitative  Classification -of  Igneous  Rocks,  cited 
in  the  Bibliography.  See  also  Harker,  A  Natural  History  of  the  Igneous 
Rocks,  and  for  a  brief  treatise,  his  Petrology  for  Students,  Cambridge. 


278  PRINCIPLES    OF    STRATIGRAPHY 

I.  The  Granite  magma,  when  holocrystalline  constitutes  granite, 
when  cryptocrystalline,  rhyolite,  quarts  felsite  (petro- 
silex)  or  quarts  porphyry;  when  glassy,  (i)  rhyolite  ob- 
sidian, (2)  per  lite,  or  (3)  rhyolite  pumice. 

II.  The  Syenitic  magma  when  becoming  holocrystalline  consti- 
tutes syenite;  when  cryptocrystalline,  trachyte  felsite,  or 
trachyte  porphyry;  when  glassy,  (i)  syenite  obsidian,  (2) 
perlite,  or  (3)  syenite  pumice. 

III.  The  Dioritic  magma  when  becoming  holocrystalline  consti- 

tutes diorite  or  quarts  diorite  (free  quartz  present)  ;  when 
cryptocrystalline,  andesite,  andesite  felsite,  or  andesite 
porphyry  and  dacite,  dacite  felsite,  or  dacite  porphyry; 
when  glassy,  (i)  andesite  obsidian,  or  (2)  andesite  pumice. 

IV.  The  Gabbroitic  magma  when  holocrystalline  constitutes  gab- 

bro  and  olivine  gabbro;  when  cryptocrystalline,  augite  an- 
desite or  augite  andesite  prophyry,  and  basalt  or  basalt 
porphyry;  when  glassy,  (i)  basalt  obsidian,  or  (2)  scoria. 
V.  The  Ultra  basic  (non-feklspathic)  magmas,  when  holocrystal- 
line constitute  pyroxenite,  and  peridotites  (with  olivine)  ; 
when  cryptocrystalline,  augitite  and  limburgite  (with  cor- 
responding porphyrys)  ;  and,  when  glassy,  basic  obsidians 
and  scorias. 

The  following  may  further  be  noted  : 

Dolerite,  a  field  name  to  be  used  for  a  holocrystalline  rock,  either 
a  diorite  or  a  gabbro,  in  which  the  ferromagnesian  minerals 
cannot  be  determined  at  sight.  (Chamberlin  and  Salisbury—  2  : 


Trap,  a  field  name  for  a  cryptocrystalline,  non-porphyritic,  dark 
rock,  of  either  dioritic  or  gabbroitic  composition. 

Diabase,  a  holocrystalline  rock  of  gabbroitic  composition,  but  with 
a  diabasic  (ophitic)  texture,  the  plagioclase  feldspar  crystals  be- 
ing lath-shaped  and  fully  crystallized  (idiomorphic),  while  the 
augite  between  them  is  allotriomorphic.  It  occurs  chiefly  as  a 
dike  rock  or  in  sills. 

Hornblendite,  a  holocrystalline  rock  composed  of  hornblende  with- 
out feldspar. 

Water  and  Ice  as  Igneous  Rocks. 

Water  solidifying  into  ice  by  a  lowering  of  temperature  must  be 
referred  to  the  igneous  rocks.  Its  texture  may  be  holocrystalline, 
but  is  more  commonly  cryptocrystalline,  or  glassy.  It  must  be 


ATMOGENIC   ROCKS  279 

placed  at  the  ultra  basic  end  of  the  scale,  being  entirely  free  from 
SiO2  when  pure.     (See  Kemp-i7.) 

Metanwrphic  Derivatives  of  Igneous  Rocks. 

These  comprise :  ( I )  Gneisses,  which  include  granite  gneiss, 
syenitic  gneiss,  dioritic  gneiss,  gabbroitic  gneiss,  pyroxenitic  gneiss, 
peridotitic  gneiss,  according  to  the  nature  of  the  pyrogenic  rock 
from  which  they  have  been  derived.  (2)  Schists,  including  some 
mica  schists  due  to  crushing  and  shearing  of  acid  igneous  rocks, 
hornblende  schists  derived  from  basic  igneous  rocks ;  chlorite  and 
perhaps  talc  schists.  (3)  Serpentines  and  some  soapstones  derived 
from  basic  igneous  rocks.  The  weathering  products  of  igneous 
rocks  will  be  discussed  at  some  length  in  a  later  chapter. 

2.  THE  ATMOGENIC  OR  ATMOSPHERIC  ROCKS  (Atmoliths).  This 
group  is  represented  by  snow  and  snow  ice,*  which  are  precipitates 
from  the  atmosphere,  as  rock  salt  and  gypsum  are  precipitates  from 
the  water.  It  forms  a  surface  rock  of  considerable  extent  at  the 
present  time  in  the  Polar  regions,  while  at  various  periods  in  the 
earth's  history  it  has  extended  widely  over  regions  now  for  the 
most  part  freed  from  it.  The  importance  of  snow  ice  in  stratigraphy 
is  emphasized  by  the  preservation  in  it  of  animals  in  an  almost  un- 
altered condition  and  by  the  glacial  deposits  to  which  it  has  given 
rise  in  various  geologic  periods.  In  composition  ice  is  simple,  con- 
sisting throughout  of  a  single  mineral  mass,  and  in  texture  it  is 
granular  crystalline,  though  appearing  compact  with  conchoidal  frac- 
ture. The  types  here  comprised  are :  I.,  Snow ;  II.,  Firn ;  and,  III., 
Glacier  Ice. 

I.  Snoiv.  This  is  a  loose  aggregate  of  needles  and  flakes  of  crys- 
talline form  and  structure,  precipitated  in  this  state  from  the  atmos- 
phere in  which  the  material  was  held  as  water  vapor.    The  crystal- 
line form  is  soon  lost  through  partial  melting  and  evaporation,  a  fine 
granular  powder  resulting.    This  is  the  first  step  in  metamorphism 
(diagenism). 

II.  Firn,  or  Neve.    This  is  an  aggregate  of  snow  grains,  either 
loosely  held  together  or  united  by  ice  cement.    These  aggregates  are 
full  of  air  bubbles.    Firn  is  formed  below  the  snow  line  and  repre- 
sents a  further  step  in  metamorphism  of  the  snow. 

III.  Snow  Ice,  or  Glacier  Ice.     This  is  a  granular  crystalline 
mass  in  which  the  individual  crystalline  ice  grains  range  from  the 

*  Water  ice  which  is  to  be  considered  an  igneous  rock  resulting  from  the 
cooling  of  a  magma  is  of  little  stratigraphic  importance.  (See  above,  p.  278.) 


280  PRINCIPLES    OF    STRATIGRAPHY 

size  of  a  pea  near  the  firn  border  to  that  of  a  hen's  egg.  The  crys- 
tals are  intimately  united,  so  that  in  fresh  ice  they  cannot  be  dis- 
tinguished. 

3.  THE  HYDROGENIC  ROCKS  (Hydroliths).    These  are  the  only 
true  aqueous  rocks  and  they  are  wholly  of  chemical  origin.    Though 
often  forming  beds  of  considerable  extent,  they  do  not  generally 
enclose  evidence  of  their  age,  though  in   some  cases  organic   re- 
mains are  found.    As  a  rule,  however,  the  age  of  a  bed  of  rock  salt 
or  gypsum  can  be  determined   only  by  the   age   of  the  enclosing 
rocks.     Chemically  formed,  or  hydrogenic  limestones,  on  the  other 
hand,  may  include  organic  remains,  as  is  the  case  in  calcareous  tufa 
and  cave  deposits.     Many  great  limestone  beds  which  are  sparingly 
fossiliferous  have  frequently  been  considered  of  chemical   (hydro- 
genic) origin,  but  it  is  not  improbable  that  many,  if  not  most,  of 
these    will    prove    to    be    of    clastic    origin.       Among    hydrogenic 
rocks   of    less    stratigraphic    importance   are    siliceous    sinters    and 
their    alteration    products    and    the    various    ferrites    or    iron    ore 
deposits,  which  owe   their  precipitation    from  water  to  inorganic 
reactions. 

4.  THE  BIOGENIC  ROCKS  (Bioliths).     These  are  the  only  true 
organic  rocks,  i.  e.,  those  due  directly  to  the  physiological  activities 
of   organisms.     They  are  among  the   most  important   rocks  with 
which  the  stratigrapher  has  to  deal,  for  they  are  the  rocks  richest 
in  organic  remains.     As  examples  may  be  mentioned  the  organic 
limestones,  such  as  coral  and  shell  rock ;  and  the  organic  oozes, 
whether  calcareous  or  siliceous.     Here  also  belong  the  deposits  of 
coals  and  vegetable  materials  in  all  stages  of  carbonization,  from 
peat  to  anthracite. 

Bioliths  may  be  divided  into  Zooliths,  or  those  of  animal  origin, 
and  Phytotttks,  or  those  of  vegetal  origin.  The  latter  include  two 
important  types,  those  formed  by  the  direct  accumulation  of  vegetal 
matter,  such  as  peat,  coals,  etc.,  which,  from  their  burnable  nature, 
have  been  called  caustobiolitJis  *  (Potonie,  see  Chapters  x  and  xi), 
or  better  caustophytoliths;  and  those  forming  pure  accumulations 
of  mineral  matter,  either  silicia  (diatoms)  or  lime  (nullipores,  etc.). 
These  are  the  acaustophytoliths.  Caustobioliths  may  also  be  of 
zoogenic  origin  (caustozooliths),  but  these  are  rare  (some  oils,  etc.). 
Finally,  caustoliths  of  non-organic  origin  are  also  known,  such  as 
chemically  formed  petroleum,  asphalt,  graphite,  and  sulphur.  Caus- 
tobioliths have  been  divided  into  three  groups,  according  to  their 
mode  of  origin.  These  are: 

*  Kau<rr6y,  verbal  adjective  of  Ket/etv — burn. 


BIOGENIC    ROCKS  281 


Caustobioliths. 

i.  Sapropelites,  ouTrpos  (sapros),  rotten;  m;Xos  (pelos),  slime, 
mud;  "T/S  (ites),  derived  from.  These  are  derived  from  the 
decaying  organic  matter  of  water  organisms,  both  animal  and  plant, 
algae,  etc.*  (sapropel,  Faulschlamm,  decay  ooze,  putrid  slime). 
When  formed  into  rock  they  constitute  sapropeliths  or  sapropelites.f 
They  differ  from  the  humus  rocks  in  their  greater  content  of  fat 
and  protein. 

2.  Humus  and  Humulith.     These  are  deposits  derived  from  de- 
caying land  plants,  including  those  of  swamps  and  marshes.     Car- 
bohydrates are  an  important  product  of  the  decay  of  the  higher 
plants.    All  peat  and  coal  deposits  belong  here.    Lithified,  they  form 
humus  rock  or  chamaeliths  (xa^MU  on  the  ground,  Greek  equiva- 
lent of  humus;  the  Latin  would  be  humulith). 

3.  Liptobiolith,  Xewrw     (leipo),  Aewrros     (leiptos,    Latinized,    Up- 
tos,   left  behind,  residual  and  biolith).      These  comprise  the  resins 
and  gums,  amber,  copal,  etc.,  which,  from  their  greater  resistance  to 
decay  remain  behind  after  the  destruction  of  the  plants  containing 
them. 

SUBDIVISION  OF  HYDROGENIC  AND  BIOGENIC  ROCKS.  In  both 
hydrogenic  and  biogenic  rocks  the  chemical  division  is  most  readily 
made  on  the  basic  elements  of  the  salts.  In  texture  hydrogenic 
rocks  are  both  crystalline  and  amorphous  while  in  biogenic  rocks  the 
amorphous  texture  predominates. 

Textures  of  Amorphous  Hydrogenics.  Among  the  amorphous 
hydrogenics  the  following  subtextures  are  most  marked : 

(a)  Botryoidal,  with  grape-like,  rounded  surfaces. 

(b)  Pisolitic,  of  large  spherules. 

(c)  Oolitic,  of  small  spherules,  also  characteristic  of  the  bio- 

genic rocks. 

(d)  Banded,  as  in  stalactic  deposits  (stalactites  and  stalagmites). 

(e)  Laminated,  or  scaly. 

(f)  Fibrous. 

(g)  Concretionary. 

(h)   Tufaceous,  as  in  calcareous  and  siliceous,  tufa  or  sinter. 
Textures  of  Biogenic  Rocks.    Among  the  biogenic  rocks  we  note 
the  following  subtextures : 

*  Mineral  structures,  such  as  shells  and  skeletons,  are  of  course  excluded, 
t  The  termination  pelite  should  be  restricted  to  oozes  or  slimes  of  endogenetic 
origin,  leaving  the  termination  lutyte  for  oozes  of  exogenetic  or  clastic  origin. 


282 


PRINCIPLES    OF    STRATIGRAPHY 


(a)  Granular,  the  texture  of  the  fine  organic  oozes. 

(b)  Oolitic,  consisting  of  minute  spherules  or  oolite  grains. 
•    (c)  Earthy  texture. 

(d)   Compact  conchoidal,  as  in  coal,  etc. 

The  following  table  gives  some  of  the  principal  hydrogenic  and 
biogenic  rocks  (Grabau~9)  : 

Table  of  the  principal  types  of  hydrogenic  and  biogenic  rocks. 


Class 

Composition 

(a) 

(b) 

(c) 

(d) 

(e) 

Alkali, 

Calcare- 

Siliceous 

Ferru- 

Carbona- 

ous 

ous 

ginous 

ceous 

Chemical 

Limestone, 

Siliceous 

Rock  Salt, 

Stalactic 

Sinter, 

Bog  Ore, 

HYDROLITHS 

Etc. 

Deposits, 

Vein 

Limonites, 

Original 

Natural 

Calcareous 

Quartz, 

Siderites, 

Soda 

Tufa,  Gyp- 

Flint, 

etc. 

sum,  An- 

Chert 

hydrite, 

etc. 

Specular 

Metamorphic 

Marble, 

Quartz 

Hematites, 

Alabaster 

Rocks 

Magnet- 

ites, etc. 

Siliceous 

Peat,  Lig- 

Organic 

Organic 

nite,  Bitu- 

Limestones 

Oozes, 

minous 

BlOLITHS 

Phosphate 

Coral  Rock 

Diatoma- 

Limonites 

coal,  some 

Original 

Rocks 

Shell  beds, 

ceous 

(organic) 

Anthracites 

(organic 

Earth 

etc.  (Caus- 

oozes,  etc.) 

Tripolite, 

tobioliths) 

etc. 

Specular 

Certain  an- 

Quartz 

hematites 

thracites, 

Metamorphic 

Marble 

Rock 

spathic 

Native 

or 

and  mag- 

coke, Bitu- 

Quartzites 

netic 

mens,    etc. 

iron  ores 

Graphite 

in  part 

ENDOGENETIC    SANDS  283 

SPHERYTES,  GRANULYTES,  AND  PULVERYTES  (pelytes).  These 
names  have  been  suggested  (Grabau-io)  for  rocks  composed  of 
aggregates  of  constructional  origin  simulating  in  texture  destruc- 
tional  or  clastic  rocks  and  having  many  features  in  common  with 
them,  such  as  stratification,  etc.  The  textures  which  characterize 
these  rocks  are  spherytic,  granulytic,  and  pulverytic,  corresponding 
to  the  textures  rudaceous,  arenaceous,  and  lutaceous  among  the  clas- 
tic rocks.  Thus  a  rock  formed  of  volcanic  bombs  would  be  a 
spheryte,  one  formed  of  lapilli  or  oolitic  grains  a  granulyte,  and  one 
formed  of  diatom  frustules,  or  minute  radiolaria  or  foraminifera,  a 
pulveryte.  The  last  three  types  would  be  of  biogenic  origin,  and 
therefore  would  constitute  biopulverytes,  two  of  them  being  bio- 
silicipulverytes,  the  material  being  silica,  the  third  a  biocalci- 
pulveryte,  the  material  being  calcite.  A  pulverytic  rock  of  hydro- 
genie  origin  would  be  a  hydropulveryte.  As  suggested  above,  the 
term  pelyte  (from  the  Greek  707X05,  slime)  might  well  be  restricted 
to  muds  and  slimes  of  endogenetic  origin,  and  so  be  used  instead 
of  the  word  pulveryte.  Thus,  instead  of  pyro-,  atmo-,  hydro-,  and 
biopulverytes,  we  may  use  the  terms,  pyropelytes,  atmopelytes,  hy- 
dropelytes,  and  biopelytes. 

Chemically  formed  oolites  are  hydrocalcigranulytes,  or,  if  of 
silica,  hydrosilicigranulytes.  The  oolitic  iron  ores  of  Wisconsin 
(Siluric)  are  probably  hydro ferrogranulytes.  Organically  formed 
oolites  are  biocalcigranulytes ;  granular  snow  (firn)  is  an  atmo- 
granulyte,  and  volcanic  lapilli  form  a  pyrogranulyte.  A  bed  of  vol- 
canic bombs  is  a  pyrospheryte,  and  one  of  unworn  coral  or  Girva- 
nella  heads  a  biospheryte  (biocalcispheryte).  All  of  these  rocks  are 
of  endogenetic  or  nonclastic  origin. 

OOLITHS,    PlSOLITHS,    ROGENSTEINE,    ETC.        Rocks    Composed    of 

spherical  grains  of  either  hydrogenic  or  biogenic  origin  are  called 
Oolites  or  Ooliths  when  the  grains  are  small,  and  Pisolites  or 
Pisoliths  (Pea  grits)  when  they  have  the  size  of  a  pea  or  over. 
Rogensteine  are  ooliths  or  pisoliths  in  which  the  grains  (ooids) 
are  held  together  by  a  more  or  less  argillaceous  cement.  In  typical 
ooliths,  so  named  from  their  resemblance  to  fish-roe,  each  grain 
consists  of  successive  concentric  shells  of  carbonate  of  lime,  and  has, 
moreover,  commonly  an  internal  radiating  fibrous  structure,  which 
gives  a  black  cross  between  crossed  nicols.  The  lime  is  often  de- 
posited around  some  foreign  body,  but  also  often  without  such  a 
body,  forming  a  sphere  hollow  at  the  center.  The  granules  consist 
sometimes  of  aragonite,  sometimes  of  calcite,  or  they  are  formed 
by  an  intermediate  substance,  ktypeit.  Great  variation  in  size  occurs. 


284  PRINCIPLES    OF    STRATIGRAPHY 

The  giant  pisoliths  *  of  Zepce,  Bosnia,  range  from  2  to  13.5  centi- 
meters in  diameter,  but  ordinary  ooliths  do  not  range  much  above 
"1.5  mm.  In  the  Bosnian  examples  the  kernal  is  magnesite  and  the 
surrounding  shells  dolomite.  Both  concentric  and  radial  structure 
is  shown  in  these  and  they  are  believed  to  have  been  formed  in  hot 
springs,  similar  to  the  pisoliths  of  the  Carlsbad  Sprudel. 

True  ooliths  and  pisoliths  are  precipitations  (hydrogenic  or  bio- 
genie)  and  their  spherical  form  is  an  original  structure.  Rocks 
of  clastic  or  worn  calcite  grains  or  fragments  of  shells,  etc.,  may 
resemble  ooliths,  and  are  indeed  often  mistaken  for  them.  To  such 
Bornemann  has  applied  the  term  pseudo-ooliths,  and  they  belong 
to  the  category  of  exogenetic  rocks,  unless,  indeed,  they  are  subse- 
quently enlarged  by  deposition  of  lime  about  them.  Concretions 
may  also  assume  the  form  of  ooliths  or  pisoliths,  but  they  are 
secondary  or  diagenetic  structures.  Three  modes  of  origin  have 
been  most  widely  discussed  by  geologists  and  one  or  the  other  has 
frequently  been  regarded  as  the  sole  mode.  These  are :  i.  Chemical, 
or  hydrogenic ;  2.  animal,  or  zoogenic ;  and,  3.  plant,  or  phytogenic. 
Each  of  these  will  be  discussed  under  its  appropriate  heading  in 
succeeding  chapters. 

II.     THE  EXOGENETIC,  OR  CLASTIC  ROCKS 

In  discussing  next  the  clastic  rocks,  the  agent  active  in  the 
production  of  their  present  characteristics  will  be  considered  as  of 
primary  importance  in  making  the  larger  divisions.  It  is  not  always 
possible  to  determine  what  was  the  cause  of  the  clastic  condition 
of  a  given  rock,  since  other  agents  subsequently  active  have  pro- 
duced those  features  which  give  the  rock  its  most  characteristic 
aspects.  Thus  a  sand  mass  may  owe  its  origin  in  part  to  atmos- 
pheric disintegration  and  in  part  to  the  mechanical  activity  of  the 
water.  Its  final  form,  however,  may  be  given  by  aeolian  action, 
the  mass  becoming  finally  by  diagenism  a  consolidated  sand-dune. 
It  will,  however,  be  observed  that  the  agent  last  active,  and  there- 
fore the  one  whose  characteristics  were  most  strongly  impressed 
upon  the  mass,  i.  e.,  the  wind,  is  not  only  responsible  for  the  form 
and  structure  which  the  deposit  eventually  takes  on,  but  also,  in  part 
at  least,  modifies  the  original  form  of  the  component  grains.  Thus 
without  overlooking  the  claims  of  the  other  agents  those  of  the  wind 
may  be  considered  as  greatest  and  the  rock  is  therefore  placed  under 
the  division  of  wind-formed  elastics,  or  anemoclastics. 

*  These  should  be  classed  as  hydrospherytes. 


EXOGENETIC   ROCKS  285 

The  relative  claims  of  the  various  agents  active  in  the  production 
of  a  given  clastic  rock  once  determined — provided  there  is  more 
than  one  agent — it  will  be  found  that  most  rocks  fall  under  one  of 
five  groups,  though  some  rocks  may  fall  so  precisely  half  way  be- 
tween two  groups  that  it  becomes  a  matter  of  individual  opinion 
where  it  should  be  placed.  The  five  principal  groups  are : 

1.  Pyroclastic  rocks,  or  pyroclasts. 

2.  Autoclastic  rocks,  or  autoclasts. 

3.  Atmoclastic  rocks,  or  atmoclasts. 

4.  Anemoclastic  rocks,  or  anemoclasts. 

5.  Hydroclastic  rocks,  or  hydroclasts. 

6.  Bioclastic  rocks,  or  bioclasts. 

The  interrelations  of  these  rocks  are  shown  in  the  following 
diagram  (Fig.  39),  on  page  286. 

» 

Textural  Groups. 

In  these  divisions  the  grain  of  the  rock  or  its  texture  is  of 
greater  importance  than  the  composition,  for,  although  the  latter  is 
often  the  prime  cause  of  selective  destruction  of  rocks,  yet  this  is 
generally  only  on  a  minor  scale,  and  the  destruction  of  the  different 
rocks  by  the  same  agent,  especially  when  mechanical,  goes  on  with- 
out much  reference  to  the  composition.  On  the  other  hand,  the  size 
of  the  grain  is  generally  directly  proportional  to  the  intensity  of  ac- 
tion of  the  agent  (aided  of  course  by  the  composition  and  struc- 
ture of  the  original  rock),  and  so  naturally  takes  a  higher  classi- 
ficatory  rank.  These  types  of  texture  or  grain  of  clastic  rocks  are 
recognized : 

1.  Rudaceous  *  texture,  or  that  of  the  rubble  rocks,  in  which  the 
grain  is  larger  than  that  of  a  sand  grain.    Consolidated  rocks 
of  this  texture  are  Rudytes  (psephytes  of  many  authors). 

2.  Arenaceous  f  texture  or  that  of  sand  rocks,  irrespective  of 
composition,  in  which  the  size  of  the  grain  varies  from  being 
barely  visible  to  that  of  a  grain  of  rice.    Consolidated  rocks 
of  this  texture  are  Arenytes  (Psammytes  of  some  authors). 

3.  Lutaceous  %  texture  or  that  of  impalpable  powder  or  rock 
flour.     Consolidated  rocks  of  this  type  are  Lutytes   (i.  e., 
mud  rocks).     (Pelytes  in  part  of  some  authors.) 

*  From  rudus,  Lat.  for  rubble, 
t  From  arena,  Lat  for  sand. 
I  From  lutum,  Lat.  for  mud. 


286 


PRINCIPLES    OF    STRATIGRAPHY 


Size  of  Grain.  In  recent  years  attempts  have  been  made  to  es- 
tablish a  more  precise  mode  of  designation  of  the  various  types 
based  on  size  of  grain.  The  following  is  the  standard  adopted  by 
the  New  York  City  aqueduct  commission  and  may  well  be  adopted 
as  a  general  standard  with  the  emendations  given  beyond. 


FIG.  39.  Diagram  showing  the  interrelations  of  the  exogenetic  rocks.  ABC 
represent  the  crust  of  the  earth  or  lithosphere.  From  within  this 
shell,  but  still  external  so  far  as  the  crust  is  concerned,  the  volcanic 
explosions  produce  the  pyroclastic  rocks  on  the  surface  of  the 
earth.  Within  the  crust  itself  are  formed  the  autoclastic  rocks. 
From  without  the  shell  the  attack  by  atmosphere,  hydrosphere  and 
biosphere  produce,  respectively,  atmoclastic  (and  anemoclastic), 
hydroclastic  and  bioclastic  rocks.  The  final  result  of  the  destruc- 
tive activities  of  the  various  agents  is  the  return  of  the  material 
either  to  the  air  as  vapor  or  to  the  water  in  solution,  or  more 
rarely  to  assimilation  by  the  biosphere  (salt,  etc.).  Fusion  may 
transfer  some  of  the  material  to  the  realm  of  the  pyrosphere.  The 
cycle  of  change  is  thus  complete  and  redeposition  will  be  as  endo- 
genetic  rocks. 

/,  Coarse  gravel  above  5.  mm. ;  2,  fine  gravel  5  to  I  mm. ;  5, 
coarse  sand  I  to  0.5  mm. ;  4,  medium  sand  0.50  to  0.25  mm. ;  5,  fine 
sand  0.25  to  o.io  mm.;  6,  superfine  sand  o.io  to  0.05  mm.;  7,  rock 
flour  (silt,  Merrill)  0.05  to  o.oi  mm. ;  8,  superfine  flour  (fine  silt, 
Merrill)  o.oio  to  0.005  mm-  J  9>  C^a7  s^ze  O-OO5  to  o.oooi  mm. 


EXOGENETIC   ROCKS 


287 


Eventually  this  classification  was  published  by  Merrill  in  1898 
(20:56*0),  the  only  difference  being  that  he  gives  the  range  of  fine 
gravel  as  between  2  and  i  millimeter,  and  classes  everything  above 
2  mm.  as  gravel.  Crosby  (3*^05)  has  given  a  somewhat  different 
valuation  for  some  of  the  types  as  follows : 

Fine  sand :  0.45  mm. ;  superfine  sand :  0.28  mm. ;  quartz  flour : 
o.i 6  mm. ;  superfine  quartz  flour :  0.08  mm. 

Keilhack  ( 16:5^%  528)  gives  the  following  classification,  accord- 
ing to  size  of  grain :  i,  grains  above  2  mm.  diameter :  gravel;  2, 
grains  from  2  to  i  mm.  diameter :  very  coarse  sand;  3,  grains  from  i 
to  0.5  mm.  diameter:  coarse  sand;  4,  grains  from  0.5  to  0.2  mm. 
diameter:  medium  sand;  5,  grains  from  0.2  to  o.i  mm.  diameter: 
fine  sand;  6,  grains  from  o.i  to  0.05  mm.  diameter:  superfine  sand; 
7,  grains  from  0.05  to  o.oi  diameter :  dust;  8,  grains  smaller  than 
o.oi  mm.  diameter:  finest  dust.  Nos.  2  to  6  inclusive  were  classed 
merely  as  sands ;  the  varietal  names  are  here  added. 

It  will  be  seen  that  the  subdivisions  of  the  sands  here  given  cor- 
respond very  closely  to  those  selected  by  the  New  York  engineers, 
who,  however,  place  the  grains  above  i  mm.  in  diameter  into  the 
category  of  gravel.  No.  7,  rock  flour  of  the  engineer's  table,  also 
corresponds  to  No.  7,  dust  of  Keilhack's  table. 

From  these  analyses,  we  may  construct  the  following  table, 
which  may  serve  as  a  standard  for  comparison : 


Table  of  standard  sizes  of  rock  fragments. 


1 .  Boulders above           1 50 .  oooo  mm. 

2.  Cobbles 150.000  to  50.0000  mm. 

3.  Very  coarse  gravel ....  50.000  to  2  5.  oooo  mm. 

4.  Coarse  gravel 25 .  ooo  to     5 .  oooo  mm. 

5.  Fine  gravel 5 .  ooo  to     2 . 5000  mm. 

6.  Very  coarse  sand  (or 

very  fine  gravel) ...  2 . 500  to     i .  oooo  mm. 

7.  Coarse  sand i  .000  to     0.5000  mm. 

8.  Medium  sand 0.500  to     0.2500  mm. 

9.  Fine  sand 0.250  to     o.  1000  mm. 

10.  Superfine  sand o.  100  to     0.0500  mm. 

11.  Rock  flour 0.050  to     o.oioo  mm. 

12.  Superfine  flour o.oio  to     0.0050  mm. 

13.  Clay  size 0.005  to     o.oooi  mm. 


Texture  rudaceous;  on 
consolidation  forming 
rudytes. 


Texture  arenaceous;  on 
consolidation  forming 
arenytes. 


Texture  lutaceous;  on 
consolidation  forming 
lutytes. 


Orth  (22),  Laufer  (18)  and  Wahnschaffe  (29)  are  in  essential 
agreement  with  Keilhack,  and  so  is  E.  Wollny.  Orth  calls  material 
from  i  mm.  to  3  mm.  very  coarse  sand  and  fragments,  above  3  mm. 


288  PRINCIPLES    OF    STRATIGRAPHY 

pebbles.  Laufer  and  Wahnschaffe  call  grade  4  of  Keilhack's  scale 
fine  sand  and  both  5  and  6  very  fine  sand.  Wollny  makes  his 
medium  sand  from  0.5  to  0.25  and  his  fine  sand  0.25  to  o.i.  From 
o.i  to  0.05  he  calls  coarse  silt,  from  0.05  to  0.025  medium  silt,  from 
the  last  to  0.005  mm.  fine  silt,  and  below  that  to  o.ooi  mm.  colloidal 
clay.  Orth,  Laufer,  etc.,  call  0.05  to  o.oi  mm.  dust,  and  everything 
below  that  finest  dust.  Wollny  calls  fragments  from  5  to  2  mm. 
medium  gravel,  from  10  to  5  coarse  gravel  and  above  10  mm.  stones. 

Thoulet  has  given  these  dimensions,  gravel:  coarse,  9.0  mm. ; 
medium  4.5  mm.;  fine  3.0  mm.;  sand:  coarse  (a)  1.32  mm.,  (b) 
0.89;  medium  (a)  0.67,  (b)  0.54,  (c)  0.45 ;  fine  (a)  0.39,  (b)  0.34, 
(c)  0.30,  (d)  0.26  mm.;  very  fine  0.04  mm.  Silt  below  0.04  mm.* 

It  will  be  seen  that  Crosby  and  Thoulet  differ  most  from  the 
others,  and  also  from  each  other.  Their  definite  sizes  are  less  sat- 
isfactory than  the  ranges  given  by  the  others. f 

Types  of  Sands  Based  on  Origin. 

Sherzer  (26)  has  recently  proposed  to  subdivide  sands  according 
to  their  mode  of  origin  into  7  groups,  each  with  a  number  of  sub- 
groups. They  are  herewith  given,  separated  into  clastic  and  non- 
clastic  sands,  and  each  is  referred  to  its  proper  place  in  the  classifi- 
cation adopted  in  this  book.  Three  additional  types  are  added  to 
make  the  series  complete  (Grabau-io:  1006). 

A.     Clastic  sands  (Exo genetic). 

1.  Glacial  sand  typej Autoclastic  =  autoarenyte 

2.  Volcanic  sand  type Pyroclastic  =  pyroarenyte 

3.  Residual  sand,  type Atmoclastic  =  atmoarenyte 

4.  Aqueous  sand  type Hydroclastic  =  hydroarenyte 

5.  ^Eolian  sand  type Anemoclastic  =  anemoarenyte 

6.  Artificial  sands  (added) Bioclastic  =  bioarenyte 

B.     Non-clastic  sands  (endogenetic,  see  page  283). 

7.  Organic  sand  type Biogenic  sand  (biogranulyte) 

8.  Concentration  sand  type Hydrogenic  sand  (hydrogranulyte) 

9.  Snow  and  firn  sand  (added) Atmogenic  sand  (atmogranulyte) 

10.  Lapilli  or  igneous  sand  (added) Pyrogenic  sand  (pyrogranulyte) 

*  These  grades  are  numbered  1,2,  etc.,  by  Thoulet. 

t  For  further  analyses  see  the  table  given  under  wind  transportation,  p.  59. 

t  In  this  he  includes  the  material  resulting  in  the  manufacture  of  talus  in 
avalanches,  rock  slides,  rock  and  mud  flows,  and  earth  movements  along  joint 
planes.  All  except  the  first,  which  is  atmoclastic,  belong  under  the  autoclastic 
group  with  the  glacial  sand  type. 


EXOGENETIC    ROCKS  289 

Sherzer  designates  as  subtypes  sands  of  one  type  modified  by 
another  agency  and  calls  them  by  a  compound  term.  Thus  an 
ague o -residual  sand  (hydro-atmoclastic  sand)  is  one  in  which  the 
granules  have  been  produced  by  the  various  residual  agencies,  and 
are  subsequently  more  or  less  modified  by  water  action.  Again  a 
residua-aqueous  sand  (atmo-hydroclastic)  is  one  in  which  water- 
rounded  grains  have  been  subjected  to  the  agencies  of  weathering, 
and  give  more  or  less  evidence  of  such  action.  The  principal  sub- 
types or  intermediate  types  may  be  grouped  as  follows : 


aeolo-aqueous     or     anemohydroclastic 
aeolo-residual     or     anemoatmoclastic 
seolo-volcanic     or     anemopyroclastic 
aeolo-glacial,  etc.     or     anemoautoclastic 
aqueo-aeolian     or     hydroanemoclastic 
aqueo-residual     or     hydroatmoclastic 
aqueo-volcanic     or     hydropyroclastic 
aqueo-glacial,  etc.     or     hydroautoclastic 
residuo-aeolian     or     atmoanemoclastic 
resi  duo-aqueous     or     atmohydroclastic 
residuo-volcanic     or     atmopyroclastic 
residuo-glacial     or     atmoautoclastic 
glacio-aeolian     or     auto-anemoclastic 
glacio-aqueous     or     auto-hydroclastic 
glacio-residual     or     auto-atmoclastic 
glacio-volcanic     or     auto-pyroclastic 


In  all  cases  the  agent  last  modifying  the  type  is  placed  first,  the 
agent  producing  the  original  type  last.  The  organic  elastics  or  bio- 
elastics  are  of  such  recent  origin  that  reworking  by  other  agents  has 
not  occurred  on  an  extensive  scale.  When  it  occurs,  the  coupling 
of  the  respective  prefix  with  bioclastic  will  designate  it.  Reworking 
of  other  sands  by  volcanic  agencies  is  of  so  rare  an  occurrence  that 
such  types  may  be  neglected,  although  in  a  complete  classification 
they  must  be  included. 

The  organic  (biogenic)  and  concentration  or  chemical  (hydro- 
genie)  sand  types  may  also  be  reworked,  producing  seoloorganic 
and  aeolo-concentration  types,  aqueo-organic  and  aqueo-concentra- 
tion  types,  etc. — i.  e.,  the  wind-  or  water-worn  and  the  weathered 
biogenic  and  hydrogenic  sands.  The  characters  of  the  undisturbed 
endogenetic  sands  will  be  more  fully  dealt  with  in  later  chapters. 
The  principles  of  classification  applied  to  sands  may  equally  be  ap- 
plied to  the  coarser  or  rudaceous  material  and  the  finer  or  lutaceous 
matter. 


290  PRINCIPLES    OF    STRATIGRAPHY 

Composition  of  Clastic  Rocks. 

In  composition  clastic  rocks  may  be  pure  or  impure,  simple  or 
complex.  If  one  mineral  type  predominates,  such  as  lime  or  quartz, 
this  fact  may  be  combined  with  the  corresponding  textural  term 
into  a  compound  word  expressive  of  both.  Thus,  if  the  material  of 
the  clastic  rock  is  pure  lime,  the  rock  becomes  a  calcirudyte,  a  cal- 
carenyte  or  a  calcilutyte,  according  to  the  texture.  If  quartz,  the 
rock  becomes  a  silicirudyte,  a  silicarenyte,  or  a  silicilutyte,  accord- 
ing to  the  texture.  If  the  rock  is  impure  it  will  still  be  possible  to 
designate  it,  keeping  in  mind  that  the  dominant  mineral  constitu- 
ent furnishes  the  name.  Thus  we  may  have  siliceous  calcirudytes, 
calcarenytes,  calcilutytes  or  calcareous  silicirudytes,  silicarenytes, 
silicilutytes.  Or  the  impurities  may  be  iron,  carbon,  clay,  etc.,  in 
which  case  we  use  the  prefixes  ferruginous,  carbonaceous,  argil- 
laceous, etc. 

Lutytes  are  most  generally  formed  among  the  argillaceous  or 
clay  rocks,  but  pure  argillutytes  are  not  very  common.  Generally 
they  are  siliceous,  calcareous  or  carbonaceous  argillutytes,  all  of 
which  are  more  familiarly  known  by  the  structural  terms  shales  or 
slates,  which  terms,  however,  express  nothing  definite  in  regard  to 
the  composition. 

Clastic  rocks  of  complex  composition,  as,  for  example,  those 
formed  from  the  reconsolidation  of  disintegrated  granites  (ark- 
oses),  can  be  spoken  of  simply  as  rudytes,  arenytes,  or  lutytes, 
without  attempt  at  defining  their  composition. 

Examples  of  elastics  under  each  group  are  as  follows : 

i.  THE  PYROCLASTICS.  In  composition  these  are  seldom  simple, 
being  mostly  complex  siliceous  rocks  shattered  by  volcanic 
explosions.  The  more  or  less  indefinite  terms  tuff,  volcanic 
breccia  and  agglomerate  are,  commonly  used.  The  essential 
types  are : 

Pyrorudytes:  coarse,  chiefly  angular  volcanic  blocks  and 
bombs,  loose  or  recemented  by  finer  material — volcanic 
breccias  and  agglomerates. 

Pyr arenytes:  coarse  tuffs  where  the  grain  is  not  above  the 
size  of  the  ordinary  sand  grain  (2  mm.).  They  gener- 
ally show  rude  stratification  and  may  contain  organic  re- 
mains. (Vide,  the  buried  cities  and  human  remains  in 
the  tuffs  of  Vesuvius  and  other  volcanoes.) 
Pyrolutytes:  fine  tuffs  composed  of  volcanic  dust  and 
ashes.  Stratified,  and  enclose  remains,  as  in  the  case  of 
pyrarenytes. 


PYROCLAST1CS    AND    AUTOCLASTICS  291 

Volcanic  sand  is  characterized  by  irregular  and  sharply  angular 
outline,  giving  no  evidence  of  erosion  except  in  the  case  of  the 
larger  particles,  where  partial  rounding  from  mutual  attrition  dur- 
ing suspension  occurs.  The  sands  are  comparatively  well  sorted, 
according  to  size,  the  finest  material  being  often  carried  far 
away.  More  or  less  well  defined  crystals  are  generally  visible  un- 
der the  microscope,  but  as  a  rule  much  of  the  material  is  amorphous, 
showing  flow  structure  or  vesicular  character.  (26 :  629,  with  refer- 
ences.) Subsequent  modification  and  rounding  by  water  or  air 
gives  us  hydropyroclastics  and  anemopyro  elastics,  while  weathering 
produces  atmopyro  elastics.  When  water  laid,  remains  of  marine  or 
fresh- water  organisms  may  be  enclosed  in  these  strata,  or  drifted 
land  organisms  may  be  entombed,  as  in  the  case  of  the  Tertiary 
"Lake  beds"  of  Florissant,  Colorado. 

2.  THE  AUTOCLASTICS.  This  group  comprises  all  rocks  shat- 
tered or  crushed  within  the  earth  either  by  pressure  of  one 
mass  upon  the  other,  or  by  movement  of  rocks  over  each 
other.  Fault-breccias  and  the  material  of  the  "crush  zones" 
must  be  classed  here,  as  well  as  fragments  produced  by 
avalanches.  Earthquake-shattered  rocks  may  also  be  in- 
cluded, though  they  may  likewise  be  considered  transitional 
to  the  pyroclastics.  By  far  the  most  important  autoclastic 
products,  however,  are  those  resulting  from  glacial  erosion. 
Ice,  including  all  the  material  frozen  in  it,  is  a  part  of  the 
earth's  crust  while  it  exists,  and  hence  any  material  ground 
up  between  the  ice  and  the  rock  on  which  it  moves  is  of  the 
type  of  the  material  crushed  between  other  moving  rock 
masses  (ex.  fault  breccia).  Furthermore,  since  all  ice-trans- 
ported material  has  received  its  most  characteristic  features 
from  that  agent,  we  may  with  propriety  include  such  material 
in  this  group,  even  though  it  was  originally  broken  by  atmos- 
pheric agencies.  Such  rocks,  if  determinable,  would  come 
under  the  compound  heading,  auto-atmoclastic. 

Fault  breccias  or  autorudytes  partake  of  the  composition  of  the 
rocks  from  which  they  were  formed,  with  probably  slight  changes 
due  to  secondary  modifications.  In  limestones  there  may  thus  occur 
pure  autocalcirudytes,  while  among  pure  quartz  rocks  autosilici- 
rudytes  may  occur.  In  general,  however,  the  composition  of  auto- 
clastic  rocks  is  quite  impure,  and  this  is  particularly  the  case  in  the 
autorudytes  and  other  types  which  result  from  the  consolidation  of 
glacial  deposits.  The  latter  are  of  the  most  importance  to  the 
stratigrapher,  for  there  can  be  little  doubt  that  they  are  represented 


292  PRINCIPLES    OF    STRATIGRAPHY 

in  many  of  the  geologic  periods  of  the  earth's' history.  Autorudytes 
of  glacial  origin,  when  unaffected  by  other  agents,  are  characterized 
by  the  polished  and  striated  surfaces  of  the  boulders,  larger  pebbles 
and  cobbles.  Flat  blocks  generally  have  only  two  sides  striated, 
while  the  margins  may  remain  angular.  The  characteristic  striation 
Js  soon  lost  through  subsequent  wear  by  streams  from  the  ice,  the 
material  thus  becoming  hydroclastic  (potamoclastic).  The  charac- 
teristics of  glacial  sands,  whether  derived  from  the  crushing  of 
igneous  or  of  clastic  rocks,  lie  chiefly  in  their  angularity  and  fresh- 
ness of  grain,  unless  subsequent  weathering  has  attacked  these.  If 
the  material  is  derived  through  crushing  of  igneous  or  other  crystal- 
line rocks,  it  will  show  a  variety  of  mineral  grains.  The  quartz 
grains  will  be  sharp-edged  and  pointed,  with  strongly  vitreous  and 
conchoidal  surfaces,  while  the  cleavable  minerals  will  show  fresh 
cleavage  faces  as  well  as  sharp  outlines.  (Sherzer-26:d?j.) 
When  pure  clastic  rocks  such  as  sandstones  are  crushed  by  ice  the 
resulting  material  will  be  pure,  with  sharply  angular  grains,  which 
may  or  may  not  be  derived  from  originally  rounded  grains. 

Glacial  boulders  and  sands  are  frequently  reworked  by  the 
glacial  streams  and  so  become  hydroautoclastic  or  aqueo-glacial 
(Sherzer).  The  finer  rock  flour,  etc.,  may  be  reworked  by  wind 
and  so  become  anemo-autoclastic  or  aeolo-glacial  (ex.  loess).  See 
further,  Chapters  XII  and  XIII. 

3.  THE  AT^OCLASTICS.  These  comprise  rocks  broken  in  situ, 
either  by  chemical  or  mechanical  means,  and  recemented 
without  further  rearrangement  by  wind  or  water.  Most  of 
the  rocks  of  this  type  are  of  complex  composition,  and  there 
is  a  characteristic  angularity  in  the  coarser  material  which 
shows  the  absence  of  water.  Stratification  also  is  coarse  or 
absent  altogether.  Characteristic  examples  are  found  in  talus 
breccias,  which  when  consolidated  form  typical  atmorudytes ; 
in  the  extensive  subaerial  accumulations  of  waste  along 
slopes  of  most  mountains,  and  in  many  of  the  Tertiary  and 
earlier  subaerial  deposits,  which  were  neither  windlaid  nor 
deposited  in  water  bodies.  Remains  of  land  plants  and 
animals  are  often  characteristic  of  these  rocks.  The  kaolinite 
and  laterite,  i.  e.,  decomposition  products  which  mantle  the 
rock  in  unglaciated  regions,  when  consolidated,  also  form 
typical  examples  of  atmoclastic  rocks. 

The  composition  of  atmoclastic  rocks  varies,  of  course,  greatly, 
according  to  the  nature  of  the  rock  from  which  they  are  derived, 
and  the  complication  of  the  atmospheric  processes  involved.  Under 


ATMOCLASTICS    AND    ANEMOCLASTICS          293 

* 

arid  climatic  conditions  mechanical  disintegration  will  predominate, 
especially  in  the  case  of  crystalline  rocks.  Through  differential  ex- 
pansion and  contraction  under  heat  and  cold  the  minerals  of  the 
rock  will  become  separated  and  a  mixed  sand  results,  in  which  the 
minerals  have  sharp  outlines,  owing  to  splintering  along  cleavage 
planes.  Reconsolidation  of  such,  a  sand  produces  arkoses,  which, 
as  in  the  case  of  the  Torridon  sandstone  of  Scotland,  may  have 
all  the  appearance  of  an  igneous  rock.  In  moist  climates  chemical 
alteration  or  decomposition  of  the  feldspars  (Mackie-iQ:^//^)  and 
other  decomposable  minerals  will  set  in,  resulting  eventually  in  the 
production  of  clay,  etc.,  in  which  quartz  and  mica  abound.  The 
chief  processes  in  this  chemical  destruction  or  decomposition  'of 
rock  minerals  consist  of  oxidation  (and  deoxidation),  hydration 
(and  dehydration),  and  carbonation;  silication  and  desilication  may 
also  occur  and  solution  of  minerals  also  belongs  here.  (Van  Hise- 
28:461.)  Under  rainy  or  pluvial  conditions  the  clay  and  mica  will 
be  removed,  the  latter  suffering  mechanical  destruction,  while  the 
quartz  will  become  mechanically  concentrated.  When  not  modified 
by  subsequent  water  or  wind  activities,  the  quartz  and  other  resist- 
ant mineral  grains  will  be  found  fresh  and  angular,  without  evi- 
dence of  subsequent  rounding,  while  complete  crystals  of  idio- 
morphic  minerals  of  the  crystalline  rock  are  among  the  resulting 
constituents.  When  modified  by  subsequent  agents,  various  sub- 
types are  produced,  namely,  hydro-atmoclastic,  anemo-atmoclas- 
tic,  etc. 

4.  THE  ANEMOCLASTICS.  These  are  the  wind-laid  deposits 
which  are  often  of  great  extent,  and  are  of  great  importance 
to  the  stratigrapher.  Anemorudytes  are  probably  unknown, 
but  anemoarenytes  and  anemolutytes  are  widely  distributed. 
Some  familiar  examples  are  anemosilicarenytes  represented 
by  solidified  sand  dunes  of  quartz  sand;  anemocalcarenytes, 
such  as  the  consolidated  wind-blown  or  seolian  rocks  of  Ber- 
muda in  which  the  sand  grains  are  wholly  calcium  carbon- 
ate; and  the  complex  anemolutytes  forming  extensive  de- 
posits of  aeolian  dust,  chiefly  of  volcanic  matter,  in  the  Ter- 
tiary strata  of  North  and  South  America,  and  in  which  some 
of  the  best  preserved  remains  of  mammals  have  been  found. 
These  deposits  approach  and  grade  into  the  pyrolutytes  which 
form  in  volcanic  regions,  and  in  fact  it  becomes  a  matter  of 
opinion  where  the  line  between  the  two  is  to  be  drawn.  The 
wind-laid  loess  is  also  a  good  example  of  an  impure  anemo- 
lutyte. 


294  PRINCIPLES    OF    STRATIGRAPHY 

In  form,  anemoclastic  sand  grains  are  apt  to  be  more  thor- 
oughly rounded  and  worn  than  similar  grains  worn  by  water.  In 
.general,  rounding  of  superfine  sand,  i.  e.,  grains  below  o.i  mm.,  is 
not  accomplished  by  water  (Chamberlin  and  Salisbury—  i  '.24.6 >; 
Daubree-5  '.256} ,  but  such  grains  may  readily  be  rounded  in  air. 
As  shown  by  Mackie  (see  Chapter  V),  particles  of  quartz  sand, 
less  than  one-fifth  the  diameter  of  those  rounded  by  water,  will  be 
rounded  to  an  equal  extent  by  wind.  Pitting  and  frosting  of  the 
surface  is  another  characteristic  result  of  aeolian  activity,  as  is 
also-  assortment  according  to  size  of  grain  and  specific  gravity  of 
mineral,  so  that  in  a  typical  seolian  sand  the  grains  are  of  approxi- 
mately uniform  size,  and  of  the  same  mineral  throughout,  generally 
quartz. 

Most  seolian  sand  and  dust  is  derived  from  some  other  type  of 
sand,  such  as  residual  material  (anemoatmoclastic),  glacial  sand 
(anemoautoclastic),  river  or  beach  sand  (anemohydroclastic),  or 
volcanic  sand  (anemopyroclastic).  Extensive  deposits  of  anemobio- 
clastic  sands  may  accumulate  around  quarries,  etc.,  especially  where 
stone  is  crushed  for  road  material.  Where  the  reworking  by  wind 
has  been  extensive,  the  evidence  of  the  original  character  may  be 
destroyed.  ^Eolian  sand  in  a  state  of  rest  may  have  its  grains 
coated  with  iron  oxide,  as  in  the  case  of  the  red  sand  of  the 
Arabian  desert.  (Philipps-23  :uo.) 

5.  THE  HYDROCLASTICS.  These  comprise  by  far  the  larger  num- 
ber of  clastic  rocks.  They  are  the  water-laid  deposits  and 
include  the  following  common  types : 

a.  Hydrorudytes,    or   conglomerates    of   variable   compo- 

sition. 

b.  Plydrosilicirudytes,  or  pure  quartz  conglomerates,  and 

various  varieties  due  to  admixture  of  simple  mineral 
matter. 

c.  HydrocalcirudyteSf  or  pure  lime  conglomerates  and  the 

varieties  due  to  iron,  silica  or  other  simple  impurities 
in  the  paste. 

d.  Hydrarenytes,  or  water-laid  sandstones  of  variable  com- 

position. 

e.  Hydrosilicarenytcs,  or  pure  quartz  sandstones  with  va- 

rieties due  to  simple  admixtures  in  the  paste. 

f.  Hydrocalcarenytes,  or  pure  lime  sandstones  with  vari- 

eties as  above. 

g.  Hydrolutytes,  or  water-laid  mud  beds  of  variable  com- 

position. 


HYDROCLASTICS  295 

h.  Hydrargillutytes,  or  pure  clay  beds  and  varieties  due  to 
the  presence  in  small  amounts  of  silica,  lime,  iron,  or 
carbon. 

i.  Hydrosilicilutytes,  or  pure  quartz-mud  rocks,  with  their 
varieties  due  to  a  slight  admixture  of  argillaceous, 
calcareous,  carbonaceous,  glauconitic,  or  ferruginous 
matter. 

j.  Hydrocalcilutytes,  or  pure  lime-mud  rocks,  with  their 
varieties  due  to  a  slight  admixture  of  argillaceous, 
siliceous,  carbonaceous  or  ferruginous  matter. 

The  prefix  "hydro"  in  all  these  cases  is  omitted  when  it  is 
understood  that  the  rocks  are  water-laid  deposits.  This  is  the  class 
of  rocks  with  which  the  stratigrapher  has  most  to  deal,  for  they 
comprise  by  far  the  largest  portion  of  the  sedimentary  rocks,  and 
they  most  commonly  contain  organic  remains  in  greater  or  less 
abundance.  In  general,  hydrorudytes  have  their  pebbles  rounded, 
the  degree  of  rounding  depending  on  the  length  of  time  that  the 
pebbles  have  been  subject  to  water  wear,  the  character  of  the  mate- 
rial, the  intensity  of  the  abrading  force,  etc.  Extensive  and  pro- 
longed wave  or  current  action  will  further  result  in  eliminating 
much  if  not  all  of  the  perishable  mineral  matter,  so  that  a  much- 
worked-over  conglomerate  will  consist  largely  or  wholly  of  quartz 
pebbles.  The  same  is  true  of  the  arenytes,  although  the  sorting 
here  is  not  so  pronounced  as  that  by  the  wind.  Pure  hydroclastic 
quartz  sands  do  occur,  however,  as  at  Escambia,  on  the  Gulf  coast 
of  Florida,  in  which  scarcely  a  fragment  of  mineral  other  than 
quartz  is  found.  The  granules  of  this  sand  range  in  size  from  o.i 
to  i.o  mm.  (fine  to  coarse  sand,  averaging  0.25  to  0.50  mm.  (me- 
dium sand).  At  West  Palm  Beach,  on  the  Atlantic  coast  of  Flor- 
ida, a  similar  pure  sand  occurs  which  apparently  has  been  trans- 
ported along  the  shore  from  the  Piedmont  region  to  the  north.  In 
both  of  these  cases  the  grains  are  subangular.  The  finest  sand  and 
the  rock  flour  and  clays  will  retain  their  angular  outlines  unim- 
paired, for,  as  Daubree  has  shown,  quartz  and  other  mineral  par- 
ticles of  o.i  mm.  or  less  diameter  will  float  in  faintly  agitated 
water. 

In  the  broader  considerations  of  hydroclastic  rocks  it  is  impor- 
tant that  current  or  river-worn  elastics  be  distinguished  from 
marine  or  other  wave- formed  elastics.  The  former  may  be  spoken 
of  as  fluvio-clastic  (potamoclastic*)  deposits,  and  the  latter  as  kymo- 
clastic.f  So  far  as  grain  is  concerned,  no  marked  distinction  exists 

*  From  7roTa/*6s,  a  river  and  K\eurr6s,  broken, 
t  From  KW/UCI,  a  wave  and  K\a<rr63,  broken. 


296  PRINCIPLES    OF    STRATIGRAPHY 

in  the  lutaceous  and  arenaceous  types,  but  the  rudaceous  sediments 
of  fluvio-clastic  origin  may  often  be  distinguished  from  those  of 
*  wave-laid  origin  by  minor  characters  of  the  component  material. 
Thus  exceedingly  well-rounded  boulders  of  moderate  size  are  more 
characteristic  of  river  than  of  wave  work.    The  remarkable  percus- 
sion or  shatter  marks  (Schlagnarben)  found  on  fine-grained  boul- 
ders transported  by  torrents  are  further  to  be  noted.    They  consist 
of  semicircular  or  crescent-shaped  slits,  appearing  as  if  made  by  a 
thumb  nail,  and  crossing  each  other  or  interlocking  in  an  indeter- 
minate manner.     They  are  due  to  a  sudden  blow  upon  the  smooth 
surface  from  a  rounded  pebble  or  boulder  of  equally  hard  rock. 
6.    THE  BIOCLASTICS.     These  are  the  clastic  rocks  which  owe 
their  essential  character  to  organisms.     The  only  class  of 
great  importance  is  that  for  which  man  is  responsible.    Thus 
bricks   (as  material),  plaster,  concrete,  cement,  etc.,  are  no 
mean  portion  of  the  material  composing  the  uppermost  lay- 
ers of  the  earth's  crust,  and  are  all  to  be  included  with  the 
bioclastic  division  of  rocks. 

SUMMARY  OF  "SEDIMENTARY  ROCKS." 

The  following  table  shows  the  more  familiar  types  of  "sedi- 
mentary"  rocks,  with  the  more  important  species  included  under 
each: 
i.     Conglomerates  "j  f  Hydrorudytes 

or  -j  Hydrosilicirudytes 

Puddingstones.  J  I  Hydrocalcirudytes 

Pyrorudytes  (agglomerates) 
Autorudytes 
Autosilicirudytes 
Autocalcirudyt.es 
Atmorudytes 
Atmosilicirudytes 
Atmocalcirudytes 
.  Biorudytes  (artificial  rubble  rock) 

Autoarenytes 

Autosilicarenytes 

Atmosilicarenytes 


2.    Breccias. 


3.     Sandstones. 


Anemosilicarenytes 
Hydrarenytes 
Hydrosilicarenytes 
;  Bioarenytes  (artificial  sandstones) 


SUMMARY   OF    SEDIMENTARY    ROCKS 


297 


Slates. 
Shales. 
Mud  rocks 

and 

Clay  stones 
(argillytes)  ., 


5.     Tuffs. 


6.    Limestone 
(calcilytes) 

and 
Dolomites. 


Autolutytes  (argillaceous) 

Autosilicilutytes  (argillaceous) 

Autoargillutytes  (pure,  siliceous,  cal- 
careous or  carbonaceous) 

Atmolutytes   (argillaceous) 

Atmoargillutytes  (pure,  siliceous,  cal- 
careous, or  carbonaceous) 

Anemolutytes   (argillaceous) 

Anemoargillutytes  (pure,  siliceous, 
calcareous,  or  carbonaceous) 

Anemosiliciluty tes   ( argillaceous ) 

Hydrolutytes  (argillaceous) 

Hydrargillutytes  (pure,  siliceous,  cal- 
careous, or  carbonaceous) 

Pyrarenytes 
Pyrolutytes 

Hydrogenic    calc-rocks    (Hydrocalci- 

lytes)    (chemical   limestones) 
Biogenic     calc-rocks     (Biocalcilytes) 

(coral    rock,    shell    rock,    oozes, 

etc.) 
Autocalcirudytes, 

calcilutytes 
Atmocalcirudytes,    calcarenytes,    and 

calcilutytes 

Anemocalcarenytes  and  calcilutytes 
Hydrocalcirudytes,   calcarenytes,   and 

calcilutytes 


calcarenytes,     and 


THE  COSMOCLASTIC  ROCKS. 

This  term  has  been  proposed  by. Prof.  H.  L.  Fairchild  for  the 
original  rocks  of  the  earth,  which,  according  to  the  Planetesimal 
hypothesis  of  earth  origin,  were  formed  through  accretion  of  frag- 
ments derived  from  space.  (Fairchild-8;  Chamberlin  and  Salis- 
bury-2,  ii,  Chapter  I.) 

SPECIAL  ROCK  TERMS. 

Rock  Terms  Emphasising  Composition.  It  is  often  necessary 
or  desirable  to  emphasize  the  composition  of  a  rock  rather  than  its 


298  PRINCIPLES    OF    STRATIGRAPHY 

texture  or  origin.  This  is  already  done  in  the  familiar  terms 
limestone,  claystone,  ironstone,  etc.  While  these  terms  are  good 
and  useful,  more  euphonious  technical  terms  might  be  found  pref- 
erable in  some  cases.  Such  terms  should  end  in  ith,  or  yte,  to 
signify  that  they  refer  to  rock  masses  rather  than  minerals.  Thus 
rocks  composed  chiefly  of  the  mineral  calcite,  or  whatever  origin, 
i.  e.,  limestones,  may  be  termed  calciliths  or  calcilytes. 
Thus  we  may  have : 

quartz  rocks  or  siliciliths  or  silicilytes 

limestones  or  calciliths  or  calcilytes 

dolomite  rock  or  dolomiths  (dolomiliths)  or  dolomytes  (dolomilytes) 

gypsum  rock  or  gypsolith  or  gypsolytes 

claystones  or  rocks  or  argilliths  or  argillytes 

iron  stones  or  ferriliths  or  ferrilytes 

carbon  rocks  (coals,  peats,  etc.)  or  carbonoliths  or  carbonolytes 

rock  salt  or  haliliths  or  halilytes 

Autochthonous*  and  Allochthonous^  Deposits.  These  terms 
were  first  introduced  by  Giimbel  in  1883  to  designate :  the  first, 
deposits  (especially  coal)  formed  in  situ,  and  the  second,  deposits 
made  from  transported  material.  The  first  comprises  all  hydro- 
genie  and  many  biogenic  deposits,  although  deep-sea  oozes  are  al- 
lochthonous.  Coal  formed  from  vegetation  in  situ  is  autochtho- 
nous, while  transported  vegetal  matter  forms  allochthonous  coal. 
Clastic  deposits  are  typically  allochthonous. 


BIBLIOGRAPHY  VI. 

1.  CHAMBERLIN,  T.  C.,  and  SALISBURY,  R.     Preliminary  paper  on  the 

driftless  area  of  the  Upper  Mississippi  Valley.  Sixth  annual  report, 
U.  S.  Geological  Survey,  pp.  199-322. 

2.  CHAMBERLIN,  T.  C.,  and  SALISBURY,  R.     1906.     Geology,  Vols.  I 

and  II. 

3.  CROSBY,  W.  O.     1908.     Report  of  the  State  Water  Supply  Commission. 

Progress  Report  for  1907,  p.  205. 

4.  CROSS,  WHITMAN  ;  IDDINGS,  JOSEPH  P.  ;  PIRSSON,  LOUIS,  V.,  and 

WASHINGTON,  HENRY  S.  1903.  Quantitative  Classification  of 
igneous  rocks  based  on  chemical  and  mineral  characters,  with  a  systematic 
nomenclature. 

5.  DAUBREE,  A.     1879.     Etudes  Synthetiques  de  Geologie  Experimentale. 

Paris. 


*  avTfc  (autos),  self;   x0(6w  (chthon),  the  earth;   i.e.,  belonging  to   the  same 
earth. 

f  axXos  (allos),  another;  xOuw  (chthori),  the  earth,  i.  e.,  from  another   region. 


BIBLIOGRAPHY   VI  299 

6.  DE  LA  BECHE,  HENRY  T.     1833.     Geological  Manual,  3rd  edition. 

7.  DILLER,  JOSEPH  S.     1898.     The  Educational  Series  of  Rock  Specimens. 

U.  S.  Geological  Survey,  Bulletin  150. 

8.  FAIRCHILD,  H.  L.     1904.     Geology  under  the  Planetesimal  Hypothesis 

of    Earth  Origin.     Bulletin  of  the  Geological  Society  of  America,  Vol. 
XV,  pp.  243-266. 

9.  GRABAU,    A.  W.     1904.     On  the  Classification  of  Sedimentary  Rocks. 

American  Geologist,  Vol.  XXXIII,  pp.  228-247. 

10.  GRABAU,  A.  W.     1911.     On  the  Classification  of  Sand  Grains.     Science, 

N.  S.,  Vol.  XXXVII,  pp.  1005-1007. 

11.  HARKER,  ALFRED.     1902.     Petrology  for  Students.     3d  edition,  Cam- 

bridge Natural  Science  Manuals. 

12.  HARKER,  ALFRED.     1909.     The  Natural  History  of  the  Igneous  Rocks. 

New  York,  Macmillan  Co, 

13.  HARRIS,  G.  F.     1898.    Narrative  of  a  Geological  Journey  through  Russia 

(Rapakiwi  described.)     Geological  Magazine,  Vol.  XXXV,  pp.  11-13. 

14.  HAUG,    EMILE.     1907.     Traite  de  Geologic.     I.    Les  Phenomenes  geo- 

logiques.     Paris,  Armand  Colin. 

15.  IDDINGS,  J.  P.,  and  Others.    1899.   Descriptive  Geology,  Petrography,  etc., 

of  the  Yellowstone  National  Park.     U.  S.  Geological  Survey,  Monograph 
XXXII,  pt.  II. 

16.  KEILHACK,    KONRAD.     1908.     Lehrbuch   der    praktischen    Geologic, 

2te  Auflage.     Stuttgart,  Ferdinand  Enke. 

17.  KEMP,  JAMES  F.    1900.   A  Handbook  of  Rocks,  without  the  Microscope. 

New  York,  D.  Van  Nostrand  &  Co.     Second  edition.     191 1,  5th  ed. 

18.  LAUFER,  E.,und  WAHNSCHAFFE,  F.    1879.    (Classification  of  Sands.) 

Abhandlungen  zur  geologischen  Special  Karte  von  Preussen.      Bd.  Ill,  i, 
p.  24. 

19.  MACKIE,    WILLIAM.      1897.     The   feldspars   present   in   sedimentary 

rocks  as  indicators  of  the  conditions  of  contemporaneous  climate.     Trans- 
actions of  the  Edinburgh  Geological  Society,  Vol.  VII,  pp.  443-468. 

20.  MERRILL,  GEORGE  P.     1898.     Mechanical  analysis  of  residual  sand 

of  diabase  and  of  washed  kaolin.     Bulletin  150,  U.  S.  Geological  Survey, 
pp.  380  and  383. 

21.  NAUMANN,    CARL   FRIEDRICH.      1850.      Lehrbuch  der  Geognosie. 

Second  edition  1858. 

22.  ORTH.     1875.     Bezeichnung  des  Sandes  nach  der  Grosse  des   Kornes. 

Neues  Jahrbuch  fur  Mineralogie,  Volume  for  1875,  p.  551. 

23.  PHILIPPS,    J.   ARTHUR.     1882.     The   sands   of   the   Arabian    Desert. 

Quarterly  Journal  of  the  Geological  Society  of  London,  Vol.  XXXVIII, 
pp. 110-113. 

24.  ROSENBUSCH,  H.     1877.     Mikroskopische  Physiographic  der  Massigen 

Gesteine.    Stuttgart.    Schweizerbart'sche  Verlagshandlung.    4th  edition 
in  1908. 

25.  ROSENBUSCH,     H.     1898.     Elemente     der     Gesteinslehre.     Stuttgart. 

Schweizerbart'sche  Verlagshandlung. 

26.  SHERZER,  W.  H.     1910.     Criteria  for  the  recognition  of  the  various  types 

of  sand  grains.      Bulletin   Geological  Society  of  America,    Vol.    XXI, 
pp.  628-662,  pis.  43-4£- 

27.  THOULET,  J.     1 88 1.     Etude  mineralogiquc  d'au  sable  de  Sahara.     Bul- 

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28.  VAN   HISE,   C.  R.     1904.     A  treatise  on  metamorphism.     Monograph 

U.  S.  Geological  Survey,  No.  XLVII. 


300  PRINCIPLES    OF    STRATIGRAPHY 

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30.  '  WALTHER,   JOHANNES.     1897.     Versuch   einer  classification  der  Ge- 

steine  auf  Grund  der  Vergleichenden  Lithogenie.  Congres  Geologique 
International.  Compte  Rendu  de  la  VIIme  session,  St.  Petersburg,  1897, 
3me  partie.  pp.  9-25. 

31.  ZIRKEL,  FERDINAND  VON.     1866.     Lehrbuch  der  Petrographie.    2nd 

ed.  1893,  Leipzig. 

Supplementary. 

32.  FINLAY,  GEORGE  I.       1913.      Introduction  to  the  Study  of  Igneous 

Rocks.     McGraw  Hill  Book  Co.,  New  York. 


CHAPTER   VII. 

STRUCTURAL  OR  TECTONIC  FEATURES  OP  ROCK  MASSES. 
ORIGINAL  STRUCTURES  AND  LITHOGENESIS  OF  THE  PYRO- 
GENIC  ROCKS. 

When  rock  masses  are  considered  on  a  large  scale,  certain  struc- 
tural features  are  seen  which  furnish  a  clue  to  the  geological  his- 
tory of  the  region.  These  can  generally  be  observed  only  in  the 
field.  Two  classes  of  such  structural  or  tectonic  features  are  recog- 
nized:  (i)  original  structures  and  (2)  secondary  or  later  struc- 
tures. To  the  first  belong  all  those  accompanying  the  phenomena 
of  rock  formation,  features  of  essential  significance  in  the  study  of 
the  origin  of  the  formation  which  they  characterize.  To  the  second 
belong  all  structures  due  to  subsequent  disturbances  such  as  faults, 
folds,  cleavage,  and  the  like,  as  well  as  metamorphism,  or  the  alter- 
ation of  rocks.  While  all  these  need  to  be  carefully  considered  in 
working  out  the  stratigraphy  of  any  region,  they  have  not  the  im- 
portance possessed  by  the  original  structures,  which  alone  furnish 
clues  to  the  method  of  formation  of  the  rock  possessing  them.  In 
this  and  the  next  eleven  chapters  the  Original  Structures  of  rocks 
will  be  discussed;  the  secondary  ones  will  be  taken  up  in  Chapters 
XIX  and  XX.  Since  each  class  of  endogenetic  rocks  has  its  own 
mode  of  origin,  the  original  structures  of  each  must  be  of  corre- 
sponding individuality. 

THE  PYROGENIC  ROCKS. 

Pyrogenic  or  igneous  rock  masses  naturally  fall  into  two  great 
divisions,  (a)  the  intrusive  and  (b)  the  effusive.  The  former 
solidify  within  the  crust  of  the  earth,  appearing  as  a  part  of  the 
surface  only  through  subsequent  erosion  of  the  overlying  masses, 
while  the  latter  reach  the  surface  in  a  molten  condition,  and  on 
solidifying  form  the  uppermost  crust  of  the  earth  at  that  point. 
In  otherwise  undisturbed  regions  intrusive  igneous  masses  are  al- 
ways younger  than  the  enclosing  rocks,  while  effusive  igneous 

301 


302 


PRINCIPLES    OF    STRATIGRAPHY 


masses  are  younger  than  the  subjacent,  but  older  than  the  super- 
jacent  strata. 

INTRUSIVE  IGNEOUS  BODIES. 

The  classification  of  intrusive  igneous  bodies  as  structural  fea- 
tures must  be  based  primarily  on  their  origin,  form,  and  relation 
to  enclosing  rock  masses,  while  size  and  attitude  with  reference  to 
horizontal  plane  are  criteria  of  minor  significance.  (Daly— 7:505.) 


A  A  A 

AAAAA   Olorlt* 


FIG.  40.  Diagrammatic  map  and  section  of  Ascutney  Mountain,  Vermont, 
illustrating  a  composite  stock  of  successive  intrusions,  in  stock  or 
boss  form,  of  diorite,  syenite,  and  granite.  A  small  boss  of 
syenite  (shown  in  black)  cuts  the  diorite.  These  bodies  cut  crys- 
talline schists,  the  attitude  of  which  is  shown  by  the  dip-strike 
symbols.  (After  Daly.) 

From  the  point  of  view  of  origin,  or  method  of  intrusion,  two 
great  divisions  of  igneous  intrusive  masses  may  be  recognized,  (a) 
the  abyssal,  deep-seated,  or  plutonic  (Tiefengesteine) ,  the  method 
of  intrusion  of  which  may  be  either  a  process  of  eating  into  the 
enclosing  rocks  (einfressen) ,  or  a  pushing  aside  of  the  surround- 
ing rocks,  and  (b)  the  injected  masses,  the  Ganggesteine  of  Rosen- 
busch,  the  Hypabyssal  division  of  Brogger.  The  abyssal  division 


INTRUSIVE    IGNEOUS    BODIES  303 

includes  two  types,  i.  The  Batholith  and  2.  the  Stock  and  Boss. 
The  distinction  between  these  two  groups  is  largely  one  of  size. 
Batholiths  are  large  intruded  masses  of  granitic  or  other  holocrys- 
talline  pyrogenics,  such  as  form  the  central  granite  core  of  mountain 
masses.  Suess  holds  that  these  masses  are  intruded  through  the 
adjacent  formations  as  a  result  of  fusion,  constituting  thus  a 
transfusion  mass  or  Durchschmelsungsmasse.  A  boss  (Fig.  40)  is 
a  subterranean  intrusive  mass  of  moderate  size  with  a  circular  or 
subcircular  ground  plan.  The  term  has  been  used  for  such  masses 
up  to  several  miles  in  diameter,  but  is  best  restricted  to  the  smaller 


\  - -*  * 
.'"'I:    , \\\ 


FIG.  41.     Ideal  section  of  the  Holmes  Bysmalith   (after  Iddings). 

masses  of  this  type.  A  stock,  on  the  other  hand,  is  characterized  by 
irregularity  of  shape,  and  often  by  smaller  size  than  that  of  the 
boss. 

The  Hypabyssal  intrusives  may  be  divided  into : 

I.     The  transverse  or  those  injected  across  the  planes  of  stratifi- 
cation of  the  invaded  formation,  and 

II.     The  parallel  or  those  injected  along  the  planes  of  stratification 
of  the  invaded  formation.     (Daly~7  :  507.) 

The  first  of  these  groups  includes,  I.  Dikes,  2.  Eruptive  veins, 
3.  Apophyses  or  tongues,  4.  Bysmaliths,  5.  Necks,  and  6.  Chono- 
liths.  A  dike  (Fig.  44)  is  characterized  by  nearly  or  quite  paral- 
lel walls,  relatively  close  together,  and  may  cut  the  planes  of  strati- 


304 


PRINCIPLES   OF   STRATIGRAPHY 


fication  at  any  angle  except  parallelism.  Dikes  may  be  simple  or 
complex.  In  the  latter  case,  they  are  multiple  when  successive  in- 
trusions of  the  same  material  occur  in  the  same  fissure;  and  com- 
posite when  showing  successive  injections  of  different  material  in 
the  same  fissure.  Eruptive  veins  are  injections  into  irregular  branch- 
ing cracks,  while  apophyses  are  tongues  of  igneous  matter  pro- 
jecting irregularly  into  the  rock  from  a  larger  intrusive  mass.  A 
bysmalith  (Iddings-i7  :?o8)  (Fig.  41)  is  an  injected  mass  of 


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FIG.  42.     Section  of  a  typical  volcanic  neck.     (After  Geikie,  Ancient  Volcanoes 
of  Great  Britain,  Vol.  II.) 

igneous  rock  filling  a  more  or  less  circular  cone  or  cylinder  in 
strata,  and  having  the  form  of  a  plug.  This  plug  may  reach  the 
surface  or  may  end  against  a  domed  roof  of  strata,  simulating  a 
laccolith  in  appearance.  It  differs  from  other  masses  of  this  type 
in  that  the  enclosing  strata  have  been  displaced  by  faulting,  a  solid 
block  of  nearly  horizontal  strata  being  lifted  at  one  time  by  the 
force  of  the  intrusions.  The  Holmes  bysmalith  of  the  Yellowstone 
is  a  typical  example.  With  laccoliths  this  type  agrees  in  having  a 
more  or  less  well-defined  floor  of  other  rock  on  which  it  rests. 
Necks  (Fig.  42)  are  the  solid  plugs  of  lava  filling  old  volcanic 
vents.  They  are  generally  regular  in  outline  and  section.  Chono- 
liths  (Daly-7:^p#)  (Fig.  43)  are  the  intrusive  masses  injected 
into  actual  or  potential  cavities  formed  by  dislocation  of  rock 
formations  such  as  is  brought  about  during  mountain  building,  and 
not  classifiable  as  dikes,  sills,  or  laccoliths,  bysmaliths,  or  necks. 
They  are  of  irregular  form,  and  show  a  complex  relation  to  the 
invaded  formation.  In  the  process  of  injection  they  may  crowd 
aside  and  mash  the  country  rock,  intruding  irregularly  into  all  the 
fissures  thus  formed.  Of  the  intruded  igneous  masses  this  is  per- 
haps the  commonest  kind. 

The  second  group  or  that  of  the  parallel  hypabyssal  igneous 
masses  comprises,  I.  Intrusive  sheets,  II.  Laccoliths,  and  III. 
Phacoliths.  The  first  of  these  includes  (a)  sills,  and  (b)  interfor- 


INTRUSIVE    IGNEOUS    BODIES 


305 


inational  sheets.     Sills  are  sheets  intruded  between  parallel  strata. 
They  have  essentially  the  characters  of  dikes,  except  that  they  are 


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FIG.  43.  Diagrammatic  map  of  a  Tertiary  "chonolith"  of  thombenporphyry 
(crosses),  cutting  intensely  folded  Palaeozoic  sediments  (broken 
lines)  and  Tertiary  sandstones  and  conglomerates  (white)  Kettle 
River,  British  Columbia.  (After  Daly.)  Late  Tertiary  lava  caps 
(dots)  cover  the  porphyry  in  the  north.  The  Tertiary  sediments 
are  tilted  and  faulted,  the  intrusions  occurring  at  the  same  time 
or  immediately  after. 

bounded  by  parallel  strata.  Like  dikes,  they  may  be  simple,  mul- 
tiple or  composite.  (Figs.  44,  45.)  Interformational  sheets  differ 
from  sills  in  that  they  are  intruded  along  a  line  of  unconformity, 


FIG.  44.     Section  of  an  intrusive  sheet  or  sill   (s)  and  connecting  dike   (d). 

and  that  therefore  the  subjacent  strata  are  not  parallel  to  it,  though 
the  superjacent  ones  are. 


3o6 


PRINCIPLES    OF    STRATIGRAPHY 


Laccoliths  differ  from  sheets  in  being  lens-like  in  mass,  thick  in 
the  center  and  dying  away  laterally.     In  the  process  of  intrusion 


W.  by  M. 


E.  by  9. 


Sta-lmtl 


FIG.  45.  Section  of  a  composite  sill,  Island  of  Skye  (after  Marker).  The 
stratified  Lias  was  cut  by  the  sill  of  basalt ;  a  later  sill,  of  grano- 
phyre,  was  intruded  along  the  middle  plane  of  the  basic  sill — the 
latter  itself  may  have  been  double. 

the  overlying  strata  are  arched.  Laccoliths  may  be  simple  or  com- 
pound, when  divided  by  strong  beds  of  the  invaded  formation. 
(Judith  Mountains.)  They  may  be  multiple  or  composite  (Fig.  46), 


FIG.  46.  Section  of  a  composite  laccolith.  (After  Weed  and  Pirsson.)  The 
laccolith  cuts  heavy-bedded  lava  flows.  Its  maximum  thickness  is 
150  feet.  Black:  basalt;  white:  granophyre. 

as  in  dikes  and  sills.  Like  sills,  they  may  also  be  interformational. 
(Fig.  47.)  In  form  they  may  be  symmetric  or  asymmetric.  These 
variations  are  illustrated  in  Fig.  51. 


FIG.  47.  Section  of  an  interformational  laccolith.  (After  Weed  and  Pirsson.) 
The  floor  of  the  porphyry  laccolith  (in  black)  is  composed  of  pre- 
Cambric  crystalline  schists;  the  cover,  of  Palaeozoic  sediments. 
The  length  of  the  section  represented  is  about  ten  miles. 


INTRUSIVE   IGNEOUS   BODIES 


307 


Phacoliths    (Harker-i5  :?6)    are    intrusions    of    igneous    rocks 
between  strata  which  have  been  folded  and  occupying  the  points  of 


N.W. 


FIG.  48.  Lenticular  intrusion  (phacolith)  in  anticline  of  Ordovicic  strata, 
Corndon,  Shropshire,  England.  (After  Lapworth  and  Watts.) 
A.  Flags  and  shales;  B.  ashes  and  andesite;  D.  dolerite. 

greatest  pressure  relief,  as  in  the  crests  and  troughs  of  a  simply 
folded  series  of  strata.     (Figs.  48,  49.)     As  Marker  points  out,  they 


FIG.  49.  Diagram  to  illus- 
trate phacolith  intrud- 
ed in  connection  with 
folding.  (After 
Harker.) 


FIG.  Soa.  Hypothetical  development  of  a 
folded  laccolith.  ist  stage. 
(After  Baltzer.) 


differ  from  laccoliths,  in  that  they  are  a  consequence  of  folding, 
instead  of  the  cause  of  the  uplift  as  in  laccoliths.  Their  distinction 
from  the  Chonoliths  of  Daly  lies  in  their  parallelism  to  the  strata 


FIG.  sob.    The  same  as  Fig.  503,  in  the 
second  stage  (Baltzer). 


FIG.  500.    The  same,  in  the  third  stage 
(Baltzer). 


between  which  they  are  intruded,  while  chonoliths  are  irregular, 
commonly,  in  part  at  least,  transverse.  A  typical  example  of  a 
phacolith  is  seen  in  the  accompanying  section  from  Corndon,  Shrop- 


3o8 


PRINCIPLES    OF    STRATIGRAPHY 


shire.  (Lapworth  and  Watts-20 :  342. )  A  remarkable  modifica- 
tion of  such  intrusions  through  later  folding  is  described  by  Balt- 
zer  (i)  from  the  Aarmassive,  in  the  Alps.  In  the  Aletschhorn 
(4,198  meters  high)  he  finds  that  the  schists  which  form  the  summit 
of  the  mountain  rest  discordantly  upon  the  surface  of  the  granite, 


FIG.  51.  Diagrams  illustrating  intrusive  masses.  A.  Laccolith  (Mt.  Holmes, 
Henry  Mts.,  Utah).  B.  Compound  laccolith  (El  Late  Mountains, 
Colorado).  C.  Laccolith  with  subsidiary  sheets  (Judith  Mts. 
type,  Montana).  D.  Laccolith  with  broken  cover  (Ragged  Top 
Mt.,  Black  Hills,  S.  Dakota).  E.  Interformational  laccolith 
(Deadwood  Gulch,  Black  Hills).  F.  Compound  laccolith — cedar- 
tree  type  (La  Plata  Mts.,  Colorado).  G.  Abruptly  protuberant 
laccolith  (Mt.  Hillers,  Henry  Mts.).  H.  Asymmetric  laccolith 
(Mt.  Marcellina,  West  Elk  Mts.,  Colorado).  K.  Intrusion  in 
Little  Rocky  Mts.  (Montana).  L.  Intrusion  in  volcanic  vents 
(Island  Skye).  M.  Bysmalith  (Mt.  Holmes).  N.  Plutonic  plug 
(Ideal).  (After  Harker.) 


CONTACTS    OF    INTRUSIVE    MASSES  309 

i.  e.,  the  relation  is  like  an  inverted  unconformity.  This  relation  is 
believed  to  be  due  to  subsequent  folding  of  the  entire  mass.  The 
process  is  illustrated  in  the  three  diagrams  on  page  307.  (Figs. 
5oa-5oc.) 

The  end  result  is  an  intrusive  mass  which  appears  to  cut  across 
folded  strata  and  so  is  indistinguishable  from  the  Chonoliths  of 
Daly. 

Igneous  versus  Sedimentary  Contact.  It  is  of  the  greatest  im- 
portance that  the  nature  of  the  contact  between  igneous  and  non- 
igneous  formations  be  determined.  Three  types  of  contacts  may 
be  recognized,  i.  Fault  contacts,  2.  Igneous  contacts,  and  3.  Sedi- 
mentary contacts.  Fault  contacts  are  secondary  contacts  and  will 
be  considered  in  a  subsequent  section,  as  they  have  no  direct  bearing 
on  the  history  of  the  igneous  mass.  Igneous  and  sedimentary  con- 
tacts, on  the  other  hand,  are  primary  and  intimately  connected  with 
the  origin  of  one  or  the  other  of  the  formations  in  contact.  The 
igneous  contact  stamps  the  igneous  mass  as  the  younger,  while  the 
sedimentary  contact  shows  the  sedimentary  formation  to  be  the 
younger  of  the  two.  As  a  rule,  when  exposures  are  sufficiently 
good,  the  nature  of  the  contact  is  not  difficult  to  determine  unless 
both  igneous  and  sedimentary  mass  have  subsequently  become  meta- 
morphosed. Sometimes  the  subsequent  intrusion  of  igneous  ma- 
terial along  the  contact  of  an  older  igneous  with  a  sedimentary  for- 
mation obscures  the  nature  of  the  original  contact. 

The  chief  criteria  for  use  in  determining  relative  ages  of  igneous 
intrusive  bodies  in  contact  with  sediments  are  the  following : 


Contacts  of  subterranean  or  abyssal  masses. 

(1)  If  the  granitoid  boss,  stock  or  batholith  is  in  contact  with 
sediments  of  known  age,  and  these  sediments  have  been  metamor- 
phosed or  partly  remelted  by  the  igneous  rock,  which  may  even 
enclose   fragments  of   the  sediment,   then  the  igneous   rock  is  of 
younger  age  than  the  sediments,  which  were  there  before  the  molten 
magma  ate  its  way  into  them. 

(2)  If  sediments  of  a  known  age  rest  unconformably  upon  a 
granitoid  mass  (granite,  syenite,  diorite,  gabbro,  etc.),  worn  frag- 
ments of  which  are  included  in  the  sediments  next  adjoining  the 
igneous  mass,  the  age  of  the  igneous  mass  is  very  much  greater 
than  that  of  the  adjacent  strata,  for  the  igneous  mass  was  exposed 
by  erosion  before  the  sediments  now  resting  upon  it  were  laid  down. 
In  such  case  the  igneous  mass  has  not  metamorphosed  the  sedi- 


3io  PRINCIPLES    OF    STRATIGRAPHY 

ments.  Such  contacts  may  be  sharp,  where  the  surface  of  the 
igneous  mass  has  been  swept  clean  before  the  deposition  of  the 
sediments,  as  in  the  case  of  the  pre-Cambric  granite  floor  of  the 
Manitou  region  in  Colorado  (Crosby-6),  upon  which  abruptly 
appear  the  clean-washed  sands  of  the  basal  Palaeozoic  of  that 
region  (Fig.  52),  or  it  may  be  a  transition  contact  where  the  old 
igneous  mass  has  been  much  decomposed,  while  the  subsequent 
sediment  is  made  up  of  the  partly  reworked  upper  layers  of  the 
old  regolith.  An  example  of  this  is  found  in  the  contact  of  the 
Lake  Superior  sandstone  of  the  Marquette  region  with  the  altered 
peridotites  of  pre-Cambric  age,  where  it  is  often  impossible  to 

M. 

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linch»    lOfeet. 

FIG.  52.  Irregularities  in  sedimentary  contact,  of  basal  Palaeozoic  sandstones 
on  pre-Cambric  granite  in  Williams  Canyon,  Colorado.  The  gen- 
eral character  of  the  contact  is  a  sharp  and,  for  the  most  part, 
very  smooth  one.  (After  Crosby.)  The  granite  mass  is  part  of 
an  abyssolith. 

determine  the  precise  line  of  contact.    Great  difference  in  age  may 
exist  between  these  two. 

For  such  an  ancient  igneous  mass,  which  has  been  uncovered  by 
erosion,  and  subsequently  covered  by  sediments,  with  which  it  is  in 
sedimentary  contact,  the  name  Abyssolyth  is  proposed.  Such  an 
abyssolyth  is  seen  in  the  granite  mass  of  Pikes  Peak,  the  contact 
of  which,  with  the  Palaeozoics,  is  a  sedimentary  one.  (Fig.  52.) 


Contacts  of  hyp  abyssal  or  injected  masses. 

Dikes,  sills,  laccoliths,  etc.,  are  younger  than  the  strata  which 
they  cut,  or  which  they  have  metamorphosed.  Their  proximal  age 
limit  is,  however,  not  determined  by  the  strata  in  which  they  occur, 
unless  some  of  these  strata  should  contain  erosion  fragments  of 
the  intrusives,  when  the  latter  must  be  considered  as  very  much 
older  than  the  strata  containing  such  fragments,  and  which  are  in 
sedimentary  cpntact  with  the  igneous  masses. 


EFFUSIVE   IGNEOUS    MASSES  311 

In  general  terms :  Strata  underlying  igneous  masses,  parallel 
with  them,  are  always  older  than  those  masses,  but  strata  lying 
directly  upon  such  igneous  rocks  must  be  considered  older  only  if 
they  have  been  altered  or  in  any  way  affected  by  the  igneous  mass 
while  the  latter  was  still  hot,  but  younger  if  they  are  not  affected 
and  especially  if  they  contain  worn  fragments  of  the  igneous  rock. 
An  exception  must,  however,  be  made  in  the  case  of  strata  de- 
posited upon  a  hot  laval  stream,  the  heat  of  which  later  affects  the 
strata  of  younger  age.  In  such  a  case  evidence  within  the  strata 
or  the  igneous  mass  will  generally  furnish  the  clue  to  the  respective 
ages  of  each.  Misinterpretation  of  the  contact  between  adjoining 
formations  may  result  in  grave  errors  regarding  the  relative  ages 
of  these  formations.  Thus  up  to  within  very  recent  times  the  great 
granitic  and  gneissic  masses  of  the  Canadian  shield  known  as  the 
Laurentian  were  believed  to  represent  the  oldest  known  rocks  of 
the  earth's  crust,  the  metamorphosed  rocks  now  called  the  Keewatin 
series  being  regarded  as  the  next  younger,  and  representing  ancient 
sediments  resting  unconformably  upon  the  Laurentian.  It  is  now 
known,  however,  that  in  many  instances  at  least  the  contact  between 
the  Laurentian  and  the  Keewatin  is  an  igneous  contact,  the  former 
being  intruded  into  the  latter,  and  hence  younger  than  it. 


EFFUSIVE  IGNEOUS  MASSES 

Effusive  masses,  i.  e.,  volcanic  flows  or  sheets  are  always 
younger  than  the  strata  on  which  they  rest  and  older  than  the 
strata  which  overlie  them.  Volcanic  sheets  are  distinguished  from 
sills,  which  are  younger  than  both  the  enclosing  strata,  by  the  fact 
that  only  the  stratum  underlying  the  flow  is  metamorphosed,  while 
the  overlying  one  generally  contains  fragments  of  the  flow.  Fur- 
thermore, the  upper  portion  of  the  flow  shows  generally  a  more  or 
less  vesicular  structure  which  indicates  the  exposed  surface  of  the 
old  lava  sheet. 

Features  of  the  Basal  Contact  of  Lava  Sheets.  The  basal  con- 
tact of  lava  sheets  may  furnish  important  evidence  of  the  physical 
condition  of  a  region  prior  to  its  invasion  by  the  lava  flow.  Thus  a 
land  area,  bare  or  covered  by  soil  either  dry  or  with  a  comparatively 
small  content  of  water,  will  give  a  relatively  smooth  and  uniform 
contact  line  with  the  overflowing  lava  sheet.  A  saturated  soil,  or 
one  covered  by  water,  will  give  a  very  different  kind  of  contact. 
The  conversion  of  the  water  into  steam  will  cause  a  violent  ebul- 
lition along  the  line  of  contact,  accompanied  by  an  inter-kneading 


3I2 


PRINCIPLES    OF    STRATIGRAPHY 


of  the  igneous  and  non-igneous  rocks,  and  not  infrequently  a  trans- 
formation of  the  basal  part  of  the  flow.  Such  features  have  been 
described  from  the  base  of  the  Newark  trap  sheets  of  the  Paterson 
region  of  New  Jersey  by  Fenner  (n).  He  finds  that  in  places 
"along  the  contact  for  a  width  of  ten  feet  or  more  the  trap  and 
mud  show  evidence  of  having  experienced  the  most  violent  agita- 
tion"— the  two  being  mixed  and  kneaded  together  in  a  surprising 
manner.  "The  mud  has  boiled  through  and  through  the  seething 


FIG.  53.  Bonldery  structure,  with  in- 
cluded sand  masses  brought 
from  below.  Trap  sheet 
near  Paterson,  N.  J.  (After 
Fenner. ) 


FIG.  54.  Bouldery  structure  in 
lower  part  of  extruded 
trap  sheet,  near  Pater- 
son, N.  J.  (After 
Fenner.) 


body  of  lava  until  particles  of  mud  of  every  size  from  minute  specks 
to  large  masses  have  become  incorporated  in  the  pasty  flow.  Both 
lava  and  mud  are  full  of  blowholes,  steam  vents,  and  other  forms 
of  irregular  pipes  and  cavities  which  attest  the  violent  escape  of 
gases."  (iiijij.)  The  amount  of  injected  mud  decreases  up- 
ward and  the  vesicular  character  gradually  gives  way  to  purer 
igneous  rock.  In  structure  this  is  still  very  peculiar,  showing  the 
effect  of  escaping  gases  through  the  mass.  A  boulder-like  structure 
is  produced,  the  "boulders"  being  of  dense  trap  with  crusts  of  dark 


EFFUSIVE    IGNEOUS    MASSES  313 

glass.  (Figs.  53,  54.)  Between  these  "boulders"  lie  vugs  of  min- 
erals especially  rich  in  zeolites. 

Emerson  (10:61)  has  described  inclusion  of  "mud  drops"  or 
mud  amygdules  in  the  upper  part  of  the  Triassic  trap  of  the  Hoi- 
yoke  region  in  the  Connecticut  Valley,  where  occur  also  the  gray 
laminated  shales  confusedly  mingled  in  the  trap,  and  appearing 
under  the  microscope  as  an  intimate  mixture  or  "complete  emulsion 
of  the  two  non-mixing  fluids,"  the  lava  and  the  mud.  He  finds  that 
the  base  of  the  sheet  has  similar  pronounced  mud  inclosures  in 
one  place,  while  at  another,  a  hundred  rods  north,  "along  the  base 
of  the  same  sheet  the  black  compact  aphanitic  trap  rests  on  the 
same  coarse  sandstone,  and  contains  .only  a  few  long  steam  holes." 
Emerson  regards  the  basal  layer  as  the  underolled  top  layer. 

The  Carbonic  lava  flows  of  the  coast  of  Fife,  Scotland,  show 
in  their  bases  a  series  of  pipes  or  funnels  which  were  evidently 
formed  by  the  steam  generated  when  the  lava  flowed  over  the  wet 
sands.  These  pipes  extend  vertically  into  the  lava  and  generally 
are  filled  with  zeolites  or  with  calcite. 

The  rhyolitic  flows  of  the  Yellowstone  National  Park  rest  in 
places  upon  a  deposit  of  well-laminated  rhyolite  dust,  while  the 
basal  part  of  the  flow  itself  along  the  contact  is  marked  by  a  thin 
layer  of  perlitic  glass.  (Iddings-i8: 358.)  In  the  Grand  Canyon 
of  the  Yellowstone  the  bottom  contact  of  a  younger  flow  of  rhyo- 
lite on  a  thick  mass  of  basalt  shows  a  tuffaceous  character  passing 
upward  into  denser  material  which  in  turn  passes  up  into  porphy- 
ritic  glass,  and  this  into  lithoidal  lava.  (i8:jpo.)  Another  small 
sheet  of  rhyolite  on  Saddle  Mountain  has  its  basal  contact  on  basal- 
tic breccia,  marked  by  white  rhyolitic  tuff,  followed  by  fissile  light 
gray  lithoidal  rhyolite  with  small  phenocrysts,  passing  up  into  dark- 
colored  spherulitic  and  glassy  rhyolite  with  lithophysse  and  small 
phenocrysts.  ( 18 :  jp^. ) 

Features  of  the  Upper  Surfaces  of  Lava  Flows.  The  upper 
surfaces  of  lava  streams  vary  with  the  nature  of  the  lava  itself  and 
the  conditions  under  which  it  is  extravasated. 

i.  Basic  lavas.  These  are  well  illustrated  in  the  character  of 
the  extravasations  of  the  Hawaiian  Islands.  The  kinds  of  sur- 
faces represented  by  these  lavas  may  be  classified  as  (a)  ropy, 
(b)  the  pillowy  or  pahoehoe  and  the  rough  or  aa. 

The  ropy  lava,  the  least  common,  has  the  aspect  of  irregular 
coarse  pieces  of  rope,  generally  intertwined  in  an  extreme  manner, 
the  strands  moreover  being  longitudinally  ridged.  The  rock  is 
moderately  vesicular.  The  pillowy  or  pahoehoe  (pr.  pah-hoy-hoy— 
literally,  with  satiny  surface)  has  been  compared  with  the  pitch 


314 


PRINCIPLES    OF    STRATIGRAPHY 


dumped  from  a  large  number  of  enormous  caldrons  and  allowed 
partly  to  run  out,  some  masses  running  together  and  some  advanc- 
ing over  preceding  masses.  (Fig.  55.)  (Duton-g;  Dana-8:o; 
Hitchcock-i6:^o.)  These  hummocks  form  a  rolling  surface,  with 
fine  wrinklings  which  produce  the  satin  aspect.  The  pillowy  masses 
have  sometimes  a  glassy  exterior  half  an  inch  or  less  thick,  forming 
tachylite,  in  which  a  variolitic  texture  may  sometimes  be  found. 
The  rough  or  aa  lava  presents  a  striking  contrast  with  the  pahoehoe. 
"It  consists  mainly  of  clinkers,  sometimes  detached,  sometimes  par- 
tially agglutinated  together,  with  a  bristly  array  of  sharp,  jagged, 


FIG.  55.     Pahoehoe  lava  of  Mauna  Loa,  Hawaiian  Islands.     (After  Button.) 

angular  fragments  of  a  compact  character  projecting  up  through 
them."  (9: 95.)  The  breaking  up  of  the  lava  occurs  during  the 
flow.  The  masses  are  sometimes  piled  together  in  confused  heaps 
to  a  height  of  25  to  40  feet  above  the  general  surface.  The  individ- 
ual fragments  vary  in  size  from  an  inch  to  ten  feet,  or  even  much 
more.  In  texture  the  lava  is  usually  less  vesiculated  than  the 
pahoehoe,  not  scoreaceous,  but  cavernous  exteriorly.  Large  pro- 
jecting masses  of  jagged  lava  occur,  some  having  been  noted  on 
southern  Hawaii,  of  slablike  form  and  very  compact — "twenty  feet 
or  more  long,  eight  feet  high  and  three  to  ten  inches  thick,  standing 
vertically  together,  with  a  curving  over  at  the  top  somewhat  like 
gigantic  shavings."  (8:10.)  Associated  with  aa  lava  are  lava 
balls  or  pseudobombs  of  concentric  structure,  sometimes  wrongly 
taken  for  bombs.  "These  lava  balls  are  smoothish  exteriorly,  more 


FEATURES    OF    LAVA    FLOWS  315 

or  less  rounded  and  boulder-like,  and  vary  in  size  from  an  inch  or 
less  to  ten  feet  or  more."  (Dana-8: 10.) 

Peach  and  Home  have  described  and  figured  the  lava  surfaces 
of  the  Ordovicic  rocks  of  the  south  of  Scotland.  (21.)  One  of 
their  striking  characteristics  is  the  pillow-shaped  or  sack-like  form 
which  they  present.  "On  a  weathered  face  they  sometimes  look 
like  a  pile  of  partially  filled  sacks  heaped  on  each  other,  the  promi- 
nences of  one  projecting  into  corresponding  hollows  of  the  other." 
(Geikie-i3  :/pj.)  The  rocks  are  finely  amygdaloidal,  the  vesicles 
being  grouped  in  lines  parallel  to  the  outer  surface  of  the  pillow-like 
block  in  which  they  occur. 

The  spaces  between  the  subspheroidal  masses  are  sometimes 
filled  with  fine  sediment,  sometimes  with  fossiliferous  limestone, 
and  again  with  radiolarian  chert,  these  being  deposited  upon  the 
surface  flow  after  cooling  or  sometimes  before.  Some  of  the  radio- 
larian cherts,  however,  appear  to  be  deposited  contemporaneously 
with  the  lava,  for  they  are  intercalated  with  it.  These  lavas  are 
believed  to  represent  submarine  eruptions,  at  successive  periods, 
while  between  these  periods,  normal  sedimentation  took  place. 
Structures  of  this  kind  have  been  found  in  the  lower  Ordovicic 
(Arenig)  lavas  of  Cader  Idris,  Merionethshire,  North  England. 

A  similar  structure  occurs  in  the  post-Carbonic  (Tertiary)  vari- 
olitic  diabase  of  the  Mont  Genevre  district  in  the  French-Italian 
border.  (Cole  and  Gregory-^.)  The  structure  of  this  lava  is 
spheroidal  on  a  large  scale,  most  commonly  "resembling -pillows  or 
soft  cushions  pressed  upon  and  against  one  another."  As  shown  in 
the  cliffs,  they  appear  as  swelling  surfaces  with  curving  lines  of 
junction.  (Fig.  56.)  Small  vesicles  occur  in  the  rude  spheroids, 
especially  toward  the  margin,  while  in  some  places  the  whole  rock 
becomes  vesicular  and  slaggy.  The  surfaces  of  these  masses  are 
covered  by  a  crust  of  variolite,  from  I  to  7  or  8  centimeters  thick, 
the  variolites  being  grouped  or  drawn  out  in  bands  parallel  to  the 
surface  and  varying  from  almost  microscopic  to  a  diameter  of 
5  cm. 

Ransome  finds  a  structure  of  this  character  in  the  basic  lava  of 
Point  Bonita,  Marin  County,  California,  and  comes  to  the  conclu- 
sion that  it  is  essentially  a  flow  structure  and  that  hence  the  rock  in 
question  is  an  extravasated  lava.  (23.)  He  regards  the  structure 
as  indicating  a  lava  of  intermediate  viscosity  between  that  pro- 
ducing the  pahoehoe  and  that  resulting  in  the  aa  surface. 

Crosby  has  described  structures  of  this  type  from  the  Carbonic 
lavas  of  the  Nantasket  region  of  eastern  Massachusetts.  (5.) 
While  the  careful  study  of  these  structures  in  the  cases  cited  has 


PRINCIPLES    OF    STRATIGRAPHY 


led  the  observers  to  the  conclusion  that  such  features  are  reliable 
as  indications  of  surface  flows,  yet  there  are  cases  in  which  these 
surfaces  have  such  an  intimate  relation  with  marine  sediments  as 
to  suggest  the  possibility  of  intrusion.  An  example  of  this  kind  is 
described  by  Fox  and  Teall  (12:211)  from  the  Greenstone  of  the 
Lizard  and  Mullion  Island,  where  intimate  association1  with  radio- 
larian  cherts  suggested  that  the  lava  was  intruded  between  the 
sheets  of  chert  near  the  surface  of  the  sea  bed  upon  which  they 
were  being  deposited.  This  intimate  association  with  radiolarian 
cherts  also  found  in  the  Arenig  lavas  of  Great  Britain  seems  at 


FIG.  56.  Spheroidal  or  pillow  lava  with  variolitic  selvages.  North  end  of 
Le  Chenaillet  Ridge,  above  the  Durance  Mont  Genevre  region, 
France.  (After  Cole  and  Gregory.) 

present  the  only  good  indication  of  the  probable  submarine  origin 
of  the  lava.  So  far  as  the  pahoehoe  type  of  surface  is  concerned, 
it  appears  to  be  equally  characteristic  of  subaqueous  and  subaerial 
extravasations.  That  constant  and  reliable  minor  differences  exist 
between  subaerial  and  subaqueous  lava  surfaces  is  scarcely  to  be 
doubted,  but  at  present  such  differences  appear  to  be  unrecognized. 
The  aa  type  of  lava  has  also  been  recognized  in  older  formations. 
In  the  pre-Cambric  rocks  of  the  Vermilion  iron-bearing  district  of 
Minnesota  occur  bunches  of  igneous  rocks  having  a  concentric 


MINOR    STRUCTURES    OF   VOLCANICS  317 

structure.  They  have  been  referred  to  the  pseudo  bombs  of  the 
aa.  (Clements-2.)  Some  of  the  Triassic  extrusives  near  Green- 
field, Massachusetts,  have  been  referred  to  this  type  by  Hitchcock. 
(16:283.) 

2.  Acid  lavas.  These  are  as  a  rule  very  viscous  and  slow 
moving,  and  may  solidify  before  they  spread  far.  The  surface  is 
generally  rough  or  ropy,  the  former  being  a  feature  of  some  acid 
lava  flows  of  Vulcano  in  the  Lipari  group  (obsidian),  the  other 
being  illustrated  by  lavas  of  Vesuvius.  As  shown  in  the  Vesuvian 
stream  of  1858;  which  was  very  viscous  and  slow  moving,  the  sur- 
face has  been  wrinkled  and  folded  in  quite  a  remarkable  manner, 
some  of  the  folds  closely  resembling  coils  of  rope.  This  is  the  sur- 
face feature  seen  in  artificial  slags,  flowing  from  a  furnace.  The 
cause  of  this  appears  to  be  the  wrinkling  of  the  chilled  surface 
crust  through  the  continued  onward  movement  of  the  liquid  mass 
below.  Sometimes  the  breaking  of  the  lava  crust  produces  a  heap 
of  large  and  small  fragments  or  blocks,  so  that  the  lava  stream 
looks  like  a  huge  mass  of  broken  fragments  confusedly  piled  to- 
gether. (Block  lava,  Schollenlava.)  Sometimes  lavas  of  the  more 
acid  type  are  very  liquid  and  flow  rapidly.  In  such  cases  a  rough 
and  ragged  cindery  surface  is  produced  suggestive  of  aa  lava.  The 
surface  suggests  the  solidification  of  a  boiling,  squirting  mass 
(spratzige  Lava).  Such  a  surface  is  seen  in  the  lava  stream  of 
1872  on  Vesuvius.  In  rapidly  cooling  lavas  the  surface  of  the 
stream  may  be  covered  with  a  crust  of  hard  slaggy  material  which, 
breaking  and  rolling  under  at  the  front  of  the  moving  lava  stream, 
forms  a  slaggy  floor  on  which  the  more  compact  lava  comes  to  rest. 
This  crust  of  slag  is  responsible  for  the  relatively  little  effect  which 
the  lava  of  a  submarine  volcano  produces  on  coming  in  contact  with 
the  water,  or  for  the  phenomenon  of  a  lava  stream  flowing  across  a 
snowfield  without  completely  melting  it.  (Credner-4  1/50.) 


MINOR  STRUCTURAL  CHARACTERS  OF  VOLCANIC  ROCKS. 

Flow  Structure.  A  banding  of  igneous  rocks  is  often  noted,  this 
banding  sometimes  simulating  stratification,  for  which  it  has  at 
various  times  been  mistaken.  It  is  produced  by  the  disposition  of 
the  crystals,  vesicles  or  other  recognizable  structures  in  more  or 
less  parallel  lines,  which,  however,  are  constantly  interrupted  by 
obstacles  around  which  the  lines  curve  in  such  a  manner  as  to  show 
that  it  was  due  to  the  flowing  of  the  viscous  mass  around  the  ob- 
stacle. Flow  structure  is  not  confined  to  surface  flows,  but  also 


PRINCIPLES    OF    STRATIGRAPHY 


occurs  in  injected  masses  such  as  dikes,  sills,  etc.,  where  it  is  often 
very  well  developed.  It  is  more  marked  in  acid  than  in  basic 
rocks,  especially  in  obsidians,  rhyolites  and  felsites,  etc.  The  flow 
structure  of  basic  rocks  is  more  generally  seen  on  a  large  scale 
in  the  orientation  of  porphyritic  crystals  or  the  arrangement  of 
vesicles  into  line.- 

Stratification  of  Flows.     A  succession  of   surface   flows  in  a 
given  region  will  produce  true  stratification  of  the  lavas  in  which 


FIG.  57.     Columnar  structure  in  basalt  near  Fingal's  Cave,  Island  of  Staffa, 
W.  Scotland. 


each  layer  becomes  in  turn  the  top  of  the  lithosphere  at  that  point. 
(See  p.  697.)  Such  volcanic  strata  may  be  distinguished  by  differ- 
ences in  texture  if  not  composition. 

Columnar  Structure.  This  is  a  contraction  phenomenon  in 
which  prismatic  columns  commonly  with  six  uniform  faces  form 
on  the  cooling  of  the  magma.  In  general  the  prisms  form  at  right 
angles  to  the  enclosing  walls.  In  dikes  the  prisms  thus  are  hori- 
zontal or  nearly  so,  while  in  flows  and  intruded  sheets  the  columns 
stand  upright.  (Ex.,  Fingal's  Cave  [Fig.  57]  ;  Giants'  Causeway, 
etc.)  Sometimes  they  are  curved,  as  in  Clamshell  Cave,  Staffa. 
Often  the  columns  or  prisms  are  non-persistent  through  the  bed, 
but  die  out  one  into  the  other,  with  a  wavy,  irregular  shape.  (Geikie- 


MINOR    STRUCTURES    OF   VOLCANICS 


319 


13 : 25-)  Though  most  common  in  basic  rocks,  this  structure  is 
also  found  in  the  acid  types,  as  is  well  shown  by  the  columnar 
obsidian  and  other  rhyolites  of  the  Yellowstone  National  Park. 
(Iddings-i8.)  (Fig.  58.) 


FIG.  58.     Columnar  structure  in   obsidian.     Obsidian  cliff,  Yellowstone   Na- 
tional Park.     (After  Iddings.) 

Variation  in  Grain.  In  both  effusive  and  intrusive  masses  a 
variation  in  the  coarseness  of  texture  or  size  of  grain  is  observable 
between  the  outer  faces  of  the  mass  and  its  interior.  In  general 
there  is  a  regular  increase  in  coarseness  toward  the  center,  due  to 
less  rapid  chilling  of  the  inner  portion  of  the  mass.  Queneau  (22) 
has  been  able  to  establish  a  table  for  determining  distance  from 


320  PRINCIPLES    OF    STRATIGRAPHY 

wall  by  size  of  grain  in  such  rocks  as  the  trap  of  the  Palisades. 
(Lane-i9.  See  also  the  various  minor  structures  of  pyrogenic 
rocks  referred  to  in  Chapter  VI.) 


BIBLIOGRAPHY  VII. 

1.  BALTZER,  A.      1903.     Die  granitischen  Intrusions-massive  des  Aarmas- 

sives.     Neues  Jahrbuch  fur  Mineralogie.     Beilage  Band  XVI,  pp.  292- 

325. 

2.  CLEMENT,   J.   MORGAN.     1903.     Vermilion   Iron-bearing   District  of 

Minnesota.     Monograph  XL,  U.  S.  Geological  Survey,  1890. 

3.  COLE,  G.  A.  J.,  and  GREGORY,  J.  W.     1890.     The  Variolitic  Rocks  of 

Mt.   Genevre.     Quarterly  Journal  of  the  Geological   Society,   London. 
Vol.  XLVI,  pp.  295-332. 

4.  CREDNER,  HERMANN.     1897.     Elemente  der  Geologic.     8te  Auflage. 

Leipzig.     Wilhelm  Engelmann. 

5.  CROSBY,  W.  O.     1893.     Geology  of  the  Boston  Basin,  Nantucket  and 

Cohasset.     Occasional  Papers  of  the  Boston  Society  of  Natural  History, 
IV,  Vol.  I,  pt.  i. 

6.  CROSBY,  W.  O.     1899.     The  Archaean  Cambrian  Contact  near  Manitou, 

Colorado.     Bulletin  of  the  Geological  Society  of  America,  Vol.  X,  pp. 
141-164. 

7.  DALY,   REGINALD   R.  A.   .1905.     Classification  of   Igneous   Intrusive 

Bodies.     Journal  of  Geology,  Vol.  XIII,  485-508. 

8.  DANA,  JAMES  D.     1891.     Characteristics  of  Volcanoes.     New  York, 

Dodd,  Mead  &  Co. 

9.  DUTTON,  C.  E.     1884.     Hawaiian  Volcanoes.     4th  Ann.   Rept.,   U.  S. 

Geological  Survey,  pp.  81-219. 

10.  EMERSON,   B.   K.     1897.     Diabase  pitchstone  and  sand  inclosures  of 

the  Triassic  trap  of  New  England.     Geological  Society  of  America,  Bul- 
letin, Vol.  VIII,  pp.  59-86,  pis.  3-9. 

11.  FENNER,  C.  N.     1908.     Features  indicative  of  physiographic  conditions 

prevailing  at  the  time  of  the  trap  extrusions  in  New  Jersey.      Journal  of 
Geology,  Vol.  XVI,  pp.  299-327. 

12.  FOX,  HOWARD  and  TEALL,  J.  J.     1893.     On  a  Radiolarian  chert  from 

Mullion  Island.     Quarterly  Journal  Geology  Society,  London,  Vol.  XLIX, 

pp.  211-220,  pi.  IV. 

13.  GEIKIE,  A.     1897.     Ancient  Volcanoes  of  Great  Britain,  Vol.  I.    London, 

Macmillan  &  Co. 

14.  GEIKIE,  A.     Ibid.     Vol.  II. 

15.  HARKER,  ALFRED.     1909.     The   Natural   History  of   Igneous  Rocks. 

New  York,  Macmillan  Co. 

16.  HITCHCOCK,  CHARLES  H.     1909.     Hawaii  and  its  Volcanoes.    Hawai- 

ian Gazette  Co. 

17.  IDDINGS,  J.  P.     Bismalith.     Journal  of  Geology,  Vol.  VI,  1898,  pp.  704- 

710. 

18.  IDDINGS,    J.    P.,   and    Others.       1899.       Geology    of    the    Yellowstone 

National  Park.     Monograph  U.  S.  Geological  Survey,  XXXII,  pt.  II. 
w    19.     LANE,  ALFRED   C.     1905.     The  Coarseness  of  Igneous  Rocks  and  its 
Meanings.     American  Geologist,  Vol.  XXXV,  pp.  65-72. 


BIBLIOGRAPHY   VII 


321 


20.  LAPWORTH    CH.  and  WATTS.     1894.     Proceedings  of  the  Geologists' 

Association,  Vol.  XIII. 

21.  PEACH,  BENJAMIN  N.,  and  HORNE,  J.      1899.      The  Silurian  Rocks 

of  Great  Britain.       Memoirs  of  the  Geological  Survey  of  the  United 
Kingdom.      Vol.  I,  Scotland. 

22.  QUENEAU,  A.  L.     1902.     Size  of  grain  in  igneous  rocks  in  relation  to  the 

distance  from  the  cooling  wall.     Columbia  School  of  Mines  Quarterly, 
Vol.  XXIII,  pp.  181-195,  6  plates. 

23.  RANSOME,  F.  LESLEY.     1893.     The  Eruptive  Rocks  of  Point  Bonita. 

Bulletin  of  the  Department  of  Geology  of  the  University  of  California. 
Vol.  I,  pp.  71-114,  plates  6  and  7. 


CHAPTER   VIII. 

STRUCTURE  AND   LITHOGENESIS   OF   THE  ATMOGENIC  ROCKS 

SNOW. 

Snow  is  a  direct  condensation  of  the  moisture  of  the  air,  when 
the  temperature  falls  below  32°  F.  (o°  C.).  This  occurs  in  high 
latitudes  throughout  much  of  the  year,  but  in  low  latitudes,  during 
the  summer  season,  only  in  high  altitudes.  It  is  in  these  regions  of 
more  or  less  continuous  precipitation  of  snow  that  it  remains  as  a 
permanent  cover  of  the  surface  throughout  the  year,  constituting 
the  permanent  snow  fields.  The  lower  limit  of  the  permanent  snow 
fields  constitutes  the  snow-line.  The  snow-line  may  be  considered 
under  two  aspects:  (a)  Its  dependence  primarily  on  climatic  con- 
ditions, giving  the  climatic  snow-line,  and  (b)  its  dependence  pri- 
marily on  orographic  features,  giving  the  orographic  snow-line. 
The  climatic  snow-line  depends  in  the  first  place  upon  the  course  of 
the  mean  summer  isotherm  of  o°  C.  (32°  F.),  but  there  are  other 
climatic  factors  which  modify  this,  as,  for  example,  the  amount  of 
precipitation  of  snow  during  the  winter  months,  exposure  to  the 
sun,  and  warm  and  dry  winds  from  the  land;  the  steepness  of  the 
mountain  sides,  and  their  altitude,  etc.  The  orographic  snow-line 
is  the  lower  limit  of  both  snow  fields  and  separate  neve  patches, 
which  owe  their  permanent  preservation  mainly  to  favorable  oro- 
graphic surroundings.  They  may  thus  occur  in  ravines  and  gullies 
far  below  the  true  snow-line. 

Height  of  Snow-line.  The  snow-line  is  always  higher  than  the 
lower  limit  of  snowfall,  and  it  is  of  course  much  higher  in  the 
equatorial  than  in  northern  regions.  Thus  in  the  Bolivian  Andes, 
near  the  equator,  it  is  5,500  meters  (18,500  feet)  on  the  west  side 
and  4,876  meters  (16,000  feet)  on  the  east  side,  while  in  latitude 
70°  N.  (Lapland)  it  is  about  915  meters  (3,000  feet),  and  in 
Greenland  (6o°-7o°  N.  lat.)  about  670  meters  (2,200  feet).  From 
numerous  observations  Humboldt  obtained  the  following  table  of 

322 


SNOW.     GLACIERS  323 

relationship   between   latitude,   the   lower   limit   of    snowfall,    and 
the  snow-line.     (Hantt— 4:3/3.) 


Altitude  of  Snowfall  and  of  Snozv-line  (Meters). 

Lower  Lower  limit 

Latitude  limit  of  of  eternal  Differences 

snowfall  snow 

o°  4,000  4,800  800 

20°  3,ooo  4,600  i, 600 

40°  o  3,ooo  3,ooo 

These  figures  are  approximate  and  represent  average  condi- 
tions. Many  temporary  and  local  variations  from  these  averages 
occur. 

The  equatorial  limits  of  regular  snowfall  (at  sea-level)  are  as 
follows,  the  figures  in  parentheses  giving  the  range  of  occasional 
snowfall:  On  the  west  coast  of  America,  45°  (34°)  N.  to  45° 
(34°)  S. ;  east  coast,  35°  (29°)  N.  to  44°  (23°?)  S.  Interior,  30° 
(19°)  N.  to  near  tropics  in  South  America.  For  the  Old  World, 
on  the  west  coast  of  Europe,  45°  (33°)  N.,  .on  the  east  coast  of 
Asia,  30°  (22.5°)  N.;  on  east  and  south  coast  of  Australia,  34°  S. 
(occasional).  For  the  interior  of  Asia  snow  falls  to  24°  (22°)  N. 
latitude;  on  the  Mediterranean  to  37°  (29°)  N.  latitude,  while 
in  the  interior  of  South  Africa  it  falls  occasionally  at  24°  S.  lati- 
tude. (Hann-4: 314.)  That  the  distribution  of  snow  and  ice 
resulting  from  it  was  different  in  former  geologic  periods  is  shown 
by  the  extent  of  former  glaciation. 

Conversion  of  Snow  into  Ice.  The  deeper  portions  of  the 
snowfield  are  gradually  converted  into  snow  ice  through  the  inter- 
mediate state  of  Urn  or  neve.  The  process  of  transformation  of 
snow  into  ice  involves  the  partial  melting  and  regelation  of  the 
granules  and  the  cementation  of  the  remainder  by  the  reconsoli- 
dated  snow  water.  This  is  a  process  of  diagenetic  metamorphism 
or  diagenesis. 

GLACIERS. 

When  the  mass  of  ice  resulting  from  the  consolidation  of  snow 
begins  to  spread,  creeping  or  flowing  away  from  the  center  of 
accumulation,  it  gives  rise  to  glaciers.  From  their  mode  of  occur- 
rence, glaciers  may  be  divided  into,  A.  true  glaciers  or  glacier 
streams,  and  B.  ice  caps,  or  glacier  sheets.  True  glaciers  are  com- 


3^4 


PRINCIPLES    OF    STRATIGRAPHY 


parable  to  streams,  and,  like  them,  are  confined  in  more  or  less 
definite  channels.  Their  length  may  be  ten  miles  or  more.  The 
most  typical  form  is  that  of  the  valley  glacier  or  alpine  glacier, 
extending  from  the  mountain  flanks  or  from  a  plateau  through  a 
well-defined  valley.  They  may  be  simple  throughout  or  multiple 
in  the  upper  reaches,  where  several  streams  unite  to  form  one 
master  stream  of  ice.  At  the  foot  of  the  valley  they  may  spread 


Moraines 
Forests 
S3  Glactens 


Pacific     Ocean, 


r  *-  * 


FIG.  59.     Map  of  the   Malaspina  Glacier  and  of  Yakutat  Bay,   Alaska;   the 
type  of  a  piedmont  glacier.     (After  Russell.) 

out  into  glacier  fans  or  piedmont  glaciers,  which  may  be  simple, 
i.  e.}  resulting  from  a  single  glacier,  or  compound,  when  formed  by 
the  confluence  of  two  or  more  glaciers  from  adjoining  valleys. 
(Example,  Malaspina  glacier,  generally  regarded  as  a  typical  pied- 
mont glacier.  Fig.  59.)  Of  secondary*  rank  among  true  glaciers 
are  cliff  glaciers  (Gehangegletscher),  resting  in  the  depressions  at 
the  foot  of  cliffs  on  the  mountain  flanks,  and  never  descending  to 
a  valley;  cirque  glaciers  (Kargletscher)  in  deep  mountain  hollows 
or  cirques  surrounded  by  high  peaks,  and  ravine  glaciers  (Schlucht- 
gletscher),  resting  in  deep  gorges  with  precipitous  walls. 


GLACIAL    SHEETS 


325 


Ice  caps,  or  glacial  sheets,  are  expansions  of  ice,  covering  and 
concealing  the  underlying  topography,  to  which  their  surfaces  do 
not  correspond.  They  may  be  compared  to  a  flood,  not  confined 
within  banks,  but  spreading  over  and  uniformly  submerging  hills 
and  valleys  alike.  The  smaller  glaciers  of  this  type  are  the  plateau 
glaciers,  such  as  are  found  in  Iceland,  parts  of  Scandinavia,  etc., 
while  the  larger  constitute  the  continental  glaciers  or  ice  sheets. 


FIG.  60.     Map  of  Greenland,  showing  the  ice  cap  and  the  ice-free  borders. 
(After  Stieler,  from  Chamberlin  and  Salisbury.) 

Of  these  the  great  ice  cap  of  Greenland,  with  an  area  of  nearly 
2,000,000  square  kilometers,  is  a  well-known  example.  (Fig.  60.) 
Another  example  of  a  little  explored  ice  sheet  is  the  continental  ice 
sheet  of  Antarctica,  which  ends  seaward  in  ice  cliffs  50  meters  or 
more  in  height,  (i.)  In  Pleistocenic  time  several  huge  ice  caps 
covered  the  northern  part  of  North  America.  (Fig.  61.)  They 
were  contiguous  along  their  margins,  where  they  interfered  the  one 
with  the  others  in  respect  to  freedom  of  movement,  interferences 
now  expressed  in  the  distribution  of  their  transported  material  and 
frequently  by  the  absence  of  erosion  along  the  line  of  contact. 
From  the  margins  of  the  ice  caps  of  the  present  day  numerous 
glaciers  descend,  many  of  them  into  the  sea,  where  their  ends  may 
break  off  and  become  icebergs.  In  continental  glaciers  no  bounding 
rock  walls  hem  in  the  ice,  though  occasionally  in  the  thinner  mar- 


326 


PRINCIPLES    OF    STRATIGRAPHY 


ginal  portion  one  of  the  higher  peaks  may  project  through  the  ice 
as  a  tmnatack* 

Stratification  of  Ice.     Since  the  ice  of  the  snow  fields  and  of 


FIG.  61.  Map  of  North  America  in  Pleistocenic  time,  showing  four  centers  of 
dispersion  of  the  ice.  I.,  Cordilleran ;  II.,  Keewatin ;  III.,  Labra- 
doran ;  IV.,  Newfoundland.  (After  Wilson.) 

glaciers  is  the  product  of  successive  deposits  of  snow  in  more  or 
less  continuous  sheets,  each  of  which  at  the  time  forms  the  surface 
layer  of  the  earth  at  that  point,  it  follows  that  snow  ice  has  a 

*  For  types  of  glacial  deposits  see  Chapter  XII. 


STRUCTURE    OF    GLACIAL    ICE 


327 


stratified  structure.  This  may  not  always  be  visible,  but,  on  the 
other  hand,  it  may  be  very  prominent.  It  is  especially  well  marked 
where  layers  of  wind-blown  dust  or  sand  were  spread  over  the 
older  layer  before  the  deposition  of  the  new  one. 


FIG.  62.     Diagram    illustrating   lateral   upturning   of    ice   layers    in   a   glacier. 
The  bottom  line  is  sea  level.     (Chamberlin  and  Salisbury.) 

Shear  Zones  and  Flow  Structure.  Instead  of  moving  uni- 
formly as  a  mass,  lines  of  more  rapid  movement  within  the  ice 
may  develop,  as  the  result  of  which  a  shear  structure  will  come 
into  existence.  This  may  simulate  stratification,  especially  when,  as 
is  commonly  the  case,  debris  from  the  bottom  is  carried  up  into 
the  ice  along  the  shear  zones.  Though  a  secondary  structure,  it 
may  be  mentioned  here  for  purposes  of  comparison. 


FIG.  63.  Diagram  illustrating  compound  or  double  glacier,  with  debris-laden 
layers  rising  laterally  and  medially,  forming  corresponding 
moraines.  The  bottom  line  is  sea-level.  (Chamberlin  and  Salis- 
bury.) 

Flow  structure  is  developed  within  many  glaciers.  This  is  most 
pronounced  near  the  front  of  the  ice  and  along  its  sides.  The 
layers  near  the  front  turn  up  and  the  debris  within  the  ice  thus 
gradually  reaches  the  surface.  Along  the  sides  the  movement  is 
also  from  below  upward,  and  where  two  valley  glaciers  have  joined 
into  a  single  trunk  glacier,  the  current  of  each  still  remains  dis- 
tinct, and  we  have  upward  moving  currents  from  both  sides  in  the 
center  as  well  as  on  each  side.  (Figs.  62,  63.) 


BIBLIOGRAPHY  VIII. 

1.  AMUNDSEN,  ROALD.     1913.     The  South  Pole.     2  volumes.     London' 

John  Murray.     New  York,  Lee  Keedick. 

2.  CHAMBERLIN,  T.  C.     1885-1886.     The  Rock  Scouring  of  the  Great  Ice 

Invasion.     Seventh  Annual  Report  of  the  Director  of  the  U.  S.  Geological 
Survey,  pp.  155-254. 

3.  CHAMBERLIN  and  SALISBURY.     1909.     Geology,  Vol.  I.     2nd  edition, 

pp.  321-22.     Extended  bibliography  on  glacier  motion,  with  summary. 


328  PRINCIPLES    OF    STRATIGRAPHY 

, 

4.  HANN,  JULIUS.     1903.     Handbook  of  Climatology.     Translated  by  R. 

de  Courcy  Ward.     New  York,  Macmillan  Co. 

5.  HOBBS,  WILLIAM    H.       1911.      Characteristics    of    existing    Glaciers. 

New  York,  The  Macmillan  Company. 

6.  PENCK,    ALBRECHT,    and    BRUCKNER,     EDUARD.       1901-1909. 

Die  Alpen  im  Eiszeit-alter.     3  Bande.     Leipzig. 

7.  REID,   HARRY   FIELDING.     1895-1913.     The  Variation  of  Glaciers. 

I-XVIII.    Journal  of  Geology,  Vols.  III-XXI. 

8.  REID,    H.  F.      1896.      The   Mechanics   of   Glaciers.      I.      Journal    of 

Geology,  Vol.  IV,  pp.  912-928. 

9.  REID,  H.  F.     1901.     De  la  progression  des  glaciers,  leur  stratification  et 

leurs  veines  bleues.     Congres  Geologique  International,  Compte  Rendu, 
VIIIme  Session,  pp.  749-755. 

10.  REID,  H.  F.     1905.     The  flow  of  Glaciers  and  their  Stratification.     Ap- 

palachia,  Vol.  II,  pp.  1-6,  2  pis.,  I  fig. 

11.  REID,   H.   F.     1907.      Ibid.      Johns  Hopkins  University  Circular,  new 

series,  No.  7,  pp.  24-26  [612-614],  l  %• 

12.  REID,  H.  F.     1908.     On  the  Internal  and  Basal  Melting  of  the  Ice  of 

Glaciers.     Zeitschrift  fur  Gletscherkunde,  Bd.  Ill,  H.  I,  pp.  68-70. 

13.  REID,  H.  F.     1909.     The  Relation  of  the  Blue  Veins  of  Glaciers  to  the 

Stratification,  etc.     Congres    Geologique    International,    IXme  Session, 
pp.  703-706. 

14.  RUSSELL,   I.   C.     1883-1884.     Existing  glaciers  of  the  United  States, 

5th  Annual  Report  of  U.  S.  Geological  Survey,  pp.  309-362. 

15.  RUSSELL,  I.   C.     1897.     Glaciers  of  North  America.     Boston  and  Lon- 

don, Ginn  &  Co. 


CHAPTER   IX. 


ORIGINAL  STRUCTURES  AND  LITHOGENESIS  OF  THE  TRUE 
AQUEOUS  OR  HYDROGENIC  ROCKS. 

True  aqueous  or  hydrogenic  deposits,  i.  e.,  precipitates  from 
solution  in  water,  may  be  grouped  under  a  number  of  divisions,  ac- 
cording to  the  mode  of  origin.  The  principal  groups  are  : 

1.  Marine,   or  oceanic   (halmyrogenic,  halogenic,*  or  thalasso- 
genicf). 

2.  Lacustrine   (limnogenic  J),  including  those  of  lakes,  ponds, 
marshes,  salinas,  and  playa  lakes. 

3.  Fluvial  (potamogenic  §). 

4.  Terrestrial,  including  those  of  springs,  both  cold  and  hot,  of 
geysers,  the  deposits  in  caverns,  mineral  veins,  etc.    They  comprise 
deposits  of  both  vadose  and  magmatic  waters.     Under  this  head 
must  also  be  placed  the  salitrales  of  Patagonia  and  other  regions. 

Chemical  deposits  of  the  open  sea  when  not  alteration  products 
are  practically  limited  to  carbonates  of  lime  and  of  magnesia,  though 
these  are  rare  in  the  modern  ocean.  In  enclosed  mediterraneans  or 
other  cut-offs  from  the  ocean,  deposits  of  calcium  carbonate  are 
formed,  while  gypsum  and  salt  may  be  precipitated  on  evaporation 
of  the  water.  Complete  evaporation  may  result  in  the  deposition  of 
the  rarer  salts,  especially  those  of  potash. 

In  lakes  chemical  deposits  are  chiefly  confined  to  the  carbonates 
of  lime,  which  may  be  extremely  abundant.  Complete  evaporation, 
however,  may  result  in  the  deposition  of  a  variety  of  salts,  including 
chlorides,  nitrates,  borates,  sulphates,  carbonates,  etc.  Chemical  de- 
posits of  fluvial  origin  are  chiefly  limited  to  the  carbonates  of  lime, 
though  deposits  of  iron  oxides  and  carbonates  may  also  be  formed. 
Finally,  the  terrestrial  deposits  of  this  type  include  carbonate  of 
lime  and  silica,  as  well  as  a  large  variety  of  additional  mineral 

*d\s  =  salt. 

f  0a\aff<ra  =  the  sea. 

=  a  marsh,  lake,  pond. 
river. 

329 


330  PRINCIPLES    OF    STRATIGRAPHY 

substances  which  fill  up  fissures  and  other  cavities,  forming  veins 
and  other  types  of  deposits.  Chief  attention  will  here  be  given  to 
the  deposits  of  carbonate  of  lime  and  magnesia,  to  gypsum  and  an- 
hydrite, and  to  chloride  of  sodium  and  some  other  common  salts. 

OCEANIC    PRECIPITATES. 

CHEMICAL  DEPOSITS  OF  THE  DEEP  SEA.  Purely  hydrogenic 
rocks,  i.  e.,  precipitates,  are  practically  unknown  in  the  open 
ocean,  but  chemical  deposits,  in  part  alteration  products,  are 
found.  Here  belong  the  manganese  concretions,  which  are  found 
widely  distributed  over  the  floor  of  the  abyssal  portion  of 
the  Pacific  Ocean  and  elsewhere.  They  generally  enclose  foreign 
objects,  pieces  of  pumice,  the  teeth  of  sharks — often  of  extinct  Ter- 
tiary species — the  ear-bones  of  whales,  etc.,  or  even  fragments  of 
siliceous  or  calcareous  sponges.  The  encrusting  material  is  dis- 
posed in  concentric  layers  and  consists  of  manganese  oxide  up  to 
63  per  cent,  and  iron  oxide  up  to  45  per  cent.,  the  iron  in  some  cases 
even  exceeding  the  manganese.  Clay  and  silica  make  up  the  re- 
mainder, one  or  the  other  having  been  found  to  approach  50  per 
cent,  of  the  mass.  Copper,  nickel,  lead,  cobalt,  molybdenum,  and 
traces  of  zinc,  lithium  and  thallium  have  also  been  found  in  these 
concretions.  The  source  of  the  manganese  has  been  thought  to  be 
the  sea  water,  in  which  it  occurs  as  the  bicarbonate,  which,  when 
coming  in  contact  with  the  oxygen  of  the  air,  is  precipitated  as  the 
peroxide.  The  small  quantity  of  this  salt  found  in  the  sea  water 
has,  however,  cast  doubt  on  this  explanation,  and  others  have  sought 
for  the  source  of  the  manganese  in  the  decomposition  products  of 
basic  volcanic  rocks  in  the  sea,  or  in  submarine  volcanic  eruptions 
or  in  mineral  springs.  (See  summary  by  Potonie-46:/(5d.)  An- 
other alteration  product  is  found  in  the  crystals  of  Phillipsite,  a 
hydrous  silicate  of  aluminium,  calcium  and  potassium,  found 
abundantly  in  the  deeper  portions  of  the  Pacific  and  Indian  oceans. 
They  not  infrequently  occur  in  the  form  of  crossed  twins.  These 
are  also  regarded  as  due  to  precipitation  of  decomposition  products 
of  submarine  volcanic  rocks,  taken  into  solution  in  the  water  of  the 
deep  sea. 

Glauconite,  too,  may  be  mentioned  here.  It  accumulates  in  the 
shallower  portions  of  the  sea,  being  more  largely  confined  to  the 
littoral  district,  i.  e.,  the  continental  shelf.  Since  this  mineral  is, 
however,  more  properly  to  be  regarded  as  an  alteration  product 
of  the  finer  marine  sediments,  its  discussion  is  best  deferred  until 
these  sediments  have  been  considered.  (See  Chapter  XV.) 


PRECIPITATION    OF    LIME    IN    THE    SEA         331 
CHEMICAL   LIME   AND   MAGNESIA   DEPOSITS. 

CHEMICAL  PRECIPITATION  OF  CARBONATE  OF  LIME  AND  MAG- 
NESIA IN  THE  OCEAN.  In  the  modern  oceans  the  chemical  precipi- 
tation of  lime  and  magnesia  as  limestones  and  dolomites  is  almost 
unknown.  It  is  true  that  crystals  of  dolomite  grow  in  vugs  and 
cavernous  openings  of  coral  reefs  (Skeats~5o),  and  calcite  and 
aragonite  crystals  were  found  abundantly  in  the  cavities  between  the 
organic  fragments  composing  the  coral  rock  in  the  deeper  portions 
of  the  Funafuti  core,  but  those  deposits  belong  rather  to  the  cate- 
gory of  diagenetic  modifications.  This  general  absence  in  the 
modern  sea  of  such  deposits  is  not  a  safe  argument  for  the  similar 
freedom  of  the  ancient  sea  from  these  deposits.  Indeed,  there  are 
many  horizons  where  limestones  and  dolomites  occur,  which,  from 
the  absence  of  organic  remains,  are  difficult  to  explain  as  of  other 
than  chemical  origin.  This  is  especially  the  case  with  the  pre- 
Cambric  limestones,  for  which  Daly  (12:163)  advocates  a  chemical 
history.  He  suggests  that  the  lime  of  the  pre-Cambric  ocean  was 
precipitated  on  the  ocean  floor  by  the  agencies  of  decaying  organic 
matter.  This  accumulated  in  quantity  owing  to  the  absence  of  the 
bottom  scavengers  which  had  not  then  come  into  existence,  and 
which  now  keep  the  sea  bottom  free  from  organic  matter  to  a 
large  extent.  Furthermore,  the  low  temperatures  of  our  sea  bot- 
toms permit  only  a  very  slow  putrefaction  of  the  organic  matter 
which  does  remain.  In  earlier  seas,  however,  temperatures  may 
have  been  much  higher,  permitting  such  putrefaction  on  a  large 
scale. 

During  putrefaction  ammonium  carbonate  is  given  off  in  large 
volumes.  This  converts  the  chloride  and  sulphate  of  calcium  into 
carbonate,  which  is  then  precipitated,  the  reactions  being: 

CaSO4  +  (NH4)2CO3  =  CaCO3  +  (NH4)2SO4 
CaCU  +  (NH4)2C03  =  CaC03  +  2NH4C1. 

Experiments  (Irvine  and  Woodhead-3O  :/p.  Quoted  by  Daly- 
II  :  101)  have  shown  that  sea  water  is  readily  modified  by  putre- 
fying organic  matter  or  effete  substances  derived  from  living  ani- 
mals. Four  small  crabs,  weighing  90.72  grams,  were  placed  in  sea 
water  absolutely  free  from  carbonate  of  lime.  After  twelve  months 
they  produced  an  alkalinity  in  the  water  equal  to  the  production  of 
45-36  grams  of  calcium  carbonate.  This  was  due  to  the  decom- 
position of  calcium  sulphate  by  the  uric  acid  and  other  effete 
matter.  In  a  second  experiment,  with  temperatures  ranging  from 


332  PRINCIPLES    OF    STRATIGRAPHY 

60  to  80  degrees  Fahrenheit,  the  decomposition  of  urine  mixed  with 
sea  water  precipitated  practically  all  the  sulphate  of  lime  present  in 
seventeen  days.  The  complete  putrefaction  after  death  of  nine 
small  crabs  in  2  liters  of  sea  water,  at  temperatures  varying  from 
70°  to  80°  F.,  resulted  in  the  precipitation  of  all  the  lime  salts  in 
the  form  of  carbonates. 

One  objection  that  has  been  raised  against  this  theory  of  lime 
deposition  is  that  in  the  decay  of  organic  matter  carbon  dioxide  is 
likewise  generated,  and  that  this  would  tend  to  keep  the  lime  in 
solution.  This  is  indeed  the  accepted  explanation  for  the  absence 
of  calcareous  deposits  in  the  deep  sea,  where  only  red  clay  is 
deposited  (see  beyond,  Chapter  XV).  Natterer  emphasizes  the 
importance  of  the  abundant  ammonia  resulting  from  the  decay  of 
the  organic  matter  on  the  sea  bottom,  and  holds  that  this  must.be 
capable  of  precipitating  lime  and  magnesia  from  the  sea  as  car- 
bonates, but  only  when  there  is  no  free  CO2  present.  The  reaction 
of  ammonium  carbonate  and  sodium  carbonate  resulting  from 
organic  decay  (Steinmann-5i  :  /pp)  with  the  calcium  sulphate  re- 
sults in  the  precipitation  of  calcium  carbonate,  which,  according  to 
Linck  (33:500)  is  aragonite  and  not  calcite.  Magnesium  carbon- 
ates and  dolomites,  however,  are  not  directly  separated  from  sea 
water  through  the  reactions  with  ammonium  and  sodium  carbon- 
ates (Philippi-45 : 432),  but  will  separate  after  an  interval  of 
time,  especially  if  the  calcium  salts  are  first  removed.  Murray  and 
Irvine  (36: 104)  found  that  a  mixture  of  sea  water  and  urine  after 
standing  several  days  furnished  the  precipitate  under  A  of  the  fol- 
lowing table,  the  urine  decomposing  and  furnishing  the  alkaline  car- 
bonate. After  filtering  out  this  precipitate  and  permitting  the  liquid 
to  stand  ten  days  longer  the  precipitate  given  under  B  was  obtained. 

A  B 

Water  and  organic  matter  (containing  7.38  % 

ammonia  in  A) 31.81  20.25 

Carbonate  of  lime 4-85  75-35 

Phosphate  of  magnesia  and  ammonia 51 . 10         

Phosphate  of  lime 12 . 24         

Carbonate  of  magnesia 1 . 02 

Phosphate  of  magnesia 3-38 

IOO.OO  100.00 

The  carbonate  of  magnesia  was  precipitated  only  after  much, 
and  perhaps  nearly  all,  of  the  calcium  was  precipitated  as  carbonate 
A  considerable  amount  of  the  precipitating  alkali,  i.  e.,  the  am- 


PRE-CAMBRIC    LIMESTONES 


333 


monia,  was  removed  from  the  mixture  in  the  first  precipitate.  From 
the  experiments  cited,  it  appears  that  hydrous  carbonate  of  mag- 
nesium can  be  precipitated  by  ammonium  carbonate  emitted  from 
decaying  animal  remains,  the  precipitation  being  much  slower  than 
in  the  case  of  calcium  carbonate,  and  being  retarded  by  the  pres- 
ence of  calcium  salts  in  the  solution.  If  the  pre-Cambric  ocean  was 
nearly  limeless,  as  argued  by  Daly,  the  proportion  of  precipitated 
magnesium  carbonate  would  be  high,  even  possibly  approaching  the 
ratio  of  true  dolomite.  The  general  proportion  of  dolomites  to 
limestones  in  the  various  formations  of  the  earth's  crust  is  shown 
in  the  following  table.  (Daly-i2  : 165.) 


Table  showing  proportion  of  dolomites  to  limestones  in  the 
geological   series. 


4 

Period 

i 

No.  of 
analyses 
averaged 

2 

Ratio  of 
CaCO3  to 
MgCO3 

3 

Ratio  of 
Ca  to  Mg 

Pre-Cambric: 
a.  From  North  America  except  those  in  b  . 
b.  From  Ontario  (Miller)  
c   Average  of  a  and  b 

28 

33 
61 

i  .64:1 
4.92:1 

2   QVI 

2.30: 
6.89: 

4IO* 

d.  Best  general  average. 

4.0 

2    58:1 

1  61: 

Cambric  (including   17  of  the  Shenandoah 
limestone) 

•?O 

2    96"! 

4    14' 

Ordovicic 

Q-I 

2    72*1 

T,  81: 

Siluric  

208 

2  oo:i 

2  .a*;: 

All  pre-Devonic 

T.Q2 

2    ^Q'l 

7  IS: 

Devonic  . 

1  06 

4   4Q:I 

6  20: 

Carbonic  (including  Mississippic)  

2^8 

8.80:1 

12.  4S: 

Cretacic  

77 

40  .  2  -\  :  I 

56.32: 

Tertiary 

26 

V7  Q2:I 

SVO9: 

Quaternary  and  Recent  

26 

25  oo:i 

^S.oo: 

Total     .  .  . 

86s 

„ 

This  table  shows  that  the  ratio  of  calcium  to  magnesium  is 
fairly  constant  for  all  pre-Devonic  rocks  (shown  by  392  analyses 
chiefly  from  North  America),  the  average  being  3.35:1.  In  the 
DevoniC  the  ratio  rises  abruptly  and  increases  rapidly  in  the  Car- 
bonic. The  Cretacic  shows  an  apparent  maximum,  but  might  be 


334  PRINCIPLES    OF    STRATIGRAPHY 

exceeded  by  Tertiary  and  later  formations  if  more  analyses  were 
available.  Daly  points  out  that  the  ratio  of  calcium  to  magnesium 
in  all  pre-Devonic  formations  is  significantly  close  to  the  same 
ratio  in  the  rivers  now  draining  pre-Cambric  terranes,  as  shown  by 
the  Ottawa  River,  where  the  average  ratio  is  3.69:  i.  From  this 
he  suggests  that  during  pre-Devonic  time  the  river-borne  magne- 
sium and  calcium  were  wholly  precipitated,  after  diffusing,  to  the 
sea  bottom.  Daly  holds  that  the  study  of  the  grain  of  unmeta- 
morphosed  Cambric  and  pre-Cambric  carbonate  rocks  convincingly 
shows  that  they  are  not  of  clastic  origin  nor  of  direct  organic  origin 
through  accumulation  of  shells  or  skeletons.  Microscopic  exami- 
nations of  typical  specimens  from  a  mass  more  than  7,000  feet 
thick  seem  to  indicate  that  neither  horizon  nor  distance  from  the 
old  shore  lines  affects  the  singularly  monotonous  grain  of  the 
rocks.  "The  constituent  particles  are  either  idiomorphic  and 
roughly  rhombohedral,  or  anhedral  and  faintly  interlocking.  The 
former  are  everywhere  of  nearly  uniform  average  diameter,  rang- 
ing from  o.oi  mm.  to  0.03  mm.,  with  an  average  of  about  0.02  mm. 
The  anhedral  grains  range  from  0.005  mm.  to  0.03  mm.,  averaging 
about  0.015  mm.  in  diameter."  (Daly-i2 :  168.)  A  similar  uni- 
formity of  grain  was  found  in  the  Archaean  dolomites  of  Idaho,  in 
the  magnesian  limestones  and  dolomites  of  the  Belt  terrane  with 
Beltina  danai,  in  the  Clarke  range,  and  in  the  Siyeh  and  Sheppard 
siliceous  limestones  of  northwestern  Montana  (Middle  Cambric). 
Similar  fine-grained  dolomites  have  been  found  by  Vogt  in  Nor- 
way, and  are  believed  to  be  chemical  precipitates.  (Vogt-55, 
quoted  by  Daly-i2 : 168.)  An  apparently  good  case  of  lime 
deposition  in  the  sea  by  chemical  separation,  through  the  influence 
of  decaying  organic  matter,  is  found  in  the  fine  calcareous  and 
magnesian  mud  at  the  bottom  of  the  Bay  of  Naples.  (Walther  and 
Schirlitz-67:jjd)  This,  mud  is  relatively  poor  in  organic  remains, 
and  seems  to  have  been  separated  from  the  lower  strata  of  water, 
which  are  poorer  in  lime  and  magnesia  than  the  upper.  Stony 
crusts  consisting  chiefly  of  calcium  carbonate,  of  ferruginous  clay, 
of  double  silicates  of  sodium  and  potassium  holding  manganese,  of 
silica,  and  of  carbonate  of  magnesia  are  found  at  the  bottom  of 
several  mediterraneans,  as,  for  example,  the  Roman  Mediterranean 
between  Crete  and  Africa  on  the  one  hand,  and  Crete  and  Asia 
Minor  on  the  other.  Also  between  Crete  and  Greece  and  in  parts 
of  the  ^Egean  Sea,  as  well  as  in  the  Red  Sea,  where  they  are  com- 
mon, and  the  bottom  waters  are  rich  in  ammonia  ( Phillipi-45 : 
429.)  Calcareous  concretions  were  dredged  by  the  Challenger  from 
a  blue  clay  in  216-255  m-  depth  west  of  New  Guinea,  and  these  are 


MARINE    HYDROGENIC    LIME   DEPOSITS         335 

regarded  as  of  purely  chemical  origin.  The  rapid  .cementation  of 
lime  sands  in  the  deeper  sea  by  the  deposition  of  lime  or  magnesium 
carbonate  is  a  further  illustration  of  this  phenomenon,  as  is  also 
the  rapid  cementation  of  reef  limestones  and  the  sands  and  rubble 
on  the  borders  of  the  reef.  Darwin  found  that  the  breccias  of 
coral  fragments  on  the  outer  margins  of  the  reefs  were  so  firmly 
cemented  that  it  was  difficult  to  chop  off  a  fragment,  even  with  a 
chisel.  The  Pourtales  plateau,  south  of  Florida,  is  a  hard  limestone 
surface  of  recent  origin.  All  loose  material  not  cemented  by  lime 
deposits  is  swept  off  the  plateau  by  the  Gulf  Stream.  Similar  sub- 
marine banks  are  found  between  the  Canaries  and  the  South  Afri- 
can coast  (the  Seine-Dacia  and  Josephine  banks),  the  Campeche 
banks  of  Yucatan,  the  Mosquito  bank  of  the  east'  coast  of  Nica- 
ragua and  elsewhere. 

What  is  true  of  modern  coral  reefs  and  banks  is  equally  ap- 
plicable to  older  deposits  of  this  character.  The  cementation  of  the 
organic  (biogenic)  limestone  of  the  reefs  of  the  various  geological 
periods  is  undoubtedly  due  to  precipitation  of  lime  from  the  sea 
water.  This,  however,  is  always  of  minor  importance,  and  the  reef 
deposits  must  be  classed  with  biogenic  rocks.  A  rapid  cementation 
of  detrital  lime  sands  and  muds  seems  to  be  indicated  in  many 
limestone  banks.  It  has  been  especially  described  for  the  Mus- 
chelkalk  (Philippi-45  '.438),  and  is  suggested  by  certain  features  in 
a  number  of  limestone  beds,  and  is  to  be  explained  as  due  to  rapid 
chemical  deposition  of  lime  between  the  grains  of  the  calcareous 
clastic  material. 

Among  the  indications  of  rapid  hardening  of  such  banks  is  the 
attachment  of  crinoids  by  flat,  disk-like  expansions,  which  is  pos- 
sible only  on  a  hard  bottom ;  by  the  attachment  of  molluscs  and 
other  hard-bottom-loving  organisms,  and  by  channelings  and  bor- 
ings which  may  be  filled  by  the  immediately  succeeding  materials. 
Such  rapid  hardening  makes  possible  the  formation  of  conglomerate 
or  of  brecciated  layers  which  contain  fragments  of  the  underlying 
limestone  layer.  Such  intraformational  conglomerates  have  been 
described  by  Walcott  from  Lower  Cambric  limestones  of  eastern 
New  York  and  Pennsylvania  and  from  Virginia  and  Tennessee  (57; 
58  134),  and  by  Wagner  from  the  Muschelkalk  of  the  vicinity  of 
Jena  (56;  Fig.  j).  Here  the  lower  bed  represents  a  worn  surface 
and  many  fissures  which  are  filled  by  the  material  of  the  succeeding 
layer.  This  upper  layer  is  also  characterized  by  a  basal  conglom- 
erate with  pebbles  of  the  lower  rock.  That  the  upper  layer  was 
also  rapidly  cemented  is  shown  by  the  occurrence  of  a  large  En- 
crinus  root  and  a  rich  molluscan  fauna  over  its  surface.  Much  care, 


336  PRINCIPLES    OF    STRATIGRAPHY 

however,  is  needed  to  distinguish  such  conglomerates  from  the  basal 
conglomerates  marking"  a  disconformity  between  the  two  layers. 
The  Cretacic  chalk  of  western  Europe  has  also  been  regarded  as  in 
part  made  up  of  chemical  precipitates.  This  refers  especially  to  the 
cement  which  unites  the  shells  of  foraminifera,  etc.  The  chemical 
part  of  the  cement  consists  of  microscopic  calcite  rhombohedrons 
and  less  regular  calcite  grains,  a  large  part  of  these  originating  from 
the  recrystallization  of  organic  aragonite  (Cayeux-Q).  Walther 
regards  the  cementing  material  of  the  fine  calcilutytes  of  the  Soln- 
hofen  region  as  due  to  chemical  precipitation  (64:212). 

Oolites  and  Pisolites  of  Chemical  or  Purely  Hydrogenic  Origin. 
These  have  been  described  from  a  number  of  localities,  occurring 
both  in  recent  formations  and  in  older  geological  deposits.  The  fa- 
miliar pisolite  of  the  Carlsbad  Springs  in  Bohemia  is  a  typical  ex- 
ample, formed  by  the  encrustation  of  minute  particles  of  quartz  or 
feldspar,  held  in  suspension  by  the  rising  waters,  and  turned  in  all 
directions,  so  as  to  produce  uniform  encrustations.  Gas  and  air 
bubbles  likewise  may  form  the  nuclei  of  such  encrustations,  which 
in  that  case  have  a  hollow  center.  The  usual  composition  is  CaCO3, 
with  a  small  quantity  of  FeCO3  (Zirkel-7o  :-/##;  Hochstetter- 
24:6*5),  but  the  mineral  is  neither  calcite  nor  aragonite,  but  a  third 
modification  "Ktypeit,"  convertible  by  heat  into  calcite.  On  the 
shores  of  seas,  the  water  of  which  holds  much  lime,  particles  of 
broken  shells,  grains  of  igneous  rocks,  etc.,  are  encrusted  by  CaCO3 
forming  a  rock  of  typical  oolitic  appearance.  On  the  shores  of 
the  Island  of  Gran  Canaria  in  the  Canary  Islands,  between  Las 
Palmas  and  Isleta,  encrustations  of  carbonate  of  lime  are  found, 
according  to  L.  von  Buch,  around  fragments  of  broken  molluscs, 
and  small  sand  grains  of  trachyte  and  basalt.  This  sand  becomes 
consolidated  into  a  porous  rock,  which  is  quarried  at  low  tide.  The 
water  of  the  waves  throughout  the  greater  part  of  the  year  has  a 
temperature  of  more  than  20°  C,  and  seems  to  be  abundantly  able 
to  dissolve  lime  and  redeposit  it  around  the  grains  of  sand,  forming 
a  "Rogenstein."  In  the  Mexican  lagoons  oolites  are  formed,  ac- 
cording to  Virlet  d'Ooust,  by  the  encrustation  with  lime  of  insect 
eggs,  and  these  oolites  closely  resemble  those  from  the  Jurassic. 

On  the  coast  of  Ascension  Island  recent  oolites  are  formed,  ac- 
cording to  Darwin,  by  the  encrustation  of  rounded  fragments  of  fos- 
sils. Similarly,  fragments  of  shells  and  grains  of  coral  sand  on  the 
north  coast  of  Tahiti  are  coated  with  lime,  according  to  Dana 
(13:57^),  and  transformed  into  oolites.  Other  examples  are  cited 
from  the  coast  of  the  Sinai  peninsula  at  Wadi  Deheese,  and  in 
the  Reede  of  Suez  (Walther-59  :££/).  These  last  two  examples 


HYDROGENIC    OOLITES  337 

are,  however,  regarded  by  Rothpletz  as  of  algous  origin  (see  be- 
yond). Linck  (33:49$)  has  obtained  for  these  recent  oolites  an 
aragonite  reaction,  while  the  fossil  oolites  are  by  him  referred  to 
calcite. 

Linck  (33:506)  has  experimented  with  the  chemical  precipita- 
tion of  lime  from  artificial  sea  water  with  results  leading  to  the  fol- 
lowing conclusions : 

The  maximum  solubility  of  calcium  carbonate  in  sea  water  is 
about  0.0191%  CaCO3.  If  this  maximum  is  exceeded  deposition 
of  CaCO3  occurs,  in  the  form  of  calcite  in  temperate  climates  and 
of  aragonite  in  tropical  climes,  but  without  the  formation  of 
sphaeruliths.  The  same  thing  is  true  of  solutions  of  calcium  car- 
bonate otherwise  free  from  salts.  If  the  calcium  sulphate  of  the 
water  is  precipitated  as  carbonate  by  sodium  or  ammonium  car- 
bonate, it  is  always  aragonite  and  of  sphserulithic  form.  These  re- 
agents will  precipitate  calcite  from  solutions  of  calcium  sulphate 
otherwise  free  from  salts,  both  at  40°  C.  and  at  18°  C.  The  solu- 
bility of  aragonite  is  thus  shown  to  be  greater  in  solutions  which 
are  poor  in  or  free  from  other  salts  than  in  those  rich  in  such 
salts,  and  that  it  is  greater  in  colder  than  in  warmer  solutions.  For 
calcite  just  the  reverse  holds  true,  and  hence,  at  a  given  tempera- 
ture, sea  water  will  hold  in  solution  more  calcium  carbonate  than 
fresh  water,  but  there  may  be  circumstances  under  which  arago- 
nite and  calcite  are  soluble  in  equal  degree,  and  so  may  be  formed 
simultaneously.  Both  calcium  carbonate  and  calcium  sulphate  are 
more  readily  soluble  in  sea  water  than  in  fresh  water.  Applying 
his  results  to  the  elucidation  of  the  question  of  the  origin  of 
marine  oolites,  Linck  finds  that  the  under  saturation  of  sea  water 
precludes  deposition  of  lime  without  the  intervention  of  a  precipi- 
tating reagent,  and  this  he  finds  in  the  sodium  and  ammonium  car- 
bonate resulting  from  the  decay  of  organic  matter.  The  precipi- 
tated material  is  usually  in  the  form  of  sphseruliths  or  concretions 
of  aragonite  with  or  without  an  inner  grain.  The  latter  is  found  in 
the  neighborhood  of  coasts,  where  the  lime  is  deposited  around 
fragments  of  shells  or  coral,  grains  of  quartz  or  other  sand,  foram- 
inifera,  etc.,  while  in  the  open  sea  they  are  without  central  kernel. 
Linck  considers  that  all  oolites  and  pisolites  are  of  inorganic  or 
chemical  origin,  and  that,  whenever  organic  remains  occur  in  the 
mass,  these  are  mechanically  enclosed,  or,  in  the  case  of  unicellular 
algae,  the  oolite  grains  serve  as  a  basis  for  attachment.  In  the 
open  sea  the  sphseruliths  sink  to  the  bottom  in  time,  while  near  the 
shore  they  are  piled  up  into  sand  dunes  and  assorted,  according  to 
size,  with  more  or  less  mechanical  wear.  In  the  course  of  time  the 


338  PRINCIPLES    OF    STRATIGRAPHY 

aragonite  spheres  are  converted  into  calcite,  with  often  complete 
retention  of  structure.  The  opinion  of  Rothpletz,  who  regards  most 
of  these  oolites  as  of  organic  (phytogenic)  origin,  will  be  given 
later  (Chapter  XI). 

DEPOSITS  IN  ENCLOSED  OR  NEARLY  ENCLOSED  BASINS.  The 
Black  Sea  (Andrussow-4)  is  characterized  by  relatively  slight  ver- 
tical currents,  owing  to  the  superficial  layer  of  water. of  less  salin- 
ity. This  layer,  125  fathoms  deep,  is  alone  furnished  with  oxygen 
from  the  surface,  while  below  that  the  water  is  poisoned  by  the 
gases  resulting  from  the  putrefaction  of  the  dead  animal  bodies 
which  have  sunk  to  the  bottom  from  the  surface  layers,  and  which, 
in  the  absence  of  scavengers,  were  left  to  decompose  in  the  relatively 
high  bottom  temperatures.  Only  anaerobic  bacteria,  especially  Bac- 
terium hydrosulfuricum  ponticum,  live  in  the  lower  strata  of  these 
waters.  At  a  depth  of  about  100  fathoms  begins  the  separation  of 
H2S.  by  these  bacteria,  the  quantity  being  33  c.c4!  to  100  liters  of 
water,  and  rapidly  increasing  until  at  500  fathoms  it  is  570  c.c.  to 
100  liters  of  water.  Further  down  the  increase  is  less  rapid.  Am- 
monium carbonate  is  also  produced  in  large  quantities.  The  black 
mud  between  300  and  717  fathoms  is  charged  with  an  abundant 
separation  of  iron  sulphide  (FeS),  according  to  the  following  reac- 
tions (Murray  and  Irvine-36 :  pj,  modified  by  Daly-n  :  xoj)  : 

RSO4  +  2C  =  2COo  +  RS 
RS  +  2CO2  +H2O  =  H0S  +  RCO3CO, 
RS  +  RCO3CO2  +  H2O  =  2RCO,  +  H2S 
Fe2O3  +  3H2S  =  2FeS  +  S  +  3H2O 

With  the  iron  sulphide  and  free  sulphur  there  is  also  formed  a 
powdery  precipitate  of  CaCO3,  which  at  a  distance  from  shore, 
where  mechanical  detritus  is  less  abundant,  forms  layers  and  thin 
banks  of  fine-grained  limestone,  whereas  nearer  the  shore  the 
powdery  lime  is  mixed  with  fine  detritus.  Shells  of  the  planktonic 
young  of  pelecypods  and  the  frustules  of  pelagic  diatoms  are 
likewise  abundant  in  these  deposits  (Andrussow-4). 

CHEMICAL  LIMESTONE  DEPOSITS  OF  LAKES  IN  ARID  REGIONS. 
While  chemical  precipitation  of  lime  is  found  in  the  sea  only  under 
exceptional  conditions,  and  is  of  merely  local  significance,  tie 
chemical  precipitation  of  lime  from  drying  lakes  in  arid  or  semiarid 
regions  becomes  a  matter  of  greater  import.  The  site  of  the  former 
Lake  Lahontan  in  the  Great  Basin  region  (western  Nevada)  was 
characterized  by  calcareous  deposits  of  great  extent,  as  was  also 
Lake  Bonneville,  the  predecessor  of  Great  Salt  Lake.  Three  types 


LIME   PRECIPITATES    IN   LAKES 


339 


of  hydrogenic  lime  are  recognized  by  Russell  (47:^/7;  48)  in  the 
basin  of  Lake  Lahontan,  where  they  covered  the  surfaces  of  nearly 
all  the  rocks,  on  the  shores  and  bottom  of  the  old  lake.  The  oldest 
deposit  is  the  Lithoid  tufa.  It  is  compact,  gray,  sometimes  form- 
ing a  cement  for  the  ancient  gravels,  and  not  infrequently  contain- 


FIG.  64.     A  group  of  crystals  of  thinolite,  or  thinolithic  tufa.    Lake  Lahontan 
basin,  Nevada.     (After  Russell.) 

ing  the  shells  of  fresh-water  gastropods.  After  an  interval  of  ex- 
posure the  second  type,  or  Thinolithic  tufa,  was  deposited  over  the 
first.  It  consists  of  orthorhombic  prisms  6  to  8  inches  in  length 
and  almost  half  an  inch  thick  (Fig.  64).  These  have  a  peculiar  in- 
ternal structure,  and  were  at  first  considered  pseudomorphs  after 
gaylussite,  but  their  structure  does  not  agree  with  that  of  any 
known  mineral.  The  entire  layer  is  from  6  to  8  feet  thick  where 


340 


PRINCIPLES    OF    STRATIGRAPHY 


best  developed.  Similar  crystals  are  found  in  the  deposit  of  the  ex- 
tinct lake  of  Mono  Valley,  California.  The  last  deposit  is  the 
Dendritic  tufa,  and  it  is  also  the  most  abundant.  Its  greatest  depth 
is  more  than  twenty  feet,  and  may  be  as  much  as  fifty.  (Fig.  65.) 
Between  Wadsworth  and  Pyramid  lakes,  the  old  floor  of  Lake  La- 
hontan  is  completely  covered  over  an  area  of  several  square  miles 
by  dome-shaped  masses  of  this  tufa,  commonly  spreading  in  mush- 


FIG.  65.     Tufa  domes,  shore  of  Pyramid  Lake,  Nevada.     A  remnant  of  Lake 
Lahontan.    The  deposit  is  of  dendritic  tufa.     (After  Russell.) 

room  fashion,  and  up  to  5  or  6  feet  in  diameter.  (Fig.  66.)  In- 
terference with  one  another's  growth  produces  polygonal  outlines. 
This  is  the  case  on  Carson  River,  where  they  sometimes  form  a 
pavement  of  hexagonal  blocks,  each  about  2  feet  in  diameter.  The 
dendritic  character  of  this  tufa  is  seen  on  weathered  surfaces. 
Where  embedded  in  the  gravel  or  silt  deposits  of  the  lake  or  the 
interpolated  river  sediments,  these  tufa  deposits  form  definite  lime- 
stone horizons,  with  or  without  fossils,  these  limestones  horizons  be- 
ing indicative  of  desert  conditions,  under  which  they  were  chemi- 
cally precipitated. 


LIME    PRECIPITATES    OF    RIVERS  341 

Older  Deposits  of  This  Type.  What  appears  to  be  a  deposit 
closely  related  to  the  last  type  is  found  in  the  upper  Permic  Mag- 
nesian  Limestone  series  of  Durham,  England.  Here  many  of  the 
beds  are  composed  of  more  or  less  spherical  masses  of  dolomite 
having  a  radiating  structure  and  varying  greatly  in  size  and  form; 
pisolitic,  botryoidal,  reniform  and  large  globular  masses  being  com- 
mon. 

LIMESTONE  DEPOSITS  FROM  RIVERS.  Throughout  the  limestone 
region  of  torrid  America,  especially  on  the  margins  of  the  bolson 
plains  of  Mexico,  a  deposit  of  limestone  is  forming  as  a  white 
superficial  crust,  sometimes  comparatively  free  from  foreign  ma- 
terial, at  others  forming  the  cement  of  conglomerates.  This  con- 


FIG.  66.     Spheroids  of  dendritic  tufa.     Basin  of  Lake  Lahontan. 
(After  Russell.) 

centrate  of  lime  is  called  tepetate,  and  consists  of  material  dissolved 
from  the  limestone  surfaces,  and  transported  in  solution  by  the  tor- 
rential rivers. 

The  Catinga  limestone  of  Bahia,  Brazil  (Branner-6: /pj),  is  a 
good  example  of  a  river-deposited  limestone.  The  material  is  de- 
rived from  the  older  Salitre  (Jurassic)  or  other  limestones,  and  the 
deposition  probably  began  as  far  back  as  the  Tertiary,  and  still  con- 
tinues. The  attitude  of  the  beds  is  generally  horizontal,  and  their 
thickness  ranges  up  to  nearly  100  feet. 

The  deposition  of  this  rock  is  due  to  the  partial  evaporation  of 
the  lime-saturated  stream  waters  as  they  leave  the  limestone  regions, 
and  to  the  liberation"  of  the  carbon  dioxide  during  the  warming 
under  the  semitropic  sun.  The  deposition  of  lime  usually  begins  at 


342  PRINCIPLES    OF    STRATIGRAPHY 

falls  or  cataracts,  and  proceeds  both  upstream  and  downstream,  rill- 
ing the  shallow  parts  first,  because  of  the  greater  exposure  of  the 
water  at  those  places.  "Any  downstream  slope  of  the  stream  bed 
that  causes  a  rippling  of  the  water  exposes  it  to  the  air,  liberates 
more  carbon  dioxide,  and  thus  causes  an  increased  deposition  of 
lime  on  the  downstream  side."  Barriers  are  thus  built  up  in  time. 
Embankments  formed  in  this  way  vary  in  height  from  half  a  meter 
to  four  meters.  The  rock  is  hard  at  the  upper  surface,  more  or 
less  overhanging  and  cavernous  on  the  downstream  side.  Where 
streams  spread  out  to  form  arms  or  embayments,  the  floors  of  these 
are  covered  with  soft,  marly  limestone.  The  same  is  true  over  the 
flat  portions  of  the  limestone  valleys.  In  the  low  grounds  water 
often  remains  stagnant  in  broad,  shallow  pools,  especially  in  some 
of  the  sink-hole  depressions.  The  deposit  here  formed  is  always 
soft  and  marly  when  fresh,  but  becomes  as  hard  as  a  normal  lime- 
stone on  ageing.  "At  many  places  these  lime  deposits,  both  the 
newer  and  older  ones,  contain  plant  impressions  and  enclose  the  re- 
mains of  land  shells."  Sometimes  the  shells  are  cemented  together 
into  a  hard-shell  limestone,  the  species  being  those  still  existing  in 
the  region.  Angular  as  well  as  water-worn  fragments  of  all  kinds 
of  rock  are  not  infrequently  found  embedded  in  this  limestone. 

"When  a  broad,  gentle  and  rather  even  slope  carries  the  lime- 
charged  waters  in  shallow  sheets  toward  a  channel,  the  lime  is  pre- 
cipitated more  rapidly  along  the  edge  of  the  plain,  where,  on  ac- 
count of  a  change  to  a  steeper  grade,  the  water  breaks  into  ripples 
or  spray.  This  causes  the  bluff  to  encroach  steadily  on  the  low 
ground,  and  the  process  must  eventually  lead  to  the  low  ground  be- 
ing entirely  filled  up."  The  bluffs  thus  formed  curve  over  at  the 
top,  and  are  full  of  caverns  due  to  the  irregularity  of  the  deposit. 
The  roofs  of  the  caverns  are  hung  with  stalactites.  "Often  the 
travertine  is  deposited  in  masses  of  such  shape  that  they  break 
from  their  own  weight  and  form  a  talus  slope  at  the  base  of  the 
bluff,  and  this,  too,  in  time  is  covered  over  by  later  deposits,  and  is 
incorporated  in  the  great  limestone  sheet."  Some  of  these  bluffs  are 
from  25  to  30  meters  high,  which  is,  therefore,  the  thickness  of  the 
great  limestone  thus  forming  on  dry  land.  The  process  is  one  of 
chemical  aggradation. 

DEPOSITS  OF  LIME  BY  SPRINGS.  Calcareous  tufa  is  a  common 
deposit  by  springs  emerging  from  limestone  formations.  The  de- 
posit of  lime  here  is  due  largely  to  the  relief  of  pressure  and  the 
escape  of  CO2,  which  held  the  lime  in  solution  (see  posted).  Or- 
ganic bodies,  such  as  leaves,  sticks,  etc.,  are  commonly  encrusted  by 
this  lime,  which  at  first  is  a  fine  slime,  but  soon  hardens  on  ex- 


LIME    PRECIPITATES    OF    SPRINGS 


343 


posure  to  the  air.  Much  lime  is  also  precipitated  upon  certain  liv- 
ing mosses  (Hypnum,  etc.)  by  what  appears  to  be  the  physiological 
activity  of  the  plant  itself  (see  p.  475).  The  calcium  carbonate  de- 
posits of  the  hot  springs  of  the  Yellowstone,  etc.,  are  probably  due 
to  organic  activities.  Nevertheless  a  considerable  part  of  the  cal- 
careous tufa  or  travertine  is  a  purely  hydrogenic  deposit.  (Fig.  67.) 
At  the  Baths  of  San  Vignone  in  Tuscany  the  travertine  is  de- 
posited at  the  rate  of  six  inches  a  year,  while  at  San  Filippo,  Sicily, 


FIG.  67.  The  Mammoth  Hot  Springs  of  the  Yellowstone  National  Park, 
showing  the  formation  of  calcareous  deposits  by  hot  springs. 
(After  Hay  den.) 

it  is  one  foot  in  four  months,  the  deposit  having  grown  to  a  height 
of  at  least  250  feet,  and  forming  a  hill  a  mile  and  a  quarter  long 
and  a  third  of  a  mile  broad.  (Lyell-34 :  402.)  The  deposits  at 
Narni,  Italy,  increase  proportionally  to  the  rate  of  flow,  little  lime 
being  deposited  in  stagnant  water.  The  amount  also  increases  with 
distance  from  source  and  consequent  length  of  exposure  to  the  air, 
and  with  decrease  in  temperature.  Percolating  ground  water  often 
deposits  lime  in  the  pores  of  clastic  strata  and  so  cements  them. 
This  is  shown  by  the  lime-sand  dunes  of  the  Bermudas,  which  are 


344  PRINCIPLES    OF    STRATIGRAPHY 

consolidated  in  this  manner  and  by  the  formation  of  conglomerates 
with  a  limestone  matrix  or  cement  within  deposits  of  the  Pleisto- 
cenic  ice  sheet,  the  lime  in  this  case  being  commonly  derived  from 
the  solution  of  limestone  fragments  included  in  the  deposit. 

The  Onyx  Marble.  A  remarkable  type  of  spring  deposit  is  the 
so-called  onyx  marble  or  Mexican  onyx  so  extensively  used  for 
decoration  and  other  purposes.  (Merrill-35.)  This  is  a  compact, 
highly  crystalline  and  commonly  beautifully  variegated  deposit  of 
calcium  carbonate,  which  occurs  interbedded  with  breccias,  or  with 
ordinary  porous  tufas  in  many  localities.  In  Yavapai  County,  Ari- 
zona, these  have  been  found  on  the  side  of  ravines  in  crystalline 
schists  which  stand  on  edge  and  are  penetrated  by  basic  dikes. 
The  deposit  occurs  interbedded  with  breccias  made  of  the  country 
rock,  and  forms  irregular,  somewhat  concentric  layers,  from  a  frac- 
tion of  an  inch  to  two  or  more  feet  in  thickness,  and  lying  essen- 
tially horizontal.  The  massive  layers  are  separated  from  one  an- 
9ther  by  porous  cellular  ones.  At  Cave  Creek,  Arizona,  large 
blocks  of  the  onyx  up  to  4  feet  or  more  in  diameter  are  embedded 
in  tufaceous  material.  In  Mexico,  whence  the  original  supply  came, 
this  rock  is  found  in  masses  up  to  ten  feet  or  more  in  diameter  in  a 
tough,  reddish  or  dark-brown  clay,  overlying  a  closely  cemented 
conglomerate.  In  one  instance  (at  Antigua  Salines)  it  is  found  in 
a  hard,  flint-like  country  rock,  and  appears  to  be  a  regular  vein 
formation.  Similar  onyx  deposits  are  found  in  western  Utah. 

In  Lower  California  this  onyx  marble  occurs  in  the  desert  region 
near  the  Gulf  coast.  It  is  found  here  in  layers,  slabs  and  blocks 
20  inches  to  3  or  more  feet  thick,  interstratified  with  tufaceous  beds 
and  ancient  lake  bed  material,  and  shows  a  most  surprising  variety 
of  delicate  colors  and  tints.  Elsewhere  in  lower  California  on  the 
steep  slopes  of  Tule  Arroyo,  a  deep  canyon  in  dark  mica  schist  and 
blue-gray  silicified  limestones  and  quartzites  standing  on  end,  simi- 
lar deposits  of  these  onyx  marbles  were  made  by  former  springs. 
At  first  a  cellular  travertine  was  formed  cementing  the  angular 
fragments  of  the  older  rocks,  with  which  the  slopes  were  strewn,  into 
a  coarse  breccia.  After  several  feet  of  such  deposits,  the  compact 
onyx  marble  succeeded,  probably  through  a  change  in  the  constitu- 
tion of  the  spring  or  the  conditions  of  deposition.  "In  time  the 
onyx-forming  action  ceased — and  for  a  period  no  calcareous  deposi- 
tion whatever  took  place,  the  slopes  becoming  once  more  covered 
with  angular  particles  of  the  older  rocks  from  higher  up,  these  in 
their  turn  becoming  cemented  into  breccias  when  the  springs  re- 
sumed their  work.  In  this  way  were  built  up  the  alternating  layers 
of  breccia,  tufa  and  onyx,  until  finally  all  deposition  practically 


LIME    DEPOSITS    OF   CAVERNS  345 

ceased,  and  spasmodic  but  fiercely  rushing  streams  cut  the  arroyo 
to  its  present  depth,  exposing  in  either  wall  the  irregularly  alter- 
nating beds  described."  (Merrill-35  :  548.)  Two  highly  carbonated 
springs  still  occur  in  the  bottom  of  the  canyon,  building  small  beds 
of  tufaceous  material. 

Considering  the  nature  of  the  country  rock  in  this  and  the  Ari- 
zona localities,  and  the  highly  carbonated  character  of  the  springs 
still  remaining,  one  is  led  to  regard  the  water  as  magmatic  or  juve- 
nile, bringing  its  burden  of  lime  from  greater  depth. 

In  Algeria,  North  Africa,  province  of  Oran,  deposits  of  this 
type  occur,  covering  an  estimated  area  of  about  12  acres.  The 
formation  consists  of  strata  varying  from  6  inches  to  4  feet  in  thick- 
ness and  separated  by  beds  of  compact  travertine.  The  deposits  are 
of  Quaternary  age,  resting  unconformably  upon  Middle  Miocenic 
limestones  and  sandstones.  Similar  deposits  are  also  found  in 
Persia. 

A  significant  fact  bearing  on  the  mode  of  deposition  of  these 
formations  is  that  these  deposits  occur  in  regions  of  comparatively 
recent  volcanic  activity,  and  it  is  highly  probable  that  the  onyx 
marbles  were  deposited  in  heated  waters  and  possibly  under  the 
surface  of  a  pool  or  shallow  lake,  which  would  prevent  too  rapid  loss 
of  CO2,  resulting  in  ordinary  porous  travertine.  Such  travertine 
was  formed  after  the  periodic  draining  of  the  lakes. 

UNDERGROUND  DEPOSITS  OF  LIME.  Caverns  are  especially  noted 
for  the  extent  and  variety  of  their  deposits  of  calcium  carbonate. 
In  certain  Missouri  caverns  once  submerged  by  a  rising  of  the 
ground  water,  i.  e.,  caverns  formerly  situated  within  the  belt  of 
cementation,  lime  was  deposited  as  crystals  of  calcite,  lining  the 
walls,  as  in  huge  geodes  (ante,  p.  177).  Caverns  within  the  belt 
of  weathering  and  hence  not  filled  by  the  ground  water  are  charac- 
terized by  the  deposition  of  stalactites  and  stalagmites  normal  to 
such  caverns.  These  are  formed  by  the  water  percolating  through 
the  limestone  of  the  roof  of  the  cavern  and  becoming  suspended  in 
drops.  Partial  evaporation  of  the  water  in  the  dry  air,  or  the 
escape  of  the  CO2  which  held  the  lime  in  solution,  results  in  the 
formation  of  a  ring  of  lime  for  each  drop,  from  the  base  of  each  of 
which  a  second  drop  becomes  suspended,  with  the  subsequent  addi- 
tion of  a  second  calcareous  ring  at  the  bottom  of  the  first  one.  By 
this  process  a  hollow  tube  is  formed,  which  grows  by  addition  be- 
low, and  increases  in  thickness  by  successive  layers  added  by  the 
water  flowing  on  the  outside  of  the  tube.  After  a  time  the  external 
deposits  increase  to  such  an  extent  that  they  will  cover  the  opening 
of  the  tube,  or  this  may  become  closed  by  deposits  within  it.  The 


346  PRINCIPLES    OF    STRATIGRAPHY 

stalactite  then  grows  after  the  manner  of  an  icicle  by  external  addi- 
tions, and  may  become  of  great  size.  By  the  confluence  of  a  series 
of  stalactites,  banded  sheets  of  lime  are  formed,  which  hang  from 
the  roof  of  the  cavern,  a  curtain  of  stone  screening  nooks  and  cham- 
bers. Stalagmites  are  formed  on  the  floor  of  the  caverns  from  the 
lime  still  contained  within  the  water  after  it  drops  from  the  stalac- 
tite. They  may  be  sheet-like,  forming  a  solid  floor  for  the  cavern, 
or  they  may  grow  up  into  mounds.  In  the  latter  case  they  are 
often  in  the  form  of  successive  caps,  one  above  the  other,  their 
edges  frequently  fringed  with  stalactites,  which  give  the  surface  of 
the  stalagmite  mound  a  fluted  appearance. 

Cavern  deposits  may  sometimes  form  on  such  a  scale  that  the 
cavern  is  filled  again  by  crystallized  marble,  which  is  often  beautiful 
enough  to  be  sought  for  commercial  purposes.  In  the  Southern 
Appalachians,  and  in  Missouri  and  Arkansas,  broken-down  caverns 
have  made  possible  the  quarrying  of  the  stalagmitic  deposits  for 
onyx  marble.  There  are  similar  deposits  in  clefts  and  caverns  in 
the  Eocenic  limestones  of  the  Nile  valley  in  Egypt.  These  have 
been  extensively  used  for  architectural  and  other  purposes.  In 
Italy,  too,  at  many  localities  such  cavern  deposits  occur,  and  have 
been  worked  since  ancient  times. 


METHOD  OF  DEPOSITION  OF  LIME  FROM  SOLUTION. 

According  to  Fresenius,  carbonate  of  lime  is  soluble  in  pure 
water,  in  the  proportion  of  I  part  in  10,800  of  cold,  and  I  part  in 
8,875  parts  of  boiling  water,  while  others  have  placed  the  proportion 
at  much  less.  "In  carbonated  waters  the  neutral  carbonate  of  lime 
unites  with  the  carbonic  acid  to  form  the  bicarbonate  of  lime,  which 
is  readily  dissolved  in  water  to  the  extent  of  0.88  gram  per  liter 
in  water  saturated  with  carbonic  acid  gas  at  the  ordinary  at- 
mospheric pressure  and  a  temperature  of  10  degrees  centigrade." 
(Weed-68  :(5j7.)  With  increased  pressure  the  solubility  increases, 
with  corresponding  increase  in  the  amount  of  CO2  absorbed,  until 
the  maximum  is  reached,  which  is  about  3  grams  per  liter.  When 
the  waters  are  free  from  carbonic  acid,  but  contain  alkaline  and 
earthy  salts,  the  formation  of  unstable  supersaturated  solutions  of 
carbonate  of  lime  is  favored.  From  this  the  lime  is  gradually  pre- 
cipitated, the  precipitation  being  more  rapid  when  the  salts  in  solu- 
tion are  the  chlorides  of  the  alkalies  and  alkaline  earths  than  when 
they  are  the  sulphates  of  these  same  bases.  Magnesium  sulphate 
and  sodium  sulphate  form  solutions  with  a  certain  amount  of  sta- 


GYPSUM    AND    SALT  347 

bility ;  but,  according  to  T.  Sterry  Hunt,  the  lime  is  all  precipitated 
in  eight  to  ten  days. 

When  the  water  is  saturated  with  carbonic  acid,  the  chlorides  of 
the  alkalies  and  alkali  earths  will  form  unstable  supersaturated 
solutions,  from  which  the  lime  crystallizes  out  at  low  temperature 
as  the  hydrous  carbonate.  The  solution  then  retains  only  0.8 
gram  of  carbonate  of  lime  per  liter,  corresponding  to  that  dis- 
solved by  the  CO2.  If,  however,  sodium  and  magnesium  sulphates 
are  present  in  the  solution  in  carbonated  waters,  the  capacity  of 
these  waters  for  carbonate  of  lime  is  nearly  doubled.  Thus  car- 
bonated water  holding  either  of  these  sulphates  in  solution  in  the 
proportion  of  I  to  100  or  less  will  take  into  permanent  solution, 
under  ordinary  temperature  and  pressure,  a  quantity  of  pure  car- 
bonate of  lime  equal  to  1.56  to  2.  grams  in  a  liter.  Thus  only  when 
free  CO2  is  present  in  pure  or  mineral  waters  will  CaCO3  be  held  in 
permanent  solution.  The  precipitation  of  this  lime  may  be  brought 
about  by  an  abstraction  of  the  carbonic  acid  necessary  to  hold  it  in 
permanent  solution.  The  abstraction  may  be  caused  by  (Weed- 
68 :  640)  : 

1.  Relief  of  pressure. 

2.  Diffusion  of  the  CO2  by  exposure  to  the  atmosphere. 

3.  Evaporation. 

4.  Heating. 

5.  Influence  of  plant  and  animal  life. 

The  first  of  these  is  mainly  active  in  nature  where  springs  issue 
on  the  surface,  while  the  second  occurs  on  a  more  extended  scale, 
as  in  the  formation  of  stalactites  and  stalagmites  and  in  the  encrus- 
tations formed  in  petrifying  springs.  Here  diffusion  of  the  CO2  is 
facilitated  by  increase  of  surface  of  exposure,  and  in  such  cases 
evaporation  generally  accompanies  diffusion.  The  deposition  of 
lime  through  evaporation  is  illustrated  by  the  tufa  deposits  of  Lake 
Lahontan.  Deposition  through  heat,  illustrated  by  the  encrustation 
in  boilers,  is  of  little  significance  in  nature.  Precipitation  through 
the  influence  of  plant  and  animal  life  belongs  under  the  head  of 
deposits  of  Biogenic  type,  and  will  be  more  fully  discussed  later. 


DEPOSITS  OF  MARINE  GYPSUM  AND  SALT. 

GYPSUM  AND  SALT  OF  MARINE  ORIGIN.  Gypsum  and  salt 
are  as  a  rule  the  products  of  similar  physical  conditions  of  pre- 
cipitation, though  they  do  not  by  any  means  always  occur  together. 


348  PRINCIPLES    OF    STRATIGRAPHY 

Both  are  notably  absent  from  the  open  ocean  and  the  ordinary  type 
of  mediterranean.  In  the  marginal  portions  of  the  more  enclosed 
mediterraneans  in  the  arid  belts  of  the  earth  such  deposits  often 
abound.  Examples  of  these  are  found  on  the  borders  of  the  Black 
Sea,  to  a  moderate  extent  on  the  borders  of  the  Red  Sea,  and  in 
the  Rann  of  Cutch  on  the  west  coast  of  India. 

Experiments  of  Usiglio.  The  precipitation  of  salt  on  the  evapo- 
ration of  sea  water  was  studied  by  Usiglio  at  Cette  (52)  on  the 
Mediterranean.  He  began  with  5  liters  of  water,  which  at  12.5°  C. 
had  a  density  of  1.0258  and  a  salinity  of  38.45  permille,  and  by  evap- 
oration in  the  air  obtained  the  results  given  in  the  accompanying 
table,  reduced  to  grams  per  liter  of  volume.  No  salt  was  deposited 
until  the  water  had  been  reduced  by  evaporation  to  nearly  one-half 
its  volume  (53.3  per  cent.)  and  a  density  of  1.0506,*  when  slight  de- 
posits consisting  chiefly  of  CaCO3  and  ferric  oxide  were  made. 
When,  on  further  evaporation,  the  density  had  increased  to  1.1304, 
hydrated  calcium  sulphate  (gypsum)  began  to  deposit,  this  contin- 
uing until  a  density  of  1.2627  was  reached.  During  the  change  in 
the  density  from  1.13  to  1.208,  84.34  per  cent,  of  all  the  CaSO4  was' 
precipitated  as  gypsum.  After  this  NaCl  was  deposited  mixed  with 
a  little  magnesium  chloride  and  sulphate,  and  this  continued  until 
the  density  was  1.2627,  when  all  the  sulphate  of  lime  had  been  de- 
posited together  with  78.23  per  cent,  of  the  total  quantity  of  NaCl. 
After  this  12.38  per  cent,  of  the  total  NaCl  was  precipitated  without 
any  gypsum.  At  a  density  of  1.2444  a  little  sodium  bromide  had 
begun  to  deposit.  Thus  between  densities  1.0506  and  1.208,  only 
0.1583  per  cent,  of  the  total  solids  had  been  deposited,  and  this 
chiefly  as  lime  sulphate  and  carbonate  and  as  iron,  but  between 
densities  1.221  and  1.318  the  following  mixture  was  precipitated: 

Calcium  sulphate o .  2828  o/oo 

Magnesium  sulphate o .  6242  o/oo 

Magnesium  chloride o .  1532  o/oo 

Sodium  chloride 27 . 1074  o/oo 

Sodium  bromide o .  2224  o/oo 


Total 28 . 3900  o/oo 

Of  this  28.3900  permille  of  total  solids,  27.1074  permille,  or 
about  95  per  cent.,  was  sodium  chloride.  The  volume  had  now 
been  reduced  to  1.62  per  cent,  of  the  original  volume  of  5  liters 

*  The  values  here  given  are  taken  from  the  table.  Slightly  different  values  for 
intermediate  densities  are  often  given.  (See  the  article  on  Salt  in  Encyclopaedia 
Britannica,  also  Clarke-io.) 


ATION  AT  THE  SUCCESSIVE  DENSITIES  IN  GRAMS 

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349 


350  PRINCIPLES    OF    STRATIGRAPHY 

(0.081  liter),  and  this,  the  mother  liquor,  still  contained  the  follow- 
ing quantities  of  salts : 

NaCl 2 . 5885  grams  per  liter,  or  12 .9425  grams  in  5  liters 

MgSO4 i .  8545  grams  per  liter,  or    9 . 2725  grams  in  5  liters 

MgCl2 3 . 1640  grams  per  liter,  or  15 . 8200  grams  in  5  liters 

NaBr 0.3300  gram    per  liter,  or    1 .6500  grams  in  5  liters     . 

KC1 o .  5339  gram    per  liter,  or    2 . 6695  grams  in  5  liters 


8 . 4709  grams  per  liter,  or  42 . 3545  grams  in  5  liters 

Up  to  this  point  the  separation  of  the  salt  had  been  fairly  regu- 
lar, but  now  the  difference  of  temperature  between  night  and  day 
became  an  influencing  factor.  At  night  nearly  pure  magnesium  sul- 
phate was  deposited ;  by  day  this  was  mixed  with  sodium  and  potas- 
sium chloride.  With  the  mother  liquor  at  a  specific  gravity  of 
1.3082  to  1.2965,  there  was  formed  a  very  mixed  deposit  of  mag- 
nesium bromide  and  chloride,  potassium  chloride  and  magnesium 
sulphate,  with  the  double  magnesium  and  potassium  sulphate,  cor- 
responding to  the  kainite  of  Stassfurt,  Germany.  A  double  chlo- 
ride of  magnesium  and  potassium  similar  to  the  carnallite  of  Stass- 
furt was  also  deposited.  The  mother  liquor,  which  had  again  risen 
to  specific  gravity  of  1.3374,  contained  •  only  pure  magnesium 
chloride. 

The  Bar  Theory  of  Ochsenius.  In  1877  Carl  Ochsenius  (37), 
following  'a  previous  suggestion  of  G.  Bischof,  sought  to  explain 
the  formation  of  extensive  salt  deposits  of  great  thickness  by  as- 
suming that  they  were  formed  in  a  nearly  enclosed  lagoon  or  bay 
cut  off  from  the  main  water  body  by  a  barrier  beach  or  bar,  across 
which  the  water  was  just  able  to  pass.  Concentration  of  the  water 
within  the  lagoon  and  over  the  bar  proceeds  by  evaporation,  and 
as  the  water  over  the  bar  becomes  denser  and  heavier  it  sinks  and 
flows  down  the  bar  and  into  the  lagoon.  If  the  surface  evaporation 
over  the  lagoon  equals  the  inflow  of  salt-bearing  waters,  it  is  evi- 
dent that  precipitation  of  salt  must  result  from  the  constant  in- 
crease in  salinity,  and  the  depth  of  the  salt  deposit  will  depend  on 
the  original  depth  of  the  lagoon  and  on  the  length  of  time  that  these 
conditions  obtain.  The  constant  addition  of  salts  to  the  water  of 
the  lagoon,  brought  about  by  the  influx  of  sea  water  and  its  evapo- 
ration from  the  surface  of  the  lagoon,  would  result  in  the  same  con- 
centration that  is  produced  by  evaporation  of  a  given  quantity  of 
sea  water,  as  in  Usiglio's  experiments.  The  same  result  would  be 
obtained.  In  Usiglio's  experiments,  NaCl  began  to  deposit  when 
one  liter  of  the  water  was  evaporated  to  0.095,  or  about  one-tenth 


BAR-THEORY    OF    OCHSENIUS  351 

of  its  original  volume.  At  that  time  there  were  38.45-1.58  or  36.87 
grams  of  salts  in  0.095  liters  of  water,  which  corresponds  to  388 
grams  in  I  liter,  or  a  salinity  of  388  permille.  The  most  saline 
body  of  water  given  in  the  list  of  salt  lakes  on  p.  154,  i.  e.,  Tinetz 
Lake,  has  a  salinity  of  only  289  permille,  while  the  next  body, 
the  Karabugas  Gulf,  has  a  salinity  of  only  285  permille.  It  is  evi- 
dent that  neither  of  these  waters  is  saline  enough  to  deposit  salts, 
and  this  is  known  to  be  the  case  (Andrussow-3).  On  the  other 
hand,  38.38  grams  in  0.190  liter,  or  a  salinity  of  202  permille,  marks 
the  point  at  which  calcium  sulphate  will  be  deposited.  It  is  evident 
that  such  precipitation  can  take  place  in  both  the  above  water  bod- 
ies, and  that  it  may  indeed  take  place  in  all  of  the  nine  lakes  cited 
first  in  the  list  on  page  154.  That  it  does  not  so  take  place  is  in 
all  probability  due  to  the  variation  in  composition  of  these  bodies 
from  normal  sea  water.  Many  of  these  lakes  deposit  magnesium  or 
other  sulphates,  and  some  of  them  have  deposited  sodium  chloride 
at  a  former  time  of  greater  salinity. 

Calcium  sulphate  is  a  usual  accompaniment  of  salt  deposits  oc- 
curring as  gypsum  or  anhydrite,  and  forming  alternating  layers 
with  the  salt,  as  in  the  so-called  annual  rings  (Jahresringe)  of  the 
Stassfurt  and  other  salts,  or  as  mixtures  recognizable  only  on  analy- 
sis. Only  in  rare  cases  is  gypsum  or  anhydrite  absent,  as  in  the 
great  deposits  of  Miocenic  age  at  Wieliczka,  where  the  salt  is  ab- 
solutely pure.  As  seen  from  the  table  of  Usiglio,  pure  calcium 
sulphate  is  deposited  first,  and  then  sodium  chloride  with  small  ad- 
mixtures of  calcium  and  magnesium  sulphate  and  some  magnesium 
chlorides.  If  now,  after  a  period  of  salt  precipitation,  the  salinity 
of  the  water  should  become  reduced  by  an  unusual  influx  of  sea 
water,  salt  deposition  will  cease,  and  after  a  while  gypsum  or  anhy- 
drite will  form  to  be  again  succeeded  by  salt  deposits.  If,  however, 
the  bar  remains  closed  for  a  period  after  the  precipitation  of  all 
the  calcium  sulphate,  only  pure  salt  will  be  deposited,  and  this  will 
continue  until  the  mother  liquor  is  nearly  depleted  of  sodium 
chloride  (see  the  table).  After  this  no  more  deposition  is  possible 
except  through  renewal  of  the  water  across  the  bar,  and  so  it 
is  evident  that  the  deposition  of  pure  salt  is  limited  in  thickness.  It 
is  apparent  that  very  thick  deposits  of  pure  salt  cannot  be  explained 
in  this  manner. 

The  influx  of  much  water  across  the  bar  may  bring  with  it  silt, 
and  this  will  be  deposited  first,  the  succession  becoming,  from  below 
up,  silt,  gypsum  and  salt.  With  the  silt  the  organisms  of  the  ad- 
joining sea  may  enter  the  bay,  but,  owing  to  the  rapid  increase  in 


352  PRINCIPLES    OF    STRATIGRAPHY 

density  of  the  water,  they  will  soon  die,  and  their  remains  become 
embedded  within  the  layer  of  silt. 

The  Bitter  Lakes  of  Sues  an  example.  A  characteristic  exam- 
ple of  this  type  of  deposit  was  formed  in  the  Bitter  Lakes  on  the 
Isthmus  of  Suez,  and  which  before  600  B.  C.  formed  the  Heroopo- 
lite  Gulf,  a  continuation  of  the  present  Gulf  of  Suez  and  the  Red 
Sea.  After  the  gulf  became  separated  by  silting  up  to  such  an  ex- 
tent that  the  supply  of  water  from  the  Red  Sea  just  balanced  the 
evaporation  from  the  surface  of  the  gulf,  and  the  salinity  was  of 
corresponding  magnitude,  salt  began  to  deposit,  and  continued  until 
some  time  after  complete  separation  from  the  Gulf  of  Suez,  and 
transformation  into  the  Bitter  Lakes,  when  only  the  intensely  saline 
mother  liquor  remained.  When  in  1861-1863  the  present  canal 
was  cut  through  these  lakes,  a  mass  of  salt  13  km.  long,  6  km.  broad 
and  averaging  8  m.  in  thickness,  was  found.  In  the  center  of  Great 
Bitter  Lake,  this  salt  mass  was  estimated  at  20  meters  in  thickness. 
The  salt  was  of  course  quickly  dissolved  by  the  fresher  waters  of 
the  canal  which  pass  through  these  lakes,  but  until  1869  the  salt 
beds  were  still  covered  by  a  layer  of  mother  liquor. 

When  discovered  (Bader— 4),  the  salt  mass  consisted  of  parallel 
layers  of  varying  thickness  separated  by  thin  layers  of  earthy  mat- 
ter and  gypsum.  Soundings  to  a  depth  of  2.46  m.  snowed  42  lay- 
ers of  similar  composition  and  varying  from  3  to  18  cm.  in  thick- 
ness, while  the  earthy  layers  between  them  were  only  a  few  milli- 
meters in  thickness.  At  a  depth  of  1.47  m.  from  the  surface  were 
found  a  bed  of  mixed  powdery  gypsum  and  clay  0.112  m.  thick  and 
a  bed  of  pure  powdery  gypsum  0.07  meter  thick.  The  clay  layers 
were  as  a  rule  richly  fossiliferous,  containing  the  shells  of  numer- 
ous genera  and  species  of  .molluscs  now  living  in  the  Red  Sea. 

There  is  here  illustrated  a  long  succession  of  flooding  and  par- 
tial drying  up  of  these  Bitter  Lakes.  On  the  influx  of  the  waters 
from  the  Red  Sea,  mud  was  deposited,  followed  quickly  by  de"posi- 
tion  of  gypsum.  After  this  the  salt  crystallized  out,  with  an  admix- 
ture of  magnesium  sulphate.  As  the  waters  became  concentrated, 
the  animals  perished  and  their  shells  sank  to  the  bottom,  where 
they  became  embedded  in  the  growing  deposit. 

The  amount  of  bittern  salts  in  the  mother  liquor  which  covered 
the  salt  beds  of  these  lakes  until  1869  was  insufficient  for  the  quan- 
tity of  salt  found  deposited  in  these  lakes.  It  must  therefore  be 
assumed  that  on  the  successive  inundations  from  the  Red  Sea  the 
mother  liquor  then  present  was  partly  carried  out  in  diluted  form, 
and  that  the  quantity  last  found  represented  only  the  residue  since 
the  last  flooding  of  the  lakes  and  the  closing  of  the  bar.  The 


BITTER    LAKES    AND    KARABUGAS    GULF        353 

amount  of  evaporation  since  that  time  was  sufficient  to  lower  the 
surface  of  the  Bitter  Lakes  appreciably  below  that  of  the  Red  Sea 


FIG.  68.     Map  of  the  Karabugas   Gulf.      (After  von  Seidlitz,  Globus,   1899.) 

(high  water),  two  thousand  million  cubic  meters  of  water  being 
necessary  to  raise  the  surface  to  the  level  of  the  canal.  (Ochsenius- 
38:  164.) 


354  PRINCIPLES    OF    STRATIGRAPHY 

The  Karabugas  Gulf.  The  Karabugas  Gulf  on  the  eastern  bor- 
der of  the  Caspian  Sea  is  frequently  cited  as  a  typical  example  of 
the  salt  lagoon,  cut  off  from  the  main  body  of  the  Caspian  Sea  by 
a  long,  partly  submerged  bar.  Ochsenius  himself  used  it  as  an 
illustration.  As  we  have  seen,  the  salinity  of  this  body  of  water, 
while  sufficient  for  the  deposition  of  gypsum,  is  not  great  enough  for 
the  deposition  of  salt.  As  will  be  seen  by  a  reference  to  the  analysis 
of  the  water  of  the  Karabugas  (p.  158),  which  is  an  example  of 
a  sulphate  chloride  bittern,  magnesium  entirely  replaces  the  cal- 
cium. This  is  also  shown  in  the  deposits  at  the  bottom  of  this 
basin,  where  over  an  area  of  1,300  square  miles  a  deposit  of  Epsom 
salts,  (sulphate  of  magnesia)  is  formed,  7  feet  thick  and  amounting 
to  an  estimated  total  of  1,000,000,000  tons.  (Fig.  68.) 

This  gulf  further  illustrates  the  enormous  destruction  of  organ- 
isms due  to  the  intense  salinity,  a  destruction  which  would  render  all 
salt  deposits  of  such  a  gulf  highly  fossiliferous.  Andrussow  calls 
attention  to  the  large  number  of  fish  which  are  carried  across  the 
bar  into  the  Karabugas,  where  they  perish.  "Their  carcasses  float 
about  as  long  as  the  water  flowing  into  the  gulf  moves  them,  after 
which  they  either  sink  to  the  bottom,  or  are  driven  onto  the  shore. 
The  carcasses  of  Clupea,  Atherina,  Cyprinus,  Luciopercoy  Acipemer 
and  Sygnathus  piled  upon  the  shores  are  partly  eaten  by  the  native 
birds,  and  the  quantities  of  dead  fish  which  lie  upon  these  shores  in 
March  can  be  measured  by  the  fact  that  the  gulls  at  this  season  of 
the  year  feed  only  on  the  eyes  of  the  fish,  and  do  not  even  take  the 
trouble  to  turn  over  the  fish  to  get  at  the  other  eye."  (Andrussow- 
3  :<?p ;  and  Walther-62  #5.) 

Among  other  organisms  killed  in  the  saline  waters  of  this  gulf, 
Cardium  edule  should  be  mentioned.  This  euryhaline  organism 
abounded  in  the  gulf  before  it  reached  the  stage  at  which  sulphates 
were  deposited.  The  shells  of  this  species  occur  in  enormous  num- 
ber on  the  shores  of  the  Karabugas.  (Andrussow-3  155.) 

It  is  a  significant  fact  that  all  deposits  of  salt  along  the  borders 
of  the  present  seas,  as  well  as  inland,  are  found  in  regions  of  rela- 
tive aridity;  that,  in  other  words,  salt  deposition  demands  a  suffi- 
ciently dry  climate  to  allow  an  excess  of  evaporation  over  precipi- 
tation or  influx.  Thus  salt  deposits  of  all  ages  and  occurrence  are 
indicative  of  dryness  of  climate. 

Natural  Salt  Pans. 

Of  the  natural  salt  pans  in  the  vicinity  of  the  seashore,  the 
Rann  of  Cutch  on  the  northwestern  coast  of  India  is  perhaps  the 


NATURAL    SALT    PANS  355 

best  known.  (Walther-6i  :  76*9.)  This  is  a  low-lying  coastal  area, 
flooded  during  the  southwest  monsoon  period  in  some  parts  to  the 
depth  of  i  meter.  The  Rann  is  the  true  salt  plane;  it  covers  an 
area  300  km.  long  and  100  km.  broad.  It  merges  into  flat  planes 
free  from  vegetation,  the  so-called  Put,  and  is  surrounded  and 
diversified  by  the  sand-dune  region,  the  so-called  Thurr.  Here  the 
dunes  are  25  to  130  meters  high,  with  flat  areas  often  carrying 
lakes  up  to  20  meters  in  depth,  and  this  region  is  inhabited  chiefly 
by  foxes,  jackals,  wolves,  rats,  snakes,  etc.  In  the  region  of  the 
Rann  proper  animal  life,  as  well  as  plant  life,  is  exceedingly  scarce. 
The  smooth,  flat  surface  of  the  Rann  is  composed  of  sandy  clay, 
which  is  constantly  kept  moist  by  the  included  salt.  The  shallow 
pools  scattered  about  on  its  surface  are  covered  in  winter  by  crusts 
of  pure  salt,  generally  only  about  10  cm.,  but  occasionally  over  a 
meter  in  thickness. 

The  Nile  delta,  too,  is  characterized  by  a  large  number  of  salinas 
or  natural  salt  pans.  These  extend  along  the  coast  from  Abu  Sir 
to  Sheik  Zayed,  and  owe  their  salt  to  the  flooding  from  the  Medi- 
terranean and  the  rapid  evaporation  due  to  the  desert  climate  of  the 
coast.  The  salt  is  often  covered  by  wandering  sand  dunes,  which 
when  they  reach  a  great  thickness  become  filled  through  efflores- 
cence with  crystals  of  gypsum  3-5  cm.  long.  These  unite  into 
heads  I  to  4  meters  broad  and  from  0.5  to  i  meter  in  thickness. 

On  the  borders  of  the  Red  Sea  are  a  number  of  salinas.  One, 
west  of  Amfila  (Hanfela)  Bay  on  the  Abyssinian  border,  lies  below 
sea-level,  and  is  surrounded  by  a  wall  of  gypsum.  The  streams 
flowing  from  the  East  Abyssinian  Mountains  into  this  depression 
evaporate,  adding  their  contribution  to  the  saline  deposits.  At 
Allolebod,  on  the  southern  coast  of  the  Red  Sea,  the  deposits  in  the 
natural  pans  show  regular  interstratification  by  layers  of  gypsum, 
similar  to  the  annual  rings  of  the  Stassfurt  salt.  These  layers  mark 
the  periodic  inundation  of  the  salt  pans.  Though  extensive,  these 
salt  deposits  can  in  no  wise  be  compared  with  those  of  past  geologic 
periods.  (Grabau-i9.) 

Evaporation  of  Cut-offs  from  the  Sea. 

When,  in  an  arid  region  a  portion  of  an  indentation  of  the  sea 
is  cut  off,  by  tectonic  movements,  by  delta  deposits,  or  otherwise, 
the  waters  thus  separated  may  evaporate,  leaving  a  salt  sea  or  salina 
in  which  the  salt  of  the  original  water  body  becomes  concentrated. 
The  Salton-sink  region  in  the  Lower  Colorado  Basin  of  California 
is  an  example  of  such  a  cut-off.  The  delta  built  by  the  Colorado 


356 


PRINCIPLES    OF    STRATIGRAPHY 


River  into  the  former  upper  end  of  the  Gulf  of  California,  cut  off 
the  head  of  this  water  body  from  the  remainder  of  the  Gulf,  convert- 
ing it  into  a  separate  lake.  This  was  at  first  converted  into  a  fresh  or 
brackish  water  lake  by  the  continued  influx  of  the  river  water,  with 
a  corresponding  rise  of  the  level  as  indicated  by  the  traces  of  old 
shore-lines  40  feet  or  so  above  the  present  sea-level,  the  deposit  of 
calcium  carbonate  and  the  presence  of  numerous  shells  of  fresh  or 
brackish  water  molluscs.  The  Colorado  repeatedly  changed  its 
mouth,  discharging  at  intervals  into  the  Gulf  of  California.  When- 
ever this  occurred  the  lake  began  to  shrink,  the  waters  evaporating 
under  the  drying  influence  of  the  Westerlies  descending  from  the 
high  coastal  ranges.  The  Salton-sink  represents  the  present  concen- 


FIG.  69.     Sketch  map  of  the  Salton  Sink  Region.     (After  Davis.) 


tration  of  these  waters,  the  bottom  of  this  lake  being  273.5  feet 
below  mean  sea-level  (Freeman  and  Bolster-i 7:46-51).  Before  the 
recent  overflows  of  the  Colorado  (1891,  1905,  1906-07)  the  waters 
of  the  Salton  Lake  were  intensely  saline  and  its  shores  were  fringed 
with  broad  belts  covered  with  white  crusts  of  salt.  The  author 
(19:5,  4)  has  estimated  that  the  salt  resulting  from  the  complete 
evaporation  of  the  sea  waters  originally  cut  off  from  the  head  of  the 
Gulf  of  California  would  form  a  bed  12.5  m.  thick  over  the  area 
of  the  present  Salton  Lake.  (Fig.  69.) 

NON-CALCAREOUS  TERRESTRIAL  PRECIPITATES. 
SALT  LAKES  AND  SALINAS. 

Salt  lakes  and  salinas  are  characteristic  features'  of  the  arid  re- 
gions of  the  earth,  and  they  occur  in  nearly  every  country.  Those 
of  the  drainless  basin  of  the  Caspian  have  long  been  well  known. 


SALT    LAKES    AND    SALINAS  357 

Of  these,  Elton  Lake,  a  natural  Bittern  with  a  salinity  of  271  per- 
mille,  furnishes  a  good  example.  It  lies  in  the  flat  clayey  steppe, 
has  clay  banks,  a  length  of  18  km.  and  a  width  of  14  km.  As 
shown  by  the  analyses  in  the  table  (p.  158,  62),  it  contains  only  o.i 
per  cent,  of  Ca,  but  17.55  Per  cent-  °f  Mg,  while  the  sodium  is  only 
11.27  per  cent.  This  is  due  to  the  fact  that  a  part  of  the  sodium 
has  crystallized  out  as  NaCl,  from  a  liquor  formerly  of  much  higher 
salinity.  Two  layers  of  salt  are  found  at  the  bottom  of  the  lake, 
the  lower  2.5  cm.,  the  upper  4  to  5  cm.  thick.  Analyses  of  these 
salts  gave  the  following: 

Upper  Bed       Lower  Bed 

NaCl 87.08  90.50 

MgCl2 3-25  2.17 

MgSO4 0.53  0.47 

CaSO4 1.13  1.49 

H2O '. .; 6.85  3.51 


99.84  98.14 

Into  this  lake  flows  a  small  stream,  the  Chara  Zacha,  which  an- 
nually carries  enough  salt  into  the  lake  to  make  a  crust  4  cm.  in 
thickness. 

Baskunchak  Lake  (Walther-6i  :7#/0,  also  in  the  Astrakhan  dis- 
trict of  Russia,  north  of  the  present  Caspian,  is  another  example. 
It  lies  on  the  eastern  border  of  the  Volga  and  has  a  length  of  16  km. 
and  a  breadth  of  9  km.  Analysis  by  Goebel  (i)  and  Nikitinsky 
(2)  gave  the  following  composition  of  the  brine: 

(I)  (2) 

NaCl 72 . 72             ,  73 . 6 1 

MgCl2 20 . 80  22 . 32 

CaCl2 3-40  2.43 

KC1 0.76                

MgSO4 0.22 

MgBr2 o .  023               

CaSO4 o.io  o.io 


97 . 803  98 . 68 

In  the  center  of  the  lake  was  found  a  salt  bed  averaging  160  cm.  in 
thickness,  the  thickness  at  500  meters  from  shore  being  considerably 
over  2  meters.  Eight  distinct  layers  are  recognizable,  separated 
by  layers  of  clay.  The  upper  layer  contained  91  per  cent.  NaCl, 
the  second  95.4  per  cent.  NaCl,  the  fourth  97.2  per  cent.,  the  eighth 


358  PRINCIPLES    OF    STRATIGRAPHY 

97.82  per  cent.,  and  below  this  lies  a  coarsely  crystalline  salt  1.5  m. 
thick  and  of  perfect  transparency  containing  98.7  per  cent.  NaCl. 
The  upper  layers  consist  of  small  crystals  which  are  dissolved  dur- 
ing the  spring  rains.  The  larger  crystals  of  the  deeper  layers  re- 
main undissolved  and  further  increase  in  size  during  the  summer, 
and  thus  the  deeper  layers  are  constantly  becoming  poorer  in  mag- 
nesium chloride  and  as  the  salt  becomes  purer  it  also  increases  in 
density. 

This  region  is  characterized  by  more  than  a  hundred  lakes  of 
varying  salinity,  many  of  which  deposit  very  pure  rock  salt.  Many 
of  these  are  covered  by  drifted  sands  which  have  dried  up  the  lakes 
and  drawn  away  the  bitterns,  so  that  the  salt  under  the  sand  is  per- 
fectly dry  and  very  pure.  Some  of  these  lakes  of  the  Astrakhan 
district  deposit  magnesium  chloride,  others  magnesium  or  sodium 
sulphate,  and  others  still,  gypsum. 

South  of  the  Caspian,  in  Persia,  is  an  extensive  desert  nearly  800 
miles  in  length  and  in  places  over  200  miles  in  width,  covered  with 
salinas  and  dry  salt,  and  dune  sand  areas.  Of  the  salinas,  that  of 
Darya  in  Namak  may  be  noted.  For  2  km.  from  the  margin 
of  the  salina  the  ground  is  muddy  and  contains  the  skeletons  of 
animals  which  probably  died  of  thirst ;  beyond  this  a  zone  of  earthy 
salt  follows,  with  the  appearance  of  a  frozen  swamp  during  a  thaw. 
Six  to  eight  kilometers  from  the  border  begins  the  pure  salt,  in  the 
form  of  irregular  polygonal  masses  20  to  90  cm.  in  length.  The 
crust  of  salt  beyond  this  extends  for  40  km.  and  is  from  2  to  3 
meters  thick,  and  very  hard. 

The  Great  Salt  Plain  of  Lop,  in  Eastern  Turkestan,  is  described 
by  Huntington  (28)  as  resembling  "the  choppiest  sort  of  sea  with 
whitecaps  a  foot  or  two  high ;  and  frozen  solid."  He  says  :  "When 
we  camped  in  what  we  hoped  was  a  soft  spot  and  tried  to  drive  in 
the  iron  tent-pegs,  most  of  them  bent  double.  We  had  to  use  an 
axe  to  hew  down  hummocks  of  rock  salt  a  foot  high  before  we 
could  get  places  smooth  enough  for  sleeping"  (p.  251).  The  rough- 
ness of  this  salt  plain  is  explained  as  follows:  "During  the  long- 
continued  process  of  drying  up  the  ancient  lake  of  Lop  deposited 
an  unknown  thickness  of  almost  pure  rock  salt.  When  the  salt 
finally  became  dry  it  split  into  pentagons  from  five  to  twelve  feet 
in  diameter,  the  process  being  similar  to  that  which  gives  rise  to 
mud-cracks.  The  wind,  or  some  other  agency,  apparently  de- 
posited dust  in  the  cracks ;  when  rain  or  snow  fell,  the  moisture 
brought  up  new  salt  from  below ;  and  thus  the  cracks  were  solidly 
filled.  When  next  the  plains  became  dry  the  pentagons  appeared 
again.  This  time  the  amount  of  material  was  larger  and  the  penta- 


SALT    LAKES    AND    SALINAS  359 

gons  buckled  up  on  the  edges  and  became  saucer-shaped.  By  count- 
less repetitions  of  this  process,  or  of  something  analogous  to  it,  the 
entire  lake-bed  became  a  mass  of  pentagons  with  ragged,  blistered 
edges."  (Huntington-28:^5^-j.)  In  the  salt  of  this  plain  Hunt- 
ington  found  4<a  half-buried  plover,  dead  for  centuries — ever  since 
the  time  when  the  bottom  of  the  lake  was  still  soft."  Aside  from 
this,  and  from  a  few  deeply  buried  roots  of  some  reeds,  Huntington 
found  no  signs  of  life  for  nearly  a  hundred  miles  of  his  journey 
in  this  region. 

In  the  African  deserts  salinas  are  equally  characteristic.  Those 
of  the  Bilma  and  Kalala  oases  in  the  Sahara  supply  much  of  Central 
Africa  with  salt.  A  new  crust  of  salt  several  inches  thick  forms 
over  these  lakes  in  a  few  days  after  the  harvesting  of  the  preceding 
salt  crop. 

Salt  deposited  by  Katwee  Lake  north  of  Albert  Edward  Nyanza 
Lake  in  Central  Africa  contains  81.7%  NaCl,  5.32%  Na2SO4, 
8.43%  K2SO4,  2.46%  Na,CO3,  0.15%  Fe2O3,  and  0.82^  H2O.  In 
the  Kalahari,  salinas  are  a  characteristic  feature.  (Passarge— 43.) 

Calcium  sulphate  in  the  form  of  gypsum  or  anhydrite  is,  as 
we  have  seen,  a  frequent  accompaniment  of  the  deposits  of  sodium 
chloride  in  the  cut-off  lagoons  of  the  sea  and  in  normal  salt  lakes. 
Gypsum  of  undoubted  marine  origin  has  been  found  on  some  small 
coral  islands  in  the  Pacific,  where  it  constitutes  a  residue  formed  by 
the  evaporation  of  lagoons,  and  may  reach  a  thickness  of  2  feet. 
Gypsum  may  also  be  deposited  by  concentrated  lake  water,  as  in 
the  case  of  Lake  Chichen-Kanab  in  Yucatan.  Gypsum  likewise 
forms  on  an  extensive  scale  in  the  playas  or  sebchas  of  desert 
regions.  At  Fillmore,  Utah,  such  a  deposit  covers  an  area  of  2 
square  miles  and  has  been  opened  to  a  depth  of  6  feet  without 
reaching  bottom.  (Russell-48  -.84.)  In  general  it  accumulates  in 
the  center  of  the  basin  in  the  form  of  gypsum,  rendering  the  bot- 
tom and  sides  of  the  basin  impervious  and  so  forming  a  foundation 
on  which  the  salt  may  accumulate,  above  which,  in  turn,  is  formed 
the  impervious  cover  of  anhydrite.  Such  deposits  in  desert  regions 
are  often  of  considerable  thickness.  The  great  depression  of  the 
Ued  Rir,  which  merges  from  the  south  into  the  Schott  Mel  Rir, 
carries  a  flooring  of  gypsum  which  extends  at  least  to  a  depth  of 
50  meters,  and  beneath  which  is  often  a  great  accumulation  of 
water  under  strong  hydrostatic  pressure.  Piercing  of  one  of  these 
gypsum  floors  in  South  Tunis  in  1885,  at  a  depth  of  90  m.,  dis- 
covered a  well  of  water  which  rushed  up  with  such  force  as  to  hurl 
blocks  weighing  12  kgm.  into  the  air.  (Ochsenius-4i  :j#.) 

In  many  sections  the  salinity  is  not  sufficient  to  produce  solid 


360  PRINCIPLES    OF    STRATIGRAPHY' 

salt  beds  whereupon  crystals  of  salt  form  in  the  clayey  deposits  left 
on  drying  of  the  water  bodies.  Salt  crystals  or  the  molds  they  occu- 
pied are  common  in  many  ancient  deposits,  for  which  a  similar  origin 
may  be  assumed. 

Salt  is  deposited  in  the  shallow  marginal  portions  of  the  great 
Salt  Lake  of  Utah  in  spite  of  the  fact  that  the  salinity  of  the  lake 
as  a  whole  is  only  230.4  permille.  Greater  concentration  exists,  of 
course,  in  the  shallow  marginal  pools.  In  South  America  salinas  are 
extensively  developed  in  Patagonia  and  elsewhere.  Darwin  (14:76) 
describes  one  of  these  as  consisting  in  winter  uof  a  shallow  lake  of 
brine,  which  in  summer  is  converted  into  a  field  of  snow-white 
salt.  The  layer  near  the  margin  is  from  four  to  five  inches  thick, 
but  toward  the  center  its  thickness  increases.  This  lake  was  two  and 
a  half  miles  long  and  one  broad.  Others  occur  in  the  neighborhood 
many  times  larger,  and  with  a  floor  of  salt,  two  and  three  feet  in 
thickness,  even  when  under  water  during  the  winter."  Analysis  of 
this  salt  gave  only  0.26  per  cent,  of  gypsum  and  0.22  per  cent,  of 
earthy  matter.  The  borders  of  these  salinas  are  formed  of  mud  in 
which  crystals  of  gypsum  up  to  three  inches  in  length  occur. 
,  Crystals  of  sulphate  of  soda  lie  scattered  about  on  the  surface,  and 
among  these  the  mud  was  thrown  up  by  numbers  of  some  kind  of 
worm,  upon  which  the  flamingos,  which  frequent  these  salinas,  seem 
to  feed.  As  already  noted,  this  salt  is  extensively  deposited  on  the 
floor  of  the  Karabugas  Gulf,  where  a  layer  seven  feet  thick  covers 
an  area  of  1,300  square  miles.  Shunett  Lake  of  Siberia  also  de- 
posits this  salt. 

The  "Salitrales"  of  Patagonia.  These  should  be  mentioned  in  this 
connection.  They  are  most  abundant  near  Bahia  Blanca.  "The  salt 
here,  and  in  other  parts  of  Patagonia,  consists  chiefly  of  sulphate  of 
soda  with  some  common  salts.  As  long  as  the  ground  remains  moist 
in  the  salitrales  (as  the  Spaniards  improperly  call  them,  mistaking 
this  substance  for  saltpetre),  nothing  is  to  be  seen  but  an  extensive 
plain  composed  of  a  black,  muddy  soil,  supporting  scattered  tufts 
of  succulent  plants.  On  returning  through  one  of  these  tracts,  after 
a  week's  hot  weather,  one  is  surprised  to  see  square  miles  of  the 
plain  white,  as  if  from  a  slight  fall  of  snow,  here  and  there  heaped 
up  by  the  wind  into  little  drifts.  This  latter  appearance  is  chiefly 
caused  by  the  salts  being  drawn  up,  during  slow  evaporation  of  the 
moisture,  round  blades  of  dead  grass,  stumps  of  wood,  and  pieces  of 
broken  earth,  instead  of  being  crystallized  at  the  bottoms  of  the 
puddles  of  water.  The  salitrales  occur  either  on  level  tracts  elevated 
only  a  few  feet  above  the  level  of  the  sea,  or  on  alluvial  land  bor- 
dering rivers."  (Darwin— 14,  Chapter  IV.)  At  a  distance  of  some 


DEPOSITS    OF    SODA,    ETC.  361 

miles  from  the  sea  the  incrustations  on  the  plain  consist  chiefly  of 
sulphate  of  soda,  with  only  seven  per  cent,  of  common  salt,  while 
nearer  to  the  coast  the  common  salt  increased  to  37  parts  in  a  hun- 
dred. 

DEPOSITS  OF  SODIUM  SULPHATE  AND  CARBONATE. 

In  the  Great  Basin  region  of  North  America  soda  lakes  are  not 
uncommon.  In  Wyoming  lakes  of  this  type  form  deposits  on  their 
floors  which  contain  40  to  45  per  cent,  sodium  sulphate,  alternating 
with  clay  layers.  The  Donney  lakes  contain  a  bed  of  soda  2  to  3 
meters  thick.  At  Wilmington  a  bed  of  natural  soda  more  than  four 
meters  thick  was  found  at  the  bottom  of  the  lake.  Similar  sedi- 
ments are  found  in  Mono  Lake,  California;  Albert  Lake,  Oregon; 
and  Owens  Lake,  California.  Sevier  Lake,  Utah,  was  covered  in 
January,  1880,  by  a  crust  of  salt  10  to  12  cm.  thick,  beneath  which 
the  following  sediments  occurred  in  descending  order : 

Sodium  sulphate 5  cm. 

Sodium  sulphate  with  NaCl 2  cm. 

Sodium  sulphate / 5  cm. 

Gray  clay  with  wood  fibers 5  cm. 

Fine  sand  with  fresh  water  shells 15  cm. 

This  lake  is  at  times  entirely  dry.  Other  lakes  depositing  sodium 
sulphate  are  Altai  Beisk,  Domoshakovo,  Kisil-Kull,  and  Schunett 
lakes  in  Siberia.  Great  Salt  Lake  likewise  deposits  sodium  sulphate 
during  the  winter,  even  casting  it  up  in  heaps  upon  the  shore  (Gil- 
bert-i8).  Lakes  depositing  alkaline  carbonates  are  also  common. 
They  occur  in  Hungary,  Egypt,  Armenia,  Venezuela,  and  in  Utah, 
California,  and  Nevada,  especially  in  the  playas  of  the  last  named 
state.  Those  of  the  Soda  Lakes  near  Ragtown,  Nevada,  may  be 
taken  as  typical,  they  having  been  worked  for  commercial  pur- 
poses. The  sodium  carbonate  of  these  lakes  is  but  slightly  con- 
taminated by  sodium  sulphate  and  chloride.  These  soda  lakes  gave 
the  following  analyses,  the  first  from  Big,  the  others  from  Little 
Soda  Lake,  the  last  being  market  soda  (Clarke-ior/p/;  226)  : 

(i)  (2)  (3) 

Na2CO3 45.05  44.25  52.20 

NaHCO3 34-66  34 . 90  25 . 05 

Na2SO4 1.29  0.99  5.10 

NaCl 1.61  1. 10  3.31 

SiO2 0.27 

Insoluble .80  2.81  

H20 16.19  15-95  14.16 


99.60         100.00         100.09 


362 


PRINCIPLES    OF    STRATIGRAPHY 


These  soda  lakes  also  deposit  crystals  of  gaylussite(CaCO3.Na2CO3- 
5H2O),  although  the  analysis  of  the  water  shows  no  calcium,  the 
minute  quantities  of  this  element  brought  in  by  springs,  etc.,  prob- 
ably combining  at  once  to  form  this  mineral  (Clarke-io:/p/;  227). 
The  carbonates  deposited  by  these  lakes  are  probably  three  in  num- 
ber: thermonatrite  (Na2CO3.H,O),  natron  (Na2CO3.ioH2O),  and 
trona  or  urao  (Na2CO3.NaHCO3.2H2O).  The  proportion  of  these 
varies,  but  the  third  is  the  most  important.  This  is  the  first  salt 
crystallizing  out  on  fractional  crystallization  of  the  waters  of  Owens 
Lake,  Inyo  County,  California,  where  sodium  carbonate  is  manu- 
factured on  a  commercial  scale.  The  following  analysis  shows  the 
composition  of  the  salts  of  successive  crystallizations  which  took 
place  during  the  experiments  (Chatard,  quoted  by  Clarke-io:/p^; 
228)  : 

Table  showing  successive  crystallisation,  resulting  from  the  evap- 
oration of  the  zvaters  of  Ozvens  Lake. 


Stage  of  Crystallization 

Nat'l 
Waters 

First 
Crop 

Second 
Crop 

Third 
Crop 

Fourth 
Crop 

Fifth 
Crop 

Specific  gravity  of  water  or 
mother  liquor  
At  temperature  (C)  
Salinity  in  permille 

1.062 

25° 
77   OQ8 

1.312 
27.9° 

78S   4Q 

1.312 

25° 

I-3I5 
26.25° 

1.327 

35-75° 

1.30 
13-9° 

Volume  

I  .OO 

O.2O 

Composition: 
H2O. 

14    SI 

4    ^ 

7     47 

2    24. 

1  1    O^ 

Na2CO3  

34  -OS 

AT.  .  7S 

22.84 

18.  19 

12    SI 

SS  04 

NaHCO3 

7   4-O 

^O    12 

IO    S^ 

406 

•}  88 

4   OO 

Na2SO4  

14.38 

3.18 

2S   44 

26  70 

10  oi 

S    7O 

NaCl 

18   16 

7   44 

^s  06 

4S    SO 

60  oo 

19   16 

Na2B4O7.  .  .                 .        . 

o  63 

NaBO2  
KC1 

4.  O7 

I    O7 

I    12 

I    14 

I    21 

2.01 
2    Q"* 

(CaMg)  CO3  

0.08 

O   14 

(AlFe)2O3 

o  os 

O   OI 

O   OI 

O   O2 

SiO2  .  . 

0.28 

o  055 

O   OQ 

o  06 

O   OS 

o  16 

Organic  matter  
Insoluble 

0.032 
o  078 

Total 

IOO    OO 

TOO  ^8s 

QQ   41 

OQ    17 

00    QO 

ioo  14 

In  Egypt  there  are  9  soda  lakes,  the  largest  10  km.  long,  3  km. 
broad,  and  6  meters  deep  (Walther-6i  :/po).    The  salt  forming  on 


BORAX    AND    BORAXES  363 

the  bottom  of  these  lakes  consists  of  a  lower  bed  5  meters  thick 
with  much  sodium  carbonate  in  its  composition  and  an'  upper  layer 
also  5  meters  thick  composed  largely  of  sodium  chloride.  The 
smaller  lakes  generally  dry  up,  only  salt  encrustations  remaining, 
while  the  sand  of  the  surrounding  desert  is  underlain  by  a  dark  gray 
clay  containing  gypsum  and  sodium  salts. 


BORAX  AND  BORAXES. 

Borates  are  deposited  by  some  lakes  of  which  Borax  Lake,  Lake 
County,  California,  is  a  typical  example.  The  analysis  of  the  water 
is  given  on  p.  159,  F4,  the  mineral  contents  of  the  water  being  chiefly 
sodium  carbonate  and  sodium  chloride,  with  borax  (Sodium  bi- 
borate,  Na2B4O7)  next  in  importance.  The  bed  of  the  lake  is  oc- 
cupied by  a  large  mass  of  crystallized  borax  of  great  purity.  A 
neighboring  smaller  lake,  Hachinchama,  furnished  a  larger  supply 
of  borax,  which  probably  came  from  neighboring  hot  springs. 

Deposits  of  borates  are  forming  in  a  number  of  ''marshes"  or 
playa  lakes  of  Nevada  and  California.  Rhodes'  marsh,  Esmeralda 
County,  Nevada,  has  a  central  area  of  common  salt  surrounded  by 
a  deposit  of  sodium  sulphate,  outside  of  which  borax  and  ulexite 
(NaCaB5O2.8H9O)  occur.  According  to  M.  R.  Campbell  (8:401) 
these  salts  of  similar  lakes  in  California  are  leached  from  beds  of 
Tertiary  sediments.  Searles's  marsh  or  borax  lake,  in  San  Berna- 
dino  County,  California,  has  furnished  the  following  succession 
through  borings  (De  Groot-i5  1535 ;  Clarke-io:  ipp;  <?J5)  : 

Surface 

1.  Salt  and  thenardite  (Na2SO4) 2  feet 

2.  Clay  and  volcanic  sand,  with  some  Tianksite:  Na22K(SO4)9 

(CO3)  2C1-. 4  feet 

3.  Volcanic  sand  and  black  clay,  with  bunches  of  trona  NasH- 

(CO8)2.  2H20 8  feet 

4.  Volcanic  sand,  containing  glauberite  Na2Ca(SO4)2;  then- 

ardite, and  a  few  crystals  of  hanksite 8  feet 

5.  Solid  trona  overlain  by  a  thin  layer  of  very  hard  material     28  feet 

6.  Mud,  smelling  of  hydrogen  sulphide  and  containing  layers 

of  glauberite,  soda,  and  hanksite 20  feet 

7.  Clay,  mixed  with  volcanic  sand  and  permeated  with  hydro- 

gen sulphide 230  +  feet 

Borax  is  chiefly  found  in  the  top  crust  or  crystallized  in  the  water 
which  sometimes  accumulates  in  the  depressions  of  the  bed  (Clarke— 
10).  The  layer  is  reproduced  by  slow  degrees,  through  capillary 
action,  which  brings  up  the  soluble  salts  from  below.  Some  20  dis- 


364  PRINCIPLES    OF    STRATIGRAPHY 

tinct  mineral  species  have  so  far  been  obtained  from  the  deposits 
(see  Clarker-io  :ipp-<?oo;  ^55),  mostly  sulphates,  borates,  and  carbon- 
ates, with  some  chlorides,  soda  niter  (NaNO3),  and  ammonium  salts. 
In  the  southern  part  of  San  Bernardino  County,  California,  near  Dag- 
gett,  occurs  a  solid  bed  of  colemanite  (CagBgOj^HgO)  from  5  to  30 
feet  in  thickness,  highly  crystalline,  and  interstratified  with  lake 
sediments.  At  one  end  it  is  much  mixed  with  sand,  gypsum,  and 
clay,  suggesting  that  it  had  been  laid  down  at  the  edge  of  an  evapor- 
ating sheet  of  water.  Colemanite  was  originally  obtained  from 
Death  Valley  Desert,  California.  The  Mohave  Desert,  on  the 
borders  of  California  and  Nevada,  and  the  Atacama  desert  of  South 
America  have  in  recent  times  been  the  chief  sources  of  boron  com- 
pounds, the  boron  in  these  deposits  having  probably  been  supplied 
by  hot  springs  and  solfataras  of  volcanic  origin.  In  the  South 
American  region,  the  principal  mineral  is  ulexite  (NaCaB5O9. 
8H2O). 

In  Tuscany  deposits  of  borates  are  formed  on  an  extensive  scale 
from  emanations  of  fumaroles  or  jets  of  steam  issuing  from  the 
ground.  The  deposits  concentrate  in  lagoons,  forming  orthoboric 
acid  or  sassolite  (H3BO3),  ammonium  borate  or  larderellite 
((NH4)2B8O134H2O)  ;  borocalcite  or  bechilite  (CaB4O74H2O),  the 
hydrous  ferric  borate;  lagonite  (Fe'"2B6O12.3H2O),  and  the  am- 
monium compound  boussingaultite  ( (NH4)2Mg(SO4)2.6H2O).  In 
the  most  concentrated  of  the  lagoons  the  orthoboric  acid  (H3BO3) 
amounted  to  19.3  grams  per  liter. 

From  Tibet  borax  deposits  have  been  known  since  very  early 
time.  In  the  lake  plain  of  Pugha,  in  Ladakh,  the  deposits  occur  at 
an  elevation  of  15,000  feet  above  the  sea.  The  deposit  covers  an 
area  of  about  2.  square  miles  and  has  an  average  depth  of  3  feet.  It 
is  formed  by  hot  springs  which  issue  at  this  elevation  with  a  tem- 
perature ranging  from  54°  to  58°  C.  The  deposit  is  impure,  other 
minerals,  including  gypsum,  occurring  with  it. 

DEPOSITS  OF  NITRATES. 

Soda  niter,  or  Chili  saltpeter  (NaNO3),  is  found  in  the  deposits 
of  Searles's  Marsh  and  in  various  other  parts  of  southern  Califor- 
nia, especially  around  Death  Valley,  and  along  the  boundary  between 
Inyo  and  San  Bernardino  counties,  forming  beds  associated  with 
the  later  Eocenic  clays.  In  Searles's  Marsh  it  is  associated  with  the 
borates,  and  the  same  holds  true  for  the  occurrences  in  the  Atacama 
and  Tarapaca  deserts,  northern  Chile.  Here  are  found  the  largest 
known  deposits  of  nitrates  in  the  world,  the  amount  being  officially 


ORIGIN   OF  SALINE  DEPOSITS  365 

estimated  at  2,316  millions  of  metric  quintals  (254,760,000  short 
tons).  The  niter  fields  lie  between  50  and  100  miles  from  the  coast, 
and  at  elevations  exceeding  2,000  feet.  The  crude  sodium  nitrate 
or  "caliche"  occurs  in  deposits  scattered  over  a  large  area  and  is 
associated  with  salt  and  ulexite.  A  section  of  one  of  the  "calichera" 
or  niter  deposits  in  the  Atacama  Desert,  50  miles  west  of  Taltal, 
shows  (Clarke-io:^o7;  242)  : 

1.  Sand  and  gravel o  ft.     1/2  inch 

2.  "  Chusca, "  a  porous,  earthy  gypsum o  ft.         6  inches 

3.  A  compact  mass  of  earth  and  stones 2  to  10  ft. 

4.  "Costra, "   a  low  grade  caliche,   containing 

much  sodium  chloride,  feldspar  and  earthy m 
matter ' I  to  3  ft. 

5.  "Caliche" itoaft. 

6.  " Coba, "  a  clay +3  inches 

The  caliche  varies  in  its  percentage  of  NaNO3  from  31.9  to  56.25. 
Sometimes  it  contains  up  to  7%  CaSO4,  at  others  up  to  10%  or  over 
MgSO4,  and  again  up  to  34.6%  Na2SO4.  Insoluble  impurities  may 
range  as  high  as  45%  or  over.  No  potassium  salts  appear  in  these 
deposits,  but  anhydrite,  gypsum,  epsomite,  halite  and  other  minerals 
are  associated  with  the  nitrates. 

In  the  Tarapaca  desert  the  bed  of  "caliche"  is  from  4  to  12  feet 
thick.  Other  localities  are  known  in  South  America,  but  they  are 
of  much  less  importance.  Potassium  nitrate,  or  saltpeter,  is  found 
as  an  immense  deposit  near  Cochabamba,  Bolivia,  associated  with 
borax.  It  contains  60.7%  KNO3,  30.7%  Na2B4O7,  and  traces  of 
NaCl,  N2O  and  some  organic  matter. 

OTHER  MINERALS  DEPOSITED  UNDER  DESERT  CLIMATES. 

Among  the  minerals  known  to  be  found  under  conditions  of  in- 
adequate rainfall  is  carnotite,  a  more  or  less  impure  hydrated  vana- 
date  of  uranium  and  potash.  It  is  found  as  a  yellow  crystalline 
powder  or  in  loosely  coherent  masses,  and  contains  radium.  It  oc- 
curs somewhat  abundantly  in  Montrose  County  and  elsewhere  in 
Colorado,  and  has  been  found  in  the  Mauch  Chunk  red  shale  of 
Pennsylvania — a  formation  formed  under  comparatively  arid  condi- 
tions. (Wherry-69.) 

ORIGIN  OF  THE   SALINE  DEPOSITS. 

The  source  of  the  various 'saline  deposits  is  a  subject  of  consid- 
erable importance,  since  it  promises  to  throw  light  on  the  condition 


366  PRINCIPLES    OF    STRATIGRAPHY 

of  accumulation  of  ancient  deposits  of  this  type,  and  hence  to  fur- 
nish a  clue  to  the  physiographic  characters  of  the  region  at  the 
time  of  such  deposition.  In  general,  we  may  divide  the  deposits  of 
salts  into  those  abstracted  from  the  hydrosphere,  either  directly  de- 
posited from  the  water  or  secondarily  redeposited  after  leaching,  and 
those  of  chemical  origin,  i.  e.,  formed  by  reactions  of  salts  with  each 
other. 

Sources  of  Sodium  Chloride. 

Marine.  Practically  all  deposits  of  sodium  chloride  may 
be  traced  back  to  the  ocean  water  as  their  original  source. 
Direct  deposition  by  evaporation  and  concentration  of  sea  water 
is,  however,  not  the  only  mode  of  origin  of  such  salts,  al- 
though many  authors,  following  Ochsenius,  have  so  regarded  it. 
The  bar  theory  has  already  been  discussed,  and  its  application  to 
the  origin  of  many  saline  deposits  has  been  indicated.  It  has  been 
shown  that  such  deposition  can  take  place  only  in  arid  regions, 
where  evaporation  concentrates  the  sea  water  within  a  nearly  cut-off 
basin,  to  the  extent  required  for  the  deposition  of  the  salts,  and 
holds  it  at  such  a  state  by  removing  a  quantity  of  water  equal  to 
that  brought  by  the  feeding  current  from  the  sea.  In  order  that 
such  a  feeding  may  be  accomplished,  it  is  necessary  that  the  salt- 
depositing  bay  be  in  the  vicinity  of  a  constant  source  of  supply,  i.  e., 
the  ocean  or  an  inland  saline  sea  of  vast  dimensions,  like  the  Cas- 
pian. In  such  an  ocean  or  inland  sea,  deposits  of  clastic  and  or- 
ganic character  would  accumulate,  so  that  for  every  great  salt  de- 
posit formed  in  the  neighborhood  of  the  sea  by  concentration  of 
sea  water,  there  should  be  a  corresponding  fossiliferous  series  of 
normal  marine  type  of  sediments.  Furthermore,  as  shown  by  the 
deposits  in  the  Bitter  Lakes  of  Suez,  and  the  Karabugas  Gulf,  the 
deposits  formed  within  the  natural  salt  pan  will  be  highly  fossilifer- 
ous, full  of  the  remains  of  the  organisms  of  the  contemporaneous 
sea  from  which  the  supply  of  salt  water  was  derived.  These  two 
criteria  are  the  most  significant,  and  when  they  fail,  as  in  the  case 
of  the  salt  deposits  of  the  Mid-Siluric  (Salman)  of  North  America, 
these  deposits  cannot  be  regarded  as  the  results  of  direct  evapora- 
tion of  sea  water.  (Grabau-iQ.) 

Leaching  of  Salt  from  Older  Formations  and  Its  Segregation. 
Extensive  salt  deposits  may  form  by  the  leaching  of  the  salt  of  an 
older  saliferous  formation  and  its  redeposition  within  a  drainless 
basin  by  concentration  through  evaporation.  That  such  salt  deposits 
are  now  going  on  is  believed  to  be  the  case  in  a  number  of  regions. 


SOURCES    OF    SODIUM    CHLORIDE  367 

A  large  part  of  the  salt  of  the  Dead  Sea  is  said  to  be  derived 
through  leaching  of  an  older  salt  bed. 

A  far  more  important,  because  more  universal,  source  of  salt  is 
found  in  the  imprisoned  or  connate  waters  of  the  older  marine  sedi- 
ments. When  sediments  carrying  such  water  are  exposed  by  erosion, 
their  saline  contents  will  be  drawn  to  the  surface  by  capillarity  and 
the  evaporation  of  the  water.  It  is  obvious  that  this  can  proceed  on 
an  extended  scale  only  in  arid  districts,  where  meteoric  waters  play 
but  a  minor  part.  The  salt  from  the  fossil  sea  water  will  form  an 
efflorescence  on  the  surface  of  the  rocks,  where  it  will  remain  until 
removed  by  the  wind  or  rain.  If  the  region  is  a  drainless  basin  the 
salt  redissolved  by  the  rain  will  be  carried  to  the  center  of  a  neigh- 
boring depression,  where  it  will  accumulate  on  evaporation  of  the 
water.  Salt  carried  by  wind  may  be  deposited  anywhere  within  or 
without  the  basin. 

The  quantity  of  salt  which  is  furnished  by  various  ancient  ma- 
rine sediments  depends  to  a  large  degree  upon  the  pore  space  of  the 
rock.  As  we  have  seen  (page  140),  this  is  sometimes  as  high  as 
60%  or  over,  but  more  generally  falls  below  40.  If  we  take  35% 
as  an  average  measure,  and  take  the  salinity  of  the  former  ocean  as 
equal  to  that  of  to-day,  i.  e.,  35  permille,  we  can  readily  see  that 
marine  sediments  include  about  i%  of  sea  salt,  which  is  three- 
fourths  NaCl.  A  marine  formation,  which  has  a  thickness  of  1,000 
meters,  as  in  the  case  of  the  Jura  of  Europe,  could  furnish  a  bed  of 
salt  approximately  10  meters  thick  and  extending  over  the  entire 
area  covered  by  such  a  formation.  If  such  salt  becomes  concen- 
trated into  a  smaller  area,  the  deposit  will,  of  course,  be  of  a  pro- 
portionally greater  thickness. 

Analyses  of  modern  marine  sediments  have  shown  an  even 
greater  salt  content,  due  to  electrolytic  separation  of  the  salt  from 
sea  water.  Thus  the  deep-sea  red  clay  contained  from  6.8  to  8% 
of  salt.  Diatomaceous  ooze  contained  $.4%  ;  Antarctic  glacial  clay, 
1.9  to  3.7%;  Globigerina  ooze,  i.o  to  3.4%.  These  differences  in 
amount  are  due  to  differences  in  absorption  power  of  the  various 
sediments.  (Andree-2  1355.) 

The  leaching  of  the  connate  salts  from  old  sediments  furnishes 
the  rivers  with  their  load  of  salt  in  solution ;  as  an  example  may  be 
quoted  the  high  percentage  of  chlorine  which  rises  to  32.63%  in 
the  Rio  de  los  Papagayos  of  Argentina.  In  this  same  river  the 
water  carries  26.48%  of  sodium,*  its  total  salinity  being  9.185  per- 
mille. This  water  runs  into  the  ocean,  but  if  similar  water  runs  into 

*This  percentage  is  of  the  total  solids,  corresponding  to  2.997  and  2.432 
permille,  respectively.  See  table  pp.  162-3. 


368  PRINCIPLES    OF    STRATIGRAPHY 

a  drainless  basin  it  is  evident  that  the  salt  will  be  deposited  on 
evaporation  of  the  water,  and  that  such  deposits  are  limited  in 
thickness  only  by  the  depth  of  the  basin  and  the  continuation  of 
erosion  of  the  tributary  area.  Salts  deposited  in  this  manner  will, 
of  course,  be  free  from  marine  organic  remains,  though  terrestrial 
organisms  or  brine  animals  may  be  enclosed.  The  area  tributary  to 
this  basin  will  show  extensive  erosion  during  the  period  of  forma- 
tion of  the  salt  deposits,  while  the  salt  beds  themselves  rest  on  the 
formation  elsewhere  eroded,  and  will  be  covered  by  a  formation 
which  elsewhere  rests  on  the  eroded  surface  of  the  formation  below 
the  salts,  or  on  an  earlier  one. 

Besides  the  segregation  of  the  salts  in  desert  regions  through 
streams,  due  credit  must  be  given  to  the  wind.  Where  rock  sur- 
faces are  covered  with  an  efflorescence  of  salt,  the  dry  wind  may 
sweep  it  away  and  redeposit  the  salt  particles  mixed  with  clay  or 
dust.  In  rare  cases  large  particles  of  salt  may  be  picked  up  by  the 
wind  and  dropped  elsewhere,  as  in  the  case  of  the  remarkable  salt 
hail  which  fell  near  the  Lucendro  bridge  of  the  Gotthard  road  on 
August  30,  1870,  at  ii  A.  M.  (Kengott,  quoted  by  Walther-6o.) 
Saline  clays  may  be  deposited  at  any  altitude  by  the  wind,  while 
playa  surfaces  may  be  dusted  over  with  a  layer  of  salt  particles, 
which  adhere  to  the  surface  rendered  damp  by  the  presence  in  the 
clay  of  hygroscopic  salts. 

Shallow  salt  lakes  or  playas  may  be  dried  by  a  covering  of 
desert  sands,  which  will  sponge  up  the  mother  liquor  and  so  leave 
only  the  pure  salt  behind.  On  reaching  the  surface  of  the  covering 
sand  dunes  through  capillary  action,  the  efflorescing  salts  may  be 
scattered  far  and  wide  by  the  winds.  Desert  salts  are  probably,  as 
a  rule,  free  from  the  potash  salts. 

These  mother  liquor  salts  crystallize,  as  a  rule,  only  at  very 
high  or  very  low  temperatures.  Thus  kieserite  (MgSO4.H2O) 
crystallizes  out  in  the  laboratory  only  on  evaporation  of  the  solution 
at  temperatures  above  100°  C.,  while  a  solution  of  carnallite 
(KMgCl3.6H2O)  first  loses  its  water  at  a  temperature  of  120°  C. 
This  same  substance,  however,  has  been  found  to  crystallize  out 
at  a  low  winter  temperature,  such  as  can  readily  be  produced  in 
continental  areas,  or  where  snow  is  mixed  with  the  brine. 


Sources  of  Calcium  Sulphate. 

Gypsum,  like  salt,  is  deposited  from  sea  water  direct,  or  from 
concentrated  lake  waters  or  in  playas.     It  may  be  said  to  have  the 


SOURCES    OF   ALKALINE    CARBONATES          369 

same  source  as  the  sodium  chloride,  being  one  of  the  constituents 
of  the  sea  water  whether  recent  or  fossil.  Gypsum  forms  as  an  ef- 
florescence or  incrustation  in  caves,  and  it  is  also  produced  exten- 
sively by  the  alteration  of  other  rocks.  Oxidation  of  pyrite  in 
calcareous  rock  often  results  in  the  formation  of  this  mineral  and 
so  does  the  double  decomposition  between  other  metallic  sulphates 
and  calcium  carbonate. 


Sources  of  Alkaline  Carbonates. 

The  origin  of  the  alkaline  carbonates  deposited  by  many  waters 
has  been  attributed  to  the  leaching  of  volcanic  rocks.  Near  Owens 
Lake  some  of  the  seepage  waters  percolate  through  beds  of  vol- 
canic ash,  and  contain  even  a  higher  proportion  of  alkaline  carbon- 
ates than  the  lake^  itself.  The  rocks  from  which  these  salts  were 
originally  derived  seem  to  have  been  mainly  rhyolites,  andesites,  and 
others  rich  in  alkalies  and  relatively  poor  in  lime.  (Clarke-io,  2d 
ed.  1229.) 

Other  sources  of  alkaline  carbonates  in  natural  waters  and  soils 
are  found  in  the  double  decomposition  between  calcium  bicarbonate 
and  alkaline  sulphates  (T.  Sterry  Hunt)  or  alkaline  chlorides  (E. 
von  Kvassay)  and  in  the  reduction  of  alkaline  sulphates  by  organic 
matter  and  the  subsequent  absorption  of  CO2  from  the  air  (E.  Sick- 
enberger).  Finally,  Ochsenius  suggested  that  alkaline  carbonates 
are  formed  by  the  action  of  CO2,  commonly  of  volcanic  origin,  on 
the  mother  liquor  salts.  In  Egypt,  Chile,  and  Bolivia  he  finds  also  a 
lack  of  association  of  lime  and  sodium  carbonate,  but  he  notes  the 
occurrence  of  eruptive  rocks  as  sources  of  CO2  exhalations.  In 
Utah  and  in  the  Sahara  he  finds  an  association  of  lime  with  the 
mother  liquor  salts,  but  no  sodium  carbonate,  because  eruptive  rocks, 
the  sources  of  CO2,  are  absent.  Finally,  in  Nevada  he  finds  the 
mother  liquor  salts  associated  with  eruptive  rocks  and  much  soda. 
He  concludes,  therefore,  that  an  association  of  lime  with  the  mother 
liquor  salts  alone  produces  no  alkaline  carbonates,  but  that  CO2 
emanations  from  volcanic  sources  (with  or  without  the  presence 
of  lime  reaction  on  these  salts)  will  produce  the  alkaline  carbonates. 
The  widespread  occurrence  of  sodium  carbonate  in  the  soils  of  arid 
regions  is  attributed  by  Hilgard  (23)  to  the  reaction  between  al- 
kaline salts  and  calcium  bicarbonate.  When  by  excessive  irriga- 
tion these  salts  are  dissolved  they  rise  to  the  surface  by  capillary 
attraction  to  form  the  crusts  of  "alkali." 


370  PRINCIPLES    OF    STRATIGRAPHY 

Sources  of  Boric  Acid  and  B orates  and  of  Nitrates. 

Boric  acid  and  saline  borates  are  commonly  formed  by  volcanic 
activities,  as  in  the  case  of  the  Tuscan  fumaroles,  where  ammonium 
salts  also  occur,  an  association  found  in  undoubted  volcanic  vents. 
Leaching  of  rocks  containing  borosilicates  (tourmaline,  axinite,  dato- 
lite,  etc.),  as  in  the  case  of  granites,  mica  schists,  etc.,  also  probably 
accounts  for  some  of  the  deposits  of  borates,  and  more  rarely  such 
deposits  originate  from  sea  water,  though  Ochsenius  and  some  other 
writers  attempt  to  refer  all  such  deposits  to  a  marine  origin.  When 
the  origin  is  undoubtedly  a  marine  one,  magnesium  borates  are  the 
result,  while  lake  deposits,  like  those  of  California  and  Chile,  con- 
tain calcium  borates,  with  nitrates  near  by.  Volcanic  waters  and 
fumaroles,  on  the  other  hand,  yield  ammonium  compounds  along 
with  the  borates.  The  sodium  nitrate  deposits  of  Chile  and  other 
regions  and  the  extensive  potassium  nitrate  beds  of  Bolivia  are  like- 
wise regarded  by  Ochsenius,  Penrose,  and  others  as  of  marine 
origin,  either  directly  or  indirectly.  Ochsenius  derives  the  Chilean 
nitrates  from  the  mother  liquors  of  salts  deposited  in  the  Andes, 
which,  flowing  downward  to  the  plains,  have  their  chlorides  partly 
converted  to  carbonates  by  CO2  of  volcanic  origin.  The  nitrogen 
is  brought  as  ammoniacal  dust  from  guano  beds  upon  or  near  the 
sea  coast,  the  heavier  phosphatic  particles  being  left  behind.  The 
sufficiency  of  the  amount  of  ammoniacal  dust  thus  carried  has  been 
questioned,  and  it  has  been  pointed  out  that  carbonates  are  com- 
paratively rare  in  the  nitrate  regions. 

Penrose  (44  :i6)  regards  the  nitrate  fields  as  a  former  ocean  bot- 
tom and  likewise  derives  his  nitrogen  from  guano,  the  iodine  from 
decomposing  sea  weeds  or  from  mineral  springs  and  the  accompany- 
ing borates  from  the  decomposition  of  rocks,  containing  boron-bear- 
ing minerals.  A  volcanic  origin  has  also  been  suggested  for  the 
nitrogen  (Clarke-io,  2d  ed.  -.246). 


SUMMARY. 

To  sum  up,  it  is  apparent  that  salt  deposits  of  to-day,  when 
not  referable  to  a  volcanic  source,  are  only  to  a  slight  extent  due  to 
direct  evaporation  of  the  water  on  the  sea  coast,  but  that  by  far 
the  more  prominent  mode  of  formation  is  a  secondary  one,  the  salt 
being  derived  from  the  enclosed  connate  waters »,of  marine  sediments 
or  from  the  products  of  alteration.  In  all  cases  a  relatively  arid 
climate  is  necessary  to  permit  extensive  evaporation,  so  that  salt 


THE    STASSFURT    SALTS  371 

deposits  may  legitimately  be  considered  as  indices  of  dry  climates 
during  the  period  of  their  formation.  Since  most  modern  salt  de- 
posits are  of  continental  origin,  a  similar  origin  may  have  obtained 
for  the  deposit  of  past  geologic  periods. 

ANCIENT  SALT  DEPOSITS. 

Salt  deposits  are  found  in  most  geological  formations  from  the 
Cambric  (?*)  to  the  Present,  and  in  all  cases  they  are  associated 
with  other  evidence  of  continental  expansion.  Until  recently  the 
salt  range  of  India  was  supposed  to  hold  the  oldest  salt  deposits, 
these  underlying  marine  strata  of  Lower  Cambric  age.  It  is  now 
held,  however,  that  these  salt  deposits  are  of  much  later  age,  perhaps 
even  as  late  as  Tertiary  time,  and  that  the  Cambric  strata  owe  their 
present  position  above  the  salt  beds  to  an  overthrust.  The  thickness 
of  many  of  the  ancient  salt  deposits  is  very  great,  individual  beds  100 
feet  thick  having  been  found  in  the  Siluric  deposits  of  Michigan. 
Deposits  of  much  greater  thickness  are  known,  but  these  are  either 
complicated  by  intercalated  anhydrite  or  polyhalite  layers,  or  they 
are  in  the  form  of  salt  domes,  a  formation  of  limited  extent,  and  of 
secondary  origin. 

THE  STASSFURT  SALTS.  The  extensive  salt  beds  of  Upper 
Permic  (Zechstein)  age  in  North  Germany  in  the  Stassfurt,  or  more 
properly  the  Magdeburg-Halberstadt  region,  may  be  taken  as  an  ex- 
ample of  a  complex  deposit  in  which  the  strata  have,  on  the  whole, 
suffered  little  alteration  or  rearrangement.  The  Border  of  succession 
is  as  follows,  in  descending  order  (Walther-65)  : 

1.  Lower  Buntsandstein  (capping  rock) 

2.  Red  clay  with  concretions  of  anhydrite  and  salt 

cavities abt.  20  m. 

3.  Anhydrite  layer  (Anhydrite  IV) abt.    4  m. 

4.  Rock  Salt abt.  40  m. 

5.  Anhydrite  III  (Pegmatitanhydrit) abt.    5  m. 

6.  Red  clay abt.  10  m. 

7.  Younger  Rock  Salt,  with  about  400  annual  rings 

**  of  Polyhalite abt.  80  m. 

8.  Main    anhydrite    (Hauptanhydrit)  Anhydrite  II 

varying from  30  to  80  m. 

9.  Salt  clay,  averaging from    5  to  10  m. 

10.     Carnallite  zone from  15  to  40  m. 

This  is  sometimes  overlain  by  a  layer  of  rock  salt,  at  others  by  a  kainite  layer 
followed  by  one  of  "sylvinite"  or  "hartsalz"  and  that  by  one  of  schoenite  before 
reaching  the  salt  clay. 

*  The  Indian  salt  deposits  are  the  only  ones  of  significance  which  have  been 
referred  to  the  Cambric. 


372  PRINCIPLES    OF    STRATIGRAPHY 

n.     Kieserite  zone  averaging 18  m. 

12.  Polyhalite  zone  averaging 35  m. 

13.  Older  Rock  Salt  with  about  3,000  "annual"  rings 

of  anhydrite  averaging 245  m. 

Nos.  n,  12,  and  13  have  a  combined  thickness 

ranging  from   150  to  perhaps   1,000    meters.* 

~  The  "annual"  rings  of  anhydrite  form  layers 

averaging  7  millimeters  thick,  separating  the 

salt  into  sheets  of  8  or  9  millimeters. 

14.  Older    anhydrite    and    gypsum    (Anhydrite     I) 

averaging 100  m. 

15.  Zechstein  limestone  or  dolomite 

1 6.  Kupferschiefer 

17.  Zechstein  conglomerate 

1 8.  Upper  Rothliegende  (base  of  section) 

The  lower  members,  beginning  with  Anhydrite  I  and  ending  with 
the  carnallite  zone  (and  sometimes  the  kainite,  sylvinite  and  schoen- 
ite  zones),  form  one  depositional  series,  the  last  being  the  salts  from 
the  mother  liquor.  This  is  followed  by  a  protecting  layer  of  clay. 
Apparently  a  second  depositional  series  began  with  the  second  or 
main  anhydrite  and  the  Younger  Rock  Salt,  but  lacks  the  mother 
liquor  salts. 

Altogether  more  than  thirty  saline  minerals  are  found  in  the 
Stassfurt  deposit.  Of  these  some  of  the  more  prominent  besides  the 
halite  and  anhydrite  are : 

Carnallite KMgCl3.6H2O 

Kieserite MgSO4.H2O 

Polyhalite 2CaSO4.MgSO4.K2SO4.2H2O 

Kainite MgSO4.KCl.3H2O 

Sylvite KC1  (Sylvinite  is  a  mixture  of  sylvite  and  rock  salt; 

Hartsalz  contains  these  substances  together  with 

Kieserite). 
Schoenite MgSO4.K2SO4.6H2O 

Borates,  especially  boracite  (Mg7Cl2B16O30),  occur  with  the  carnal- 
lite  and  in  the  overlying  zone.  A  noteworthy  fact  is  that  these  de- 
posits are  absolutely  unfossiliferous,  in  spite  of  the  fact  that  organic 
remains  would  here  have  a  chance  for  perfect  preservation. 

These  deposits  have  been  commonly  regarded  as  illustrations  of 
the  Bar  Theory,  but  against  this  interpretation  strong  objections 
have  been  urged,  especially  by  Walther  (62:63)  and  by  Erdmann 
(16).  Walther  uses  as  his  main  arguments  against  such  an  origin 
the  absolute  want  of  organic  remains  in  these  deposits,  and  the  fur- 

*  This  is  probably  the  result  of  thickening  through  subsequent  diagenetic 
processes,  the  average  of  the  salt  deposits  in  undisturbed  regions  being  about 
350  meters. 


THE    STASSFURT    SALTS  373 

ther  fact  that  anhydrite  is  the  first  deposit  and  not  gypsum,  as  would 
be  the  case  for  evaporating  sea  water.  The  second  series  of  deposits 
above  the  mother  liquor  salts  again  begins  with  anhydrite  instead 
of  gypsum.  Walther  (65)  regards  these  deposits  as  due  to  evapora- 
tion of  a  shallow  late  Permic  or  Zechstein  sea,  entirely  cut  off  from 
the  ocean,  and  surrounded  by  a  country  changing  gradually  from 
pluvial  to  desert  conditions.  This  old  sea  extended  from  the  Urals 
in  Russia,  on  the  east,  over  North  Germany,  and  the  region  of  the 
North  Sea  to  the  center  of  England.  On  the  south  its  boundary 
was  partly  formed  by  the  Bohemian  mass,  and  the  old  Vindelician 
and  Armorican  Mountain  chains,  the  former  in  the  region  of  the 
present  Danube  plain,  the  latter  extending  through  France,  Belgium, 
South  England,  and  Ireland.  In  the  north,  and  on  the  southeast, 
the  separation  was  caused  by  the  development  of  extensive  broad 
marsh  lands.  During  the  gradual  evaporation  of  this  sea,  the  salt 
deposits  accumulated  in  the  deeper  areas  of  the  basin,  where  to-day 
they  cover  scarcely  the  fiftieth  part  of  the  original  area  of  the  salt 
sea.  As  partial  areas  were  laid  bare  the  salt  deposited  there  was 
again  dissolved  by  the  streams  and  carried  to  the  pools  which  still 
existed,  and  thus  the  concentration  became  more  and  more  pro- 
nounced. Under  the  influence  of  changing  temperature  and  mois- 
ture with  the  change  of  seasons,  the  nature  of  the  precipitate  varied, 
and  thus  the  salt  beds  are  separated  at  regular  intervals  by  layers  of 
anhydrite  or  polyhalite,  forming  the  annual  rings.  Their  number 
suggests  that  the  deposition  of  the  Stassfurt  salt  occupied  a  period 
of  about  10,000  years.  Erdmann  ( 16)  holds  that  the  amount  of  an- 
hydrite in  the  deposits  is  too  great  to  be  derived  solely  from  the 
drying  up  of  this  sea,  and  he  therefore  supposes  that  additional 
amounts  of  calcium  sulphate  were  brought  into  it  by  the  streams 
from  the  surrounding  regions. 

According  to  Van't  Hoff  and  Weigert  (54 11140)  anhydrite  forms 
from  gypsum  in  sodium  chloride  solutions  at  30°  C.  (+86°  F.), 
while  in  the  sea  water  this  transformation  takes  place  at  25°  C. 
(+77°  F.).  At  ordinary  temperatures,  according  to  Vater,  calcium 
sulphate  crystallizes  from  a  saturated  solution  of  salt  in  the  form  of 
gypsum.  Such  high  temperatures  are  not  to  be  found  in  water  of 
bays  still  in  connection  with  the  sea,  especially  in  the  present  latitude 
of  the  Stassfurt  salt  deposit,  unless  indeed  the  temperature  of  the 
whole  earth  was  higher.  The  Red  Sea,  which  to-day  has  the  highest 
temperature  of  any  mediterranean,  has  a  bottom  temperature  of 
21.5°  C,  its  mean  temperature  being  22.69°  C.  The  Persian  Gulf, 
on  the  other  hand,  has  a  mean  temperature  of  24°,  owing  to  its 
greater  shallowness  (see  Chapter  IV).  Where  influx  of  cooler 


374  PRINCIPLES    OF    STRATIGRAPHY 

ocean  water  is  prevented,  however,  the  temperature  of  the  entire 
body  may  easily  rise  to  the  required  degree.  When  the  deeper 
layers  had  become  a  concentrated  brine  the  successive  influxes  of 
calcium  sulphate,  probably  during  the  rainy  period  when  the  streams 
brought  this  mineral  in  solution  from  the  surrounding  country,  were, 
on  passing  through  these  layers  of  brine,  deposited  directly  as  anhy- 
drite, in  alternate  layers  with  the  salt  deposits.  That  these  influxes 
of  calcium  sulphate  were  not  due  to  successive  ingressions  of  the 
open  sea  is  shown  by  the  utter  lack  of  marine  organic  remains  in 
these  strata.  In  this  manner  were  formed  the  3,000  or  more  layers 
of  anhydrite  which  divide  the  older  rock  salt.  With  the  progress  of 
concentration,  the  supernatant  solution  became  a  bittern  -rich  in  mag- 
nesium salts,  whereupon  the  calcium  sulphate  united  with  these  salts, 
forming  polyhalite  (2CaSO4.MgSO4.K2SO4.2H2O).  The  polyhalite 
stratum  of  Stassfurt  is  essentially  a  bed  of  rock  salt,  containing, 
with  other  impurities,  from  6  to  7  per  cent,  of  polyhalite.  With 
further  concentration  of  the  mother  liquor,  kieserite  (MgSO4.H2O) 
was  deposited,  this  requiring  a  temperature  above  72°  C.  for  its  dep- 
osition. The  zone  named  after  it  contains  about  17%  of  this  min- 
eral, together  with  13  of  carnallite,  3  of  bischofite.  2  of  anhydrite, 
and  65  of  rock  salt.  At  this  stage  polyhalite  was  no  longer  de- 
posited. 

The  final  step  in  the  concentration  of  the  mother  liquor  produced 
the  carnallite  zone.  The  average  composition  of  this  zone  is  55 
per  cent,  of  carnallite,  25  of  rock  salt,  16  of  kieserite,  and  4  of 
various  other  minerals.  The  carnallite  (KMgC\^.6H2O)  was  formed 
from  the  chlorides  which  had  hitherto  remained  in  solution,  and  it 
represents  the  more  or  less  complete  drying  up  of  the  bittern  lake. 
The  protecting  layer  of  clay  must  have  been  formed  by  winds,  for 
water  would  have  caused  a  resolution  of  the  carnallite. 

The  reestablishment  of  the  conditions  of  deposition,  first  for  anhy- 
drite and  later  for  rock  salt,  which  produced  the  "younger  succes- 
sion," suggests  a  renewed  invasion  of  the  sea.  This  is  negatived, 
however,  by  the  absence  of  organic  remains  either  in  the  salt  clay 
or  in  the  succeeding  anhydrite.  This  younger  series  may,  therefore, 
be  wholly  of  continental  origin,  the  anhydrite  and  salt  being  both 
derived  from  connate  waters. 

The  change  to  a  dry  climate  over  the  region  of  North  Germany 
is  understood  when  we  take  into  consideration  the  fact  that  at  the 
beginning  of  Permic  time  the  Armorican  Mountain  chain  began  to 
rise,  extending  from  the  region  of  what  is  now  central  France  north- 
westward to  the  present  Irish  Isle.  This  placed  a  barrier  directly 
across  the  path  of  the  prevailing  Westerlies,  which  then  were  ap- 


ORIGIN    OF    STASSFURT    SALTS  375 

parently  much  as  they  are  to-day.  As  a  result,  rainy  conditions 
prevailed  on  the  windward  side  of  these  mountains,  where  the  old 
mediterranean  or  Thetis  Sea  of  that  day  was  situated,  but  arid 
conditions  were  produced  over  the  region  beyond  these  mountains 
by  these  winds,  which  on  crossing  the  mountains  became  aridifiers. 
As  a  result  of  this  change  in  climate  the  region  of  North  Germany, 
Belgium,  etc.,  previously  one  of  much  moisture  and  characterized 
by  the  formation  of  luxurious  coal  swamps,  became  the  theatre  of 
deposition  of  the  red  sands  of  the  lower  Permic  or  Rothliegende. 
The  lower  division  of  this  deposit  forms  a  transition  from  the  coal- 
bearing  formations  preceding  and  contains  at  first  some  coal  and 
plant  remains.  Extensive  forests  of  calamites,  ferns,  and  conifers 
covered  the  rising  lands,  for  at  first  the  barrier  was  not  sufficient  to 
keep  the  moist  winds  out.  The  progressive  development  of  the 
mountain  system  finally  involved  some  of  the  earlier  Rothliegende 
deposits,  so  that  the  later  division,  mostly  free  from  plant  remains, 
rests  unconformably,  in  part  on  the  folded  and  eroded  lower  divi- 
sion. There  is  thus  indicated  a  progressive  aridification  of  the 
region,  due  no  doubt  to  the  continued  growth  of  the  Armorican 
Mountain  system  which  became  more  and  more  effective  as  a  bar- 
rier for  the  moisture-laden  southwest  winds. 

The  Rothliegende  desert  was  invaded  by  the  Zechstein  Sea  from 
the  North  Russia  region,  marked  at  first  by  invading  channels  with 
a  marine  fauna,  while  elsewhere  sand-dunes,  now  forming  the 
Weissliegende,  covered  the  lowlands.  Then  followed  the  peculiar 
conditions  producing  the  Kupferschiefer,  which  were  probably  due 
to  a  separation  of  the  early  waters  from  the  ocean  to  the  north,  to 
form  a  shallow,  brackish  lake  into  which  streams  from  the  sur- 
rounding old  land,  the  Harz,  Frankenwald,  Erzgebirge,  and  rhein- 
ische  Schiefergebirge,  carried  mineral  matter  in  solution.  The  abun- 
dant fish  fauna  of  this  lake  eventually  succumbed  to  the  gradual 
fouling  of  these  stagnant  waters  and  the  carcasses  were  buried  in 
the  black  muds,  which  also  enclosed  the  metallic  precipitates.  The 
renewed  invasion  of  this  area  by  the  Russian  Sea  then  led  to  the 
formation  of  the  marine  Zechstein  with  its  Bryozoa  reefs  and  rich 
fauna,  and  for  a  long  time  the  conditions  of  an  open  sea  existed 
over  North  Europe.  That  the  winds  from  the  southwest  still  main- 
tained their  drying  characteristic  is  shown  by  the  deposits  of  western 
England,  which  remained  of  the  arid  type,  and  extended  down  to, 
and  perhaps  partly  into,  the  Zechstein  (Magnesian  limestone)  Sea. 
The  marine  fauna  of  the  Zechstein  found  conditions  of  existence 
more  favorable  where  the  old  Kupferschiefer  muds  were  absent,  as 
around  the  margins  of  the  old  lands  and  the  projecting  islands  of 


376  PRINCIPLES    OF    STRATIGRAPHY 

older  rock.  Here  the  fauna  is  richest,  and  the  reefs  often  rest  di- 
rectly upon  the  eroded  old  land.  Over  the  floor  of  the  sea,  however, 
underlain  by  the  black  muds,  conditions  of  existence  were  less 
favorable,  probably  because  the  gases  resulting  from  the  decay  of 
the  vast  number  of  fishes  in  these  muds  were  constantly  rising,  and 
so  the  fauna  is  much  poorer  as  well  as  more  or  less  dwarfed  in 
species  and  in  individuals. 

With  the  persistence  of  the  aridifying  winds  it  required  only  a 
second  closing  of  the  inlet  of  the  North  Russian  waters  to  convert 
the  Zechstein  Sea  into  a  salt  pan,  through  the  gradual  evaporation 
of  the  water.  It  is  probable  that  the  connection  with  the  sea  was 
temporarily  reestablished  at  least  once  during  this  period,  this  being 
indicated  by  the  formation  of  the  upper  salt  series.  With  the  pro- 
gressive drying  up  of  this  sea,  the  red  continental  sands  encroached, 
and  eventually  covered  the  entire  region  of  the  former  Zechstein 
Sea,  forming  the  Bunter  Sandstein,  the  base  of  the  Trias.  Thus 
actual  desert  conditions  were  established  over  Northwest  Europe 
and  continued  until  the  invasion  of  the  Muschelkalk  Sea. 

THE  SILURIC  SALTS  OF  NORTH  AMERICA.  These  present  a  rather 
different  type  of  deposit.  In  southern  Michigan  this  formation 
reaches  a  thickness  of  nearly  a  thousand  feet.  It  includes  nine 
separate  salt  beds,  several  of  them  100  feet  thick,  while  the  lowest 
one  is  160  feet  thick  (Lane~32:pl.  xl).  The  annual  rings  character- 
istic of  the  Stassfurt  salt  seem  to  be  wholly  wanting  here,  and  the 
same  is  true  for  the  potash  salts.  The  various  beds  of  salt  are 
separated  by  layers  recorded  in  the  wells  as  shale  or  limestone,  some 
of  which,  however,  are  most  probably  gypsum  or  anhydrite.  In  cen- 
tral New  York  the  following  succession  is  shown  in  descending 
order : 

BERTIE  WATER  LIME — Upper  Monroe 60  ft. 

SALINA  GROUP: 

Camillas  shales  and  gypsum 250-300  ft. 

Syracuse  salt 100-470  ft. 

Vernon  red  shales 200-525  ft. 

Pittsford  shales 41  ft. 

GUELPH  dolomite  of  the  Niagaran 

The  salt  series  (Syracuse)  is  thinner  than  in  Michigan.  In  the 
well  sunk  at  Ithaca,  New  York,  it  has  a  thickness  of  only  470  feet 
and  includes  seven  salt  beds  ranging  in  thickness  from  17  to  54  feet, 
with  shale  partings  ranging  from  6  to  82  feet  in  thickness.  Where 
actually  exposed,  as  in  the  Livonia  and  other  salt  shafts,  something 
akin  to  the  annual  rings  of  Stassfurt  is  seen,  in  thin  intercalated 
layers  of  gypsum  and  shaly  material.  These  are,  however,  discon- 


SILURIC    SALTS    OF   AMERICA  377 

tinuous  and  only  locally  developed.  The  beds  are  all  horizontal  and 
in  rare  cases  are  any  of  the  layers  distorted  as  is  so  commonly  the 
case  in  the  North  German  salt  deposits.  Pieces  of  rock,  either  shale 
or  limestones  are  not  uncommonly  embedded  in  the  salt ;  sometimes 
these  pieces  are  large,  and  seem  to  represent  a  broken-up  cover  of 
clay  or  lime,  which  subsequently  sank  into  the  upper  salt  layers,  or 
was  buried  by  the  new  formed  strata. 

The  Pittsford  shale  at  the  base  of  the  series  represents  a  change 
from  the  preceding  Niagaran  (Guelph)  sea  to  the  continental  con- 
ditions under  which  the  salt  was  deposited.  The  shale  alternates 
with  dolomitic  layers  which  contain  the  last  survivors  of  the  Guelph 
fauna.  Near  the  middle  of  the  mass  occur  a  few  black  shale  layers 
crowded  with  fragments  and  molts  of  entire  individuals  of  six  spe- 
cies of  Eurypterida,  including  the  genera  Eurypterus,  Pterigotus, 
and  Hughmilleria,  and  several  species  of  Phyllocarida,  and  at  least 
one  Synxiphosuran  (Pseudoniscus  roosevelti).  Followed  eastward 
for  two  hundred  miles,  this  fauna  is  found  in  black  shale  layers 
in  the  Shawangunk  conglomerate  of  eastern  New  York  and  Penn- 
sylvania, which  is  interpreted  as  a  great  continental  fan  formed 
along  the  rising  Appalachians  during  the  same  period,  and  form- 
ing part  of  the  upward  movement  of  the  North  American  continent 
of  that  time,  which  resulted  in  the  complete  withdrawal  of  the 
Niagaran  sea  of  that  period.  (Grabau-2o.) 

The  close  of  the  Pittsford  shale  epoch  marks  the  period  of  de- 
struction of  the  animal  life  of  the  Siluric  sea  in  North  America,  the 
red  Vernon  shales,  a  distinct  continental  type  of  deposit  400  feet  or 
more  in  thickness,  succeeding  in  central  New  York.  These  can  like- 
wise be  traced  eastward,  where  they  swell  enormously,  forming  the 
Longwood  shales  of  New  Jersey  some  2,000  feet  thick,  and  through- 
out of  continental  origin.  While  the  red  Vernon  shales  of  central 
New  York  were  depositing,  salt  formed  in  the  deeper  basin  of  south- 
ern Michigan.  Some  of  this  may  have  resulted  from  the  final  evap- 
oration of  the  waters  of  the  Niagaran  sea,  for  the  salt  there  lies  fre- 
quently directly  upon  the  limestone.  No  gypsum  or  anhydrite  has 
been  recorded,  but,  as  before  noted,  it  is  not  improbable  that  some 
of  the  limestone  beds  recorded  in  the  well  sections  are  in  reality 
anhydrite.  The  salt  of  central  New  York  was  probably  derived 
altogether  from  connate  waters  enclosed  in  the  recently  formed 
marine  Niagaran  and  earlier  strata  which  underlay  and  surrounded 
the  salt  basins  and  which  suffered  extensive  erosion  during  this  pe- 
riod. While  these  salt  deposits  were  forming,  red  sedimentation 
was  still  going  on  in  eastern  New  York,  New  Jersey,  and  Pennsyl- 
vania. The  centra]  New  York  salt  basin  extends  from  the  Oatka 


378  PRINCIPLES    OF    STRATIGRAPHY 

valley  in  Wyoming  county  to  Morrisville  in  Madison  county  and 
southward  for  an  undetermined  distance.  Western  New  York  is 
free  from  salt,  which  was  either  not  deposited,  or  was  removed 
by  erosion  during  Upper  Siluric  time. 

Immediately  above  the  red  Vernon  shales  the  salt  is  coarsely 
crystallized,  the  crystals  being  commonly  embedded  in  the  mud. 
Limestone,  shale  and  gypsum  occur  as  fragments  mixed  with  the 
clear  salt  crystals,  the  whole  forming  a  brecciated  mass.  Sometimes 
in  the  basal  salt  beds  there  is  an  abundance  of  layers  and  irregular 
masses  of  shale  and  limestone,  while  in  other  localities  the  salt  is 
almost  pure.  At  Livonia  this  basal  layer  is  succeeded  by  8  feet  of 
stratified  marlyte  grading  upward  into  impure  magnesian  limestones, 
both  shales  and  limestones  being  full  of  seams  and  veins  of  salt, 
often  with  columnar  structure  in  the  larger  veins.  Overlying  the 
limestone  is  the  main  salt  bed.  It  is  often  very  pure  and  well 
stratified.  Shaly  matter  and  gypsum  occur  in  thin  streaks,  but,  on 
the  whole,  the  impurities  are  not  more  than  two  or  three  per  cent. 
of  the  entire  bed.  Non-continuous  layers  of  limestone  or  shale 
several  inches  thick  sometimes  occur.  The  crystals  of  salt  are  much 
smaller  than  those  of  the  mixed  salt,  and  vary  considerably  in  size 
in  the  different  layers.  The  salt  is  again  capped  by  a  layer  of  mixed 
salt  like  that  found  below.  Gypsous  shales  are  common  here,  these 
containing  more  or  less  disseminated  salt.  Irregular  and  more  per- 
sistent layers  of  dark  magnesian  limestone  also  occur  in  the  upper 
part  of  the  salt  bed.  They  are  up  to  two  or  three  feet  in  thickness 
and  full  of  salt  seams  and  grains,  and  have  the  appearance  of  having 
been  formed  above  the  salt  and  of  having  settled  down  into  it.  The 
roof  of  the  salt  bed  likewise  consists  of  large  and  small  blocks  of 
gypsous  shale,  the  spaces  between  the  blocks,  sometimes  several 
inches  in  width,  being  filled  with  salt.  These  salt  veins  sometimes 
extend  upward  into  the  overlying  rock  for  200  feet,  though,  as  a 
rule,  they  are  much  shorter. 

The  total  thickness  of  the  salt  beds  of  central  New  York,  in- 
cluding the  shale  layers,  ranges  from  100  to  190  feet,  but  southward 
it  thickens  to  470  feet,  in  the  Ithaca  well.  The  limestone  layers  in 
this  formation  show  evidence  of  exposure  to  the  air  during  their 
formation,  by  the  abundance  of  mudcracks  which  are  filled  by  salt, 
gypsum  or  black  mud.  They  are  entirely  unfossiliferous,  as  is  this 
whole  series  of  deposits. 

The  Camillus  shales  overlying  the  salt  are  gray,  often  containing 
beds  of  magnesian  limestone  and  great  masses  of  gypsum,  together 
with  some  anhydrite.  This  gypsum  has  been  regarded  as  an  altera- 
tion product,  being  formed  from  impure  limestones  of  the  water  lime 


ORIGIN    OF    SALINA    SALTS 


379 


type.     Numerous  hopper-shaped  cavities  formerly  occupied  by  salt 
crystals  occur  in  the  shalier  beds. 

When  we  consider  the  former  extent  of  the  Niagaran  strata, 
from  central  New  York  to  the  Rocky  Mountains  and  from  the  Ohio 
or  southward  to  Hudson  Bay,  and  its  thickness,  which  in  Wisconsin 
is  still  over  800  feet,  and  realize  that  much  of  this  was  worn  away 
during  Salina  time  by  the  streams  flowing  into  the  Salina  basins  of 
New  York,  Michigan,  and  Canada  West,  we  can  understand  that 
the  connate  sea  water  held  in  these  strata  was  quite  sufficient  to 


FIG.  70.     Map  and  cross-section  of  Rhang-el-Melah,  a  salt  dome  in  Algeria. 
(After  M.  Ville.) 


furnish  all  the  salt  of  the  Salina  deposits.  The  intercalated  lime- 
stone and  shale  layers  likewise  had  their  origin  in  the  erosion  prod- 
ucts obtained  from  these  Niagaran  formations.  The  fact  that  all 
around  the  Salina  area  the  Upper  Siluric  strata  rest  on  Niagaran 
except  where  the  continental  deposits  of  Salina  time  intervene,  and 
the  further  fact  that  no  undoubted  marine  equivalents  of  the  Salinan 
are  known  in  North  America,  greatly  strengthen  the  argument  for 
the  wholly  continental  origin  of  these  salt  deposits. 

THE  SALT  DOMES.    These  should  be  briefly  mentioned  here,  as 
accumulations  of  salt  in  circumscribed  areas,  often  to  a  thickness  of 


380  PRINCIPLES    OF    STRATIGRAPHY 

several  thousand  feet.  They  are  of  all  ages  and  owe  their  form  to 
rearrangement  of  the  salt  mass  through  the  force  of  crystal  growth 
inherent  in  the  salt,  and  in  this  process  they  have  often  seriously 
disturbed  the  enclosing  strata.  (Hahn-2i;  Harris-22;  see  further 
under  diagenesis,  Chapter  XX.)  (Fig.  70.) 

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34.  LYELL,  CHARLES.    1875.    The  Principlesof  Geology,  I2th  edition,  Vol.  I. 

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CHAPTER   X. 

MORPHOLOGY    AND    LITHOGENESIS    OF    THE    TRUE    ORGANIC 
OR    BIOGENIC   ROCKS.     ZOOGENIC    DEPOSITS. 

Biogenic  rocks,  or  Bioliths  as  Chr.  G.  Ehrenberg  has  termed 
them,  are  deposits  of  organic  material,  or  material  formed  through 
the  physiological  activities  of  the  organisms.  In  general,  Bioliths 
may  be  divided  into  those  in  which  the  organic  matter  is  preserved 
in  the  form  of  carbon  or  compounds  of  carbon,  and  those  in  which 
only  the  inorganic  mineral  matter,  abstracted  from  the  food  or 
the  medium  in  which  the  organism  lives  (air,  water,  or  soil),  is 
preserved.  The  former  are  almost  wholly  restricted  to  plant- 
formed  (phytogenic)  deposits,  or  phytoliths,  and  the  latter  are 
best  represented  by  animal-formed  (zoogenic)  deposits  or  zooliths. 
As  the  organic  carbon  deposits,  whether  plant  or  animal,  all  have 
the  property  of  combustibility,  they  have  been  designated  causto- 
bioliths,*  while  the  non-combustible  organic  deposits  of  purely  min- 
eral character  are  designated  acaustobioliths. 

The  following  classification  of  the  types  of  biogenic  deposits, 
or  Bioliths  (Biolites),  may  be  made: 

A.     Zoogenic  Deposits  or  Zooliths. 

1.  Coral  reefs. 

2.  Sponge  reefs. 

3.  Bryozoa  reefs. 

4.  Shell  colonies. 

5.  Shell  limestones. 

6.  Crinoidal   limestones. 

7.  Calcareous  oozes. 

a.  Foraminiferal  oozes. 

b.  Pteropod  oozes. 

c.  Cyprid  oozes. 

*From  Kau<m/c6s  =  capable  of  burning,  Bios,  life,  \l0os,  stone.  Caustoliths  of 
inorganic  origin  also  exist:  e.  g.,  sulphur  deposits. 

384 


CORAL   REEFS  385 

8.  Siliceous  oozes. 

a.  Radiolarian  oozes. 

b.  Sponge  spicule  oozes. 

9.  Phosphate   (guano)   deposits. 
B.     Phytogenic  Deposits  or  Phytoliths. 

1.  Nullipore  reefs  and  limestones. 

2.  Algous  travertine. 

3.  Phytogenic  oolites. 

4.  Chara  marls  and  limestones. 

5.  Diatomaceous  oozes. 

6.  Caustophytoliths. 

a.  Sapropeliths. 

b.  Peat. 

c.  Lignites,  brown  coal,  etc. 

d.  Coals. 

e.  Deep  sea  vegetal  deposits. 

In  the  present  chapter  only  the  zoogenic  deposits  will  be  dis- 
cussed, the  phytogenic  being  referred  to  the  next  chapter. 


CORAL  AND  OTHER  REEFS. 

Coral  reefs  have  been  formed  in  all  geological  periods,  from  the 
Cambric  to  the  present,  and  recent  investigations  seem  to  indicate 
the  existence  of  archaeocyathid  corals  in  reef-like  association  during 
the  pre-Cambric  (Animikie)  in  the  Canadian  region.  Reefs  are 
complex  structures,  and  corals  often  play  only  a  minor  part  in  their 
construction.  Calcareous  algae,  or  Nullipores,  are  commonly  among 
the  most  important  reef  organisms  (Marshall  Howe~5o),  while 
Hydrocorallines  are  equally  abundant.  In  fossil  reefs  Sponges  and 
Bryozoa  are  often  the  most  important  reef  organisms.  The  term 
coral  will  be  used  here  in  its  more  general  or  comprehensive  sense, 
so  as  to  include  the  hydrocorallines,  both  the  recent  millepores  and 
their  fossil  representatives,  the  Stromatoporoids.  Among  the  corals 
proper  two  classes  are  represented :  Madreporaria,  or  stone  corals, 
and  the  Alcyonarla.  The  latter,  however,  furnish  only  a  small  con- 
tribution to  the  reef.  Many  other  lime-secreting  organisms  occur 
besides  corals  and  nullipores.  They  are,  however,  of  secondary 
significance,  and,  on  the  whole,  contribute  only  a  fraction  of  its 
mineral  matter  to  the  reef. 

The  general  characteristics  of  modern  coral  reefs  will  first  be 
discussed,  and  this  will  be  followed  by  a  review  of  reefs  of  the  past. 


386  PRINCIPLES    OF    STRATIGRAPHY 

CHARACTERS  AND  DEVELOPMENT  OF  MODERN  CORAL  REEFS. 

TYPES  OF  MODERN  CORAL  REEFS. — Three  types  of  coral  reefs 
are  recognized  in  the  modern  seas :  the  fringing  reef,  barrier 
reef,  and  atoll  The  Fringing  Reef,  or  shore  reef  (Figs.  71-2),  is 
a  platform  of  coral  rock  closely  bordering  a  continent  or  island  of 
earlier  ©rigin  and  extending  some  distance  from  the  shore.  Sea- 
ward the  platform  of  coral  rock  is  often  somewhat  higher  than 
the  inner  end,  rising  into  low  ridges  or  mounds  of  living  or  dead 
coral  and  coral  sand  often  awash  at  low  tide.  It  is  intersected  by 
channels  and  a  pronounced  but  shallow  channel  extends  between  it 
and  the  shore.  Its  seaward  side  is  often  rather  steep,  but  it  descends 
into  comparatively  shallow  water.  This  is  the  zone  of  active  coral 
growth  as  well  as  destruction,  for  here  wave  activity  is  most  marked. 
Within  the  outer  rim  conditions  of  life  are  less  favorable,  since 


FIG.  71.  Island  with  fringing  reef, 
and  submarine  platform  over 
which  the  surf  breaks.  (After 
Le  Conte.) 


FIG.  72.  Diagrammatic  cross-section 
of  the  island  and  reef  shown  in 
preceding  figure.  a,  a,  Dead 
coral  material  added  to  island. 
(After  Le  Conte.) 


here  the  water  is  more  stagnant,  and  the  channels  are  scoured  out 
by  the  tidal  currents  and  the  solvent  action  of  the  water.  The 
influx  of  fresh  water  and  clastic  sediment  from  the  land  also  hin- 
ders coral  growth  to  a  considerable  extent  within  the  outer  rim  of 
the  fringe.  Typical  examples  of  fringing  reefs  are  found  on  the 
borders  of  the  Sandwich,  Solomon,  Friendly,  and  Navigator  islands, 
the  New  Hebrides  and  Mariana  islands  and  many  others,  all  in  the 
Pacific,  also  in  the  Seychelles  and  Nicobar  islands  and  in  Mau- 
ritius, as  well  as  parts  of  the  coast  of  Madagascar  and  Mozambique 
in  the  Indian  Ocean.  In  the  Red  Sea  they  occur  on  both  the 
Arabian  and  African  shores,  and  in  the  Atlantic  on  the  coast  of 
Florida  and  around  nearly  the  whole  of  the  islands  of  the  West 
Indies. 

The  Barrier  Reef  (Figs.  73-4)  is  situated  further  from  shore 
and  consequently  has  a  greater  depth  of  water  both  between  it  and 
the  land  and  on  the  seaward  side.  It  may  be  formed  from  the 
fringing  type  by  the  subsidence  of  the  land  and  the  simultaneous  up- 
ward growth  of  the  corals  on  the  outer  border  of  the  reef  (Darwin)  ; 


MODERN    CORAL    REEFS 


387 


by  the  seaward  growth  of  the  front  of  the  reef  and  the  enlargement 
by  solution  of  the  channel  between  the  reef  and  the  land  without  sub- 
sidence (Murray,  Agassiz),  and,  finally,  by  the  independent  upward 
growth  of  the  corals  into  reefs  on  a  suitable  platform  at  a  distance 
from  the  shore.  The  Great  Barrier  Reef  on  the  northeast  coast 
of  Australia  extends  for  1,250  miles  from  Torres  Strait  in  9.5°  S. 
lat.  to  Lady  Elliott  Island  in  24°  S.  lat.  At  Cape  York  the  sea- 


FIG.  73.  Barrier  reef  around  cen- 
tral island.  The  surf  (white) 
shows  the  location  of  the  reef, 
which  is  dotted  with  small  coral 
islands.  (After  Le  Conte.) 


FIG.  74.  Diagrammatic  section  of  the 
island  shown  in  the  preceding 
figure,  showing  location  of  reefs 
(dotted).  (After  Le  Conte.) 


ward  edge  of  this  reef  is  nearly  90  miles  distant  from  the  coast  and 
it  descends  to  a  depth  often  exceeding  1,800  feet.  It  represents  "a 
great  submarine  wall  or  terrace,  fronting  the  whole  northeast  coast 
of  Australia,  resting  at  each  end  in  shallow  water,  but  rising  from 
very  great  depths  about  the  center.  Its  upper  surface  forms  a  pla- 
teau, covered  by  10  to  30  fathoms  of  water,  but  studded  all  over 
with  steep-sided  block-like  masses  which  rise  up  to  low  water 
level."  ( Jukes-Browne-53 ;  54.)  These  individual  reefs  are  espe- 


FIG.  75.  An  atoll  formed  of  discon- 
nected' coral  islands  arising  from 
a  submerged  reef  which  is  out- 
lined by  surf  (white).  (After 
Le  Conte.) 


FIG.  76.  Diagrammatic  section  of  an 
atoll,  showing  depth  of  central 
lagoon,  and  relation  of  the  islands 
to  the  reef.  (After  Le  Conte.) 


cially  numerous  along  the  edge  of  the  bank  and  protect  the  com- 
paratively shallow  water  over  the  reef,  as  well  as  the  numerous 
inner  reefs  scattered  over  the  surface,  from  the  effects  of  the  waves 
of  the  open  ocean.  In  most  barrier  reefs,  the  outer  edge  is  in 
places  often  awash  at  low  tide  and  islands  and  bars  of  dead  coral 
and  sand  are  formed.  These  may  coalesce  and  in  time  become  cov- 
ered with  vegetation.  Thus  a  strip  of  land  is  formed,  lying  some 
hundred  yards  or  less  from  the  extreme  outer  edge  of  the  reef. 


388 


PRINCIPLES    OF    STRATIGRAPHY 


Where  the  barrier  reef  is  not  far  from  land,  gaps  always  occur  in  it 
opposite  the  mouths  of  rivers. 

Other  examples  of  barrier  reefs  occur  in  the  Pacific,  where 
they  encircle  some  of  the  Society  Islands,  including  Tahiti,  the 
Fiji  Islands,  and  New  Caledonia.  The  last  is  400  miles  long  and 
about  ten  miles  distant  from  shore.  The  Pelew  Islands  and  the 
Comoro  Isles  in  the  Mozambique  Channel  are  surrounded  by  bar- 
rier reefs  and  other  examples  occur  in  the  middle  of  the  Red  Sea. 

The  Atoll  is  an  elliptical,  oval  or  roundish  ring  of  coral,  its 
continuity  broken  here  and  there  by  channels  which  lead  into  the 
central  lake-like  expanse  of  water,  the  lagoon.  The  outside  water 
is  commonly  very  deep,  while  the  water  of  the  atoll  is  shallow. 
Thus,  off  the  Cocos-Keeling  atoll,  the  depth  sounded  at  a  distance 


FIG.  77.     The  atoll  of  Whitsunday  Island.      (From  Le  Conte.) 

of  2,200  yards  from  the  reef's  edge  was  1,200  fathoms,  while  the 
depth  of  the  lagoon  is  only  from  two  to  seven  fathoms  (3.5  to  13 
meters).  In  the  atolls  of  the  Low  Archipelago  the  depth  varies 
from  35  to  70  meters  (20  to  38  fathoms),  in  the  Marshall  group 
from  50  to  60  meters  (30-35  fathoms),  and  in  the  Maldive  group 
up  to  90  meters  (45  to  49  fathoms).  (Figs.  75-77.) 

The  openings  in  the  reefs  are  always  on  the  leeward  side,  and  so 
the  water  within  the  lagoon  is  seldom  much  disturbed.  In  it  live 
swarms  of  organisms  of  all  kinds,  including  fishes  and,  preeminently, 
sharks.  The  calcareous  alga  Halimeda  grows  abundantly  over  the 
floor  of  the  lagoon  of  Funafuti  in  the  Ellis  group,  and  of  many 
other  atolls  in  the  Pacific,  and  it  has  been  collected  in  quantity  in 
the  lagoon  of  Diego  Garcia  in  the  Chagos  group  in  the  Indian 
Ocean  and  elsewhere. 

Atolls  are  especially  abundant  in  the   Pacific  and  the  Indian 


MODERN  CORAL  REEFS  389 

oceans.  Of  the  Pacific  atolls  the  largest  group  forms  the  Low 
Archipelago  in  the  center  of  the  Pacific,  south  of  the  equator,  and 
next  the  Caroline  Archipelago  in  the  western  part  of  the  Pacific, 
north  of  the  equator.  The  Marshall  group,  the  Gilbert  Islands,  the 
Ellis  Island  group  with  Funafuti,  and  a  number  of  scattered  atolls, 
lie  between  the  two  first  mentioned  archipelagoes.  In  the  Indian 
Ocean  the  Laccadives,  the  Maldives,  the  Chagos,  and  the  Sava  de 
Malha  groups  form  the  largest  of  the  associations  of  atolls.  The 
Cocos-Keeling  islands  may  also  be  mentioned  as  isolated  but  typical 
atolls  in  the  eastern  part  of  the  Indian  Ocean  (lat.  12°  S.,  long. 
96°  E.). 

From  the  geological  point  of  view,  a  classification  based  on  the 
relationship  of  the  reef  to  the  continental  block  is  perhaps  of  even 
more  fundamental  significance.  On  such  a  basis  reefs  may  be  di- 
vided into  oceanic,  those  encircling  oceanic  islands  or  resting  on 
oceanic  platforms,  and  epicontinental  or  neritic,  those  growing  upon 
or  on  the  border  of  the  continental  shelf  and  around  the  islands  per- 
taining thereto.  Each  group  may  be  represented  by  fringing  and 
barrier  reefs,  as  well  as  by  atolls,  though  the  latter  are  more  com- 
monly confined  to  the  oceanic  type. 

In  general  only  the  epicontinental  type  is  represented  in  the 
older  deposits  of  the  known  earth's  crust,  though  some  of  these  may 
well  have  had  deep,  marginal  depressions  similar  to  those  found  off 
many  of  the  western  Pacific  reefs.  The  dolomite  reefs  of  the  Tyrol 
have,  however,  been  regarded  as  atolls.  Of  existing  examples  of 
epicontinental  reefs  the  Great  Barrier  Reef  of  Australia  may  be 
considered  the  best  representative.  In  their  composition  and  in- 
ternal structure  and  in  the  factors  influencing  their  distribution,  all 
reefs  are  more  or  less  alike. 

FACTORS  LIMITING  THE  DISTRIBUTION  OF  MODERN  CORAL  REEFS. 
The  geographic  distribution  of  modern  coral  reefs  falls  within  that 
portion  of  the  oceans  lying  approximately  between  28°  north  and 
south  latitudes,  in  those  depths  in  which  the  mean  annual  tempera- 
ture does  not  fall  below  +  68°  F.  (+  20°  C),  nor  rise  very  much 
above  that  point.  Most  of  the  existing  coral  reefs  are  found  in  the 
Pacific  Ocean,  whose  average  surface  temperature  is  the  highest  of 
the  four  oceans  (19.1°  C,  66.38°  F.,  maximum  27.60°  C.,  80.69° 
F.).  (See  Chapter  IV.)  The  Indian  Ocean  comes  next  with  a 
mean  annual  temperature  of  17°  C,  62.6°  F.  (27.88°  C,  82.18°  F. 
maximum),  and  it  is  next  in  importance  with  reference  to  the  dis- 
tribution of  coral  reefs.  The  Atlantic  (mean  annual  temperature 
16.9°  C.,  62.42°  F.,  maximum  26.83°  C.,  80.38°  F.),  finally,  is  sur- 
prisingly poor  in  coral  reefs,  though  numerous  fringing  reefs  occur 


390  PRINCIPLES    OF    STRATIGRAPHY 

in  the  West  Indies,  off  the  coast  of  Florida  and  on  the  coast  of 
Brazil.  This  is  clearly  due  to  the  fact  that  the  tropical  belt  is  most 
contracted  in  the  Atlantic.  The  Bermuda  Islands  are  a  remarkable 
exception  to  the  general  law  of  distribution  of  coral  reefs,  for  they 
are  found  in  the  latitude  32°  N.,  and  are  therefore  the  farthest  re- 
moved from  the  equator  of  any  modern  coral  reefs.  Their  occur- 
rence in  such  a  position  is  favored  by  the  Gulf  Stream,  which  brings 
the  warm  waters  of  the  tropics.  No  coral  reefs  are  known  in  the 
eastern  part  of  the  Atlantic. 

The  eastern  part  of  the  Pacific  is  likewise  free  from  reefs,  and 
this  is  to  be  correlated  with  the  fact  that  the  cooler  ocean  currents 
from  north  and  south  converge  here,  as  in  the  east  Atlantic,  to  form 
the  equatorial  currents.  The  coral  reef  area  of  the  Pacific  lies  west 
of  the  i2Oth  meridian  (E.),  the  greatest  area  lying  between  130°  E. 
and  145°  W.  longitude  and  between  15°  N.  and  25°  S.  latitude. 
The  most  extensive  eastern  group  is  that  of  the  Low  Archipelago 
with  Ducie  Island,  its  eastern  outpost.  The  largest  western  group 
is  that  of  the  Caroline  Archipelago,  but  many  scattered  atolls  and 
fringing  reefs  occur  to  the  west  of  this,  notably  in  the  China  Sea, 
where  the  Paracelle  group  forms  an  extensive  cluster  of  atolls  in 
lat.  112°  W.,  long.  17°  N.  The  fringing  reefs  of  the  Sandwich 
Islands  form  a  large  single  and  isolated  group  in  the  mid-Pacific 
north  of  the  equator. 

The  coast  of  the  mainland  and  the  islands  of  the  western  Pacific 
within  the  coral  zone  are  generally  bordered  by  reefs  either  fringing 
or  barrier,  beginning  with  the  Great  Barrier  Reef  on  the  south,  and 
extending  to  the  fringing  reefs  of  the  Loo  Choo  group. 

The  Indian  Ocean  is  generally  lined  by  fringing  reefs,  which  ex- 
tend with  interruptions  from  Madagascar  north  along  both  sides  of 
the  Red  Sea,  in  the  Persian  Gulf  around  Ceylon  and  the  Nicobar 
Islands  and  south  along  the  coast  of  Sumatra  and  Java  to  Australia. 
In  the  western  half  lies  the  great  group  of  atolls,  the  Maldives  and 
Laccadives,  extending  from  the  equator  north  to  lat.  13°  and  the 
Chagos  and  Sava  de  Malha  groups.  The  fringing  reefs  of  the 
Seychelles  and  of  Mauritius  also  fall  in  this  half  of  the  Indian 
Ocean.  The  eastern  half  contains  only  the  Cocos-Keeling  group 
and  some  atolls  off  the  northwest  coast  of  Australia. 

In  general,  then,  reefs  of  various  kinds  occur  in  the  three  larger 
oceans,  but  are  mainly  confined  to  the  western  half  of  these  oceans. 
The  Indian  Ocean  alone  has  representatives  in  the  eastern  half,  but 
they  are  far  less  abundant  than  in  the  western.  The  Atlantic  has 
no  typical  atolls,  though  the  Bermudas  come  near  to  representing 
them. 


MODERN  CORAL  REEFS  391 

Depth  of  Water.  The  greatest  depth  at  which  reef -building 
corals  flourish  is  20  to  25  fathoms,  though  occasionally  reef-build- 
ing species  may  extend  down  to  40  or  45  fathoms.  At  this  depth 
Madrepora  has  been  found  growing  on  the  Macclesfield  and  Tizard 
banks  of  the  China  Sea.  These  corals  were,  however,  as  a  rule,  of 
much  slighter  build  than  those  found  in  shallow  water.  The  depth 
here  given  is  of  course  not  the  downward  limit  of  corals  as  a  whole, 
for  some  species  are  known  to  extend  to  great  depths  (see  Chap- 
ter XXVIII).  Reef  corals,  however,  flourish  best  in  shallow  water, 
their  most  luxuriant  growth  being  above  15  or  10  fathoms  and  to 
just  below  low-tide  level.  Indeed  many  coral  reefs  luxuriate  in 
spite  of  the  fact  that  they  are  exposed  at  exceptionally  low  tides, 
as  shown  in  Great  Barrier  Reef  of  Australia  (Saville-Kent-77). 
The  alcyonarian  Heliopora  and  the  hydrocoralline  Millepora,  how- 
ever, are  active  reef  builders  at  35  and  40  fathoms,  and  nullipores 
extend  to  a  depth  of  35  fathoms. 

Intensity  of  Light.  That  the  range  in  depth  is  in  part  to  be  cor- 
related with  the  intensity  of  the  sunlight  is  shown  by  the  fact  that 
species  of  reef  corals  placed  in  a  light-proof  life  car  die  after  the 
light  has  been  excluded  for  several  weeks.  At  Fort  Jefferson  in  the 
Tortugas,  reef  corals  grow  on  the  peripheral  piles  of  the  govern- 
ment wharf,  but  are  absent  from  the  permanently  shaded  portions. 
(Vaughan-87  -.240.) 

Now,  as  has  been  shown  by  the  investigations  of  the  optics  of 
sea  water  (see  ante,  p.  204),  the  visible  depth  in  the  open  ocean 
in  33°  north  latitude  is  roughly  50  meters  (27^3  fathoms),  and  in 
50°  north  latitude  it  is  40  meters  (22  fathoms).  In  the  tropics 
the  depth  is  even  greater,  and  it  thus  appears  that  the  reef-building 
species  flourish  within  the  zone  of  visibility  and  therefore  of  great- 
est intensity  of  the  sunlight. 

Temperature.  As  long  ago  shown  by  Dana,  the  minimum  an- 
nual temperature  of  the  water  must  be  68°  F.  (20°  C.),  or  the  mean 
annual  temperature  must  be  above  70°  F.  (21.2°  C.).  (Murray-68: 
25-27.)  All  the  principal  coral-reef  regions  lie  within  the  equatorial 
belt  where  the  range  of  temperature  is  not  over  10°  Fahrenheit 
(5-5°  C.),  and  recent  observations  and  experiments  have  shown 
that  the  precipitation  of  carbonate  of  lime  both  by  organisms  and  by 
inorganic  agencies  is  most  active  at  high  temperatures.  Saville- 
Kent  (77:p£),  indeed,  insists  that  reef  building  is  influenced  by 
temperature  much  more  than  by  the  species  of  corals,  for  he  finds 
that  the  same  species  which  build  the  reefs  in  tropical  waters  are  not 
reef-building  in  extratropical  regions.  He  further  holds  that  it  is 
only  in  the  shallower  water  where  precipitation  of  lime  is  caused 


392  PRINCIPLES    OF    STRATIGRAPHY 


by  evaporation  that  coral  conglomerates  and  limestones  occur. 
Corals  as  such  are,  however,  by  no  means  restricted  to  the  tropics. 
Astrangea  dance  grows  on  the  southern  shore  of  Massachusetts  at 
Woods  Holl,  and  Lophohelia  prolifera  and  Dendrophyllia  ramea 
form  dense  beds  at  a  depth  of  from  100  to  200  fathoms  off  the 
coasts  of  Norway,  Scotland  and  Portugal. 

Other  Physical  Conditions.  For  the  successful  growth  of  reef 
corals  it  is  further  necessary  that  the  water  should  be  generally  in  a 
state  of  agitation,  the  stagnation  of  the  inner  marginal  waters  of  the 
reefs  or  the  lagoons  being  for  the  most  part  unfavorable  to  the 
growth  of  coral.  This  is  chiefly  due  to  the  fact  that  still  water  per- 
mits fine  sediment  to  be  deposited,  and  this  quickly  kills  the  polyps. 
On  the  other  hand,  very  powerful  surf  is  equally  deleterious  to  the 
coral  polyps,  for  it  will  throw  the  shingles  against  the  soft  polyps 
and  so  destroy  them.  Moreover,  the  heavy  breakers  will  tear  off 
the  branching  madrepores,  and  loosen  even  the  massive  maean- 
drinas,  owing  to  the  fact  that  the  dead  base  of  the  colony  is  often 
so  much  riddled  by  boring  organisms  that  it  easily  succumbs  to  the 
onslaught  of  the  waves.  When  such  a  great  mass  of  coral  is 
loosened,  it  will  be  rolled  along  the  reef,  rounding  and  grinding  the 
other  corals  in  its  course.  (Bourne-i4:  440.) 

A  strong  current  likewise  seems  to  be  unfavorable  to  the  growth 
of  corals,  if  it  sets  directly  against  them.  Thus  at  Diego  Garcia, 
and  especially  at  the  east  end  of  East  Islet  in  the  Chagos  group, 
strong  direct  currents  strike  the  reef,  which  is  barren  here  and  suf- 
fering rapid  erosion,  where  the  whole  force  of  the  current  falls 
directly  upon  them.  "As  the  current  parts  and  flows  round  the 
obstacle  one  meets  with  a  reef  covered  with  debris,  but  barren  of 
live  coral ;  further  on,  as  the  current  moderates  in  force,  one  finds 
a  few  growing  heads  of  coral ;  and  finally,  at  the  further  end  of  the 
reef,  where  the  current  has  abated  its  force  considerably,  there  is  a 
luxuriant  bed  of  living  corals  and  Alcyonaria."  (Bourne-i4.)  The 
same  facts  have  been  observed  at  Celebes,  and  the  conclusion  seems 
to  be  supported  by  many  observations  "that  direct  and  strong  cur- 
rents are  unfavorable  to  coral  growth,  that  moderate  tangential 
currents  are  extremely  favorable,  and  sluggish  or  still  water  again 
unfavorable."  A  hard  rock  bottom  is  furthermore  a  necessity  for 
good  coral  growth,  these  organisms  finding  it  impossible  to  become 
attached  to  muddy  or  silty  bottoms. 

A  normal  composition  of  sea  water  is  required,  and  the  normal 
salinity  of  35  permille  seems  to  be  most  favorable,  as  in  the  open 
oceans,  but  a  surface  salinity  decreased  to  32.1  permille,  as  in  the 
China  Sea  (volume  salinity  34  permille),  or  even  31.5  permille,  as 


MATERIALS    OF    CORAL    REEFS  393 

In  the  Andamanian  marginal  mediterranean  (volume  salinity  33 
permille)  does  not  prevent  their  growth.  On  the  other  hand,  a 
surface  salinity  of  38.8  permille,  that  of  the  Red  Sea  (39  permille 
volume  salinity),  is  not  too  high  for  their  development. 

COMPOSITION  AND  STRUCTURE  OF  THE  REEF.  Our  knowledge  of 
the  composition  and  structure  of  the  deeper  parts  of  a  modern  coral 
reef  has  been  obtained  from  examination  of  the  accessible  parts  of 
reefs  and  from  a  deep  boring  made  on  the  atoll  of  Funafuti  in  the 
Ellis  Island  group,  for  the  purpose  of  ascertaining  these  facts. 
Three  attempts  were  made,  beginning  in  1896,  and  the  depth  finally 
reached  was  1,114  feet  (l&5  fathoms).  (David-22.)  This  boring 
passed  only  through  pure  limestone  of  organic  origin  to  the  depth 
reached,  without  trace  of  any  other  rock.  The  organic  remains 
found  were  chiefly  corals,  calcareous  algse  and  Foraminifera,  be- 
sides other  types.  A  boring  made  from  the  deck  of  a  ship  into  the 
floor  of  the  lagoon,  where  the  water  was  17  fathoms  deep,  showed 
a  deposit  consisting  of  the  calcareous  alga  Halimeda  opuntia,  with 
an  abundant  admixture  of  Foraminifera,  and  having  a  thickness  of 
over  100  feet.  At  a  depth  of  245  feet,  Madrepora,  Porites  and 
Heliopora  were  encountered,  forming  a  solid  mass  of  coral  rock. 
As  these  corals  are  shallow-water  types,  it  is  evident  that  subsi- 
dence has  taken  place  and  that  the  lagoon  of  Funafuti  has  been 
filled  up  to  a  depth  of  at  least  245  feet  (nearly  41  fathoms). 


Materials  Composing  the  Reef. 

The  most  important  of  the  reef  corals  of  modern  reefs  are  the 
branching  Madrepores,  Pocilloporas  and  Porites  and  the  heads  of 
Astrseans  and  Maeandrinas.  Among  the  hydrozoans  Millepora  is 
very  abundant,  the  common  species  being  M.  complanata  and  M. 
alcicornis.  In  addition  to  the  corals  a  number  of  species  of  nulli- 
pores  occur  on  the  reefs,  and  often  become  as  important  as,  if  not 
more  so  than,  the  corals  themselves.  This  is  the  case  with  the  reefs 
of  Christmas  Island,  of  Fiji  and  Funafuti,  where,  besides,  a  promi- 
nent part  is  taken  by  Foraminifera,  Echinodermata,  Bryozoa,  Pele- 
cypoda  and  other  organisms. 

Within  the  lagoon  of  some  atolls  corals  flourish  in  abundance. 
At  Diego  Garcia  in  the  Chagos  group  the  more  delicate  branching 
species  of  the  Madreporaria  flourish  in  considerable  numbers,  and 
true  reef-building  species  of  Porites,  Maeandrina,  Pocillopora  and 
others  are  also  found.  "Many  of  the  species  growing  in  the  lagoon 
at  a  distance  of  five  miles  and  upward  from  its  outlet  are  identical 


394  PRINCIPLES    OF    STRATIGRAPHY 

with  those  growing  on  the  outer  reef.  In  addition  to  them  are  nu- 
merous species  such  as  Seriatopora  stricta,  Mussa  corymbosa, 
Favia  lobata,  Fungia  dentata,  and  many  others  that  are  not  found 
on  the  outside."  This  is  due  to  the  fact  that  these  corals  are  either 
free  (Fungia)  or  attached  by  such  slender  stems  that  they  could 
not  maintain  themselves  in  the  strong  surf  and  currents  of  the  open 
ocean. 

Within  the  lagoon  these  species  grow  close  together  and  form 
knolls  and  patches,  which,  together  with  the  clastic  debris  washed 
into  the  lagoon,  tends  to  fill  it  up  completely.  The  distribution  of  the 
organisms  in  the  atoll  of  Funafuti  in  the  Ellis  Island  group  (long. 
179°  E.  and  lat.  8°  30'  S.)  may  be  taken  as  representative  (Firickh- 
31).  "On  the  ocean  side  up  to  as  far  in  as  the  wash  of  the  waves 
reaches  at  low-water  spring  tide,  the  reef  platform  is  densely  cov- 
ered with  vigorously  growing  organisms."  A  thinly  branching 
Lithothamnion  is  the  most  abundant,  appearing  in  small,  isolated 
shrub-like  clusters,  from  I  to  5  inches  in  diameter  and  varying  simi- 
larly in  height.  Between  these  grow  small  Madrepora  loripes, 
Brook.  On  the  outer  edge  of  the  platform  lichenous  and  knobby 
Lithothamnia  occur,  but  no  Porites  nor  Heliopora  cccrulea.  None 
of  these  species  forms  patches  of  great  size,  owing  to  the  intense 
intraspecific  struggle  for  existence  which  takes  place  here,  though 
eventually  Lithothamnion  seems  to  be  the  victor  over  the  corals  and 
hydrocorallines.  This  vigorous  growth  extends  for  only  2  or  3 
feet  downward  at  the  edge  of  the  reef  below  the  level  of  low-water 
spring  tide,  below  which  the  reef  becomes  comparatively  destitute  of 
organisms. 

The  Lithothamnion  zone  is  dissected  by  a  large  number  of  nar- 
row cross  channels,  which  give  it  a  fringed  appearance.  The  edge 
is  generally  somewhat  raised  and  rough  on  account  of  the  Litho- 
thamnion growth,  and  the  encrustation  of  the  surface  by  Foramin- 
ifera,  like  Carpenteria  and  Polytrema.  This  feature  is  less  marked 
or  wholly  absent  on  the  lagoon  side  of  the  coral  reef  platform.  Dif- 
ferent species  of  Lithothamnion  characterize  this  fringe  in  differ- 
ent parts  of  the  atoll.  Thus  in  the  eastern  or  windward  portion  a 
lichenous  form  abounds,  while  in  the  western  or  leeward  portion 
of  the  lagoon  rim  a  thinly  branching  species  and  another  lichenous 
form  with  stony  knobs  entirely  replace  the  first  species. 

Next  to  the  Lithothamnion,  the  branching  nullipore  Halimeda 
abounds  on  the  reef,  both  on  the  lagoon  and  ocean  slopes.  It  lives 
to  the  45-fathom  level,  while  the  Lithothamnion  has  been  found 
alive  at  200  fathoms'  depth.  The  hydrocorallines  are  chiefly  repre- 
sented by  the  branching  Millepora  alcicornis  and  the  more  massive 


ORGANISMS    OF    CORAL    REEFS  395 

M.  complanata.  The  first  is  restricted  to  the  lagoon  side,  the  second 
also  occurs  on  the  ocean  side.  Among  the  corals  Hcliopora  ccerulea 
is  by  far  the  most  important,  but  is  scarcely  found  on  the  outer  rim 
of  the  atoll.  It  occurs  on  the  lagoon  side,  where  it  often  forms  the 
chief  lime  contributor  next  to  the  algae.  The  yellow  Porites  limosa 
and  a  purple  species  of  Forites  also  occur  on  the  lagoon  side,  but 
seem  to  be  rare  or  absent  on  the  ocean  side.  Large  blocks  of  rock 
made  of  dead  Porites  abound  in  some  sections,  showing  this  coral 
to  have  been  formerly  of  great  importance.  Besides  these  species, 
the  branching  Madrepora  loriceps  abounds  on  the  western  rim  of 
the  atoll,  but  is  rare  elsewhere.  Pocillopora  of  several  species  also 
occurs.  Astrsean  corals  seem  of  far  less  importance  at  Funafuti 
than  at  other  coral  reefs.  The  reef  platform  has  a  width  of  1,300 
yards  where  it  supports  the  islet  of  Fualopa,  but  it  is  mostly  much 
narrower.  It  consists  of  a  smooth,  barren  surface  formed  on  dead 
Lithothamnion  coral  sand,  and  coral  fragments,  generally  overlying 
a  basal  stratum  of  dead  Helipora  ccerulea,  Porites  or  both.  In 
many  cases  this  old  Helipora  reef  still  forms  the  surface  of  the 
platform  within  the  Lithothamnion  fringe,  the  islet  being  built  upon 
it  by  the  accumulation  of  coral  and  Lithothamnion  sand  and  breccia. 
A  dense  growth  of  sea  weed  is  characteristic  of  the  submerged  por- 
tion of  the  platform. 

In  general,  the  ocean  rim  of  the  leeward  portion  of  the  atoll 
is  characterized  by  the  enormous  quantity  of  branching  Litho- 
thamnion with  its  vivid  coloration,  the  great  abundance  of  Madre- 
pora loriceps,  the  general  small  size  of  all  the  species  and  the  ab- 
sence of  Heliopora  cocrulea  and  Millepora  alcicornis.  The  plat- 
form is  smooth  and  not  divided  into  zones,  while  the  transverse 
channels  are  short  and  shallow. 

On  the  windward  side,  the  branching  and  knobby  forms  of 
Lithothamnion  are  wholly  absent,  while  the  lichenous  form  present 
has  a  dark  color.  Corals  are  scarce,  Madrepora  loriceps,  Heliopora 
carulea  and  Millepora  alcicornis  being  wholly  wanting,  while  Pocil- 
lopora grandis,  though  rare,  is  the  predominant  type.  No  large 
masses  of  coral  are,  however,  found.  The  platform  is  divided  into 
erosion,  corrosion,  seaweed  and  Lithothamnion  zones,  while  trans- 
verse channels  are  numerous,  deep  and  long. 

From  the  platform  surface  rise  the  islands  built  by  the  calcare- 
ous debris  derived  from  the  destruction  of  the  corals  and  nulli- 
pores  and  the  old  reef  rock.  As  might  be  expected,  the  islets  are 
most  abundant  on  the  windward  side  of  the  atoll,  where  by  far  the 
greatest  part  of  the  rim  is  covered  by  them,  while  on  the  leeward 
side  they  are  few  and  much  smaller.  The  leeward  islets  consist  of 


396  PRINCIPLES    OF    STRATIGRAPHY 

the  debris  of  the  reef  organisms  with  plentiful  Halimeda  sands,  but 
the  windward  islets  are  largely  composed  of  the  material  torn  from 
the  reef  platform,  and  sand  is  scarce. 

In  places  where  the  islets  are  absent,  the  leeward  rim  passes 
gradually  from  an  area  covered  by  living  organisms  nearest  the 
ocean  into  a  central  portion  of  perfectly  bare  and  smooth  Litho- 
thamnion  rock.  Thence  to  the  edge  next  to  the  lagoon  the  condi- 
tions of  the  ocean  face  of  the  reef  repeat  themselves,  but  on  a 
smaller  scale. 

On  the  lagoonward  slopes  sands  abound,  consisting  either  wholly 
of  Halimeda  fragments  or  of  these  mixed  with  Foraminifera  and 
shell  fragments.  On  the  seaward  side  the  platform  generally  ends 
in  a  cliff  or  vertical  wall,  one  or  two  fathoms  deep,  beyond  which 
the  general  submarine  slope  of  the  atoll  begins. 


Structure  of  Coral  Reefs. 

In  most  modern  coral  reefs  it  is  found  that  the  lens-shaped  clus- 
ters of  growing  corals  or  reef  mounds  are  scattered  over  the  foun- 
dation platform  "like  tufts  of  vegetation  in  a  sandy  plain"  (Dana- 
20: 174),  and  that  they  are  surrounded  and  connected  by  coral  sand 
resulting  from  the  destruction  of  the  reefs  by  the  waves  and  by 
organisms.  The  individual  reef  mound  generally  rises  as  an  iso- 
lated lens-like  mass  above  the  sea  bottom  to  near  the  surface  of  the 
water,  and  is  composed  of  coral  heads  and  branching  forms,  between 
which  coral  sand  and  shells  and  shell  fragments  of  molluscs,  echino- 
derms  and  other  organisms  accumulate.  The  form  varies  from  a 
shallow  lens,  which  is  almost  a  layer,  to  that  with  lateral  slopes  as 
high  as  45  degrees  or  over.  A  peculiar  variety  known  as  "cha- 
peiros"  were  described  by  Professor  Hartt  (46:  ipi,  ipp-^oo)  from 
the  coast  of  Brazil.  These  grow  in  small,  scattered  patches,  "and, 
without  spreading  much,  often  rise  to  the  height  of  forty  to  fifty 
feet  or  more,  like  towers,  and  sometimes  attain  the  level  of  low  wa- 
ter ...  at  the  top  they  are  usually  very  irregular,  and  some- 
times spread  like  mushrooms  or  ...  umbrellas.  Some  of  these 
chapeiros  are  only  a  few  feet  in  diameter."  They  grow  thickly 
scattered  over  considerable  areas  in  those  waters.  According  to 
Dana,  "the  rock  of  these  submerged  coral  heads  is  but  a  loose  ag- 
gregation of  coral  in  the  position  of  growth,  except  possibly  in  their 
lower  portion,  where  the  open  spaces  may  be  filled  with  sand  and 
fragments  cemented  together." 

Except  where  reefs  rise  from  great  oceanic  depths,  their  sub- 


STRUCTURE  OF  CORAL  REEF        397 

merged  slopes  are  generally  low,  frequently  falling  much  below  10 
degrees.  This  is  particularly  the  case  in  the  Bermudas,  where  the 
slopes  are  very  gentle.  The  following  are  given  for  Hamilton 
Island  in  this  group.  (Dietrich,  quoted  by  Walther-o/D : 905. ) 
Westward  the  shallow  reef  extends  for  19.4  kilometers,  then  for  the 
next  8.9  kilometers  the  slope  averages  21  degrees  50  minutes,  carry- 
ing the  depth  to  3,566  meters.  Then  for  the  next  n  kilometers  it 
rises  again  at  an  average  angle  of  one  degree  20  minutes  to  a 
depth  of  3,310  meters,  falling  again  for  the  next  36  kilometers  at  an 
average  angle  of  2  degrees  27  minutes  to  4,846  meters  in  depth.  On 
the  same  island  the  slope  to  the  south-southwest,  after  passing  the 
reef  which  extends  for  4.3  kilometers,  averages  3  degrees  22  min- 


150  Yards 


FIG.  78.  Section  of  Keeling  atoll,  drawn  from  the  outer  coast  at  low  water, 
across  one  of  the  small  islands  to  the  lagoon.  A — Level  of  the  sea 
at  low  water.  At  A  the  depth  is  25  fathoms,  and  the  distance 
rather  more  than  150  yards  from  the  edge  of  the  reef.  B — Outer 
edge  of  flat  part  of  reef,  which  dries  at  low  water ;  the  edge  either 
consists  of  a  convex  mound,  as  represented,  or  of  rugged  points, 
like  those  a  little  farther  seaward,  beneath  the  water.  C— A  flat 
coral  rock  covered  at  high  tide.  D — A  low  projecting  ledge  of 
brecciated  coral  rock  washed  by  the  waves  at  high  water.  E — A 
slope  of  loose  fragments,  reached  by  the  sea  only  during  gales; 
the  upper  part,  which  is  from  six  to  twelve  feet  high,  is  clothed 
with  vegetation.  The  surface  of  the  islet  gently  slopes  to  the 
lagoon.  F — Level  of  the  lagoon  at  low  water.  (After  Darwin.) 

utes  for  a  distance  of  20.5  kilometers,  carrying  the  depth  to  1,234 
meters.  Then  it  rises  again  at  an  angle  of  3°  8'  for  the  next  5.5 
kilometers  until  the  depth  is  only  933  m.  Following  this  a  slope  of 
3°  55'  for  8  km.  carries  the  depth  again  to  1,481  meters,  beyond 
which  for  the  next  26.7  km.  the  average  angle  increases  to  4°  9', 
carrying  the  depth  to  3,420  meters.  Southward  after  passing  the 
reef  (2-9  km.  from  shore),  the  margin  of  the  reef  falls  at  an  angle 
of  8°  n'  to  a  depth  of  3,328  meters,  which  is  reached  23.1  km. 
from  the  edge  of  the  reef.  On  the  north  side  of  David  Island  the 
reef  extends  for  15.35  km.,  then  falls  at  an  angle  of  10°  8'  to  a 
depth  of  2,798  meters,  reached  at  a  distance  of  15.65  km.  from  the 
edge  of  the  reef.  On  the  Bermudas  the  angle  of  slope  of  the  edge 
of  the  reef  varies  from  3°  22'  toward  the  S.S.W.  to  8°  11'  toward 
the  S.,  10°  8'  to  the  north  and  21°  50'  to  the  west. 


398  PRINCIPLES    OF    STRATIGRAPHY 

Of  41  slopes  determined  on  the  Bahama  Islands  the  lowest  is 
o°  and  the  highest  28°  18'.  Seventy-five  per  cent,  of  the  slopes  are 
below  10°,  while  one-third  of  the  entire  number  of  determined 
slopes  falls  below  5°. 

On  Keeling  Island,  on  the  other  hand,  only  a  few  slopes  fall  be- 
low 10°.  Nearly  half  the  number  of  slopes  recorded  by  Dietrich 
lie  between  30  and  43  degrees,  one  being  as  high  as  63°  21'. 

A  section  made  by  Darwin  on  this  reef  showed  that  "the  water 
deepens  for  a  space  between  one  and  two  hundred  yards  wide,  very 
gradually  to  25  fathoms  (45.72  meters),  beyond  which  the  sides 
plunge  into  the  unfathomable  ocean  at  an  angle  of  45°.  To  the 
depth  of  ten  or  twelve  fathoms  (18-22  meters)  the  bottom  is  ex- 
ceedingly rugged,  and  seems  formed  of  great  masses  of  living  coral 
similar  to  those  on  the  margin."  (Darwin-2i  :  22.)  The  corals 
and  Hydrozoa  growing  here  were  Millepora  alcicornis,  Madrepora 
cf .  corymbosa,  Porites  and  Astneans.  The  madrepore  was  not  found 
in  the  shallow  part  of  the  reef  nor  in  the  lagoon,  and  this  and  the 
Astraeans  seem  to  be  restricted  to  the  outer  slope.  Below  12 
fathoms  and  especially  at  a  depth  greater  than  20  fathoms,  the  bot- 
tom was  covered  with  coral  sand,  while  at  200  to  300  fathoms,  and 
even  at  360  fathoms,  the  floor  consisted  of  finely  triturated  frag- 
ments of  stony  zoophytes,  particles  of  the  lamelliform  genera  not 
being  recognized,  while  shell  fragments  were  rare.  (Fig.  78.) 

At  a  distance  of  2,200  yards  from  the  breakers,  no  bottom  was 
found  with  a  line  7,200  feet  in  length,  hence  the  submarine  slope 
of  this  coral  island  is  steeper  than  that  of  any  volcanic  cone.  (Dar- 
win.) Submarine  cliffs  are  also  indicated. 

In  the  shallow  part  of  the  reef  Porites  in  places  forms  nearly 
the  entire  floor  in  great,  irregular,  rounded  masses  from  four  to 
eight  feet  broad  and  little  less  in  thickness.  These  mounds  are  sep- 
arated from  each  other  by  narrow,  crooked  channels  about  six  feet 
deep,  generally  intersecting  the  reef  at  right  angles.  On  the  upper 
surface  of  these  masses  the  polyps  were  often  dead,  but  growth  oc- 
curred around  the  margin.  This  was  due  to  the  exposure  of  these 
corals  at  lowest  tides,  the  upward  limit  of  growth  having  been 
reached.  Further  seaward  the  entire  mass  was  alive.  The  same 
is  true  of  the  Millepora.  Closely  within  the  line  marked  by  these 
partly  dead  polyps,  and  thus  above  the  zone  of  coral  growth,  flourish 
three  species  of  nullipores,  one  thin  like  a  lichen,  one  with  stony 
knobs  as  thick  as  a  man's  finger,  and  one  moss-like,  with  thin,  rigid 
branches.  These  also  require  the  breakers,  for  they  do  not  exist  in 
any  abundance  in  the  protected  hollows  in  the  back  part  of  the  reef. 
They  thus  form  only  a  fringe  about  20  yards  in  width,  but  located 


STRUCTURE  OF  CORAL  REEF        399 

where  they  form  an  effective  protection  against  the  breakers.  They 
form  an  artificial  breakwater  rising  about  3  feet  higher  than  the 
rest  of  the  reef.  This  is  a  very  common  occurrence  in  modern 
reefs.  Steep  slopes  are  found  around  many  modern  atolls,  and  it 
appears  that  where  the  currents  run  with  greatest  force  near  the 
reef  the  slopes  are  steeper.  In  the  Maldive  and  Chagos  atolls  such 
steep  slopes  are  common.  At  Heawandoo  Pholo  50  and  60  fathoms 
were  found  close  to  the  edge  of  the  reef,  and  at  300  yards'  dis- 
tance no  bottom  was  obtained  with  a  3OO-yard  line.  On  Egmont 
Island  a  slope  of  45°  was  found,  while  the  slopes  on  the  Cardoo 
atoll  were  so  great  that  no  bottom  was  obtained  with  a  line  200 
fathoms  long  at  only  sixty  yards  from  the  reef. 

The  general  character  of  the  slopes  on  the  Low  Archipelago 
closely  corresponds  to  that  found  on  the  Keeling  atoll,  the  slope  a 
short  distance  beyond  the  edge  of  the  reef  being  45°.  In  some 
cases,  however,  the  slope  is  that  of  a  vertical  cliff.  Perpendicular 
or  even  overhanging  cliffs  are,  however,  also  found  in  the  quiet 
water  of  the  lagoon,  while  in  other  cases,  where  the  water  is  gen- 
erally tranquil,  though  not  always  so,  as  on  the  leeward  side  of 
Mauritius,  the  slope  is  a  very  gentle  one. 

The  shores  of  the  lagoons  within  the  atolls  also  vary  greatly. 
At  Keeling  atoll  (Fig.  78)  they  shelve  gradually  where  the  bottom 
is  of  sediment,  and  irregularly  or  abruptly  where  there  are  coral 
reefs.  In  the  Marshall  group,  on  the  other  hand,  the  slope  is  often 
abrupt  so  that  we  pas's  directly  "from  a  depth  of  two  or  three 
fathoms  to  twenty  or  twenty-four,  and  you  may  pursue  a  line  in 
which  on  one  side  of  the  boat  you  may  see  bottom,  and  on  the  other 
the  azure  blue  deep  water."  (Chamisso,  quoted  by  Darwin— 21.) 
In  the  Matilda  atoll  of  the  Low  Archipelago  the  surface  of  the  great 
exterior  reef  slopes  gently  toward  and  beneath  the  surface  of  the 
lagoon,  and  then  ends  abruptly  in  a  little  cliff  3  fathoms  deep.  At 
its  foot  a  ledge  forty  yards  wide  extends,  shelving  gently  inward 
like  the  surface  reef,  and  is  terminated  by  a  second  little  cliff  5 
fathoms  deep,  beyond  which  the  bottom  of  the  lagoon  slopes  off 
to  twenty  fathoms,  its  average  central  depth.  The  ledges  appear 
to  be  formed  of  coral  rock,  often  porous,  so  that  the  sounding  lead 
descends  several  fathoms  through  holes  in  them.  Some  lagoons, 
on  the  other  hand,  have  gentle  slopes  to  the  center. 

Sections  made  by  Captain  Maclear,  R.  N.,  of  the  small  island 
of  Masamarhu  in  the  Red  Sea  show  not  only  the  nature  of  the 
slopes  of  a  coral  island,  but  also  give  indisputable  proof  of  sub- 
sidence since  the  commencement  of  the  growth.  "In  each  case  the 
surface  of  the  fringing  reef,  after  shelving  very  gently  downward 


400 


PRINCIPLES    OF    STRATIGRAPHY 


to  a  depth  of  about  three  or  four  fathoms,  is  bounded  by  a  sub- 
marine cliff.  This  in  one  section  (No.  i)  continues  almost  un- 
broken to  a  depth  of  about  500  feet,  except  that  a  kind  of  edge  or 
terrace  is  clearly  indicated  at  a  depth  of  rather  less  than  100  feet. 
In  the  other  section  the  foot  of  the  great  submarine  cliff  is 
found  at  about  500  feet,  but  .  .  .  the  cliff  is  distinctly  divided  into 
two  precipices  by  a  shelving  bank  of  coral  and  sand,  which  begins  at 
a  depth  of  about  140  feet  and  reaches  the  brow  of  the  lower  preci- 
pice at  about  260  feet.  This  bank  is  covered  by  'sand  and  coral.'  At 


No.  I. 


Soalt  of  feet 


Is/ant 


FIG.  79.  Section  i  of  Masamarhu  Island  in  the  Red  Sea,  showing  the  char- 
acters of  the  slopes  according  to  Captain  Maclear.  (After  Saville- 
Kent.) 

this  depth  in  each  section  the  island  is,  as  it  were,  defended  by  a 
deep  and  narrow  ditch,  the  edge  of  its  steep  glacis  being  formed  by 
a  sharp  arete  of  coral  which  in  one  case  rises  into  soundings  of 
about  250  feet."  (Bonney-i3.)  From  this  the  first  section  rapidly 
falls  to  a  second  ditch,  the  bottom  of  which  is  more  than  1,200  feet 
below  sea-level,  while  its  counterscarp  rises  more  than  300  feet. 
Beyond  this,  after  a  level  stretch,  the  slope  descends  at  about  30 
degrees.  The  second  ditch  is  wanting  in  the  second  section.  Coral 
and  sand  are  found  in  the  bottom  of  the  ditches,  and  the  two 
aretes  are  formed  by  coral  apparently  grown  in  situ.  This  would 


STRUCTURE    OF    CORAL    REEFS 


401 


indicate  subsidence  from  about  25  fathoms  to  the  present  depth  of 
these  points.     (Figs.  79,  80.) 

Cavernous  character  of  reefs.  Observation  on  modern  reef 
knolls  shows  that  the  mass  as  a  whole  is  often  cavernous,  large, 
empty  spaces  remaining  where  branching  corals  reach  across  to 
form  a  solid  canopy.  These  caverns  are  the  favorite  haunts  of  the 
echinoderms,  Mollusca  and  Crustacea  which  inhabit  the  reefs,  and 
through  the  openings  by  which  they  communicate  with  the  open  sea 
the  pelagic  fish  of  the  reefs  find  constant  in-  and  egress.  Such 

No.  II. 


FIG. 


SKETCH  01  MA&AMARHU  I 

Shan" nf  approtimate 

ositioner  Sectifas  ' 


Section  2  of  Masamarhu  Island  in  the  Red  Sea.      The  small  map 
shows  the  location  of  the  sections.     (After  Saville-Kent.) 


caverns  may  be  preserved  after  the  coral  rock  is  uplifted  into  dry 
land,  and  Walther  (90:91,?)  has  argued  for  such  an  initial  origin  of 
many  limestone  caverns  in  earlier  geological  formations. 

In  general  the  structure  and  form  of  barrier  reefs  around 
oceanic  islands  differ  in  no  essential  from  those  of  the  atolls,  so  that 
the  designation  of  such  a  barrier  as  an  atoll  with  high  land  rising 
within  the  lagoon  (Balbi)  is  quite  applicable.  Such  are  the  reefs 
of  Tahiti  and  others  in  the  Society  Archipelago,  of  Vanikoro  and 
of  others.  The  distance  from  shore  of  the  reef  is  from  one  to  one 
and  a  half,  and  occasionally  even  more  than  three  miles,  in  the 
Society  Archipelago  (Ellis).  In  the  few  cases  where  encircled 
highlands  exist  in  the  Caroline  Archipelago  greater  distances  are  ob- 


402  PRINCIPLES    OF    STRATIGRAPHY 

served.  Thus  on  the  south  side  of  Hogoleu  this  is  no  less  than  20 
miles,  6  miles  on  the  east  and  14  miles  on  the  south. 

The  central  mountains  in  the  Society  and  other  groups  are  gen- 
erally bordered  by  a  fringe  of  flat  and  often  marshy,  alluvial  land, 
from  one  to  four  miles  in  width,  and  consisting  of  coral  sand  and 
detritus  thrown  up  from  the  lagoon  channel,  and  of  soil  washed 
down  from  the  hills.  These  island  hills  vary  greatly  in  height  and 
character.  At  Tahiti  the  height  is  7,000  feet,  though  the  maximum 
diameter  of  the  reef  is  only  thirty-six  miles.  At  Maurua  the  cen- 
tral peak  is  about  800  feet  high,  and  the  maximum  diameter  only 
a  little  more  than  two  miles.  In  other  cases  it  is  much  lower;  at 
Manouai  only  50  feet.  In  most  cases  the  rock  is  that  of  an  old 
volcano,  while  in  some  cases  it  is  old  crystalline  rock  and  in  others 
raised  coral  reef  rock.  The  number  of  peaks  varies  from  one  to 
nearly  a  dozen  (Hogoleu). 

What  has  been  said  of  barrier  reefs  around  oceanic  islands  also 
applies  to  the  fringing  reefs  of  such  islands.  These  differ  from  the 
encircling  barriers  only  in  the  narrowness  of  the  dividing  water 
channel  or  moat.  Thus  on  the  western  side  of  Mauritius  the  reef 
generally  lies  at  a  distance  of  about  half  a  mile  from  the  shore, 
though  in  some  parts  it  is  distant  from  one  to  two  and  even  three 
miles.  In  general,  the  fringing  reef  rests  on  the  gently  sloping  sub- 
merged portion  of  the  island  mass,  which  in  most  cases  does  not  de- 
scend, within  the  limits  of  the  reef,  to  depths  greater  than  those  at 
which  coral  polyps  flourish.  Where  such  a  greater  depth  exists  it  is 
to  be  accounted  for  either  by  progressive  subsidence  and  upbuilding 
of  the  reef,  or  by  outward  growth  upon  a  basis  of  coral  detritus, 
which  forms  a  talus  in  front  of  the  growing  reef.  Fringing  reefs 
are  breached  by  passages  in  front  of  every  river  and  streamlet 
which  descends  from  the  enclosed  land.  Such  breaches  are  found 
in  barrier  reefs  only  in  front  of  the  larger  streams  where  the  width 
of  the  lagoon  channel  is  not  too  great.  The  width  of  the  reef  varies 
with  the  inclination  of  the  substratum. 

Characters  of  Epicontinental  Reefs.  Reefs  resting  for  the  main 
part  upon  the  continental  shelf  or  its  margin  are  found  to-day  in 
the  western  portions  of  the  three  oceans  covering  the  tropical  belt, 
namely,  the  Pacific,  Indian  and  Atlantic.  The  largest  and  most  char- 
acteristic are  those  of  the  western  Pacific,  the  Great  Barrier  Reef 
of  Australia  occupying  the  first  place  among  these.  This,  as  already 
noted,  extends  with  a  few  interruptions  for  about  a  thousand  miles ; 
its  average  distance  from  the  land  is  between  twenty  and  thirty 
miles,  while  in  some  parts  this  distance  increases  to  between  fifty 
and  seventy  miles.  It  encloses  a  great  lagoon  strip  which  varies  in 


EPICONTINENTAL    REEFS  403 

depth  from  ten  to  twenty-five  fathoms,  and  has  a  sandy  bottom. 
Southward,  where  the  reef  increases  in  distance  from  the  shore, 
the  depth  of  the  lagoon  increases  to  forty  and  in  some  places  more 
than  sixty  fathoms.  Just  outside  of  the  reef  the  water  descends 
to  profound  depths. 

The  surface  of  the  reef  consists  of  a  hard,  white  agglomerate  of 
many  kinds  of  corals  with  numerous  projecting  points.  The  outer 
rim  is  highest,  and  is  traversed  by  narrow  gullies,  and  is  breached 
at  rare  intervals  by  ship  canals. 

In  form  the  Great  Barrier  Reef  is  a  triangular  wedge,  widening 
gradually  from  the  shore  outward  for  a  distance  of  from  30  to  90 
miles.  Just  outside  of  the  reef  the  descent  to  abyssal  depths  is 
abrupt,  the  outer  face  of  the  reef  forming  a  great  wall  in  some  cases 
exceeding  1,800  feet  in  height,  and  fronting  the  whole  northeast 
coast  of  Australia.  Along  the  outer  edge  of  the  platform  produced 
by  the  reefs  is  the  true  barrier,  a  linear  series  of  reefs  breached  by 
narrow  passages.  Inside  the  barrier  is  a  clear  and  broad  channel 
generally  from  15  to  20  fathoms  deep,  with  its  bottom  covered  by 
unconsolidated  lime  sand  or  by  a  sand  largely  composed  of  the 
foraminiferan  Orbitolites,  these  remains  in  some  cases  also  making 
up  the  whole  sand  of  the  beach  either  of  the  coral  islets  or  the  neigh- 
boring shores.  Outside,  in  the  deep  sea,  the  dredge  obtained  only 
a  fine-grained,  impalpable,  pale,  olive-green  mud,  which  was  wholly 
soluble  in  dilute  hydrochloric  acid,  and  when  dried  had  the  charac- 
ter and  consistency  of  chalk. 

Great  masses  of  Porites  and  Maeandrina  flourish  on  the  outer 
border  of  the  reef,  and  these  when  detached  from  their  anchorage 
are  rolled  about  by  the  waves  and  worn,  while  at  the  same  time 
grinding  down  the  rock  mass  beneath  until  the  whole  coral  head  is 
reduced  to  fine  sand  or  mud.  Such  rounded  detached  masses  of 
Mseandrina  6  or  8  feet  in  diameter  are  common  among  the  loose 
blocks  rolled  up  from  the  outer  slope  onto  the  reef.  They  may  be 
seen  just  inside  the  surf  at  low  water,  extending  for  some  miles, 
and  are  known  as  "Turks'  heads."  Madrepora,  Millepora  and 
other  genera  also  characterize  the  outer  reef  together  with  numer- 
ous species  of  astrseans.  Inside  the  channel  mentioned  lie  the  "in- 
ner reefs"  separated  from  each  other  by  narrow  waterways  through 
which  the  tide  rushes  with  great  force.  Sometimes  these  tidal  cur- 
rents continue  in  the  same  direction  even  for  two  or  three  days,  es- 
pecially after  great  storms  have  driven  Jarge  volumes  of  water  into 
the  reef  area.  Between  the  inner  reefs  and  the  mainland  of  old  rock 
lies  a  shallow  channel,  mostly  free  from  coral  growth. 

Among  the  inner  reefs  are  many,  which  are  to  a  large  extent 


404  PRINCIPLES    OF    STRATIGRAPHY 

composed  of  one  type  of  coral.  Thus  on  the  Organ  Pipe  Reef  of 
Thursday  Island  Tubipora  musica  predominates,  while  another  reef 
of  this  island  is  largely  composed  of  the  blue  Heliopora  coerulea. 
Other  important  contributors  to  the  Great  Barrier  Reef  material 
are  Euphyllia,  Galaxea,  Mussa,  Trachyphyllia,  Symphyllia,  Gonias- 
traea,  Prionastnea,  Favia,  Fungia,  etc. ;  none  of  these  are,  however, 
as  important  as  are  the  various  species  of  Porites  and  Madrepora. 
The  hydrocorallines,  Millepora  and  the  red  Distichopora  also  add 
materially  to  the  lime  of  the  great  series  of  reefs. 

The  reefs  on  the  eastern  coast  of  Africa  are  of  the  fringing 
type,  extending  for  a  distance  of  nearly  forty  miles,  from  lat.  i° 
15'  to  i°  45'  S.,  and  with  an  average  distance  from  shore  of  some- 
what more  than  a  mile.  The  depth  of  the  lagoon  is  very  slight,  and 
this  continues  for  some  distance  outside  of  the  reef,  where  it  is  only 
from  8  to  14  fathoms  at  a  distance  of  a  mile  and  a  half  from  the 
reef.  The  external  margin  of  the  reef  is  formed  of  projecting 
points,  within  which  there  is  a  space  from  6  to  12  feet  deep  with 
patches  of  living  coral  on  it.  At  Mombas  (lat.  4°  S.)  a  reef  fringes 
the  coast  for  thirty-six  miles,  at  a  distance  of  from  half  a  mile  to 
one  mile  and  a  quarter  from  the  shore.  The  channel  within  this 
reef,  ranging  in  depth  from  6  to  15  feet,  is  navigable  for  canoes 
and  small  craft.  Outside  of  the  reef  the  depth  is  about  30  fathoms 
at  a  distance  of  nearly  half  a  mile.  Part  of  this  reef  is  very  sym- 
metrical, with  a  uniform  breadth  of  200  yards  (Darwin-2i). 

The  reefs  of  the  Florida  coast  form  an  interesting  example  of 
the  fringing  type  on  a  shallow  continental  platform.  The  southern 
coast  of  Florida  rises  from  12  to  15  feet  above  the  sea-level,  in  the 
form  of  a  curving  ridge,  which  encloses  an  extensive  fresh-water 
swamp,  the  Everglades.  The  surface  of  this  lies  only  two  or  three 
feet  above  sea-level,  and  is  dotted  over  with  small  islands,  the  so- 
called  hummocks.  Some  distance  outside  of  the  southern  border 
of  the  land  lies  a  row  of  small  islands  or  "keys"  of  dead  coral 
rock  and  sand,  ranging  from  5  to  30  miles  distant  from  shore  and 
continued  westward  in  a  curved  line  far  beyond  the  western  coast 
of  the  peninsula.  The  islands  are  low  and  of  limited  extent,  that  of 
Key  West  near  the  western  end  of  the  line  being  less  than  4  miles 
long,  while  the  longest  of  the  islands  is  only  15  miles  in  length. 
The  keys  slope  toward  their  northern  shore,  and  present  a  steep 
face  to  the  south,  where  they  are  separated  from  the  living  reefs 
by  an  open  channel.  Between  the  keys  and  the  southern  coast  of 
the  mainland  the  water  is  very  shallow  and  navigable  only  to  the 
smallest  boats.  This  lagoon  is,  moreover,  dotted  with  small,  low 
mangrove  islands.  The  mangrove  trees  growing  here  extend  their 


FLORIDA    REEFS 


405 


aerial  roots  in  all  directions,  forming  a  tangle,  which  becomes  effi- 
cient in  checking  sediment-laden  currents  and  causes  them  to  de- 


FIG.  81.  Map  of  Florida,  showing  the  keys  and  reefs.  (After  Le  Conte.)  a — 
Southern  coast;  a' — keys;  a" — living  reef;  d-d' — older  coral  rock; 
e — everglades;  e' — shoal  water;  e" — ship  channel;  GSS — Gulf 
Stream. 

posit  their  load.  Hence  the  inner  lagoon  will  gradually  silt  up,  and 
this  has  already  progressed  so  far  that  a  considerable  portion  of  the 
area  forms  mud  flats  at  low  tide.  (Figs.  81,  82.)  Here,  then,  a 


FIG.  82.  Diagrammatic  section  of  Florida  along  the  line  N.S.  in  the  preceding 
figure,  showing  the  relative  position  of  the  various  parts,  lettering 
the  same.  The  dotted  lines  indicate  hypothetical  former  condi- 
tions. (After  Le  Conte.) 


406  PRINCIPLES    OF    STRATIGRAPHY 

clastic  mud  sediment  rich  in  organic  matter  rests  directly  upon  the 
ancient  coral  reef  now  represented  by  the  keys,  a  relationship  ex- 
pressed in  the  rocks  of  the  older  geological  periods  by  the  super- 
position of  a  black  carbonaceous  shale  above  an  earlier  coral  lime- 
stone. * 

Outside  of  the  line  of  keys  and  from  3  to  15  miles  distant  from 
it  is  a  line  of  living  coral  reefs,  consisting  of  mounds  made  up  of 
branching  madrepores,  Porites,  etc.,  besides  many  smaller  genera 
such  as  Manicina,  Agaricia,  etc.  Corallina  and  Lithothamnion  also 
add  a  large  percentage  of  calcareous  material  to  the  reef. 

These  reefs  are  for  the  most  part  submerged,  rising  only  here 
and  there  to  the  surface.  Between  them  and  the  keys  lies  the  outer 
lagoon,  a  long,  narrow  channel  five  to  six  fathoms  deep  and  naviga- 
ble for  small  vessels.  Here  the  sedimentation  consists  of  coral 
sand  and  of  the  shells  of  marine  organisms,  thus  producing  a  nor- 
mal marine  limestone,  which  is  either  in  the  form  of  a  coral  breccia 
or  a  more  or  less  oolitic  calcarenyte.  Outside  the  living  reef,  the 
bottom  rapidly  descends  to  the  abyssal  depths  of  the  Florida  Straits 
(2,916  feet). 

While  nullipores,  or  the  stony  algae,  luxuriate  in  the  outer  zone 
of  the  reef,  where  they  form  a  distinct  Nullipore  zone  in  the  face 
of  the  strong  surf,  the  more  delicate  branching  and  brittle  corallines 
are  confined  to  the  channels  and  lagoons  within  the  reef,  where 
they  often  form  thick  carpets  in  the  quiet  water.  Thus  the  shallow 
parts  of  the  bottom  of  the  ship  channel  between  the  living  Florida 
reefs  and  the  old  reefs  or  keys  are  covered  with  the  so-called  "coun- 
try grass,"  one  of  these  calcareous  algae.  This  is  especially  notice- 
able between  Fowey  Rocks,  Triumph  Reef  and  Long  Reef  on  the 
one  side,  and  Soldier  Key  and  Ragged  Keys  on  the  inside  ( Agassiz- 
2 : 126,  127) .  The  floor  of  Hawk  Channel,  which  has  a  depth  of 
from  6  to  7  fathoms,  is  covered  with  disintegrated  corals  and  coral- 
lines (Pourtales;  Dana-2O  :<?//),  while  some  of  the  keys  in  the  Dry 
Tortugas  and  Marquesas  are  wholly  composed  of  fragments  of 
corallines  bound  together  into  a  solid  mass.  Among  these  coral- 
lines a  large  species  of  Opuntia  is  especially  noticeable. 

It  has  been  shown  by  Agassiz  that  the  keys,  the  southern  rim 
of  the  mainland,  and  a  strip  including  the  north  shore  of  the  Ever- 
glades and  extending  as  far  north  on  the  eastern  shore  as  St.  Au- 
gustine, are  of  coral-reef  origin.  When  this  last  strip  was  the  living 
reef,  the  platform  in  front  was  being  built  out  into  the  sea  by  the 
accumulations  of  the  shells  of  organisms  which  lived  in  abundance 
in  the  genial  waters  of  the  Gulf  Stream  border.  When  the  platform 
was  sufficiently  extended  a  new  line  of  reefs  came  into  existence, 


THEORIES    OF    ORIGIN    OF    REEFS  407 

forming  a  barrier  reef  at  a  distance  from  shore  where  now  lies  the 
outer  rim  of  the  Florida  mainland.  The  lagoon  behind  this  new 
reef  was  of  the  character  of  the  present  outer  lagoon,  and  received 
normal  marine  sediments,  until  with  progressive  upbuilding  the 
outer  reef  was  converted  into  a  series  of  dead  keys  and  a  new  line 
of  reefs  came  into  existence  upon  the  meanwhile  extended  sub- 
marine platform.  This  new  line  was  subsequently  converted  into 
the  present  line  of  keys,  the  preceding  row  became  the  southern 
coastal  rim,  and  the  old  lagoon  behind  it  was  converted  by  suc- 
cessive steps  into  the  present  Everglades.  The  present  inner  lagoon 
channel  between  the  mainland  and  the  keys  is  gradually  approach- 
ing the  same  fate,  and  it  and  the  line  of  keys  will  in  turn  be  added 
to  the  mainland,  while  the  present  living  reef  will  gradually  emerge 
as  a  line  of  islands  and  the  lagoon  behind  it  suffer  filling  up.  It  is 
not  likely  that  a  new  line  of  reefs  will  form  outside  of  the  present 
one,  as  the  force  of  the  Gulf  Stream  will  prevent  further  extension 
on  the  Pourtales  Plateau  of  the  submarine  platform  which  serves  as 
the  foundation  of  the  reef..  (Le  Conte-59;  60.) 

It  is  to  be  noted  that  as  the  building  of  the  new  reef  progresses, 
leading  to  the  extinction  of  the  preceding  inner  reef,  a  new  type 
of  sedimentation — the  mud-flat  type — will  come  into  existence  be- 
hind the  older  reef,  while  contemporary  calcareous  deposits  will 
accumulate  in  the  outer  lagoon  and  on  the  reef.  Thus  the  top  of 
the  limestone  series  formed  by  these  shell  accumulations  and  reefs 
will  rise  progressively  seaward,  while  mud-flat  and  later  continental 
conditions  will  progressively  replace  the  marine  conditions  from 
the  landward  side  outward.  Precisely  such  conditions  existed  in  the 
Onondaga  (Middle  Devonic)  period  of  New  York  and  Pennsyl- 
vania, where  the  coral- forming  conditions  progressed  toward  the 
northwest,  while  the  black  Marcellus  muds  replaced  them  on  the 
south  and  east. 

THEORIES  OF  ORIGIN  OF  TYPES  OF  CORAL  REEFS.  Of  all  the 
reef  types,  the  fringing  reef  alone  requires  no  special  explanation 
of  origin,  since  here  the  corals  grow  in  shallow  water  under  normal 
conditions  of  habitat.  All  continental  or  island  shores  in  the  tropics, 
in  which  the  submarine  slope  is  a  moderate  one,  are  suitable  for 
coral  reef  development,  provided  mechanical  detritus  is  absent  or  of 
negligible  amount  and  the  other  necessary  conditions,  clearness  and 
saltiness  of  the  sea,  absence  of  large  streams,  sufficient  wave  activi- 
ties, absence  of  cooling  currents,  sufficiency  of  food  supply,  etc., 
concur.  Corals  will  grow  under  such  conditions  out  to  the  zone  of 
depth  limit  (20-25  fathoms).  Where  the  submerged  platform  on 
which  the  corals  grow  is  increased  in. extent  seaward  by  the  accumu- 


408  PRINCIPLES    OF    STRATIGRAPHY 

lation  of  organic  or  other  debris,  as  in  the  case  of  the  Florida 
region,  coral  reefs  may  progressively  develop  seaward  in  what  was 
originally  water  of  too  great  a  depth  for  normal  coral  growth. 

Oceanic  barrier  reefs  and  atolls,  on  the  other  hand,  rise  from 
depths  greater  than  those  at  which  reef  corals  flourish,  and  so  these 
types  need  further  explanation.  Two  principal  theories  have  been 
proposed  for  their  explanation:  the  subsidence  theory  of  Darwin, 
elaborated  and  strengthened  by  Dana,  and  the  spreading  ring  theory 
proposed  by  Murray  and  elaborated  by  Alexander  Agassiz. 

Subsidence  Theory  of  Darzvin.  Fringing  reefs  surrounding 
oceanic  islands  may  be  progressively  converted  into  barrier  reefs 
and  finally  into  atolls  by  a  constant  subsidence  sufficiently  slow  to 
permit  the  reef  corals  to  grow  upward  and  maintain  themselves  in 
a  relatively  uniform  depth  within  the  normal  limit.  By  such  a  sub- 
sidence the  older  dead  coral  masses  are  carried  constantly  to  lower 
depths,  while  the  top  of  the  reef  flourishing  on  this  foundation 
of  dead  coral  constantly  keeps  near  to  the  surface  of  the  sea.  The 
channel  between  the  reef  and  the  rock  island  will  become  wider  as 
more  of  this  island  is  submerged,  while  at  the  same  time  it  becomes 
filled  by  the  coral  sand,  and  broken  coral  masses  thrown  over  the 
reef  and  the  land-derived  detritus  supplied  by  the  streams  from 
within.  Growing  nullipores  and  other  organisms  will  likewise  help 
in  filling  the  constantly  widening  lagoon.  When  subsidence  has  pro- 
gressed so  far  that  the  central  land  mass  has  become  entirely  sub- 
merged, the  barrier  reef  has  changed  to  the  atoll  and  the  ring  lagoon 
to  the  open  lake-like  body  of  water  within  the  ring  of  coral  reefs 
and  islets. 

This  explanation  readily  accounts  for  the  observed  gradation  be- 
tween the  fringing  reefs  and  atolls  noted  in  the  islands  of  the  Pa- 
cific, where  every  stage  seems  to  be  represented.  It  accounts  for  the 
steep  slopes  and  the  occasional  cliffs  of  the  outside  of  the  reef 
which  descend  to  abysmal  depths,  as  well  as  the  occurrence  of  dead 
reef  corals  at  depths  where  they  cannot  live — corals  which  have 
been  carried  by  subsidence  of  their  foundation  beyond  their  normal 
depth  and  drowned.  This  theory  accounts  also  in  a  satisfactory  way 
for  the  remarkable  distribution  of  the  various  kinds  of  reefs  in  the 
Pacific,  as  shown  by  Dana.  In  the  middle  of  the  atoll  area  of  the 
Pacific  there  is  an  extensive  area  2,000  miles  long  by  1,000  miles 
wide  free  from  islands.  This  is  roughly  surrounded  by  a  belt  of 
small  atolls,  outside  of  which  occurs  the  region  of  large  or  grouped 
atolls,  then  a  belt  in  which  the  reefs  are  mostly  barriers  and  finally 
the  belt  of  fringing  reefs.  This  distribution  is  of  course  to  be 
traced  only  in  a  general  way.  Outside  of  the  last  belt  there  is  even 


THEORIES    OF    ORIGIN    OF    REEFS  409 

some  evidence  of  elevation.  The  subsidence  theory  accounts  for 
this  distribution  by  assuming  that  the  central  area  has  gone  down 
so  fast  that  the  corals,  could  not  gain  a  foothold  or  were  drowned 
out  completely.  The  small  atolls  show  a  rapid  and  great  sub- 
mergence, but  not  sufficient  to  prevent  coral  growth  entirely,  the 
upward  growth  barely  keeping  pace  with  the  subsidence,  and  with 
no  opportunity  for  spreading.  The  successive  belts  show  the  de- 
crease in  the  amount  of  subsidence,  so  that  we  ,pass  progressively 
from  large  atolls  to  barrier  reefs  and  finally  to  fringing  reefs,  where 
the  zone  of  no  subsidence  is  reached,  beyond  which  the  movement 
seems  to  have  been  in  the  opposite  direction  and  dead,  fringing 
reefs  cling  to  the  sides  of  high  islands  often  at  a  considerable  ele- 
vation above  the  present  sea-level. 

Evidence  of  subsidence.  The  most  convincing  proof  of  the  cor- 
rectness of  this  theory  for  the  explanation  of  at  least  some  of  the 
coral  reefs  of  the  Pacific  is  furnished  by  the  deep  boring  on  the 
atoll  of  Funafuti,  which  showed  organic  limestone  consisting  of 
corals,  Foraminifera,  calcareous  algae  and  other  organisms  to  a 
depth  of  1,114  feet,  the  extent  of  the  boring.  The  boring  made  in 
the  lagoon  showed  the  existence  of  solid  masses  of  shallow-water 
corals  (Porites,  Madrepora,  Heliopora)  at  a  depth  of  245  feet  un- 
der a  layer  of  calcareous  algae  (Halimeda  opuntia)  and  Forami- 
nifera, more  than  a  hundred  feet  thick.  Other  evidence  of  sub- 
sidence is  furnished  by  sacred  structures  erected  by  the  natives  on 
certain  coral  islands.  These  now  stand  in  the  water,  and  the  paths 
worn  by  the  feet  of  the  devotees  are  at  present  passages  for  ca- 
noes. (Dana-2O.) 

Davis  has  recently  shown  (23)  that  Dana  furnished  con- 
vincing proof  of  the  theory  of  subsidence  in  the  region  of  some 
coral  atolls.  This  lies  in  the  fjord-like  bays  which  indent  much 
eroded  mountain  islands,  around  which  coral  reefs  grow.  If  no 
subsidence  has  taken  place,  these  valleys  would  be  more  or  less 
filled  by  alluvial  deposits,  since  clastic  material  is  constantly  brought 
into  the  sea  by  the  wash  from  the  mountain.  Where,  however,  the 
valleys  are  unobstructed  embayments,  and  continue  as  such  under  the 
water,  the  evidence  of  progressive  subsidence  with  corresponding  en- 
croachment of  the  sea  up  the  valleys  seems  clear.  As  Dana  says : 
"The  very  features  of  the  land,  the  deep  indentations,  are  sufficient 
evidence  of  subsidence  to  one  who  has  studied  the  character  of  the 
Pacific  islands."  And,  again :  "When  ...  we  find  the  several  val- 
leys continued  on  beneath  the  sea,  and  their  enclosing  ridges  stand- 
ing out  in  long,  narrow  points,  there  is  reason  to  expect  that  the  land 
has  subsided  after  the  formation  of  the  valleys.  For  such  an  island 


4io 


PRINCIPLES    OF    STRATIGRAPHY 


as  Tahiti  could  not  subside  even  a  few  scores  of  feet  without  chang- 
ing the  even  outline  into  one  of  deep  coves  or  bays,  the  ridges  pro- 
jecting out  to  sea  on  every  side.  .  .  .  The  absence  of  such  coves, 
on  the  contrary,  is  evidence  that  any  subsidence  which  has  taken 
place  has  been  comparatively  small  in  amount."  (Davis-23 :  i#j.) 
The  following  diagram  (Fig.  83),  illustrating  this  principle,  is 
copied  from  Davis. 

The  Spreading  .Ring  Theory  of  Murray.  Sir  John  Murray's 
theory  of  coral  reef  formation  is  an  elaboration  of  the  early  expla- 
nation of  the  forms  of  coral  reefs  propounded  by  the  poet-natu- 


FIG.  83.  Block  diagram  illustrating  the  effects  of  subsidence  of  a  much  dis- 
sected island  around  the  borders  of  which  grow  coral  reefs.  The 
effect  of  subsidence  is  produced  by  adding  to  the  surface  of  each 
successive  block  an  amount  equal  to  the  postulated  -subsidence. 
The  deep  embayments  in^the  middle  block,  from  which  terrigenous 
sediment  is  absent,  can  be  produced  only  by  subsidence.  (After 
Davis.) 

ralist  Adalbert  von  Chamisso.  It  is  based  on  the  existence  of  sub- 
marine banks  of  volcanic  or  other  origin,  rising  to  within  a  moderate 
depth  beneath  the  surface  of  the  sea.  The  existence  of  such  banks 
has  been  abundantly  shown  by  soundings  of  the  Challenger  and 
other  exploring  expeditions.  Such  submerged  surfaces  afford  a 
habitat  for  lime-secreting  organisms,  such  as  deep-sea  corals,  echino- 
derms,  molluscs,  crustaceans,  etc.,  and  their  shells  and  skeletons  will 
gradually  raise  the  surface  of  the  submerged  bank  until  it  comes 
within  the  zone  of  reef-coral  growth.  As  pointed  out  by  Chamisso, 
the  corals  on  the  outer  side  of  a  growing  mass  are  situated  most 
favorably  with  regard  to  wave  activity,  food  supply,  etc.,  and  so  the 
reef  will  rise  to  the  surface  as  an  atoll.  The  nearer  it  approaches 
the  surface,  the  more  unfavorable  will  become  the  atoll  for  the 


THEORIES    OF    ORIGIN    OF    REEFS     *          411 

growth  of  corals,  and  these  eventually  die  out  on  the  interior,  while 
they  continue  to  flourish  vigorously  on  the  exterior  of  the  atoll.  By 
the  accumulation  of  coral  debris  on  the  outer  slope  of  the  reef  a 
foundation  is  formed  for  the  spreading  of  the  coral  ring,  as  in  the 
case  of  the  Florida  reefs,  and  so  the  diameter  of  the  atoll  increases, 
while  at  the  same  time  the  solvent  action  of  the  water  in  the  lagoon 
and  the  scouring  action  of  the  tide  will  enlarge  the  area  of  the  en- 
closed water  body.  It  may,  however,  be  questioned  if  the  great 
depth  of  some  lagoons,  40  to  50  fathoms,  can  be  accounted  for  in 
this  way,  especially  as  in  many  cases  the  tendency  is  to  fill  up  the 
lagoon  by  nullipore  growth  and  accumulation  of  debris. 

That  such  an  origin  must  be  accepted  for  certain  atoll  reefs  is 
shown  by  the  observations  of  Guppy  (41)  on  certain  uplifted 
islands  of  the  Solomon  group.  On  Ugi,  Santa  Anna,  Treasury  and 
Stirling  islands,  he  found  unmistakable  evidence  of  a  nucleus  of 
volcanic  rock,  which  was  covered  by  an  earthy,  stratified  deposit  of 
mixed  foraminiferal  and  volcanic  material  similar  to  the  deep-sea 
muds,  several  hundred  feet  thick,  and  highly  fossiliferous,  contain- 
ing the  remains  of  pteropods,  pelecypods  and  echinoderms.  On  the 
flanks  of  these  elevated  beds  are  found  deposits  of  coralline  lime- 
stone varying  from  16  to  100  feet  in  thickness,  and  representing  the 
reef  deposits  now  elevated  above  the  sea-level.  Santa  Anna  has  the 
form  of  an  uplifted  lagoon,  the  coral  rock  80  feet  in  thickness  and 
resting  on  a  friable,  somewhat  argillaceous  rock  resembling  a  deep- 
sea  deposit.'  Here  we  have,  then,  a  clear  example  of  reefs  growing 
on  a  platform,  built  up  of  foreign  material,  and  similar  features  are 
shown  on  the  Fiji  Islands  and  the  Great  Barrier  Reef,  and  on  the 
reefs  of  the  Bahamas,  Florida  and  the  Bermudas  in  the  West  At- 
lantic. All  of  these  areas  show  either  stationary  conditions  or 
actual  evidence  of  recent  elevation. 

Multiple  Origin  of  Reefs.  On  the  whole,  the  subsidence  theory 
seems  to  be  applicable  to  many,  though  far  from  all,  oceanic  reefs, 
where  at  the  same  time  spreading  of  the  coral  ring  by  outward 
growth  may  have  cooperated.  Epicontinental  reefs,  on  the  other 
hand,  or  those  forming  on  the  margins  of  the  continents  and  around 
continental  islands,  are  probably  in  all  cases  to  be  explained  by 
growth  on  suitable  foundations,  without  subsidence,  the  reef  ex- 
panding as  the  platform  on  which  it  grows  expands.  Such  an  ori- 
gin is  almost  certain  for  the  Great  Barrier  Reef  of  Australia,  and 
for  the  Florida  reefs,  and  such  an  origin  is  to  be  postulated  for 
most  of  the  older  reefs,  which  all  or  nearly  all  belong  to  the  epi- 
continental  type. 

RATE  OF  GROWTH  OF  REEF  ORGANISMS.    Comparatively  little  is 


4i2  PRINCIPLES    OF    STRATIGRAPHY 

known  regarding  the  rate  of  growth  of  the  organisms  forming  the 
reefs.  Experiments  and  observations  on  Funafuti  reef  organisms 
showed  that  the  lichenous  forms  of  Lithothamnion  grow  very 
slowly,  no  appreciable  increase  in  size  occurring  in  five  months. 
When,  however,  the  alga  was  killed  by  too  long  exposure  to  the 
sun  at  low  tide,  turning  white  as  a  result,  a  resubmergence  caused 
the  pink  color  to  reappear  in  a  few  days  by  the  spreading  from  a 
center  where  some  cells  still  remained  alive.  Halimeda,  however, 
the  alga  producing  the  greatest  amount  of  calcareous  debris,  grows 
more  rapidly,  a  cluster  3  inches  in  height  and  of  equal  thickness, 
and  weighing  14.38  grains  after  it  was  dried,  growing  in  a  period 
of  six  weeks. 

The  rate  of  increase  of  Millepora  on  Funafuti  was  found  to  be 
16.5  per  cent,  per  annum  for  the  massive  M.  complanata,  while  the 
branching  M.  alcicornis  showed  an  average  increase  in  size  of  I 
inch  in  34.7  weeks.  The  latter  species  also  covers  objects  entangled 
in  its  mass,  and  fragments  of  Halimeda  and  other  corallines  may 
thus  be  enclosed.  Of  the  corals,  Porites  limosa  was  found  to  in- 
crease in  weight  at  the  regular  rate  of  47.27  per  cent,  per  annum. 
The  encrusting  coral  Hydnophora  microcona  was  found  to  spread 
at  the  rate  of  one  inch  in  39  months.  Astraopora  ocellata,  though 
forming  new  calices  between  the  old  ones,  showed  no  measurable 
increase  in  size  during  the  period  of  observation.  Pocillopora 
grandis  increased  in  all  directions  at  a  rate  of  one  inch  in  13.5 
weeks ;  while  small  pieces  of  P.  verrucosa  were  found  to  increase  in 
weight  at  the  startling  rate  of  150  per  cent,  per  annum.  This,  how- 
ever, was  partly  due  to  the  expansion  of  the  living  matter  over  the 
broken  surface,  and  the  formation  of  new  calices  there,  a  feature  not 
normal  under  natural  conditions.  A  similar  large  increase  was 
found  for  P .  paucistellata.  The  mushroom  coral  Montipora  in- 
cognita showed  a  rate  of  growth  in  one  direction  of  half  an  inch  in 
three  months,  and  an  average  increase  in  three  directions  measured 
one  inch  in  35.7  weeks. 

An  extensive  growth  of  the  coral  Orbicella  annularis  took  place 
upon  a  bell  olive  jar  and  decanter  recovered  in  1857  from  the  wreck 
of  a  vessel  supposed  to  be  the  British  frigate  Severn,  lost  off  Turk's 
Island  in  the  West  Indies  in  1793.  These  specimens  are  now  pre- 
served in  the  Museum  of  the  Boston  Society  of  Natural  History. 
(Crosby,  18:^09;  Verrill-88.)  During  the  64  years  of  submerg- 
ence Orbicella  annularis  attached  to  the  bell  spread  out  on  all  sides. 
The  thickness  at  the  center  is  about  8  inches  and  the  breadth  15. 
The  olive  jar  and  glass  decanter  are  cemented  together  by  a  similar 
mass  of  the  same  species.  The  wreck  lay  in  from  three  to  ten 


RATE  OF   GROWTH   OF  REEF   ORGANISMS       413 

fathoms  of  water,  and  it  was  covered  astern  of  the  middle  by  thick- 
branching  Madrepora,  the  branches  of  which  were  twelve  inches  in 
diameter  and  sixteen  feet  in  height.  This  makes  a  rate  of  growth 
for  this  coral  of  three  inches  per  year. 

Darwin  cites  some  experiments  made  on  the  east  coast  of  Mada- 
gascar in  December,  1830,  by  Dr.  Allan,  of  Forres.  Twenty  corals 
were  weighed  and  placed  apart  on  a  sand  bank  in  water  3  feet  deep 
at  low  tide,  each  of  them  reaching  in  the  following  July  nearly  to 
the  surface  and  being  quite  immovable,  while  some  had  grown  over 
the  others.  A  block  of  concrete  taken  at  Fort  Jefferson,  Tortugas, 
and  which  had  been  in  the  water  only  twenty  years,  had  a  specimen 
of  Mceandrina  labyrinthica  growing  on  it,  which  measured  a  foot  in 
diameter  and  four  inches  thick  in  the  most  convex  part.  (Dana- 
20:  124.)  At  Key  West,  a  Mseandrina  had  grown  to  a  radius  of 
six  inches  in  twelve  years.  An  Oculina  diffusa  planted  as  a  germ 
in  this  same  region  grew  in  14  years  to  a  height  of  four  inches  and 
a  breadth  of  8  inches,  while  a  M&andrina  clivosa  in  the  same  time 
reached  a  height  of  two  and  a  quarter  inches  and  a  breadth  of  seven 
and  a  half  inches. 

The  rate  of  growth  of  coral  reefs  is,  however,  much  slower  than 
the  rate  of  growth  of  the  corals  and  other  organisms  composing 
them,  since  these  grow  only  in  isolated  patches.  Estimates  on  the 
rate  of  increase  in  height  of  reefs  allow  two  hundred  years  for  every 
foot  of  increase. 

COMPACTING  AGENTS  OF  CORAL  REEFS.  The  isolated  coral  heads 
of  the  reefs  do  not  of  themselves  produce  the  solid  limestone 
masses  characteristic  of  these  structures,  unless  they  are  bound 
together  either  by  chemical  precipitation  of  lime  in  the  interstices 
or  by  organic  agencies.  Qn  Funafuti  (74: 147)  it  is  the  lichenous 
Lithothamnion  which  performs  this  office  most  effectively,  cement- 
ing the  coral  masses  to  each  other  and  to  the  reef  as  a  whole. 
This  nullipore  will  attack  both  living  and  dead  corals  and  will  cause 
every  interstice  as  well  as  every  space  between  the  branches,  if 
present,  to  be  transformed  into  one  solid  mass.  Thus  the  coral  mass 
will  be  permanently  added  to  the  reef,  enlarging  it  by  the  amount 
of  its  bulk  when  taken  possession  of  by  the  Lithothamnion.  Obser- 
vations show  that  a  coral  once  attacked  by  the  nullipore  will  remain 
stunted,  and  thus  the  amount  of  addition  to  the  reef  depends  on 
the  period  of  growth  reached  by  the  coral  when  attacked  by  the 
Lithothamnion. 

On  the  Great  Barrier  Reef  it  was  found  that  reef  forming  was 
less  a  function  of  the  species  of  coral  than  of  the  temperature,  for 
the  same  species  forming  solid  reefs  in  the  warmer  portions  of  the 


4i4  PRINCIPLES    OF    STRATIGRAPHY 

reef-area  remained  unconsolidated  in  the  southern  part,  where  the 
temperature  was  lower. 

A  characteristic  feature  of  the  closing  stages  of  reef  formation 
at  any  locality  seems  to  be  the  production  of  coarse  oolitic  sands. 
Dana  (20  '.156)  points  out  that  such  oolitic  beds  "appear  to  be  con- 
fined to  the  superficial  formation  of  a  reef,  that  is,  to  the  beach 
and  wind-drift  accumulations."  The  same  thing  was  shown  by 
Agassiz. 

DESTRUCTION  OF  THE  CORAL  REEF. 

Formation  of  Coral  and  Other  Organic  Lime  Sand  and  Mud. 
The  agents  at  work  destroying  the  reef  rock  are  both  inorganic  and 
organic.  (74:140.)  The  most  effective  inorganic  agent  is  the 
surf  which  constantly  beats  against  the  outer  edge  of  the  reef. 
Alone,  however,  it  is  of  little  effect,  unless  it  succeeds  in  breaking 
off  branches  of  the  corals,  which  may  then  be  hurled  up  onto  the 
reef,  or  over  it  into  the  lagoon.  Coral  polyps  seem  to  flourish  best 


FIG.  84.     Organic  limestone  of  corals,  corallines,  serpula  tubes,  echinoderm 
fragments,  etc.     Pourtales  plateau.     (After  A.  Agassiz.) 

where  the  surf  is  strongest,  so  that  we  have  the  anomaly  of  a  rock 
mass  growing  into  the  very  teeth  of  one  of  the  most  powerful 
agents  of  rock  destruction.  Wherever  the  surf  encounters  loose 
blocks  of  stone,  such  as  volcanic  bombs,  or  coral  heads  torn  from 
their  foundations,  it  at  once  assumes  all  of  its  force  as  an  agent  of 
destruction,  ior  it  will  roll  about  these  rock  masses  and  so  grind  the 
coral  rock  beneath  them  to  powder.  On  the  Florida  reefs  boulders 


DESTRUCTION    OF    CORAL    REEFS  415 

of  coral  occur  formed  from  the  heads  of  large  maeandrinas  and 
astrseans  torn  by  the  waves  from  their  anchorage  and  rolled  about, 
grinding  down  the  rock  beneath  them  and  also  being  worn  them- 
selves. 

Perhaps  by  far  the  largest  contribution  of  coral  sand  and  mud 
is  made  by  the  activities  of  organisms.  Darwin  found  that  two 
species  of  the  Parrot  fish  (Scarus),  "one  inhabiting  the  surf  outside 
the  reef  and  the  other  the  lagoon,  subsist  entirely  ...  by  browsing 
on  the  living  polypifers."  (21.)  On  opening  several  of  these  fish, 
he  found  their  intestines  distended  by  small  pieces  of  coral  and 
finely  ground  calcareous  matter,  which  must  pass  daily  from  them 
as  the  finest  sediment.  On  Funafuti,  on  the  other  hand,  no  evi- 
dence of  such  destruction  of  coral  rock  by  fish  was  found,  though 
they  apparently  fed  to  some  extent  on  the  Lithothamnion.  In  like 
manner  the  reported  destruction  of'  coral  masses  by  holothurians 
found  no  confirmation  on  Funafuti,  where  these  echinoderms  live 
wholly  on  the  organic  matter  of  the  sand  and  mud.  Worms,  mol- 
luscs and  crustaceans,  however,  appear  to  be  active  destroyers  of 
coral  rock,  though  at  Funafuti  the  molluscs  were  found  to  live 
among  the  coral  masses  without  interfering  with  them.  On  these 
reefs,  however,  the  Lithothamnion  rock  was  found  riddled  by 
Gephyrean  worms  and  an  Aspidosiphon  "from  two  to  three  inches 
in  length,  but  very  thin,  and  possessing  a  long  retractile  proboscis, 
by  which  it  is  seen  at  low  tide  to  feed  off  the  Lithothamnion-cov- 
ered  rock  immediately  surrounding  its  abode.  ...  A  small  piece 
of  reef  rock,  a  few  inches  in  diameter,  when  broken  off,  will  show 
as  many  as  10  or  15  of  these  animals."  Echinoderms  also  dwell 
in  cavities  which  they  have  hollowed  out  of  the  reef  rock,  and 
which,  except  for  the  recuperative  growth  of  the  Lithothamnion, 
they  would  rapidly  destroy.  Among  the  most  efficient  coral  de- 
stroyers are  probably  the  Crustacea,  and  they  are  generally  credited 
with  the  production  of  much  of  the  coral  sand.  Not  only  the  corals 
themselves,  but  the  shells  of  molluscs  and  the  tests  of  echinoderms 
are  ground  up  by  these  voracious  feeders,  the  resultant  being  a 
mixture  of  lime  sand  and  flour,  which  by  the  sorting  action  of  the 
waves  is  distributed  in  beds  around  the  reef. 

Much  coral  sand  will  become  lodged  in  the  interstices  of  the 
reefs  between  the  growing  coral  masses,  thus  binding  the  whole 
into  a  solid  mound.  One  of  the  marked  features  of  this  mound 
of  coral  rock  is  the  absence  of  stratification,  and  when  solidified  the 
mound  will  be  an  irregular,  structureless,  often  lens-shaped  mass 
of  lime  rock  embedded  in  stratified  calcarenytes  and  calcilutytes. 
Along  the  margin  of  the  reef  the  clastic  lime  rocks  will  be  deposited, 


4i6  PRINCIPLES    OF    STRATIGRAPHY 

generally  with  a  steep  inclination  dependent  on  the  slope  of  the 
reef  itself,  but  it  will  form  nearly  horizontal  beds  at  a  distance  from 
the  reef.  Close  to  the  reef  the  clastic  material  is  often  a  rudyte, 
consisting  of  worn  fragments  of  coral  embedded  in  the  sand.  Cal- 
carenytes  are,  ho\vcver,  the  most  characteristic  clastic  sediments 
around  the  reef,  while  calcilutytes  or  lime-mud  rocks  are  deposited 
at  a  distance,  where  the  fine  lime  mud  settles  in  deeper  and  more 
quiet  water.  Around  modern  coral  reefs  the  water  after  a  storm 
is  milky  for  great  distances,  owing  to  the  presence  in  suspension  of 
the  lime-rock  flour.  Agassiz  has  noticed  this  fine  sediment  in  sus- 
pension at  a  distance  of  12  to  20  kilometers  from  the  reef.  After 
a  prolonged  storm  4  to  5  centimeters  of  coral  mud  were  laid  down 
between  two  tides.  (Agassiz-2.) 

In  the  lagoon  of  Keeling  atoll  the  fine  lime  debris  resulting 
from  the  erosion  of  the  reef  appears  like  chalk,  but  when  dry  is 
seen  to  be  very  fine  sand.  Finer  grained,  purely  calcareous  lime 
mud  forms  large  soft  banks  from  the  southeast  shore  of  the  lagoon, 
covered  with  a  thick  growth  of  Fucus.  Similar  material  is  obtained 
from  the  Bermuda  reefs  and  has  often  been  mistaken  for  true 
chalk.  Dunes  of  these  sands  are  not  infrequently  heaped  up  on 
the  higher  parts  of  the  reef,  and  the  steep,  submerged  slopes  are 
covered  with  them,  even  where  the  angle  of  the  slope  is  as  high  as 
55°.  Similar  white  lime  sands  and  muds  are  deposited  along  the 
Brazilian  coast  for  a  space  of  1,300  miles,  from  the  Abrolhos  Islands 
to  Maranhao. 

The  sand  and  rolled  coral  heads  soon  become  cemented  into  a 
hard  platform  of  coral  rock  more  or  less  structureless  in  character, 
this  being  accompanied  in  many  cases  by  the  growth  of  Lithotham- 
nion.  In  Keeling  atoll  this  flat  submerged  platform  "varies  in 
width  from  100  to  200,  or  even  300,  yards,  and  is  strewed  with  a 
few  large  fragments  of  coral  torn  up  during  gales."  (Darwin — 21.) 
This  platform  is  uncovered  only  at  low  water,  and  Darwin  found 
the  rock  so  well  cemented  that  he  could  break  off  a  piece  only  with 
the  aid  of  a  chisel.  Calcarenytes  composed  of  the  rounded  par- 
ticles of  shells,  corals,  spines  of  echini,  and  other  calcareous  struc- 
tures occur  with  the  rocks  of  pure  coral  mud.  These  sands  are 
found  even  where  the  slopes  are  as  high  as  50°.  The  reef  rock 
itself  is  often  so  altered  in  its  older  portion  that  no  organic  struc- 
ture can  be  ascertained  in  it. 

Close  to  the  reef  there  is  often  an  interlocking  of  organic  and 
clastic  lime  rock,  for  at  intervals  the  reef  organisms  will  extend 
outward  over  the  region  previously  covered  by  the  coral  sand,  after 
which  this  sand  may  again  overwhelm  the  fringe  of  the  reef. 


FOSSIL    REEFS:    CAMBRIC  417 

FOSSIL  CORAL  AND  STROMATOPORA  REEFS. 

CAMBRIC  AND  PRE^-CAMBRIC.  The  oldest  reef-forming  organisms, 
the  Archccocyathida,  were  originally  referred  to  the  sponges,  and 
more  recently  to  the  primitive  perforate  madreporarian  corals,  of 
which  group  they  probably  form  a  distinct  order.  They  have  been 
reported  from  a  number  of  localities  in  the  Cambric,  including  both 
Western  United  States  (California,  Nevada)  and  the  eastern  part 
of  North  America  (Newfoundland,  Labrador),  Sardinia,  Spain, 
Northern  Siberia  and  Australia.  In  a  number  of  these  localities 
they  have  been  found  to  constitute  layers  or  strata  of  which  they 
formed  the  principal  portion,  but  they  did  not  build  massive  reefs 
comparable  to  those  of  the  present  day.  Since  they  were  all  simple 
corals,  and  of  a  very  porous  character  of  skeleton,  they  were  not 
especially  adapted  to  the  formation  of  reefs.  Nevertheless,  they 
constituted  an  important  limestone  builder  of  this  period,  forming 
in  the  straits  of  Belle  Isle,  Labrador,  beds  of  coral  limestone 
varying  in  thickness  from  25  to  50  feet.  In  many  cases  evidence  of 
shallow  water,  such  as  conglomerates,  ripple  marks,  trails,  etc.,  are 
found  in  association  with  the  beds  of  Archaeocyathidoe.  In  Sardinia 
(Bornemann)  and  in  Australia  similar  extensive  reefs  of  these 
corals  are  found,  in  some  cases  extending  up  into  the  Ordovicic. 

The  recent  finding  of  archaeocyathid  fossils  forming  limestone 
masses  in  the  Animikie  of  Canada  makes  this  one  of  the  oldest  if 
not  the  oldest  reef-building  coral.  The  probabilities  are  that  these 
corals  lived  in  shallow  and  comparatively  warm  waters. 

The  Hydrocoralline,  Cryptozoon,  formed  an  important  reef 
builder  in  the  upper  Cambric  and  lower  Ordovicic  of  North  Amer- 
ica. It  always  occurs  in  layers  which  often  have  a  considerable 
extent.  The  individual  heads  are  spherical,  from  i  to  2  feet  in 
diameter,  or  plate-like,  with  a  thickness  of  one  or  two  feet,  and 
from  5  to  100  feet  in  horizontal  extent.  These  are  not  reefs  as  we 
apply  the  term  to  such  structures  in  the  modern  sea,  though  super- 
ficially they  must  have  had  the  appearance  of  a  platform  of  coral 
heads  not  dissimilar  to  some  parts  of  the  broader  portion  of  the 
Great  Barrier  Reef  of  Australia.  They  may  perhaps  be  referred  to 
as  "bedded  reefs,"  and  their  distribution  is  probably  synchronous 
with  that  of  the  stromatoporoid  and  other  hydrocoralline  genera. 

These  types  apparently  also  formed  similar  bedded  reefs  in  the 
pre-Cambric  sediments  of  North  America.  Walcott  has  figured  a 
"reef"  of  Cryptozoon  (  ?)  frequcns  ( ?—C.  occidental,  Dawson) 
from  the  Algonkian  limestone  (Belt  terrane)  of  northwestern  Mon- 
tana, where  it  forms  beds  from  6  inches  to  3  feet  or  more  in  thick- 


4i8  PRINCIPLES    OF     STRATIGRAPHY 

ness.  (Walcott-89,  pi.  n.)  It  also  occurs  in  similar  beds  in 
Alberta  and  British  Columbia,  and  in  Arizona. 

ORDOVICIC.  Reefs  of  the  bedded  type  have  been  reported  from 
the  Lower  Ordovicic,  Cryptozoon  minnesotensis  forming  the  chief 
reef  builder.  Little  is  known  about  the  detail  of  occurrence,  thick- 
ness, and  extent  of  these  reef  masses,  which  have  been  found  in 
many  localities  in  the  eastern  United  States  and  Canada.  In  the 
Middle  Ordovicic  (Chazyan)  the  genera  Stronmtocerium  and  Sty- 
laraca  form  similar  developments  in  New  York,  Tennessee,  Ken- 
tucky and  Oklahoma.  In  the  Black  River  horizon  Stromatocerium 
is  reenforced  by  Columnaria  and  Tetradium,  in  Tennessee  and 
Kentucky,  and  these  genera  also  form  reef-like  associations  in  the 
Cincinnatian  of  these  states.  These  same  genera,  together  with 
Beatricia,  Labechia,  Calapcecia,  etc.,  form  reef-like  associations  in 
the  Richmond  of  North  America  from  Baffin  Land  and  Anticosti 
to  the  Mississippi  Valley  and  also  in  Colorado,  Nevada,  Wyoming 
and  Alaska.  (Vaughan-87 1244.)  None  of  these  is  to  be  regarded  as 
a  typical  reef,  these  structures  being  rather  of  the  type  of  plate-like 
expansions  or  bedded  reefs,  often  of  not  more  than  a  single  layer 
of  hydrocorallines.  They  were  undoubtedly  an  important  source 
of  the  lime  sands  and  lime  muds  of  the  formations  in  which  they 
occur,  though  in  many  cases  they  seem  to  lie  in  undisturbed  position 
as  of  growth.  It  is  not  improbable,  however,  that  the  corals  an^ 
hydrocorallines  of  one  section  were  ground  up  to  form  the  sand 
which  covers  undisturbed  layers  of  the  same  horizon. 

SILURIC.  Coral  reefs  are  well  developed  in  the  Siluric,  where 
typical  Palaeozoic  reef  builders — Favosites,  Heliolites,  Halysites, 
Syringopora,  etc. — among  the  corals,  and  stromatoporoids  among 
the  hydorcorallines  abound.  They  have  been  especially  described 
from  Wisconsin  and  from  the  Island  of  Gotland  in  the  Baltic  Sea. 
Others  occur  in  the  Upper  Siluric  of  western  Ontario  and  Michi- 
gan, in  the  Louisville  limestone  of  the  Falls  of  the  Ohio,  the  Lewis- 
town  limestone  of  Pennsylvania,  and  in  the  Wenlock  of  England 
and  in  Bohemia. 

Niagaran  Reefs  of  Wisconsin.  The  Siluric  strata  of  south- 
eastern Wisconsin  are  characterized  by  typical  coral  reefs  which 
form  mounds  almost  entirely  composed  of  coral  and  Stromatopora 
masses,  and  separated  from  each  other  by  interspaces  of  some 
extent,  in  which  the  coral  sand  and  mud  were  deposited  in  stratified 
layers.  (Chamberlin-i5  '.364;  Grabau-4o.)  These  mounds  stand 
out  in  relief,  owing  to  the  peculiar  resistance  of  the  structureless 
reef  rock  to  erosion,  while  the  bedded  strata  of  calcarenyte  and 
calcilutyte  between  them  more  easily  suffered  denudation.  In  the 


FOSSIL   REEFS:    SILURIC  419 

older  days  quarries  were  opened  in  these  reefs,  but,  owing  to  the 
absence  of  stratification  planes  or  seams,  the  operations  were  more 
difficult  and  costly,  and  the  old  quarries  were  abandoned  when  the 
bedded  strata  were  discovered. 

The  exposed  face  of  the  old  quarry  is  generally  thoroughly 
weathered,  and  it  shows  an  all  but  structureless  surface^  the  chief 
characteristic  of  which  is  the  total  absence  of  stratification.  The 
reefs  consist  largely  of  stromatoporoids,  among  which  the  genus 
Clathrodictyon  seems  to  abound.  The  reefs  as  exposed  are  gen- 
erally several  hundred  feet  in  diameter,  with  a  height  of  perhaps 
50  feet.  They  thus  constitute  a  series  of  independent  reef  mounds 
rising  from  a  platform  which  is  sometimes  composed  of  organic 
accumulations  and  at  others  of  clastic  material.  On  the  borders 
of  the  reef  mounds  the  material  consists  of  coral  sand,  consolidated 
into  calcarenyte,  and  this  dips  away  from  the  reef  in  all  directions. 
This  dip  is  not  due  to  any  tectonic  deformations,  but  is  the  original 
dip  of  the  clastic  material  on  the  flanks  of  the  reef.  The  dips 
observed  in  the  Shoonmaker  quarry  near  Wauwatosa  range  as  high 
as  54  degrees  close  to  the  reef,  while  dips  of  28  to  34  degrees 
are  more  common,  and  others  as  low  as  18  degrees  occur.  Further 
away  the  strata  become  practically  horizontal.  (Grabau~4O.)  At 
the  Distillery  quarry  in  Milwaukee  (foot  of  Twenty-ninth  Street) 
dips  of  40  degrees  toward  the  east  and  west  and  of  20  degrees  and 
more  to  the  south  have  been  observed.  The  two  reefs  mentioned 
and  a  third  in  the  grounds  of  the  National  Military  Asylum  form 
a  triangle,  in  the  center  of  which  quarries  have  been  opened  to  a 
great  depth  in  evenly  bedded,  rather  fine-grained  calcarenyte,  this 
being  the  coral  and  crinoid  sand  derived  from  the  reef  and  swept 
together  in  even-bedded  strata  in  the  inter-reef  spaces.  These 
limestones  are  sparingly  fossiliferous,  the  roving  orthoceratitic 
cephalopods  alone  occurring  in  abundance.  The  strongest  possible 
contrast  existed  between  the  reef  mounds,  on  the  one  hand,  on  the 
borders  of  which  flourished  a  rich  fauna  of  corals,  bryozoans, 
brachiopods,  molluscs,  trilobites,  and  crinoids,  and  the  nearly  bar- 
ren sandy  bottoms  of  the  comparatively  shallow  sea  on  the  other; 
desert  areas  surrounding  luxuriant  oases  of  animal  and  plant  life. 

A  typical  reef  mound  exposed  by  quarrying  operations  near 
Cedarburg,  20  miles  north  of  Milwaukee  (Grabau~4o),  shows  a 
thickness  of  about  30  or  40  feet  of  coral  rock,  though  the  full 
measure  is  not  exposed.  The  diameter  of  the  old  reef  mound  was 
perhaps  300  feet  from  north  to  south.  Much  of  the  reef  rock  has 
become  dolomitizecl,  and  in  many  of  the  bedded  strata  the  corals 
have  been  dissolved  out.  The  central  part  of  the  reef  consists  of 


420  PRINCIPLES    OF    STRATIGRAPHY 

stromatoporoids,  with  perhaps  a  moderate  development  of  Favo- 
sites  and  other  corals.  On  the  flanks  of  the  reef  numerous  smaller 
corals  are  found,  together  with  an  abundance  of  crinoids,  brachio- 
pods,  molluscs,  and  some  trilobites.  The  peripheral  dips  of  the 
bedded  strata  are  of  the  usual  character,  and  here,  as  in  the  other 
reefs,  a  repeated  interfmgering  of  the  reef  rock  and  the  .bordering 
clastic  strata  is  marked.  Several  miles  from  Groth's  quarry,  just 
described,  is  Anschiitz  quarry,  on  the  road  to  Grafton.  Here  the 
bedded  strata  on  the  flanks  of  the  reef  are  well  shown,  their  char- 
acter being  that  of  a  typical  calcarenyte  locally  known  as  sand- 
stone. The  general  arrangement  of  the  Siluric  reef  mounds  of 
Wisconsin  is  in  more  or  less  linear  series  parallel  to  the  old  shore 
of  the  period,  but  probably  at  a  considerable  distance  from  that 
shore.  (Chamberlin-i5.)  The  arrangement  appears  to  have  been 
that  of  a  barrier  reef,  the  eastward  extent  of  which  can  be  traced 
through  northern  Michigan,  where  an  abundant  coral  fauna,  prob- 
ably in  reef  association,  is  found  on  Drummond  Island  and  else- 
where. Its  eastern  extent  appears  to  have  been  in  the  vicinity  of 
Lockport,  New  York,  but  neither  there  nor  in  Michigan  have  actual 
reef  structures  been  observed.  Farther  south  occurred  independent 
reefs,  remains  of  which  are  now  found  at  Louisville,  Kentucky,  at 
the  Falls  of  Ohio.  Probably  many  other  reefs  of  this  age  exist  in 
the  Hudson  Bay  region,  where  strata  of  this  age  still  await  detailed 
exploration. 

Siluric  Reefs  of  Gotland.  One  of  the  finest  exhibitions  of  Palae- 
ozoic coral  reefs  is  found  on  the  western  coast  of  the  Island  of 
Gotland  in  the  Baltic  Sea.  (Wiman-93;  Hedstrom-47 ;  Munthe- 
65.)  Here  the  erosion  by  the  waves  both  at  the  present  altitude 
and  during  a  former  period  of  higher  water  has  exposed  a  series  of 
wonderful  sections  through  the  ancient  reefs  such  as  are  probably 
not  to  be  found  anywhere  else  in  the  world,  though  equally  fine 
sections  of  Mesozoic  and  later  reefs  are  well  known.  There  appear 
to  be  two  main  horizons  in  which  the  reefs  occur,  separated  by  a 
disconformity,  one  series  being  best  exposed  in  the  northern  and 
the  other  in  the  southern  part  of  the  island. 

In  general  aspect  the  "reefs"  are  lenticular  mounds  locally 
known  as  "klintar."  They  stand  out  as  bold  cliffs  on  the  shore, 
their  massive,  structureless  character  offering  great  resistance  to 
both  wave  and  atmospheric  erosion,  whereas  the  bedded  enclosing 
strata  are  more  rapidly  reduced  by  both  agencies,  and  so  produce 
indentations  and  reentrants  in  the  coast  line.  (Fig.  85.) 

Unlike  the  Siluric  reefs  of  Wisconsin,  those  of  Gotland  are 
practically  unaltered  by  subsequent  dolomitization,  and  hence  their 


FOSSIL    REEFS:    SILURTC 


421 


structural  character  and  composition  can  be  readily  ascertained. 
The  materials  of  which  they  consist  are  partly  corals,  among  which 
are  Halysites  and  Favosites,  both  massive  and  branching  forms, 
Striatopora,  Pachypora  and  Syringopora,  which  latter  is  especially 
adapted  by  its  loose  method  of  growth  to  retain  the  coral  sand  pro- 
duced by  the  erosion  of  the  reef.  Stromatopora  heads  are  like- 
wise common  in  these  reefs,  and  often  of  large  size,  and  with  them 
occur  calcareous  algae  (Sphaerocodium)  and  Spongiostroma,  which 
sometimes  constitute  as  much  as  50  per  cent,  of  the  reef-building 
types,  though  when  occurring  alone  they  form  beds  instead  of 
reefs. 

On  the  borders  of  the  Gotland  reefs  characteristic  interfmgering 
of  the  organic  and  detrital  limestone  is  often  well  shown,  as  for 
instance  at  the  cliff  of  Hoburgen  in  the  southern  part  of  the  island. 
Often  masses  of  stratified  sand  appear  to  be  included  in  the  reef 
mass,  a  phenomenon  also  observed  in  the  reefs  of  Wisconsin.  The 


FIG.  85.     Diagram  of  the  reef  structure  at  Gotland,  and  the  relation  of  the 
reefs  to  the  bedded  formations.     (After  Wiman.) 

detrital  lime  sand  is  thickest  on  the  border  of  the  reef,  and  it  is 
often  well  stratified,  dipping  away  from  the  reef  as  in  the  Wiscon- 
sin examples.  Overturned  coral  heads  are  common  on  the  border  of 
the  reef,  these  being  torn  from  their  original  anchorage  and  rolled 
about  by  the  waves  of  the  Siluric  sea,  which  used  them  as  mill- 
stones to  grind  the  coral  and  other  organic  rock  into  sand  and 
mud,  which  was  either  deposited  within  the  interstices  of  the  reef 
or  swept  outward  to  form  bedded  strata  of  limestone.  The  detrital 
lime  sand  is  in  part  the  result  of  such  destruction  of  the  corals  and 
the  brachiopod  and  molluscan  shells,  but  to  a  large  extent  it  is 
derived  from  the  dismemberment  of  crinoids,  the  stems  and  calices 
of  which  yield  an  abundance  of  discs  and  plates  through  the  natu- 
ral dissociation  of  these  components  on  the  maceration  of  the 
dead  organism.  Much  of  this  crinoidal  detritus  is  already  of  suffi- 
ciently small  grain  to  be  directly  included  among  the  stratified 
sediments  forming  outside  the  reef.  Crinoidal  conglomerates, 
formed  of  the  discs  of  the  larger  crinoid  stems,  as  well  as  coral 
conglomerates,  are  of  common  occurrence  on  the  borders  and  sum- 
mits of  the  reefs. 


422  PRINCIPLES    OF    STRATIGRAPHY 

The  Gotland  reefs  often  rest  on  marly  clay  beds  or  on  oolitic 
sands.  When  the  latter  is  the  case,  it  appears  that  these  oolitic 
sands  immediately  succeed  a  shallow-water,  if  not  terrestrial  quartz 
sandstone,  and  are  themselves  of  very  shallow-water  origin,  show- 
ing an  abundance  of  wave  activities.  The  reefs  were  thus  evidently 
built  in  water  of  no  considerable  depth,  as  is  further  shown  by  the 
structure  of  the  reef  borders  themselves.  Where  the  reef  rests  on 
the  marl  shales,  the  latter  show  evidence  of  relative  plasticity  at 
the  time  of  reef  formation,  for  the  reefs,  with  growing  size  and 
weight,  sank  into  the  marly  muds  to  some  extent,  forcing  the 
mud  away  in  either  direction  or  causing  the  layers  to  bend  down 
under  the  reef. 

The  reefs  of  this  section  apparently  formed  a  barrier  parallel 
to  the  old  Scandinavian  land,  in  part  of  which  graptolite-bearing 
shales  seem  to  have  been  deposited  at  the  same  time.  The  earlier 
reef  series  shows  its  proximity  to  the  land  by  the  fact  that,  in  the 
lagoons  between  the  reef  mounds,  terrestrial  or  semiterrestrial 
organisms,  the  eurypterid  Pterygotus  and  the  scorpion  Palaeophonus, 
were  found  together  with  marine  organisms.  It  is  highly  probable 
that  the  reef  was  dotted  with  islets,  and  that  perhaps  even  fresh- 
water lagoons  existed,  and  this  would  serve  to  explain  the  exist- 
ence of  these  continental  organisms.  It  is  noteworthy  that  the 
Pterygotus  beds  occur  at  the  lower  boundary  of  a  distinct  hiatus, 
which  marks  a  period  of  land  condition  for  the  entire  island,  and 
was  probably  of  much  greater  extent. 

Upper  Siluric  Reefs  of  North  America.  Reef  structures  are 
known  from  the  Upper  Siluric  (Monroan)  formation  of  western 
Ontario  and  Michigan  and  the  equivalent  Lewistown  limestone  of 
Pennsylvania.  They  probably  occur  in  formations  of  similar  age 
in  northwest  Canada.  The  best  example  of  these  reefs  occurs  in  the 
Anderdon  limestone  quarry,  about  a  mile  northeast  of  Amherst- 
burg,  Ontario.  (Sherzer  and  Grabau-8o:  43.)  Its  thickness  is 
only  from  6  to  8  feet,  but  its  horizontal  extent  is  unknown.  It  is 
probably  of  the  nature  of  a  series  of  lenses  of  organic  limestone, 
surrounded  by  and  passing  into  the  finest  lime  mud  strata  (cal- 
cilutytes)  derived  from  the  destruction  of  the  reef.  The  organisms 
of  the  reef  are  mainly  stromatoporoids,  Stromatopora  galtense  and 
Clathrodictyon  ostiolatum  predominating.  With  these  occurs  the 
small  branching  stromatoporoid,  Idiostroma  nattressi,  which  was  es- 
pecially adapted  to  capture  the  coral  sand  and  mud  produced  by  the 
grinding  action  of  rolled  Stromatopora  heads.  Corals  of  the  genera 
Favosites,  Diptophyllum  and  Cladopora,  all  well  adapted  to  capture 
coral  sand,  on  account  of  their  loosely  branching  habit,  and  simple 


FOSSIL   REEFS:     DEVONIC  423 

corals  of  less  importance  as  reef  builders  also  occur.  Brachiopods 
and  molluscs  appear  to  be  rare,  however.  A  remarkable  feature  of 
this  reef  is  the  enclosing  rock,  which  is  a  calcilutyte  and  wholly 
unfossiliferous  so  far  as  exposed,  except  in  the  upper  layers.  Or- 
ganisms seem  to  have  been  confined  entirely  to  the  reef,  while  the 
surrounding  area  was  the  site  of  the  deposition  of  the  finest  lime 
mud.  It  is  highly  probable  that  the  fineness  of  this  mud  explains 
the  absence  of  macroscopic  forms  of  life,  because  few  animals  can 
exist  in  muddy  water  such  as  this  must  have  been. 

Elsewhere  in  this  horizon  reef  structures  ,of  similar  type  are 
developed.  They  are  well  shown  in  the  Lewistown  limestone  of 
central  Pennsylvania,  where,  near  Tyrone,  they  consist  almost  wholly 
of  stromatoporoids  of  the  same  species  as  at  Anderdon,  together 
with  the  Favosites,  Cladopora  and  Diplophyllum  found  there.  In 
the  Manlius  limestone  of  New  York  State  similar  Stromatopora 
reefs  are  found.  These  are  more  especially  of  the  bedded  type, 
consisting  of  one  or  more  layers  of  Stromatopora  heads  of  various 
sizes  and  belonging  to  a  number  of  genera  and  species.  Other  or- 
ganisms are  rare,  and  the  enclosing  strata  are  mostly  calcilutytes. 

It  is  a  common  fact  that  such  bedded  Stromatopora  reefs  are 
enclosed  in  calcilutytes,  and  this  seems  to  be  due  in  part  to  the 
absence  of  other  organisms  which  could  furnish  lime  sand.  The 
mutual  attrition  of  the  massive  Stromatopora  heads  seems  to  have 
resulted  chiefly  in  the  formation  of  lime  mud.  If  so,  the  progress 
of  sedimentation  here  must  have  been  an  exceedingly  slow  one. 

DEVONIC  CORAL  REEFS.  The  Devonic  formations  abound  in 
coral  reefs  both  in  North  America  and  Europe.  They  occur  in  the 
lower  Devonic  of  Konjepruss,  Bohemia,  in  the  Onondaga  of  New 
York,  and  the  Falls  of  Ohio,  the  Traverse  group  of  Michigan,  the 
Devonic  of.  Canada,  of  Belgium,  the  Eifel  and  elsewhere.  The 
details  of  the  reef  structure  of  only  a  few  of  these  have  been  inves- 
tigated, and  these  will  be  discussed  at  some  length. 

Lower  Devonic  Reefs  of  Konjepruss,  Bohemia.  As  exposed  in 
the  quarries  near  Konjepruss,  the  lower  Devonic  limestone  of  Bo- 
hemia (F2  of  Barrande)  shows  a  massive,  structureless  reef  facies, 
in  which  the  zoogenic  limestone  is  largely  composed  of  massive 
Favosites  and  stromatoporoids,  while  brachiopods,  molluscs,  trilo- 
bites  and  small  corals  also  abound,  especially  on  the  margin  of  the 
reef.  Laterally  this  reef  limestone  merges  into  a  stratified,  coralline 
limestone  (see  Kayser  and  Holzapfel-55).  The  reefs  are  under- 
lain by  the  Upper  Siluric  platey  limestones  and  black  graptolite 
shales,  but  whether  they  rest  directly  on  these  deposits  or  arc 
preceded  by  shell  layers  has  not  been  ascertained. 


424  PRINCIPLES    OF    STRATIGRAPHY 

The  Onondaga  Reefs  of  New  York.  The  Onondaga  limestone 
of  the  State  of  New  York  is  a  good  example  of  an  ancient 
formation  resulting  from  the  growth  of  numerous  coral  reefs  and 
the  accumulation  of  their  attendant  deposit  of  clastic  lime  sands. 
(Grabau-40.)  The  formation  varies  in  thickness  from  about  50 
feet  in  the  eastern  part  of  the  state  to  about  200  feet  in  the  western, 
and  is  in  part  continued  westward  into  Ohio  and  Michigan  by  the 
Columbus  and  Dundee  limestones,  the  age  of  which,  however,  ap- 
pears to  be  somewhat  younger.  Throughout  this  extent  the  forma- 
tion rests  upon  an  old  land  surface,  or  the  deposits  of  continental 
origin  formed  during  that  period,  and  partly  reworked  by  the  trans- 
gressing sea.  At  first  more  or  less  siliceous  limestones  containing 
shells  of  molluscs  and  brachiopods  were  formed  (Schoharie  grit, 
Decewville  beds),  and  on  this  foundation  the  corals  began  to 
grow.  It  appears  that  the  corals  formed  a  series  of  barrier  reefs 
roughly  parallel  to  the  old  coast  line,  which  passed  through  New 
Jersey,  southeastern  Pennsylvania,  central  Maryland  and  West  Vir- 
ginia. Close  to  the  shore  in  the  northern  part  clastic  deposits, 
chiefly  grits,  were  forming,  but  the  southern  section  is  marked  by 
the  accumulation  of  black  muds  (Romney  shale)  with  a  depau- 
perate fauna  of  few  species.  The  conditions  were  much  the  same 
as  we  find  now  in  Florida,  where  the  inner  lagoon  is  a  region  of 
black  mud  deposits  with  a  mingling  of  marine  and  fresh-water 
organisms.  In  Pennsylvania  and  in  New  York  a  succession  of 
reefs  was  apparently  formed  paralle4  to  this  southeastern  shore, 
each  series  progressively  farther  removed  to  the  north  and  west 
from  this  coast.  The  gradual  advance  of  the  inner  lagoon  con- 
ditions toward  the  northwest  is  shown  by  the  progressive  creeping 
out  of  the  black  mud  deposits  over  the  old  dead  reefs,  the  Onondaga 
limestone  being  progressively  covered  by  the  black  Marcellus  muds, 
which  are  to  a  large  extent  the  lagoon  equivalents  of  the  reef 
limestone  farther  seaward.  In  most  localities  the  deposits  formed 
immediately  over  the  dead  reefs  continue  to  be  of  lime  sands 
derived,  no  doubt,  from  the  still-living  reefs  farther  out  to  sea. 
These  lime  sands  were,  however,  abundantly  charged  with  silica, 
probably  in  the  form  of  sponge  spicules  and  diatoms,  and  these 
gave  rise  to  the  layers  of  chert  found  in  these  upper  rocks  in  such 
abundance  in  some  localities,  and  on  which  account  this  rock  early 
received  the  name  of  Corniferous  limestone.  These  corniferous  de- 
posits swell  between  the  reefs,  where  most  probably  the  lagoons 
were  situated,  and  they  are  buried  in  turn  by  the  encroaching  black 
mud  deposits  which  represent  conditions  of  deposition  unlike  those 
found  in  the  open  sea.  That  the  deposits  of  black  mud  were  pro- 


FOSSIL   REEFS:     DEVONIC  425 

gressively  replacing  the  deposits  of  limestone  is  shown  by  the  fact 
that  the  highest  layer  of  these  rocks  in  western  New  York,  the 
Agoniatite  limestone,  extended  eastward  during  a  temporary  east- 
ward transgression  of  the  sea,  and  rests  on  50  feet  of  these  black 
muds  in  eastern  New  York,  where  the  Onondaga  is  only  50  feet 
thick,  and  on  175  feet  of  black  muds  in  Maryland,  where  the  Onon- 
daga limestone  is  absent.  In  western  New  York,  where  the  Onon- 
daga is  about  200  feet  thick,  it  consists  of  reefs  in  the  lower  part, 
followed  by -shell  limestones  and  cherty  beds  in  the  upper.  This  in 
turn  is  followed  by  over  50  feet  of  black  shale  practically  barren 
of  fossils  except  in  a  few  localities,  and  there  sometimes  including 
the  remains  of  eurypterids  and  other  arthropods  adapted  to  brack- 
ish or  fresh  waters  and  rarely  found  except  in  the  deposits  of  shal- 
low coastal  lagoons,  protected  embayments  or  fresh-water  lakes  or 
rivers.  In  Ohio  and  southern  Michigan  the  deposits  of  limestones 
of  the  Onondaga  type  began  much  later,  and  also  continued  much 


FIG.  86.  Diagram  showing  successive  advances  of  the  coral  reefs  and  accom- 
panying clastic  lime  sands  and  the  covering  muds  of  the  inner 
lagoons. 

later,  so  that  the  overwhelming  black  muds  reached  that  part  of  the 
sea  only  toward  the  close  of  the  deposition  of  black  Marcellus  muds 
in  western  New  York.  (Fig.  86.) 

Few  of  the  actual  reefs  have  been  located  and  described,  this 
being  due  more  to  lack  of  attention  directed  toward  their  structure 
than  to  their  non-exposure.  It  is  also  important  to  bear  in  mind 
that  modern  quarrying  operations  are  carried  on  in  the  bedded 
strata  of  inter-reef  origin,  and  that  the  structureless  reefs,  so  diffi- 
cult to  operate  in,  are  avoided.  This  is  strikingly  shown  by  the 
quarries  opened  in  these  limestones  in  western  New  York  (Wil- 
liamsville),  two  of  which  are  found  on  opposite  flanks  of  a  reef 
several  hundred  feet  in  diameter;  the  reef  itself  being  untouched. 
( Grabau~4O  '-340. )  In  the  quarries  the  various  dips  away  from  the 
reef  are  shown,  these,  however,  not  often  exceeding  10°.  (Fig.  87.) 
On  one  side  the  sloping  floor  of  the  quarry  is  formed  by  the 
upper  surface  of  the  reef,  and  here  the  composition  of  the  reef 
can  be  ascertained.  Enormous  heads  of  branching  Syringoporas, 


426  PRINCIPLES    OF    STRATIGRAPHY 

Eridophyllum,  Synaptophyllum  and  Diplophyllum  occur  here,  their 
interstices  rilled  in  with  coral  sands.  Favosites  likewise  abound, 
the  heads  being  often  of  enormous  size.  Large  Cystiphyllums  and 
Cyathophyllums  also  occur,  and  crinoid  stems  are  equally  abundant. 
In  the  bedded  limestones  near  the  reef,  fragments  of  Favosites 
abound,  and  sometimes  heads  of  great  size  occur,  but  they  are 
partly  worn,  and  very  commonly  overturned.  Here  we  have  the 
coral  breccia  formed  of  the  dead  coral  heads  on  the  borders  of  the 
reef,  enclosed  in  the  coral  sand  derived  from  the  reef  by  the  grind- 
ing action  of  the  waves  which  rolled  about  these  fragments  of 
coral  and  used  them  as  tools  for  their  destructive  work.  Brachio- 
pods,  bryozoans,  molluscs  and  other  lime-secreting  organisms  are 
also  plentiful  on  the  borders  of  the  reef,  while  the  remains  of  giant 
placoderm  fishes  found  in  these  deposits  further  complete  the 


FIG.  87.  Section  of  a  reef  in  the  Onondaga  limestone  of  Williamsville,  N.  Y. 
Two  quarries  have  been  opened  in  this  section,  one  on  either  side 
of  the  reef.  The  left-hand  (eastern)  quarry  does  not  quite  touch 
the  reef,  but  the  floor  of  the  right-hand  (western)  quarry  rests 
partly  upon  the  reef  and  exposes  the  low  secondary  reef-mound. 

faunal  list  and  show  us  some  of  the  organic  agents  influential  in  the 
destruction  of  the  coral  reef  and  the  production  of  the  coral  sand. 
These  fishes  are  especially  abundant  in  the  later  deposits  of  this 
series  in  Ohio  and  Michigan,  from  which  19  species  have  been 
obtained  as  against  8  species  from  the  Onondaga  of  New  York. 

In  some  portions  of  the  Ohio  limestones  small  globular  bodies, 
Calcisph&ra  robusta,  abound,  sometimes  making  up  the  limestone. 
These  resemble  the  spore  capsules  of  the  fresh-water  lime-secreting 
alga,  Chara,  and  may  be  part  of  a  plant,  or  more  probably  a  foram- 
iniferan,  of  the  kind  living  abundantly  to-day  in  the  quiet  waters 
of  the  lagoons  within  the  coral  reefs.  (See  description  of  Funa- 
futi.) 

Reefs  of  this  age  are  likewise  found  in  southern  Indiana  and 
adjacent  portions  of  Kentucky  (Jeffersonville  limestone  of  the 
Falls  of  the  Ohio). 

Middle  Devonic  Reefs  of  Michigan.  In  the  Hamilton  or  Trav- 
erse group  of  Michigan  reefs  are  well  developed,  and  almost  every 


FOSSIL    REEFS:     DEVONIC 


427 


characteristic  of  the  structure  of  Palaeozoic  reefs  is  shown.  The  best 
examples  are  found  in  the  eastern  area  of  the  northern  part  of  the 
Southern  Peninsula  in  the  vicinity  of  Alpena.  Here  their  occur- 
rence is  marked  in  the  topography  by  low  mounds  or  swellings  which 
rise  above  the  general  level  of  the  country,  a  feature  observed  in 
Siluric  coral  reefs  as  well,  as,  for  example,  in  the  neighborhood  of 
Visby,  on  the  Island  of  Gotland,  where  such  knolls  form  a  marked 
feature  of  the  topography,  many  of  them  being  surmounted  by 
windmills. 

The  Alpena  reefs  (Grabau~4o)  are  mostly  well  exposed  in  the 
quarries  which  are  extensively  opened  up  in  this  rock,  the  purity  of 
which  makes  it  desirable  for  chemical  and  other  purposes.  Analyses 
of  the  reef  rock  have  given  over  99%  of  calcium  carbonate.  The 


FIG.  88.  Diagram  of  the  reef  structure  in  the  Traverse  (Middle  Devonic) 
limestones  of  Alpena,  Mich.  The  black  masses  represent  corals 
(Favosites,  Acervularia,  etc.)  and  stromatoporoids.  The  dip  of 
the  calcarenytes  and  calcilutytes  on  the  margin  of  the  reefs  and 
the  interfmgering  of  the  reef  and  clastic  formations  are  shown. 

reef  mounds  are  of  the  usual  lens  shape,  the  height  averaging  35 
feet,  while  their  diameter  at  the  base  is  several  hundred  feet.  The 
chief  reef-builders  are  large  heads  of  Favosites,  Acervularia,  and 
stromatoporoids,  many  of  them  three  or  four  feet  in  diameter, 
while  occasional  stromatoporoids  up  to  10  feet  in  diameter  also 
occur.  Branching  species  of  Favosites  are  common,  and  bryozoans, 
crinoids  and  brachiopods  help  to  swell  the  organic  content  of  the 
reef.  Between  these  organisms  the  coral  sand  abounds,  binding  the 
whole  into  a  solid,  structureless  mass,  in  which  lines  of  stratification 
are  entirely  wanting.  Even  where  the  coral  sand  fills  extensive 
cavities  in  the  reef  mass,  no  stratification  is  shown.  In  such  cases 
the  coral  heads  may  be  found  wholly  enclosed  in  the  sand,  and 
often  overturned.  For  the  most  part,  however,  the  coral  heads  lie 
in  their  normal  position  of  growth,  successive  heads  growing;  on  a 
foundation  of  older  corals  embedded  in  crystalline  sand.  ( Fig.  88L) 
On  the  borders  of  the  reef-mounds  the  clastic  lime  sand  forms 
beds  which  are  often  steeply  inclined.  Close  to  one  of  the  mounds, 


428  PRINCIPLES    OF    STRATIGRAPHY 

for  example,  the  dip  was  28°,  then  rapidly  changed  to  14°,  and  then 
-more  gradually  to  2°.  The  sand  here  is  finer  than  that  filling  the 
cavities  in  the  reef,  but  it  often  includes  fragments  and  partly  worn 
heads  of  Favosites,  Stromatopora,  etc.,  lying  in  all  positions.  Occa- 
sionally the  material  is  a  coral  breccia,  but  for  the  most  part  it  is 
a  calcarenyte.  Farther  away  from  the  reef-mound  it  frequently 
becomes  a  calcilutyte  or  rock  made  up  of  the  finest  lime  flour. 
Throughout  the  marginal  zone  there  is  an  interlocking  of  organically 
formed  and  fragmental  lime  rock,  indicating  a  periodic  spreading 
outward  of  the  reef  and  a  subsequent  overwhelming  of  each  ex- 
panded rim  by  fragmental  deposits.  These  spreading  fringes  of  the 
reef  consist  mainly  of  the  smaller  branching  corals  and  of  bryozo- 
ans,  which  at  times  extend  far  out  on  the  foundation  of  coral 
sand.  '  These  expanded  rims,  formed  when  erosion  temporarily 
ceased,  extend  outward  to  form  the  dividing  planes  between  the 
successive  strata  of  the  bedded  limestones,  where  they  are  often 
replaced  by  films  of  silty  or  even  clayey  material.  These  periodic 
cessations  of  erosive  activity  on  the  reef  and  the  spreading  of  the 
reef  fauna  over  the  surrounding  beds  of  unfossiliferous  coral  sand 
must  be  due  to  the  local  protection  of  the  reef  mass  from  the 
waves.  This  may  be  brought  about  by  the  becoming  effective  of 
some  outer  barrier  formed  by  the  slow  growth  of  an  outer  reef 
which  has  become  of  sufficient  height  to  break  the  force  of  the 
waves,  or  by  the  building  of  a  temporary  sand  or  shell  bar.  At 
such  times  the  various  minor  organisms  of  the  reef  fauna  find  it 
possible  to  spread  in  all  directions  in  the  relatively  quiet  water,  and 
so  form  a  layer  of  fossiliferous  material  between  the  thicker  layers 
of  coral  sand  limestone.  It  is  on  these  dividing  planes,  as  every 
collector  knows,  that  the  largest  number  of  specimens  is  found,  the 
limestones  themselves  only  rarely  carrying  unworn  fossils. 

In  some  cases,  however,  the  dividing  planes  close  to  the  reef 
mark  a  period  of  especial  destructiveness,  when  the  smaller  corals 
and  other  organisms  torn  from  the  reef  are  rolled  outward  and 
come  to  rest  in  more  or  less  worn  conditions  as  a  bed  of  organic 
conglomerate  upon  the  uniformly  grained  clastic  limestones.  In 
some  cases  the  spreading  organic  rims  are  marked  by  the  death  of 
the  corals,  especially  the  simple  types,  and  by  their  partial  solu- 
tion. The  cyathophylloid  corals  often  have  their  epithecas  dis- 
solved away.  On  such  a  partly  corroded  surface  Bryozoa  and  other 
attached  organisms  grow,  showing  that  conditions  unfavorable  to 
the  true  corals  did  not  affect  some  of  the  other  organisms.  These 
conditions  are  well  shown  in  the  upper  part  of  the  reefs  near 
Alpena. 


FOSSIL    REEFS:     DEVONIC  429 

On  the  western  side  of  the  State  of  Michigan,  in  the  Petoskey 
and  Traverse  Bay  regions,  at  present  only  the  marginal  portions  of 
the  reefs  are  shown  in  the  outcrops  and  cuttings ;  here  the  rock  is 
made  up  of  fragments  of  Acervularia  davidsoni,  Favosites  and 
stromatoporoids  embedded  in  the  crystalline  sand,  these  often  form- 
ing a  veritable  coral  conglomerate,  such  as  is  found  on  the  flanks  of 
modern  coral  reefs.  Farther  away  from  the  reef  the  coral  frag- 
ments cease,  once  the  rock  becomes  a  well-stratified  calcarenyte  or 
calcilutyte.  That  the  waters  in  which  these  beds  were  deposited 
were  shallow  is  shown  by  the  occasional  cross-bedding  and  the  ripple 
marks  found  in  these  strata,  as  well  as  by  the  repeated  phenomenon 
of  contemporaneous  erosion  and  deposition,  and  the  wedging  out  of 
certain  strata  and  the  thickening  of  others.  Not  infrequently 
seams  of  carbonaceous  material  separate  some  of  the  layers  of  the 
limestone,  and  in  these  layers  plant  remains  are  not  uncommon. 

The  sections  exposed  below  the  city  of  Petoskey  in  the  Traverse 
Bay  region  are  very  instructive  in  this  connection.  As  stated,  they 
represent  the  marginal  portions  of  the  reefs  and  show  a  succession 
of  erosion  planes  dividing  the  entire  mass  into  strata  from  a  few 
feet  to  10  or  20  feet  in  thickness.  These  strata  show  successive 
accumulations  of  coral  sand  with  worn  pebbles  of  corals  or  stroma- 
toporoids, generally  of  the  size  of  a  man's  fist  or  larger,  and  ar- 
ranged in  strata  which  in  some  cases  are  horizontal,  in  others  dip 
in  various  directions  at  low  angles.  There  is  a  certain  succession 
of  remains  in  the  various  strata,  those  of  the  higher  beds  being  dis- 
tinct from  those  of  the  lower.  In  the  upper  beds  the  branching 
stromatoporoid  Idiostroma  ccespitosum  is  the  chief  organism,  and 
this  is  often  found  in  the  position  of  growth,  its  finger-like  branches 
spreading  to  capture  the  coral  sand.  Most  of  this  coral  sand  has 
since  been  dolomitized  with  the  result  that  the  mass  is  rendered 
porous.  The  coral  pebble  strata  are  often  traceable  for  miles  with- 
out apparent  change  in  character. 

These  successive  erosion  planes  suggest  that  periodic  subsi- 
dence was  going  on  here  during  the  growth  of  the  reef,  each  stratum 
being  eroded  when  its  growth  had  brought  it  to  within  the  level 
of  wave  activity.  The  change  in  fauna  with  the  change  in  the 
growth  of  the  reef  is  analogous  to  the  changes  in  fauna  found  at 
successive  steps  in  the  building  of  modern  reefs.  A  striking  fea- 
ture of  the  clastic  strata  of  this  region  is  the  frequent  intercalation 
of  calcilutytes  made  from  the  finest  lime  flour.  These  and  the 
equally  pure  beds  of  calcarenyte  are  in  some  cases  separated  by 
layers  of  carbonaceous  shales  indicating  a  period  of  plant  growth, 
and  probably  even  local  terrestrial  conditions  in  the  form  of  vege- 


43° 


PRINCIPLES    OF    STRATIGRAPHY 


tation-covered  islets,  such  as  are  characteristic  of  coral  reefs  to-day. 
Devonic  Reefs  of  the  Attawapishkat  River,  Canada.  In  the 
southern  part  of  the  Province  of  Keewatin,  in  Canada,  reef  struc- 
tures occur  in  the  Devonic  limestones.  (Bell-i2:,?7G,  ?8G.}  These 
have  been  exposed  in  natural  sections  by  the  Attawapishkat  River, 
an  affluent  of  James  Bay.  These  reefs  have  the  character  of  great 
spongy  and  cavernous  limestone  masses  often  occupying  the  full 
height  of  the  cliffs,  which  is  about  40  feet.  They  are  structureless 
masses  of  rudely  lens-like  character  and  "largely  made  up  of  fos- 
sils, although  the  number  of  species  does  not  appear  to  be  great." 
The  principal  forms  are  brachiopods  (Meristella,  Stropheodonta), 
a  trilobite  and  corals.  Stromatoporoids  are  probably  also  among 
the  abundant  reef-builders.  The  thinly  bedded  limestones  which 
enclose  the  reefs  dip  away  from  them  at  various  angles,  and  are 
sparingly  fossiliferous.  These  beds  are  more  easily  removed  by 


FIG.  89.  Reef  mounds  enclosed  in  bedded 
formations  of  Devonic  age.  Atta- 
wapishkat River,  Canada.  (After  Bell.) 


FIG.  90.  A  single  reef  mass 
left  by  erosion  of  the 
bedded  rocks.  Attawa- 
pishkat River,  Canada. 
(After  Bell.) 


erosion,  with  the  result  that  the  reef  masses  stand  out  in  bold  relief 
like  the  Klintar  of  Gotland.  The  numerous  islets  in  the  Attawap- 
ishkat River  "appear  to  consist  of  single  masses,"  each  of  these 
reef-cores  being  left  in  relief  by  the  removal  of  the  surrounding 
strata.  They  are  locally  known  as  wigwams  by  the  native  Indians. 
(Figs.  89,  90.) 

Middle  Devonic  Reefs  of  the  Eifel  and  Belgium.  The  Middle 
Devonic  Stringocephalus  beds  of  the  Eifel  show  in  many  sections 
a  typical  reef  structure  similar  to  that  already  described  for  the 
Devonic  of  North  America.  As  in  other  cases,  the  reef  masses 
stand  out  in  relief,  forming  high  cliffs  of  structureless  limestone 
often  dolomitized.  The  structure  and  topography  are  in  many 
cases  modified  by  the  eruption  through  these  limestones  of  Tertiary 
volcanic  rocks.  The  chief  reef-building  organisms  in  these  de- 
posits are  Favosites,  Cyathophyllum,  Endophyllum,  Stromatopora 
and  Actinostroma.  Brachiopods,  gastropods,  pelecypods  and  ceph- 
alopods  are  also  characteristic  and  sometimes  abundant.  The  usual 


FOSSIL    REEFS:     MISSISSIPPI  431 

inclined  marginal  strata  have  been  noted  in  a  number  of  sections 
in  the  Eifel,  and  the  character  of  the  reefs  is  not  unlike  that  of 
the  more  massive  American  reefs,  such  as  that  of  the  Niagaran  of 
Wisconsin.  The  reef  masses  rest  upon  a  foundation  of  crinoidal 
limestone. 

The  corresponding  Middle  Devonic  Calcaire  de  Givet  (Givetien) 
of  Belgium  has  the  reef  structure  well  developed.  (Dupont-27.) 
The  reefs  have  at  first  impression  the  appearance  of  amorphous 
limestone,  passing  into  more  or  less  saccharoidal  rock.  On  weath- 
ered surfaces  a  somewhat  brecciated  structure  appears,  together 
with  numerous  outlines  of  corals  or  sponges,  slightly  left  in  relief 
by  the  solution  of  the  enclosing  limestone.  Stromatoporoids  make 
up  a  large  part  of  the  reef,  but  they  have  been  profoundly  altered, 
so  that  it  is  difficult  now  to  separate  the  Stromatoporoids  along  their 
laminae  or  structure  planes  even  with  a  hammer.  It  is  only  on 
weathered  surfaces  that  the  true  composition  of  the  reef  is  shown, 
the  fresh  surfaces  showing  only  a  compact  rock  often  with  con- 
choidal  fracture,  full  of  cavities,  but  without  trace  of  the  Stroma- 
toporoids or  other  organic  content.  As  in  other  cases,  the  reef  is 
structureless,  no  stratification  being  visible.  The  reef-formers  be- 
side the  Stromatoporoids  (Stromatactis  and  Pachystroma),  include 
Favosites,  Alveolites  and  more  rarely  cyathophylloids.  Cyatho- 
phyllum  cccspitosum  occurs  on  the  margin  of  some  of  the  reefs  in 
crowded  heads  from  1.5  to  2  meters  in  diameter.  -The  flanking  beds 
of  clastic  limestone  show  well-marked  stratification,  and  between 
the  reef  knolls  these  clastic  limestones  often  contain  beds  of  crin- 
oidal fragments,  and  others  largely  composed  of  shells. 

Dupont  deduces  from  the  arrangement  of  the  reef  masses  that 
they  constituted  fringing  reefs  to  the  land  of  that  period,  and  he 
has  found  indications  of  a  breach  in  the  reef  line  in  the  Frasnien 
reef  north  of  the  Couvin,  which  is  analogous  to  the  interruptions  in 
the  reef  opposite  the  mouths  of  streams  coming  from  the  fringed 
land.  Reef  structures  of  similar  character  are  found  in  the  Devonic 
of  the  Karnic  Alps  on  the  Austro-Italian  border.  (Frech-34;  35.) 
The  reefs  are  chiefly  in  the  Middle  Devonic,  and  composed  of  Alve- 
olites, Heliolites,  Stromatoporas,  etc.,  while  Stringocephalus  and 
other  brachiopods  are  among  the  other  characteristic  organisms  of 
the  reefs.  The  reefs  themselves  rest  on  bedded  Lower  Devonic 
(Konjeprussian)  limestones  composed  of  an  abundance  of  brachio- 
pods and  crinoids,  of  corals  and  of  other  organisms. 

MISSISSIPPI  REEFS.  These  are  less  abundant  and  are  not  so 
widespread  as  the  Devonic  reefs.  None  have  as  yet  been  described 
from  America,  though  they  are  known  to  exist  in  some  sections. 


432  PRINCIPLES    OF    STRATIGRAPHY 

Mississippic  Reefs  of  Belgium.  In  the  Mississippic  (Tour- 
nasien  and  Viseen)  of  Belgium  occurs  a  distinct  reef  facies  known 
as  "Calcaire  de  Waulsort"  and  belonging  in  part  to  both  of  the 
above  subdivisions.  This  limestone  is  a  massive,  structureless  ag- 
glomeration of  the  stromatoporoids  Stromatocus  bulbaceus  Dupont 
and  Ptylostroma  fibrosa  Dupont.  To  the  surfaces  of  these  hydro- 
corallines  adhere  numerous  fronds  of  the  bryozoan  Fenestella. 
Corals  play  only  a  small  part  in  these  reefs,  including  Amplexus 
coralloides  and  a  few  other  rare  types.  The  reefs  are  in  the  form 
of  small  massive  heaps  or  islets  scattered  through  the  bedded  lime- 
stones which  surround  them  and  are  marginally  entangled  with 
them.  These  limestones  are  of  diverse  character,  and  chiefly 
marked  by  the  clearness  of  their  stratification.  Two  varieties  of 
this  limestone  may  be  distinguished,  the  amorphous  and  the  crin- 
oidal.  The  latter,  formed  from  the  dissociated  joints  of  crinoid 
columns,  commonly  fill  the  channels  in  the  reef  mass  proper.  As  in 
the  case  of  the  Devonic  reefs,  these  also  are  disposed  in  fche  form 
of  fringing  reefs  parallel  to  the  old  shore,  and  separated  from  it 
by  a  lagoon  canal  of  greater  or  less  width.  In  one  case  the  reef 
has  been  followed  for  a  distance  of  60  kilometers. 

Mississippic  Reefs  of  Great  Britain.  In  the  Mountain  limestone 
of  Great  Britain  certain  structures  occur  which  have  been  inter- 
preted by  Tiddeman  (84;  85)  as  reefs,  but  this  interpretation  was 
challenged  by  Marr  (62).  The  structures  in  question  occur  in 
the  Craven  district  of  Yorkshire,  on  the  south  side  of  the  Craven 
fault  system,  in  the  Pendleside  and  Clitheroe  limestones.  "The 
form  and  the  system  of  arrangement  of  the  white  limestones  [of 
the  knolls]  are  peculiar.  The  stratification  of  the  deposits  is  usu- 
ally somewhat  obscure,  and  the  masses  rise  in  the  form  of  conical 
or  ovoid  eminences  up  to  a  height  of  300  or  400  feet.  The  change 
of  thickness  occurs  in  a  very  limited  horizontal  extent.  These 
eminences  ordinarily  present  upon  their  sides  strata  which  dip 
away  from  the  mass  in  all  directions;  but  when  the  rocks  of  the 
eminences  have  been  quarried,  or  denuded  by  atmospheric  agents, 
one  sees  that  the  stratification,  rough  as  it  is,  preserves  its  hori- 
zontality  or  agrees  with  the  direction  of  inclination  of  the  sur- 
rounding country.  .  .  ."  (Tiddeman-85  -.321 ;  Marr's  transla- 
tion-62.) 

"At  the  foot  of  these  mounds,  or  reef  knolls,  as  I  would  call 
them,  we  have  in  many  places  a  breccia  formed  of  fragments  of 
the  limestone,  which,  I  take  it,  have  been  broken  off  the  reef  above 
between  wind  and  water,  and  have  subsequently  been  covered  up 
by  the  mud  of  the  Bowland  shales  and  compacted  into  a  breccia. 


FOSSIL    REEFS:     PERMIC  433 

Fragments  of  limestone  similarly  consolidated  occur,  though  more 
rarely,  on  the  sides  of  these  knolls  themselves.  I  would  call  these 
reef-breccias."  (Tiddeman-84:<5o<?.)  The  knolls  are  crammed 
with  brachiopods,  pelecypods,  crinoids,  corals,  etc.,  many  fairly 
perfect.  This,  however,  is  true  only  in  a  general  sense,  for  in 
places  the  limestone  is  apparently  entirely  devoid  of  fossils,  though 
this,  as  in  the  case  of  many  of  the  other  reefs  cited,  may  be  due 
to  obliteration  of  the  organic  structure. 

Marr  (62)  has  pointed  out  the  abundant  evidence  of  folding 
and  thrusting  in  the  rocks  of  this  region,  and  he  would  explain 
these  knolls  as  due  wholly  to  tectonic  movements,  the  thickening 
of  the  limestone  being  due  to  folding  and  thrusting.  That  the 
region  has  been  much  disturbed  is  clearly  evident  from  the  facts 
given  by  Marr,  but  that  the  knolls  are  wholly  due  to  tectonic  causes 
seems  doubtful.  The  original  reefs  of  the  limestones  would  serve 
as  centers  of  resistance  in  which  the  cumulative  effects  of  the 
thrusts  would  be  most  strongly  marked. 


FOSSIL  REEFS  OF  BRYOZOA  AND  OTHER  ORGANISMS. 

BRYOZOAN  REEFS  OF  THE  GERMAN  ZECHSTEIN.  In  the  Zech- 
stein  of  the  southeastern  district  of  Thuringia  in  Germany  reef 
structure  is  well  developed.  The  reef-forming  organisms  here  are, 
however,  no  longer  corals  but  Bryozoa.  These  bryozoan  reefs  form 
large  block-like  masses  of  structureless  dolomite  which  lies  scattered 
within  the  normal  bedded  Zechstein  strata.  When  erosion  has 
carved  away  the  enclosing  bedded  strata,  the  reef  mass  stands  out 
in  relief,  forming  frequently  isolated  bastion-like  mounds,  not  un- 
commonly surmounted  by  a  castle  or  an  ancient  burg.  The  reef- 
forming  organisms  are  chiefly  closely  crowded  masses  of  Acanth- 
ocladia  anceps,  'Fenestella  retiformis,  Phyllopora  and  other  Bryo- 
zoa. Corals  are  wholly  absent,  but  brachiopods  are  well  represented 
by  Productus  horridus,  Strophalosia  goldfussi,  Terebratula  elon- 
gata,  and  Spiriferina  cristata,  while  the  pelecypods  are  represented 
by  Pseud  omonotis  speluncaria  and  Prospondylus  liebeamus.  The 
most  abundant  organism,  however,  is  a  lime-secreting  sponge  or 
hydrocoralline,  Evinospongia,  which  covered  the  cliffs  up  to  the 
level  of  the  sea.  These  reefs  grew  upon  the  cliffs  of  older  rocks 
which  projected  as  islands  and  as  lines  of  crags  above  the  floor  of 
the  early  Zechstein  sea.  They  extended  along  the  southern  border 
of  the  Harz  old  land  and  the  East  Thuringian  peninsula,  from 
Kostritz  past  Possneck,  where  they  are  especially  well  developed, 


434  PRINCIPLES    OF    STRATIGRAPHY 

past  Saalfeld  to  Eisenach  and  southward  around  the  peninsula  to 
Laebenstein.  The  floor  of  the  Zechstein  sea  had  previously  been 
covered  with  the  black  Kupferschiefer  mud  rich  in  decaying  organic 
matter,  chiefly  the  carcasses  of  dead  fish  and  decomposing  algae,  and 
in  which  the  copper  now  obtained  from  it  was  precipitated.  These 
deposits  did  not  cover  the  ledges  upon  which  the  reefs  subsequently 
grew  when  normal  marine  conditions  were  established.  These  reefs 
grew  to  the  height  of  40  to  100  meters,  with  steep  sides  which,  how- 
ever, often  show  the  interfmgering  with  the  clastic  limestone  which 
surrounds  their  flanks.  This  limestone  is  often  almost  devoid  of 
organic  remains,  forming  a  dark  "Stinkstein"  or  a  blue  compact 


FIG.  91.  Dolomite  reefs  of  South  Tyrol.  Richthofen  reef  on  left  with  tongue- 
like  extensions  into  the  contemporaneous  marls.  Sett  Sass  on 
right.  C  D — Structureless  Schlern-dolomite.  (Kayser.) 

lime,  both  well  stratified,  and  succeeded  by  a  porous  dolomitic 
"Rauchwacke."  The  growth  of  the  reefs  came  to  an  end  with  the 
closing  of  the  outlet  from  the  open  ocean  to  this  epicontinental  sea, 
and  the  beginning  of  gypsum  and  salt  deposition  (referred  to  in 
the  preceding  chapter),  the  reefs  being  eventually  buried  under 
hydrogenic  or  clastic  deposits. 

THE  TRIASSIC  REEFS  OF  THE  TYROL.  The  dolomites  of  the 
southern  Tyrol  are  regarded  by  many  geologists  as  examples  of 
fossil  reefs  on  a  gigantic  scale.  They  consist  of  huge,  structure- 
less and  more  or  less  circumscribed  masses  of  limestone  or  dolo- 
mite representing  a  distinct  facies  of  the  mid-Triassic,  which  is 
elsewhere  represented  by  the  bedded  and  often  highly  fossiliferous 
Cassian,  and  underlying  Wengen  and  Buchensteiner  divisions  of  the 


FOSSIL   REEFS:    TRIASSIC  435 

Ladinian.  The  masses  are  often  of  great  thickness,  that  of  the 
Schlern-dolomite  reaching  over  3,000  feet  (1,000  meters),  and  they 
are  commonly  of  limited  horizontal  extent.  Tongue-like  offshoots 
of  the  "reef  rock"  extend  into  the  surrounding  bedded  strata  as  is 
the  case  with  modern  coral  reefs.  The  reef  character  of  these 
masses  was  first  pointed  out  by  von  Richthofen  (72),  and  they 
were  subsequently  more  fully  described  by  Mojsisovics  (64). 
This  author  calls  attention  to  the  fact  that  the  position  which  these 
isopic  masses  occupy  with  reference  to  the  heteropic  strata  enclosing 
them  is  that  of  a  reef  mass  growing  upon  a  basis  of  volcanic  or 
other  origin,  but  rising  above  the  level  of  the  sea  floor  on  which 
the  heteropic  deposits  were  forming.  The  latter,  therefore,  have 
their  bases  at  a  lower  level  than  the  reef  masses,  which  always 
project  above  the  synchronous  bedded  deposits  surrounding  them. 


8W. 


SO. 


FIG.  92.  Section  of  the  Schlern-massif,  showing  the  relationship  of  the  dolo- 
mite "reef  rock"  to  the  bedded  formations,  South  Tyrol.  (After 
Mojsisovics.) 

The  chief  structural  characters  pointing  to  the  reef  origin  of  these 
masses  are :  the  resemblance  of  the  isolated  dolomite  masses  to 
upraised  reefs ;  the  great  concentration  of  the  dolomite  masses 
thousands  of  feet  thick  tailing  off  laterally  into  marly  deposits  of 
much  less  thickness,  but  formed  during  the  same  interval  of  geo- 
logic time  and  often  showing  inclined  bedding  near  the  reef;  the 
absence  of  bedding  in  the  "reef  masses" ;  and  the  occurrence  of 
interfingering  masses  and  of  blocks  of  the  dolomite  material  on  the 
slopes  of  the  "reefs"  and  apparently  intercalated  among  the  sur- 
rounding sedimentary  deposits.  (Figs.  91,  92.)  On  the  other  hand, 
many  observers  (Ogilvie-7o,  Diener  and  Artharber-24  and  others) 
hold  that  the  structural  features  are  due  to  faulting  and  that  the 
dolomite  masses  are  fragments  of  once  continuous  deposits  of 
marine  origin.  They  do  not  deny,  however,  that  they  constitute 
distinct  facies  of  the  Cassian,  Wengen  and  Buchenstein  or  even 
earlier  beds. 

Corals  are  very  rare  in  the  dolomite,  calcareous  algse  and  echino- 
derms  constituting  the  chief  organic  remains.    This  has  forced  the 


436  PRINCIPLES    OF    STRATIGRAPHY 

advocates  of  the  reef  theory  to  regard  these  deposits  as  more  strictly 
nullipore  reefs,  in  which  corals  played  only  a  secondary  part.  The 
organisms  of  these  massive  dolomites  have  for  the  most  part  been 
destroyed  during  the  alteration  of  the  deposit,  but  it  has  been  possi- 
ble to  ascertain  that  the  chief  lime  contributors  were  a  coral, 
Thecosmilia  subdichotoma,  and  a  coralline  alga,  Diplopora  annu- 
lata.  The  abundance  of  this  and  other  calcareous  algae  is  the  cause 
for  the  frequent  interpretation  of  this  mass  as  a  nullipore  reef. 
Brachiopods  (Koninckina  leonhardi,  Rhynchonella  faucensis),  pele- 
cypods  (Daonella  parthanensis)  and  cephalopods  (Ptychites  acutus, 
Gymnites  palmai,  Japonites  ganghoferi,  Hungarites  bavaricus,  etc.) 
occur  at  a  few  points,  as  for  example,  in  the  massif  of  the  Zug- 
spitze,  but  are  as  a  rule  very  rare.  Large  gastropods  (Chemnitzia) 
occur  at  many  localities  in  the  reef  masses.  The  bordering  heter- 
opic  limestones  sometimes  consist  largely  of  Diplopora  fragments, 
and  as  a  rule  are  very  rich  in  organic  remains,  especially  close  to 
the  reef. 

Recently  the  problem  has  been  attacked  by  Professor  Skeats 
(82)  from  the  chemical  and  petrographical  side.  He  started  with 
the  ascertained  facts  that  in  modern  coral  islands  remote  from  land 
areas  and  volcanic  rocks  the  amount  of  insoluble  residue  in  the  reef 
rock  is  negligible.  The  same  is  true  also  of  many  coral  rocks  asso- 
ciated with  volcanic  rocks,  though  those  in  the  proximity  of  the  vol- 
canic masses  were  found  to  contain  a  considerable  quantity  of  in- 
soluble material,  amounting  in  some  cases  to  4  per  cent,  or  over. 
With  this  as  a  basis,  he  made  numerous  analyses  of  the  dolomites, 
which  showed  the  prevailing  purity  of  the  rock,  the  percentage  of 
insoluble  residue  being  in  the  majority  of  cases  less  than  one  per 
cent.,  and  frequently  almost  zero.  Where  residue  is  present,  it  can 
generally  be  attributed  to  association  with  contemporaneous  vol- 
canic rocks,  as  is  the  case  in  the  raised  coral  reefs  of  Fiji. 

Taking  the  purity  of  the  rock,  the  absence  of  structure  and  its 
occurrence  as  enormously  thick  masses  in  the  surrounding  clastic 
strata  into  consideration,  there  appears  to  be  no  other  mode  of  ori- 
gin than  that  due  to  the  growth  of  corals,  with  an  abundance  of  cal- 
careous algae,  foraminifera  and  echinoderms,  such  as  are  found  in 
some  modern  coral  reefs.  These  Triassic  reefs  formed  a  barrier 
reef  to  the  land  mass  lying  to  the  north,  whose  main  axis  consisted 
of  the  crystalline  rocks  now  forming  the  central  chain  of  the  Alps. 
In  the  beginning  of  Triassic  time  continental  sediments  spread  north 
from  these  highlands,  forming  the  Bunter  Sandstein  deposits  of  Ger- 
many. In  mid-Triassic  time,  however,  a  marine  invasion  from  the 
north  caused  the  deposition  of  the  Muschelkalk,  only  to  be  fol- 


FOSSIL    REEFS:    JURASSIC  437 

lowed  again  by  non-marine  sedimentation  in  later  Middle  and  Upper 
Triassic  time.  While  the  period  during  which  reefs  were  forming 
corresponds  largely  to  that  during  which  the  Wellenkalk  and 
Muschelkalk  were  forming  north  of  the  Alps,  it  probably  continued 
to  some  extent  into  the  time  when  the  continental  sedimentation  be- 
gan in  the  north. 

In  view  of  this  relationship  of  the  reef  to  the  old  coast  line,  the 
development  of  certain  accessory  features  becomes  of  interest. 
Thus  the  interfingering,  the  cross-bedding  and  the  irregular  over- 
lapping structure  characteristic  of  the  more  or  less  inclined  beds 
on  the  flanks  of  the  reef  (Uebergussschichtung)  with  their  irregu- 
lar swelling  and  the  union  and  separation  of  layers,  are  confined  to 
the  parts  of  the  reefs  farthest  away  from  the  old  shore,  i.  e.,  the 
southern  or  outer  side  of  the  reef,  where  it  was  exposed  to  the 
wave  destruction  and  where  it  rose  steeply  from  the  sea.  The 
lagoon  side,  on  the  other  hand,  is  characterized  by  the  abundance  of 
Diplopora  related  to  the  modern  Cymopolia,  delicate,  branching 
corallines,  which  abound  only  in  the  protected  waters  of  the  lagoons, 
and  do  not  occur  on  the  outer  side  of  the  reef,  where  the  stony 
nullipores  find  a  congenial  habitat. 

In  the  upper  bedded  strata  of  the  Cassian  formation,  coarse 
oolites  are  common  in  the  eastern  part  of  the  reefs,  a  feature  asso- 
ciated with  the  closing  stages  of  reef  formation  at  the  present  day. 
The  Raibler  beds  overlying  the  reefs  also  are  oolitic,  and  contain 
many  layers  of  calcarenytes.  A  remarkable  feature  of  these  dolo- 
mite reefs  is  the  accompanying  eruptive  series  of  augite  porphyry 
lavas,  which  began  after  the  reef  had  already  assumed  massive  pro- 
portions. The  reef  masses  thus  appear  to  have  set  a  limit  to  the 
extent  of  these  lava  flows  in  one  direction,  and  they  spread  over  the 
submerged  flanks  on  which  the  clastic  sediments,  formed  by  the 
destruction  of  the  reef,  had  accumulated.  The  result  was  the 
formation  of  a  remarkable  limestone  tuff  breccia,  which  is  com- 
monly found  at  the  base  of  these  flows. 

THE  JURASSIC  REEFS  OF  SOLNHOFEN.  In  the  Jurassic  beds  of 
the  Solnhofen  district  in  Bavaria,  famous  for  its  lithographic  stones 
and  the  beautifully  preserved  fossils  found  in  it,  reef  structures  are 
well  developed  and  have  recently  been  fully  described  by  Walther 
(91).  The  thin-bedded  lithographic  layers  (calcilutytes)  are  found 
to  rest  in  shallow  basins  in  a  coarse,  unstratified  or  rudely  stratified 
limestone  with  which  they  interfinger  at  the  margin  of  the  basins, 
and  which  even  rises  above  the  level  of  the  youngest  of  the  litho- 
graphic stones  (Figs.  93-95).  These  coarse,  unstratified  limestones 
are  reefs  on  a  large  scale,  composed  chiefly  of  sponges,  corals  and 


438  PRINCIPLES    OF    STRATIGRAPHY 

bivalve  molluscs,  among  which  large  and  coarse  types,  such  as  oys- 
ters, Pecten,  Hinnites,  Lima  and  especially  the  curiously  twisted 
Disceras  predominate.  The  last  is  so  abundant  in  some  places,  e.  g., 
Kelheim,  that  the  beds  have  become  known  as  the  "Disceras  lime- 
stones." These  molluscs  flourished  on  the  margin  of  the  reefs, 
where  the  wave  activities  were  strong,  and  food  plentiful.  Large 
and  coarse  gastropods  were  also  plentiful,  including  Nerinea,  Ceri- 
thium,  Turbo,  Pleurotomaria  and  others.  With  these  also  occur 
large  brachiopods  (Terebratula  and  Waldheimia),  which  occupied 
the  cavities  in  the  reefs,  and  sea  urchins,  which  had  heavy  skeletal 
parts  and  crawled  about  on  the  reefs.  All  these  are  now  incor- 
porated in  the  coarse  reef  rock  which  constitutes  a  large  portion  of 
this  formation.  These  organisms  are  best  preserved  on  the  margins 
of  the  reefs,  the  main  portion  having  more  commonly  the  appear- 
ances of  a  structureless  limestone  or  dolomite  (Franken  dolomite, 


FIG.  93.     Section  through  the  reef  region    (Jurassic)   of  the  Altmiihl,  in  the 
Pappenheim-Eichstadt  region    (near  Solnhofen)   in  Bavaria.     The 
reef  rock  is  structureless,  the  thin  bedded  "Plattenkalke"  or  litho- 
graphic beds  are  shown  in  the  lagoon-like  depressions  in  the  reef. 
(After  Walther.) 

Kelheim  limestone).  This  rock  is  well  shown  in  the  gorge  of  the 
Danube  at  Kelheim,  and  in  numerous  other  natural  and  artificial  ex- 
posures in  Franken.  As  a  rule,  the  reef  masses  stand  out  in  relief 
in  the  present  topography,  while  the  inter-reef  portion,  occupied  by 
the  thin-bedded  calcilutytes  (Plattenkalke),  is  often  worn  out  into 
a  hollow  or  depression.  The  individual  knolls  seem  to  have  had  an 
arrangement  suggestive  of  atolls,  though  on  the  whole  this  series  of 
reefs  is  more  properly  to  be  regarded  as  forming  a  barrier  reef  to 
the  old  Jurassic  land.  (Fig.  93.) 

The  reef-rocks  of  the  Swabian  Alb  have  recently  been  studied  by 
Dr.  Fritz  Berckhemer,*  who  finds  that  the  Hydrozoan  Ellipsactinia 
is  one  of  the  principal  reef-builders,  holding  the  place  of  the  stro- 
matoporoids  of  the  Palaeozoic,  and  of  the  milleporoids  of  later  time. 
These,  together  with  nullipores  and  the  lime-sand  derived  from 

*  Fritz  Berckhemer.  Eine  vorlaufige  Mitteilung  tiber  den  Auibau  des 
Weissen  Jura  c  (Quenstedt)  in  Schwaben.  Jahreshefte  d.  Vereins  f.  Vaterl. 
Naturkunde  in  Wurtemberg,  69  Jahrgang,  1913  pp.  Ixxvi-lxxii. 


FOSSIL   REEFS:    JURASSIC  439 

the  destruction  of  the  reef,  make  up  the  "reef  masses"  which  sur- 
round the  basins  in  which  the  platy  limestones  (Plattenkalke)  were 
deposited.  In  many  cases,  these  Hydrozoa  reefs  rest  upon  or  over 
the  sponge  reefs  of  a  lower  horizon. 

The  presence  of  islands  on  these  reefs  is  shown  by  the  eolian 
more  or  less  oolitic  limestones  with  pronounced  eolian  cross-bed- 
ding, shown  in  the  quarries  of  Schnaitheim  and  Zandt.  These  have 
precisely  the  structure  of  the  eolian  rocks  of  Bermuda.  Walther 
suggests  that  the  organisms  of  the  reefs  near  Nattheim  were 
abruptly  killed  and  preserved  by  the  mud  spread  over  them,  and  so 
they  escaped  the  usual  fate  of  the  coral  reef  organisms,  which  are 
destroyed  by  boring  organisms,  and  changed  to  structureless  dolo- 
mite. Subsequent  silicification  has  resulted  in  the  wonderful  preser- 
vation of  this  coral  fauna,  for  which  this  region  has  become  famous. 

The  basins  containing  the  fine  and  thin-bedded  lithographic  rock 
form  the  strongest  possible  contrast  to  the  enclosing  reef  mass.  In 


•        •»•/•••'•         i      .  r  .  \^  ' 

'••••         •    f.'.XA,  OV      /,..\,    •      •'•    ' 


FIG.  94.  Diagrammatic  section  of  a  lagoon  in  reef-rock,  with  lithographic 
limestone  layers  of  extreme  thinness  (Plattenkalke)  occupying  the 
depressions.  (After  Walther.) 

these  sediments  of  impalpable  lime  mud  the  most  delicate  organisms 
were  preserved  with  a  marvelous  perfection.  The  feathers  of  the 
ancient  bird,  Archseopteryx ;  the  wing  membrane  of  the  flying 
saurians,  the  dragon-flies  and  other  insects,  with  the  veining  of  their 
wings  perfectly  retained,  are  wonderfully  well  preserved,  and  even 
the  delicate  jellyfish  left  its  impressions  in  marvelous  perfection. 
Sometimes  secondary  reefs  occur  in  the  midst  of  the  basin,  indicat- 
ing a  temporary  encroachment  of  the  reef  builders,  which  later  on 
were  again  overwhelmed  by  the  fine  mud  which  produced  the  litho- 
graphic calcilutytes.  The  strata  are  often  very  thin,  and  very  uni- 
formly bedded.  The  heavier  bedded  ones  are  used  for  lithographic 
purposes,  the  thin  ones  for  roofing  and  flagging  purposes.  At  inter- 
vals argillaceous  layers  occur,  and  some  of  the  beds  retain  a  mud- 
crack  structure.  The  evidence  adduced  by  Walther  goes  to  show 


440  PRINCIPLES    OF    STRATIGRAPHY 

that  the  clayey  beds  are  due  to  deposition  of  terrigenous  dust,  and 
in  them  the  terrestrial  insect  fauna  was  buried. 

It  appears,  then,  that  these  lagoon-like  depressions  or  basins  in 
the  coral  reefs  of  the  Jurassic  sea  of  that  region  were  slowly  filled 
by  the  fine  lime  mud  derived  from  the  destruction  of  the  reefs,  by 
terrestrial  dust  brought  by  the  strong  winds  from  the  distant  land 
and  by  chemical  precipitation  of  lime.  Thus  were  formed  the  fine- 
grained lime  deposits,  which  reach  in  places  a  thickness  approaching 
a  hundred  feet.  In  the  more  clayey  beds  and  between  the  layers 
were  preserved  the  insects  and  plants  blown  from  the  mainland  or 
the  marine  types  brought  there  during  the  flooding  of  the  lagoons. 
Walther  has  shown  from  the  position  of  these  remains  that  with 


FIG.  95.  Section  of  the  reef  rock  (Franken  dolomite,  Jurassic)  of  Kelheim, 
Bavaria.  The  thin  bedded  "Plattenkalke"  are  shown  by  horizontal 
lining.  Those  in  the  upper  left-hand  portion  show  distortion 
through  gliding.  ("Krumme  Laage,"  see  page  781.)  (After 
Walther.) 

few  exceptions  they  were  brought  there  dead,  and  left  as  stranded 
carcasses  on  the  ooze  of  the  lagoon  bottom,  which  was  mostly  cov- 
ered by  little  water  if  not  altogether  exposed.  The  repeated  evi- 
dence of  shallow  water,  and  even  complete  exposure  of  the  lagoons 
to  the  air,  suggests  that  these  deposits  were  accumulating  during  a 
slow  subsidence  of  the  region  and  that  the  filling  of  the  lagoons  in 
general  kept  pace  with  the  sinking  of  the  reefs.  The  absolute  uni- 
formity of  the  entire  series  of  thin-bedded  limestones  further  shows 
that  the  physical  conditions  remained  uniform  during  their  deposi- 
tion. Walther  assumes  that  the  old  shore  of  the  Vindelician  land 
was  some  20  km.  to  the  south,  but  no  clastic  mud  was  carried  by  the 
currents  to  these  reefs.  Instead,  the  terrigenous  dust  incorporated  in 
the  thin  sediments  represents  wind-blown  material.  It  is  in  these 
dust-bearing  layers  that  most  of  the  fossils  are  found,  especially  the 
insects,  of  which  there  are  72  genera  and  103  species,  35  per  cent. 


FOSSIL    REEFS:     JURASSIC  441 

of  these  being  dragon-flies.  The  peculiar  character  of  the  fauna, 
and  the  indications  which  it  furnishes  of  having  been  stranded  on 
surfaces  of  calcareous  mud,  suggest  that  the  lagoon  was  nearly  dry 
and  flooded  only  during  exceptionally  high  tides  or  during  storms, 
after  which  the  water  soon  ran  off  again.  (Walther-9i.)  (Fig.  96.) 
Some  such  conditions  are  represented  to-day  by  the  lagoons  of  Lil 
and  Mejt,  in  the  Marquesas  Archipelago,  where  the  water  is  brackish, 
and  poor  in  organisms,  while  at  Jabor  and  Jaluit  the  lagoons  have 
become  fresh.  (Agassiz-8:  ji,  273,  284.)  Where  abundant  rain 


FIG.  96.  A  horseshoe  crab  (Limulus)  and  the  marks  of  its  death  struggles, 
showing  that  it  was  left  stranded  on  the  mud  forming  the  lagoon 
deposits.  (After  Walther.) 

water  dissolves  some  of  the  limestones,  the  eolian  sand  is  soon  solidi- 
fied by  the  redeposition  of  this  lime  in  the  interstices,  as  in  the  case 
of  the  Bermuda  sands.  Moreover,  some  of  this  dissolved  lime  may 
be  reprecipitated  in  the  lagoon,  a  process  believed  by  Walther  to 
have  taken  place  in  the  lagoons  of  the  Solnhofen  region.  As  a  re- 
sult of  these  and  other  chemical  activities  in  the  lagoons  of  these 
reefs,  we  have  not  only  the  rapid  and  complete  encasement  of  the 
dead  organisms  and  their  perfect  preservation  in  consequence,  but 
also  the  remarkable  preservation  of  the  muscle  fibers  of  reptiles, 
fishes,  etc.,  which  have  been  transformed  into  a  rock  containing 
70%  of  Ca3P2O8,  12%  of  CaCO3,  3.5%  of  CaSO4,  6.5%  of  CaFl2, 
3%  of  Na3PO4  and  0.5%  each  of  Mg3P2O8  and  K3PO4,  together 
with  small  quantities  of  water  and  organic  substances. 

The  lagoon  in  which  the  Plattenkalke  were  formed  was  thus 
apparently  a  great  lifeless  surface,  on  which  the  carcasses  of  land 
and  sea  animals,  cast  there  during  storms  or  brought  by  the  wind, 
or,  as  in  the  case  of  the  flying  reptiles  and  the  early  bird,  Archae- 
opteryx,  dropped  there  on  the  death  of  the  animal,  were  so  quickly 
enclosed  by  the  fine,  chemically  precipitated  lime  ooze  that  the  usual 
forces  of  destruction,  scavengers,  bacteria,  etc.,  did  not  succeed  in 
destroying  them  or  dissociating  their  parts.  They  were  entombed  in 
a  hermetic  and  antiseptic  mud  case,  and  thus  preserved  in  all  their 
perfection  of  form  and  delicacy  of  structure  which,  until  the  re- 


442 


PRINCIPLES    OF    STRATIGRAPHY 


cent  discoveries  of  the  wonderfully  preserved  Cambric  fauna  of 
British  Columbia,  had  not  its  equal  the  world  over. 

Conditions  like  those  which  existed  in  the  Solnhofen  region  dur- 
ing Jurassic  time  are  unknown  in  any  modern  coral  reef ;  neither 
were  they  repeated  in  any  of  the  numerous  reefs  known  from  the 
Palaeozoic,  Mesozoic  or  Cenozoic  periods  of  the  earth's  history. 
They  remain  an  example  of  a  unique  type  of  reef  resulting  through 
a  remarkable  concatenation  of  topographic,  climatic,  lithologic  and 
faunistic  conditions  not  met  before,  nor  since  attained. 

THE  SPONGE  REEFS  OF  THE  SWABIAN  JURA.  In  the  Upper  or 
White  Jura  of  Swabia,  massive,  structureless  limestones  and  dolo- 
mites are  found,  which  prove  to  be  reefs  built  largely  of  lime-secret- 


FIG.  97.  "Sponge  Reef"  of  the  lower  White  Jura  of  Swabia.  (E.  Fraas.) 
R — Structureless  reef  limestone,  a,  /3,  7,  associated  bedded  Juras- 
sic limestones,  marls,  etc.  S.  Talus.  (From  Kayser.) 


ing  sponges.  These  reefs  from  their  massive  character  stand  out  in 
relief  through  the  erosion  of  the  softer  enclosing  rock,  and  so  form 
pinnacles,  buttresses  or  even  isolated  outliers  of  the  Swabian  Alb, 
which  since  the  earliest  days  have  formed  the  favorite  site  of  castles 
and  other  strongholds.  These  sponge  reefs  sometimes  extend 
through  several  subdivisions  of  the  Upper  (White)  Jura,  as  shown 
in  the  accompanying  figure  (Fig.  97),  after  E.  Fraas,  where  the 
reef  is  surrounded  by  bedded  sediments  of  the  stages  a,  ft  and  y- 
The  reef  contains  many  other  well-preserved  organisms  besides 
sponges,  among  which  latter  the  genus  Cnemidiastrum  predomi- 
nates. On  the  flanks  of  the  reef  a  breccia  of  reef  rock  is  found 
with  some  clay,  and  this  passes  into  the  normal  bedded  strata  of 
clastic  limestones. 

MIOCENIC  REEFS  OF  THE  AUSTRO-RUSSIAN   BORDER.     The  low 


FOSSIL   REEFS:    TERTIARY  443 

ranges  of  hills  known  as  "Mjodoboren"  in  Galicia  (Austria),  and  as 
"Toltry"  in  Podolia  across  the  border  in  Russia,  and  which  extend 
northward  into  Volhynia  and  southward  into  Bessarabia,  have  com- 
monly been  explained  as  representing  Bryozoa  reefs  (Hieber-48; 
Teisseyre-83)  of  Upper  Miocenic  (Sarmatian)  age.  In  reality  they 
represent  reefs  of  earlier  Miocenic  age  (Mediterranstufe)  covered 
by  bryozoan  layers  of  Sarmatian  age  (Michalski).  The  Toltry 
reefs  consist  chiefly  of  corals  and  Vermetus  masses,  and  form  a 
structureless  limestone,  which  eastward  and  westward  passes  into 
stratified  clastic  limestones  and  nullipore  beds.  These  are  on  the 
whole  horizontal,  but  in  the  neighborhood  of  the  reefs  have  an  ir- 
regular and  often  inclined  position,  similar  to  the  overlap  and  inter- 
lap  structure  on  the  borders  of  modern  reefs.  The  reef  limestone, 
called  Vermetus  limestone,  rises  above  the  level  of  the  enclosing 
bedded  limestones  and  constituted  a  barrier  reef  parallel  to  the 
Miocenic  shore  which  existed  several  kilometers  to  the  east.  Upon 
these  mid-Miocenic  reefs  settled  in  later  Miocenic  (Sarmatian)  time 
the  Bryozoa  Leprailia  terebrata  Sinz,  and  the  worm  tubes  Serpula 
gregalis  Eichw.,  which  formed  structureless  limestone  masses  cover- 
ing the  older  reefs.  Over  the  clastic  limestones  enclosing  the  older 
reefs  and  in  the  depressions  in  the  Vermetus  limestones  were 
formed  oolitic  and  conglomeratic  limestones  containing  Ervilia 
podolica,  Cardium  obsoletum,  Trochus,  etc. 

PLIOCENIC  BRYOZOA  REEFS  OF  KERTCH.  The  peninsula  of 
Kertch,  which  partly  separates  the  Black  Sea  and  the  Sea  of  Azov, 
has  been  famous  for  more  than  a  century  for  its  remarkable  reef 
limestones,  first  described  as  composed  of  Bryozoa  by  Pallas  in  1803. 
They  form  picturesque  hillocks  and  stacks  along  both  the  Azov  and 
Black  Sea  coasts,  many  of  them  dissociated  by  erosion  from  the 
mainland  and  rising  as  partly  submerged  towers  and  stacks  from 
the  shallow  waters.  They  are  developed  in  a  less  degree  on  the 
opposite  peninsula  of  Taman,  where  the  same  formations  are  repre- 
sented by  more  clastic  and  argillaceous  deposits.  These  reefs  have 
been  described  and  illustrated  in  great  detail  in  a  monograph  de- 
voted to  them  by  Andrussow  ( 1 1 ) .  They  form  knolls  or  tower-like 
masses  of  unstratified  limestone,  consisting  almost  wholly  of  the 
Bryozoan  Membranipora  (Pleuropora)  lapidosa  (Pallas),  and  are 
embedded  in  stratified  clastic  limestones  and  argillaceous  beds  be- 
longing to  the  Maotic  stage  of  the  Pliocenic.  Many  of  these  beds 
are  largely  composed  of  molluscan  shells,  chiefly  Modiola  volhynica 
Eichw.  var.  minor  Andrussow,  while  others  are  fragmental  layers 
in  which  the  material  is  largely  broken  shells,  mingled  with  Bryo- 
zoa and  Serpula  fragments.  Where  these  layers  meet  the  reef 


444  PRINCIPLES    OF    STRATIGRAPHY 

knolls,  they  are  commonly  inclined,  and  an  interlapping  of  the  clastic 
layers  with  layers  composed  of  Membranipora  and  Serpula  masses 
is  common. 

The  reef  itself  consists  of  a  cavernous  limestone  composed  of 
knolls  of  Membranipora  with  the  intervening  areas  largely  filled  by 
a  small  Spirorbis  shell.  The  surface  is  commonly  marked  by  wind- 
ing channels  and  irregular  depressions,  in  which  Maotic  mollusc 
shells  abound.  Especially  numerous  is  the  shell  Sphenia  cimmeria 
Andrus.  which  makes  up  masses  of  shell  limestone,  sometimes  in 
cavities  within  the  reef  itself.  The  sides  of  the  reef  masses  are 
commonly  very  steep,  often  vertical  and  at  times  overhanging,  and 
the  surface  of  the  reef  at  all  stages  of  growth  possessed  a  higher 
hypsometric  *  niveau  than  did  the  surrounding  bedded  material. 
The  height  of  the  reef  masses  ranges  up  to  30  meters.  Sometimes 
they  are  embedded  in  argillaceous  layers,  derived  probably  from  the 
neighboring  land. 

BEDDED  REEFS. 

A  type  of  reef  differing  from  the  lenticular  one  described  is  found 
in  a  number  of  Palaeozoic  rocks,  where  stromatoporoids  are  the 
chief  or  only  reef  organism.  Instead  of  forming  local  aggregations 
built  up  into  lens-like  mounds,  the  heads  of  the  stromatoporoids  are 
evenly  distributed  in  beds  of  slight  thickness,  but  of  wide  horizontal 
extent.  They  grew  apparently  on  a  shallow  sea  bottom,  at  a  con- 
siderable distance  from  the  shore,  as  shown  by  the  frequent  worn 
character  or  overturned  position  of  the  heads,  and  by  the  scarcity 
or  absence  of  siliceous  sediment.  Sometimes  the  reef  consists  of 
a  single  layer  of  "heads,"  which  may  measure  up  to  5  or  6  feet  in 
diameter ;  at  other  times  it  consists  of  superimposed  heads  or  frag- 
ments of  heads,  forming  beds  twenty  or  more  feet  in  thickness  and 
traceable  for  several  thousand  feet  or  even,  with  some  interrup- 
tions, for  miles.  Sometimes  this  sheet  reef  contains  only  a  small 
number  of  heads  more  or  less  worn,  and  embedded  in  calcarenyte 
derived  from  the  wear  of  the  stromatoporoids,  and  sometimes  it  is 
entirely  replaced,  for  a  short  distance,  by  the  coral  sand.  Chan- 
nels, filled  with  the  coral  sand,  are  characteristic  features,  and 
these  and  the  larger  interruptions  of  the  continuity  of  the  reef  pro- 

*  Andrussow  has  proposed  the  term  Palfeohypsometric  to  express  the  relative 
position  which  the  deposits  had  at  the  time  of  formation,  while  folding  and  dis- 
location may  have  entirely  changed  this  relationship,  the  present  hypsometric 
position  of  such  deposits  not  being  the  same  as  that  which  they  possessed  at 
the  time  of  their  formation. 


ALTERATION    OF    REEF    ROCK  445 

duce  a  varied  aspect  in  the  sections  where  they  are  exposed.  Char- 
acteristic examples  of  sheet  reefs  of  this  type  are  found  in  the  up- 
permost Siluric  beds  (Manlius)  of  central  and  eastern  New  York 
and  in  the  mid-Devonic  limestones  (Transverse  group)  of  western 
Michigan. 


Loss  OF  STRUCTURE  THROUGH  ALTERATION  OF  REEF  LIMESTONES. 

In  many  of  the  foregoing  examples  of  fossil  reefs  the  organic 
structure  of  the  limestone  has  been  wholly  or  almost  completely  de- 
stroyed through  subsequent  alteration  of  the  rock.  In  the  Niagara 
reefs  of  Wisconsin  the  stromatoporoid  structure  is  scarcely  recog- 
nizable, except  in  a  few  cases  on  weathered  surfaces.  The  same  is 
true  of  the  Devonic  and  Carbonic  reefs  of  Belgium,  and  especially 
of  the  dolomites  of  the  Tyrol.  In  all  these  cases  dolomitization  is 
one  of  the  chief  factors  in  the  destruction  of  the  organic  structure, 
while  recrystallization  of  the  undolomitized  limestones  has  had  a 
similar  effect.  Such  changes  are  not  uncommonly  observed  in  mod- 
ern coral  limestones,  where  the  hard  parts,  composed  of  aragonite, 
as  in  reef-forming  corals  (Madreporaria),  gastropoda  and  some 
calcareous  algae  are  rendered  unrecognizable  by  recrystallization  as 
calcite,  and  where  dolomitization  obliterates  the  structure  of  even 
the  more  stable  calcite  organisms.  Sections  of  modern  coral  lime- 
stones have  shown  that  three  types  of  mineral  structure  may  be 
recognized,  due  to  different  degrees  of  alteration  of  the  rock. 
(Skeats-8i :  105;  82  : 128;  Cullis-iQ :  404.) 

1.  Limestones  consisting  largely  of  calcite,  but  containing  also 
organisms  with  hard  parts  of  aragonite,  while  not  infrequently  sec- 
ondary aragonite  has  been  deposited  in  crystallographic  continuity 
with  the  aragonite  of  the  organism. 

2.  Limestones  produced  from  gradual  alteration  and  recrystal- 
lization of  the  first  type  of  limestone,  thus  resulting  in  a  rock  in 
which  organic  remains  and  matrix  alike  consist  entirely  of  calcite. 

3.  Limestones  produced  from  either  the  first  or  second  type  by 
the  replacement  of  some  of  the  calcium  carbonate  by  magnesium 
carbonate,  resulting  in  the  occurrence  in  the  rock  of  generally  idio- 
morphic  crystals  of  dolomite;  continued  replacement  will  result  in 
the  complete  change  of  the  limestone  to  dolomite.     When  the  rock 
is  completely  clolomitized,  it  becomes  usually  quite  structureless, 
the  crystals  of  dolomite  being  almost  entirely  allotriomorphic.* 

*  See,  further,  dolomitization  in  Chapter  XIX. 


446  PRINCIPLES    OF    STRATIGRAPHY 

BALLSTONE  REEFS. 

In  the  Siluric  (Clinton  and  Lockport)  horizons  of  western  New 
York  and  the  Wenlock  of  western  England,  reef-like  accumulations 
of  an  impure  argillaceous  calcilutyte  occur,  of  a  lens-like  or  ball- 
like  form,  and  embedded  in  shales  or  fragmental  limestones,  which 
arch  more  or  less  around  them.  They  vary  from  two  to  fifty  feet 
in  diameter,  though  one  in  the  Lockport  has  a  length  of  no  feet. 
When  not  spherical,  they  range  in  thickness  from  one  to  fifteen 
feet.  In  England  these  have  long  been  known  as  Ball  Stones,  but 
their  origin  has  not  heretofore  been  described.  While  in  large  part 
composed  of  fine,  calcareous  mud,  the  structural  groundwork  of 
these  lenses  is  formed  by  branching  and  fan-like  types  of  Bryozoa 
or  other  organisms  which  grew  upon  the  sea  bottom  in  colonies, 
and  which  captured  the  fine  sediment  from  the  water  and  formed 
a  suitable  medium  for  its  retention.  On  these  reefs,  as  rich  feeding 
grounds,  lived  a  multitude  of  brachiopods,  molluscs,  trilobites  and 
other  organisms,  whose  remains  are  now  found  in  or  around  these 
lenses,  while  many  of  them  are  comparatively  rare  or  unknown  in 
the  adjoining  strata.  In  western  New  York  ( Grabau~39  :pp ; 
Sarle~76)  these  ball  reefs  are  found  in  the  upper  Clinton  limestone 
(Irondequoit  limestone),  and  are  either  entirely  embedded  in  this 
otherwise  clastic  lime  rock  (calcarenyte)  or  lie  in  its  upper  portion, 
partly  enclosed  in  the  overlying  Rochester  shales.  More  rarely  are 
reefs  of  this  type  found  in  the  higher  Lockport  dolomite.  They 
are  generally  in  the  form  of  flattened  lenses  due  to  the  cessation  of 
growth  before  they  had  reached  their  full  size.  These  reefs  are 
often  closely  crowded,  so  that  it  has  been  possible  to  step  from 
one  reef  knoll  to  the  others  in  places  where  erosion  has  exposed 
their  upper  surfaces.  The  bryozoans  forming  the  foundation  of 
these  structures  are  several  species  of  fistuliporoids,  these  some- 
times being  the  only  organic  material  found  in  the  reefs.  Tri- 
lobites, especially  the  cephala  and  pygidia  of  Illsenus,  abound  near 
the  margin,  and  brachiopods  are  also  -common,  most  abundant 
among  them  being  Whitfieldella  nitida.  The  silt  captured  by  these 
organisms  was  exceedingly  fine,  so  that  the  rock  is  a  typical  argil- 
laceous calcilutyte,  and  breaks  with  a  conchoidal  fracture.  On  fresh 
surfaces  the  bryozoans  are  not  visible,  except  when  their  epithecal 
surface  is  exposed,  but  weathering  generally  brings  out  their  struc- 
ture. 

The  Wenlock  Ballstones  are  generally  more  spherical  than  those 
of  New  York,  in  which  the  lens  form  prevails.  They  are  found  at 
various  levels  in  the  thin-bedded  limestones  of  Wenlock  Edge  in 


SHELL    COLONIES 


447 


Shropshire,  and,  according  to  the  observations  of  the  author  of  this 
volume,  are  in  all  essentials  similar  to  those  of  the  New  York 
Siluric.  They  form  a  marked  contrast  to  the  surrounding  rock, 
which  is  generally  a  well-bedded  calcarenyte,  not  only  by  their  struc- 
tureless form,  but  by  the  compactness  and  fineness  of  the  material 
composing  them.  The  foundation  of  those  balls  appears  to  be 
formed  by  a  branching  coral,  while  other  organisms  seem  to  be 
rare. 


STRUCTURES   FORMED   BY  THE  GROWTH   OF  SHELL 

COLONIES. 

TEPEE  BUTTES.  Gilbert  and  Gulliver  have  described  a  series  of 
buttes  or  erosion  hills  of  conical  outline  carved  from  the  Cretacic 
Pierre  shales  along  the  Arkansas  River  and  some  of  its  tributaries 
in  Colorado.  (Gilbert  and  Gulliver-38.)  From  their  resemblance 


FIG.  98. 


View    of   a    group    of   Tepee-Buttes    near    Canyon    City,    Colorado. 
(After  Gilbert  and  Gulliver.) 


to  the  Indian  "tepee"  or  conical  hut,  they  have  applied  the  name  of 
tepee  buttes  to  them.  (Figs.  98,  99.)  The  buttes  have  an  irregularly 
cylindrical  core  of  limestone,  varying  from  2,  to  24.  feet  in  diameter 
in  different  examples.  The  average  diameter  is,  however,  10  to  15 
feet,  while  the  height  is  unknown.  (Fig.  100.)  This  limestone  core 
consists  of  an  aggregation  of  shells,  "embedded  in  a  matrix  which  is 
composed  of  fragments  of  shell,  water-worn  grains  of  calcite,  foram- 
inifera  and  clay."  The  shells  are  mostly  those  of  Lucina  occi- 
dentalis  var.  ventricosa,  which  makes  up  by  far  the  larger  part  of  the 
core.  With  these  occur  other  characteristic  marine  Cretacic  species. 
The  core  is  enclosed  in  the  Pierre  shales,  the  passage  from  the 
limestone  to  the  shale  being  abrupt.  There  is,  however,  a  certain 


448 


PRINCIPLES    OF    STRATIGRAPHY 


amount  of  interpenetration  of  the  limestone  and  shale.  "Processes 
of  the  limestone  embrace  portions  of  the  shale,  and  the  contiguous 
shale  contains  outlying  lumps  of  the  limestone."  The  best  exposed 
cores  have  a  stratified  appearance,  with  beds  from  one  to  three  feet 
in  thickness,  and  separated  by  more  or  less  continuous  horizontal 


FIG.  99.     A  single  tepee-butte,  showing  the  top  of  the  limestone  core.     (After 
Gilbert  and  Gulliver.) 

partings  of  shale.  The  presence  of  these  shale  partings  indicates 
that  the  core  was  not  built  any  faster  than  the  surrounding  de- 
posits of  mud. 

Various  explanations  have  been  offered  by  the  authors  cited  for 
the  origin  of  these  cores.  The  best  of  these,  and  the  one  favored 
by  the  authors,  regards  these  accumulations  of  shells  as  colonies, 


FIG.  loo.  Ideal  section  of  a  tepee-butte,  showing  the  core  of  organic  lime- 
stone, the  enclosing  bedded  shales,  and  the  cover  of  talus.  (After 
Gilbert  and  Gulliver.) 


which,  having  begun  in  a  given  place,  continued  there  through  a 
long  period  of  deposition,  the  later  organisms  living  on  the  shell 
heaps  of  their  dead  predecessors  without  migrating  much  outward 
onto  the  surrounding  muddy  ocean  bottom.  Professor  Shaler  has 
suggested  that  Lucina  may  have  had  a  byssus,  by  means  of  which 
it  would  attach  itself  to  the  dead  shells  of  earlier  genera- 
tions, which  would  readily  explain  the  localization  of  these  deposits. 
On  these  shell  heaps  would  be  the  best  feeding  ground  for  other 


CRI-NOIDAL    LIMESTONE  449 

animals,  whose  remains  would  thus  become  incorporated  with  the 
Lucina. 

OTHER  EXAMPLES.  On  the  modern  coast  we  sometimes  find 
colonies  of  Mytilus  edulis  growing  in  isolated  spots,  surrounded  by 
black  mud  deposits.  As  the  colony  increases  the  young  individuals 
will  attach  themselves  to  the  older  shells,  remaining  chiefly  within 
the  circumscribed  area  occupied  by  the  original  colony,  since  any 
transgression  outside  this  area  would  be  checked  by  the  soft  mud, 
which  offers  no  means  of  attachment.  In  this  manner,  on  a  slowly 
subsiding  bottom,  a  core  of  shell  limestone  may  be  formed,  sur- 
rounded by  mud,  in  which  only  occasional  shells  are  found. 

Some  of  the  "Reef  Knolls"  described  by  Tiddeman  (85)  from 
the  Carbonic  limestones  of  the  Clitheroe  district,  England,  appear 
to  be  due  to  colonies  of  shell-building  animals,  more  than  to  the 
growth  of  reef  corals.  Their  structure,  however,  is  more  like  the 
coral  reefs  than  the  tepee  butte  cores. 


BEDDED  ZOOGENIC  DEPOSITS. 

CRINOIDAL  LIMESTONES.  Among  the  limestones  of  all  geologic 
formations,  beds  composed  largely  or  wholly  of  crinoid  remains  are 
common.  These  remains  are  generally  the  stem  joints,  and  they 
vary  greatly  in  size,  from  that  of  a  pin  head  or  smaller  to  those 
over  one  inch  or  more  in  diameter.  Generally  the  fragments  of  each 
bed  are  more  or  less  uniform  in  size,  this  latter  depending  on  the 
species  of  crinoid  which  has  flourished  in  that  region.  Crinoids 
are  admirably  adapted  to  the  formation  of  limestone  beds,  because, 
on  the  death  of  the  animal,  the  long  stems,  as  well  as  the  calices  and 
arms,  readily  separate  into  their  component  ossicles,  and  thus  with 
little  rearrangement  furnish  the  material  in  proper  size  of  grain  for 
a  limestone  bed.  Kirk  (56)  has  recently  brought  forward  much 
evidence  to  show  that  many  crinoids  separate  from  their  anchorage 
and  become  more  or  less  planktonic  in  later  life.  Thus  schools  of 
floating  crinoids  may  be  washed  into  shallow  water,  there  to  accu- 
mulate as  crinoidal  limestones.  The  crinoidal  character  of  an  an- 
cient limestone  is  not  always  noticeable  on  the  fresh  surface,  but 
on  weathering  this  structure  is  brought  out.  When  accumulations 
occur  within  the  zone  of  wave  activity,  cross-bedding  and  other 
shallow  water  structures  may  result. 

SHELL  LIMESTONES.  Beds  of  unbroken  shells  or  coquina  are 
likewise  found  in  different  geologic  horizons.  Often  great  beds  of 
limestone  occur,  in  which  one  species  of  shell  predominates  to  the 


45° 


PRINCIPLES    OF    STRATIGRAPHY 


practical  exclusion  of  others.  Such  are  the  great  beds  of  Pen- 
tamerus  oblongus  extending  widely  through  the  Siluric  of  Gotland 
and  New  York;  the  beds  of  Anoplotheca  in  the  Clinton  of  the 
Rochester  region,  and  those  composed  of  Exogyra  or  other  shells 
in  the  Cretacic  of  Texas ;  the  limestones  entirely  made  up  of  Tur- 
ritella  mortoni  in  the  Eocenic  of  Virginia,  and  numerous  other  ex- 
amples. Rocks  of  this  type  generally  form  thin  beds  among  the 
clastic  sediments.  From  the  nature  of  the  material,  these  beds  can 
be  only  rudely  stratified,  and  irregularities  in  thickness  may  be  ex- 
pected where  wave  action  has  not  been  strong. 

CALCAREOUS  AND  SILICEOUS  OOZES.  These  often  form  beds  of 
considerable  thickness,  as  in  the  case  of  the  chalk.  These  accumu- 
lations when  pure  always  indicate  either  a  remoteness  of  the  shore, 
with  perhaps  deep-water  conditions,  or  a  very  low  relief  of  the  land, 
which  has  been  peneplaned  to  such  an  extent  that  no  clastic  sedi- 
ments are  derived  from  it.  The  oozes  formed  in  the  modern  ocean 
include  the  following  types: 

1.  Calcareous:  a,  Foraminiferal;  b,  Pteropod;  c,  Entomostra- 
can ;  d,  Coccolith,  and  e,  Rhabdolith  ooze. 

2.  Siliceous:  a,  Radiolarian;  b,  Diatom. 


i.     The  Calcareous  Oozes. 

Recent  Foraminiferal  Oozes.  These  are  represented  in  the  mod- 
ern sea  by  the  Globigerina  ooze  (Fig.  105),  so  named  from  the  pre- 
ponderance of  the  shells  of  Globigerina,  which  is  represented  by  ten 


FIG.  101.    Globigerina  bulloides.  x  40. 
(After  Wyville  Thomson.) 


FIG.   102.     Orbulina  unvversa.     x  40. 
(After  Wyville  Thomson.) 


species,  while  Pulvinulina  is  represented  by  five  species.  The  total 
number  of  species  of  foraminifera  making  up  this  ooze  is  only  21, 
distributed  in  9  genera,  but  only  four  species  are  of  great  impor- 
tance in  the  making  of  this  ooze.  These  are  Globigerina  bulloides 


GLOBIGERTNA    OOZE  451 

(Fig.  101),  in  the  northern  hemisphere  and  most  of  the  tropical 
seas ;  Globigerina  dutertrei,  for  the  higher  southern  latitudes ;  and, 
further,  Orbulina  unwersa  (Fig.  102)  and  Hastigerina  pelagica. 
The  foraminifera  of  this  ooze  all  inhahit  the  upper  200  meters  of 
the  ocean,  leading  a  planktonic  existence  (Chapter  XXVIII).  It  is 
only  on  the  death  of  these  organisms  that  their  shells  sink  to  the  bot- 
tom and  become  incorporated  in  contemporaneous  sediments  of  other 
origin,  or,  if  this  is  rare  or  absent,  to  accumulate  as  extensive,  more 
or  less  pure  deposits  of  shells.  The  ooze  is  never  absolutely  com- 
posed of  foraminiferal  shells,  for  the  shells  of  other  planktonic  or- 
ganisms also  enter  into  the  composition.  Among  these  are  the 
shells  of  pelagic  molluscs,  such  as  the  pteropods  arid  heteropods, 
both  often  of  considerable  size;  ostracods  (Crithe  producta,  Cy- 
thcre  dictyon)  ;  minute  planktonic  algae,  Coccolithophores  or  coc- 


FIG.  103.    Pulvinulina.    A  multicham-      FIG.    104.      Coccolithophora.      (After 
bered    foraminiferal    shell    (after  A.  Agassiz.)     x  600. 

Murray)  much  enlarged. 

eoliths  (Fig.  104)  and  rhabdoliths.  These  pelagic  admixtures  are 
further  supplemented  by  those  of  sea-bottom  or  benthonic  origin, 
among  which  bottom-living  Foraminifera  may  constitute  as  high  as 
3  per  cent,  of  the  mass.  Furthermore  there  are  clastic  lime  and 
other  fragments;  spines  of  echinoderms,  shells  pf  molluscs;  worm 
tubes;  deep-sea  corals;  Bryozoa,  etc.  In  all,  these  never  make  up 
more  than  25%  of  the  mass,  and,  according  to  Murray  and  Re- 
nard,  on  the  average  only  9%.  From  the  amount  of  pelagic  cal- 
careous organisms  in  these  deposits,  Murray  and  Renard  have  cal- 
culated that  there  are  at  least  sixteen  tons  of  floating  carbonate  of 
lime  in  one  square  mile  of  water  surface,  distributed  through  the 
upper  100  fathoms  of  the  sea.  The  clastic  material  is  often  less 
than  i%  and  averages  3.3%  in  the  118  samples  obtained  by  the 
Challenger  expedition.  In  depth  the  Globigerina  ooze  is  most  abun- 
dant between  2,500  and  4,500  meters,  its  mean  depth  being  3,660 


452  PRINCIPLES    OF    STRATIGRAPHY 

meters.     The  118  samples  obtained  by  the  Challenger  expedition 
were  distributed  as  follows : 

Percent- 
age of 
CaC03 

Less  than  1,000  fathoms (1,830  m.)  5  j 

Between  1,000  and  1,500  fathoms (1,830-2,750  m.)     13  \  60-70% 

Between  1,500  and  2,000  fathoms (2,750-3,660  m.)     35  J 

Between  2,000  and  2,500  fathoms (3,660-4,570  m.)     49  62% 

Below  2,500  fathoms (4,570  m.)  16  50% 

118 

It  will  be  observed  that  the  percentage  of  CaCO3  in  the  oozes 
decreases  with  depth,  being  only  50%  in  the  samples  from  the 
greater  depths.  The  average  of  the  118  samples  gave  64.5%  of 
CaCO3,  30.6%  of  non-calcareous  silt,  3.3%  mineral  particles,  and 
1.6%  siliceous  organisms.  The  lime  was  distributed  as  follows: 
; 

Remains  of  pelagic  organisms 53 . 1  % 

Remains  of  benthonic  organisms 2.1% 

Remains  of  other  organisms 9 . 3% 


64.5% 

Among  the  mineral  matter  other  than  lime  associated  with  the 
Globigerina  oozes  may  be  mentioned  glauconite,  and  phosphate  and 
manganese  concretions. 

Sir  John  Murray  concluded  from  experiments  made  that  it  takes 
the  dead  foraminiferal  shells  from  three  to  six  days  to  sink  to  a 
depth  of  4,500  meters,  the  rate  being  slowest  in  the  deeper  water. 
Solution  of  the  lime  of  the  shells  by  the  sea  water  increases  rapidly 
with  depth,  owing  to  the  increase  in  pressure.  Thoulet  found  that 
the  rate  varied  greatly  with  the  size  of  the  shells  and  particles, 
those  averaging  0.75  mm.  in  diameter  taking  1.09  days  to  reach  a 
depth  of  4,500  meters,  while  those  having  a  diameter  of  only  0.12 
mm.  required  7.47  days  for  the  same  distance. 

Not  infrequently  fragments  and  blocks  of  terrestrial  rocks  are 
found  in  the  Globigerina  deposits,  as,  for  example,  fossiliferous 
Palaeozoic  rocks  marked  by  glacial  scratches,  and  found  by  the 
French  expedition  northeast  of  the  Azores,  1,100  km.  from  the  Euro- 
pean coast,  carried  there  by  drift  ice  probably  during  the  last  glacial 
period;  and  the  coarse  fragments  of  crystalline  rock  found  in  the 
South  Atlantic  between  Tristan  da  Cunha  and  Kapstadt,  in  35°  to 
36°  S.  lat.,  and  others  from  the  Indian  Ocean. 

The  areal  distribution  of  the  Globigerina  ooze  is  a  considerable 


FOSSIL  FORAMINIFERAL  OOZES  453 

one,  being  in  round  numbers  105  million  square  kilometers  or  29.2 
per  cent,  of  the  entire  oceanic  surface  (Krummel-57: 188).  Its 
principal  distribution  is,  however,  in  the  Atlantic  Ocean,  where  it 
occupies  more  than  44  million  square  kilometers,  overshadowing  all 
the  other  deep-sea  sediments.  In  the  Indian  Ocean  31  million 
square  kilometers  of  bottom  are  covered  by  this  deposit,  but  in  the 
Pacific  it  covers  only  30  million  square  kilometers,  a  comparatively 
small  percentage  of  the  bottom  of  that  ocean. 

Fossil  Foraminiferal  Oozes.     Typical   foramini  feral  oozes  are 
found  in  fossil  form  mainly  in  the  chalk  of  the  west  of  Europe  and 


FIG.  105.     Globigerina  ooze,     x  20.     (After  Murray  and  Renard.) 

elsewhere.  Deposits  of  foraminiferal  shells,  of  large  benthonic 
types,  are,  however,  developed  in  other  horizons.  Such  are  the  Fu- 
sulina  limestones  of  the  Carbonic  and  Permic,  and  the  Nummulite 
and  Orbitoidal  limestones  of  the  Tertiary.  These  are  best  classed 
as  shell  rocks.  Chalk,  on  the  other  hand,  is  a  distinct  foraminiferal 
ooze,  a  calcipulverite,  but,  unlike  the  Globigerina  rock,  it  is  not 
formed  of  pelagic,  but  of  benthonic  or  bottom  types.  (Fig.  106.) 
Among  these  the  biserial  Textularia  holds  the  same  position  that 
Globigerina  does  in  the  modern  deposit,  while  another  benthonic 
form,  Rotalia,  is  also  common.  Pelagic  forms,  however,  are  not 
wholly  absent,  nor  should  we  expect  them  to  be.  Nineteen  species 
have  been  recognized  as  found  both  in  the  modern  Globigerina  ooze 
and  the  Cretacic  chalk,  but  this  identification  of  species  is  largely 
due  to  the  lack  of  distinctive  characteristics.  Coccoliths  also  are 


454 


PRINCIPLES    OF    STRATIGRAPHY 


common  in  the  chalk,  and  diatoms,  Radiolaria  and  sponge  spicules 
probably  were  as  plentiful  in  the  chalk  as  in  the  modern  deposits, 
but  these  siliceous  structures  have  since  been  dissolved,  and  the  sil- 
ica redeposited  as  flint.  Among  the  clastic  admixtures  quartz  is  also 
common,  indicating  the  neighborhood  of  land. 

The  principal  species  of  the  chalk  is  Tcxtularia  globulosa  (Fig. 
1 06,  a),  which  lives  to-day  in  the  estuary  of  the  Dee  near  Chester, 
but  of  course  forms  no  extensive  foraminiferal  deposits  there. 
(Murray-671477.) 

In  the  island  of  Malta,  Oligocenic  limestones  (Aquitanien)  oc- 
cur which  are  made  up  largely  of  pelagic  Globigerina,  and  nearly 


B 


Fia  106.  Preparation  of  white  chalk,  showing  the  foraminifera,  etc.  (After 
Zittel.)  A— Chalk  from  Sussex,  Eng.  B— Chalk  from  Farafrah, 
Libyan  desert.  Both  x  60.  a — Textularia  globulosa;  b — Rotalia 
(Discorbina)  marginata.  C — dried  residue  of  milky  chalk  water 
with  coccoliths.  x  700. 

40  per  cent,  of  the  species  of  this  rock  still  live  in  the  neighboring 
Mediterranean.  These  beds  further  contain  phosphate  concretions 
and  green  sands  such  as  characterize  the  modern  sea  bottom  .in 
depths  from  500  to  2,000  meters,  and  also  sharks'  teeth  similar  to 
those  found  by  the  Challenger  in  the  greater  oceanic  depths.  The 
percentage  of  lime  in  the  Globigerina  deposits  of  Malta  ranges 
from  95  to  98.6.  These  deposits  appear  to  have  been  formed  in 
the  greater  depths  of  a  mediterranean  rather  than  in  the  open  sea. 
Similar  foraminiferal  deposits  have  been  obtained  from  the  Plio- 
cenic  of  Sicily  and  Calabria. 

In  this  connection  it  must  be  noted  that  foraminiferal  limestones 
are  not  necessarily  deep-sea  or  even  submarine  deposits,  for  the 


CALCAREOUS   OOZES  455 

shells  of  littoral  species  may  be  washed  up  onto  the  shore,  where 
they  form  an  extensive  foramini feral  sand,  as  in  the  case  of  the 
Orbiculina  shells  of  the  Bahamas.  These  shells  may  then  be  blown 
inland  to  form  beds  of  foraminiferal  limestone  often  of  great  purity, 
at  a  distance  from  the  shore  on  the  dry  land.  Such  is  the  case 
with  the  limestone  of  Junagarh  on  the  Kathiawar  peninsula,  West 
India  (see  Chapter  XIII),  and  the  foraminiferal  limestones  of 
Jamaica  may  have  a  similar  history. 

Zoogenic  oolites.  Among  the  numerous  theories  advanced  to 
explain  the  origin  of  the  oolites  is  that  of  their  zoogenic  origin,  the 
role  of  oolite-former  being  commonly  assigned  to  Foramini f era. 
Thus  Ehrenberg  regarded  the  oolites  of  the  Jura  of  many  locali- 
ties as  formed  by  the  more  or  less  recrystallized  shells  of  Melonites 


FIG.    107.     Pteropod    ooze,      x    10.      (After    Murray    and    Renard.) 

(Mikrogeologie).  The  oolite-forming  organism  described  by 
Bornemann  as  Siphonema  incrustans  and  referred  to  alg^e  was 
relegated  by  Nicholson  to  the  Foraminifera  on  account  of  its  re- 
semblance to  the  recent  foramini feran  Syringamnina  fragilissima 
Brady,  while  Sorby  and  Withered  also  regard  it  as  a  foraminiferan, 
the  former  finding  its  resemblance  closest  to  Hyperamnina  vagans 
Brady.  This  organism  forms  oolites  in  the  Siluric  and  Devonic. 
The  oolites  of  the  Muschelkalk  regarded  by  Bornemann  as  due  to 
algous  growths  are  referred  by  Frantzen  to  zoogenic  origin,  as  lime 
separated  by  acid  of  the  animal  organisms.  By  others  these  same 
oolites  have  been  regarded  as  of  purely  hydrogenic  origin. 

Recent  Pteropod  Ooze.  (Fig.  107.)  This  is  found  in  only  a  few 
tropical  and  subtropical  regions  resting  like  the  foraminiferal  oozes 
upon  the  swells  and  submarine  ridges.  In  all  there  are  known  6 


456  PRINCIPLES    OF    STRATIGRAPHY 

genera  and  35  species  of  planktonic  pteropods  in  this  ooze,  but  only 
three  genera,  Limacina,  Clio  and  Cavolinia,  are  abundantly  repre- 
sented. With  these  occur  the  heteropods  Carinaria,  Atlanta  and 
Oxygyrus.  These  shells  make  up  from  one-quarter  to  one-half  the 
entire  mass,  the  remainder  being  chiefly  Foraminifera.  The  depth  at 
which  these  delicate  shells  occur  is  between  1,000  and  2,700  meters; 
below  this  they  give  way  to  purer  Globigerina  ooze.  In  the  Atlantic 
these  deposits  occur  especially  around  the  Azores,  on  the  outside 
of  the  Antilles,  west  of  the  Canary  Islands,  and  on  the  South  At- 
lantic rise  between  Ascension  and  Tristan  da  Cunha.  In  the  Indian 
Ocean  they  occur  off  the  African  coast  from  the  equator  to  Soko- 
tora,  and  to  the  west  of  Cape  Comorin  near  the  Nicobar  and  Men- 
tawie  Islands.  In  the  Pacific  they  surround  the  Fiji  Islands,  occur 
east  of  the  Great  Barrier  Reef,  around  the  Kermadec  and  Hawaiian 
Islands,  and  especially  in  the  region  of  the  Paumota  or  Low  Archi- 
pelago. The  total  area  covered  by  these  deposits  does  not  exceed 
one  and  a  half  million  square  kilometers. 

Fossil  Pteropod  Oozes.  These  are  known  from  various  hori- 
zons ;  in  the  Upper  Devonic  of  New  York  State  occurs  a  lime- 
stone composed  almost  entirely  of  Styliolina  fissurella,  embedded  in 
dark  shales,  which  are  sparingly  or  not  at  all  fossiliferous.  The 
limestone  varies  in  thickness  from  6  inches  to  a  few  feet,  and  has 
been  traced  from  the  Genesee  Valley  to  Lake  Erie,  a  distance  of 
over  sixty  miles.  Clarke  has  estimated  that  40,000  individuals  oc- 
cur on  the  average  in  a  cubic  inch  of  the  rock  ( 16 115) .  In  the  Cam- 
bric, beds  of  limestones,  largely  composed  of  Hyolithes  and  Ortho- 
theca,  occur,  and  some  Upper  Siluric  horizons  carry  layers  formed 
of  Tentaculite  shells  (Manlius  limestone  of  New  York,  etc.). 

Entomostracan  Oozes.  These  are  seldom  of  great  purity  as 
oceanic  deposits.  The  Ostracoda,  Crithe  and  Cythere  are  abun- 
dant among  the  plankton  of  the  ocean,  and  their  shells  are  found 
mingled  with  Foraminifera  and  pteropods.  No  pure  marine  ostra- 
cod  ooze  has  been  obtained  from  the  deep  sea.  These  organisms 
also  occur  in  salt  pools  (Cypris  salina,  etc.),  in  the  estuaries  of 
rivers  (Cypris,  Potamocypris,  Pontocypris,  Cythere,  etc.)  and  in 
fresh-water  lakes  and  pools.  At  the  Ayin  Musa  Springs  near  Suez, 
calcareous  deposits  are  formed  by  the  abundant  accumulation  of 
the  shells  of  Cypris  delecta  (Fraas-32  : 182).  Limestones  of  Cypris 
shells  have  also  been  found  in  the  fresh-water  Tertiary  deposits  of 
western  America.  Eolian  deposits  of  this  type  are  also  known. 

Coc eolith  and  Rhabdolith  Oozes.  Coccoliths  are  the  minute 
oval  plates  of  lime  which  cover  the  planktonic  Coccolithophora, 
small  algae  of  the  order  Calcocytea,  while  rhabdoliths  are  slender 


SILICEOUS    OOZES  457 

rods,  radially  arranged  in  the  Rhabdosphaera.  Both  are  members 
of  the  family  Coccolithophoridae,  of  the  order  Chrysomondacese, 
minute  organisms  referred  by  some  to  the  algae,  and  by  others  to 
the  Flagellata  among  the  Protozoa.  (See  Chapter  XXIV.)  They 
make  up  an  important  part  of  the  Globigerina  ooze  of  the  present 
day,  and  their  remains  also  abound  in  older  deposits.  In  the  North 
Atlantic  certain  dredgings  in  4,004  m.  brought  up  ooze  in  which 
coccoliths  formed  68  per  cent,  of  the  sediment.  Certain  chalks 
have  also  been  found  to  consist  almost  wholly  of  coccoliths  and 
rhabdoliths.  The  size  of  the  individual  coccolith  plates  ranges 
from  o.ooi  to  0.003  mm-  in  diameter,  and  Huxley  has  divided  them 
into  two  groups :  discoliths,  disk-shaped,  convex  on  one  side  and 
concave  on  the  other,  and  cyatholiths,  of  a  form  somewhat  resem- 
bling that  of  a  shirt  stud.  Minute  calcareous  disks  of  this  kind  are 
separated  out  of  a  solution  of  lime  sulphate  or  lime  chloride  by  the 
action  of  ammonia  generated  by  the  decomposition  of  organic  mat- 
ter, and  from  this  it  has  been  inferred  that  coccoliths  are  of  inor- 
ganic origin. 

2.     The  Siliceous  Oozes. 

These  comprise  the  radiolarian  and  diatomaceous  oozes,  the  first 
animal  and  the  second  plant  structures. 

Radiolarian  Oozes.  (Fig.  108.)  These  are  typically  abyssal  de- 
posits ;  the  shells,  owing  to  the  resistance  which  they  offer  to  solu- 
tion, can  sink  into  depths  below  those  at  which  foraminiferal  shells 
dissolve,  and  so  they  are  typically  found  associated  with  the  deep- 
sea  red  mud.  Indeed,  the  deposit  is  seldom  if  ever  free  from  the 
red  mud,  which  forms  a  sort  of  medium  in  which  the  radiolarian 
shells  are  embedded.  When  more  than  20  per  cent,  of  the  sediment 
is  made  up  of  Radiolaria,  it  is  called  a  Radiolarian  ooze.  The  most 
abundantly  represented  and  best  preserved  of  these  planktonic 
Radiolaria  are  the  Nessellaria  and  Spumellaria,  while  the  Phaeo- 
daria  are  more  sparingly  and  the  Acantharia  not  at  all  represented 
in  the  deposits,  though  abundant  in  the  plankton.  This  is  due  to 
the  fact  that  the  skeletons  of  the  last  group  are  not  siliceous,  but 
consist  of  acanthin,  which,  like  chitin,  is  readily  destroyed  after  the 
death  of  the  organism. 

The  Challenger  found  this  ooze  in  its  deepest  soundings  in  the 
western  Marian  deep  in  8,184  meters.  It  contained  54.4  per  cent, 
of  Radiolaria  and  other  siliceous  organisms,  3.1  per  cent,  of  pelagic 
and  o.i  per  cent,  of  benthonic  Foraminifera,  0.8  per  cent,  of  other 


458 


PRINCIPLES    OF    STRATIGRAPHY 


lime-secreting  organisms,  1.7  per  cent,  mineral  matter  and  40  per 
cent,  of  the  fine  red  mud. 

The  geographic  distribution  of  this  deposit  is  much  less  than 
that  of  the  Foraminifera,  the  total  area  covered  by  it  being  only 
something  over  12  million  square  kilometers,  or  3.4  per  cent,  of  the 
total  ocean  bottom.  It  seems  to  be  entirely  wanting  in  the  Atlantic, 
and  restricted  to  the  region  around  the  Cocos  and  Christmas 
islands  in  the  Indian  Ocean.  In  the  Pacific  it  finds  its  greatest  dis- 
tribution between  5°  and  15°  north  latitude,  and  between  Central 
America  and  165°  west  longitude.  A  few  other  isolated  patches  in 
the  Pacific  contain  this  deposit. 


FIG.  108. 


Radiolarian  ooze  from  the  Indian  Ocean,  x  40.  (After  Kriim- 
mel.)  i.  Tricyrtida;  2.  Dicyrtida;  3.  Discoidea;  4-  Prunoidea; 
5.  Larcoidea;  6.  Coronida;  7.  Sphseroida ;  8.  Chaetoceras  (Dia- 
tom) ;  9.  Sponge-spicules. 


Fossil  radiolarian  oozes  also  occur,  but  in  most  cases  it  may  be 
questioned  whether  they  are  really  deep-sea  deposits.  An  example 
is  the  radiolarian  rock  described  by  Rust  (75:181),  which  has  been 
regarded  as  of  deep-sea  origin,  but  Walther  has  insisted  that  the 
high  content  of  Carbonaceous  material  and  the  quantity  of  littoral 
sediments  oppose  this  view.  The  island  of  Barbados  also  furnishes 
a  colored  clay  which  contains  an  abundance  of  radiolaria  (Barbados 
earth),  and  this  has  been  regarded  as  a  deep-sea  deposit  similar 
to  that  found  in  the  Pacific  at  5,000  m.  and  now  brought  to  the 
surface  by  a  local  elevation.  Limestones  similar  to  the  modern 
Globigerina  ooze  also  occur  on  this  island. 


RADIOLARITES  .       459 

Radiolaria  have  been  found  in  cherts  of  various  ages  from  the 
Ordovicic  on,  and  some  of  these  cherts  are  believed  to  be  due  to 
the  segregation  of  silica  furnished  by  the  Radiolaria  and  other  silica- 
secreting  organisms. 

The  Jurassic  Radiolarite  of  the  Alps.  In  certain  portions  of  the 
Austrian  Alps,  a  remarkable  deposit  of  radiolarian  mud  is  found 
in  the  upper  Jura.  (Hahn-43,  i:j#p.)  This  radiolarite,  as  it  is 
called,  consists  of  intensely  blood-red,  more  rarely  greenish,  jaspery 
layers,  alternating  with  dense,  brown-red  or  greenish  gray  quartz- 
ose  and  argillaceous  marls,  the  total  having  a  thickness  varying  from 
i o  to  25  m.,  the  increase  being  due  to  increase  in  the  marly  layers. 
Under  the  microscope  it  appears  as  an  extremely  fine-grained,  al- 
most homogeneous  mud  rock,  filled  with  minute  spherical  crystal 
bodies,  referable  to  Radiolaria.  The  original  ornamentation  of  these 
bodies  is  seldom  preserved  in  the  argillaceous  layers,  but  the  jasper 
contains  Spumellarians  in  a  wonderful  state  of  preservation.  This 
rock  thus  appears  to  be  of  the  type  of  radiolarites  which  represent 
the  deep-sea  radiolarian  oozes,  and  are  found  to-day  in  depths  of 
from  3,000  to  7,000  meters. 

These  radiolarites  rest  on  Upper  Lias,  or  on  variegated  am- 
monite limestone  or  breccias  of  Middle  Liassic  age.  Some  indica- 
tions point  to  a  disconformable  relation  with  the  underlying  rock, 
there  being  apparently  ah  absence  of  Dogger  and  part  of  the  Malm. 
This  would  suggest  land  conditions  with  erosion  prior  to  sub- 
mergence, the  sinking  being  a  rapid  one  down  to  the  depths  at 
which  such  ooze  will  accumulate. 

Upward  the  radiolarite  passes  into  gray  calcilutytes  with 
Aptychus  of  Tithonic  age.  This  indicates  a  gradual  shoaling  of  the 
water,  which  culminated  in  land  conditions  in  the  next  succeeding 
period. 

Similar  deposits  of  Radiolarite  have  been  described  from  the 
Lower  Carbonic  beds  of  the  Rhine  district  ( Wilckens-92 :  J5^)  and 
from  various  parts  of  Great  Britain.  These  examples  of  older 
radiolarites  are  believed  to  be  of  shallow-water  origin.  Such  cherts 
are  well  shown  in  the  Carboniferous  (Mississippic)  limestone  series 
of  Gower  in  western  England  (Dixon  and  Vaughan-25  :  521).  They 
are  finely  and  sharply  laminated,  many  of  the  laminae  being  lenticu- 
lar or  wedge-shaped.  They  are  also  found  in  the  lower  Culm  of 
Devon  (Codden  Hill  beds),  from  which  they  were  first  described 
by  Hinde  and  Fox,  who,  however,  regarded  them  as  deep-sea  de- 
posits. From  the  nature  of  the  deposits  themselves,  as  well  as  from 
the  character  of  the  including  rocks,  others  have  come  to  the  con- 


460 


PRINCIPLES    OF    STRATIGRAPHY 


elusion  that  these  rocks  are  of  shallow-water  or  lagoon  origin 
(Dixon  and  Vaughan-25  '.522. ) 

The  Onondaga  coral  reefs  of  western  New  York  are  succeeded 
and  sometimes  replaced  by  very  cherty  limestones,  and  it  is  not  im- 
possible that  the  chert  layers  in  the  so-called  Corniferous  limestone 
represent  shallow-water  radiolarites  accumulated  in  the  lagoon  be- 
hind the  coral  reefs. 

Recent  Diatomaceous  Ooze.  (Fig.  109.)  This  is  a  phytogenic 
deposit,  but  is  best  considered  in  this  connection.  It  is  most  abundant 
in  the  ocean  in  the  higher  latitudes  of  both  hemispheres,  and  origi- 
nates from  the  phytoplankton  of  the  colder  and  less  saline  waters 
of  the  polar  regions.  The  diatom  frustules  of  the  ooze  obtained  in 
the  southern  hemisphere  belong  to  a  number  of  genera  (Navicula, 
Coscinodiscus,  Fragillaria,  Synedra,  Asteromphalus,  Rhizosolenia, 


FIG.  109.  Diatom  ooze,  x  200.  (After  C.  Chun.)  1-5.  Coscinodiscus;  6 
Asteromphalus ;  7.  Fragilaria  antarctica ;  8,  9.  Synedra ;  10.  Rhiz- 
osolenia; ii.  Chaetoceras;  12.  Navicula  (?);  13,  14.  Dictyochi  and 
Radiolaria. 

etc.),  and  associated  with  them  are  fragmentary  frustules,  Radio- 
laria, sponge  spicules,  lime  particles,  etc. 

These  sediments  form  a  circumpolar  belt  in  the  southern  hemi- 
sphere, and  likewise  form  a  band  across  the  northern  Pacific.  The 
southern  area  comprises  nearly  22  million  square  kilometers.  In  the 
tropical  regions  diatomaceous  sediments  also  occur.  They  have 
been  found  to  constitute  a  veritable  tripolite  or  infusorial  earth  at 
depths  from  2,700  to  5,200  meters  under  the  Peru  stream  between 
Callao  and  Galapagos.  Between  the  Marian  and  Philippine  Islands 
the  floor  of  the  Pacific  is  covered  in  patches  by  the  frustules  of  Cos- 
cinodiscus rex,  one  of  the  largest  known  forms,  with  a  diameter  of 
0.8  mm.  This  occurs  in  depths  ranging  from  4,500  to  6,000  meters. 
Altogether  about  23  million  square  kilometers  of  the  ocean  bottom, 


DIATOM  AND   PHOSPHATE  DEPOSITS  461 

or  about  6.4  per  cent,  of  the  entire  sea  floor,  are  covered  with  this 
deposit. 

Diatoms  likewise  live  in  fresh  water  and  deposits  of  diatomace- 
ous  ooze  may  form  under  such  conditions. 

Fossil  Diatomaceous  Earths  of  Both  Fresh  and  Salt  Water 
Origin.  These  are  widely  distributed  over  the  world,  especially  in 
Tertiary  deposits.  They  ordinarily  go  under  the  name  of  Infusorial 
earth  or  Tripolite,  so  named  from  the  deposits  at  Tripoli  in  North 
Africa.  The  most  extensive  is  that  found  at  Richmond,  Virginia, 
which  extends  for  many  miles,  and  is  in  some  places  at  least  40  feet 
in  thickness.  Other  deposits  are  found  in  the  Great  Basin  in  Ne- 
vada, Oregon,  and  California,  where  they  form  beds  of  great  thick- 
ness usually  interstratified  with  volcanic  material. 


PHOSPHATE  DEPOSITS. 

Guano.  A  subordinate  type  of  zoogenetic  rock  is  the  guano, 
formed  from  the  droppings  of  innumerable  birds  which  inhabit  iso- 
lated islands  and  promontories  on  the  sea  coast.  Near  Iquique, 
Province  of  Tarapaca,  Chile,  such  a  deposit  with  a  thickness  of  10 
meters  is  known,  and  it  is  estimated  that  it  may  have  formed  in 
1,100  years.  The  deeper  strata  of  these  formations  are  generally 
darker  in  color  and  more  crystalline.  Deposits  of  the  excrements  of 
seals  sometimes  alternate  with  those  of  birds  in  certain  places  on  the 
coast  of  Tarapaca.  Here  these  deposits  contain  numerous  smooth 
fragments  of  porphyry  from  3  to  10  cm.  in  length,  derived  from  the 
stomach  content  of  these  seals.  (Tschudi  in  Walther-Qor^j.) 

A  number  of  distinct  phosphate  minerals  are  found  in  guano. 

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92.  WILCKENS,    O.     1908.     Radiolarit    im    Kulm    der    Ottendorn-Elsper- 

Doppel-Mulde.     Zeitschrift    der    deutschen    Geologischen  Gesellschaft, 
Monatsblatt,  1908,  p.  354. 

93.  WIMAN,  KARL.     1897.     Ueber  Silurische  Korallenriffe.     Bulletin  of  the 

Geological  Institute  of  Upsala,  Vol.  Ill,  pp.  31 1-325,  pis.  8-10. 


CHAPTER    XL 

CHARACTER   AND    LITHOGENESIS    OF    ORGANIC    OR    BIOGENIC 
ROCKS— (CONTINUED).     PHYTOGENIC  DEPOSITS. 

Phytoliths,  or  rocks  formed  from  the  remains  of  plants,  may 
be  classed  with  reference  to  their  material  as  acaustophytoliths  and 
caustophytoliths.  The  latter  comprise  the  peats,  coals,  bitumens, 
etc.,  while  the  former  include  calcareous  or  siliceous  mineral  matter 
secreted  by  the  growing  organism.  With  reference  to  their  source 
of  origin,  phytoliths  may  be  classed  as  autochthonous,  or  such  as 
are  deposited  where  they  grew,  or  allochthonous,  those  brought 
from  other  localities  and  so  deposited  in  foreign  soil. 

Autochthonous  acaustophytoliths  have  been  mentioned  in  the 
preceding-  chapter,  in  the  growth  of  nullipores  on  coral  reefs,  and 
allochthonous  acaustophytoliths  have  been  described  in  the  diatoma- 
ceous  oozes.  In  this  chapter  we  shall  discuss  more  fully  the  two 
classes  of  phytoliths,  beginning  with  those  depositing  mineral  mat- 
ter other  than  carbon. 


ACAUSTOPHYTOLITHS. 

DEPOSITS  FORMED  BY  LIME-SECRETING  ALGJE.  Among  the  plants 
belonging  to  the  comparatively  low  division  of  algae  are  a  number 
which  secrete  carbonate  of  lime  or  silica  and  deposit  it  either  as  a 
coating  on  the  exterior  or  within  their  tissues. 

MODERN  MARINE  FORMS.  Among  the  lime-  and  silica-secret- 
ing algae  of  the  modern  ocean  the  following  may  be  especially  men- 
tioned. 

Order  Cyanophycea,  or  Blue-Green  Alg<z. 

This  order  contains  several  lime-secreting  members,  some  of 
which  become  important  as  rock  builders. 

Phytogenic  Oolites.     On  the  shores  of  Great  Salt  Lake,  Utah, 

467 


468  PRINCIPLES    OF    STRATIGRAPHY 

Rothpletz  (36)  has  noted  that  the  genera  Glceocapsa  and  Glceo- 
thece,  which  are  rich  lime-secreters,  form  snow-white  oolite  grains 
which  are  scattered  among  the  sand  and  pebbles  of  the  low  shores, 
and  blown  landward  into  dunes  ranging  up  to  6  feet  in  height. 
"The  cells  of  the  Gloeocapsa  are  2  ^  *  in  diameter  and  spherical, 
those  of  the  Glceothece  2  to  3  /x  thick  and  4  to  5  //,  long.  The  lime 
is  enclosed  in  the  alga-body  in  the  form  of  rounded  tubercles,  which 
often  mass  themselves  together  into  larger  irregular  tubercular 
bodies.  It  is  a  fine-grained  aggregate  of  calcite  which  always  en- 
closes numerous  dead  alga  cells  that  have  already  lost  their  green- 
ish coloring."  Three  forms  were  recognized:  ist,  irregular  tuber- 
cular bodies,  several  millimeters  in  diameter ;  2nd,  spherical  or  oval 
forms,  about  one-third  millimeter  in  diameter;  and,  3rd,  thin  rods, 
about  half  a  millimeter  long  and  one-tenth  millimeter  broad.  These 
oolites  are  forming  day  by  day  through  the  secretion  of  lime  by 
these  algae. 

Since  analysis  of  the  water  of  Great  Salt  Lake  (see  Chapter 
IV)  shows  only  a  small  quantity  of  calcium  chloride  or  sulphate 
and  no  carbonate,  no  lime  would  be  precipitated  from  the  lake  it- 
self, except  for  the  activities  of  these  minute  plants.  When  it  is 
considered,  however,  that  the  streams  tributary  to  this  lake  bring 
in  quantities  of  carbonate  of  lime,  all  of  which  is  precipitated  as 
oolite  grains,  it  becomes  a  question  whether  the  algous  growth  is 
so  active  as  to  use  up  all  this  lime  or  whether  "the  strong  brine  of 
the  lake  seems  to  be  incapable  of  holding  calcium  carbonate  in  solu- 
tion" (Clarke-8:/4<5)  and  it  is  therefore  precipitated  chemically.f 

Similar  oolites  are  forming  on  the  shores  of  the  Red  Sea,  where 
they  are  widely  distributed  along  the  west  coast  of  the  Sinai  penin- 
sula. Here  they  are  drifted  inland  often  for  many  kilometers,  or 
even  days'  marches  distant  from  the  shore,  and  constitute  white 
dune  sands  of  oolitic  material,  a  continental  formation  built  of 
material  of  marine  origin.  These  grains  generally  contain  vermi- 
form and  often  branching  canals,  more  or  less  filled  with  calcite. 

*  i  fj.  =  o.ooi  mm.,  called  a  micron. 

t  Of  the  rivers  tributary  to  Great  Salt  Lake,  the  following  may  be  noted 
with  their  percentage  of  CO3  and  Ca  (Clarke-8:J45): 

CO3  Ca 

A.  Bear  River  at  Evanston,  Wyoming 52 . 68  23 . 69 

B.  Bear  River  at  Corrine,  Utah ' 21 . 53  10. 12 

C.  Jordan  River  at  intake  of  Utah  and  Salt  Lake 

Canal 2 . 67  7 . 59 

D.  Jordan  River  near  Salt  Lake  City trace  10.26 

E.  City  Creek,  Utah 52-57  24 . 19 

F.  Ogden  River  at  Ogden,  Utah 33 .68  16.05 

G.  Weber  River  at  mouth  of  Canyon 40 .  oo  18.19 


PHYTOGENIC   OOLITES  469 

These  are  believed  to  be  due  to  the  presence  of  thread-like  algae 
living  symbiotically  on  the  lime-secreting  species  and  being  encased 
by  the  deposits  of  lime. 

In  the  low  coastal  tract  in  the  further  environs  of  Suez,  Quater- 
nary oolites  of  this  type  are  found,  built  up  subaerially  into  beds 
and  dunes  and  frequently  consolidated  into  hard  oolitic  limestones 
(Bauermann).  These  oolites,  however,  generally  contain  a  foreign 
sand  grain,  but  the  lime  surrounding  them  has  the  structure  of  the 
oolites  of  Great  Salt  Lake  and  on  solution  leaves  the  organic  resid- 
uum found  in  these. 

Some  observers  contend  that  the  oolites  of  the  Red  Sea  region 
have  a  radial  structure,  but  this  is  denied  by  others.  Linck,  more- 
over, holds  that  this  radial  structure,  when  it  occurs,  does  not  indi- 
cate organic  growth.  He  interprets  the  rods  as  minute  crystals  of 
aragonite  deposited  in  a  purely  hydrogenic  manner. 

Oolites  regarded  as  due  to  the  growth  of  algae  have  been  de- 
scribed from  the  salt  lakes  of  the  Kalahari  desert  of  Africa. 
(Kalkowsky-26.)  From  his  studies  Rothpletz  concludes  that  the 
"majority  of  the  marine  calcareous  oolites  with  regular  zonal  and 
radial  structure  are  of  plant  origin ;  the  product  of  microscopically 
small  algae  of  very  low  rank,  capable  of  secreting  lime."  (Roth- 
pletz-Cragin~36:^7p.)  On  the  other  hand,  Linck,  who'  approached 
the  subject  from  the  experimental  point  of  view,  is  equally  positive 
that  these  oolites  are  'wholly  of  chemical  origin,  deposited  either 
freely  or  upon  a  foreign  nucleus,  under  the  influence  of  chemical 
reaction,  as  aragonite  (really  ktypeit)  and  that  when  organic  re- 
mains, such  as  algae,  etc.,  were  enclosed  they  lived  upon  the  growing 
shells  of  inorganic  origin  or  were  mechanically  enclosed  by  the 
chemical  deposit.  The  algous  rods  (Algenstabchen)  of  Rothpletz 
he  regards  as  minute  crystals  of  aragonite.  The  aragonite  oolites 
are  subsequently  altered  to  calcite,  which  is  the  condition  of  most 
fossil  oolites.  (See  further  under  fossil  oolites,  posted,  p.  471,  and 
oolites  of  chemical  origin,  ante,  p.  336,  Chapter  IX.) 

Order  Chlorophycece,  or  Green  Alga. 

In  this  division  the  chief  lime-secreting  algae  of  the  modern 
sea  are  the  genera  Halimeda  and  Udolea  of  the  group  Siphonales. 
These  grow  in  the  shallower  portion  of  the  coral  reefs  connecting 
dead  coral  masses.  (Agassiz-i  :&?.)  Halimeda  opuntia  and  H.  tri- 
dens  form  masses  of  lime  on  the  shores  of  St.  Thomas.  (Challen- 
ger Narrative-7:/^7.)  It  is  a  jointed  plant  and  readily  broken  up 
into  small  lime  rods.  An  analysis  of  Halimeda  gave  CaCO3,  90.16%, 


470  PRINCIPLES    OF    STRATIGRAPHY 

MgCO3,  S-S%  ;  CaSO4  and  SiO2,  0.5%  ;  organic  matter  3.8%.  This 
alga  forms  extensive  limestone  deposits  within  the  lagoons  of  coral 
atolls,  as  in  the  case  of  Funafuti,  and  in  the  Red  Sea. 

Order  Phceophycece  or  Brown  Algce. 

This  division,  which  contains  the  great  algae  (Laminaria,  Ma- 
crocystis),  the  floating  Sargassum,  and  the  attached  rock  weed  or 
Fucus,  has  no  important  lime-secreting  members,  but  the  diatoms, 
important  on  account  of  their  siliceous  frustules,  belong  here.  Their 
general  character  and  importance  have  already  been  discussed  in 
the  preceding  chapter. 

Order  Rhodophycece  or  Floridecc — Red  Alga. 

This  division  contains  several  very  important  types  which  act 
in  part  as  rock-builders.  These  include  the  genera  Corallina,  Jania, 
Melobesia,  Lithothamnion,  and  Lithophyllum  and  they  are  dis- 
tributed from  the  equator  to  the  arctic  regions.  The  living  plant 
often  contains  as  much  as  85%  CaCO3  and  many  of  the  more  mas- 
sive ones  (Lithothamnion,  etc.)  build  heavy  barriers  on  the  outer 
zone  of  coral  reefs,  where  wave  activity  is  most  pronounced.  Litho- 
thamnion fasciatum  occurs  in  the  Arctic  Sea  on  the  coast  of  Nor- 
way at  a  depth  of  70  m.,  on  the  Russo-Lapland  coast  from  10 
to  55  meters,  at  Spitzbergen,  18-36  m.,  and  at  Nova  Zembla  in  45 
meters.  L.  polymorphic  and  Corallina  officinalis  are  found  on 
the  Great  Banks  in  22  m.  (Walther).  L.  racemus  forms  masses  of 
the  size  of  a  fist  in  the  Gulf  of  Naples  on  the  Secca  di  Gajola  in 
25  meters  depth,  while  the  smaller  L.  ramolosum  abounds  in  45  to 
60  meters  on  the  Secca  di  Benda  Palummo,  or  pigeon  bank.  (Wal- 
ther-5o  :^.?p ;  52:47.) 

In  the  Caribbean  Sea  nullipores  occur  down  to  depths  of  284  m. 
(Agassiz-2:/^/)  and  in  the  Gulf  of  Naples  Lithothamnion,  Coral- 
lina and  Lithophyllum  occur  at  depths  of  30  to  65  m.  (Wal- 
ther— 50 :22p. )  The  name  "Nullipore"  is  generally  applied  to  all 
these  lime-secreting  algae.  It  is  derived  from  the  old  Lamarckian 
genus  Nullipora,  which  included  four  species  of  calcareous  organ- 
isms, all  probably  belonging  to  the  family  Corallinaceae  of  the  re( 
algae. 

The  name  Lithothamnion  was  generally  applied  to  the  unseg- 
mented  coralline  algae,  but  has  more  recently  been  restricted,  while 
other  generic  groups — Lithophyllum,  Goniolithon,  Phyinatolithon, 
etc. — have  been  separated  from  the  original  group. 


CHARA   MARLS;    FOSSIL  OOLITES  471 

The  nullipores  are  often  the  most  important  lime-contributors 
to  the  coral  reefs,  far  more  important  than  the  corals  themselves. 
This  has  been  found  to  be  the  case  in  Funafuti  reef  (Finckh),  the 
Fiji  reefs  (Gardiner),  the  Chagos  group  (Gardiner),  etc.  In  all 
these,  animal,  especially  coral  life  is  relatively  unimportant,  while 
plant  life  (nullipores)  flourishes  luxuriantly.  (See  the  photograph 
of  a  Lithothamnion  reef  in  Nature,  Vol.  LXXII,  pp.  571,  572.) 

In  Bermuda,  too,  corals  play  a  subordinate  part  in  the  reef 
formation,  Lithothamnion  taking  its  place  among  the  principal  reef 
builders  (Agassiz-3).  Nullipores  also  grow  on  the  Challenger  Bank, 
raising  the  surface  from  considerable  depths  to  within  the  zones  of 
coral  growth.  (Howe-24.) 

LIME-SECRETING  ALG.E  OF  FRESH  WATER.  These  are  chiefly 
represented  by  Chlorophycese  of  the  family  of  the  Stoneworts  or 
Characea,  and  they  are  widely  distributed  in  the  fresh-water  lakes 
of  the  temperate  regions,  and  form  extensive  deposits  of  marl. 
Analyses  of  Chara  from  the  fresh-water  lakes  of  Michigan  showed 
that  something  over  0.61  gram  of  soluble  mineral  matter  occurs  in 
an  average  plant.  This  mineral  matter  is  nearly  94%  CaCO3  and 
is  deposited  as  an  encrustation  on  the  outside  of  the  plant.  This 
encrustation  renders  the  stems  and  branches  of  the  alga  almost 
white,  and  very  brittle.  On  the  average  from  50  to  80  plants  were 
found  on  a  square  decimeter  of  lake  bottom.  Extensive  beds  of 
marl  or  bog  lime  have  in  this  manner  accumulated  at  the  bottoms 
of  ponds  and  small  lakes.  (Davis-i4.)  Marl  beds  composed 
chiefly  of  the  remains  of  Chara  hispida  have  been  found  in  various 
parts  of  Scotland  and  elsewhere.  Extensive  deposits  of  "Characese- 
lime"  have  been  formed  in  the  lakes  of  Denmark  by  the  growth  of 
Chara.  (Wesenberg-Lund-56 1/55- 156. )  Such  deposits  are  also 
known  among  the  older  rocks.  The  organs  of  fructification  of  the 
Characeae  sometimes  accumulate  in  such  quantities  as  to  form  parts 
of  extensive  beds  of  limestones  in  both  recent  and  earlier  forma- 
tions. 

In  the  Devonic  of  Ohio,  and  in  other  formations,  occur  lime- 
stones often  to  a  large  extent  composed  of  small  spherical  and 
fluted  bodies  described  under  the  name  of  Calcisph&ra  robusta  Wil- 
liams. These  have  also  been  regarded  as  the  organs  of  fructifica- 
tion of  one  of  the  Characeae. 

FOSSIL  PHYTOLITHS  OF  ALGOUS  ORIGIN. 

FOSSIL  OOLITES.     These  occur  in  all  geological  horizons  either 
as  autochthonous  or  as  allochthonous  deposits.    The  latter  generally 


472  PRINCIPLES    OF  » STRATIGRAPHY 

show  evidence  of  wind  transportation,  as  in  the  case  of  modern 
oolite  dunes  of  the  Florida  coast,  the  shores  of  the  Great  Salt  Lake 
of  Utah,  and  the  coast  of  the  Arabian  Sea.  Such  transported  ma- 
terial generally  shows  eolian  cross-bedding,  a  feature  very  com- 
monly associated  with  fossil  oolites.  This  is  well  shown  in  the 
Siluric  oolites  of  Gotland  and  better  still  in  the  Jurassic  oolites 
of  England,  where  remarkably  fine  examples  of  wind  bedding  are 
seen. 

The  oolites  of  the  Upper  Siluric  (Monroan)  of  Michigan  have 
been  referred  by  Sherzer  (43)  to  an  origin  similar  to  that  of  the 
Great  Salt  Lake  oolites.  Rothpletz  regards  those  from  the  Lias  and 
the  Triassic  Wetterstein  Kalk  of  the  northern  Alps  as  due  to  algous 
growths.  From  the  Carbonic  of  England,  oolites  have  been  de- 
scribed and  referred  to  algous  origin.  The  same  is  true  of  the 
well-known  oolites  of  the  Jurassic  of  England  which  have  given 
many  of  the  formations  their  local  names  (Superior  oolite,  Great 
oolite,  etc.)  These  oolites  show,  according  to  Wethered  (58;  59), 
organic  structures  similar  to  those  described  by  Nicholson  and 
Etheridge  as  Girvanella  problematica  from  the  upper  Siluric  of  the 
Girvan  district  of  Ayrshire.  Both  oolites  and  pisolites  of  these  hori- 
zons show  often  a  concentric  encrustation  of  organic  fragments  by 
organisms  forming  flexuous  or  contorted  tubules.  Several  species 
have  been  distinguished  by  Wethered  (58),  among  them  Girvanella 
pisolithica,  which  forms  the  Peagrit  of  the  Inferior  oolite  and 
coralline  oolite. 

Rogensteine  of  the  Bunter  Sandstein.  The  remarkable  ooliths 
of  the  Bunt  Sandstein  of  North  Germany  known  as  Rogensteine 
have  been  described  in  great  detail  by  Kalkowsky  (27).  This 
author  restricts  the  name  oolith  to  the  rock  having  an  oolitic  struc- 
ture, and  proposes  the  term  "ooid"  for  the  individual  grains.  The 
diameter  of  the  ooids  never  falls  below  o.i  mm.,  though  smaller 
grains  occur  (0.1-0.5  mm.),  which  he  regards  as  ooids  in  the  mak- 
ing— "embryonic  ooids.*'  The  maximum  size  is  7  mm.,  only  one 
case  exceeding  that  having  been  known.  He  finds  in  all  cases  for- 
eign bodies  forming  the  nuclei  of  the  ooids,  these  bodies  being 
commonly  small  crystals  of  calcite,  or  again  scales  and  rods  of  a 
fine-grained  clay  slate.  Kalkowsky  finds  the  following  structures 
represented : 

1.  Concentric  structure,  layers  of  clear  calcite  of  varying  width, 
alternating  with  more  or  less  opaque  calcite  layers  carrying  im- 
purities of  clay. 

2.  Fine  radial  structure,  produced  by   radial  arrangement  of 
fine  threads  of  CaCO3. 


FOSSIL  OOLITES  473 

3.  Spindle  structure,  the  concentric  layers   are  traversed   by 
elongated  spindles  which  become  pointed  toward  the  periphery  and 
the  center  of  the  ooid,  the  structure  of  the  spindles  being  an  ir- 
regular mass  of  calcite  grains. 

4.  Cone  shaped,  conical  bodies  traverse  the  concentric  layers, 
their  points  at  the  center  of  the  ooid.     These  cones  are  built  up  of 
concentric  layers  of  a  radius  often  somewhat  smaller  than  that  of 
the  ooid  itself,  and  separated  by  interradii   containing  clay  and 
sand  and  having  a  somewhat  radial  structure. 

By  a  combination  of  these  structural  groups,  eight  or  nine  differ- 
ent ooid  types  were  produced.  Special  types  among  these  are  the 
roller  form,  the  hemiooids,  the  polyooids,  and  the  cystiform  ooids. 
These  ooids  are  held  together  by  a  cement  of  CaCO3.  Kalkowsky 
regards  these  structures  as  due  to  secretion  of  lime  by  minute  algae 
of  low  organization,  all  traces  of  which  are  destroyed  by  recrystal- 
lization. 

Walther  (53:^0)  suggests  that  the  Rogensteine  of  the  Bunt 
Sandstein  of  North  Germany  may  have  been  formed  in  salt  seas 
in  the  desert,  similar  to  those  now  forming  through  algous  growth 
in  the  Great  Salt  Lake  of  Utah,  and  in  the  Salt  Lakes  of  the  Kala- 
hari desert. 

The  stromatoliths  of  Kalkowsky  are  large  masses  of  calcareous 
material  having  a  stratified  as  well  as  fibrous  structure.  He  re- 
gards them  as  structures  similar  to  the  ooids,  only  vastly  larger 
and  growing  chiefly  in  one  direction,  i.  e.,  upward.  In  size  they 
are  found  up  to  one  meter  in  diameter,  and  they  often  form  beds 
of  considerable  extent. 

Alteration  of  Oolites.  Linck  (Chapter  IX)  finds  that  recent 
oolites  consist  or  have  consisted  of  aragonite,  and  that  fossil  oolites, 
so  far  as  investigated,  are  calcite,  from  which  he  concludes  that  al- 
teration to  calcite  is  a  change  which  all  oolites  undergo  with  lapse  of 
time.  It  may  also  be  briefly  noted  that  oolites  of  chemical  as  well  as 
organic  (phytogenic)  origin  may  be  altered  by  replacement  by  other 
minerals.  Thus  siliceous  as  well  as  iron  oolites  are  known,  both 
probably  due  to  replacement  of  calcareous  oolites.  Of  the  former 
a  good  example  is  found  in  silicified  oolites  of  the  salt  seas  of  the 
Kalahari  desert  in  Africa  (Kalkowsky-26),  and  in  the  Ordovicic 
limestones  of  central  Pennsylvania  (Ziegler-6i).  Of  the  latter  a 
typical  example  occurs  in  the  basal  iron  ores  of  the  Siluric  in  Wis- 
consin where  the  grains  are  regular  pellets  of  uniform  character, 
probably  of  phytogenic  origin.  Linck  holds  that  original  oolites 
(chemically  formed)  of  aragonite  are  saturated  with  iron  solutions, 


474  PRINCIPLES    OF    STRATIGRAPHY 

so  that  the  aragonite  is  changed  to  iron  carbonate  which   subse- 
quently alters  to  iron  oxide  as  outlined  by  Sorby  and  others. 

SPH^ROCODIUM  AND  GIRVANELLA  DEPOSITS.  In  the  Palaeozoic 
and  later  limestones  of  many  countries  are  found  rounded  masses  of 
lime  ranging  in  size  up  to  several  centimeters  and  referred  to  the 
genera  Sphaerocodium  and  Girvanella.  These  often  occur  in  suf- 
ficient abundance  to  constitute  a  large  part  of  the  rock  mass,  as  in 
the  case  of  the  Sphaerocodium  beds  of  the  Siluric  of  Gotland. 
Sphaerocodium  forms  rounded  masses  generally  coating  foreign 
bodies  and  consists  of  a  simple  network  of  unicellular  threads,  which 
result  in  the  formation  of  successive  shells  of  calcareous  tissue. 
The  genus  has  been -found  abundantly  represented  in  the  Siluric  of 
Sweden  and  in  the  Triassic  of  the  Alpine  region. 

Girvanella  consists  of  irregularly  twisted,  tubes  and  forms  ir- 
regular knobby  or  rod-like  masses,  also,  as  a  rule,  adhering  to 
foreign  bodies.  It  has  been  found  in  the  Ordovicic  of  England  and 
America  and  in  the  Carbonic  limestone  (Mississippic),  the  Superior 
oolite  and  the  Coralline  oolite  of  England. 

Other  algous  types  of  the  Palaeozoic,  with  similar  mode  of 
growth,  are  Siphonema,  found  in  the  Ordovicic,  and  Zonotrichites 
from  the  Rhaetic.  (Rothpletz-35 ;  37.)  Algae  have  also  been  de- 
scribed from  the  Trenton  limestone  of  New  York.  (Ruede- 
mann-38. ) 

FOSSIL  NULLIPORES.  The  fossil  nullipores  are  well  represented 
in  older  geological  formations.  As  already  noted,  the  Triassic  reefs 
of  the  Tyrol  are  regarded  by  many  as  chiefly  of  nullipore  origin. 
The  leading  alga  is  a  coralline,  Diplopora,  which  occurs  largely  as 
dissociated  joints  of  the  branches.  These  algae  are  closely  related 
to  the  living  Cymapolia,  which,  like  Halimeda,  is  a  jointed  siphona- 
ceous  member  of  the  Chlorophyceae  or  green  algae.  The  red  algae 
(Rhodophyceae)  are  also  well  represented  from  the  Jura  to  the 
Pliocenic,  some  fifteen  or  more  species  being  known  in  a  fossil  state. 
Sometimes  they  formed  extensive  encrustations  on  the  shores  and 
islands  of  ancient  seas,  as  in  the  case  of  the  Miocenic  Leythakalk 
of  the  Vienna  basin,  formed  chiefly  by  Lithothamnion  ramossimum 
Reuss.  This  nullipore  forms  bundles  and  mats  of  numerous  short, 
wart-like  or  club-shaped  branches  from  2  to  5  mm.  in  diameter.  As 
the  lime  is  in  the  form  of  calcite,  it  is  commonly  well  preserved  to- 
gether with  other  calcite  structures,  while  associated  fossils  of 
aragonite  are  for  the  most  part  dissolved  away  and  the  lime  re- 
deposited  as  calcite  among  the  algous  masses.  (See  Mojsisovics— 
29:498.) 

FOSSIL  CHARA,    Fossil  stems  and  fruits  of  Chara  are  responsible 


METHOD   OF   LIME   DEPOSITION  475 

for  many  fresh-water  limestones,  as  long  ago  pointed  out  by  Lyell. 
Such  a  fresh-water  limestone  was  described  by  him  from  a  com- 
paratively recent  deposit  in  Forfarshire.  In  the  Eocenic  of  the  Paris 
Basin,  Char  a  lyelli  is  rock- forming.  Chara-like  bodies  have  also 
been  discovered  in  abundance  in  Devonic  limestones  of  Ohio,  as 
above  noted. 


TRAVERTINE  AND  SILICEOUS  SINTER  FORMED  BY 
IN  HOT  SPRINGS. 

In  the  waters  of  hot  springs,  the  world  over,  algae  of  various 
types  have  been  observed  to  grow,  in  temperatures  ranging  from 
below  100°  to  200°  F.  (55).  In  the  hot  springs  of  the  Yellow- 
stone National  Park  they  occur  in  waters  between  the  temperature 
of  90°  and  185°  F.,  more  having  been  found  in  warmer  waters; 
but  in  California  they  have  been  found  in  waters  of  a  temperature 
of  200°  F.  These  algse  through  their  physiological  activities  sep- 
arate lime  or  silica  from  the  waters  of  these  hot  springs,  producing 
extensive  deposits  of  travertine,  or  of  siliceous  sinter,  according 
to  the  nature  of  the  spring  and  its  water.  Not  all  the  deposits  of 
travertine  or  siliceous  sinter  are  due  to  this  cause ;  many  are  of 
purely  hydrogenic  origin,  being  precipitated  from  the  water  by  loss 
of  pressure,  by  diffusion  or  by  abstraction  of  the  solvent  gases,  by 
evaporation,  or  by  chemical  reaction.  In  widely  separated  regions, 
however,  plants  have  been  found  active  in  the  separation  of  these 
mineral  matters  from  the  water — examples  being  the  travertine  de- 
posits of  the  Carlsbad  Sprudel  in  Bohemia,  and  the  hot  springs 
of  Yellowstone  National  Park,  in  the  United  States,  and  the  geyser- 
ite  or  siliceous  sinter  deposits  of  the  latter  region.  The  extensive 
sinter  deposits  of  Iceland  and  New  Zealand  are  probably  also  in 
large  part  due  to  algous  growth. 

METHOD  OF  LIME  DEPOSITION  BY  PLANTS. 

We  have  seen  above  that  lime  carbonate  is  held  in  solution  by 
the  excess  of  CO2  in  the  water  and  that  any  agent  which  causes 
the  abstraction  of  the  CO2  also  causes  the  precipitation  of  much  of 
the  calcium  carbonate.  Plants  obtain  the  carbon  of  which  their 
tissues  are  built  by  decomposing  the  carbon  dioxide  derived  either 
from  the  air  or  from  the  water,  according  to  the  mode  of  life  of 
the  plant.  It  is  thus  obvious  that  where  aquatic  life  is  abundant, 
much  CO2  will  be  abstracted  from  the  water,  and  thus  deposition 


476  PRINCIPLES    OF    STRATIGRAPHY 

of  the  lime  carbonate  is  brought  about.  Algae  are  most  effective 
in  this  respect,  different  algae  accomplishing  the  separation  in  differ- 
ent ways.  According  to  Dr.  Colin  (10),  who  studied  in  detail 
the  algous  limestones  of  the  Carlsbad  Sprudel,  the  lime  is  deposited 
first  in  minute  crystals  in  the  slime  between  the  vegetable  threads 
and  upon  their  surface.  At  first  these  crystals  are  separate,  but 
continued  growth  in  numbers  produces  star-like  clusters  which  by 
enlargement  grow  into  grains  of  calcareous  sand.  Further  growth 
results  in  the  union  of  the  grains  into  a  solid  mass  of  travertine. 

"The  exact  relation  of  the  crystals  and  grains  of  carbonate  of 
lime  varies  in  the  different  species  of  algae.  In  the  Oscillaria:  of 
Carlsbad,  and  allied  species,  the  crystals  form  in  the  slimy  intercel- 
lular tissue ;  in  Halimcda,  the  carbonate  of  lime  forms  a  sieve-like 
cover  about  the  tips  of  the  algae  filaments;  and,  in  Acetularia  it 
occurs  as  a  tube  about  the  stalk  of  the  plant.  In  the  Charae  the  lime 
is  separated  and  deposited  in  the  cells  and  cell  walls  of  the  back 
alone,  while  in  the  Corallines  [Corallina,  Lithothamnion,  etc.]  it 
is  found  only  within  the  cells."  (Weed-55  :<5//j.)  In  the  last  men- 
tioned types,  especially  in  Lithothamnion  and  allied  forms,  the 
surface  layer  alone  is  living,  the  lime  occupying  the  successive 
strata  of  dead  cells  beneath.  In  this  manner  thick  masses  of  lime- 
stone are  built  up.  Solution  of  the  lime  in  acid  sets  free  the  dead 
cell  walls  which  will  either  remain  behind  as  a  tangled  mass  of  fila- 
ments, or  float  as  pellicles  on  the  surface  of  the  solution.  Rothpletz 
found  this  to  be  the  case  in  the  green  fission-algae  secreting  the  lime 
of  the  oolites  as  well  as  in  the  red  algae,  which  form  extensive  lime- 
stone deposits. 

Where  calcium  carbonate  is  absent,  as  in  the  Great  Salt  Lake,  or 
occurs  only  in  small  quantities,  as  in  sea  water,  the  lime-secreting 
plants  decompose  the  calcium  chloride,  phosphate  or  sulphate  and 
deposit  it  within  their  tissues  as  carbonate.  The  same  is  believed  to 
be  true  of  many  animals,  which  take  the  lime  from  the  sea  water 
in  the  form  of  the  sulphate,  but  deposit  it  in  their  shells  and  skele- 
tons as  carbonate.  The  reaction  is  brought  about  through  the 
formation  of  ammonium  carbonate  as  a  decomposition  product, 
which  in  turn,  precipitates  the  calcium  in  the  form  of  carbonate 
from  the  solution  within  the  dead  cells. 


SEPARATION  OF  SILICEOUS   SINTER  BY   PLANTS. 

The  silica  is  at  first  deposited  in  and  upon  the  plants  in  the 
form  of  a  gelatinous  substance,  often  quite  brilliantly  colored,   in 


SEPARATION   OF   SILICEOUS    SINTER  477 

golden-yellow,  orange,  or  red,  and  in  the  hottest  waters  pale  flesh- 
pink  or  even  white.  "These  algae  are  often  so  thickly  encrusted 
by  silica  that  the  plant  structure  is  not  recognizable  even  under  the 
microscope,  and  their  presence  is  often  only  to  be  distinguished  by 
the  color."  (Weed-55  idj/.)  The  color  varies  with  the  temperature, 
so  that  in  the  differently  heated  portions  different  colors  obtain.  The 
order  of  color  from  progressive  cooling  is  white,  pale  flesh-pink, 
bright  orange,  yellowish-green,  emerald.  The  most  luxuriant  growth 
exists  in  the  pools  into  which  the  waters  flow,  where  leathery  sheets 
of  tough  gelatinous  material  with  .coralloid  and  vase-shaped  form 
abound.  In  some  cases,  the  algae  twelve  to  fifteen  inches  long  unite 
their  tops  into  a  solid  roof,  which  may  become  the  floor  of  a  second 
story  of  algous  growth  in  a  new  basin.  "The  exact  manner  in 
which  the  algae  of  these  waters  eliminate  the  silica  from  solution 
is  not  known,  but  the  process  appears  to  be  due  to  the  vital  growth 
of  the  plant,  for  both  the  algae  filaments  and  their  slimy  envelope 
are  formed  of  gelatinous  silica.  Upon  the  death  of  the  algae  which 
have  separated  this  jelly  from  the  spring  waters  there  is  a  loss  of  a 
large  part  of  its  water  and  a  change  to  a  soft,  cheesy,  but  more 
permanent  form.  This  dehydration  is  carried  still  farther  if  the 
silica  be  removed  from  the  water  and  dried,  but  if  allowed  to 
remain  in  the  cold  water  pools  there  is  a  further  separation  of  silica, 
possibly  due  to  organic  acids,  formed  by  the  decaying  vegetation 
reacting  upon  the  silica  salts  of -the  water.  This  hardens  the  exist- 
ing structures,  in  certain  cases,  and  generally  covers  the  pillars  with 
a  frost-like  coating  of  silica."  (Weed-55  -.664.) 

It  is  in  the  inner  dead  layers  of  the  algous  mass  that  the  gelatine 
hardens  first  into  silica,  the  outer  layer  continuing  alive.  Fibrous 
varieties  of  sinter  are  formed  in  many  of  the  Yellowstone  and  New 
Zealand  hot  springs  by  the  growth  of  the  algae  CalothrLv,  Mastigo- 
nema,  and  Leptothrix,  the  first  two  producing  a  "furry"  sinter  in 
strata  from  a  sixteenth  of  an  inch  to  half  an  inch  thick,  the  last 
forms  fibrous,  straw-like  masses. 

Mosses  and  diatoms  have  also  been  found  active  in  separating 
out  the  silica  of  the  hot  springs  of  the  Yellowstone.  The  moss 
(Hypnum  a  dun  cum  var.  grasilescens,  Br.  &  Sch.)  grows  on  the 
lower  parts  of  the  slopes  where  the  water  is  cooled  to  blood  heat, 
and  has  lost  much  of  its  lime  and  part  of  its  silica.  The  silica  is 
abstracted  from  the  water  by  the  physiological  activities  of  the 
plant  and,  in  turn,  encloses  and  buries  the  moss.  Diatoms  are  espe- 
cially active  in  the  tepid  marshes,  Denticula  valida  being  the  pre- 
dominant type,  though  a  number  of  other  species  occur.  Extensive 
beds  of  diatomaceous  earth  are  formed  by  their  siliceous  skeletons. 


478  PRINCIPLES    OF    STRATIGRAPHY 

VEGETAL  DEPOSITS.    (CAUSTOPHYTOLITHS.) 

The  actual  accumulations  of  vegetal  matter  in  the  strata  of  the 
earth's  crust  are  perhaps  of  even  greater  significance  than  the  lime 
and  silica  deposits  caused  by  plants.  There  are  few  horizons  which 
have  not  some  kind  of  plant  deposit  in  the  form  of  carbonaceous 
material.  They  occur  even  in  the  Algonkian,  where  a  bed  of  an- 
thracite two  meters  thick  is  found  in  the  upper  part  of  the  middle 
Algonkian  or  Jatulian  formation  north  of  Lake  Onega  in  Finland. 

As  already  noted,  Caustophytoliths  have  been  divided  into  those 
formed  from  plants  living  where  their  remains  are  found  to-day, 
autochthonous  Caustophytoliths,  and  those  transported  to  their  pres- 
ent place  of  occurrence,  or  allochthonous.  Autochthonous  caus- 
tophytoliths  may  be  terrestrial  or  aquatic,  according  to  the  condition 
of  life  of  the  plants,  i.  e.,  whether  land  or  aquatic  plants.  Alloch- 
thonous Caustophytoliths  are  primarily  allochthonous,  when  the  ma- 
terial of  which  they  were  made  was  transported  in  the  living,  or  at 
least  undecomposed,  condition  to  the  place  where  it  is  now  found, 
and  secondarily  allochthonous,  when  transportation  occurred  after 
the  plant  had  become  a  caustophytolith. 

Modern  autochthonous  deposits  of  vegetal  matter  are  found  in 
the  sea,  especially  in  enclosed  bodies  of  sea  water,  in  marine 
marshes,  fresh  water  swamps,  and  in  bogs  and  wet  woods.  Alloch- 
thonous deposits  may  be  found  embedded  in  marine,  lacustrine,'  flu- 
viatile  or  even  aeolian  deposits. 

PETROGRAPHICAL  TYPES  OF  VEGETAL  DEPOSITS. 
As  noted  in  Chapter  I,  vegetal  deposits  may  occur  in  one  or  another 
of  the  following  types:  I,  Sapropeliths ;  2,  Humuliths;  and,  3, 
Liptobioliths.  Each  of  these  groups  will  be  considered  at  some 
length. 

SAPROPELITHS. 

These  are  accumulations  of  the  decaying  organic  tissues  of 
aquatic  animals  and  plants  at  the  bottom  of  the  sea,  or  in  fresh 
water  lakes  and  ponds.  In  the  unconsolidated  state  it  is  a  foul  or- 
ganic slime  (Faulschlamm) ,  or  slime  of  decomposing  organic  mat- 
ter derived  from  the  water.  In  so  far  as  plants  contribute  to  this 
slime,  it  is  of  algous  origin,  since  any  deposit  formed  by  higher 
plants  normally  belongs  to  the  next  type,  the  humuliths.  The  chief 
chemical  difference  between  such  sapropelitic  material  and  that 
formed  by  land  and  swamp  plants  is  the  higher  fat  and  protein 
content  of  the  former.  Sapropeliths  accumulate  only  in  relatively 


SAPROPELITHS  479 

quiet  waters,  since  strong  agitation  of  the  water  results  in  the 
inclusion  of  much  oxygen  and  the  consequent  complete  oxidation  of 
the  organic  matter — a  feature  observed  in  strongly  agitated  lakes. 

The  decaying  vegetal  matter  rarely  accumulates  in  any  great 
quantity  as  an  absolutely  pure  caustobiolith.  Most  commonly  inor- 
ganic or  organic  mineral  impurities  are  present  in  greater  or  less 
quantity.  Among  them  clay  or  mud  is  often  a  very  important 
constituent,  forming  argillaceous  sapropeliths  (if  the  clay  is  of 
small  amount)  or  more  commonly  sapropelargilliths  or  in  general 
sapropellutytes.  Lime  of  clastic  or  organic  origin  may  form  the 
admixture  producing  sapropelcalc  rocks  (sapropelitic  calcilutytes, 
sapropelitic  calcipulverytes,  etc.),  while  silica,  especially  that  of 
diatoms,  produces  a  siliceous  or  diatom  sapropelith.  Marine  sapro- 
pelargillites  are  common  on  many  shallow  sea  coasts,  especially  in 
protected  areas,  where  they  constitute  deposits  of  black  mud.  These 
mud  flats  exposed  at  low  tide  are  extensive  generators  of  hydrogen 
sulphide,  which  leads  to  the  precipitation  of  sulphides,  especially 
those  of  iron.  In  this  way  the  foundations  are  laid  for  the  forma- 
tion of  highly  carbonaceous  lutytes  or  black  shales  rich  in  iron 
pyrites  and  with  the  remains  of  a  more  or  less  depauperate  fauna. 
Such  deposits  are  forming  in  the  estuaries  along  the  Atlantic  coast, 
and  in  a  fossil  state  these  seem  to  be  represented  in  part  at  least  by 
the  Devonic  Genesee  shale  of  New  York  State.  They  are  further 
forming  in  the  lagoons  behind  the  coral  reefs  of  Florida,  and  in  a 
fossil  state  these  are  represented  by  the  Middle  Devcnic  Marcellus 
shale  of  New  York,  and  perhaps  to  a  certain  extent  by  the  Utica 
shales  of  eastern  North  America.  Again  they  are  forming  to-day 
in  the  depths  of  the  Black  Sea,  and  this  type  appears  to  be  repre- 
sented by  the  Permic  Kupferschiefer  of  Thuringia,  and  possibly 
the  oil  shales  of  the  Calciferous  series  (Lower  Carbonic)  of  Scot- 
land. The  Posidonia  shales  of  the  Jurassic  of  Europe,  and 
some  of  the  Upper  Devonic  (Portage)  shales  of  New  York  have 
also  been  interpreted  on  this  basis.  (Pompeckj-3i  and  Clarke-Q.) 
This  interpretation  is,  however,  questionable.  The  black  shales  of 
southern  United  States,  i.  e.,  the  Chattanooga,  are  probably  more 
nearly  referable  to  the  class  of  argillaceous  humuliths.  The  various 
fossil  sapropellutytes  furnish  oil  on  distillation  and  may  in  part  be 
the  source  of  the  petroleum  in  the  underlying  rocks. 

Purer  sapropeliths  from  the  Tertiary  are  known  as  Dysodil 
(Greek  <W<o8r;s  =  ill-smelling),  on  account  of  their  bad  odor  on 
burning.  Carbonic  sapropeliths  are  represented  by  Cannel  coal,  a 
characteristic  of  which  is  that  it  burns  with  a  bright  flame.  Both 
Dysodil  and  Cannel  coal  are,  however,  commonly  impure,  the  im- 


480 


PRINCIPLES    OF    STRATIGRAPHY 


purity  or  "ash"  being  primary,  i.  e.,  due  to  the  non-burnable  mineral 
matter  originally  a  part  of  the  plants,  or  secondary,  due  to  the  ad- 
mixture of  foreign  material,  either  mechanical  sediment  or  chemi- 
cal precipitate.  Though  rare,  absolutely  pure  sapropelitic  deposits 
occur.  According  to  the  stage  of  consolidation  and  age,  these  have 
received  distinct  names,  as  shown  in  the  first  columns  of  the  sub- 
joined table  after  Potonie  (32:55). 


Pure 
Sapropeliths 

With  admixture  of  organic 
lime  or  silica 

With  admixture  of  clastic 
material,  clay  or  sand 

Sapropelite 
(unconsolidated) 

(sapro  +pel) 

Saprocollyte 
(hardened  sapro- 
lite) 

(sapro+colla,  glue) 

Calcareous  sapro-  Diatom- 
pelite                     pelite 
Sapropelitic  cal- 
ciliths 

Argillaceous  (and  arena- 
ceous) sapropelite  and 
sapropelitic    argillyte 
or  microarenyte 

Recent  and  subfossil 
sapropeliths 

Diatomaceous-calc   sapro- 
pelite and  Diatomaceous 
sapropelcalcilith      (often 
also     containing     clayey 
sediment,  etc.) 

Saprodittyte 
(pure  Dysodil) 

(sapro    +    odemeis, 
odor) 

SapantTiraconyte 
(sapro  -1-  anthrax, 
coal  =  sapropelite 
coal,  *.  e.,  purest 
cannel  coal 

Bituminous  marl,   shales, 
etc. 

Most  bituminous  calcilytes 

Most  bituminous  argillites 
and  argillaceous  lutytes 
(ex.  Jurassic  Posidonia, 
shales) 

Zechstein      Marl      shales 
(Kupferschiefer) 

Fossil  sapropeliths 

In  the  purest  state  largely  or  almost  entirely 
biogenic  and  therefore  aquatic — autochtho- 
nous formations,  i-  e.,  produced  through 
autochthonous  sedimentation. 


Allochthonous,  with  ref- 
erence to  the  lutaceous 
or  finely  arenaceous  con- 
stituents, but  autoch- 
thonous, with  reference 
to  the  organic  constitu- 
ents, therefore  produced 
by  allochthonous  and 
autochthonous  sedimen- 
tation. 

Petroleum.    Among  the  fossil  sapropelytic  substances  petroleum 
takes  the  first  rank.     It  is,  however,  to  be  regarded  as  a  diagenetic 


CANNEL    COAL  481 

product  from  sapropelytes,  the  result  of  distillation.  Both  animal 
and  plant  remains,  especially  algae,  are  now  generally  regarded  as 
the  material  from  which  petroleum  is  distilled,  and  the  rocks  rich 
in  such  deposits,  namely,  the  sapropelytic  rocks,  must  therefore 
form  the  mother  rock  of  petroleum  of  organic  origin. 

Sapanthraconyte  or  Cannel  Coal.  This  has  an  amorphous 
structure  and  a  clull  luster  of  a  greasy  or  silky  character,  quite  dis- 
tinct from  the  luster  of  true  coal.  The  contrast  is  well  shown  by 
the  carbonized  remains  of  the  rhizomes  of  plants  preserved  in  the 
fossil  slimes  of  ancient  marsh  bottoms.  Thus  stigmaria  embedded 
in  cannel  coal  will  show  the  bright  luster  of  true  coal  in  contrast 
with  the  duller  cannel  coal.  The  vertebraria  or  rhizomes  of  Glos- 
sopteris  occurring  in  the  Petroleum  shales  of  the  Southern  Per- 
mic  show  a  similar  Contrast.  Cannel  coal  is  found  in  America  in 
the  Carbonic  of  Ohio,  Indiana,  and  especially  eastern  Kentucky, 
where  Breckenridge  is  a  noted  locality.  It  is  especially  valuable 
for  the  manufacture  of  gas  on  account  of  its  abundance  of  volatile 
hydrocarbons.  Remains  of  fishes,  crustaceans  (Cypris),  meros- 
tomes  (eurypterids),  etc.,  and  more  rarely  amphibians,  are  found 
in  some  localities,  these  in  most  cases  being  fresh-water  species. 
At  Linton,  Ohio,  more  than  50  species  of  fishes  and  amphibians 
were  found  in  the  cannel  coal.  Analyses  of  cannel  coal  gave  the 
following  results.  (Dana-n  1662.) 

(For  comparison  analyses  of  anthracite  and  of  bituminous  coal 
are  given)  : 

Locality  C  H  O  N  S  Ash 

Cannel  coal  from  Brecken- 
ridge, Hancock  Co.,  Ky. .  68.13  6.49  5.83  2.27  2.48  12.30 

Cannel  coal  from  Wigan.  ..   80.07  5-53         8-IQ        2-12         i-5<>        2.70 

Cannel  coal  or  "Torbanite" 

from  Scotland 64 . 02  8 . 90  5 . 66  0.55  o .  50  20 . 32 

Anthracite  coal  from  Penn- 
sylvania   92.59  2.63  1.61  0.92  ....  2.25 

Bituminous  "non- caking" 

coal  from  Brier  Hill,  Ohio.  78.94  5.92  11.50  1.58  0.56  1.45 

Microscopic  algae  are  often  well  preserved  in  cannel  coals.  Pol- 
len of  Cordaites  spores,  wood  and  numerous  algae  were  found,  to- 
gether with  fish  remains,  Crustacea  and  coprolites  in  the  "Boghead" 
or  Permic  cannel  coal  of  Autun  (Bertrand-4).  Cannel  coal  and 
ordinary  (humus)  coal  are  often  associated,  the  sapropelites  form- 
ing the  foundation  for  the  growth  of  land  or  swamp  plants.  Thus 
a  layer  of  cannel  coal  will  often  underlie  one  of  bituminous  or  of 


482  PRINCIPLES    OF    STRATIGRAPHY 

anthracite  coal,  and,  moreover,  the  two  may  become  interstratified, 
the  one  or  the  other  predominating,  according  to  the  length  of  time 
during  which  the  conditions  responsible  for  either  existed.  Where 
the  beds  are  relatively  thin  the  coal  is  spoken  of  as  banded  cannel 
or  bituminous  coal,  as  the  case  may  be.  A  section  from  Reckling- 
hausen  in  Westphalia  illustrates  a  complex  relationship.  In  de- 
scending order  we  find : 

5.  Bituminous  coal about  10  cm. 

4.  Banded  coal about  95  cm. 

3.  Cannel  coal about  8-15  cm . 

2.  Banded  coal about  10  cm. 

i.  Cannel  coal about  i . 3  m. 

This  section  shows,  first,  a  water  body  in  which  algse  and  other 
truly  aqueous  plants  lived  and  accumulated  as  decomposition  slime, 
followed  by  marshy  conditions  with  growth  of  higher  plants,  but 
with  repeated  inundations  to  furnish  the  decomposition  slime  from 
which  the  bands  of  cannel  coal  were  formed.  This  is  followed  by  a 
second  period  of  complete  submergence,  with  the  formation  of  can- 
nel coal.  Then  the  alternating  conditions  were  repeated,  with  the  re- 
sult that  more  banded  coals  were  formed,  and  the  area  was  finally 
converted  into  a  marsh  or  moor  with  the  formation  of  pure  bitumi- 
nous or  gas  coal. 

The  algous  origin  of  cannel  coals  has,  however,  been  seriously 
questioned  by  Jeffrey  (25).  He  finds,  on  the  basis  of  numerous 
well-prepared  microscopic  sections  from  widely  separated  regions, 
that  the  organisms  found  in  abundance  in  boghead  coals  are  not 
of  the  nature  of  colonial  gelatinous  algae,  as  has  been  asserted  by 
Renault,  Bertrand  and  Potonie,  but  are  spores  of  vascular 
cryptogams.  This,  Jeffrey  holds,  also  overthrows  the  algal  hy- 
pothesis of  the  origin  of  petroleum  and  similar  substances,  these  in- 
stead having  been  mainly  derived  from  the  waxy  and  resinous 
spores  of  vascular  cryptogams  laid  down  on  the  bottoms  of  shal- 
low lakes  during  the  coal  period.  'These  lacustrine  layers,  either 
as  cannels,  bogheads,  or  bituminous  shales,  according  to  the  sporal 
composition  and  the  admixture  of  earthy  matter,  are  the  mother 
substance  of  petroleum.  Pressure  and  temperature  either  separ- 
ately or  combined,  in  the  presence  of  permeable  strata,  have  brought 
about  the  distillation  of  petroleum  from  such  deposits."  (Jeffrey- 
25:^90.) 

Jet  (Ger.  Gagat,  Fr.  jais,  and  jayet).  This  mineral,  for  which 
Giimbel  suggested  the  name  gagatite,  is  a  sapropelith  obtained  in 
black  sapropelargillytes  of  Mesozoic  and  younger  formations.  What 


JET;   BLACK   SHALES  483 

are  perhaps  the  most  important  deposits  are  found  in  the  Liassic 
rocks  (zone  of  Ammonites  serpentinus)  of  Yorkshire,  England, 
being  especially  obtained  near  Whitby,  where  it  is  mined  and 
wrought  into  all  sorts  of  ornaments  and  toys,  and,  together  with 
the  famous  ammonites  of  the  same  formation,  sold  as  native  curiosi- 
ties. -The  jet  here  occurs  in  thin  lenticular  masses  between  the 
layers  of  the  hard  bituminous  shale  (sapropelargillyte)  and  occa- 
sionally shows  under  the  microscope  the  structure  of  coniferous 
wood,  referred  to  araucarians.  Scales  of  fish  and  other  organisms 
of  jet  rock  are  frequently  impregnated  with  this  bituminous  matter, 
which  may  replace  the  original  tissues.  Drops  of  liquid  bitumen  are 
also  found  in  the  cavities  of  some  of  the  fossils.  Petroleum  and 
inflammable  gases  are  likewise  associated  with  jet  deposits  and  iron 
pyrite  occurs,  often  replacing  the  fossils.  The  Lias  of  Wiirttem- 
berg  in  Germany  also  furnishes  jet,  especially  the  Posidonia  shale, 
which  is  of  the  age  of  the  Whitby  beds.  Of  the  same  age  is  the 
shale  furnishing  the  original  deposits  on  the  river  Gagas  in  ancient 
Lycia,  Asia  Minor.  Jet  has  also  been  obtained  from  Tertiary  de- 
posits. 

Jet  is  characterized  by  its  hardness,  which  is  greater  than  that 
of  asphalt,  its  conchoidal  fracture,  and  by  the  fact  that  it  is  less 
brittle  than  anthracite,  and  is  susceptible  of  a  high  polish.  Its  com- 
mon association  with  driftwood  leads  to  the  supposition  that  its 
chief  source  is  carbonized  wood  enriched  by  secondary  impregnation 
with  bituminous  matter  obtained  from  sapropelite.  Analysis  of  the 
jet  from  Holznaden,  Wiirttemberg,  gave  C  71.0%,  H  7.7%,  O 
23-3%>  N  trace,  S  trace,  Ash  0.9-2.9%. 


Black  Shales. 

Many  black  or  blackish  blue  shales  of  various  horizons  show 
characters  which  stamp  them  as  sapropelargillites.  The  best  known 
of  these  is  the  Posidonia  shale  of  the  West  European  Upper  Lias 
(Lias  €  ).  This  shale,  so  named  from  the  abundance  of  the  pe- 
lecypod  Posidonia  bronni,  Voltz,  is  typically  developed  in  Wiirttem- 
berg, where  especially  the  locality  of  Holzmaden  near  Stuttgart 
has  become  famous  on  account  of  the  wonderful  preservation  of  the 
great  marine  saurians  found  in  these  shales.  Other  localities  are 
Whitby  and  Lyme  Regis  in  England.  The  wide  distribution  of  this 
formation,  as  well  as  its  organic  contents,  proves  it  to  be  of  marine 
origin,  though  from  the  nature  of  the  occurrence  of  the  fauna,  as 


484  PRINCIPLES    OF    STRATIGRAPHY 

well  as  the  character  of  the  rock,  it  must  be  assumed  that  the 
regions  were  not  open  sea,  but  a  coast  lagoon  or  perhaps  a  marginal 
epicontinental  sea,  laid  bare  to  some  extent  at  low  tide  with  the 
formation  of  extensive  mud  flats  on  which  were  stranded  animals 
and  plants  drifted  in  from  the  sea,  and  washed  from  the  land.  The 
fact  that  the  lower  side  of  the  fossils  is  generally  better  preserved 
than  the  upper  shows  that  the  organisms  were  partly  embedded  and 
corroded  on  the  exposed  surfaces  by  the  acids  generated  on  the 
mud  flats  from  the  decaying  organic  matter.  Had  the  water  been 
deep,  the  carcasses  of  the  Ichthyosaurians,  etc.,  could  not  have  been 
stranded  in  the  mud,  but  would  probably  have  continued  to  float 
until  they  were  cast  on  the  shore  or  until  decay  had  brought 
about  the  dissociation  of  the  skeletal  elements,  which  would  then 
become  scattered  on  the  bottom.  Instead  of  this,  not  only  are  they 
intact,  but  the  skin  of  the  Ichthyosaurians  has  been  found  as  a  car- 
bonaceous film  surrounding  the  skeleton  in  its  normal  relationship. 
Besides  these  saurians  numerous  well  preserved  Pentacrini  are 
found  which  were  carried  into  those  water  bodies  attached  to  drift- 
wood. Gastropods,  worms,  cephalopods,  and  crustaceans  also  occur, 
and  fish  are  likewise  common  and  well  preserved.  Land  plants, 
conifers,  and  cycads  abound,  and  land  animals,  especially  insects 
and  pterosaurs,  also  occur.  The  driftwood  is  commonly  trans- 
formed into  jet,  by  the  secondary  enrichment  of  the  decaying  wood 
by  bituminous  matter  from  the  mud.  Besides  these  macroscopic 
remains,  the  shale  abounds  in  microscopic  fossils  of  sponges  (?) 
(Phymatoderma),  Foraminifera,  coccoliths,  and  diatoms  (  ?).  Other 
black  shales  of  a  similar  origin  are  probably  found  in  the  Devonic 
Ohio  black  shale  with  its  rich  fish  fauna,  and  the  Upper  Devonic 
black  shales  of  New  York.  The  Marcellus  shale  of  New  York  has 
already  been  referred  to  as  a  similar  sapropelargillyte,  but  formed 
in  the  lagoons  behind  the  Onondaga  coral  reef.  The  oil  shales  of 
Australia,  with  the  rhizomes  of  Glossopteris,  the  so-called  "vertebra- 
ria"  often  replaced  by  or  transformed  into  jet,  also  belong  here. 
Finally,  it  must  be  emphasized  that  black  shales  also  are  formed 
by  the  decay  of  land  and  swamp  plants  and  that  these,  therefore, 
belong  more  truly  with  the  true  coals  and  other  humuliths.  (See 
page  513.) 


Sapropelcalcilyths,  Sapropelsilicilyths,  and   Sapropelferrilyths. 

Bituminous  or  asphaltic  limestones  are  formed  when  lime  sands 
or  muds  or  organic  calcipelytes  are   deposited  along  with  much 


HUMULITHS  485 

organic  matter,  either  animal  or  plant.  Fusulina  limestones  often 
contain  asphaltic  material  in  abundance,  and  the  same  is  true  to  a 
certain  extent  of  Stromatopora  limestones,  where  the  organic  matter 
may  be  represented  by  concentric  films  of  asphaltum  or  other  bitu- 
minous matter.  Nummulitic  as  well  as  nullipore  limestones  may,  in 
like  manner,  have  a  bituminous  constituency.  The  finest  calcilutytes 
are  often  impregnated  with  bituminous  matter,  especially  if,  as  in 
the  Upper  Cambric  of  Sweden,  they  are  intercalated  in  bituminous 
shales  (sapropelargyllites).  Such  rocks  when  struck  with  a  ham- 
mer give  out  a  fetid  odor  which  causes  them  to  be  classed  as  fetid 
limestones,  or  "stinkkalk."  Metamorphism  of  limestones  o'f  this 
type  would  result  in  the  production  of  graphitic  marbles.  Sapro- 
pelites  in  which  silica  forms  the  leading  accessory  constituent  are 
represented  by  diatomaceous  oozes  in  which  the  decay  of  the  or- 
ganic matter  has  produced  the  bitumen.  The  Eocenic  Menilite 
shales  of  the  Paris  basin  and  the  Oligocenic  Menilite  shales  of 
Galicia  are  typical  examples.  The  latter  might  perhaps  be  regarded 
as  the  source  of  the  petroleum  of  that  region.  Sapropelferrilytes 
are  bituminous  iron  carbonates  such  as  are  deposited  under  certain 
conditions  in  some  bogs. 


RECENT  HUMULITHS. 

These  are  formed  by  the  growth  in  situ  of  plants,  either  such 
as  grow  on  the  land  or  those  living  in  marshes  and  swamps  (autoch- 
thonous) or  formed  from  material  rafted  or  drifted  together  (al- 
lochthonous).  Marshes,  swamps,  and  bogs  are  the  chief  sites  of 
accumulation  of  such  deposits  at  the  present  time,  and  a  consid 
eration  of  these  must  precede  the  discussion  of  the  older  deposits  of 
humuliths,  i.  e.,  the  coals. 

In  general  we  may  adopt  the  word  moor  for  all  the  surfaces 
of  land,  whether  high  or  low,  which,  with  more  or  less  wetness,  are 
covered  by  successive  growths  of  vegetation,  the  remains  of  which 
accumulate  to  form  beds  of  peat.  Three  kinds  of  moor  may  be 
distinguished :  the  marine  low  moor,  or  marsh ;  the  fresh  water 
low  moor,  or  swamp;  and  the  upland  moor,  or  bog.  The  restric- 
tion of  the  terms  here  given,  and  in  part  at  least  advocated  by 
Shaler  many  years  ago,  will  prove  useful  and  make  for  precision. 
Shaler  (42:264}  has  given  us  a  useful  classification  of  modern 
moorlands  which,  with  some  slight  changes,  chiefly  ^rearrange- 
ments, is  as  follows  (Parsons~3o)  : 


4«6  PRINCIPLES    OF    STRATIGRAPHY 


f  Below  mean  tide.  .    .(\ 
A     ,  ,    .  ,  12.  Mud  banks 

A.  Marine  marshes  .....  <  ; 

[  Above  mean  tide.  ...  1  3-  Grass  marshes 

\  4.  Mangrove  marshes 

f  Lake  swamps  .  .          ;  /  £'  Lake  margin  swamps 

B.  Fresh-water  swamps  .  I  6"  QuakmS  bo&  or  swamPs 

(  River  swamps  .......  J  7-  Terrace  swamps 

\  8.  Estuarine  or  delta  swamps 

r  Upland  bogs  ........  \  9.  Climbing  bogs 

C.  Terrestrial  Bogs  .....  J  /  10.  Wet  wood  bogs 

L  Ablation  bogs 

A  more  recent  classification  of  peat  moors,  adopted  by  the 
students  of  the  West  European  peat  deposits,  has  reference  to  the 
succession  of  plant  types  found  in  the  moors.  It  applies  to  the 
fresh-water  swamps  and  terrestrial  bogs  only.  Three  types  are 
recognized  :  a,  Low  moor,  or  flat  moor  (Flachmoor,  Verlandungs- 
moor)  ;  b,  Intermediate  or  Transition  moor  (Zwischenmoor,  Ueber- 
gangsmoor)  ;  and,  c,  High  moor  or  Upland  moor  (Hochmoor). 

The  transition  moors  are  less  well  characterized  than  the  low 
and  high  moors,  and  the  tendency  of  some  authors  is  to  eliminate 
them  altogether.  A  further  group,  however,  the  forest  moor,  or 
dry  peat  moor,  is  separated  by  most  modern  authors.  For  pur- 
poses of  mapping,  the  following  divisions  of  modern  fresh-water 
or  terrestrial  deposits  of  caustobioliths  have  been  recognized  in 
Germany  (Ramann-33  : 


I.  Slime  deposits  (fresh-water  sapropelytes). 

II.  Flat  or  low  moor  deposits  —  Terrigenic  moor  deposits   (Ver- 
landungsmoorablagerungen)   comprising  : 

A.  Peat:  formed  by 

1.  Reed  association  or  a  Phragmitetum  *  (Phrag  mites, 

America;  Arundo,  Europe). 

2.  Sedge    association    or    Cyperacetum    or    Caricetum 

(Cyperus,  Car  ex,  etc.),  including: 

a.  Magnocaricetum  or  tall  sedge  plantation. 

b.  Parvocaricetum  or  low  sedge  plantation. 

3.  Moss  association  or  Hypnetum  (Hypnum  and  certain 

species  of  Sphagnum,  etc.). 

B.  Mold. 

III.  Forest  peat  (dry  peat). 

IV.  Highmoor  peat. 

*  The  ending  etum  designates  a  plantation,  grove  or  association  in  which  the 
plant  to  whose  name  it  is  suffixed  forms  the  principal  type. 


MARINE    MARSHES  487 

The  reed  association  or  phragmitetum  is  not  wholly  restricted  to 
the  low  moors,  but  also  occurs,  though  more  sparingly,  on  the  high 
moors.  The  same  may  be  said  of  certain  sedge  associations  or 
cyperacetes.  Among  the  mosses  certain  species  of  Hypnum  (as,  for 
example,  H.  fluitans,  giganteum,  and  trifarium,  in  Europe,  and  cer- 
tain Sphagnums)  occur  with  the  reed  associations,  partly  forming 
floating  mats  or  growing  among  the  reeds.  The  sphagnums  are 
most  characteristic  of  the  high  moors. 

The  following  classification  comprises  the  important  subdivi- 
sions of  the  areas  of  deposition  of  modern  caustobioliths : 

A.  Marshes — Marine. 

1.  Sapropelite  region — submerged. 

a.  Eel  grass  marsh. 

b.  Mud  flat  region. 

2.  Humulite  region — emerged. 

a.  Grass  or  Spartina  marsh. 

b.  Mangrove  marsh. 

B.  Swamps — Fresh  Water. 

1.  Sapropelite  region. 

2.  Humulite  region. 

a.  Moss  or  Hypnetum  zone. 

b.  Sedge  or  Cyperacetum  zone. 

c.  Reed  or  Phragmitetum  zone. 

d.  Tree  or  arboretum  zone. 

(1)  Alder  or  Alnetum  zone. 

(2)  Cypress  or  Taxodetum  zone. 

(3)  Tupelo  or  Nyssetum  zone. 

C.  Bogs — Terrestrial. 

1.  Forest  moors. 

2.  Upland  bogs  (High  Moors). 

Marine  Marshes. 

The  development  of  marine  marshes  proceeds  in  the  following 
manner  (Shaler-4i  :  359;  Davis,  W.  M.-i6)  :  An  off-shore  sand 
bar  is  built  by  the  waves  on  the  gently  sloping  sandy  sea-bottom, 
or  a  barrier  beach  is  built  between  two  projecting  headlands.  The 
scouring  action  of  the  tides  will  keep  open  a  channel  through  this 
beach  so  that  a  connection  between  the  sea  and  the  lagoon  is  always 
maintained.  Bars  may  be  built  in  water  from  20  to  30  feet  in  depth, 
and  are  due  to  the  breaking  of  the  large  waves  off  shore,  which 
then  pile  up  in  front  of  them  the  detritus  which  they  have  dug  up 


488  PRINCIPLES    OF    STRATIGRAPHY 

from  the  sea-bottom.  The  bar  grows  until  at  last  it  rises  above  the 
level  of  ordinary  tides,  and  thus  becomes  a  barrier  beach.  Mean- 
while, at  low  tide,  the  sun  dries  out  the  upper  portion  of  the  sand, 
which  then  becomes  mobile,  and  is  piled  up  into  shoreward  advanc- 
ing sand-dunes.  Thus  a  barrier-beach  of  some  breadth  may  be 
formed.  While  this  is  going  on,  deposition  of  sediments  within  the 
lagoon  behind  the  beach  takes  place,  for  here  the  water  is  mostly 
quiet,  while  sediment  is  carried  in  both  by  streams  from  the  land 
and  by  the  tide.  As  soon  as  an  accumulation  of  mud  or  fine  sand 
over  the  bottom  has  begun,  it  is  taken  possession  of  by  eel  grasses 
(Zostera  marina,  etc.),  which  soon  cover  the  bottom  with  a  dense 
growth.  These  plants,  belonging  to  the  pond-lily  family,  have  be- 
come adapted  to  a  marine  habitat,  and  cannot  live  outside  of  the 
salt  water.  Wherever  these  plants  grow  sufficiently  near  the  sur- 
face they  form  at  low  tide  a  tangle,  passage  through  which  is  ac- 
complished only  with  difficulty  by  the  swimmer  or  the  oarsman. 
"A  tidal  current  of  two  miles  an  hour,  swift  enough  to  carry  much 
sediment,  is*  almost  entirely  deadened  in  this  tangle  of  plants.'' 
(Shaler-4i.)  As  a  result,  the  sediment  will  sink  down  between  the 
leaves  of  the  plant  and  there  will  rapidly  accumulate  a  bottom  de- 
posit of  mud,  which  encloses  the  vertical  stems  of  the  plants.  With 
the  fine  sediment,  fronds  of  sea-weed  are  carried  by  the  current, 
and  these  with  pebbles  or  shells  attached  to  their  bases  will  settle 
to  the  bottom  and  become  buried  in  the  mud.  The  presence  of 
decaying  vegetal  and  animal  matter  gives  a  characteristic  color 
and  odor  to  these  deposits  which  may  readily  be  observed  wher- 
ever the  mud  flats  are  exposed  at  low  tide.  Wliere  the  mud  is  cal- 
careous, extensive  beds  of  calcilutytes  may  be  formed  in  this  man- 
ner, which  may  even  retain  the  vertical  impressions  of  the  plants  or 
other  organisms  which  have  "combed"  out  the  mud  from  the  sea 
water.  What  appears  to  be  a  good  example  of  this  kind  is  found 
in  the  Ordovicic  (Lowville)  limestone  of  the  Black  River  valley, 
etc.,  in  New  York,  where  the  remains  of  the  vertical  stems  form  a 
characteristic  feature  of  the  rock,  the  appearance  on  cross-section 
having  given  rise  to  the  term  "Bird's  Eye,"  by  which  the  rock  is 
commonly  known. 

Where  the  mud  has  accumulated  to  such  an  extent  that  at  low 
water  the  flat  is  uncovered  the  eel  grass  will  die,  and  its  place  is 
gradually  taken  by  the  marsh  grasses.  For  a  time  mussels  will 
occupy  patches  of  the  mud  flat  surface,  and  a  mussel  bed  of  some 
thickness  may  be  formed  on  the  substratum  of  black  mud.  Micro- 
scopic examination  of  the  mud  will  show  that  it  consists  of  ill- 
assorted  and  generally  angular  grains.  The  marsh  grasses  com- 


MARINE    MARSHES  489 

monly  push  their  growth  from  the  shore  outward.  Their  roots 
and  stems,  partly  submerged  at  each  tide,  readily  entangle  sediment 
and  so  the  level  of  the  deposits  is  rapidly  raised  to  where  it  will 
be  covered  only  at  the  highest  tide.  At  this  stage  portions  of  the 
marsh  are  sometimes  inhabited  by  enormous  numbers  of  the  fiddler 
crab  (Gelasimus).  At  this  point  the  process  is  generally  arrested 
except  for  the  decay  of  the  older  vegetation  and  the  growth  of 
new  crops.  The  appearance  of  the  marsh  and  its  structure  are 
shown  in  the  following  map  and  section,  copied  from  Shaler  (Figs, 
no,  noa.)  In  cases  where  much  sand  is  carried  into  the  lagoon  by 
the  tidal  currents,  the  eel-grass-mud-flat  stage  may  be  entirely 
omitted,  the  marsh-grass  stage  following  directly  upon  the  sandy 
filling  of  the  lagoon. 

The  salt  marsh  vegetation  consists  chiefly  of  grasses  and  sedges. 


IIMUMHMHBHHHMi 


A.  Bed  rock.  B.  Sand  and  gravel.          C.  Eel  grass  layer.          D.  Upper  marsh. 

FIG.    no.     Ideal    section    of   a    salt   marsh    formed    behind   barrier    beaches. 
(After  Shaler.) 

Among  the  former  the  genus  Spartina  leads  with  seven  species, 
not  all  of  which  are,  however,  of  marine  habitat.  Some  species 
are  of  world-wide  distribution,  while  others  occupy  a  restricted 
area.  In  vertical  range  the  species  also  vary.  In  the  lowest  zone 
occupied  by  those  plants,  i.  e.,  the  zone  limited  downward  very 
nearly  by  half  tide  and  upward  by  ordinary  high  tide,  the  tall, 
coarse,  rank-smelling  salt  thatch,  Spartina  glabra  Muhl.,  var.  altcrni- 
flora  Loisel  and  Merr,  is  the  sole  representative  of  these  grasses, 
except  for  occasional  stragglers  from  the  zone  above.  This  plant 
has  large,  hollow,  jointed  stems,  broad,  yellowish-green  leaves,  and 
grows  from  two  to  four  or  even  six  feet  high.  It  produces  numer- 
ous seeds,  and  sends  strong,  thick  and  very  characteristic  under- 
ground stems  in  all  directions  into  the  substratum  on  which  it 
grows.  From  these,  at  nodal  intervals,  spring  the  long,  fibrous, 
much  branched  roots.  The  underground  stems,  and  those  parts  of 
the  aerial  branches  buried  in  the  mud  are  the  most  frequently  pre- 
served, and  these  are  readily  distinguished  from  other  plants  by 
their  size  and  straw  color,  which  is  retained  for  a  long  time.  The 
aerial  parts  of  the  plant,  i.  e,,  the  leaves  and  stems,  become  very 
brittle  at  the  end  of  the  growing  season  and  are  broken  off  by 


490  PRINCIPLES    OF    STRATIGRAPHY 

the  waves  and  shore  ice.  They  often  accumulate  along  the  high- 
water  line  or  are  carried  out  to  sea. 

This  plant,  which  is  thus  submerged  for  about  half  the  time, 
is  especially  abundant  in  the  banks  of  the  tidal  creeks.  The  deposits 
which  it  forms  are  rich  in  mineral  matter,  they  themselves  rarely 
forming  accumulations  approximating  in  purity  those  due  to  the 
species  growing  at  a  higher  level.  Above  the  salt  thatch  zone  is 
the  peat  zone  proper,  which  is  submerged  by  salt  water  only  from 
i  to  4  hours  each  day.  Many  species  grow  here,  sedges  (Carex) 
as  well  as  grasses,  but  only  two  are  common  on  the  northern  coast, 
Spartina  patens  Muhl.  and  Distichlis  spicata  (L.)  Greene.  These 
salt  marsh  grasses  are  both  short,  from  6  to  12  or  14  inches  tall, 
with  rather  slender,  tough,  wiry  stems,  and  dull  grayish-green,  slen- 
der, involute  leaves.  Their  root  stocks  are  slender,  tough  and  numer- 
ous, their  roots  long,  fibrous,  and  branching.  The  peat  formed  by 
these  plants  cannot  be  mistaken  for  that  of  any  other  form  of  vege- 
table deposit  with  which  it  is  likely  to  be  associated.  "It  differs 
from  the  turf  formed  by  sedges  in  the  persistence  with  which  the 
underground  stems  retain  their  form  and  individuality  instead  of 
collapsing  and  flattening,  in  the  lack  of  the  remains  of  leaves  and 
aerial  branches,  in  color,  in  the  absence  of  definite  lamination,  in 
the  amount  of  silt  generally  contained,  and,  more  than  all  else,  in 
the  presence  of  the  white  or  light-colored  finely  branching  roots, 
which  penetrate  the  mass  in  every  direction  and  make  up  the  great 
bulk  of  the  material."  (Davis-i5  '.632.) 

The  leaves  and  stems  of  these  two  salt  marsh  grasses  are  more 
persistent  than  those  of  the  salt  thatch,  but  they  also  are  largely 
removed  during  the  winter  by  ice,  wind,  and  tides.  A  fresh  water 
species,  S.  cynosuroides  Willd.  with  a  culm  2  to  6  feet  high  and 
narrow  leaves  2  to  4  feet  long  and  a  half  inch  or  less  in  width 
below  and  tapering  to  a  slender  point,  inhabits  the  banks  of  rivers 
and  lakes,  or  occurs  in  rich  soil  from  the  Atlantic  to  the  Pacific. 

Sedges,  Carex  salina  and  Carex  maritima,  are  also  characteristic 
of  the  salt  marshes,  and  often  add  a  considerable  part  to  the  peat 
formed. 

The  tidal  marshes  are  dissected  by  meandering  channels  through 
which  the  salt  water  ebbs  and  flows  twice  a  day.  These  channels 
are  generally  narrow  and  deep,  the  width  being  determined  by 
various  factors,  chief  among  which  is  the  scouring  force  of  the 
tidal  current,  and  the  resisting  force  and  growing  power  of  the 
marsh  vegetation. 

During  the  slow  conversion  of  the  lagoon  into  a  marsh  the 
sand  dunes  from  the  beach  commonly  advance  over  the  growing 


MARINE    MARSHES 


491 


mass,  while  at  the  same  time  the  waves  may  cut  back  the  beach 
line.  Thus  it  may  happen  that  a  section  of  a  marsh  is  exposed 
along  the  shore,  below  the  cover  of  dune  sand.  Examples  of  such 
old  marshes  showing  on  the  coast  may  be  seen  at  Cape  Cod,  near 
the  Nausett  Lights,  on  the  coast  of  Nantucket,  along  the  western 
coast  of  Long  Island  (near  Bath  Beach),  and  elsewhere. 

The  sequence  of  events  thus  outlined  would  lead  to  the  forma- 
tion of  the  following  succession  of  deposits  (Davis,  C.  A.- 
15:626-7}:  At  the  bottom  the  section  should  show  sand,  silt,  •  or 
mud  up  to  about  twelve  feet  below  low-water  mark;  between  this 
level  and  that  of  low  water  should  occur  silt  surrounding  the  easily 
recognizable  remains  of  the  eel  grass  and  mingled  with  it  should 


FIG.  noa.     Map  of  the  Plum  Island   (Massachusetts)   marshes,  dissected  by 
meandering  tidal  streams.     (After  Shaler.) 

be  the  shells  of  molluscs  and  the  remains  of  other  marine  organisms. 
Above  this  should  occur  another  layer  of  silty  mud  up  to  the  level 
above  which  the  salt  water  grasses  grow.  The  next  higher  stratum 
should  contain  the  remains  of  these  plants  in  constantly  increasing 
numbers,  until  they  form  the  bulk  of  the  stratum.  This  would 
result  from  the  observed  fact  that  there  is  a  level  above  the  low-tide 
mark  below  which  these  plants  do  not  go,  while,  at  the  greatest 
depth  at  which  they  do  grow,  the  number  of  individuals  is  small 
compared  with  that  found  higher  up,  where  these  grasses  find  their 
most  favorable  conditions  for  growth.  "At  the  top  of  the  section 
should  be  a  distinct  turf,  formed  of  the  characteristic  plants  grow- 
ing on  the  surface,  which,  because  of  the  very  definite  fixed  habits 
of  these  species,  would  be,  relatively,  very  thin."  (Davis-i5.) 


492  PRINCIPLES    OF    STRATIGRAPHY 

Considerable  variation  from  this  normal  section  is  to  be  ex- 
pected, for  salt  marsh  building  may  be  interrupted  at  any  stage  by 
blowing  sands,  and  the  whole  may  be  greatly  complicated  by  sub- 
sidence or  elevation  of  the  coast.  In  some  cases  studied,  as  on  the 
Massachusetts  coast,  the  structure  of  the  marsh  does  not  conform 
to  this  succession  in  some  of  its  major  features,  showing  that  the 
history  here  has  been  quite  different  from  that  outlined.  "In  many 
cases  .  .  .  the  deposits  below  the  surface,  instead  of  contain- 
ing eel  grass  and  salt  thatch  remains,  was  entirely  composed  of  the 
very  different  and  definitely  recognizable  sort  of  vegetation  that 
never  grows  where  salt  water  reaches,  i.  e,,  the  deposits  were 
largely  of  fresh  water  origin."  These  deposits  often  show  consid- 
erable accumulation  of  woody  material,  including  stumps  of  large 
pine  trees,  near  the  surface  and  for  a  few  feet  below.  "The  struc- 
ture of  these  marshes  also  often  showed  salt  water  intrusion  in 
varying  degree  in  different  parts  of  the  same  area,  the  deposit  of 
the  salt  marsh  material  being  progressively  thicker  as  the  ocean  was 
approached."  (Davis-i5.)  In  the  case  of  these  marshes,  the  salt 
water  deposits  were  made  up  of  the  species  of  plants  which  grow 
at  or  near  high-tide  level,  while  eel  grasses  and  species  which  can 
stand  partial  submergence  were  rare  or  absent.  Even  where  no 
fresh  water  peat  was  found  underlying  the  salt  peats  the  species 
making  up  the  latter  were  those  growing  at  present  at  high  tide 
level  or  above,  although  the  peat  formed  by  these  was  often  below 
present  low-water  level.  This,  if  not  due  to  compacting,  indicates 
subsidence  of  the  coast  during  or  since  the  formation  of  the  peaty 
deposits.  Oscillation  of  the  coast,  or  at  any  rate  of  the  tidal  range, 
is  indicated  by  the  intercalation  in  some  cases  of  fresh  water  peat 
between  layers  of  salt  marsh  peat.  Salt  marshes  of  this  type  must 
be  interpreted  as  follows :  On  a  flat  coastal  plain,  above  the  reach 
of  tide,  owing  to  the  moist  climatic  conditions  and  probably  to  the 
growth  of  trees  .preventing  free  drainage,  are  formed  swampy  areas 
in  which  an  accumulation  of  fresh  water  peat  goes  on  to  an  in- 
definite extent.  By  a  slight  but  constant  progressive  subsidence 
of  this  coast  the  sea  enters  in,  kills  the  fresh  water  peat,  and  be- 
gins to  cover  more  or  less  permanently  a  part  of  the  coastal  strip  of 
this  plain.  Since  the  growth  of  marsh  grasses  on  the  open  exposed 
coast  is  ordinarily  an  impossibility,  owing  to  the  violent  wave  work, 
it  follows  that  the  first  step  in  the  conversion  of  the  fresh  to  the 
salt  marsh  is  the  building  of  the  barrier  beach.  If  the  barrier 
beach  is  built  far  enough  from  the  shore,  owing  to  the  gradual 
shoaling  of  the  water,  a  broad  lagoon  of  salt  water  will  be  left  be- 
tween it  and  the  shore,  and  in  this  the  salt  peat  may  gradually  form, 


MARINE    MARSHES  493 

as  outlined  above  in  Shaler's  hypothesis.  Such  marsh'  deposits  are 
now  forming"  on  the  Long  Island  and  New  Jersey  coasts.  As  the 
coast  slowly  subsides  the  marsh  grasses  will  encroach  upon  the 
dead  fresh  water  swamps,  and  since  the  subsidence  is  a  slow  one 
only  the  plants  growing  at  high  water  level  or  above  will  enter  into 
the  constitution  of  this  deposit.  Among  these  on  the  Massachu- 
setts coast,  the  grass  Spartina  patens  Muhl.  is  the  chief  type,  which 
will  form  successive  layers  if  the  subsidence  is  slow,  and  so  a  pro- 
gressive overlap  of  the  Spartina  patens  layer  over  the  fresh  water 
peat  will  take  place,  with  the  result  that  this  peat  thickens  seaward 
because  in  that  direction  deposition  began  earlier.  During  all  this 
time  the  lagoon  beyond  the  area  of  the  fresh  water  peat  deposit 
may  be  slowly  rilling  up  and  the  ordinary  salt  peat  would  form, 
beginning  with  the  more  euryhaline  species  of  salt  grasses,  such  as 
Spartina  glabra,  and  followed  by  the  more  stenohaline  species,  such 
as  S.  patens.  Progressive  erosion  and  landward  migration  of  the 
outer  bar  would  eventually  result  in  the  entire  removal  of  the 
purely  marine  peat  series,  so  that,  as  in  the  case  of  the  Massachu- 
setts marshes,  the  only  part  remaining  behind  the  bar  is  the  com- 
pound peat  mass,  commonly  of  fresh  water  peat  at  the  bottom  and 
salt  water  peat  on  top. 

In  such  cases  as  these  the  bar  has  successively  migrated  shore- 
ward until  it  has  reached  if  not  transgressed  the  original  shore 
which  existed  at  the  time  that  the  fresh  water  peat  was  forming  on 
the  coastal  plain. 

If  the  subsidence  is  more  rapid  than  the  upbuilding  of  the 
Spartina  patens  peat,  the  more  frequent  submergence  of  the  surface 
will  kill  that  species  and  its  place  is  taken  by  the  more  euryhaline 
5".  glabra,  which,  in  turn,  may  be  succeeded  by  a  mussel  bed  or 
mud  flat. 

Conversion  of  salt  peat  into  coal.  The  burial  of  a  salt  peat 
marsh  under  silts  of  marine  or  terrestrial  origin  would  tend  to  its 
preservation  and  ultimate  conversion  into  coal.  Such  coal  will, 
however,  be  very  high  in  ash,  for  the  high  tides,  especially  during 
stormy  periods,  will  spread  much  silt  over  them,  while  wind-blown 
sand  from  the  shore  may  also  add  a  quantity  of  mineral  matter. 
Hydrogen  sulphide  is  generated  in  great  abundance  in  peat  beds 
to  which  salt  water  has  access.  This  is  apparently  due  to  the  action 
of  certain  bacteria  on  the  sulphates  contained  in  the  water.  By 
reaction  with  iron  compounds  of  the  silt  and  other  mineral  mat- 
ter iron  sulphides  are  formed,  which  are  deposited  as  iron  pyrite. 
This  mineral  is  abundant  in  the  inorganic  constituent  of  the  salt 
marsh  peat.  Such  formation  of  hydrogen  sulphide  does  not  occur 


494  PRINCIPLES    OF    STRATIGRAPHY 

in  fresh  water  peats,  unless  these  are  subsequently  submerged  by 
marine  waters. 

Mangrove  Marshes. 

These  occur  in  the  tropics  and  take  the  place  of  the  salt  grass 
marshes  of  temperate  climes.  The  mangroves  comprise  some 
twenty  species,  characterized  by  numerous  slender  trunks  varying 
from  five  to  sixty  feet  in  height.  These  rise  to  just  above  the  level 
of  high  tide,  and  are  crowned  with  heavy  foliage,  which,  when  the 
tide  is  full,  appears  to  float  upon  the  water.  From  the  crown, 
stolonal  processes  are  sent  off  and  these,  in  turn,  give  rise  to  de- 
scending roots,  which,  after  reaching  the  sea-floor,  become  fixed  and 
serve  to  support  the  trees  against  the  effects  of  the  tides  and  waves. 
Shaler  believes  that  the  mangrove  thickets  may  advance  over  the 
sea-floor  at  the  rate  of  twenty  or  thirty  feet  in  a  century.  Their 
seaward  extent  is  limited  by  the  deepening  of  the  water  and  the 
force  of  the  waves,  and  by  fish  which  feed  upon  the  growing  ex- 
tremities of  the  roots.  The  densely  interwoven  stems  and  roots  of 
the  mangrove  form  an  effective  barrier  for  the  retention  of  silt. 
The  flow  of  water  from  the  land  is  checked,  and  sediment  deposited, 
until  the  roots  and  stems  are  completely  buried,  when  the  plants  die 
and  give  way  to  other  types  of  vegetation.  Commingled  with  these 
buried  trunks  and  roots  we  find  a  considerable  littoral  fauna,  a 
part  of  which  was  directly  attached  to  the  bases  of  the  mangrove 
or  crawled  about  on  them,  and  another  part  which  lived  on  or  in 
the  mud  which  accumulated  between  the  stems.  (See  further,  Chap- 
ter XXVIII.) 

Fresh  Water  Swamps. 

The  sapropelite  region  of  swamps  is  largely  confined  to  the 
deeper  parts  of  the  lakes  where  planktonic  fresh  water  algae  sink 
to  the  bottom  upon  their  death  and  where  Characese  grow  and  pro- 
duce a  layer  of  sapropelcalcilite  or  marl.  The  formation  of  sapro- 
pelite is,  probably,  far  less  extensive  than  in  marine  waters,  for 
terrestrial  vegetation  will  take  root  in  all  shallow  waters  or  push 
out  as  floating  mats  from  the  shore,  the  deposits  resulting  being, 
therefore,  chiefly  humuliths.  Floating  algae  are  rare  in  all  except 
the  smaller,  more  stagnant,  lakes  or  pools,  and  thus  the  chief  de- 
posits of  this  type  on  the  deeper  lake  bottoms  are  the  Chara  marls. 
Fresh  water  swamps  may  be  subdivided  into  lake  swamps,  river 
swamps,  and  estuarine  swamps,  which  merge  into  the  marine 
marshes. 


FRESH-WATER    SWAMPS 


495 


Lake  Swamps.  Around  the  margins  of  lakes  and  fresh  water 
ponds  a  variety  of  plants  are  found  more  or  less  submerged.  The 
number  of  species  of  flowering  plants  having  such  a  habitat  is  com- 
paratively small,  the  endogenous  plants  predominating,  with  the 
water  lily  family,  especially  Potamogeton,  as  the  leading  class.  Of 
the  flowerless  plants  Hypnum  and  Sphagnum,  two  mosses,  and  the 
alga  Chara  are  the  most  significant.  The  depth  at  which  seed  plants 
will  grow  ranges  from  15  to  25  feet,  very  few,  such  as  the  water 
lilies,  being  able  to  establish  themselves  in  depths  greater  than  10 
feet.  As  the  25-foot  limit  is  approached  the  number  of  species 
rapidly  diminishes,  this  being  apparently  due  to  the  decrease  in 
light  and  heat  available.  Of  the  plants  growing  in  deeper  water, 
the  algae,  especially  the  species  of  Chara,  should  be  mentioned  as 


7  c  s- 


FIG.  TII.  Diagram  of  plant  zones  in  small  lake  near  Merryman's  Lake,  Mich- 
igan. (After  Davis.)  o,  Chara;  i,  floating  bladder  worts ;  2, 
yellow  pond  lily;  3,  lake  bulrush;  4,  Sartwell's  sedge;  5, 
bottle  sedge;  6,  spike  rush;  7,  cat-tails. 

significant,  These  are  instrumental  in  raising  the  bed  of  the  lake 
or  pond  by  the  formation  of  marl  (ante,  p.  471).  Floating  or 
planktonic  plants  also  abound  in  most  fresh  water  ponds  and  lakes, 
especially  in  the  stagnant  portions.  The  most  important  of  these 
are  the  Bladderworts  (Utricularia),  of  which  there  is  a  number 
of  species,  and  Myriophyllum  which  may  cover  whole  surfaces  of 
the  ponds. 

The  most  important  species  of  peat-forming  plants  in  lakes  do 
not  grow  in  water  over  two  feet  in  depth.  These  comprise,  among 
others,  the  cat-tail  flags  (Typha),  the  Bur  reeds  (Sparganium),  the 
Water  Plantain  (Alisma),  the  Arrow-heads  (Sagittaria),  some 
grasses  (Zizania),  the  wild  or  Indian  rice  (Phragmites),  Reed 
grass,  and  several  sedges,  in  addition  to  the  pond  lilies.  Hypnum 
and  Sphagnum  grow  near  the  surface. 

In  lakes  more  than  25  feet  in  depth,  filling  by  the  formation  of 


496  PRINCIPLES    OF    STRATIGRAPHY 

marl  or  sapropelite  from  floating  plants  has  to  occur  to  bring  the 
bottom  to  the  required  level  where  the  higher  plants  can  gain  a 
foothold.  These  will  slowly  build  up  the  floor  of  the  lake  by  partly 
decayed  vegetal  matter,  the  rate  increasing  with  progressive  shoal- 
ing, owing  to  the  increase  in  the  number  of  plant  species  and  their 
greater  luxuriance.  The  succession  of  types  is  shown  in  the  pre- 
ceding diagram  (Fig.  in),  copied  from  Davis. 

In  the  rilling  of  lakes  by  vegetal  growth  a  prominent  part  is  taken 
by  the  plants  which  build  floating  mats  from  the  shore  outward. 
Chief  among  these  in  our  temperate  climes  is  the  sedge  Carex  fili- 
fonnis  L.,  which  forms  a  mat  of  felted  and  interwoven  stems  and 
roots,  making  a  buoyant  structure  capable  of  supporting  consider- 
able weight.  This  sedge  may  grow  with  its  rhizomes  submerged  a 
foot  or  more  below  the  surface  of  the  water  and  its  roots  extending 
much  farther  downward.  These  mats  may  be  from  a  few  inches 
to  two  feet  in  thickness  near  their  lakeward  end,  while  toward  the 
shore  they  become  more  and  more  solid  and  eventually  no  longer 
float.  The  solid  portion  gradually  extends  lakeward,  partly  by  the 
accumulation  of  more  or  less  decayed  vegetal  matter  beneath  the 
mat,  and  the  pond  thus  becomes  filled.  The  sedge  is  sometimes 
largely  replaced  by  the  cat-tail  Typha  latifolia,  which  likewise  aids 
in  the  building  of  the  mat.  As  the  surface  of  the  mat  approaches 
the  level  of  the  water,  dense  growths  of  the  moss  Hypnum  will 
occur ;  other  plants  follow,  including  ferns  and  the  Sphagnum  moss, 
and,  finally,  the  tamaracks  and  spruces  will  begin  to  migrate  out- 
ward, and  the  pond  passes  from  the  quaking  bog  stage  to  the  more 
or  less  wooded  tamarack  swamp  (see  Fig.  112).  As  the  forest  ad- 
vances the  sedges  begin  to  die,  being  unable  to  flourish  in  the  shade. 
The  ground  becomes  covered  by  a  heavy  growth  of  Sphagnum 
moss,  which  may  grow  to  some  extent  in  the  water,  but  more  com- 
monly forms  a  surface  growth  which  may  reach  a  thickness  of 
several  feet.  The  stumps  and  trunks  of  dead  and  fallen  trees  are 
gradually  embedded  in  this  growing  mass  of  vegetal  material,  be- 
coming an  integral  part  of  the  accumulating  peat  deposit.  As  the 
Sphagnum  forms  the  most  conspicuous  part  of  the  surface  of  the 
swamp  and  is  a  vigorously  growing  plant,  it  has  commonly  been 
credited  with  being  the  chief  agent  in  the  production  of  swamp 
peat,  the  plant  itself  being  known  as  the  peat  moss.  It  appears, 
however,  that  this  moss  must  be  regarded  as  only  a  contributor 
so  far  as  swamp  peat  is  concerned. 

In  a  consideration  of  lake  swamps  we  must  not  neglect  the  fact 
that  lake  basins  come  into  existence  in  a  great  variety  of  ways  (see 
ante,  p.  116),  and  that  in  some  cases  these  basins  may  from  the 


FRESH-WATER  SWAMPS  497 

outset  be  so  shallow  as  to  quickly  assume  the  character  of  a  swamp 
or  bog,  without  passing  through  all  the  stages  described.  Further- 
more, it  has  been  shown  that  lakes  may  actually  be  produced  by  the 
growth  of  vegetation,  as  in  an  upland  moor,  this  forming  either  a 
barrier  or  an  enclosing  rim.  In  such  a  case  the  bog  precedes  the 
lake,  which  may  subsequently  be  rilled  by  the  development  and  en- 
croachment of  the  swamp  vegetation. 

River  and  Estuarine  Swamps.  These  are  produced  where  the 
borders  of  the  rivers  with  broad  flood  plains  are  raised  through  the 
building  of  natural  levees  by  the  overflowing  stream.  The  vegeta- 
tion growing  on  the  borders  of  a  river  will  tend  to  arrest  the  sedi- 
ment carried  by  the  rising  water  in  times  of  flood,  when  the  flood 
plains  on  either  side  are  inundated.  These  higher  marginal  ridges 
will  therefore  separate  the  lower  flood  plain  from  the  river,  and 
thus  the  waters  resulting  from  the  overflow  of  the  river  will  find 


FIG.  112.  Diagram  showing  how  plants  fill  depressions  from  the  sides  and 
top.  (i)  zone  of  Chara  and  floating  aquatics;  (2)  zone  of  pond- 
weeds  or  potamogetons ;  (3)  zone  of  water-lilies;  (4)  floating 
sedge  mass;  (5)  advance  plants  of  conifers  and  shrubs;  (6) 
shrub  and  sphagnum  zone;  (7)  zone  of  tamarack  and  spruce; 
(8)  marginal  fosse.  (After  Davis.) 

it  impossible  to  return  to  the  river  on  its  subsidence.  Thus  exten- 
sive swampy  lands  are  formed  over  the  inundated  parts  of  the 
flood  plain,  which  may  also  enclose  an  extensive  series  of  shallow 
lakes.  The  back  Swamps  of  the  Mississippi  are  examples  of  this 
sort  of  occurrence. 

Delta  surfaces  may  be  covered  with  swamps  in  the  same  manner 
that  lakes  are  formed  on  deltas,  through  irregular  deposition  and 
obstruction  of  drainage.  At  the  heads*  of  estuaries,  fresh-water 
swamps  may  likewise  form  which  further  out  may  merge  into  or 
pass  beneath  grass  marshes  due  to  encroachment  of  the  sea. 

From  a  consideration  of  the  succession  of  plant  associations  dur- 
ing the  gradual  filling  of  a  lake,  it  must  be  apparent  that  in  the  re- 
sulting deposits  there  will  be  noticeable  a  stratification,  due  to  the 
superposition  of  successive  types  of  dead  vegetal  matter.  In  gen- 
eral, these  may  be  grouped  according  to  their  decreasing  hygro- 
phylous  characters  into  the  following  divisions :  I,  limnic;  2,  tel- 


498  PRINCIPLES    OF    STRATIGRAPHY 

matic;  3,  semiterrestric,  and,  4,  terrestric.  The  needs  of  the  plant 
associations  in  mineral  food  also  vary  with  the  development  of  the 
swamp  or  bog,  the  earliest  plants  deriving  their  food  from  the 
water  or  the  bottom  on  which  they  grow,  while  the  succeeding 
groups  must  depend  more  and  more  upon  the  older  plant  deposits 
for  their  mineral  nourishment,  and  this  becomes  less  and  less  in 
amount.  We  have  thus  a  series  with  decreasing  demand  on  the 
substratum  for  food,  and  these  are  classed  in  descending  order,  as 
eu-j  meso-  and  oligotraphent  types,  and  they  may  be  found  among 
various  hygrophylous  types.  From  the  deposition  of  these  types  of 
vegetation  we  get  eu-,  meso-  and  oligotrophic  types  of  peat  deposits, 


FIG.  113.  Ideal  section,  showing  the  approximate  relation  (i)  of  the  different 
types  of  peat,  and  (2)  the  plant  societies  at  Algal  Lake,  northern 
Michigan.  (After  C  A.  Davis.)  The  succession  of  plant  asso- 
ciations from  without  inward  is:  (i)  Tamarack-spruce-cedar 
swamp,  with  young  tamarack  at  the  inner  border;  (2)  open 
sedge  marsh,  with  islands  of  tamarack  wood;  (3)  swamp  loose- 
strife (Decodon  verticillatum)  gradually  advancing  lakeward,  and 
forming  "stools"  on  which  grow  mosses,  ferns,  sedges  and 
shrubs,  finally  killing  the  loosestrife;  (4)  cat-tail  flags;  (5) 
potamogeton.  The  peat  formed  by  these  plants  thickens  away 
from  the  lake,  and  is  humus  peat.  Below  this,  and  forming  the 
lake  bottom,  is  a  mass  of  sapropelitic  peat,  composed  of  green 
algae,  with  diatoms,  and  an  abundance  of  pollen-grains  of  conifers, 
forming  a  structureless  mass. 

the  last  of  which  normally  occurs  in  the  upper  part  of  the  stratified 
series. 

It  is,  however,  apparent  that  in  the  gradual  closing  of  a  lake  by 
vegetal  deposits,  those  formed  near  the  shore  will  have  the  largest 
supply  of  mineral  food,  especially  where  affluents  bearing  such  food 
enter,  and  that  the  waters  within  the  growing  rivers  of  eutrophic 
vegetation  will  become  poorer  and  poorer  in  foodstuff,  so  that  the 
inward  succession  of  plant  associations  will  take  on  successively  a 
meso-  and  an  oligotraphent  character,  and  the  deposits  of  peat  in 
such  a  basin,  when  completely  filled,  will  be  eutrophic  peat  around 
the  margin,  mesotrophic  next  within,  while  in  the  center  it  will  be 
oligotrophic,  and  thus  of  a  distinct  character.  Thus  within  the  same 


FRESH-WATER  SWAMPS 


499 


horizontal  section  there  will  be  a  marked  change  in  the  peats  filling 
a  single  basin.  Such  differences  are  frequently  observed  in  single 
basins,  and  also  between  adjoining  basins,  where  slight  differences 
in  the  physical  characters  may  bring  about  marked  variation  in  the 
result.  The  range  of  variation  is  enormously  increased  under  the 
influence  of  fluctuating  climatic  conditions  such  as  nearly  every 
country  experiences  sooner  or  later. 

An  inverted  order  of  superposition  may  result  from  a  raising 
of  the  water  level,  often  due  to  the  growth  of  a  retaining  rim  of  peat, 


V'V 


-/-/  -  i  - 1  - 


•  O'.  .  o 

'•:&•".-. 


i   Younger   Sphagnetum    Peat 

"5cheuch£erteto-  5phacrnetu.*m  Peat 

"i'f  Boundary  horizon--  LriophoretuTn  Peat 

I  (E.v agin  at  urn  callunetum    Peat) 
3-    Older  Sph.agTietu/m  Peat 

JScheuchzerietum  Peat,  Car  iceto-SphagnetajTi  or 
I    Erlophoretum  Peat  (E.vaqiTmtum  etc.) 
5 1  PiTieto-BetaletaTnPeat;Ui|erof  pine  stamps  In  upper 
6  L  part,and  beneath  that  of  ten  lor  i  barnt  surfaces 
Almeium  Peat 

7.   Phracpitetiun  Peat 

8  Peat  mud 

a   Liver- colored  mad  (Lebbermudde) 

IQ  Lime  mud 
"•  Clay  mud 
12  Diluvial  bottom 


Semi  terrestrial 

Teltnatic  or 
5envterrestrial 
Terrestrial 


Semiterres  trial 
feUatic 

Limnic 
Formation 


FIG.  114.     Section  through  a  North  German  peat  bog,  showing  the  succession 
of  strata.     (After  Ramann.) 

or  through  sinking  of  a  floating  mat.  A  floating  mat  is  composed  of 
interlacing  roots  and  stolons  of  hygrophytes,  above  which  form 
semiterrestrial  or  even  oligotrophic  peats.  When  the  weight  be- 
comes too  great,  the  floating  mat  sinks  with  its  load,  and  the  meso- 
trophic  and  eutrophic  deposits  will  again  form.  Thus  a  layer  of 
oligotrophic  peats  may  occur  interpolated  between  layers  of  eutro- 
phic peat  deposits. 

A  section  seven  meters  deep  through  a  North  German  peat 
series  in  which  the  peat- forming  processes  had  come  to  an  end  gave 
the  succession  shown  in  the  above  diagram  (Fig.  114). 


500  PRINCIPLES    OF    STRATIGRAPHY 

In  general,  the  three  principal  zones  given  on  p.  486  (the  reed 
or  Phragmitetum,  the  sedge  or  Cyperacetum  and  the  moss  or  Hyp- 
netum  zones)  may  be  recognized  as  those  which  tend  to  succeed  each 
other  in  the  process  of  filling  the  lake  or  pond,  though  one  or  an- 
other of  them  may  at  times  be  absent.  Toward  the  last  the  water- 
loving  trees  begin  to  migrate  into  the  swamp,  among  which  in  our 
northern  climes  are  the  alders  (Alnus  incana,  A.  sermlata,  A.  mari- 
tima  near  the  coast,  and  A.  glutinosa  in  western  Europe),  forming 
the  Alnetum  zone.  Elsewhere  in  the  United  States  the  tamarack 
(Larix  americana)  takes  the  place  of  the  alders,  forming  the  Lare- 
tum.  In  the  southern  states  the  Cypress  (Taxodiwn  distichum)  or 
the  Tupelo  (Nyssa  uniflora)  occupies  this  zone,  forming,  respec- 
tively, a  Taxodetum  and  a  Nyssetum.  Under  and  among  these  trees 
a  rich  herbaceous  flora  flourishes,  including  ferns,  sedges,  the 
Equisetum  ftuviatile,  the  pitcher  plant,  Saracenia,  violets,  Galium, 
Impatiens  and  a  host  of  others.  Sphagnum,  however,  is  absent.  In 
the  cypress  swamps  of  Florida  ( Stevenson-46 : 144,  etc.)  and  the 
Gulf  Coast,  logs  and  woody  roots  are  common.  At  New  Orleans 
the  cypress  and  other  trees  were  found  superimposed  one  upon  the 
other,  in  an  upright  position,  with  their  roots  as  they  grew.  A 
cypress  swamp  dissected  in  cutting  a  canal  from  Lake  Pontchartrain 
showed  three  tiers  of  stumps  in  the  9  feet  excavated,  these  ranging 
one  above  the  other.  The  earlier  trees  apparently  rotted  away  at  the 
level  of  the  ground  before  the  later  ones  grew  over  the  same  site. 
The  peat  in  the  cypress  swamp  is  formed  by  an  accumulation  of 
the  forest  litter,  the  swamps  themselves  being  due  for  the  most  part 
to  impeded  drainage  on  an  almost  level  surface.  The  depth  of  the 
material  has  been  reported  as  in  some  cases  more  than  150  feet. 
Among  the  largest  swamps  on  our  coastal  plain  are :  Okefenoke 
Swamp  in  southern  Georgia,  and  the  smaller  Dismal  Swamp  of 
Virginia  and  North  Carolina,  which  covers  about  500  square  miles. 

In  Okefenoke  Swamp,  which  lies  50  miles  from  the  ocean  and 
115  feet  above  the  mean  tide,  the  peat  is  about  10  feet  thick,  and 
cypress  stumps  abound.  The  wetter  portions  are  often  free  from 
trees  and  show  a  luxuriant  growth  of  cane,  pickerel  weed  and  water 
lilies,  but  little  or  no  Sphagnum.  (Harper-23.) 

The  Dismal  Swamp  (49)  is  only  a  few  feet  above  sea-level, 
and  has  a  peaty  deposit  at  least  fifteen  feet  deep  (C.  A.  Davis), 
resting  on  Pliocenic  sands.  Lake  Drummond  lies  on  its  western 
border  (see  ante,  p.  120).  Sphagnum  plays  only  a  small  part  in 
the  peat  formation  of  this  swamp,  the  canes,  a  grape,  the  bald 
cypress  (Tax odium  distichum)  and  the  junipers  (Juniperus  vir- 
giniana)  being  the  chief  peat- forming  plants.  Of  these  the  junipers 


TERRESTRIAL    BOGS  501 

occupy  the  drier  spots,  but  the  others  generally  grow  in  the  water. 
The  projecting  knees  of  cypress  and  the  arched  roots  of  Nyssa  are 
much  in  evidence.  The  knees  are  formed  only  where  the  cypress 
grows  in  water,  and  serve  as  a  sort  of  breathing  organ  or  pneuma- 
tophore.  They  are  excrescences  from  the  roots,  rising  above  the 
water,  of  a  subcylindrical  form,  and  crowned  by  a  cabbage-shaped 
expansion  of  bark,  rough  without  and  often  hollow  within.  When 
through  a  rise  of  water  these  knees  are  submerged  the  trees  will 
die. 

Extensive  cedar  swamps  (Chamcccyparis  thyoides)  occur  on  the 
Atlantic  coastal  plain  of  the  United  States  north  of  Florida.  The 
peat  increases  in  thickness  inward  from  the  shore  to  perhaps  15 
feet,  and  is  full  of  tree  trunks  buried  at  all  depths,  these  having 
either  rotted  away  or  become  uprooted.  The  peat  is  very  pure,  con- 
taining only  3.35  per  cent,  of  ash.  The  trees  on  the  surfaces  of 
these  marshes  have  broad,  spreading  roots,  which  do  not  penetrate 
very  far  into  the  ground,  but  rely  upon  the  great  horizontal  extent 
of  their  shoots,  which  penetrate  very  deeply. 


Terrestrial  Bogs. 

These  include  the  forest  bogs  or  moors  and  the  high  moors. 
They  may  be  the  regular  successors  of  the  lake  and  river  swamps, 
but  more  often  they  develop  independently  upon  a  rocky  or  sandy 
substratum.  Such  are  the  familiar  upland  moors,  covering  the  hill- 
sides in  Great  Britain  and  Scandinavia,  as  well  as  large  parts  of 
northern  Germany,  and  broad  areas  of  northern  Asia,  and  of  Can- 
ada and  the  northern  United  States. 

Forest  Moors.  Beeches,  pines  and  spruces  succeed  the  tamarack 
and  alders,  and  form  the  transition  to  the  high  moors.  Here  the 
ground  is  dry,  and  a  wood  flora  appears,  often  characterized  by 
orchids.  In  these  woods  dry  peat  or  forest  peat  results  from  the 
falling  and  partial  decay  of  the  trunks,  branches  and  leaves  of  the 
trees.  The  character  of  the  resulting  peat  varies  with  the  type  of 
vegetation,  especially  with  the  predominant  arboreal  types.  Decay 
is  partly  accomplished  through  the  influence  of  microorganisms. 
The  destruction  of  the  dry  peat  and  its  conversion  into  earthy  mold 
or  its  entire  decay  are  furthered  by  the  growth  of  a  number  of 
grasses,  especially  the  common  hair-grass,  Deschampsia  flexiiosa 
Trin.  The  growth  of  peat  mosses  among  the  trees  in  the  transition 
of  the  bogs  to  the  high  moor  type  will  result  in  killing  these  trees 
through  increasing  moisture.  Decay  at  the  point  of  exposure  above 


5°2 


PRINCIPLES    OF    STRATIGRAPHY 


the  moss  will  result  in  the  breaking  off  of  the  trunk  at  that  point, 
and  the  subsequent  complete  embedding  of  the  stumps  in  the  peat. 
Such  old  pine  and  other  stumps  are  common  features  of  the  upland 
bogs. 

Upland  Bogs,  or  High  Moors.     These  are  built  up  by  the  re- 


FIG.  115.  Section  through  a  mature  peat  deposit  near  Hermansville,  Menom- 
inee  Co.,  Michigan.  (After  Davis.)  i,  Surface  vegetation;  2, 
layer  containing  roots  and  coarse  vegetable  debris ;  3,  fully  de- 
composed dark  peat ;  4,  light-colored  structureless  peat. 

mains  of  peat  mosses,  especially  the  Sphagnum  mosses  and  related 
types.  These  form  the  bulk  of  the  peat  in  the  upland  bogs,  though 
in  some  cases  they  are  largely  replaced  by  one  or  more  members  of 
the  pondweed  family,  especially  Scheuchseria  palustris,  or  of  the 
sedge  family,  notably  the  cotton  grass,  Eriophoruni  vaginatum  L., 


TERRESTRIAL    BOGS  503 

and  the  bulrush,  Scirpits  caspitosus,  L.,  and  other  species.  Thus 
in  the  upland  bogs  of  Great  Britain,  Sphagnum  is  of  little  impor- 
tance as  a  peat-maker,  its  place  being  taken  by  Scirpus  cccspitosus 
and  Eriophorum  vaginatum.  Other  types,  such  as  the  heather, 
Calluna  vulgaris  and  Erica  tetrali.v,  are  among  those  dominant  in 
some  localities.  The  Scandinavian  and  north  German  moors,  on 
the  other  hand,  are  chiefly  made  up  of  species  of  Sphagnum.  Where, 
however,  the  Sphagnum  is  exposed  during  the  winter  for  lack  of 
snow  covering,  as  along  the  coast  of  Norway,  it  disappears,  and  its 
place  is  taken  by  the  bulrush,  Scirpus  cccspitosus.  Heather  peat, 
formed  by  Calluna  vulgaris,  is  also  found  in  the  high  moors  of 
North  Germany,  as  is  also  Molinia  peat,  formed  by  Molinia  cccru- 
Ica.  Both  Sphagnum  peat  and  peat  formed  by  the  Scheuchzeria, 
the  cotton  grass  and  by  Scirpus  cccspitosus  are  found  in  Canada 
and  the  northern  United  States.  The  place  of  the  heather  is  taken 
by  Vaccinium  (blue  berries,  cranberries,  etc.),  Andromeda  and 
other  members  of  the  Heath  family. 

In  northern  Germany  (Ramann-34:  ijp)  the  high  moors  gen- 
erally consist  of  an  older,  strongly  decayed  Sphagnum  peat  and  a 
newer,  little  decomposed,  more  porous  Sphagnum  peat,  the  two  be- 
ing separated  by  a  dividing  layer  of  peat  formed  by  Eriophorum 
vaginatum  and  Calluna  vulgaris  (Eriophoretum  and  Callunetum, 
see  the  section,  Fig.  114).  Overlying  these  is  a  peat  layer  formed 
of  the  most  recent  growths,  the  heaths,  lichens,  etc.  The  double 
character  of  the  Sphagnum  peat  is  explained  by  the  gradual  diminu- 
tion of  the  water  raised  in  the  peat  bog  by  capillarity,  so  that,  as  the 
bog  rises  by  continuous  growth,  a  time  will  come  when  the  amount 
of  water  is  too  small  for  further  Sphagnum  growth.  Then  other 
plants  take  the  place  of  the  moss,  until  by  decomposition  the  latter 
has  been  reduced  again  in  volume,  and  as  a  result  become  less 
permeable  to  surface  waters.  Moist  conditions  wiH  then  return, 
and  a  new  growth  of  Sphagnum  begins.  Owing  to  the  fact  that 
the  old  Roman  roads  were  built  upon  the  dividing  layer  of  terres- 
trial peat,  it  becomes  possible  to  measure  the  rate  of  growth  of  the 
upper  peat  layer,  which  must  have  accumulated  during  the  past  two 
thousand  years. 

The  external  form  of  the  high  moor  is  domed,  and  permits  the 
run-off  of  the  rain  water,  which  produces  moist  margins,  where 
hygrophytes  of  various  kinds  will  grow. 

The  upland  peat  bogs  of  Great  Britain  generally  occur  on  un- 
dulating and  sloping  ground.  When  the  slopes  of  the  surface  do  not 
exceed  10°,  the  peat  generally  grows  to  considerable  thickness,  but 
where  these  slopes  are  greater  the  peat  is  also  much  thinner. 


504  PRINCIPLES    OF    STRATIGRAPHY 

Marshes  ("flows")  seldom  occur,  since  lakes  and  pools  were  rare 
in  the  original  surface.  The  peat  rests  either  directly  on  the  rock 
surfaces  or  on  the  surface  of  glacial  deposits,  the  contact  being  a 
sharp  one.  In  the  Pennines  the  peats  cover  elevations  like  the 
Cross  Fell,  whi-ch  rises  to  879  meters.  It  here  sometimes  has  a 
thickness  of  4.5  meters.  The  peat  is  largely  formed  from  the  com- 
mon reed,  Phragmites  communis.  Sphagnum  is  scarce  in  this  peat, 
as  already  noted  for  the  whole  of  Great  Britain.  In  places  the  peat 
contains  an  old  forest  bed,  sharply  marked  off  from  the  other  de- 
posits and  at  an  altitude  not  exceeding  780  m.  A  section  of  a  peat 
bog  in  this  district  gave  ( Samuelson-40 :  200)  : 

c.  Scirpus  caspitosus  peat,  yellow  brown  in  color,  very  rich  in 
humus,  not  moldered,  containing  remains  of  dwarf  shrubs. 
Washing  gave  only  numerous  small  specimens  of  Cenococcum 
geophilum 125  cm. 

b.  Phragmites- Car  ex  peat,  containing  numerous  large  stools, 
stems,  twigs,  and  roots  of  birch.  The  finerf  material  con- 
sists to  a  great  extent  of  wood  detritus.  No  coal  found. 
Nutlets  of  Ajuga  reptans  and  seeds  of  Viola  sp.  were 
washed  out  from  a  peat  sample.  Pollen  grains  of  elm, 
hazel  and  pine,  spores  of  ferns  and  leaves  of  Sphagnum 
were  also  found 75  cm. 

a.  Boulder  clay. 

This  peat,  as  that  of  other  regions  of  northern  Europe,  espe- 
cially Fennoscandia,  shows  the  occurrence  of  an  Alpine  vegetation 
during  the  period  of  formation  of  the  early  peat.  In  the  Cross  Fell 
the  remains  of  these  are  not  found  in  situ,  however.  Then  followed 
a  period  when  the  region  was  an  extensive  reed  swamp,  and  this 
was  succeeded  by  wet  birch  forests,  which  in  turn  were  replaced  by 
the  wet  moorland. 

A  section  of  a  peat  moor  in  the  southern  Uplands  of  Scotland 
gave  the  following  succession  in  descending  order,  the  altitude  being 
about  300  meters  above  sea-level  (Samuelson-4o:.?o/)  : 

6.  Scirpus  caspitosus  peat,  mixed  with  Eriophorum  va'ginatum, 
and  also  containing  solitary  Calluna  stems.  Pollen  grains 
of  alder,  birch,  grasses,  hazel,  pine,  Typha  latifolia,  etc. 
and  spores  of  Poly  podium  vulgar  e  and  Sphagnum  occur.  .  .  100  cm. 

5.  A  sharply  marked  layer  of  pine  " stools"  with  individuals 
sometimes  exceeding  50  cm.  in  diameter;  rarely  burnt — 
surrounding  peat  highly  moldered  and  contains  numerous 
stems  of  Calluna  and  birch  twigs;  a  hazelnut  also  found.  .  30  cm. 

4.  Eriophorum  vaginatum  peat,  rich  in  humus,  containing  some 
birch  fragments — very  likely  the  roots  penetrating  from 
above — washing  gave  Cenococcum  geophilum,  some  Calluna 
shoots,  stones  of  Empetrum  nigrum — pollen  grains  of  birch, 
hazel,  pine,  etc.,  also  found 45  cm. 


TERRESTRIAL    BOGS  505 

3.  Eriophorum  vaginatum  peat  very  little  moldered,  Sphagnum 
rare,  Empetrum  stems  numerous — few  small  birch  twigs. 
Stones  of  Empetrum,  numerous,  achenes  of  Potentilla 
comarum,  etc.,  also  pollen  of  birch,  pine,  etc.,  and  spores 
and  leaves  of  Sphagnum  and  brown  fungus  hyphas 20  cm. 

2.  Forest  peat,  rather  rich  in  humus,  hard  and  firm.  Fine 
material  consists  chiefly  of  wood  detritus.  In  the  peat 
are  numerous  trunks  and  twigs  of  birch — no  coal — wash- 
ing gave  achenes  of  Potentilla  comarum,  seeds  of  Viola  and 
numerous  fruits  of  different  Carex  species.  No  determin- 
able  microorganisms 45  cm. 


The  two  forest  beds  (2  and  5)  appear  to  be  of  wide  extent  over 
the  Scottish  uplands,  the  peat  layers  between  varying  in  thickness 
and  to  some  extent  in  composition.  The  lowest  bed  always  consists 
of  the  remains  of  a  birch  forest.  The  dividing  peat  generally  con- 
tains arctic  plants. 

In  the  Grampians,  Carex  peat  (150  cm.)  rests  directly  upon  the 
boulder  clay,  or  sometimes  has  a  stratum  of  Sphagnum  peat  at  the 
base.  Scirpus  cccspitosus  peat  or  Eriophorum  vaginafiim  peat  fol- 
lows this. 

In  the  northwest  Highlands  of  Scotland  similar  successions  are 
met  with.  In  Coire  Bog,  in  Easter  Ross,  the  following  section  oc- 
curs (Lewis  quoted  by  Samtfelson-4o)  : 

DOMINANT  PLANT  ACCOMPANYING  PLANT 

1 .  Scirpus — Sphagnum 3  ft. 

2.  Pinus  sylvestris  L 

3.  Sphagnum 1-3  ft. 

4.  Pinus  sylvestris  L 

5.  Eriophorum 5  ft.            Calluna  (abundant  in  upper  layers) 

6.  Betula  alba  L 2-3  ft.             Menyanthes  trifoliata  L. 

Eriophorum  vaginatum  L. 

7.  Empetrum nigrum L iJ4ft.  Eriophorum,  Polytrichum 

8.  Salix  arbuscula  L Betula  nana.  L.  (abundant  in  upper 

layers).  Dry  as  octopetala  L.  Po- 
tentilla comarum,  Nestl.  (abundant 
in  the  lower  layers). 

Total  peat 13-16  ft. 

9.  Sand 

10.  Closely  packed  stones 

While  most  Swedish  and  many  German  authors  refer  the  strat- 
ification of  the  peat  to  successive  changes  in  the  level  of  ground  wa- 
ter as  outlined  above,  other  authors  follow  James  Geikie,  who  re- 
fers this  alternation  of  vegetation  to  changes  in  climatic  conditions 


506 


PRINCIPLES    OF    STRATIGRAPHY 


accompanying  changes  in  physical  outline  of  Great  Britain.  His 
succession  of  late  glacial  and  interglacial  stages  in  Scotland  is  as 
follows : 

5.   Upper  Turbarian  or  Sixth  Glacial  Stage. 

High-level  corrie  glaciers,  with  snow  line  at  3,500  feet;  peat  overlying 
Upper  Forest;  raised  beaches  at  25  to  30  feet;  somewhat  cold  and  wet 
climate. 

4.   Upper  Forestian  or  Fifth  Interglacial  Stage. 

Upper  Forest  overlying  lower  peat;  relatively  dry  and  genial  climate; 
land  area  somewhat  more  extensive  than  now. 

3.  Lower  Turbarian  or  Fifth  Glacial  Stage. 

Valley-glaciers,  with  average  snow-line  at  2,400  to  2,500  feet;  Lower 
Peat  overlying  Lower  Forest;  raised  beaches  at  45  to  50  feet;  cold  and 
wet  climate. 

2.  Lower  Forestian  or  Fourth  Interglacial  Stage. 

Lower  Forest  overlying  morainic  accumulations  of  Fourth  Glacial 
stage;  genial  climate;  land  area  of  greater  extent  than  now. 

I.  Mecklenburgian  or  Fourth  Glacial  Stage. 

District  ice-sheets  and  large  valley  glaciers  of  Highlands  and  Southern 
Uplands;  raised  beaches  at  100  to  135  feet;  Arctic  climate,  with  snow- 
line  ranging  from  1,000  feet  in  west  and  northwest  to  1,500  feet  or 
thereabout  in  Central  Scotland. 

The  typical  succession  of  strata  of  the  Scottish  peat  bogs  agrees 
with  this  series  of  changes,  this  being  as  follows : 


\ 

Peat  Deposits 

Blytt's  Climatic  Period 

Geikie's  Climatic  Period 

5.   Upper  Peat  Deposits 

The  Subatlantic  Period 

Upper  Turbarian 

(moist  and  cold) 

4.   Upper  Forest  Bed 

The  Subboreal  Period 

Upper  Forestian 

pine  or  birch  —  re- 

(warm and  dry) 

placed  in  the  Shet- 

lands  by  a  Calluna 

layer 

3.  Middle   Peat   Deposit 

The  Atlantic  Period 

Lower  Turbarian 

commonly    with    a 

(warm  and  moist) 

thin  layer  near  the 

middle     containing 

arctic  plants  (second 

arctic  bed) 

i 

2.  Lower  Forest  Bed 

The  Boreal  Period 

Lower  Forestian 

chiefly  of  birch  re- 

(warm and  dry) 

mains 

i.  Lower  Peat  Deposit 

The  Subarctic  and  Arctic 

Arctic   Tundra   time,   at 

containing    the   re- 

Periods 

close  of  Mecklenburg- 

mains of   the   first 

ian  ice  age 

arctic     flora     (first 

arctic  bed) 

THE    TUNDRA  507 

The  Arctic  Tundras.  The  permanently  frozen  areas  of 
northern  Europe,  Asia  and  America  are  covered  for  the  most  part 
by  a  growth  of  peat  which  rises  in  the  form  of  rounded  hills  or 
banks  of  approximately  uniform  height.  Frozen  solid  in  winter, 
they  are  thawed  out  on  the  surface  during  the  summer  months. 
Throughout  northern  Europe  the  old  peat  vegetation,  which  con- 
sisted largely  of  Sphagnum,  has  perished,  only  on  the  borders  of 
the  natural  drainage  channels  are  cotton  grass  and  Sphagnum  still 
found  growing.  The  causes  of  this  widespread  destruction  of  the 
peat  moss  and  of  the  consequent  cessation  of  peat  formation  are 
the  rising  of  the  permanently  frozen  ground-level  beneath  the  moss, 
and  the  overgrowing  of  the  moss  by  lichens,  especially  Lecanora 
tartarea,  which  covers  both  living  and  dead  organisms  with  a  uni- 
form mantle.  The  peat  protects  the  ice  beneath  it  from  melting,  so 
that  in  Lapland  ice  exists  the  year  round  under  peat  only.  Melt- 
ing of  the  peat  bogs  proceeds  down  to  a  depth  of  30  to  40  cm. 
With  the  increase  in  thickness  of  the  peat,  the  ice  is  more  protected 
and  its  surface  rises,  the  result  being  that  the  plants  are  less  and  less 
supplied  with  moisture.  This  eventually  leads  to  their  destruction. 
The  tundra  of  Alaska  covers  the  whole  surface,  except  the  faces  of 
steep  cliffs,  along  the  borders  of  Behring  Sea  and  the  Arctic  Ocean. 
It  is  typically  "a  swampy,  moderately  level  country,  covered  with 
mosses,  lichens  and  a  great  number  of  small  but  exceedingly  beauti- 
ful flowering  plants,  together  with  a  few  ferns.  The  soil  beneath 
the  luxuriant  carpet  of  dense  vegetation  is  a  dark  humus,  and  at  a 
depth  exceeding  about  a  foot  is  always  frozen."  (Russell-39 :  /^J.) 
Lakelets  and  ponds  abound  in  the  level  parts,  and  they  occur  even 
on  the  hillsides,  where,  except  for  the  spongy  retaining  vegetation, 
no  such  accumulation  would  be  possible.  The  dense  vegetation  ex- 
tends up  the  mountainsides  wherever  conditions  are  favorable  and 
covers  even  steep  crags.  "On  the  steep  slopes,  as  in  the  swamps, 
the  vegetation  is  always  water-soaked,  owing  to  the  extreme  hu- 
midity of  the  climate  in  which  it  thrives."  Mosses  and  lichens  char- 
acterize the  flora  with  a  notable  absence  of  trees.  "Cryptogamic 
plants  make  more  than  nine-tenths  of  its  mass.  On  their  power  to 
grow  above  as  they  die  and  decay  below  depends  the  existence  of 
the  tundra."  Two  species  of  Equisetum  flourish  with  rank  luxur- 
iance over  great  areas  along  the  Yukon.  Excavations  show  "that 
the  fresh  luxuriant  vegetation  at  the  surface  changed  by  insensible 
gradations  to  dead  and  decaying  matter  a  few  inches  below  and 
finally  became  a  black,  peaty  humus,  retaining  but  few  indications 
of  its  vegetable  origin."  (Russell-39:  126.)  The  depth  of  the 
humus  layer  at  St.  Michaels  is  about  two  feet.  A  mile  east  of  the 


508  PRINCIPLES    OF    STRATIGRAPHY 

village  it  is  about  twelve  feet.  "In  the  delta  of  the  Yukon  a  depth 
of  over  fifteen  feet  was  seen  at  one  locality.  A  depth  of  150  to  300 
feet  has  been  assigned  by  several  observers  to  the  tundra,  where  it 
is  exposed  in  a  sea  cliff  on  Eschscholtz  Bay,  at  the  head  of  Kotzebue 
Sound."  Here  the  surface  layer  of  humus  is  rich  in  mammalian 
remains.  It  is  evident  that  the  conditions  here  differ  from  those 
found  in  North  Europe,  where  the  rising  ground  ice  eventually  puts 
a  stop  to  further  peat  formation.  Russell  thinks  that  in  Alaska 
"there  is  apparently  no  reason  why  this  process  [of  growth  above, 
decay  below,  and  conservation  of  the  partly  decayed  vegetation  by 
freezing]  might  not  continue  indefinitely,  so  as  to  store  up  vegetable 
matter  in  a  way  that  is  only  paralleled  in  the  most  extensive  coal 
fields."  (39:^70 

"On  the  flood  plains  of  the  larger  rivers,  and  generally  through- 
out all  the  lowlands  of  Alaska,  peaty  deposits  are  forming  in  the 
same  manner  as  on  the  tundra,  modified,  however,  by  the  growth  of 
arborescent  vegetation  and  by  the  intrusion  of  sand  and  clay  in 
places  that  are  flooded  during  the  high-water  stage  of  the  rivers. 

"At  many  localities  along  the  Yukon,  sections  of  peaty  deposits 
are  exposed  often  eight  or  ten  feet  thick  and  several  long.  The 
bluffs  .  .  .  are  from  fifteen  to  twenty  feet  high  .  .  .  and  nearly 
always  frozen  solid.  .  .  .  Some  of  the  vegetable  layers  are  in- 
terstratified  with  sand  and  clay;  others  at  the  surface  are  still  in- 
creasing in  thickness  and  have  a  dense  forest  growing  on  them. 
Not  infrequently  there  is  a  stratum  of  clear  ice  interbedded  with 
the  layers  of  peat,  sand  and  clay."  (Russell-39.) 

The  moist,  cool  climate  prevailing  over  eastern , Canada  has  also 
been  conducive  to  the  extensive  growth  of  peat  bogs,  which  cover 
all  the,  area  around  the  St.  Lawrence  and  the  Ottawa,  as  well  as 
on  Newfoundland  and  on  the  smaller  islands  off  the  coast.  On 
Anticosti  Island  in  the  Gulf  of  St.  Lawrence  there  are  peat  beds 
covering  in  some  cases  areas  from  one  hundred  to  more  than  a 
thousand  acres  in  extent,  with  a  thickness  of  ten  feet  or  over. 
(Twenhofel-48:  66.)  The  peat  rests  on  sands  and  gravels,  some- 
times with  Mya  arenaria,  and  at  other  times  it  rests  directly  upon 
the  eroded  limestone  surface  of  early  Palaeozoic  age.  The  lower 
peat  deposits  often  contain  tests  of  sea  urchins  (Strongylocentrotus 
drobachiensis) ,  fragments  of  lobsters  and  crabs,  gastropods,  etc., 
which  are  brought  there  by  birds,  chiefly  crows,  or  which  have  been 
washed  up  by  unusually  high  waves  and  tides.  These  marine  or- 
ganic remains  are  often  very  abundant.  In  the  wooded  areas, 
where  trees  have  only  a  slight  foothold  owing  to  the  shallowness  of 


PEAT  IN   THE  TROPICS  509 

the  soil,  fallen  trees  abound  and  are  entombed  in  the  growing  and 
only  partially  decaying  vegetation. 

The  temperature  of  Anticosti  ranged,  during  the  six  years  from 
1897  to  1902,  from  4-26°  C,  which  occurred  once,  to  — 39°  C, 
which  occurred  twice.  The  average  temperature  for  June,  July  and 
August  is  about  +  12.5°  C.,  that  of  the  winter  months  about  —  10° 
C.,  or  an  annual  average  of  about'-f  2°  C.  Precipitation  during  the 
three  months  of  the  growing  season  varies  from  23  to  28  centi- 
meters, the  mean  annual  rainfall  lying  between  50  and  100  cm., 
but  nearer  the  latter.  Cloudiness  and  fogginess  often  prevail. 
(Twenhofel-48.)  In  southern  latitudes  peat  is  more  rarely  formed 
from  mosses.  In  the  Chonos  Archipelago  (S.  L.  44°  to  46°)  every 
piece  of  level  ground  is  covered  with  Astilia  puniata  and  Donatia 
magellanica,  which  by  their  joint  decay  compose  a  thick  bed  of 
elastic  peat.  (Darwin— 12  :  24-26.) 

Astilia  is  the  chief  peat  former  of  Tierra  del  Fuego.  Fresh 
'leaves  appear  constantly  around  the  growing  stem,  while  the  lower 
ones  decay.  ( Stevenson-46  :  563  (161).)  Every  plant  in  the  Falk- 
land Islands  becomes  converted  into  peat,  but  the  most  important 
plants  are  a  variety  of  "crowberry1'  also  common  on  Scottish  Hills 
(Empetrum  rubrum),  a  creeping  myrtle  (Myrtus  nummularia),  a 
dwarf  species  of  water  marigold  (Caltha  appendiculata)  and  some 
sedges  and  sedge-like  plants.  "The  roots,  preserved  almost  unal- 
tered,, may  be  traced  downward  in  the  peat  for  several  feet,  but 
finally  all  structure  is  obliterated  and  the  whole  is  reduced  to  an 
amorphous  structureless  mass."  ( Stevenson-46 :  564 


Peat  in  the  Tropics. 

Sphagnum  does  not  occur  south  of  N.  L.  29°,  but  peat  is  formed 
by  a  variety  of  plants  south  of  this  line.  The  cypress  swamps  of 
Florida  contain  thick  deposits  of  peat,  with  cypresses,  grasses,  ferns 
and  myrtle  making  up  the  bulk  of  the  vegetation.  On  Bermuda  a 
thickness  of  at  least  50  feet  is  assigned  to  the  peat  in  one  of  the  two 
great  peat  swamps.  "The  climate  is  such  that  plants  of  Carbonifer- 
ous type  could  grow' well,  for  the  banana  thrives,  while  palms  and 
Indian  rubber  trees  attain  great  size."  (  Stevenson-46  -.567  (165). ) 
Extensive  peat  bogs  are  found  in  the  Amazon  region  and  in  the  in- 
terior of  Africa.  In  the  region  between  the  Gulf  of  Guinea  and  the 
sources  of  the  Niger,  extensive  peat  deposits  are  formed  by  the 
sedge  Eriosporq  pilosa  Benth.  On  the  Island  of  Sumatra  occurs 
a  large  swamp,  90  km.  from  the  coast,  on  the  left  bank  of  the  river 


5io  PRINCIPLES    OF    STRATIGRAPHY 

Kampar.  It  has  a  width  of  12  kilometers  and  an  area  of  more 
than  80,000  hectares,  and  is  covered  by  trees  rising  mostly  to  a 
height  of  30  m.  It  contains  a  peat  deposit  which  has  been  sounded  to 
a  depth  of  9  meters.  This  peat  consists  largely  of  decayed  woody 
tissue.  The  larger  roots  of  trees,  with  their  upward  pointing  pneu- 
matophores,  form  a  solid  basis  in  this  swamp,  which  makes  tra- 
versing possible.  The  numerous  varieties  of  trees  have  mostly  slen- 
der stems,  bearing  only  a  small  crown  of  leaves,  but  with  broad, 
buttressed  roots  rising  three  to  four  meters  above  the  ground,  and 
with  remarkable  aerial  roots  projecting  in  bundles  for  a  meter  or  a 
meter  and  a  half  from  the  trunk.  Gymnosperms  and  monocotyl- 
edons are  wholly  wanting  among  the  taller  trees  of  this  swamp, 
these  being  chiefly  composed  of  dicotyledons.  Among  the  smaller 
trees  and  bushes  monocotyledons  occur,  though  sparingly.  Tree 
palms  are  rare,  but  bushes  of  this  family  abound,  especially  several 
species  of  a  small  Calamus.  A  small  tree  fern  (Alsophila?)  was 
also  found  scatteringly.  The  herbaceous  vegetation  is  sparingly  rep- 
resented both  in  species  and  individuals.  Grasses  and  sedges  are 
practically  wanting,  the  ground  between  the  trees,  where  not  occu- 
pied by  the  aerial  roots  or  "knees,"  being  strewn  with  decaying 
leaves.  Sphagnum  is  wholly  wanting,  and  other  mosses,  liverworts, 
lichens  and  herbaceous  Pterydophytes  are  rare.  Epiphytes  occur 
only  in  the  leafy  crown  of  the  trees  on  account  of  the  smooth  char- 
acter of  their  trunks.  Phanerogamous  water  plants  appear  to  be 
rare,  but  thread-like  algae  were  found  to  be  numerous  where  the 
forest  was  lightened  through  uprooting  of  trees  by  the  winds.  To- 
ward the  margin  of  this  tropical  swamp  the  vegetation  gradually 
changes,  merging  into  that  of  the  surrounding  drier  land.  (Potonie- 

32.) 

FOSSIL  HUMULITHS. 

The  Humuliths  of  former  geological  periods  are  represented  by 
the  following  types : 

Lignite, 
Brown  Coal, 
Bituminous  Coal, 
Anthracite, 
Graphite. 

Lignite  is  wood,  especially  that  of  coniferous  trees,  which  is  in 
its  early  stages  of  alteration,  but  still  shows  the  woody  characters 
in  unmistakable  manner.  Lignites  are  found  in  Mesozoic  deposits 


FOSSIL    HUMULITHS  511 

and  are  especially  abundant  in  and  characteristic  of  the  Tertiary, 
where  they  are  often  associated  with  brown  coal. 

Brown  Coal  is  a  compact  or  earthy,  altered  peat  deposit,  espe- 
cially characteristic  of  the  Tertiary  rocks.  It  represents  one  of  the 
intermediate  stages  from  peat  to  mineral  coal,  and  still  often  shows 
evidence  of  its  organic  origin.  It  varies  from  pale  brown  or  yel- 
low to  deep  brown  or  black,  though  some  shade  of  brown  is  the 
prevailing  color.  It  contains  from  55  to  75  per  cent,  of  carbon,  has 
a  specific  gravity  of  0.5  to  1.5  and  burns  easily  with  a  sooty  flame 
and  strong  odor,  leaving  a  light  ash.  The  most  extensive  deposits 
are  in  the  Oligocenic  of  North  Germany,  but  peat  beds  altered  to 
Brown  coal  have  also  been  observed  in  post-Tertiary  deposits. 

Bituminous  Coal.  This  coal,  also  called  soft  coal,  is  found  in 
the  Mesozoic  and  the  Carbonic.  It  is  black,  compact,  usually  brit- 
tle, with  cubical  or  conchoidal  cleavage,  and  has  a  shiny  luster.  It 
contains  from  75  to  90  per  cent,  of  carbon  and  generally  some  sul- 
phur. Its  specific  gravity  ranges  from  1.2  to  1.35,  and  it  burns 
with  a  bright,  clear  flame.  Some  varieties  cake  on  burning,  others 
are  consumed  to  ashes.  Generally  no  trace  of  organic  matter  is 
recognizable,  except  under  the  microscope. 

Anthracite,  or  hard  coal,  is  the  most  highly  mineralized  form  of 
coal,  with  a  black  color,  strong,  metalloid  or  vitreous  luster  and 
conchoidal  fracture.  Its  specific  gravity  ranges  from  1.35  to  1.7, 
and  it  contains  over  90  per  cent,  of  carbon.  It  kindles  with  diffi- 
culty, but  burns  in  a  strong  draught  with  great  heat  and  without 
smoke,  caking  or  odor.  It  occurs  in  disturbed  regions  where  the 
volatile  matter  has  been  driven  off  through  heat  and  metamorphism. 
Some  anthracites  also  originate  through  extensive  loss  of  the  vola- 
tile gases  before  entombment. 

Graphite,  or  pure  carbon,  is  found  chiefly  in  ancient  crystalline 
rocks,  such  as  gneisses,  mica  schists,  metamorphic  limestones,  etc. 
When  originating  from  organic  matter  it  is  the  product  of  extreme 
metamorphism,  but  it  may  also  be  formed  in  purely  inorganic 
manner. 

Ancient  Moors. 

Among  the  moors  of  past  geological  time,  those  of  the  Anthra- 
colithic  or  Carbonic  period  deserve  especial  attention,  for  they  have 
not  only  furnished  a  large  part  of  the  coal  supply  of  the  world,  but 
their  wonderful  luxuriance  of  growth  and  strangeness  of  type  in- 
vest them  with  peculiar  interest,  and  make  the  restoration  of 
these  ancient  swamps  and  forests  and  their  subsequent  burial  a 
problem  full  of  fascination. 


512  PRINCIPLES    OF    STRATIGRAPHY 

Comparison  with  modern  moors  leads  to  the  conclusion  that 
those  of  Carbonic  time  were  of  the  flat  or  low  moor  variety,  or 
that  type  in  which  arboreal  vegetation  plays  a  more  significant  part 
than  it  does  in  our  upland  bogs.  While  the  seashore  or  marsh  type 
was  not  unrepresented,  it  is  apparent  from  the  character  of  the 
vegetation  that  the  prevailing  moor  type  of  that  period,  now  repre- 
sented by  our  coal  beds,  was  of  the  fresh-water  swamp  or  morass 
type.  The  character  of  the  vegetation  itself  points  to  this,  since 
the  tissues  of  the  Carbonic  trees  are  of  coarse-cell  type  like  those 
of  the  rapid-growing  trees  of  our  swamps,  instead  of  the  close- 
celled  type  characteristic  of  upland  bogs  and  due  to  slower  growth. 
Of  all  the  known  modern  swamps  that  of  Sumatra,  above  de- 
scribed, comes  nearest  to  representing  the  conditions  of  the  Car- 
bonic moors,  for  the  character  of  the  vegetation  seems  to  point  un- 
mistakably to  a  moist,  tropical  climate  for  at  least  part  of  our  Car- 
bonic coal  deposits. 

The  place  of  the  modern  bulrushes  and  other  reeds  was  taken 
in  Carbonic  time  by  the  gigantic  reed-like  relatives  of  the  modern 
Equisetum,  i.  e.,  the  Calamites.  The  usual  occurrence  of  these 
plants  in  sandstones  preceding  coal  beds  indicates  that  they  per- 
formed much  the  same  land- forming  office  in  those  days  that  the 
reeds  do  to-day.  They  have  in  common  with  them  the  characteris- 
tic power  of  sectional  repetition  of  parts  which  enables  the  plant 
to  continue  growth  and  putting  forth  of  roots,  even  though  it  is 
progressively  buried  by  the  accumulating  silt. 

The  tree  types  succeeding  the  calamites,  the  Lepidophytes,  in- 
cluding Lepidodendra  and  Sigillaria,  were  true  swamp  plants  with 
horizontally  spreading  roots,  the  Stigmaria.  These  fossil  roots  have 
a  remarkable  similarity  to  the  spreading  roots  of  Pinus  and  other 
moor  trees  of  the  present  day,  and,  like  these,  were  adapted  for 
growth  on  wet  ground,  where  firmness  of  foundation  was  secured 
by  great  horizontal  spreading,  and  where  it  was  not  necessary  to 
penetrate  into  the  soil  for  moisture,  as  in  regions  of  low-lying 
ground-water  level.  A  basal  enlargement  of  the  trunks  of  trees, 
such  as  characterizes  Nyssa  uniflora  and  others  of  our  swamp  trees, 
is  also  often  seen  in  these  Carbonic  types.  This  feature  likewise 
tends  to  keep  the  tree  erect,  owing  to  the  greater  weight  of  the 
basal  portion.  Structures  suggestive  of  the  cypress  knees  or  pneu- 
matophores  of  our  subtropical  swamps  have  also  been  found  asso- 
ciated with  the  Sigillaria,  while  structures  suggestive  of  the  breath- 
ing pores  or  lenticels,  so  characteristic  of  the  basal  portions  of  the 
trunks  of  trees  in  the  tropical  swamps,  occur  in  the  Carbonic 
Lepidophytes,  where  they  form  the  Syringodendron  surface. 


COALS    AND    COAL    SHALES  513 

The  characters  of  the  Ferns  and  the  Sphenophyllaceae  of  the 
Carbonic  likewise  point  to  moist  tropical  conditions  during  that 
period,  and  since  the  coal  deposits  resulting  from  the  growth  of 
these  plants  are  so  widely  distributed  in  regions  which  to-day  have 
a  temperate  climate,  it  is  apparent  that  conditions  now  characteristic 
of  the  equatorial  region  of  the  world  were  during  the  Carbonic 
period  more  widely  distributed.  In  Chapter  II  a  possible  cause 
for  the  increase  in  temperature  was  discussed,  this  being  the  greater 
supply  of  CO2  in  the  atmosphere  which  would  retain  the  heat  and 
so  raise  the  temperature  of  the  entire  earth's  surface.  The  removal 
of  this  atmospheric  constituent  and  the  storage  of  the  carbon  in 
the  tissues  of  plants  would  bring  about  a  progressive  lowering  of 
the  temperature,  and  this  refrigeration  of  the  climate  would  bring 
on  the  glacial  conditions  known  to  have  existed  in  Permic  time.  It 
is  a  notable  fact  that  the  coal-forming  period  was  preceded  by  a 
period  of  wide  and  extensive  submergence  and  the  building  of  lime- 
stones in  all  parts  of  the  world.  This  would  result  in  setting  free 
much  CO2,  and  hence  would  supply  the  conditions  favorable  to  the 
development  of  the  tropical  coal  swamp  on  the  emergence  of  the 
land.* 

The  coals  formed  during  the  Mesozoic  periods  have  probably  a 
history  similar  to  that  of  the  Carbonic  coals,  though  seashore  con- 
ditions and  those  of  lagoons  and  estuaries  may  have  been  more 
common.  The  Tertiary  coals,  especially  those  of  northern  Europe, 
appear  to  have  been  formed  in  swamps  closely  similar  to  our  mod- 
ern cypress  swamps  of  southern  North  America.  Many  of  the 
species  found  in  the  brown-coal  deposits  of  North  Germany,  such  as 
the  Magnolias,  Liquidambar,  Sassafras,  Catalpa,  Swamp  Cypress, 
etc.,  are  still  living  in  these  swamps,  though  they  have  become  ex- 
tinct in  Europe.  The  remarkable  depth  of  the  brown-coal  deposits 
of  North  Germany,  reaching  north  of  Cologne  nearly  100  meters, 
gives  some  indication  of  the  length  of  time  required  to  accumulate 
such  a  mass  of  vegetal  material  by  successive  periods  of  growth  and 
decay.  As  in  the  case  of  the  Carbonic  deposits,  the  Tertiary  coal 
period  was  preceded  by  extensive  limestone  deposits  and  succeeded 
by  a  period  of  gradual  refrigeration  which  culminated  in  the  Pleis- 
tocenic  glaciation. 

Black  Soil  and  Shales  of  Humulithic  Origin. 

Long-continued  growth  of  vegetation  produces  in  some  regions 
a  thick  accumulation  of  a  dark  loam,  such  as  is  seen  in  the  black 

*  See  also  p.  90,  and  the  reference  to  Koken's  work  in  Chapter  XXIII. 


514  PRINCIPLES    OF    STRATIGRAPHY 

cotton  soil  (regur)  of  India  and  in  the  black  earth  (tchernozom) 
of  Russia.  Such  deposits  may  subsequently  harden  into  black,  car- 
bonaceous shales.  Examples  of  such  shales  are  probably  to  be 
found  in  the  Chattanooga  black  shale  of  eastern  Alabama,  etc.,  of 
Lower  Mississippi  age.  This  in  places  includes  thin  layers  of 
coal,  arid  in  other  respects  bears  evidence  of  having  been  a  former 
residual  soil,  the  black  color  of  which  is  due  to  the  abundance  of 
partially  decayed  land  vegetation. 


Burial  of  Peat  Deposits. 

Peats  formed  near  the  coast,  even  when  of  fresh-water  or 
swamp  origin,  may  be  buried  by  a  subsidence  of  the  land  and  a  con- 
sequent transgression  of  the  sea.  Such  subsidence  may  be  so  slow 
that  salt-water  or  marsh  peat  may  transgress  over  the  fresh-water 
peat,  as  in  the  case  of  the  Massachusetts  coast  (see  ante,  p.  493). 
Where  subsidence  is  more  rapid,  fresh-water  peat  may  be  covered 
by  marine  sands,  as  in  the  Bay  of  Morlaix,  Brittany  (Finistere), 
where,  according  to  Cayeux,  two  layers  of  peat  with  Arundo 
phragmites  are  separated  and  again  covered  by  marine  sands.  In 
the  flat,  maritime  plain  of  Pas-de-Calais,  a  section  now  three  meters 
above  the  sea-level  shows  : 

Marine  sand  with  Cardium  edule,  i  meter. 

Marine  clay  with  Hydrobia  ulvcc,  I  meter. 

Peat. 

Marine  sandf  with  Cardium  edule. 

In  the  mouth  of  the  Shelde  similar  deposits  of  peat,  i  to  1.5 
meters  thick,  are  enclosed  between  sediments  with  marine  organ- 
isms. At  Cotentin,  in  Normandy,  20  meters  of  peat  are  overlain  by 
marine  sands,  and  similar  deposits  are  found  in  other  parts  of 
France,  in  Belgium,  Holland  and  elsewhere.  As  shown,  however, 
by  the  deposits  of  Anticosti,  the  presence  of  such  marine  organisms 
in  the  strata  covering  the  peat  need  not  always  indicate  subsidence 
after  the  formation  of  the  peat. 

The  section  made  by  the  river  Tay  in  the  Carse  lands  of  south- 
eastern Scotland  shows  a  peat  bog  now  forming  the  river  bed  and 
covered  by  about  17  feet  of  alluvial  material,  which  near  the  top 
contains  cockles,  mussels  and  other  marine  forms.  The  peat  of 
this  region  rests  in  part  on  alluvial  sands  and  in  part  on  marine 
clays,  and  is  itself  of  terrestrial  origin.  It  is  "highly  compressed 
and  splits  readily  into  laminae,  on  whose  surfaces  are  small  seeds 
and  wing  cases  of  insects.  As  a  rule,  but  not  always,  it  is  marked 


BURIAL   OF    PEAT    DEPOSITS  515 

off  sharply  from  the  overlying  clay  and  silt."  The  upper  layers  of 
the  peat  represent  transported  material  from  farther  up  the  stream, 
and  consist  of  silt  with  twigs  and  branches  and  trunks  of  trees. 
Other  examples  are  cited  by  Stevenson  (46). 

Glacial  till  ;is  not  an  infrequent  cover  for  peat  deposits.  Sir 
William  Dawson  (17:63)  has  described  an  early  Quaternary 
bog  in  Nova  Scotia,  where  the  peat  was  covered  by  20  feet 
of  boulder  clay  and  so  compressed  that  it  had  almost  the  hardness 
of  coal.  In  the  New  England  States  such  peat  buried  under  gla- 
cial drift  is  not  uncommon,  and  it  has  been  observed  in  widely  sep- 
arated districts  in  the  glaciated  area.  In  Montgomery  County, 
Ohio,  a  bed  of  peat,  15  to  20  feet  thick,  and  with  its  surface  formed 
by  Sphagnum  grasses  and  sedges,  underlies  90  feet  of  gravel  and 
sand.  The  peat  contains  coniferous  wood,  bones  of  elephant,  mas- 
todon and  teeth  of  giant  beaver.  In  southwestern  Indiana  and 
part  of  Illinois  an  ancient  soil,  2  to  20  feet  thick,  and  containing 
peat,  muck,  rooted  stumps,  branches  and  leaves,  lies  at  a  depth  of 
60  to  1 20  feet  below  the  surface. 

Peat  deposits  on  the  flood  plains  and  deltas  of  rivers  are  likely 
to  be  buried  under  the  silt  and  mud  when  the  river  rises,  and  like- 
wise, when  through  a  change  in  climate  or  other  cause  a  river  be- 
gins to  rapidly  aggrade  its  flood  plain.  In  such  cases  the  peat  de- 
posits will  be  buried  under  regular  strata  of  sand  and  clay  of  con- 
tinental origin,  and  it  would  happen  that  the  trees  still  standing  are 
gradually^  buried  in  the  silt  and  sand.  "Even  the  slender  canes  of 
the  Mississippi  delta,  killed  by  salt-water  invasion,  remain  standing 
after  they  have  been  surrounded  by  several  feet  of  silt."  (Steven- 
son-46.)  The  filling  of  the  hollow  bark  of  still  erect  trees,  in  which 
the  wood  has  decayed,  by  sand  and  mud  and  so  ensuring  their  pres- 
ervation in  an  erect  form,  is  a  familiar  fact  to  students  of  the  Coal 
Measures.  The  well-known  section  at  South  Joggins,  Nova  Scotia, 
shows  erect  Sigillaria  and  other  trees  in  considerable  number.  The 
most  important  part  of  the  section  containing  these  trees  is  as  fol- 
lows (Dawson-i8)  : 

Sandstone  with  erect  Calamites  and  Stigmaria  roots 6  ft.  6  in. 

Argillaceous  sandstone,  Calamites,  Stigmaria  and  Alethop- 

teris  cuchitica i  ft.  6  in. 

Gray  shale,  with  numerous  fossil  plants,  and  also  Naiadites, 

Carbonia  and  fish  scales 2  ft.  4  in. 

Black  coaly  shale,  with  similar  fossils I  f t.  I  in. 

Coal  with  impression  of  Sigillaria  bark o  ft.  6  in. 

"On  the  surface  of  the  coal  stand  many  erect  Sigillariae,  pene- 
trating the  beds  above,  and  some  of  them  nearly  three  feet  in 


PRINCIPLES    OF    STRATIGRAPHY 


diameter  at  the  base  and  nine  feet  in  height.  In  the  lower  part  of 
many  of  these  erect  trees  there  is  a  deposit  of  earthy  matter  black- 
ened with  carbon  and  vegetable  remains  and  richly  stored  with  bones 
of  small  reptiles,  land  snails  and  millipedes."  Dawson  considers 
that  "on  decay  of  the  woody  axis  and  inner  bark  they  must  have 
constituted  open  cylindrical  cavities,  in  which  small  animals  shel- 


FIG.  116.  Buried  peat  bed  near  Marquette,  Michigan,  with  bog-iron  stratum 
below  and  sand  dune  above.  Exposure  made  by  easterly  storm. 
(After  Davis.)  a,  stump  of  buried  tree;  b,  sand  stratum,  with 
roots  and  other  plant  remains ;  c,  e,  and  g,  pine  needles ;  d, 
sand  with  grass  remains;  f,  iron  sand;  h,  pure  sand,  cross- 
bedded;  i,  peat  stratum,  with  standing  pine  stump;  k,  bog  iron. 
(Height  of  section  about  15  feet.) 

tered  themselves,  or  into  which  they  fell  and  remained  imprisoned. 
These  natural  traps  must  have  remained  open  for  some  time  on  a 
subaerial  surface."  Fifteen  out  of  twenty-five  erect  trees  proved 
to  have  these  contents,  in  one  no  less  than  twelve  reptilian  skeletons 
occurring.  In  a  few  instances  portions  of  the  cuticle,  ornamented 
with  horny  scales  and  spines,  had  been  preserved.  In  these  de- 
posits, it  is  evident  that  the  trees  after  being  buried  up  to  a  certain 
depth  rotted  away  on  the  surface  or  were  blown  down,  and  that 


BURIAL    OF    PEAT    DEPOSITS  517 

then  the  inner  tissues  decayed  until  only  the  bark,  embedded  in  up- 
right position  in  the  mud,  remained  behind.  The  bark  of  fallen 
trees  is  generally  pressed  flat  on  the  decay  of  the  inner  tissues  by 
the  weight  of  the  superincumbent  sediment.  In  Alaska  the  Yahtse 
River,  "issuing  as  a  swift  current  from  beneath  the  glacier,  has  in- 
vaded a  forest  at  the  east,  and  has  surrounded  the  trees  with  sand 
and  gravel  to  a  depth  of  many  feet.  Some  of  the  dead  trunks,  still 
retaining  their  branches,  project  above  the  mass,  but  the  greater  part 
of  them  have  been  broken  off  and  buried  in  the  deposit.  Other 
streams,  east  from  the  Yahtse,  have  invaded  forests,  as  indicated 
by  dead  trees  standing  along  their  borders.  Where  the  deposit  is 
deepest  the  trees  have  already  disappeared,  and  the  forest  has  been 
replaced  with  sand  flats.  The  decaying  trunks  are  broken  off  by 
the  wind,  and  are  buried  in  prostrate  position.  This  deposit  con- 
solidated would  resemble  closely  a  Coal  Measure  conglomerate." 
(Russell,  cited  by  Stevenson-46.) 

Modern  tree  trunks  have  been  found  on  the  coast  with  their  in- 
terior decayed  and  rilled  with  sand  down  into  the  roots.  (Potonie- 
32.)  Sand  dunes  advancing  over  a  peat  bed  will  put  an  effective 
stop  to  further  peat  formation  and  serve  as  a  factor  in  preserv- 
ing the  peat  so  formed.  It  is  not  improbable  that  many  of  the 
sandstones  which  succeed  the  coal  beds  of  our  Carbonic  series  owe 
their  origin  to  such  covering  wind-blown  sands. 

In  advancing  over  the  peat  the  sand  dunes  will  likewise  advance 
over  the  forests  associated  with  the  peat  and  bury  them.  This  can 
be  seen  in  many  regions  where  only  the  tops  of  large  trees  project 
above  the  sands,  as  on  the  shores  of  Lake  Michigan,  etc. 

In  rare  cases  peat  deposits  may  be  buried  by  landslides,  by  mud 
flows,  etc.  In  all  cases  where  the  deposit,  first  spread  over  the 
swamp  or  bog,  is  a  fine  one,  impressions  of  the  last  fallen  leaves 
and  branches  may  be  preserved  in  great  detail.  In  this  manner  are 
formed  the  roof  shales  with  their  wonderful  wealth  of  plant  im- 
pressions, which  makes  it  possible  for  us  to-day  to  reconstruct  the 
vanished  flora  of  the  Coal  Period.  The  clay  or  soil  in  which  the 
plants  had  their  roots  is  in  most  cases  preserved  as  a  "fire  clay," 
that  is,  a  clay  which  can  be  used  for  pottery  which  has  to  with- 
stand intense  heat.  It  contains  little  iron,  and  is  nearly  free  from 
lime  and  alkalies,  of  which  the  clay  was  deprived  by  the  growth  of 
the  plants. 

LIPTOBIOLITHS. 

These  may  be  dismissed  with  a  few  words.  The  exudations  of 
resins,  gums,  wax,  etc.,  from  resinous  trees  are  characterized  by 


518  PRINCIPLES    OF    STRATIGRAPHY 

relative  stability  of  composition,  and  are  not  easily  decomposed. 
They  may  thus  form  accumulations  of  greater  or  less  extent,  while 
the  plant  tissues  which  they  enclose  decay  wholly.  The  subfossil 
Copal  is  a  typical  example,  while  from  older  rocks  (Oligocenic)  of 
North  Germany  comes  the  amber.  Many  minor  types  of  liptobio- 
liths  occur  in  nature,  but  they  are  of  more  mineralogical  than  geo- 
logical value. 

^         ALLOCHTHONOUS  VEGETAL  DEPOSITS. 

Vegetal  material  transported  from  other  localities  and  deposited 
where  it  did  not  grow  is  found  frequently  at  the  present  time,  both 
upon  the  land  and  in  the  sea.  It  also  occurred  in  the  past.  On  the 
Missouri,  Mississippi  and  other  rivers,  rafts  and  whole  floating 
islands  of  vegetation  are  known,  and  logs  are  found  scattered 
widely  through  deposits  to  which  they  are  wholly  foreign.  "These 
drifted  materials  are  everywhere  distinguishable  from  plants  buried 
in  situ,  for  they  have  been  deprived  of  all  tender  parts;  of  the 
harder  woods  in  Carboniferous  times  there  are  few  traces  except 
decorticated  stems,  casts  of  the  interior,  indeterminate  forms 
grouped  under  Knorria,  Sternbergia  and  some  other  names." 
( Stevenson-46 : 642.) 

"In  all  extensive  deposits  of  driftwood  the  trees  are  battered, 
stripped  of  leaves,  bark  and  often  of  branches ;  they  are  scattered 
on  the  strand  or  piled  in  irregular  loose  heaps,  where,  exposed  to 
the  air,  they  decay;  or,  if  in  more  favorable  conditions,  the  inter- 
stices become  rilled  with  sediment,  the  trees  become  merely  logs  in 
shale  or  sandstone,  even  their  genus  being  unrecognizable  except  by 
microscopic  study  of  the  structure."  ( Stevenson-46 :  557. ) 

The  coal  deposits  of  the  Commentry  basin  in  France  have  long 
been  held  to  be  a  good  example  of  a  fossil  allochthonous  coal.  It  is 
now  known,  however,  that  this  coal  is  formed  in  situ,  after  all. 
Stigmaria  are  found  in  place,  while  the  trees  are  arranged  in  all 
positions,  upright,  leaning  and  prostrate.  The  resemblance  to  a 
forest  ravaged  by  a  hurricane  is  very  close. 

Marine  Vegetal  Deposits.  Marine  plants,  owing  to  the  buoyancy 
which  they  possess  on  account  of  the  numerous  air  spaces  in  their 
tissues,  will  float  on  the  surface  of  the  water  until  stranded  on  the 
shore  or  on  a  mud  flat.  Their  presence  in  the  deep  sea  deposits 
is  not  noted,  because  they  will  continue  to  float  until  decomposed. 
On  the  other  hand,  in  the  shallower  portions  of  the  littoral  district 
marine  plants  may  accumulate  in  abundance.  Spores  of  plants  are 
not  infrequently  found  in  marine  sediments.  But  by  far  the  most 


DEEP   SEA  VEGETAL   DEPOSITS  519 

noteworthy  deposits  of  plants  in  marine  sediments  are  the  deep- 
sea  accumulations  of  leaves  and  driftwood  of  terrestrial  origin. 
In  the  Caribbean,  on  the  lee  side  of  the  West  Indian  Islands,  the 
Blake  dredged  "masses  of  leaves,  pieces  of  bamboo  and  of  sugar 
cane,  dead  land  shells,  and  other  land  debris"  at  a  depth  of  over 
1,000  fathoms,  and  ten  or  fifteen  miles  from  land.  ( Agassiz-i :  291.) 
The  Albatross  in  its  dredging  expedition  on  the  west  coast  of  Cen- 
tral America  between  the  Galapagos  Islands,  the  west  coast  of  Mex- 
ico, and"  the  Gulf  of  California,  found  nearly  everywhere  a  muddy 
bottom  or  one  composed  of  Globigerina  ooze,  and  generally  con- 
taining terrigenous  matter.  Scarcely  a  single  haul  of  the  trawl 
was  made  which  did  not  bring  up  a  "considerable  amount  of  de- 
cayed vegetable  matter,  and  frequently  logs,  branches,  twigs,  seeds, 
leaves,  fruits,"  much  as  found  by  the  Blake  on  the  east  coast,  but 
in  vastly  greater  quantities.  Even  at  a  depth  of  over  2,000  fathoms 
these  remains  were  found.  ( Agassiz-2  :  n,  12.) 

The  Challenger  also  found  twigs,  woods,  and  seeds  at  a  depth 
of  800  fathoms  near  Ki  Island,  and  also  within  20  fathoms  off  the 
coast  of  Amboina  Island,  both  west  of  New  Guinea.  South  of 
Mindanao,  at  a  depth  of  2,150  fathoms,  palm  fruits,  and  fragments 
of  wood  and  bark  were  found,  while  about  50  miles  off  the  coast 
of  Luzon  at  a  depth  of  1,050  fathoms  were  dredged  fragments 
of  leaves,  stems  and  wood,  the  latter  overgrown  with  Serpula. 

The  distance  from  shore  to  which  material  is  carried  by  flota- 
tion is  often  indicated  by  the  state  of  preservation  of  the  mate- 
rial. White  says :  "If  the  material  is  macerated,  corroded,  rolled, 
defoliated,  skeletonized,  incrusted,  or  bears  other  signs  of  having 
been  for  some  time  in  the  water  it  is  liable  to  have  been  trans- 
ported for  some  distance.  ...  If  long  in  sea  water  the  frag- 
ments are  likely  to  bear  the  marks  of  abundant  marine  organisms, 
particularly  if  in  tropical  sea  water.  On  the  other  hand,  the  occur- 
rence of  clean,  unbroken^  smooth  leaves,  and  particularly  of  large 
segments  of  fern  fronds,  with  their  full  complement  of  carbonace- 
ous residues,  is  prima  facie  evidence  of  minimum  exposure  to  water 
and  of  the  least  subjection  to  the  action  of  swift  currents  or  waves." 
(White-60.) 

BIBLIOGRAPHY  XI. 

(See  also  Bibliography  X.) 

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tross, from  February  to  May,  1891.      Harvard  College,   Museum  Com- 
parative Zoology,  Vol.  XXIII,  pp.  1-89. 


520  PRINCIPLES    OF    STRATIGRAPHY 

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17.  DAWSON,  SIR  WILLIAM.     1868.    Acadian  Geology.    2nd  edition,  Lon- 

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18.  DAWSON,  SIR  W.     1882.     On  the  Results  of  Recent  Explorations  of  Erect 

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19.  FINCKH,  ALFRED  E.     1904.     Biology  of  the  Reef-forming  Organisms 

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PP-  79-93). 

21.  GARDINER,  STANLEY  J.     1898.     The  Coral  Reefs  of  Funafuti,  Rotuma 

and  Fiji,  together  with  some  Notes  on  the  Structure  and  Formation  of 
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23.  HARPER,  R.  M.     1909.     Okefenoke  Swamp.     Popular  Science  Monthly, 

Vol.  LXXIV,  pp.  596-613. 

24.  HOWE,  MARSHALL  A.     1912.    The  Building  of  "Coral"  Reefs.    Science, 

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25.  JEFFREY,  EDWARD   C.    1910.     Th©  Nature  of  Some  Supposed  Algal 

Coals.  Proceedings  of  the  American  Academy  of  Arts  and  Sciences, 
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26.  KALKOWSKY,  E.     1901.     Die  Verkieselung  der  Gesteine  in  der  Nord- 

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27.  KALKOWSKY,  E.     1908.     Oolith  und  Stromatolith  im  Norddeutschen 

Bundsandstein.  Zeitschrift  der  deutschen  geologischen  Gesellschaft, 
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28.  LYELL,  CHARLES.    1829.    On  a  Recent  Formation  of  Fresh  Water  Lime- 

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29.  MOJSISOVICS,    VON    MOJSVAR,    EDMUND.     1879.     Die    Dolomit 

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30.  PARSONS,  ARTHUR  L.    1904.    Peat;  Its  formation,  Uses  and  Occurrence 

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31.  POMPECKJ,  J.  F.     1901.     Die  Jura-Ablagerungen  zwischen  Regensburg 

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et  seq. 

POTONIE,  H.  1910.  Die  Entstehung  der  Steinkohle  und  der  Kausto- 
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RAMANN,  E.  1910.  Einteilung  und  Bau  der  Moore.  Zeitschrift  der 
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ROTHPLETZ,  A.  1891.  Fossile  Kalkalgen  aus  den  Familien  der  Codia- 
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ROTHPLETZ,  A.  1892.  On  the  Formation  of  Oolite.  (Botanisches 
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RUEDEMANN,  R.  1909.  Some  Marine  Algae  from  the  Trenton  Lime- 
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BIBLIOGRAPHY   XI 


523 


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113-127. 


CHAPTER    XII. 

ORIGINAL  CHARACTERS  AND  LITHOGENESIS  OF  THE  EXOGENETIC 
ROCKS.     THE  PYROCLASTICS  AND  THE  AUTOCLASTICS. 

The  original  structures  of  Exogenetic  or  clastic  rocks  are  mainly 
those  formed  during  their  deposition.  Therefore  the  structures  of 
each  division  of  these  rocks  will  show  individual  peculiarities,  and 
hence  each  division  will  be  considered  by  itself. 


PYROCLASTIC  ROCKS. 

MODERN  PYROCLASTICS.  Tuffs  and  volcanic  breccias  (pyrolu- 
tytes,  pyrarenytes,  and  pyrorudytes)  are  typically  formed  about  the 
volcanic  vents  which  have  furnished  the  material.  (Their  essential 
lithic  characteristics  have  been  described  in  Chapter  VI.)  Ordi- 
narily the  distance  from  the  volcano  at  which  the  deposit  will  form 
will  be  dependent  on  the  fineness  of  grain.  Thus  pyrorudytes  will 
be  formed  close  to  the  volcano,  while  the  pyrolutytes  will  often 
form  at  great  distances  from  the  vent.  These  latter  are  often  car- 
ried very  far  by  the  winds,  and  finally  deposited  as  aeolian  or  wind- 
blown volcanic  ash  (anemopyrolutyte).  In  such  cases  the  structure 
of  the  deposit  partakes  of  that  of  other  anemoclastic  rocks.  Many 
tuffs  are  deposited  in  water,  and  so  become  closely  allied  to  typical 
hydroclastic  rocks  and  partake  of  their  structure.  The  finer  water- 
laid  volcanic  tuffs  (Hydropyrolutytes)  often  show  a  perfect  stratifi- 
cation, and  they  sometimes  are  rich  in  organic  remains.  An  ex- 
ample of  finely  bedded  pyrolutytes  is  found  in  the  fine  paper  shales 
of  volcanic  ashes  of  Florissant,  Colorado,  where  a  wealth  of  beauti- 
fully preserved  insects,  leaves,  and  silicified  trees  testifies  to  the 
adaptability  of  these  deposits  to  the  preservation  of  fossils.  These 
deposits  are  commonly  referred  to  a  Tertiary  lake  caused  by  the 
damming  of  a  valley  by  a  lava  flow.  The  possibility  that  the  de- 
posits are  those  of  a  river  flood  plain  or  playa  lake  must  not  be 
overlooked.  The  great  abundance  of  insects,  spiders,  and  leaves, 
the  erect  tree  trunks,  and  the  scarcity  of  aquatic  animals  point  this 

524 


PYROCLASTIC   ROCKS  525 

way.  The  aquatic  forms  found  comprise  a  thin-shelled  Planorbis, 
always  occurring  in  a  crushed  condition,  a  Physa  and  a  single  speci- 
men of  a  bivalve,  and  eight  species  of  fishes.  Birds'  feathers  and 
bones  and  the  skeletons  and  feathers  of  entire  birds  have  also  been 
found.  Strongly  sun-cracked  layers  point  to  repeated  desiccation 

!  of  the  shallow  lake,  and  this  condition,  first  recognized  by  Lesque- 

!  reux,  is  not  excluded  by  the  character  of  the  fish,  the  water  plants, 
water  insects  or  molluscs.  (Scudder-22;  23.) 

Volcanic  debris  falling  on  the  surface  of  the  land  will  show 
little  regularity  of  deposition.  The  coarser  material  will  exhibit 
no  bedding  lines  or  only  the  very  rudest  ones,  while  volcanic  sand 
or  ashes  may  not  infrequently  show  a  moderate  stratification,  which 
will  generally  be  more  marked  in  the  finer  material.  Where  the 
ashes  come  to  rest  on  a  slope  these  stratification  planes  will  be  in- 
clined. 

Organic  Remains  of  Modern  Pyroclastics.  Organic  remains  are 
not  infrequent  in  pyroclastic  rocks.  They  are  best  preserved  in  the 
finer  grained  deposits.  Of  these  the  remains  of  man  and  his  works 
are  often  the  most  abundant  in  the  modern  tuffs,  whole  cities  and 
their  inhabitants  having  not  infrequently  been  buried.  At  Hercu- 
laneum  and  Pompeii  human  bodies  were  completely  encased  in  the 
fine  mud  from  Vesuvius,  which  on  hardening  formed  a  perfect 
mold  of  the  body,  so  that  plaster  casts  could  afterward  be  made 
from  them. 

OLDER  PYROCLASTIC  DEPOSITS.  From  South  America  and  from 
portions  of  the  Great  Plains  of  western  North  America,  Tertiary 
iieolian  tuffs  (Anemopyrolutytes)  rich  in  the  bones  of  mammals, 
have  been  described.  In  the  Eocenic  deposits  of  the  Wind  River 
Basin  in  Wyoming,  a  white  tuff  bed  13  feet  in  thickness  lies 

1  interbedded  with  the  Wind  River  sands  and  clays.  (Sinclair  and 
Granger-28  :oj  et  seq. )  It  rests  on  a  heavy  brown  sandstone  con- 

;  taining  rolled  pebbles  of  tuff  and  is  succeeded  by  greenish  shales. 
In  the  upper  4  or  5  feet  of  tuff  occurs  much  pumice;  snow  white 
grains  from  the  size  of  bird-shot  to  small  peas  are  found  enclosed 
in  a  fine-grained  gray  matrix.  The  most  abundant  macroscopic 
mineral  enclosed  in  the  white  pumice  is  biotite,  while  small  frag- 
ments of  feldspar  are  occasionally  found.  Under  the  microscope  the 
fine  felt-like  mass  of  volcanic  glass  of  the  pumice  encloses  in  the  or- 
der of  relative  abundance  :  ( I )  orthoclase,  often  zonal,  sometimes 
twinned,  either  with  recognizable  crystallographic  boundaries,  more 
or  less  broken,  or  in  small  laths;  (2)  plagioclase;  (3)  olive  green 
biotite;  (4)  hornblende;  and,  (5)  black  opaque  grains,  probably 
iron  oxide. 


526  PRINCIPLES    OF    STRATIGRAPHY 

The  lower  part  of  the  tuff  consists  of  a  finer  grained  mass,  in 
which  the  round  mass  of  felt-like  glass  fibers  and  wisps  contains 
angular  fragments  of  feldspar,  quartz,  biotite,  and  hornblende  in 
greater  abundance  than  in  the  upper  part.  Balls  of  hard  green 
shale  occur  in  the  tuff  and  these  and  channel-filling  of  contempo- 
raneous origin  point  to  a  fluviatile  deposition  of  the  material. 

In  the  Bridger  of  the  same  region  occurs  a  white  tuff  ranging 
in  thickness  from  25  to  75  feet  which  carries  frequent  lignitic  beds 
varying  in  thickness  from  six  inches  to  a  foot.  No  clay,  sand  or 
gravel  occurs  as  in  tuffs  of  fluviatile  origin,  and  it  is  believed  that 
this  bed  is  a  lacustrine  deposit.  In  regions  where  the  tuff  bed  is 
absent  it  is  replaced  by  arkose  beds  with  clay  pellets  and  apparently 
wind-blown  pyroclastics,  the  whole  traversed  by  tubules  suggestive 
of  root  canals,  and  representing  the  terrestrial  part  of  the  accumu- 
lation. 

In  the  Oligocenic  of  this  region  pyroclastic  material  is  more 
pronounced.  In  the  erosion  troughs  formed  at  the  close  of  the 
Eocenic  volcanic  mud  flows  accumulated,  beginning  with  a  fine- 
grained buff-colored  tuffaceous  shale,  in  which  was  found  a  skull 
of  Titanotherinm  heloceras.  This  was  followed  by  mud  flows  carry- 
ing large  angular  or  rounded  blocks  of  hornblende  andeSite,  up  to 
3  or  4^feet  in  diameter  and  consisting  of  ash,  pumice,  lapilli  and 
pebbles  and  cobbles  of  pre-Tertiary  quartz,  granite,  and  gneiss, 
forming  an  agglomerate  46  feet  in  thickness  -near  Wagon-bed 
spring.  Its  distribution  was  controlled  by  the  preexisting  valleys 
and  so  it  is  absent  in  many  localities.  Repeated  flows  seem  to  be 
indicated  by  what  appear  like  channels  of  erosion  in  some  of  the 
older  flows,  filled  with  andesite  cobbles  embedded  in  gray  ash. 
The  volcanic  eruption  seems  to  have  continued  throughout  the 
lower  Oligocenic,  showering  the  surrounding  country  with  ash  and 
dust.  This  in  some  localities  accumulated  to  a  thickness  of  over 
500  feet.  Locally  this  ash  is  quite  unconsolidated,  but,  as  a  rule,  it 
shows  calcareous  cementation  and  it  may  pass  upward  into  a 
tuffaceous  limestone.  Angular  fragments  of  more  or  less  devitrified 
pumice,  and  sharp  splinters  of  isotropic  glass,  make  up  more  than 
fifty  per  cent,  of  the  soft  ash.  The  rest  consists  of  angular  frag- 
ments of  plagioclase,  orthoclase  resembling  microcline,  hornblende, 
biotite  and  some  quartz  besides  some  other  minerals.  The  quartz 
and  microcline  are  believed  to  have  been  intermingled  wind-blown 
material,  from  the  gneiss  debris  which  forms  alluvial  fans  elsewhere 
in  this  region.  Tuffs  of  volcanoes  near  or  in  the  sea  will  commonly 
enclose  remains  of  marine  organisms.  Examples  of  these  have 


LITHOGENESIS    OF   EXOGENETIC   ROCKS        527 

been  described   from  the   Cambric  of   North  America,   and   from 
other  deposits.     (See  further,  Chapter  XXII.) 

AUTOCLASTIC    ROCKS. 

We  may  define  an  autoclastic  rock  as  made  of  the  fragmental 
material  resulting  from  the  movement  of  one  rock  mass  over  an- 
other, both  contributing  from  their  substance  to  the  clastic  material, 
though,  owing  to  different  degrees  of  hardness,  that  furnished  by 
one  of  the  masses  may  be  most  prominent,  while  that  contributed 
by  the  other  may  be  almost  if  not  wholly  destroyed  during  the 
movements. 

CLASSIFICATION  OF  AUTOCLASTIC  ROCKS.  According  to  the  type 
of  movements  in  the  formation  of  an  autoclastic  rock  we  may 
classify  the  products  as  follows : 

1.  Exogenous,  or  those  due  to  external  forces,  including: 

a.  Those  due  to  compressive  strains,  i.  e.,  thrust-fault  brec- 

cias. 

b.  Those  due  to  gravitational  strains,  comprising: 

(1)  Breccias,  etc.,  formed  by  ordinary  gravity  or  normal 
faulting  subsequent  to  the  formation  of  the  strata,  a 
secondary  structure,  and 

(2)  Breccias  and  brecciated   structures   formed  by  slip- 
ping or  gliding  of  material  during  the  process  of  ac- 
cumulation under  the  influence  of  gravity,  and  re- 
sulting in  the  production  of  intraformational  brec- 
cias, or,  when  the  brecciation  is  incomplete,  contorted 
stratification.     Glacial  deposits  are  best  placed  here. 

2.  Endogenous  or  endolithic   structures,   or  those  due  to   in- 

ternal forces,  including: 

c.  Those  due  to  movements  resulting  from  solution  and  re- 

crystallization,  as  in  ice,  salt,  etc. 

d.  Those  due  to  increase  or  decrease  in  volume  from  hydra- 

tion,  carbonation,  oxidation,  etc.,  or  the  reverse,  as 
in  change  of  anhydrite  to  gypsum,  or  the  removal  of 
certain  elements,  as  in  dolomitization  of  limestones. 
The  distortion  of  salt  layers,  of  gypsum  beds,  and 
limestones  producing  the  contorted  structure  which, 
from  its  resemblance  to  the  coiled  intestine,  has  been 
called  enterolithic  structure  (German,  Gekrose),  may 
be  cited  as  illustrations. 

The  more  important  types  may  be  described  in  detail. 


528  PRINCIPLES    OF    STRATIGRAPHY 

FAULT  BRECCIAS. 

So  far  as  understood,  fault  breccias  due  to  thrusting  and  those 
due  to  gravitational  readjustment  are  not  essentially  different  in 
character,  except  that  the  former  may  frequently  be  parallel  to  the 
bedding  planes  of  stratified  rocks  in  which  such  thrusting  has  taken 
place,  while  the  latter  are  likely  to  cross  these  planes  at  an  angle. 
Both  are,  however,  secondary  features  formed  within  the  rock 
mass,  after  its  deposition  if  not  its  consolidation.  In  these  dynamic 
movements,  autorudytes,  autoarenytes,  and  autolutytes  result,  and 
they  are  often  accompanied  by  the  formation  of  slipping  surfaces  or 
slickensides.  The  coarser  rocks  of  this  type  often  simulate  hydro- 
elastics,  owing  to  the  fact  that  during  the  movement  of  the  rock 
masses  past  each  other  the  angles  of  the  fragments  were  worn  off 
and  have  become  rounded  by  mutual  friction.  (Van  Hise-3o:d79.) 
In  this  condition  the  bed  may  readily  be  mistaken  for  a  hydroclastic 
conglomerate  (hydrorudyte).  Such  beds  have  been  termed  pseudo- 
conglomerates.  Typical  autorudytes  or  dynamic  breccias  consist 
generally  of  more  or  less  angular  fragments  embedded  in  a  matrix 
of  crushed  material.  In  all  cases  the  autorudytes  are  composed, 
of  the  material  of  the  enclosing  rock  with  the  fragments  derived 
from  the  most  brittle  of  the  beds  from  which  it  was  formed.  Thus 
an  autorudyte  formed  from  interstratified  layers  of  limestone  and 
quartzite  will  have  its  fragments  mainly  composed  of  the  quartzite. 

Since  autorudytes  so  often  simulate  normal  conglomerates,  it 
becomes  important  to  determine  the  criteria  by  which  the  two  may 
be  distinguished.  For  it  is  obvious  that,  if  the  former  is  mistaken 
for  the  latter,  it  will  lead  to  an  entirely  erroneous  interpretation  of 
the  history  of  that  region.  This  is  particularly  the  case  where  the 
autorudyte  may  be  mistaken  for  a  basal  conglomerate.  Alternating 
beds  of  shales  or  pure  lutytes,  and  fine  lutaceous  arenytes  or  gray- 
wackes,  may  by  deformation  be  broken  up  in  such  a  manner  that 
the  arenytes  yield  pebbles,  more  or  less  rounded  by  mutual  fric- 
tion, while  the  shale  flows  and  fills  the  spaces  between  the  frag- 
ments. (Van  Hise-3<D.) 

The  pseudo-conglomerate  thus  produced  will  have  "a  slate  ma- 
trix and  pebbles  of  graywacke  [argillaceous  silicarenyte]  which,  so 
far  as  its  own  characters  are  concerned,  could  not  be  discriminated 
by  any  one  from  a  true  conglomerate."  (Van  Hise~3O.)  Auto- 
clastic  limestone  pebbles  of  a  rounded  character  are  common  in  the 
Cambro-Ordovicic  rocks  of  the  Taconic  region,  and  in  other  dis- 
turbed Palaeozoics  in  many  portions  of  the  world.  They  are  ex- 
tremely characteristic  of  pre-Cambric  rocks. 


AUTOCLASTIC   ROCKS  529 

The  following  criteria  are  given  by  Van  Hise  as  aids  in  dis- 
criminating between  autorudytes  and  true  conglomerates  (hydro- 
rudytes)  : 

1.  "An  autoclastic  rock  must  derive  its  material  mainly  from 
the  adjacent  formation     .     .     .     from  the  superior  formation  as 
well  as  from  the  inferior.     ...     In  true  basal  conglomerates,  on 
the  other  hand,  while  the  material  is  very  frequently  derived  in 
large  measure   from  the   immediately   subjacent    formations,   they 
also  usually  contain  a  small  proportion  of  material  from  various 
foreign  sources,  and     .     .     .     not     .     .     .     from  the  overlying  for- 
mations, as  may  the  autoclastic  rocks." 

2.  "In  an  autoclastic  rock,     .     .     .     the  pebbles     .     .     .     will 
in  many  cases  be  found  to  be  less  rounded  than  in  a  true  basal  con- 
glomerate.    If     ...     followed  for  some  distance  a  considerable 
variation    will    frequently   be    found — fragments    being   here   well 
rounded  and  there  very  imperfectly  rounded.     The  well-rounded 
fragments  are  concentrated,  as  are  also  the  angular  fragments.    A 
basal  conglomerate,  on  the  other  hand,  has  a  considerable  uniform- 
ity in  the  degree  of  the  rounding  of  its  pebbles  in  passing  along 
the  same  horizon,  but  at  the  same  place  the  large  fragments  may  be 
angular  and  the  small  ones  well  rounded     .     .     ." 

3.  "In  many  cases  the  interstices  of  an   autoclastic  rock  are 
filled  with  material   of  a  vein-like  character,  whereas  in  a  basal 
conglomerate  the  filling  material  is  largely  fine  detritus.     But  some- 
times    .     .     .     the  filling  material  of  an  autoclastic  rock  may  be 
water-worn  grains  of  sand,  which  have  been  separated  by  dynamic 
action,  and  are  therefore  indistinguishable  from  the  ordinary  matrix 
of  a  true  conglomerate." 

4.  "In  most  instances  a  bed  of  autoclastic  rock,  if  followed, 
may  be   traced   into   on  ordinary   brecciated   or  partly   brecciated 
form.    A  basal  conglomerate,  on  the  other  hand,  if  followed  along 
the  strike  and  dip,  may  change  its  character,  but  it  will  be  a.  gradual 
change  into  the  ordinary  mechanical  sediments,  whereas  an  auto- 
clastic rock  is  likely  to  have  very  sudden  variations  in  character." 
(Van  Hise-3o:<5So-<S/.) 


INTRAFORMATIONAL  BRECCIAS. 

These  are  contemporaneous  phenomena,  formed  as  one  of  the 
sequential  divisions  of  a  single  rock  series.  They  are  almost  wholly 
confined  to  calcareous  rocks,  and  seem  to  be  most  typical  of  calci- 
lutytes  or  fine  calcarenytes.  Such  rocks,  composed  largely  of  the 


530  PRINCIPLES    OF    STRATIGRAPHY 

finest  lime-mud,  accumulate  in  shallow  water  or  in  part  even  above 
the  normal  level  of  the  sea.  In  form  they  probably  constitute  a 
sort  of  mud  flat  delta,  the  mud  being1  brought  and  spread  out  in 
part  at  least  by  streams,  which  must  have  derived  it  from  the 
erosion  of  earlier  limestones.  Mud  cracks  or  desiccation  fissures 
testify  to  the  shallow  water  in  which  these  sediments  were  accumu- 
lating. On  exposure  partial  hardening  permits  the  formation  of  a 
superficial  crust,  which  may  subsequently  break  or  become  de- 
formed by  the  sliding  of  the  entire  mass  seaward.  Such  sliding  has 
been  observed  in  modern  deposits  as  discussed  more  fully  in  Chap- 
ter XX. 

Fracturing  and  Piling  Up  of  Material.  If  the  surface  layers 
alone  slide,  a  fracturing  will  result  which  produces  a  mass  of 
angular  or  subrounded  flat  mud-cakes,  which  will  be  piled  together, 
as  the  result  of  this  sliding,  in  a  confused  mass,  the  fragments  most 
frequently  standing  on  end,  but  also  inclined  in  all  directions.  They 
will  be  surrounded  by  the  fine  still  fluid  mud  which  wells  up  around 
them  and  in  which  these  fragments  become  embedded.  Thus  is 
formed  an  "edgewise  conglomerate,"  as  these  accumulations  have 
come  to  be  known,  a  contemporaneous  feature  abounding  in  the 
finer  calcilutytes  and  calcarenytes  of  all  horizons.  Both  the  cakes 
and  the  enclosing  matrix  may  contain  organic  remains ;  the  former 
would  carry  such  fine  organic  fragments  as  sponge  spicules,  plant 
fibers,  etc.,  which  may  be  washed  in  with  the  mud  or  may  exist 
in  the  water  in  which  it  is  deposited,  while  the  matrix  becomes 
normally  fossil-bearing  since  it  is  a  part  of  the  submerged  deposits. 
Professor  Seeley  (24)  (Brown-i)  has  considered  the  cakes,  as  a 
whole,  due  to  organic  growth,  and  described  them  under  several 
species  of  the  new  genus  Wingia.  The  intraformational  conglom- 
erates described  by  Walcott  (31),  though  mostly  of  a  much  coarser 
character,  probably  in  part  represent  such  gliding  conglomerates. 
Examples  where  such  cakes  of  lime-mud  carrying  fossils  were 
formed  through  fracturing  on  drying  have  been  described  by  Hyde 
(16)  from  the  Coal  Measure  limestones  of  Ohio.  In  these  cases, 
however,  no  sliding  seems  to  have  occurred,  the  fragments  being 
embedded  where  formed.  These  "desiccation  conglomerates"  will 
be  referred  to  again  in  Chapter  XX. 

Distortion  of  Layers  in  Gliding.  If  a  large  mass  of  rock  slides 
there  will  be  less  of  fracturing  and  more  of  distortion  of  the  layers 
along  the  gliding  zone  and  this  will  be  pronounced  in  proportion  to 
the  weight  and  compactness  of  the  beds  overlying  the  ^gliding  plane. 
Good  examples  of  such  distortion  are  found  in  the  Trenton  lime- 
stone of  New  York  (Hahn-i2)  as  exposed  in  the  gorge  at  Trenton 


AUTOCLASTIC    ROCKS  531 

Falls,  where  several  such  layers  are  visible.  It  is  also  well  shown 
in  the  fine  calcilutytes  of  the  Solnhofen  beds  (Jurassic)  of  Ba- 
varia, a  formation  shown  by  many  characters  to  be  of  shallow  water 
origin.  (See  further,  Chapter  XX.) 

GLACIAL  DEPOSITS. 

If  we  consider  ice  as  water  in  the  solid  form,  glacial  deposits 
must  be  classed  under  the  hydroclastic  division  of  rocks.  It  is 
manifest,  however,  that  the  essential  features  of  glacial  deposits  are 
those  which  most  strongly  differentiate  them  from  ordinary  hydro- 
elastics,  be  they  fluvial,  lacustrine,  or  marine.  In  some  characters 
they  may  resemble  atmbclastic  and  in  others  autoclastic  deposits,  but 
their  most  marked  characteristics  are  not  shared  with  any  other 
type.  Nevertheless,  the  method  of  formation  of  the  most  typical 
glacial  elastics  is  closely  analogous  to  that  of  autoclastic  fault  brec- 
cias. Both  are  produced  by  the  movement  of  one  rock  mass  over 
another,  for  ice  in  this  relation  has  the  essential  characters  of  a  solid 
rock,  and  both  furnish  material  for  the  resulting  rudyte  or  finer 
rock,  though  that  furnished  by  the  ice  is  readily  destroyed.  It  is 
true  that  material  not  produced  by  mutual  attrition  of  the  two  rock 
masses,  the  basal  rock  and  the  ice  rock,  may  be,  and  commonly  is, 
incorporated  in  the  subglacial  material,  but  this  merely  points  the 
essential  peculiarities  of  this  autoclastic  rock.  It  is  also  true  that 
the  movement  of  glaciers  cannot  be  directly  compared  with  that  of 
rock  masses  involved  in  faulting,  in  so  far  as  it  is  a  gliding  partly 
due  to  internal  forces  as  well  as  to  gravity.  Still  the  essential  fact 
remains,  that  clastic  material  is  produced  by  the  movement  of  one 
rock  mass  over  another  and  that  both  rock  masses  contribute  from 
their  substance  to  the  production  of  this  material.  In  this  respect, 
then,  glacial  debris  may  be  compared,  on  the  one  hand,  with  that 
formed  by  gravity  faulting,  and,  on  the  other,  with  that  formed 
by  gliding  masses  resulting  in  the  production  of  intraformational 
breccias.  Since  the  ice  also  moves  by  constant  internal  readjust- 
ments from  recrystallization,  the  products  of  such  motion  may  to  a 
certain  extent  be  compared  with  enterolithic  deformations. 

Characters  of  Modern  and  Pleistocenic  Glacial  Deposits.  The 
material  resulting  from  the  plucking-  and  abrasive  action  of  the  ice 
varies  in  grain  from  the  finest  rock  flour  to  boulders  of  almost 
unlimited  size.  Except  where  disintegration  of  the  rock  surface 
previous  to  glaciation  has  occurred,  the  fine  material  will  all  be 
rock  flour  with  clay  notably  absent.  The  arenaceous  material  also 
shows  in  its  angularity  and  sharpness  of  grain  that  it  has  been 


532  PRINCIPLES    OF    STRATIGRAPHY 

produced  by  mechanical  crushing  of  fresh  rocks.  Such  sand,  from 
the  Mer-de-Glace,  Switzerland,  shows  sharp,  fresh,  angular  frag- 
ments with  the  barest  traces  of  weathering,  and  very  little  wear. 
The  composition  is  varied,  and  the  assortment  very  poor.  The 
quartz  grains  of  glacial  sands  show  the  characteristic  conchoidal 
fracture,  sharp  edges  and  keen  points.  Cleavable  minerals  show 
fresh,  clean  surfaces  and  little,  if  any,  trace  of  internal  decomposi- 
tion. In  composition  the  variation  is  very  great,  dependent,  of 
course,  upon  the  original  character  of  the  rock  ground  up  by  the 
ice.  The  assortment  according  to  size  is  also  very  marked. 

Till  or  boulder  clay  is  an  intimate  mixture  of  rock  flour  and 
glacial  sand,  together  with  a  varying  per  cent,  of  clay  derived 
from  rocks  decomposed  prior  to  glaciation.  Crosby  holds  that  very 
little  of  the  original  residuary  soil  is  incorporated  in  the  till  cover- 
ing New  England,  for  the  color  of  this  till  is  bluish  and  shows  no 
traces  of  oxidized  material  below  a  certain  level,  where  recent 
oxidation  has  been  active.  "Experiments  show  that  an  admixture 
of  a  very  small  proportion  of  highly  oxidized  residuary  clay,  like 
that  of  the  south,  with  a  typical  till,  is  readily  detected  in  the 
change  of  color."  (Crosby— 7:^5^.)  In  the  most  typical  till,  i.  e., 
that  due  wholly  to  glacial  erosion  of  a  country  from  which  all 
decomposed  material  is  absent,  the  amount  of  kaolinite  is  ex- 
tremely slight,  all  the  finer  material  being  rock  flour  due  to  me- 
chanical crushing.  An  analysis  of  till  from  drumlins  of  the  Boston 
Basin,  from  Somerville  to  Nantasket,  gave  Crosby  the  following 
results  expressed  in  percentages  of  the  total  material  exclusive  of 
the  boulders  and  other  stones  over  2  inches  in  diameter 
(Crosby-6)  : 

i.  Coarse 17.08! 

Gravel \    2.  Medium 2 . 99  \ 24 . 90 

3-  Fine 4.83] 

4.  Coarse 3.33 

Sand -j    5.  Medium 9.25 

6.  Fine 6 . 93 


Rock  Flour. 


7.  Coarse 12.80 

8.  Medium 6. 52  [ 43-86 

9.  Fine 24. 14 

10.  Superfine 0.30 

1 1 .  First  decanting ...  o .  86 

Clay \  12.  Second 9 . 13  ^ 11.67 

13.  Third 1.78 

99-94 


GLACIAL   DEPOSITS  533 

Thus,  after  exclusion  of  the  larger  stones  the  till  consists  of 
about  25%  of  gravel,  20%  of  sand,  40  to  45%  of  extremely  fine 
sand  or  rock  flour  and  only  about  12%  of  clay.  (See  also 
Ries-iQ.) 

The  intimate  admixture  of  coarse  and  fine  material  in  the  un- 
modified glacial  drift  or  till  renders  its  pore  space  of  the  slightest 
and  so  makes  it  an  admirable  impervious  layer,  through  which 
ground  water  cannot  penetrate.  This  is  well  shown  in  the  unoxi- 
dized  character  of  much  of  the  till,  its  color  when  freshly  ex- 
cavated being  of  a  bluish  slate.  Only  the  surface  layers,  or  some 
included  layers  of  modified  sand  or  gravel,  may  show  such  oxida- 
tion. Modified  till  differs  mainly  in  the  somewhat  worn  character 
of  the  granules,  the  progress  of  weathering  in  the  decomposable 
minerals  and  the  better  assortment  of  the  material*  according  to 
size.  With  this  comes  increased  pore  space  and  consequently  pene- 
tration of  ground  water  accompanied  by  oxidation,  and  a  change  to 
ochery  or  brown  colors.  All  gradations  may  be  observed,  from 
the  slightly  modified  drift  barely  moved  by  the  waters  from  the 
melting  ice  sheet,  to  the  much  worn  and  fairly  well-assorted  ma- 
terial of  the  glacial  streams,  which  quickly  assumes  all  the  charac- 
teristics of  water-laid  deposits  and  must  be  classed  with  the  hydro- 
elastics. 

The  pebbles  and  boulders  of  the  glacial  drift  also  show  dis- 
tinctive peculiarities.  One  essential  is  their  imperfectly  worn  char- 
acter. Most  commonly  they  are  in  the  form  of  flattened  masses 
highly  polished  and  striated  on  the  flat  faces,  but  angular  or  but 
slightly  worn  on  the  other  sides.  Rounded  boulders  are  the  ex- 
ception. In  size  they  vary  enormously,  and  this  is  often  true  for 
the  lithologic  character  as  well.  Crosby  has  found  that  much  of 
the  coarse  material  of  some  New  England  deposits  was  of  compara- 
tively local  origin,  these  deposits,  moreover,  having  been  subject 
to  a  certain  amount  of  transportation  by  water.  Of  some  tons  of 
material  coarse  enough  for  ready  identification  about  50  per  cent, 
came  from  a  belt  of  rock  extending  for  13  miles  north  of  the 
deposit,  and  40  per  cent,  from  the  next  8  to  10  miles,  while  only 
10  per  cent,  came  from  distances  greater  than  23  miles  (7:^57-^). 

Transportation  of  the  coarser  material  by  glacial  streams  results 
in  more  or  less  perfect  rounding  of  the  boulders,  and  the  effacement 
of  the  striations  on  the  surface.  Moreover,  the  attendant  assorting 
of  the  material  according  to  size  will  result  in  the  greater  concen- 
tration of  such  bouldery  deposits,  whereas  in  the  true  till  the 
boulders  are  scattered  and  embedded  in  the  finer  material. 

Boulders  of  ice  as  well  as  ice  sand  derived  from  the  gliding  ice 


534  PRINCIPLES    OF    STRATIGRAPHY 

mass  are  apt  to  be  incorporated  in  the  forming  deposit,  but  such  boul- 
ders are  by  virtue  of  their  composition  subject  to  speedy  destruc- 
tion. As  a  result  a  depression  will  be  formed  in  the  glacial  deposit, 
due  to  the  caving-in  of  the  overlying  material  into  the  hollow  left 
by  the  vanishing  ice  boulder.  Such  kettle  holes  are  common  in 
both  modified  and  unmodified  glacial  deposits  and  serve  to  identify 
them  as  such. 

Ancient  Glacial  Deposits. 

Boulder  clays  and  modified  glacial  deposits  are  found  at  a  num- 
ber of  geological  horizons  from  the  pre-Cambric  onward.  The 
rock  formed  by  the  consolidation  of  such  deposits  is  known  as 
tillite  and  its  essential  character  is  found  in  the  heterogeneous  mix- 
ture of  the  material,  the  absence  of  stratification  and  the  striation 
of  the  larger  blocks,  and  the  fragments  of  dense  texture.  Several 
of  the  more  prominent  cases  may  be  discussed  in  some  detail. 

The  Pre-Cambric  Tillite  of  Canada.  In  the  Lower  Huronian 
of  the  Cobalt  region  in  Canada  an  extensive  boulder  bed  and  tillite 
have  been  found,  indicating  glacial  origin.  (Coleman-2,  3,  4,  5.) 
The  tillite  is  a  consolidated  boulder  clay  or  till  and  the  boulders 
are  angular  or  subangular,  and  not  infrequently  striated,  but  no 
striation  of  the  underlying  rock  has  yet  been  observed.  The  boul- 
ders are  often  2  or  3  feet  or  more  in  diameter  and  distant  a  couple 
of  miles  from  the  exposures  of  the  rocks.  Some  of  the  boulders  of 
this  conglomerate  are  tons  in  weight,  and  the  areal  extent  of  the 
mass  has  been  traced  over  1,000  miles  east  and  west  and  750  miles 
north  and  south,  while  the  thickness  at  Cobalt  is  about  five  hundred 
feet.  The  boulder  clay  of  this  horizon  and  that  of  the  Permo-Car- 
bonic  and  other  regions  is  almost  indistinguishable  in  hand  speci- 
mens or  in  thin  sections  under  the  microscope.  Some  stratified 
slaty  beds  have  been  found  at  Cobalt  in  the  great  mass  of  unstrati- 
fied  conglomerate  suggesting  a  possible  interglacial  period.  The 
glacial  origin  of  these  has  been  questioned  by  Knight  (17)  and 
others. 

Cambric  Glacial  Deposits.  These  have  been  recorded  from 
northern  Norway,  where  in  the  Varanger  fjord  an  unstratified  tillite 
with  striated  boulders  rests  upon  a  striated  rock  surface  of  the  pre- 
Cambric  Gaisa  series  and  is  succeeded  by  beds  of  Cambric  age. 
( Strahan-29. )  From  the  Yantzi  Canyon  in  China,  lat.  31°,  Bailey 
Willis  (33)  has  obtained  striated  boulders  occurring  in  tillite  per- 
haps 150  feet  thick  and  overlain  by  Middle  Cambric  marine  deposits. 
Still  more  striking  and  better  known  are  the  Cambric  tillites  of  South 


ANCIENT    GLACIAL   DEPOSITS  535 

Australia  (lat.  30°  to  43°  S.).  (Howchin-izj.,  15;  David-8,  9.) 
They  extend  for  460  miles  from  north  to  south  and  250  miles  from 
east  to  west,  and  have  a  thickness  of  1,500  feet.  Numerous  boul- 
ders and  pebbles  showing  glacial  striae  have  been  obtained  (see  the 
figures  given  by  Howchin-i5),  the  character  of  these  boulders  in- 
dicating a  southward  movement.  Intercalated  with  the  tillite  are 
beds  of  limestone  and  radiolarian  beds.  No  striations  have  been 
found  on  the  underlying  rocks.  (David-8,  9.) 

In  South  Africa  (lat.  29°  S.)  tillite  of  late  pre-Cambric  or 
early  Cambric  age  forms  a  part  of  the  Griquatown  series  of  Cape 
Colony,  occurring  over  almost  1,000  square  miles.  It  contains 
typical  scratched  boulders. 

The  Pennic  Glacial  Deposits.  These  have  been  observed  in 
India,  Australia,  South  Africa  (Davis-io;  Schwartz-2i),  and  South 
America  (White-32).  The  South  African  deposit  constitutes  the 
Dwyka  conglomerate,  the  lowest  member  of  the  Karoo  formation 
(Davis-ioi^oo).  It'varies  in  thickness  up  to  1,000  feet  or  more  and 
extends  from  the  Indian  Ocean  between  29°  and  33^2°  south  lati- 
tude northward  approximately  to  Belfast,  westward  to  the  Vaal 
River  and  thence  in  latitude  29°  to  within  less  than  a  hundred 
miles  of  the  Atlantic,  and  southward  to  within  about  150  miles  of 
Capetown.  Its  former  extent  was  apparently  much  greater.  "It 
rests  for  the  most  part  unconformably  on  a  grooved  and  striated 
surface  of  older  rocks,  but  along  its  southern  border  it  follows  con- 
formably a  series  of  sandstones  and  shales.  It  consists  chiefly  of 
an  unstratified  and  consolidated  clastic  ground  mass  with  sub- 
angular  or  rounded  scraps,  stones,  and  boulders  of  many  kinds, 
the  finer  textured  stones  and  boulders  being  usually  well  scratched. 
It  is  conformably  overlaid  by  a  coal-bearing  series  of  shales  and 
sandstones."  (Davis-io^oo.) 

"The  glacial  origin  of  the  Dwyka  formation  is  as  unquestionable 
•as  is  that  of  the  drift  sheets  of  northeastern  America  or  of  north- 
western Europe;  but  the  Permian  ice-sheet,  by  which  the  Dwyka 
was  formed,  moved  in  general  southward,  from  the  region  of  the 
equator  toward  the  region  of  the  pole."  (Davis-ioi^o/.)  The 
indications  are  that  the  Dwyka  ice  "was  a  broad  and  continuous 
ice  sheet  which  spread  across  about  600  miles  of  country,  east  and 
west,  and  which  advanced  at  least  500  miles  poleward  from  its 
apparent  source.  It  moved  across  a  region  which  bore  subdued 
mountains  here  and  there,  but  which  was  reduced  to  moderate  relief 
by  previous  erosion  over  large  areas."  (Davis-ior^/j?.) 

Along  its  southern  margin  in  latitude  33*^2°  south  it  invaded  a 
water-covered  area.  A  number  of  fluctuations  are  recorded,  and 


536  PRINCIPLES    OF    STRATIGRAPHY 

upon  the  final  recession  a  climate  favoring  a  luxuriant  growth  of 
plant  life  succeeded,  as  testified  to  by  the  coals  of  the  overlying 
Ecca  formation.  "Demonstrably  marine  deposits  are  nowhere  asso- 
ciated with  the  Dwyka,"  not  even  where  it  "repeatedly  reaches  the 
shore  of  the  Indian  Ocean" ;  but  marine  Devonic  fossils  occur  in 
the  Bokkeveld  s*eries  2,500  feet  or  more  below  the  basal  member  of 
the  Dwyka  in  the  Karoo  district,  while  between  them  lies  the  con- 
formable Witteberg  series,  forming  the  transition  from  marine  to 
glacial  continental.  The  structural  evidence  shows  that  mountains 
were  absent  at  this  time,  though  high  lands  existed  which  supplied 
the  material  of  the  Karoo  formation. 

Davis  has  presented  the  facts  which  show  that  neither  great 
elevation  nor  changes  in  land  area  or  land  form  were  able  to  produce 
a  glacial  climate  in  subtropical  South  Africa,  nor  could  any  conceiv- 
able arrangement  of  ocean  currents  produce  it.  General  refrigeration 
alone,  either  by  a  decrease  of  solar  radiation  or  by  a  change  in  the 
constitution  of  our  atmosphere,  without  shifting  of  wind  belts, 
would  have  to  be  so  extreme  as  to  reduce  the  summer  temperature 
of  South  Africa  to  such  an  extent  that  the  summer  rains  would  be- 
come summer  snows,  while  the  winters  would  still  be  dry,  and  ex- 
tremely cold.  Such  a  refrigeration  would  freeze  up  all  the  tem- 
perate lands  of  the  globe  and  would  hardly  be  in  harmony  with 
the  rich  marine  and  land  life  of  the  Permic  deposits  found  in  these 
regions,  nor  with  the  evidence  of  warm  climate  furnished  by  arid 
deposits  of  this  period  in  other  regions.  A  shifting  of  the  pole,  as 
elsewhere  suggested,  to  such  an  extent  that  it  would  lie  somewhere 
in  the  Indian  Ocean  would  account  satisfactorily  not  only  for  the 
Dwyka  conglomerate,  but  also  for  the  Talchir  glacial  formation 
of  northwestern  India,  the  movement  of  the  glaciers  forming 
this  being,  like  those  which  formed  the  Dwyka,  away  from  the 
equator,  but  in  the  opposite  direction.  It  would  also  account  for 
the  Muree  glacial  formation  of  southeastern  Australia. 

Koken  (i7a)  has  discussed  this  question  at  length,  with  special 
reference  to  India,  and  he  gives  a  map  of  the  world  showing  the 
possible  position  of  the  poles  at  that  time  under  the  theory  of 
polar  displacement.  He  places  the  North  Pole  near  Tultenango, 
Mexico  (lat.  20°  N.,  long.  100°  W.,  of  to-day),  and  the  South  Pole 
in  the  middle  of  the  Indian  Ocean  (lat.  20°  S.,  long.  80°  E.,  of 
to-day). 

ENDOLITHIC   BRECCIATION. 

Endolithic  brecciation,  or  the  shattering  of  the  strata  by  forces 
at  work  within  the  rock  mass  itself,  is  best  shown  in  formations 


ENDOLITHIC    BRECCIATION  537 

containing  anhydrite,  which  by  hydration  is  changed  to  gypsum. 
This  process  involves  an  increase  in  volume,  estimated  by  some 
(Credner,  Fritsch,  Bauer,  Geikie)  as  low  as  33  per  cent.,  and  by 
others  (Naumann,  Zirkel,  J.  D.  Dana)  as  high  as  60  per  cent. 
J.  Roth,  indeed,  has  calculated  that  the  increase  in  volume  resulting 
when  anhydrite  takes  up  two  molecules  of  water  of  crystallization 
to  form  gypsum  is  as  high  as  62.3  per  cent. 

It  is  probably  true  that  calcium  sulphate  is  largely  deposited  in 
the  anhydrous  state,  especially  when  it  originates  under  arid  condi- 
tions (see  ante,  Chapter  IX).  Certain  it  is  that  anhydrite  abounds 
in  many  of  the  older  strata  along  with  gypsum,  and  it  is  not  im- 
probable that  in  such  cases  the  gypsum  is  the  result  of  hydration  of 
the  anhydrite.  In  view  of  the  great  force  exerted  within  the  rock 
mass  by  the  expansion  due  to  this  hydration,  we  would  expect  to 
find  the  results  in  a  shattering  and  deformation  of  the  enclosing 
strata.  This  expectation  is  commonly  realized,  for  such  endolithic 
brecciation  is  a  frequent  if  not  constant  accompaniment  of  gypsum- 
bearing  strata,  especially  in  the  Palaeozoic.  Cases  have  been  de- 
scribed from  the  Salina  and  Monroe  beds  of  New  York,  Ohio, 
Michigan,  and  Canada.  (Grabau  and  Sherzer-i  i  :2p ;  Kraus- 
18:1(57-171.)  Brecciation  of  this  type  is  not  uncommon  in  salt 
deposits,  where  through  recrystallization  a  pronounced  pressure 
results,  which  may  even  affect  the  enclosing  strata,  deforming  and 
disrupting  them.  This  subject  will  be  more  fully  discussed  in  the 
chapter  on  diagenism. 


BIBLIOGRAPHY  XII. 

1.  BROWN,  THOMAS  C.  1913.     Notes  on  the  Origin  of  Certain  Palaeozoic 

Sediments,  Illustrated  by  the  Cambrian  and  Ordovician  Rocks  of  Center 
County,  Pennsylvania.     Journal  of  Geology,  Vol  XXI,  pp.  232-250. 

2.  COLEMAN,  A.  P.     1907.     A  Lower  Huronian  Ice  Age.     American  Journal 

of  Science,  4th  series,  Vol.  XXIII,  pp.  187-192. 

3.  COLEMAN,  A.  P.     1908.     Ancient  Ice  Ages  and  Their  Bearing  on  Astro- 

nomical Theories.     Journal  of  the  Astronomical  Society  of  Canada,  Vol. 
II,  No.  3,  pp.  132-135- 

4.  COLEMAN,  A.  P.     1908.     The   Lower   Huronian   Ice   Age.     Journal   of 

Geology,  Vol.  XVI,  pp.  149-158. 

5.  COLEMAN,  A.  P.     1908.     Glacial  Periods  and  Their  Bearing  on  Geological 

Theories.     Bulletin  of  the  Geological  Society  of  America,  Vol.  XIX,  pp. 
347-366. 

6.  CROSBY,    WILLIAM    OTIS.     1891.     Composition   of   Till   or    Boulder 

Clay.     Boston  Society  of  Natural  History  Proceedings,  Vol.  XXV,  pp. 
115-140. 

7.  CROSBY,  W.  O.     1896.     Englacial  Drift.     American  Geologist,  Vol.  XVII, 

pp.  203-234. 


538  PRINCIPLES    OF    STRATIGRAPHY 

8.  DAVID,  T.  W.  EDGEWORTH.     1903.     Australasian  Association  for  the 

Advancement  of  Science.     Report  of  the  Ninth  Meeting,  pp.  199-200. 

9.  DAVID,   T.  W.   E.     1906.     Glaciation  in  Lower  Cambrian,  Possibly  in 

Pre-Cambrian  Time.     International  Geological  Congress.    Compte  Rendu, 

Mexico,  pp.  271-274;  275-298. 
10.     DAVIS,    WILLIAM    MORRIS.     1906.     Observations    in    South    Africa. 

Bulletin  of  the  Geological  Society  of  America,  Vol.  XVII,  pp.  377-450. 
n.     GRABAU,  AMADEUS  W.,  and  SHERZER,WILLIAM  H.    1910.'  Monroe 

Formation  of  Michigan.     Michigan  Geological  and  Biological  Survey, 

Publication  2. 
12.     HAHN,  F.  FELIX     1912.     Untermeerische  Gleitungen  bei  Trenton  Falls 

(Nord    Amerika),    und    ihr    Verhaltniss  zu  Ahnlichen    Storungsbildern. 

Neues  Jahrbuch  fur  Mineralogie,  Geologic  und  Palaeontologie,    Beilage 

Band  XXXVI,  pp.  1-41,  pis.  I-III. 
13".     HATCHER,    J.    B.     1900.     Sedimentary    Rocks    of    South    Patagonia. 

American  Journal  of  Science,  4th  Series,  Vol.  IX,  pp.  85-108. 

14.  HOWCHIN,  WALTER.     1903.     Report    of    South    Australian    Glacial 

Investigation  Committee,  Australasian  Association  for  the  Advance- 
ment of  Science,  Report  of  the  Ninth  Meeting;  Hobart,  Tasmania, 
1902,  pp.  194-199- 

I4a.  HOWCHIN,  WALTER.  1906.  The  Geology  of  the  Mount  Lofty 
Ranges,  Part  II,  Transactions  and  Proceedings  and  Report  of  the 
Royal  Society  of  South  Australia,  Vol.  XXX,  pp.  227-262  (especially 
pp.  228-234). 

15.  HOWCHIN,  W.     1908.     Glacial  Beds  of  Cambrian  Age  in  South  Australia. 

Quarterly  Journal  of  the  Geological  Society  of  London,  Vol.  LXIV,  pp. 
234-263,  pis.  XIX-XXVI. 

/  16.  HYDE,  JESSE  E.  1908.  Desiccation  Cqnglomerate  in  the  Coal  Measure 
Limestones  of  Ohio.  American  Journal  of  Science,  4th  series.  Vol. 
XXV,  pp.  400-408. 

17.  KNIGHT,  CYRIL  W.     1909.     On  the  Lower  Huronian  Ice  Age.    Canadian 

Mining  Journal,  Vol.  XXX,  pp.  727-728. 

I7a.  KOKEN,  E.  1907.  Indisches  Perm  und  die  Permische  Eiszeit.  Neues 
Jahrbuch  fur  Mineralogie,  etc.  Festband,  pp.  446-546.  Map. 

18.  KRAUS,  EDWARD  H.     1905.     On  the  Origin  of  the  Caves  of  Put-in- 

Bay  Island,  Lake  Erie.     American   Geologist,  Vol.  XXXV,  pp.  167-171. 

19.  RIES,    HEINRICH.     1906^     Clays,    Their    Occurrence,  Properties    and 

Uses.     John  Wylie  and  Son. 

20.  ROGERS,  A.  W.       1905.      An    Introduction    to    the  Geology    of    Cape 

Colony.  London. 

21.  SCHWARTZ,   ERNEST  H.   L.     1906.     The  Three  Palaeozoic  Ice  Ages 

of   South  Africa.     Journal  of  Geology,  Vol.  XIV,  No.  8,  pp.  683-691. 

22.  SCUDDER,  SAMUEL  H.     1882.     The  Tertiary  Lake  Basin  of  Florissant, 

Colorado,  between  South  and  Hayden  Parks.  United  States  Geo- 
logical and  Geographical  Survey  of  the  Territories,  Vol.  VI,  pp.  279-300. 

23.  SCUDDER,  S.  H.     1883.     Ibid.,  I2th  Annual  Report,  pp.  271-293. 

24.  SEELEY,  A.     1906.     Geology  of  Vermont.     Report  of  the  State  Geologist 

for  1906,  pp.  174-78. 

25.  SHERZER,  W.  H.     1910.     Criteria  for  the  Recognition  of  Sand  Grains. 

Bulletin  of  the  Geological  Society  of  America,  Vol.  XXI,  pp.  625-662. 

26.  SINCLAIR,  WILLIAM  J.     1906.     Volcanic  Ash  in  the  Bridger  Beds  of 

Wyoming.  Bulletin  of  the  American  Museum  of  Natural  History, 
Vol.  XXII,  pp.  273-280, 


BIBLIOGRAPHY   XII  539 

27.  SINCLAIR,  W.  J.     1909.     The  Washakie,  a  Volcanic  Ash  Formation 

Ibid.,  Vol.  XXVI,  pp.  25-27. 

28.  SINCLAIR,   W.    J.,  and    GRANGER,    WALTER.     1911.     Eocene   and 

Oligocene  of  the  Wind  River  and  Big  Horn  Basins.     American  Museum 
of  Natural  History  Bulletin,  Vol.  XXX,  pp,  83-117. 

29.  STRAHAN,    AUBREY.     1897.     The    Glacial    Phenomena    of    Palaeozoic 

Age  in  the  Varanger  Fjord.     Quarterly  Journal  of  the  Geological  Society 
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Institute  of  Washington  Publications. 


CHAPTER   XIII. 

ORIGINAL  STRUCTURE  AND  LITHOGENESIS  OF  THE  ATMOCLASTIC 
AND  ANEMOCLASTIC  ROCKS 

A.     ATMOCLASTIC    ROCKS. 

Typical  atmoclastic  rocks  owe  their  origin  entirely  to  disintegra- 
tion or  disruption  of  older  rocks,  while  the  accumulation  and  ar- 
rangement of  this  material  are  brought  about  by  atmospheric  agen- 
cies under  the  influence  of  gravity.  The  most  typical  atmoclastic 
rocks  are  those  produced  in  situ  by  subaerial  decay  and  not  subse- 
quently disturbed.  Here  belong  the  laterite  and  kaolinite,  the  for- 
mation of  which  was  described  in  Chapter  II,  pp.  37,  39.  Taken  by 
itself,  such  rock  may  show  a  complete  absence  of  stratification  and  a 
gradation  in  texture  from  coarse  blocks  next  to  the  unaltered  rock  to 
fine  soil  and  humus  at  the  surface  where  disintegration  and  de- 
composition affect  rocks  of  uniform  grain  such  as  granites  or  other 
holocrystallines.  A  downward  gradation  into  the  older  rock  may  be 
pronounced  which,  if  the  upper  layers  are  reworked  by  water  or 
other  agencies,  forms  an  apparent  transition  bed  between  widely  dis- 
tinct formations.  The  products  of  atmospheric  disintegration  may 
become  rearranged  by  flowing,  sliding  or  gliding  under  the  influ- 
ence of  gravity.  The  talus  at  the  foot  of  a  cliff  is  an  example  of 
such  rearrangement.  The  surface  gradient  of  such  an  accumulation 
is  generally  high,  varying  from  60  degrees  or  over  in  the  coarsest 
series  to  23  degrees  or  even  less  in  the  fine-grained  series. 

Stagnant  atmoclastic  material  is  the  exception ;  in  general  move- 
ment to  lower  levels  occurs.  When  more  or  less  saturated  with 
water,  the  angle  of  slope  is  correspondingly  lowered,  and  the  talus 
approaches  more  and  more  the  character  of  an  alluvial  fan.  The 
atmoclastic  sediments  then  grade  into  the  hydroclastic  or  aqueous 
type.  If,  on  the  other  hand,  the  wind  is  a  factor  in  rearrangement 
and  deposition  of  the  material,  this  becomes  an  anemoclastic  rock 
and  has  to  be  treated  as  such. 

The  waste  of  the  land  is  on  the  march  to  the  sea.  Everywhere 

540 


ATMOCLASTIC    ROCKS  541 

the  loose  rock  debris  is  streaming  toward  the  ultimate  repository, 
the  sea,  or  to  the  rock-rimmed  desert  basins  of  the  earth,  from 
which  in  many  cases  there  is  no  escape.  This  great  waste  stream, 
as  it  has  been  aptly  termed,  covers  much  of  the  surface  of  the  land, 
and  may  consist  wholly  of  debris,  or  of  debris  and  water  in  varying 
proportions.  As  the  amount  of  water  increases  the  fluidity  of  the 
mass  rises,  and  the  rate  of  its  motion  is  increased,  while  the  angle 
at  which  graded  conditions  prevail  is  decreased.  Thus  where  the 
material  is  pure  waste  the  angle  will  commonly  be  more  than  20 
degrees,  and  steeper  in  proportion  as  the  material  is  coarser.  Fur- 
thermore, the  material  of  the  talus  heap  is  constantly  undergoing 
disintegration,  and,  as  it  becomes  finer,  the  potential  angle  of  slope 
is  lowered.  The  actual  lowering  will  be  accomplished  by  a  process 
of  "creep,"  which  is  often  greatly  aided  by  frost  action  and  by  tem- 
porary saturation  with  water,  which  may  become  instrumental  in 
suddenly  lowering  the  angle  through  landslides. 

The  totality  of  the  deposits  formed  by  subaerial  agencies  on 
the  plains  in  front  of  the  mountains  is  classed  as  piedmont  waste 
deposits.  They  may  be  formed  wholly  by  "dry  creep"  from  the 
mountains,  or,  as  is  most  generally  the  case,  by  combined  creep 
and  the  wash  of  mountain  streams.  Alluvial  fans  or  dry  deltas 
thus  form  the  connecting  link  between  the  atmoclastic  and  the 
hydroclastic  types  of  deposits,  for,  though  strictly  belonging  to  the 
fluviatile  division  of  the  latter,  they  partake  of  many  of  the  charac- 
teristics of  the  former,  and  are  indeed  partly  produced  by  subaerial 
creep.  (Walther-52;  Penck-37  :.?5 ;  Barrell-2.) 


CHARACTERISTICS  AND  OCCURRENCE  OF  MODERN  ATMOCLASTIC 

FORMATIONS. 

Extensive  recent  formations  of  atmoclastic  origin  are  found  only 
in  the  comparatively  arid  regions  of  the  world,  and  as  these  are  the 
last  which  have  come  under  the  detailed  observation  of  the  geolo- 
gist, though  they  cover  about  a  fifth  of  the  land  surface  of  the  earth, 
their  significance  with  reference  to  the  former  history  of  the  earth 
has  been  largely  overlooked.  It  is  only  within  recent  years  that  the 
desert  regions  of  the  world  have  been  studied  in  detail  and  their 
phenomena  applied  toward  the  interpretation  of  the  genesis  of  older 
formations  of  the  earth's  crust.  So  long  as  the  destructive  powers 
of  the  atmosphere  and  streams  were  regarded  as  their  chief  at- 
tributes, while  the  sea  was  held  to  be  the  chief  receptacle  of  the 
product  of  this  destructive  activity,  it  was  natural  that  the  marine 


542  PRINCIPLES    OF    STRATIGRAPHY 

origin  of  all  formations  should  be  considered  axiomatic,  except 
where  fossils  indicated  fresh  water,  in  which  case  fresh-water  lakes 
or  inland  seas  of  any  desired  magnitude  were  postulated  as  the 
medium  in  which  these  formations  were  deposited.  Now,  how- 
ever, that  we  have  the  extensive  observations  on  the  subaerial  origin 
of  formations  of  great  thicknesses,  embodied  in  the  epoch-making 
works  of  Walther  and  others,  there  is  no  longer  any  excuse  for  ac- 
cepting the  time-worn  marine  or  fresh- water  lake  origin  of  all  the 
sedimentary  formations.  It  becomes  more  and  more  apparent  that, 
where  formerly  marine  conditions  were  regarded  as  the  only  pos- 
sible ones  for  the  deposition  of  certain  formations,  desert  con- 
ditions are  often  the  more  probable  explanation,  while  formations 
generally  referred  to  a  lacustrine  origin  prove  in  many  cases  to  be 
subaerial  deltas  and  flood-plain  deposits  of  streams  or  the  accumu- 
lation of  wind-transported  material  upon  a  relatively  dry  land  sur- 
face. It  is  no  longer  one  of  the  axioms  of  the  stratigrapher  that 
all  stratified  deposits  were  laid  down  under  water ;  in  fact,  we  must 
be  prepared  to  question  the  subaqueous  origin  of  all  formations  that 
do  not  show  by  the  occurrence  of  either  marine  or  fresh-water  fos- 
sils throughout  that  they  were  formed  under  water.  The  possibility 
of  the  existence  of  unfossiliferous  subaqueous  formations  is  not  ex- 
cluded, and  the  subsequent  destruction  of  the  organic  contents  of 
the  formation  must  be  considered.  At  the  same  time  the  possibility 
of  a  subaerial  origin  of  all  unfossiliferous  clastic  formations,  or  of 
those  containing  marine  or  fresh-water  fossils  only  at  great  inter- 
vals, must  be  borne  in  mind,  while  the  occurrence  of  remains  of 
terrestrial  organisms  should  be  considered  as  prima  facie  evidence 
of  subaerial  origin  of  the  formations  containing  them  until  their 
subaqueous  origin  is  positively  established. 

TEXTURE  OF  ATMOCLASTIC  ROCKS.  Among  the  characters  of 
atmoclastic  rocks  should  first  be  mentioned  their  coarseness  of 
grain,  especially  near  the  mountains  from  which  the  material  has 
been  obtained.  In  the  talus  region  the  material  will  not  only  be 
coarse,  but  the  blocks  will  for  the  most  part  be  angular.  Often  the 
structure  is  suggestive  of  morainal  accumulations.  (Walther-52: 
1 03.)  Large  and  small,  round  and  angular  blocks  abound  in  the 
sandy  ground  mass  with  a  total  absence  of  sorting,  the  result  of  the 
indiscriminate  piling  together  of  the  material  by  the  tremendous 
flood  rains  of  the  desert.  The  evidence  of  violent  impact  is  further 
shown  by  the  abundance  of  concussion  marks  and  the  total  absence 
of  the  woody  vegetation  which  is  ground  to  fragments  and  washed 
away  by  the  floods.  Portions  of  the  delta  built  by  less  violent  floods 
show  interbedded,  well-stratified,  sandy  layers,  and  these  become 


ATMOCLASTIC    ROCKS  543 

more  characteristic  at  a  distance  from  the  mountains,  where  they 
also  are  finer  grained  and  frequently  clayey.  On  the  surface  of 
the  dry  delta  the  coarse  blocks  gradually  give  way  to  finer,  rounded, 
flat  or  irregularly  worn  pebbles,  with  streams  of  coarser  material 
between  the  finer  gravel,  and  with  at  intervals  flat  surfaces  of  luta- 
ceous  material  (playas  or  takyrs)  beautifully  marked  by  polygonal 
sun  cracks. 

MOVEMENT  OF  ATMOCLASTIC  MATERIAL.  The  movement  of  at- 
moclastic  material  is  twofold.  There  is,  first,  the  quiet,  more  or 
less  continuous  creep  and  flowage  of  the  material  under  the  influ- 
ence of  gravity,  and  conditioned  by  the  change  from  coarse  to  finer 
material  under  the  disintegrating  atmospheric  influences.  Sec- 
ondly, there  is  the  sudden  movement,  exemplified  by  landslides  or 
rock  avalanches.  These  are  very  generally  conditioned  by  a  satu- 
ration of  the  rock  debris  on  a  mountainside  by  water,  which  thus 
renders  the  mass  more  fluid  and  lowers  the  potential  angle  of  sta- 
bility. A  third  type  of  movement  may  be  considered  as  combining 
the  characteristics  of  both  of  the  preceding  types,  and  thus  repre- 
senting a  compound  of  gliding  and  creeping  movements.  Sliding  of 
rock  and  soil  as  the  result  of  earthquakes  may  also  be  considered 
here. 

Slow  Movements  of  Rock  and  Soil. 

Rock  and  Soil  Creep.  The  creep  of  soil  is  always  a  slow  process. 
It  scarcely  affects  the  surface,  which  is  covered  by  a  blanket  of 
vegetation,  beneath  which  the  maximum  movement  takes  place. 
Gotzinger  (18)  holds  that  creep  is  largely  due  to  the  work  of  satu- 
rating waters  which  increase  the  volume  of  the  mantle  rock  and  set 
it  in  motion  by  forcing  the  particles  upward  and  outward,  this  mo- 
tion being  translated  into  a  maximum  one  down  the  slope  of  the 
surface  on  which  the  soil  rests.  Frost  is,  of  course,  an  important 
agent  in  causing  the  downhill  movement  of  the  soil  cover.  If  such 
creep  takes  place  over  inclined  or  vertical  beds  of  rock,  the  upper 
ends  of  these  beds  will  suffer  overturning  or  bending  in  the  direc- 
tion of  the  creep. 

Solefluction  or  Rock  Flow.  To  the  more  rapid  movement 
of  the  rock  debris  saturated  with  large  quantities  of  water,  the 
name  solefiuction  has  been  applied  (Anderson-i).  This  was 
first  described  from  Bear  Island  in  the  North  Atlantic  (lat.  74^° 
N.),  where  on  account  of  the  hard  winters  much  rock  debris  is 
produced  by  mechanical  weathering.  The  melting  of  extensive  snow 
masses  in  spring  produces  a  large  quantity  of  water,  which  trans- 


544  PRINCIPLES    OF    STRATIGRAPHY 

forms  the  surface  material  into  a  pasty  mass,  and  this  under  the 
influence  of  gravity  will  move  slowly  down  even  gentle  slopes,  the 
movement  being  a  flowage  at  a  rate  much  exceeding  that  of  the 
slow,  subaerial  creep.  Along  the  valleys  mud  streams  or  mud  gla- 
ciers are  formed,  the  movement  of  which  may  be  prolonged  during 
a  considerable  period  of  time.  Such  mud  streams  consist  of  ma- 
terial of  all  sizes  from  the  finest  grains  to  huge,  angular  blocks. 
The  rapidity  of  movement  of  the  mud  streams  of  Bear  Island  is 
shown  by  the  fact  that  vegetation  rarely  gets  a  foothold  on  these 
masses  of  debris.  The  width  of  the  mud  streams  of  Bear  Island 
ranges  up  to  35  meters  and  the  depth  to  about  2  meters. 

The  "stone  rivers"  of  the  Falkland  Islands  form  other  examples 
of  such  atmoclastic  accumulations.  (Darwin-n.)  Valleys  here 
are  filled  by  gray  masses  of  rock  debris,  with  a  width  of  several 
hundred  meters  to  several  kilometers,  and  having  from  a  distance 
a  glacier-like  aspect.  Beginning  in  the  uplands,  they  descend  to  the 
low  country,  several  streams  uniting,  until  finally  the  entire  mass 
debouches  into  the  sea.  The  streams  include  vast  accumulations  of 
quartzite  blocks  of  irregular  form,  though  parallelepipedal  forms 
predominate.  In  length  they  vary  from  l/z  to  7  meters,  the  width 
being  half  as  great,  while  their  thickness  depends  on  that  of  the 
original  beds  of  the  parent  rock  from  which  they  are  derived. 
These  blocks  are  angular  and  are  piled  one  above  another  in  an  ir- 
regular manner.  It  has  been  held  that  these  streams,  which  are  now 
mostly  covered  by  vegetation,  came  into  existence  when  the  Falk- 
land Islands  were  experiencing  a  rougher  climate,  comparable  to 
some  extent  to  that  of  Bear  Island  to-day.  The  original  arrange- 
ment of  the  strata  into  hard  quartzite  beds  enclosed  in  soft  layers  is 
considered  as  having  a  fundamental  influence  on  the  formation  of 
these  rock  streams,  this  arrangement  being  the  usual  one  where  such 
streams  are  well  developed. 

Stone  glaciers,  a  modification  of  the  rock  stream  phenomenon, 
have  been  described  from  Alaska  (Capps-7).  They  vary  in  length 
from  one  to  five  kilometers,  and  in  width  from  100  to  500  meters. 
The  angle  of  surface  slope  varies  from  9  to  18  degrees,  and  the  size 
of  the  rock  fragments  averages  20  cm.  for  porphyry,  but  more  for 
diorite  and  limestones  and  less  for  slates.  Blocks  several  feet  in 
diameter  also  occur.  In  form  these  stone  glaciers  resemble  true  gla- 
ciers, being  thickest  in  the  center,  where  they  also  show  evidence  of 
more  rapid  motion.  Frontally  these  glaciers  end  in  a  face  up  to 
30  meters  in  height  and  having  a  slope  generally  of  35°,  the  maxi- 
mum slope  of  material  of  such  coarseness.  The  whole  aspect  of 
the  mass  suggests  motion. 


ROCK    GLACIERS  545 

The  interstices  between  the  blocks  are  occupied  by  ice  at  a 
short  distance  beneath  the  surface,  and  the  freezing  and  rethawing 
are  in  large  part  responsible  for  the  present  movement. 

The  original  accumulation  of  these  rock  glaciers  was  believed 
to  be  due  to  a  large  extent  to  transportation  of  the  rock  masses  by 
true  glaciers  and  their  deposition  along  the  path  of  the  glacier, 
rather  than  at  the  front  in  a  moraine.  Some  modern  ice  glaciers 
of  this  region  pass  downward  into  rock  glaciers,  and  furnish  a  sug- 
gestion of  the  mode  of  origin  of  those  accumulations.  Rock  streams 
thought  to  owe  their  origin  in  part  to  ice  glaciers  were  described  by 
Howe  (24)  from  the  San  Juan  Mountains  in  Colorado,  while  others 
observed  in  Veta  Peak,  Colorado,  were  found  to  be  wholly  inde- 
pendent of  ice  work.  In  the  San  Juan  Mountains  these  streams  are 
found  in  the  valleys  in  the  higher  peaks,  and  they  are  tongue-like, 
having  a  length  ranging  up  .to  one  kilometer  and  a  width  up  to  600 
meters,  while  the  thickness  ranges  from  20  to  40  meters.  The  ma- 
terial is  a  mixture  of  large  and  small  angular  blocks,  the  largest 
having  a  diameter  of  5  meters.  A  sharp  demarcation  exists  between 
the  stone  streams  and  the  talus  of  the  rock  walls,  from  the  foot  of 
which  the  stream  starts.  The  rock  stream  of  Veta  Peak  is  remark- 
able in  that  it  consists  of  fragments  of  a  whitish  porphyry  derived 
from  the  summit  of  the  mountain,  and,  although  the  rock  stream 
passes  down  between  banks  of  red  shale  and  sandstone  for  a  dis- 
tance of  1,700  feet  or  more,  not  one  particle  of  any  other  kind  of 
rock  than  porphyry  is  to  be  seen.  The  porphyry  fragments  are  of 
approximately  uniform  size,  fine  material  being  for  the  most  part 
wanting.  Only  a  few  large  fragments  occur,  the  average  size  being 
from  i  to  2  feet  in  diameter,  only  one  over  6  feet  having  been  noted. 
The  length  of  the  stream  is  something  over  a  mile,  while  the  drop 
of  the  surface  from  the  head  to  the  foot  of  the  stream  in  that 
distance  is  about  2,200  feet.  The  width  in  the  lower  part  of  the 
stream  is  500  feet,  but  its  two  feeding  branches  are  each  about  1,000 
feet  wide  above  the  junction.  The  depth  is  estimated  at  from  130 
to  300  feet. 

Rock  Slides  and  Falls. 

These  are  common  in  nearly  all  mountain  regions.  They  may 
occur  in  the  surface  soil  and  debris  which  cover  the  slope,  and  in  the 
decomposed  rock  masses  of  the  mountainside,  or  they  may  occur  in 
fresh  rock.  In  the  former  case,  saturation  by  water  is  commonly 
a  preliminary  occurrence,  the  slide  occurring  when  the  inertia  and 
friction  of  the  rock  masses  are  overcome.  Such  slides  leave  con- 


546  PRINCIPLES    OF    STRATIGRAPHY 

cave  scars  in  the  mountainside  and  accumulate  in  convex  masses 
in  the  valley  bottoms. 

Such  a  rock  fall  in  one  of  the  upper  Ganges  branches  in  the 
Himalayas  brought  down  800,000,000  tons  of  rock  in  three  days, 
filling  the  narrow  valley  to  a  depth  of  a  thousand  feet  with  debris. 
(See  ante,  p.  127.)  The  rock  fall  here  was  facilitated  by  the  loos- 
ening and  undermining  of  the  sloping  strata  of  rock. 

A  remarkable  case  of  rock  fall  occurred  in  the  little  town  of 
Frank,  Alberta,  Canada,  in  1903,  where  the  Cretacic  sandstones  and 
shale  of  Turtle  Mountain  suddenly  gave  way  and  fell  into  the  val- 
ley below,  forming  a  huge  heap  of  debris,  which  spread  out  in  the 
valley  bottom.  The  cause  of  the  slide  was  the  loosening  of  the  mass 
through  coal-mining  operations. 

In  1 88 1  a  great  rock  fall  occurred  in  the  village  of  Elm  in 
Switzerland.  Loosened  by  undermining  in  a  slate  quarry,  a  huge 
mass  of  rock  broke  away  on  the  mountainside  and  fell  onto  the 
plateau  in  which  the  quarry  was  situated.  Striking  this  surface, 
the  mass  broke,  and  numerous  large  fragments  were  hurled  by  the 
impact  through  the  air,  and  fell  into  the  valley  below,  where  they 
formed  a  rock  stream  which  in  all  essentials  resembles  that  of  the 
Alaskan  region  above  described.  (Heim-2O.) 

In  both  of  the  above-mentioned  cases  of  rock  falls  or  slides  the 
fragments  showed  percussion  marks,  while  chips  were  sometimes 
split  off  as  with  a  hammer.  The  recent  extensive  rock  slides  of  the 
Panama  Canal  are  other  examples  of  such  phenomena. 

Rock  and  Soil  Slides  Started  by  Earthquakes.  Slides  are  not  in- 
frequently started  by  earthquakes,  especially  where  slopes  are  steep 
and  the  material  more  or  less  water-soaked.  As  a  result  of  the 
earthquake  of  November  16,  1911,  a  portion  of  the  shores  of  the 
Lake  of  Constance  (Bodensee)  sank  into  the  sea.  The  lake  border 
(Seehalde)  was  deformed  for  a  total  length  of  about  16  km.;  on 
the  left  for  a  distance  of  10  km.  to  the  extent  of  y2  km.,  and  on 
the  right  shore  for  a  distance  of  6  km.  length  to  the  amount  of 
about  iy2  km.  The  edge  of  the  sublacustrine  shelf  was  locally 
translated  2.4  to  18  m.  lakeward,  the  point  of  abrupt  descent 
(Absturztiefe)  was  moved  between  1.4  to  8  m.,  the  elevations  on  the 
border  of  the  break  rose  from  0.2  to  2  m.  In  the  expansion  about 
9,000  cubic  meters  of  rock  and  soil  material  were  moved. 

ANCIENT  EXAMPLES  OF  ROCK  STREAMS  AND  SLIDES. 

Many  brecciated  rock  masses  occurring  in  older  geological  for- 
mations, of  which  the  explanation  is  in  doubt,  may  here  find  an 


ANCIENT    ROCK    STREAMS 


547 


interpretation.  Known  examples  of  this  type  are  the  Siluro-De- 
vonic  breccias  of  Mackinac  and  vicinity  in  Michigan,  the  limestone 
breccias  of  Gibraltar,  the  rubble  drift  of  south  England  and  the 
rock  streams  of  the  Ural  in  the  vicinity  of  the  mines  of  Bakalsk. 

THE  MACKINAC  LIMESTONE  BRECCIA.     (Grabau-i8.)     This  is  a 
remarkable  example  of  a  breccia  made  up  of  large  and  small  angu- 


FIG.  117.  Diagram  illustrating  the  relation  of  the  brecciated  limestone  to  the 
bedded  rocks  at  St.  Ignace,  Michigan.  The  stack  is  shown  again  in 
Fig.  118.  The  dotted  line  represents  the  hypothetical  former  ex- 
tent of  the  brecciated  material. 

lar  fragments  of  finely  bedded  upper  Siluric  (Monroan)  limestones 
and  dolomites,  derived  from  a  still  intact  cliff  of  this  limestone  near 
St.  Ignace  in  the  Upper  Peninsula.  The  deposit  is  best  seen  in  the 
cliffs  of  Mackinac  Island,  nearly  the  entire  mass  of  which  seems  to 
be  composed  of  this  rock,  which  must  here  have  a  thickness  of  be- 
tween 200  and  300  feet  or  more.  The  fragments  are  of  all  sizes 


FIG.  118.  View  of  the  ancient  stack  of  brecciated  limestone  at  Point  St. 
Ignace.  The  cliff  of  bedded  strata  is  to  the  right  of  the  railroad 
(lower  right-hand  corner).  (After  Hobbs.) 


from  that  of  a  pinhead  to  blocks  ten  feet  or  more  in  diameter,  and 
their  position  in  the  breccia  is  such  that  the  stratification  lines  of 
the  individual  blocks  dip  in  all  directions.  The  distance  to  which 
these  blocks  have  been  carried  from  the  parent  ledges  is  many 
miles,  and  the  width  of  this  ancient  stream  is  unknown.  At  St. 
Ignace  the  high  ground  behind  the  beach  consists  of  the  stratified 


548  PRINCIPLES    OF    STRATIGRAPHY 

Monroe  dolomites  in  undisturbed  horizontal  position,  but  in  front 
of  these  at  a  level  represented  in  the  cliffs  by  bedded  strata  are 
erosion  stacks  of  the  brecciated  rock,  carved  from  the  cliff  during  a 
period  of  higher  level  of  the  lakes.  The  position  is  such  as  to  indi- 
cate that  these  stacks  are  evidently  a  part  of  the  rock  stream,  while 
the  cliffs  behind  the  stacks  are  a  part  of  the  original  cliff.  In  one 
part  of  Mackinac  Island  the  breccia  is  found  to  be  underlain  by 
shales  and  thin  limestones  of  Monroan  (or  Salinan?)  age.  (Figs. 
117,  118.) 

That  the  rock  stream  represented  a  subaerial  flow  of  the  rocks 
is  shown  by  its  character.  Fine,  rounded  quartz  grains,  blown  from 
a  distance,  are  incorporated  in  the  mass.  The  age  of  this  stream  is 
Lower  Devonic,  the  Middle  Devonic  Onondaga  strata  enveloping  and 
enclosing  it  and  partly  incorporating  it  as  a  somewhat  reworked 
product. 


RESIDUAL  SOILS. 

The  product  of  rock  decay  in  situ,  whether  of  the  nature  of 
laterite  or  kaolinite,  pure  or.  impure,  not  only  furnishes  material 
for  other  agents  to  rework,  but  may  also  be  recomposed  in  situ 
without  much  or  any  disturbance.  The  same  is  true  of  crystalline 
sand  resulting  from  disintegration  through  insolation  of  granitic  and 
other  coarse-grained  crystalline  rocks.  If  the  upper  layers  are  re- 
worked by  a  transgressing  sea  or  by  wind  or  rivers,  a  perfect 
gradation  from  the  unaltered  crystalline  to  the  overlying  stratified 
rocks  may  be  produced.  Such  a  gradation  is  seen  in  the  basal 
arkose  of  the  Lake  Superior  sandstone,  where  it  rests  on  the  pre- 
Cambric  peridotites.  The  indistinctness  of  the  contact  has  led  some 
observers  to  regard  it  as  of  the  igneous  type.  Residual  soils  of 
limestone  regions  would  have  a  sharper  contact  with  the  underlying 
parent  rock  from  which  they  are  derived  by  solution.  They  consist 
of  the  residual  clay  left  after  the  removal  of  the  lime  in  solution. 
Such  clay  is  rendered  carbonaceous,  if  the  old  land  surface  presents 
obstructed  drainage,  and  swampy  conditions  prevail  as  on  a  pene- 
plain. In  extreme  cases  layers  of  coal  of  the  terrestrial  (humulith) 
type  may  be  formed.  Eolian  dust  may  be  added,  and  the  whole 
subsequently  reworked  by  a  transgressing  sea  and  covered  by 
marine  deposits  into  which  it  will  grade.  Thus  a  complex  deposit  of 
dark  clay  shales  will  be  produced,  the  age  of  which  ranges  from  the 
period  of  exposure  of  the  region  to  subaerial  solution  to  the  period 
of  resubmergence  by  the  sea.  Some  of  the  mid-Palaeozoic  black 


EOLIAN    DEPOSITS  549 

shales  of  North  America,  notably  the  Chattanooga  shale  of  Ten- 
nessee, seem  to  have  been  produced  in  this  manner. 


B.    ANEMOCLASTIC  OR  EOLIAN  DEPOSITS. 
ANEMOLITHS. 

Deposits  which  owe  their  location  and  form  to  transportation 
and  deposition  by  wind  are  commonly  known  as  eolian  deposits, 
and  when  consolidated  become  eolian  rocks  or  anemoliths.  At  first 
regarded  as  of  relatively  little  importance,  they  are  being  recognized 
in  constantly  increasing  number  among  the  clastic  rocks  of  the 
geological  column,  and  their  thickness,  great  horizontal  extent  and 
often  marked  structural  characters,  as  well  as  the  evidence  they 
furnish  regarding  the  former  physical  geography  of  the  region  in 
which  they  are  found,  render  them  of  special  significance  to  the 
student  of  earth  history. 

SOURCE  OF  MATERIAL  OF  EOLIAN  DEPOSITS.  The  ultimate  origin 
of  the  material  entering  into  eolian  deposits  is  extremely  diverse. 
Only  a  small  part  is  directly  due  to  the  corrasive  action  of  the  wind, 
freighted  with  sand  grains  or  other  material,  which  act  as  the  tool 
in  the  erosive  work  (see  ante,  Chapter  II).  A  large  part  is  de- 
rived from  the  products  of  atmospheric  decay  or  is  directly  pro- 
duced by  insolation,  and  so  is  primarily  of  atmoclastic  origin.  But 
the  mechanically  produced  sand  and  rock  flour,  whether  due  to 
stream  or  wave  work,  or  derived  through  the  grinding  of  the  rock 
masses  into  sand  and  powder  by  glaciers,  form  no  mean  source  of 
wind-transported  material.  Not  unimportant  in  this  connection  is 
the  dust  produced  by  organisms,  such  as  herds  of  animals  pounding 
a  rock  mass  to  powder  beneath  their  hoofs,  and,  above  all,  the  activi- 
ties of  man  in  breaking  up  rocks  by  mechanical  means,  and  grind- 
ing to  powder  the  surface  of  the  country  under  the  wheels  of  his 
vehicles.  The  annual  amount  of  dust  produced  by  heavy  or  rapid 
traffic  over  an  ordinary  road  is  probably  far  in  excess  of  the  me- 
chanically formed  detritus  produced  by  erosive  action  of  an  ordi- 
nary stream  in  a  bed  of  similar  width.  The  dust  produced  in  quar- 
rying and  mining  operations  forms  no  mean  addition  to  the  material 
furnished  for  eolian  transport,  while  coal  dust,  the  product  of  in- 
complete combustion,  sometimes  constitutes  an  important  mineral 
impurity  of  the  air  (see  ante,  Chapter  II).  Where  rocks  are  ground, 
as  in  cement  mills  or  in  stone  crushers,  the  air  for  considerable  dis- 
tances all  around  is  murky  with  suspended  dust.  This  settles  on 
and  around  the  vegetation  of  the  neighborhood,  but  may  also  be 


550  PRINCIPLES    OF    STRATIGRAPHY 

transported  for  a  considerable  distance.  In  the  course  of  long 
periods  of  time,  deposits  of  considerable  extent  and  thickness  may 
accumulate,  though  at  present  no  data  are  available  by  which  their 
extent  can  be  measured. 

An  important  contribution  of  clastic  material  available  for  eolian 
work  is  due  to  the  explosive  activities  of  volcanoes.  The  finer 
grades  of  pyroclastics  are  spread  far  and  wide,  and  furnish  one  of 
the  most  significant  of  eolian  deposits.  As  has  been  shown  in  an 
earlier  chapter,  some  of  this  material  is  held  suspended  in  the  air 
for  a  long  period  of  time,  and  settles  far  from  the  place  of  its  pro- 
duction. The  dust  from  Krakatoa  encircled  the  globe  several  times 
before  settling.  Material  which  has  thus  been  carried  to  a  distance 
from  the  source  of  production,  although  in  point  of  origin  belong- 
ing strictly  to  the  pyroclastics,  must,  in  view  of  its  assortment  and 
transportation  by  wind,  be  regarded  as  atmoclastic,  since  the  mode 
of  deposition,  more  than  the  mode  of  production  (clastation  *), 
gives  the  resulting  rock  mass  its  chief  structural  characteristics. 

It  should  finally  be  noted  that  material  for  eolation  is  also  sup- 
plied by  endogenetic  processes.  Thus  certain  pyrogenics,  the  finer 
grained  lapilli,  may  be  subject  to  wind  transportation  and  assorta- 
tion,  and  on  deposition  may  acquire  a  typical  eolian  structure.  They 
would  commonly  be  admixed  with  and  not  separable  from  ordinary 
eolian  pyroclastics.  The  most  typical  of  atmogenic  deposits,  snow, 
is  also  most  commonly  exposed  to  eolian  modification,  snow  dunes 
or  snow  drifts  being  among  the  common  forms  assumed  by  this  de- 
posit. Besides  the  form,  this  deposit  also  shows  the  other  common 
characters  of  wind-drifted  material,  such  as  uniform  size  of  grains 
and  dune  bedding  structure,  though  the  latter  is  brought  out  only 
when  dust  layers  alternate  with  the  layers  of  snow.  The  ability  of 
the  wind-driven  snow  crystals  to  act  as  agents  of  erosion  has  been 
noted  in  an  earlier  chapter  (p.  52). 

Hydrogenic  and  biogenic  deposits  may  also  be  found  among  the 
material  subject  to  eolation.  Thus  salt  crystals  and  gypsum  flakes 
separated  from  lakes  or  marginal  lagoons  may  be  blown  away  by  the 
wind.  The  dune-forming  oolites  of  Great  Salt  Lake,  believed  to  be 
of  phytogenic  origin,  and  the  wind-blown  deposits  of  foramini feral 
shells  in  many  regions,  are  examples  of  the  biogenic  anemoliths. 
Finally,  accumulations  of  wind-blown  organic  fragments,  such  as 
seeds,  leaves  or  whole  plants,  whether  microscopic  or  macroscopic, 
must  be  classed  among  the  biogenic  anemoliths.  These  are  proba- 
bly never  of  great  significance. 

See  p.  17. 


EOLIAN    DEPOSITS  551 

The  various  types  of  wind-deposited  rock  material  or  anemo- 
liths may,  then,  be  grouped  as  follows : 


Endogenetic 
(non  clastic) 
A  nemoliths 

1.  Pyrogenic 

2.  Atmogenic 

3.  Hydrogen!  c 

4.  Biogenic 

a.  Zoogenic 

b.  Phytogenic 


Exogenetic 

(clastic) 
Anemoliths 

1.  Pyroclastic 

2.  Autoclastic 

3.  Atmoclastic 

4.  Anemoclastic 

5.  Hydroclastic 

6.  Bioclastic 


The  term  anemolith  in  this  case  refers  to  deposition  by  wind, 
while  the  origin  of  the  material  is  indicated  by  the  qualifying  term. 
The  immediate  sources  of  the  material  for  sand  dunes  are  the  beach 
sands  of  sea  and  lake,  the  flood  plains  and  terraces  of  rivers,  gla- 
cial deposits  and  disintegrating  rocks  of  the  region.  The  dunes  of 
our  coast  are  largely  fed  by  the  beach  sands.  River  terraces  and 
flood  plains  furnish  much  of  the  material  for  the  dunes  of  river 
valleys,  while  glacial  sands  sometimes  directly  furnish  material  for 
dunes,  as  on  the  uplands  of  Cape  Cod,  and  in  the  North  German 
lowlands.  Desert  dunes  may  be  derived  from  disintegrating  sand- 
stones, as  in  the  case  of  the  Libyan  and  Nebraskan  dunes,  or  from 
the  flood  plains  of  rivers,  as  in  the  case  of  the  Kizil  Kum  and 
Kara  Kum  of  the  Transcaspian  deserts.  Dry  lake  bottoms  may  also 
form  a  temporary  source  of  eolian  material. 

TEXTURAL  TYPES  OF  ANEMOLITHS. 

Two  textural  types  of  anemoliths  may  be  recognized,  anemo- 
lutytes  or  dust  deposits  and  anemoarenytes  or  eolian  sand-dune  de- 
posits. Anemolutytes  will,  as  a  rule,  show  no,  or  but  little,  dis- 
cernible bedding  structure,  and  this  may  also  be  true  of  the  fine 
grades  of  anemoarenytes.  The  loess  may  be  taken  as  a  typical  ex- 
ample of  this  kind  of  deposit.  Eolian  sands  (anemoarenytes),  es- 
pecially the  coarse  types,  commonly  accumulate  in  the  form  of  sand 
dunes,  and  these  will  show  a  typical  dune-bedding  structure.  This 
is  also  true  of  biogenic  and  atmogenic  anemoliths. 


GENERAL  CHARACTERISTICS  OF  MODERN  EOLIAN  DEPOSITS. 

The   chief    characters    of    eolian    deposits    are    their   thorough 
sorting,  according  to  size  of  grain  and  mineral  material,  the  round- 


552  PRINCIPLES    OF    STRATIGRAPHY 

ing  and  pitting  of  the  individual  grains,  and  the  kind  and  character 
of  stratification  and  cross-bedding.  The  form  of  the  deposits  is  of 
less  significance,  since  that  form  may  be  altered  or  destroyed  subse- 
quently. 

Sorting  of  Material  According  to  Size  and  Specific  Gravity.  A 
series  of  experiments  was  made  by  J.  A.  Udden  (51)  with  a  cylin- 
der suspended  ninety  feet  above  the  ground  on  a  bluff  overlooking 
the  Mississippi  River,  and  arranged  so  as  to  catch  the  dust  carried 
by  winds  of  different  velocities  ranging  from  14  miles  to  29  miles 
per  hour.  From  these  experiments  Udden  concluded  that  "the  dif- 
ferent grades  of  materials  are  so  far  separated  from  each  other 
in  the  direction  of  the  wind  movement  that,  even  with  considerable 
changes  in  velocity,  the  principal  area  of  the  deposition  of  sedi- 
ments of  one  grade  will  not  far  encroach  upon  that  of  the  deposi- 
tion of  material  much  coarser  or  much  finer."  Thus,  fine  gravel 
or  sand  will  never  be  carried  to  the  region  of  the  main  dust  de- 
posits, and  wind-formed  sediments  will  be  quite  uniform  in  com- 
position for  any  given  area.  A  similar  conclusion  was  reached  by 
von  Zittel  in  reference  to  the  sands  of  the  Libyan  desert.  (Zittel- 

56.) 

It  may  thus  be  stated  as  the  first  important  character  of  eolian 
deposits  that  they  are  well  sorted,  according  to  size  and  specific 
gravity  of  the  material,  and  this  means  that  the  deposits  of  a  given 
locality  will  consist,  to  a  very  large  extent,  of  one  mineral  type. 
Thus,  an  original  mixture  of  grains  of  various  kinds  may  by  pro- 
longed eolian  action  be  sorted  into  nearly  pure  accumulations  of  the 
grains  of  the  different  minerals.  As  will  be  more  fully  shown  be- 
yond, calcareous  particles  are  thus  separated  from  others  and  segre- 
gated into  eolian  limestones,  while  clay  and  other  dust  particles  are 
removed  from  the  sands  which  result  from  the  decomposition  of 
igneous  rocks,  leaving  only  pure  quartz  behind.  The  clay  itself 
accumulates  to  form  deposits  of  loess.  In  the  Sinai  desert,  where 
the  quartz  is  derived  from  the  decomposition  of  dark-red  granite, 
it  represents  approximately  one-fourth  the  volume  of  the  original 
rock.  (Walther-52: 133.)  The  formation  of  a  dune  10  meters 
high  and  20  meters  broad  results  in  the  accompanying  liberation  of 
perhaps  5,000  cubic  meters  of  finest  particles  of  feldspar  and  horn- 
blende, which  are  carried  away  by  the  wind.  As  most  of  the  quartz 
sand  is  probably  derived  from  granites,  it  is  apparent  that  the 
amount  of  fine  material  produced  must  be  enormous.  Much  of  this 
is  carried  as  dust  by  the  wind. 

Size  of  grains  in  eolian  deposits.  The  size  of  the  grains  in 
eolian  deposits  varies  greatly.  According  to  Sokolow,  no  undoubted 


EOLIAN    DEPOSITS  553 

eolian  deposits  are  known  in  which  the  diameter  of  the  grains  'ex- 
ceeds 4  or  5  mm.  (48)  ;  more  usually  it  is  less  than  I  mm.  The 
sands  of  the  Libyan  desert  range  from  0.5  mm.  to  2.0  mm.  in 
diameter  with  the  grains  of  a  given  sample  of  nearly  uniform  size. 
Grains  of  the  Sylvania  sandstone  of  Michigan  and  Ohio,  a  fossil 
eolian  deposit,  vary  in  average  size  in  different  samples  from  0.18 
to  0.3  mm.,  though  an  occasional  grain  0.5  mm.  or  more  in  diame- 
ter occurs.  Dune  sands  from  Michigan  City,  Indiana,  have  an 
average  diameter  of  grain  of  nearly  0.3  mm.,  while  various  samples 
from  Albuquerque,  New  Mexico,  averaged  from  this  size  to  0.13 
mm.  in  diameter  (Sherzer  and  Grabau-45 ;  The  Sylvania  Sand- 
stone~77).  Eolian  dust  deposits  range,  of  course,  downward  to  the 
finest  particles,  which  will  settle  out  of  the  atmosphere,  or  which 
may  be  washed  out  of  it  by  rains  or  captured  by  hygroscopic  salt- 
covered  surfaces. 

Rounding  of  Sand  Grains.  The  process  of  rounding  of  sand 
grains  has  been  discussed  at  length  in  Chapter  V,  p.  253,  where  it 
was  also  pointed  out  that  wind-blown  sands  are  more  perfectly 
rounded,  especially  the  finer  grades,  than  grains  of  similar  size  sub- 
jected only  to  water  wear.  Besides  the  wearing  off  of  the  corners 
and  the  general  dulling  of  the  surface  from  prolonged  wear,  pitting 
of  the  grains  also  results  from  the  violent  impact  of  grain  on  grain 
to  which  they  are  all  subjected. 

In  general  it  may  be  stated  that  sand  grains  of  eolian  origin 
are  more  or  less  perfectly  rounded,  and  this  together  with  their 
well-assorted  character  makes  valuable  criteria  by  which  such  eolian 
sands  may  be  recognized.  In  general,  the  greater  the  amount  of 
transportation  and  the  more  frequent  the  rehandling  of  the  sand  by 
the  wind,  the  more  perfect  will  be  the  rounding,  as  well  as  the  as- 
sortment. Sands  of  parts  of  the  Libyan  desert,  derived  from  an 
older  sandstone,  the  Nubian,  and  carried  in  some  cases  a  distance 
of  a  hundred  miles  or  more,  show  a  pronounced  rounding  of  grain, 
as  well  as  perfection  of  assortment,  while  sands  from  the  desert 
near  Albuquerque,  New  Mexico,  derived  from  the  not  very  distant 
crystallines  are  poorly  assorted,  and  many  of  the  smaller  grains  are 
still  angular.  Sands  of  shore  dunes  such  as  those  derived  from  the 
glacial  sands  of  Lake  Michigan  show  only  moderate  rounding,  the 
transportation  and  wearing  having  been  of  comparatively  slight  ex- 
tent. Similar  conditions  occur  in  dune  sands  from  the  Pacific 
coast,  while  a  like  subangular  form  also  persists  in  sands  from  West 
Palm  Beach,  Florida.  Eolian  sands  along  the  Nile  valley,  derived 
primarily  from  the  disintegration  of  the  crystallines,  are  not  only 
very  poorly  assorted,  but  they  also  are  mostly  angular  with  only 


554  PRINCIPLES    OF    STRATIGRAPHY 


the  larger  grains  rounded.  Others,  however,  carried  in  from  the 
desert,  are  well  rounded  and  assorted. 

Stratification  and  Cross-bedding  of  Eolian  Deposits.  Eolian  de- 
posits may  or  may  not  be  well  stratified.  Deposits  of  dust  of  a 
loess-like  character  often  show  an  entire  absence  of  bedding  planes, 
the  material  being  homogeneous  throughout.  Walther  found  in  the 
deserts  of  Turkestan  near  Askabad  layers  of  loess-like  material  a 
meter  or  more  in  thickness  without  apparent  bedding,  interpolated 
between  layers  of  stratified  sand  and  gravel.  In  the  steppes  sur- 
rounding the  desert,  the  coarse  and  rigid  stems  of  the  steppe  plants 
check  the  wind  current,  which  then  drops  much  of  its  load  of  dust. 
Rain  will  wash  the  dust  from  the  air  and  from  the  leaves  of  the 
plants  on  which  it  has  settled.  This  accumulates  around  the  plants 
through  which  it  is  protected  from  further  removal  by  the  wind. 
The  same  office  is  performed  by  the  coarse  blades  of  the  Buffalo 
grass  (Biichloe  dactyloides,  Bouteloua  oligostachya)  and  other 
plants  which  abound  in  the  semiarid  Great  Plains  east  of  the  Rocky 
Mountains  in  North  America.  As  the  dust  accumulates  the  mantle 
of  vegetation  will  rise  to  a  higher  level.  The  roots  of  the  dead 
plants,  however,  will  continue  to  penetrate  the  deposit  until  their 
decay  leaves  a  series  of  vertical  tubes,  or  a  series  of  carbonaceous 
streaks  penetrating  the  structureless  mass.  The  tubes  may  subse- 
quently be  filled  by  mineral  matter,  as  in  the  case  of  many  loess 
deposits,  where  the  filling  of  the  tubes  is  by  calcite,  and  where  their 
presence  is  believed  to  be  in  part  the  cause  of  the  remarkable  ver- 
tical cleavage  of  these  deposits.  Older  fossil  examples  of  this  type 
are  also  known,  one  of  the  best  being  the  well-known  Portage  sand- 
stone of  Devonic  age,  which  is  exposed  in  the  banks  of  the  Genesee 
gorge  at  Portage,  New  York.  The  fine,  uniform,  structureless  tex- 
ture of  this  rock  makes  it  an  excellent  building  stone,  though  the 
presence  of  the  vertical  tubes,  described  originally  as  fucoids 
(Fucoides  verticalis),  often  mars  this  quality  for  certain  purposes. 
The  loess-like  origin  of  this  rock  seems  undoubted,  though  the  accu- 
mulation was  near  the  coast,  rather  than  inland. 

Dust  carried  by  wind  to  regions  of  more  extensive  rainfall 
will  be  washed  from  the  air  by  the  rain  and  accumulate  as  a  more 
or  less  stratified  loess.  In  like  manner  dust  carried  across  sur- 
faces rendered  hygroscopic  by  the  presence  of  salts  will  adhere  to 
these  surfaces  and  so,  as  a  rule,  become  finely  stratified. 

On  the  whole,  it  must,  however,  be  emphasized  that  regular 
stratification  is  not  characteristic  of  eolian  deposits.  Where  strata 
show  fine  or  uniform  bedding  water  always  has  played  more  or  less 
of  an  active  part  in  its  deposition,  though  the  idea  of  standing  wa- 


SAND    DUNES  555 

ter  bodies,  passive  influence,  or  receptive  waters  is  not  necessarily 
involved  in  this  concept.  Irregular  stratification  and  cross-bedding 
of  a  complex  type  may,  however,  be  regarded  as  one  of  the  most 
characteristic  structural  features  of  the  coarser  eolian  deposits. 

Eolian  cross-bedding  is  especially  characterized  by  discontinuity. 
The  successive  cross-bedded  layers  or  wedges  are  limited  above  and 
below  by  erosion  planes,  which  are  of  contemporaneous  origin. 
While  deposition  goes  on  in  one  section  of  the  deposit,  erosion  of  a 
previously  formed  one  in  part  supplies  the  material,  or  alternate 
deposition  and  erosion  may  characterize  any  portion  of  the  series. 
Furthermore,  as  will  be  more  fully  discussed  in  the  summary  chap- 
ter on  these  structural  features,  the  varying  currents  will  result  in 
the  inclination  of  the  cross-bedding  in  different  directions  in  the 
successive  sections.  Horizontal  beds  will  be  rare  or  wanting,  a 
feature  readily  distinguishing  this  type  from  the  diagonal  bedding 
due  to  torrential  action.  Finally,  as  Huntington  (25)  has  insisted, 
the  tangency  of  the  inclined  beds  with  reference  to  the  erosion  sur- 
face below,  or  their  gradual  bending  toward  parallelism  with  this 
plane  as  they  approach  it,  is  one  of  the  most  reliable  criteria  by 
which  eolian  deposits  can  be  recognized. 


SAND  DUNES,  THEIR  ORIGIN  AND  FORM. 

Wherever  along  the  beach  the  sun  has  dried  out  the  sands, 
they  have  lost  the  coherency  which  they  possessed  when  saturated 
with  water,  and  are  then  readily  blown  about  by  the  winds.  As  a 
result,  sand  dunes  are  formed  along  most  coasts,  these  dunes  grad- 
ually traveling  inland,  and  burying  forests,  fertile  lands  and  build- 
ings unless  their  landward  march  is  checked  by  a  barrier,  either 
natural  or  artificial.  The  distance  to  which  wind-blown  material  is 
carried  depends  chiefly  on  the  fineness  of  the  material,  its  specific 
gravity  and  the  strength  of  the  wind.  Examples  of  such  transpor- 
tation have  been  given  in  Chapter  II. 

The  sand  particles  move  under  the  direct  influence  of  the  wind, 
and  their  rate  of  movement  depends  on  their  size  and  the  strength 
of  the  wind.  According  to  Sokolow  (48:15),  when  the  wind 
velocity  is  4.5  m.  per  second,  quartz  sand  grains  of  0.25  mm.  diame- 
ter will  glide  only  along  the  surface  of  the  ground  without  rising 
freely  above  it.  With  a  wind  velocity  of  15  meters  per  second, 
however,  sand  grains  of  I  mm.  diameter  will  be  raised  some  dis- 
tance into  the  air.  With  the  wind  of  no  great  strength  and  the  sand 
not  very  fine,  movement  of  the  grains  is  along  the  surface  of  the 


556  PRINCIPLES    OF    STRATIGRAPHY 

ground,  or  only  a  few  centimeters  above  it.  Since  the  sand  grains 
of  the  shore  dunes  have  in  large  part  an  irregular,  more  or  less 
flattened  form,  their  movement  is  not  a  rolling,  but  a  gliding  one. 
The  larger  grains  move  only  by  jerks,  and  only  under  the  influence 
of  strong  gusts  of  wind.  A  greater  force  is  needed  to  start  the 
movement  of  a  grain,  which  then  will  continue  its  progress  even  un- 
der a  diminished  wind  force. 

While  a  steady  and  continuous  wind  will  cause  a  uniform  and 
constant  onward  movement  of  sand  grains,  with  the  result  that 
eventually  all  the  finer  particles  are  removed  by  the  wind,  a  more 
or  less  interrupted  series  of  wind  gusts  or  variable  winds  will  re- 
sult in  the  irregular  movement  of  the  particles  and  their  temporary 
arrangement  into  wave-like  forms.  On  a  small  scale  these  consti- 
tute wind  ripples,  while  the  larger  ones  are  the  dunes. 

Wind  ripples  are  common  on  sandy  surfaces  where  the  irregu- 
lar motion  of  the  wind  creates  eddies  and  cross  currents.  (See 
Chapter  XVII  for  formation  of  ripples.)  With  a  given  wind  they 
vary  in  height  and  distance  apart,  according  to  the  size  of  the  sand 
grains  composing  them.  Sokolow  gives  the  following  table  of  such 
relationship : 


Size  of  grain 

Height  of 
ripple 

Distance 
between  ripples 

0.2  mm. 
1  .0  mm. 
2  to  3  .  o  mm. 

10  mm. 
25  to    40  mm. 
70  to  100  mm. 

8  to    10  cm. 
25  to    35  cm. 
60  to  1  20  cm. 

The  form  of  the  ripples  is  symmetrical,  with  a  gentler  windward 
and  a  steeper  leeward  side.  Up  the  windward  side  the  sand  grains 
are  rolled  or  pushed  until  they  reach  the  crest  and  roll  down  the 
leeward  side.  In  this  manner  the  ripples  advance  in  the  direction 
of  wind  motion,  this  advance  being  at  a  variable  rate  dependent 
on  the  size  of  the  grain  and  the  strength  of  the  wind.  Helman 
(21  : 384)  obtained  the  following  average  rates  of  advance  for  sand 
ripples  on  continental  dunes  or  barchans  in  the  sandy  desert  of 
the  Khanat  of  Chiwa  in  Turkestan : 

Strength  of  Wind  Average  advance  of  ripples 
(meters  per  second)  in  millimeters 

6  9.0 

4  5-2 

3  3-3 

Similar  results  have  been  obtained  by  Sokolow  on  shore  dunes. 


SAND    DUNES  557 

Types  of  Sand  Dunes. 

Three  types  of  sand  dunes  are  recognized,  their  characters  being 
largely  determined  by  their  location.  These  are:  ist,  shore  dunes, 
or  those  formed  from  the  sands  left  to  dry  on  the  retreat  of  the 
water;  2nd,  river-bed  dunes,  and,  3rd,  inland  or  desert  dunes. 
While  all  of  these  have  fundamental  features  in  common,  they, 
nevertheless,  show  individual  characteristics  due  to  the  topographic 
diversity  and  structural  peculiarities  of  the  respective  regions  in 
which  they  occur. 

( i )  Strand  Dunes.  These  are  a  common  feature  of  the  coasts, 
being  found  on  the  shores  of  the  sea  and  of  the  larger  lakes.  Typi- 
cal and  well-known  examples  of  seashore  dunes  are  found  in  the 
Provincetown  region  of  Cape  Cod,  Massachusetts,  and  from  there 
southward  along  Long  Island  coast  and  the  sandy  coast  from  New 
Jersey  to  Florida.  They  are  further  found  on  the  shores  of  the 
Baltic,  especially  on  the  narrow  sand  bars  which  separate  off  the 
Kurische  and  Frische  Haff  on  the  east  Prussian  coast,  and  on  the 
west  coast  of  Kurland  an'd  the  Gulf  of  Riga  in  Russia.  (Berendt- 
4.)  Extensive  dune  areas  are  also  found  on  the  east  and  south 
coast  of  the  North  Sea,  especially  in  Denmark,  and  the  coast  of  the 
Netherlands  and  Flanders  from*the  mouth  of  the  Elbe  to  Pas-de- 
Calais,  while  the  French  coast  of  the  Bay  of  Biscay  bears  the  most 
extensive  dune  accumulations  of  all.  Finally,  extensive  shore  dunes 
are  developed  on  the  eastern  and  southern  coast  of  Lake  Michigan, 
and  to  a  lesser  extent  on  the  shores  of  the  other  Great  Lakes  of 
North  America.  Shore  dunes  are  most  typically  developed  where 
a  broad  flat  zone  of  sand  fronts  a  low  country,  as  in  the  examples 
cited,  but  they  may  also  occur  where  such  a  sand  zone  lies  at  the 
foot  of  rocky  cliffs.  In  such  cases  the  dunes  will  accumulate  on 
the  summit  of  the  cliff,  as  on  the  Normandy  coast  of  France,  the 
west  coast  of  Jutland  and.  the  West  Schleswig-Holstein  coast,  far- 
ther south,  where  the  height  of  the  cliff  in  one  case  (Island  of  Sylt 
among  the  north  Friesian  islands)  was  34  meters  and  that  of  the 
dunes  upon  it  reached  a  height  of  28  meters.  They  are,  however, 
never  found  where  rocky  coasts  descend  directly  into  the  waters, 
as  on  the  northern  New  England  coast  and  the  rocky  coast  of  the 
maritime  provinces  of  Canada,  the  rocky  coasts  of  Great  Britain 
and  of  Scandinavia  and  Finland.  The  best  development  of  coastal 
dunes  seems  to  be  on  a  sinking  coast,  over  90%  of  the  coast  dunes 
of  Europe  being  thus  located,  according  to  Sokolow. 

The  most  important  coastal  dunes  of  Europe  (Sokolow),  if 
not  of  the  world,  are  found  on  the  French  coast  of  the  Gulf  of  Bis- 


558  PRINCIPLES    OF    STRATIGRAPHY 

cay,  extending  without  interruption  from  the  mouth  of  the  Adour 
to  that  of  the  Garonne,  a  distance  of  over  240  km.  They  are  ar- 
ranged in  parallel  rows,  ten  being  the  maximum  number,  covering 
a  strip  of  coast  from  4  to  8  and  in  some  places  even  10  km.  wide, 
and  approximating  an  area  of  120,000  hectares  (296,520  acres). 
Their  height  ranges  up  to  90  meters,  making  them  the  highest 
known  coastal  dunes.  It  is  true  that  there  are  dunes  with  a  height 
of  from  120  to  180  meters  on  the  west  coast  of  Africa  between  Cape 
Bojador  and  Cape  Verde,  but  these  appear  to  be  desert  dunes  which 
have  reached  the  coast  from  the  Sahara  under  the  influence  of  pre- 
vailing northeast  winds. 

The  country  bounded  seaward  by  the  great  dune  belt  of  the 
Biscayan  dunes  is  a  low,  marshy  tract  known  as  the  Landes,  which 
by  many  geographers  is  believed  to  be  subsiding,  and  the  shore  of 
which  is  retreating  at  a  rapid  rate.  Near  Houtin,  in  the  northern 
part,  the  sea  advances  at  a  rate  estimated  at  not  less  than  2  meters 
per  year,  while  great  difficulty  is  experienced  by  St.  Jean-de-Luz, 
south  of  Biarritz,  at  the  southern  end  of  the  dune  region,  from  the 
encroachments  of  the  sea. 

On  the  south  coast  of  the  North  Sea  along  the  entire  coast  of 
Belgium  (Flanders)  and  the  Netherlands,  to  the  mouth  of  the 
Elbe,  extends  a  nearly  uninterrupted  dune  belt,  which  altogether 
forms  a  length  far  exceeding  that  of  the  coast  of  the  Landes.  These 
dunes  are' not  as  high  as  those  of  the  Biscayan  coast,  averaging  15 
to  20  meters,  with  the  highest,  near  Petten,  attaining  only  35  meters. 
The  coast  here  is  known  to  subside  at  a  rate  where  measured  of  i.i 
meters  per  century,  and  as  further  indicated  by  the  gradual  deep- 
ening of  the  Zuidersee,  formerly  a  swamp,  but  now  an  embayment 
of  the  sea. 

The  dunes  of  the  Danish  coast  of  the  North  Sea  are  of  especial 
interest  on  account  of  their  rapid  inland  advance.  This  section, 
together  with  the  coast  of  Schleswig-Holstein,  forms  the  second 
largest  dune  region  of  Europe,  covering  an  area  of  67,000  hec- 
tares (165,557  acres),  many  of  the  dunes  reaching  a  height  of  30 
meters.  The  retreat  of  this  coast  has  been  discussed  in  an  earlier 
chapter,  but  an  example  may  be  repeated  here  to  show  the  rate  of 
dune  advance.  In  1757  it  was  found .  necessary  to  tear  down  the 
church  of  the  village  of  Rantum  on  the  Island  of  Sylt  on  the  west 
coast  of  Schleswig-Holstein,  because  it  was  reached  by  the  advanc- 
ing dunes.  In  1791  or  1792  the  entire  dune  chain  had  passed  over 
the  church  ruins,  these  then  lying  on  the  shore  which  had  advanced 
to  this  point.  Sixty  years  later  the  site  of  the  church  was  700  feet 
from  shore,  the  depth  there  being  12  feet.  The  second  church  has 


SAND    DUNES  559 

since  been  buried  by  the  advancing  dunes.  ( Forchhammer- 1 6  :<?/.) 
A  similar  case  is  shown  in  the  changes  produced  by  migrating  dunes 
on  the  Kurische  Nehrung,  in  East  Prussia,  where  a  church  was 
buried  and  again  resurrected  by  the  advancing  dunes  between  the 
years  1809  and  1869. 

On  the  south  coast  of  the  Baltic  exists  another  important  dune 
area  of  Europe,  its  strongest  expression  being  found  on  the  Ku- 
rische and  Frische  Nehrung,  two  very  long  narrow  sandbars  sep- 
arating off  shallow  lagoons  on  the  coast  of  East  Prussia.  The 
height  of  the  dunes  here  reaches  60  meters  and  more,  and  hence 
these  are,  next  to  those  of  the  Gascony  coast,  the  most  important 
coastal  dunes  of  Europe. 

Dunes  of  great  size  and  covering  an  extended  area  occur  on 
the  North  African  coast  of  the  Mediterranean,  especially  on  the 
Great  Syrt.  Elsewhere  on  the  Mediterranean  coast  they  are  of  little 
importance. 

The  dunes  of  the  east  coast  of  North  America  have  been  studied 
to  a  much  less  extent  than  those  of  the  European  coast.  Perhaps 
the  best-known  region  is  that  of  the  extreme  tip  of  Cape  Cod  at 
Provincetown,  where  the  dunes  reach  a  height  not  exceeding  30  or 
40  meters.  This  entire  section  is  a  region  of  sandbars  and  beaches 
built  by  the  waves  and  shore  currents  from  material  washed  from 
the  Truro  and  Wellfleet  coast,  a  region  exposing  high  cliffs  of  gla- 
cial and  earlier  sands  to  the  open  Atlantic.  The  dunes  built  at 
Provincetown  slowly  advance  southward  and  westward,  burying 
forests  and  hamlets  in  their  path,  though  their  march  has  to  some 
extent  been  arrested  in  the  Provincetown  region  by  artificial  means, 
at  an  expenditure  of  $28,000  between  the  years  1826  and  1838. 

On  the  Long  Island  coast  the  dunes  are  moderate,  but  on  the 
New  Jersey  coast  and  on  that  of  the  Carolinas  they  reach  a  consid- 
erable height  and  extent,  and  in  their  inland  march  bury  forests 
and  even  buildings. 

(2)  Lake  Shore  Dunes:  These  are  well  illustrated  by  the  dunes 
so  extensively  developed  on  the  eastern  shore  of  Lake  Michigan 
from  the  Straits  of  Mackinac  to  the  Chicago  area.  Here  extensive 
glacial  sands  in  part  forming  beach  lines  of  a  subsequent  lake  stage 
of  greater  extent  than  the  present  are  heaped  into  sand  dunes  by 
the  prevailing  westerly  winds.  Some  of  these  sand  dunes  on  the 
northwest  coast  of  Michigan  are  grassed  over  and  wooded,  but 
others  are  still  in  an  active  state  of  movement,  advancing  upon  and 
burying  the  forests.  In  height  these  dunes  range  to  a  hundred  feet 
or  more,  especially  in  the  southern  area,  as  in  Dune  Park,  In- 
diana. Near  Muskegon,  Michigan,  occurs  one  of  the  largest  dunes 


560  PRINCIPLES    OF    STRATIGRAPHY 

in  the  world.    It  is  several  hundred  feet  high,  and  from  its  advance 
has  become  known  as  "Creeping  Joe." 

(3)  River  Flood-Plain  and  River-Bottom  Dunes.  Rivers  flow- 
ing through  broad,  open  valleys,  especially  in  semiarid  regions,  are 
often  accompanied  by  an  extensive  development  of  border  dunes, 
while  those  rivers  flowing  through  narrow  canons  are  essentially 
free  from  such  accumulations.  In  a  humid  climate  dunes  are  sel- 
dom formed  on  river-bottoms,  even  though  these  may  be  broad  and 
supplied  with  an  abundance  of  sand.  In  illustration  of  this  it  may 
be  noted  that  river  border  dunes  are  not  common  in  western  Eu- 
rope, except  in  the  sunny  and  somewhat  drier  regions  of  southern 
France  and  Spain.  Thus,  while  in  the  North  German  plains  and  in 
England  the  few  dunes  which  have  been  formed  in  the  past  are 
low  and  soon  covered  with  vegetation,  the  valley  of  the  Gardon  in 
Languedoc  shows  dunes  10  meters  high,  while  dunes  rising  to  a 
height  of  25  meters  are  found  in  the  sandy  desert  region  on  the 
right  bank  of  the  Guadalquivir  in  Andalusia  in  southern  Spain.  In 
eastern  Europe,  on  the  other  hand,  river  dunes  are  much  more  ex- 
tensively developed.  Thus  even  the  smaller  streams  of  the  northern 
half  of  the  Russian  regions  have  dunes  rising  to  a  height  of  5 
meters,  while  southern  Russia,  with  its  dry  continental  climate, 
shows  them  extensively  developed.  A  nearly  continuous  dune  belt, 
reaching  sometimes  a  width  of  12  km.,  and  with  dunes  averaging  10 
or  12  m.  in  height,  extends  along  the  middle  course  of  the  Dnieper 
below  Kief,  while  the  lower  course  of  this  stream  shows  a  still 
more  extensive  dune  area,  especially  in  the  government  of  Taurida. 
The  sands  here  are  found  on  the  left  bank  of  the  Dnieper,  and  ex- 
tend over  an  area  more  than  150  km.  long,  with  a  maximum  width 
of  30  km.  In  the  midst  of  this  area,  however,  are  often  spots  free 
from  sand,  while  in  some  parts  a  broad  area  of  meadow  and  wooded 
land  separates  the  sand  area  and  the  river.  The  height  of  the 
dunes  is  mainly  from  5  to  7  m,,  but  exceptional  cases,  where  the 
height  rises  to  11.2  m.,  have  been  noted.  The  sand  is  almost  exclu- 
sively quartz  rock,  with  only  a  very  slight  admixture  of  feldspar 
and  dark  grains,  probably  of  iron  oxide.  The  grains  are  well 
rounded,  often  spherical,  angular  grains  being  wholly  wanting.  The 
color  of  the  dunes  as  a  whole  is  a  light  golden  yellow.  The  sands 
of  the  middle  Dnieper  are  somewhat  coarser,  but  they  do  not  ex- 
ceed on  the  average  the  diameter  of  0.4  mm.  In  roundness,  purity 
and  color  the  sands  of  the  two  areas  are  much  alike.  A  still  greater 
development  of  river  border  dunes  is  found  in  the  valleys  of  the 
Don  and  the  Donetz.  In  the  Don  valley  the  dune  zone  has  a  width 


SAND    DUNES  561 

ranging  from  8  to  18  km.,  the  average  being  12  or  13  km.,  while 
the  height  of  the  dunes  may  reach  30  meters.  In  the  Donetz  valley 
the  width  of  the  zone  is  sometimes  10  km.,  but  the  height  of  the 
dunes  does  not  as  a  rule  exceed  5  or  7  m.  The  shores  of  the 
Volga  in  the  Kazan  district  also  furnish  extensive  dunes,  which 
wander  far  into  the  steppes.  Still  more  extensive  dune  develop- 
ment is  found  in  the  river  valleys  of  central  Asia,  as,  for  example, 
along  the  River  Oxus,  or  Amudaria,  and  the  Jaxartes  or  Syrdaria, 
both  of  which  are  tributary  to  the  Aral  Sea.  (Walther-52  ://p.) 
These  streams  bring  vast  quantities  of  sand  and  mud  from  the 
Tian-Shan,  Great  Pamir,  and  Hindu  Kush  mountains,  in  which 
they  rise,  and  spread  them  over  the  low  ground  of  their  flood  plains, 
which  range  in  width  up  to  10  km.  The  thickness  of  the  deposit 
made  by  the  Oxus  was  found  to  be  23  m.  at  Tschardschui.  The 
rivers  rise  3  meters  from  March  to  July  and  overflow  the  flood 
plains,  depositing  the  sandy  sediment.  As  the  water  of  the  Jax- 
artes falls,  the  hot  northern  winds  soon  dry  the  deposit,  and  carry 
away  all  the  finer  dust  particles,  leaving  only  the  pure  quartz  sand, 
which  is  heaped  into  dunes.  These  wander  southward  across  the 
Kizil  Kum  desert,  sometimes  at  a  rate  of  20  meters  during  a 
stormy  day,  but  generally  the  sand  masses  move  at  an  average  rate 
of  6  miles  per  year.  Reaching  the  Oxus,  these  sands  are  incor- 
porated in  its  sediment,  and  the  operations  of  sorting  the  deposits 
on  the  flood  plain  of  this  river  are  repeated  and  the  sands  again 
heaped  into  dunes,  which  wander  southward  across  the  Transcas- 
pian  or  Kara  Kum  desert,  until  they  reach  the  borders  of  the 
Caspian  Sea.  The  activities  of  the  streams  are  unceasing,  and  the 
supply  of  material  in  the  mountains  in  which  they  rise  is  practically 
inexhaustible.  Thus  there  is  a  constant  succession  of  sand  dunes 
wandering  southward  across  these  deserts,  and  layer  upon  layer  of 
sand  accumulates,  each  showing  the  characteristic  eolian  structures, 
and  helping  to  build  up  a  deposit  of  pu^e,  unfossiliferous  sand  of 
almost  unlimited  thickness. 

In  North  America  dunes  are  rare  and  insignificant  in  the  river 
valleys  of  the  eastern  and  central  region,  but  are  more  frequently 
found  in  the  drier  climates  of  the  west.  Perhaps  the  most  exten- 
sive river  dune  area  on  this  continent  is  that  of  the  Columbia  and 
Snake  rivers  in  Oregon  and  Washington  between  Dallas  and 
Riparia,  the  sand  being  derived  from  the  flood  plains  of  the  rivers, 
which  are  widely  exposed  during  the  dry  season. 

(4)  Inland  or  Desert  Dunes.  The  largest  areas  of  shifting 
sands  are  the  deserts.  Their  occurrence  is  even  more  dependent  on 


562  PRINCIPLES    OF    STRATIGRAPHY 

aridity  of  climate  than  is  the  case  with  river  dunes,  for  moisture 
will  permit  the  growth  of  vegetation  and  so  check  the  movements  of 
the  sands.  Where,  however,  the  cover  of  vegetation  is  destroyed  by 
man  or  other  agencies,  dunes  may  occur  even  in  moist  climates,  as 
is  the  case  in  northern  France,  Belgium  and  the  North  German 
lowlands. 

The  height  of  continental  dunes  may  range  up  to  150  or  even 
200  meters,  and  the  area  covered  by  them  is  often  very  large.  In 
Hungary  the  total  dune  area  covers  some  13,200  sq.  km.,  with  single 
dunes  rising  52  m.  in  height.  Large  areas  also  occur  in  European 
Russia,  but  the  greatest  dune  districts  are  in  the  deserts  of  Asia, 
Africa  and  Australia.  In  the  Sahara  dunes  cover  only  one-ninth 
of  the  total  area  (Zittel-56),  but  even  so  this  aggregates  a  total 
of  18,000  geographical  square  miles.  Arabia  is  largely  a  land  of 
drifting  sands.  Almost  the  whole  southern  area  is  occupied  by  the 
terrible  Desert  of  Roba-el-Khali  or  the  desert  Dehna,  which  is  wholly 
covered  by  eolian  sands  and  is  without  the  relief  of  oases.  Its 
length  is  150  geographic  miles,  its  width  80.  Sands  form  nearly 
one-third  of  the  entire  surface  of  Arabia,  or  not  less  than  15,000 
geographic  square  miles.  (Palgrave-35  :  pi.)  In  the  northern  part 
of  the  peninsula  is  the  Nefud  desert  of  red  sands,  while  other  sandy 
deserts  of  Asia  are  found  in  Syria,  Iran,  Baluchistan,  northern  In- 
dia, eastern  Turkestan  and  Mongolia,  where  continuous  sandy 
desert  areas  extend  for  hundreds  of  kilometers  (Przhevalsky-39). 
In  North  America  extensive  sand  dune  areas  of  the  continental 
type  are  found  between  the  Rockies  and  the  Sierra  Nevada,  in  the 
Colorado  and  Mohave  deserts  of  southern  California  and  in  the 
Sand  Hill  region  of  Nebraska  and  the  adjoining  area.  In  Nebraska 
this  region  covers  an  area  of  more  than  18,000  square  miles,  or 
almost  one-fourth  of  the  total  area  of  the  state.  The  sand  is  largely 
derived  from  the  disintegration  of  the  Tertiary  sandstone,  and  to 
this  is  due  in  part  its  purity.  The  size  of  the  grains  varies  consid- 
erably, but  the  average  centers  around  0.25  to  o.i  mm.,  the  maxi- 
mum scarcely  rising  above  i.o  mm. 

The  sand  hills  of  Nebraska  enclose  numerous  valleys,  ranging 
in  size  from  mere  basins. to  valleys  a  mile  in  width  and  many  miles 
long.  Numerous  lakelets  generally  arranged  in  groups  occur  in 
these  valleys,  the  individual  lakes  ranging  from  small  ponds  a  hun- 
dred yards  across  to  bodies  of  water  a  mile  or  more  wide  and  four 
or  five  miles  long.  In  Cherry  county  fifty  or  more  such  lakes  form 
a  single  group.  These  lakes  exist  because  the  climate  is  now  moist, 
for  which  reason  also  much  of  the  sand-hill  region  is  covered  with 
vegetation,  though  many  bare  areas  of  drifting  sand  still  occur. 


SAND   DUNES  563 

The  chief  agent  in  holding  the  dunes  and  making  the  spread  of  vege- 
tation possible  is  the  bunch  grass  (Andropogon  scoparius),  though 
the  sand  grass  (Calamovilfa  longifolia}  and  the  needle  or  silk  grass 
(Stipa  coniata)  are  also  important  as  binders.  The  most  charac- 
teristic plant  next  to  the  bunch  grass  is  the  dagger  weed  (Yucca 
glauca),  which  often  occurs  in  great  abundance.  At  the  present 
time  hollows  or  "blow-outs"  are  more  characteristic  of  these  sand 
hills  than  new  dunes.  These  blow-outs  begin  where,  from  over- 
grazing or  fires,  the  vegetation  is  destroyed,  and  will  increase  in 
size  until  they  are  from  300  to  900  feet  in  circumference  with  sides 
of  bare  sand  sloping  inward  at  an  angle  of  about  30  degrees  to  the 
bottom,  which  may  be  from  20  to  75  feet  or  more  beneath  the  rim. 
(Pool-38.)  In  South  America  continental  dunes  are  best  devel- 
oped in  the  great  Atacama  desert  of  Chile,  west  of  the  Andean 
chain.  Finally  many  of  the  deserts  of  Central  and  West  Australia 
are  characterized  by  dunes  of  great  extent. 


The  Forms  of  Dunes. 

Three  main  dune  forms  may  be  recognized,  of  which  all  others 
constitute  more  or  less  divergent  modifications.  These  are:  1st, 
the  conical  hill;  2nd,  the  long  ridge,  generally  occurring  in  parallel 
groups,  and,  3rd,  the  crescent-shaped  dune  or  barchan.  The  cres- 
cent or  barchan  type  is  most  characteristic  of  the  inland  desert 
regions.  It  presents  a  gently  convex  surface  to  the  wind,  while  the 
lee  side  is  steep  and  abrupt.  The  horns  of  the  crescent  mark  the 
lateral  advance  of  the  sands.  Its  wide  distribution  and  all  but  uni- 
versal presence  in  the  sandy  deserts  of  all  continents  make  this 
type  the  normal  one  for  sand  hills  formed  on  an  open  area.  In- 
deed, it  is  probable  that  in  very  many  cases  the  linear  ridges  are 
mere  modifications  of  this  type,  formed  by  the  lateral  confluence 
of  many  simple  barchans.  This  is  often  shown  in  the  wavy  form  of 
the  crest  line,  as  in  the  case  of  the  dimes  of  the  Transcaspian 
desert. 

On  the  coast,  barchans,  though  present,  are  less  characteristic. 
Here  we  find  the  linear  series  more  commonly  developed,  because 
a  nearly  constant  and  uniform  supply  of  sand  is  furnished  by  the 
parallel  coast,  and  because  the  sloping  coast  itself  exerts  a  directing 
force.  Coastal  dunes  never  have  a  symmetrical  cross  section,  the 
windward  side  generally  having  a  gentle  slope  of  from  10°  to  20°, 
which  may  in  places  be  somewhat  convex,  while  the  leeward  slope  is 
generally  much  steeper,  being  often  as  high  as  30°. 


564  PRINCIPLES    OF    STRATIGRAPHY 


Origin  of  Intercalated  Dust  and  Clay  Layers,  and  of  Clay  Balls  in 

Sand  Dunes. 

The  depressions  between  the  sand  dunes  when  not  occupied  by 
standing  water,  as  in  the  moist  sand-hill  region  of  Nebraska,  often 
represent  a  flat  playa  or  takyr  surface,  the  dried  mud  bed  of  a 
temporary  lake,  which  evaporated  soon  after  its  formation  under 
the  influence  of  a  dry  climate.  Such  surfaces  are  common  in  most 
desert  regions,  and  they  are  not  infrequently  characterized  by  mud 
cracks,  footprints  and  trails  of  various  animals.  When  the  sand 
dunes  advance  over  such  a  surface  a  horizontal  bed  of  clay  will 
separate  the  diagonally  bedded  eolian  sands.  This  clay  bed  will 
of  course  be  of  limited  extent  only,  wedging  out  around  the  margin 
of  the  playa.  If  the  clay  layer  of  the  playa  surface  is  very  thin 
(i  to  2  cm.),  the  pieces  into  which  it  splits  on  drying  will  curl  up 
like  shavings,  and  in  such  a  condition  they  may  be  blown  by  the 
wind  into  the  dune.  Here,  on  becoming  moistened  by  the  winter 
rains,  they  will  be  compressed  into  flat  lenticles  of  clay  and  form 
the  "clay  galls"  so  common  in  modern  as  well  as  ancient  eolian 
deposits. 

Clay  and  dust  accumulations  are  not  confined,  however,  to  the 
depressions  between  the  dunes.  A  light  wind,  active  for  a  period  of 
time,  may  dust  over  the  dune  with  a  coating  of  argillaceous  par- 
ticles, which  then  become  incorporated  in  the  sand  mass  as  oblique 
partition  layers.  Such  occurrences  are  not  uncommon  in  the  Trans- 
caspian  (Kara  Kum)  and  other  deserts.  They  appear  as  steeply 
inclined  sheets  of  clay  penetrating  the  dunes,  and  are  not  infre- 
quently found  in  the  form  of  parallel  "clay  dikes,"  10  to  15  meters 
in  length,  in  the  interdune  areas,  where  they  may  rise  a  centimeter 
above  the  flat  surface,  representing  the  residual  base  of  a  cross- 
bedded  dune,  the  top  of  which  has  moved  onward. 


Peat  and  Lignite  Deposits  in  Sand  Dunes. 

Shore  dunes  often  transgress  across  peat  deposits  formed  in 
swamps  or  marshes  behind  the  dunes.  Such  peat  deposits,  some- 
times with  old  tree  stumps,  are  found  on  the  shores  of  Nantucket, 
and  are  sometimes  buried  under  deep  masses  of  dune  sand,  as  at 
the  Nauset  lights  on  Cape  Cod.  They  are  characteristic  of  other 
regions  as  well.  Forests  buried  by  advancing  dunes  are  killed, 
and  the  wood,  if  buried  long  enough,  is  converted  into  lignite.  The 


OLDER    EOLIAN    DEPOSITS  565 

same  thing  is  true  of  coatings  of  vegetation  which  are  buried  by  the 
readvancing  sands.  In  the  sand  dunes  of  Cape  Cod  many  such  ex- 
amples are  found,  and  the  same  is  true  for  the  sand  hills  of  Ne- 
braska. Indeed,  this  may  be  seen  in  almost  all  coastal  dunes  where 
vegetation  has  gained  a  temporary  foothold.  Such  sands  would 
thus  become  lignitic,  and  the  fragments  of  lignitized  and  broken 
wood  may  be  scattered  and  incorporated  in  the  sands  over  a  wide 
area.  The  lignitic  sands  of  the  Raritan  formation  of  New  Jersey 
apparently  had  such  a  history. 


Transgressive  Relation  of  Dune  Sands  to  Subjacent  Formations. 

The  southward  transgressing  dunes  of  the  Kara  Kum  or  Trans- 
caspian  desert  spread  layers  of  sand  over  the  older  fluvial  or  marine 
deposits.  The  pure  quartz  sands  of  the  Libyan  desert,  derived  from 
the  disintegration  of  the  Nubian  sandstone  a  hundred  miles  away, 
transgress  across  the  floor  of  Cretacic  and  Tertiary  limestones,  and 
the  weathered-out  fossils  of  these  formations  are  enclosed  in  the 
basal  part  of  the  sands. 

In  the  profile  of  the  earth's  crust  many  cases  of  such  trans- 
gressive  relation  of  unfossiliferous  sandstones  upon  fossiliferous 
marine  deposits  are  found.  Examples  are  the  St.  Peter  on  the 
Beekmantown  limestone,  the  Sylvania  on  the  Monroe  dolomites, 
the  Bunter  Sandstein  upon  the  marine  Zechstein,  the  Keuper  upon 
the  Muschelkalk  and  many  others.  Such  deposits  point  strongly  to 
an  origin  comparable  to  that  of  modern  desert  sands  which  overlie 
marine  sediments  of  an  earlier  age. 


EXAMPLES  OF  OLDER  EOLIAN  DEPOSITS. 

The  Loess  as  an  Example  of  a  Dust  Deposit.  The  loess  is  a 
continental  deposit  of  loosely  arranged,  angular  grains  of  calcare- 
ous silt  loam,  typically  intermediate  in  fineness  between  sand  and 
clay  and  of  remarkably  uniform  mechanical  composition.  Normally 
it  is  without  stratification,  and  Breaks  off  in  vertical  slabs,  with  the 
result  that  perpendicular  cliffs  are  formed.  Loess  was  first  de- 
scribed from  the  valley  of  the  Rhine,  but  is  also  known  from  south- 
eastern Europe,  from  North  America,  and  especially  from  China, 
.where  it  was  fully  described  by  von  Richthofen  (42).  Here  the 
loess  sometimes  has  a  thickness  of  a  thousand  feet  or  over,  and  is 
believed  to  be  primarily  the  disintegrated  rock  material  brought  by 


566  PRINCIPLES   OF    STRATIGRAPHY 

the  winds  from  the  Desert  of  Gobi  in  central  Mongolia,  Evidence 
of  fluvial  action  is,  however,  not  wanting,  many  gravel  beds  of  great 
extent  and  great  distance  from  their  source  pointing  to  river  activi- 
ties. It  has  been  thought  (Wright-54)  that  the  distribution  indi- 
cates a  vast  body  of  standing  water  which  temporarily  occupied  the 
loess-covered  area  in  late  Tertiary  or  Quaternary  time,  but  this  in- 
terpretation does  not  sufficiently  account  for  the  absence  of  fossils 
in  the  loess,  nor  does  it  do  justice  to  the  ability  of  rivers  and  wind 
to  distribute  fine  sediments  in  broad  level  plains.  For  the  whole 
of  Asia  the  loess-covered  area  comprises  about  1,324,000  square 
kilometers  (511,150  square  miles)  (v.  Tillo),  which,  with  an  aver- 
age estimated  thickness  of  30  meters,  gives  a  total  of  nearly  40,000 
cubic  kilometers  of  loess  material.  All  this  material  has  of  course 
been  removed  from  the  rock  surfaces  of  the  country  where  it  origi- 
nated. (Walther-5i  150.)  The  loess  is  characteristically  pene- 
trated by  vertical  tubes,  the  calcite-filled  hollows  left  by  the  decay 
of  grasses  and  roots.  These  help  to  produce  a  vertical  splitting  of 
the  mass,  which  otherwise  shows  no  planes  of  separation,  since 
stratification  is  for  the  most  part  absent.  As  a  result,  the  walls 
of  loess  left  on  the  dissection  of  the  loess  area  by  the  Yellow  River 
and  its  tributaries  form  vertical  bluffs  of  great  height.  "Millions 
of  Chinese  live  on  the  valley  floors  of  dissected  basins  of  this  kind, 
for  the  loess  is  extremely  fertile  where  well  watered.  Great  num- 
bers of  the  people  inhabit  cave-like  dwellings  excavated  in  loess 
bluffs;  in  a  thickly  populated  district  not  a  house  may  be  seen. 
The  yellowish  color  of  loess  prevails  everywhere.  It  gives  color 
and  name  to  the  great  river  of  the  region  and  to  the  sea  into  which 
the  river  flows."  (Davis-i3 : 5/7,  318.)  The  loess  of  the  Mis- 
sissippi Valley  region  and  of  the  plains  generally,  is  also  commonly 
interpreted  as  a  deposit  of  wind-blown  material,  though  indications 
of  aqueous  activities  are  not  wanting.  The  principal  evidence  for  the 
eolian  origin  of  this  "Prairie  loess"  (Shimek-46)  is  found  (i)  in 
the  absence  in  the  deposit  of  shells  belonging  to  distinctively  water 
species;  (2)  the  presence  of  land  shells  of  species  that  live  on  the 
shores  of  ponds;  (3)  the  difficulty  of  imagining  a  submergence  of 
the  loess-covered  area  of  such  character  as  to  account  for  its  pe- 
culiarities ;  for  in  a  permanently  standing  body  of  water  the  uni- 
formity of  distribution  of  material  of  the  given  degree  of  fineness 
characteristic  of  the  loess  could  not  be  secured;  (4)  the  reasonable 
influence  of  vegetation  in  arresting  wind-blown  dust.  Professor 
Wright  (55'^oj)  gives  some  facts  which  seem  to  oppose  the  eolian 
origin  of  the  Mississippi  valley  loess:  (i)  The  distribution  of  the 
loess  in  about  equal  proportions  upon  both  sides  of  the  Missouri 


x  -  LOESS  567 

River,  as  well  as  the  presence  of  the  loess  where  the  prevailing 
winds  are  least  likely  to  pile  it  up.  (2)  The  exclusive  dependence 
upon  wind  for  the  distribution  of  the  loess  leaves  out  of  considera- 
tion the  difficulty  of  accounting  on  this  basis  for  the  extensive  level- 
topped  terraces  which  frequently  occur.  (3)  The  agency  of  water 
in  the  distribution  of  loess  is  favored  by,  or  at  any  rate  consistent 
with,  the  fact  that  the  loess  is  quite  uniformly  found  to  be  thickest  on 
the  margin  of  the  streams  flowing  out  of  the  glaciated  region,  and 
that  it  is  of  somewhat  coarser  texture  nearer  the  streams,  thinning 
out  at  a  distance  from  them,  and  merging  gradually  into  a  more 
clayey  deposit.  The  stratification  of  the  loess  is  also  considered  as 
indicating  deposition  by  water.  Boulders  and  granitic  pebbles  have 
been  found  in  the  loess  on  the  Osage  River,  which  can  be  accounted 
for  only  on  the  supposition  that  they  were  'carried  there  by  floating 
ice.  The  source  of  the  material  of  the  Mississippi  Valley  loess 
seems  to  be  in  close  connection  with  the  deposits  of  the  last  glacial 
period.  This  is  shown  not  only  by  the  distribution,  but  also  by  the 
not  infrequent  interstratification  of  loess  and  marginal  glacial  drift 
and  till.  The  close  relationship  of  the  Asiatic  and  European  loess 
to  the  ice  border  has  also  been  suggested,  but  for  Asia  this  is  at  least 
somewhat  doubtful.  Indeed,  the  source  of  a  part  even  of  the  Amer- 
ican loess  is  traceable  to  the  nonglaciated  arid  regions  of  the  west. 
Our  present  knowledge  of  the  character  of  the  deposits  desig- 
nated loess  leads  to  the  conclusion  that  the  source  of  the  material 
is  various,  being  in  part  the  dust  blown  from  the  deposits  in  front 
of  the  ice  sheet,  in  part  the  dust  derived  from  deserts  and  steppes, 
and  in  part  the  silt  of  river  flood  plains  or  other  sources.  The 
glacial  origin  fits  best  the  American  and  European,  and  the  desert 
origin  the  Asiatic  deposits,  but  none  are  probably  of  simple  char- 
acter throughout.  Though  a  marine  origin  has  been  advocated  for 
the  loess  by  some  writers,  the  consensus  of  opinion  is  that  the  loess 
is  a  continental  deposit.  The  evidence,  further,  points  to  the  wind 
as  the  chief  agent  in  distribution,  distribution  by  rivers  being  of 
secondary  importance.  Deposition  was  for  the  most  part  upon  dry 
land,  vegetation  playing  no  doubt  an  important  part  in  the  separa 
tion  of  the  dust  from  the  air,  though  rain  also  must  be  credited 
to  a  certain  extent  with  this  function.  It  is,  however,  essentially 
a  steppe  deposit.  All  such  loess  is  practically  without  stratification. 
Some  loessic  material  was  no  doubt  deposited  in  standing  water 
and  more  perhaps  on  river  flood  plains,  but  the  totality  of  this  was 
far  below  that  of  purely  eolian  origin.  Secondary  reworking  and 
redistribution  by  wind,  rivers  and  waves  also  occurred,  and  is  going 
on  at  the  present  time.  To  a  certain  extent  this  is  also  true  of  the 


568  PRINCIPLES    OF    STRATIGRAPHY 

primary  distribution  and  deposition  of  loess,  for  loess  is  forming  to- 
day in  China  and  Central  Asia,  and  in  many  other  regions  of  the 
world.* 

Fossils  and  concretions  in  the  loess.  The  fossils  of  the  loess  are 
few  and  found  only  at  intervals.  They  are  for  the  most  part  shells 
of  land  snails  (Helix,  Pupa,  Succinea)  and  of  pond  and  stagnant 
water  types  (Planorbis,  Paludina,  etc.).  Bones  of  land  vertebrates 
are,  however,  not  uncommon  in  many  loessial  deposits,  while  stems 
and  roots  of  grasses  and  other  plants,  more  or  less  replaced  or 
mineralized,  are  characteristic  features  in  certain  regions,  espe- 
cially in  China.  Curiously  formed  calcareous  concretions  known  as 
Loessmannchen,  Loesspuppchen,  or  Loesskindel  are  also  found  in 
many  deposits  of  loess.  These  often  occur  in  horizontal  tiers,  giv- 
ing a  semblance  of  stratification  to  the  deposit.  They  are,  however, 
of  secondary  origin,  and  the  arrangement  is  not  necessarily  indica- 
tive of  original  stratification,  but  may  represent  successive  levels  of 
ground  water.  An  analysis  of  the  concretions  of  the  German  loess 
gave  (Blanck-5)  : 

SiO2  ...................  34-824        MgCO3  .................   1.890 

A1203.  K20  ...................   i  .048 


Fe203      '  Na20  ...................  1.202 

CaO  .................  .  o  .  203  P2O5  ...................  0-157 

CaCO3  .................  55-294  SO3  ..........  ..........  0.090 

MgO  ..................  0.178  H20  ...................  0.377 

Cenozoic  and  Mesozoic  Loess-like  Deposits,  Deposits  of  this 
type  are  probably  more  widespread  than  is  realized  at  present.  The 
White  River  clays  of  Oligocenic  age  in  western  North  America 
have  been  regarded  by  W.  D.  Matthew  (31)  as  probably  of  this 
type,  though  the  included  sandstones  are  in  part  at  least  fluviatile 
and  in  part  perhaps  dune  sands.  The  chief  characters  stamping 
these  deposits  as  eolian  loess  are  the  fineness  of  their  texture,  the 
lack  of  stratification  and  the  absence  of  plants,  fish  or  aquatic  rep- 
tiles or  invertebrates,  as  well  as  the  larger  number  of  land  mam- 
mals. All  of  these  characters  are  incompatible  with  the  theory  of  a 
lacustrine  origin  of  these  deposits  commonly  held  for  them.  A  loess- 
like  origin  has  also  been  suggested  for  the  Harrison  beds  of  Ne- 
braska, a  Miocenic  formation.  (Loomis-3o://.)  Anemolutytes 
comparable  to  the  modern  loess  seem  to  be  represented  by  the 
Keuper  marls  of  western  Europe.  These  have  been  regarded  as  the 
loessic  deposits  'formed  around  the  borders  of  the  Triassic  desert, 

*  For  a  comprehensive  bibliography  of  the  loess  see  Stuntz  and  Free  (50) 
pp.  124-140. 


ANCIENT   LOESS-LIKE   DEPOSITS  569 

in  which  the  New  Red  sandstone  of  Britain  was  accumulating, 
partly  at  least  as  a  sand-dune  formation.  (Lomas-29.) 

Paleozoic  Loess-like  Deposits.  Unstratified  deposits  of  fine 
and  uniform-grained  rocks,  free  from  organic  remains  and  having 
a  general  loess-like  character,  are  not  uncommon  in  Palaeozoic  and 
later  formations.  As  already  noted,  the  Nunda  or  Portage  sand- 
stone of  central  New  York,  a  formation  of  Upper  Devonic  age,  has 
the  characteristics  of  a  consolidated  loess.  This  is  especially  seen 
in  the  Genesee  Valley  near  the  type  locality,  where  the  rock  for 
considerable  thicknesses  shows  a  lack  of  stratification  and  a  fine- 
ness and  uniformity  of  grain  strongly  suggestive  of  these  charac- 
ters in  Pleistocenic  loess.  There  is  a  notable  absence  of  fossils,  ex- 
cept vertical  tubes  (Fucoides  verticals),  similar  in  many  respects  to 
those  found  in  more  recent  loess.  The  rock,  furthermore,  splits 
with  a  decided  vertical  tendency,  forming  slabs  of  varying  thick- 
ness. This  deposit  was  probably  not  formed  far  from  the  sea,  and 
was  succeeded  by  normal  marine  sediments. 

Certain  portions  of  the  St.  Peter  sandstone  also  appear  to  be 
of  this  character,  as  shown  by  the  fineness  and  uniformity  of  grain, 
absence  of  stratification  and  splitting  into  vertical  slabs.  Much  of 
this  sandstone  appears,  however,  to  be  of  dune  origin,  subsequently 
in  part  reworked  by  a  transgressing  sea. 

Many  other  Palaeozoic  formations  will  probably  prove  on  fur- 
ther study  to  have  a  loess-like  origin.  This  appears  to  be  especially 
so  in  the  case  of  those  fine-grained,  nonstratified  deposits  which  are 
associated  with  continental  formations  of  another  type,  such  as 
fluviatile  beds,  dune  deposits,  salt  and  gypsum  beds,  etc.  Often  such 
loess-like  deposits  are  of  a  red  color,  owing  to  the  presence  of  iron 
in  the  ferric  oxide  stage.  The  red  Vernon  shale  of  eastern  New 
York  apparently  furnishes  a  good  example  of  this  type  of  deposit. 
This  formation  is  of  mid-Siluric  age,  and  marks  in  the  opinion  of 
many  the  beginning  of  a  period  of  widespread  continental  sedimen- 
tation under  arid  climatic  conditions.  This  red  shale  in  the  Syra- 
cuse area  is  followed  by  the  salt  deposits  of  Salina  age. 

The  red  color  of  this  formation  is  due  to  the  presence  of  de- 
hydrated ferric  oxide,  of  which  2.25  per  cent,  occurs  in  the  entire 
mass.  Ferrous  oxide  of  iron  is  present  in  small  quantities  (0.75 
per  cent.)  (Miller-34:/5/).  The  iron  is  distributed  in  small  quan- 
tities, but  with  great  uniformity  throughout  the  mass.  It  is  not  im- 
possible that,  as  Miller  argues,  the  color  was  not  originally  red,  but 
yellowish,  the  iron  being  in  the  form  of  the  hydrate.  Subsequent 
dehydration  would  produce  the  red  color.  In  this  connection  it 
is  interesting  to  know  that  the  ordinary  yellow  loess  commonly  con- 


570 


PRINCIPLES    OF    STRATIGRAPHY 


tains  a  higher  percentage  of  ferric  oxide  than  that  found  in  these 
red  lutytes.  Thus  of  seven  analyses  of  North  American  loess,  the 
lowest  gave  Fe2O3  2.52%  and  FeO  0.31%  and  the  highest  Fe,O3 
5.22%  and  FeO  0.35%.  Another  had  Fe2O3  3.74%  and  FeO 
1.02%.  The  average  of  the  seven  is  3.35%  Fe2O3  and  0.56%  FeO. 
(Clarke-io:  486.)  It  is  thus  seen  that  so  far  as  the  red  color  of 
the  Vernon  shale  is  concerned  it  is  due  only  to  the  anhydrous  con- 
dition of  the  ferric  oxide,  and  not  to  the  greater  abundance  of  this 
mineral. 


FIG.   119.     Cross-bedding  in   Sylvania  Sandstone    (Siluric).      (After   Sherzer 
and  Grabau).     Scale   i  :6o. 


Older  Deposits  of  Dune  Type. 

Consolidated  deposits  showing  the  characters  and  structures  of 
dune  sands  have  been  obtained  from  many  of  the  geological  hori- 
zons of  the  past,  and  closer  attention  to  the  structural  details  of 
rock  masses  will  probably  reveal  their  presence  in  still  other  forma- 
tions. Among  Tertiary  sandstones  which  have  been  regarded  as 
of  this  origin  or  show  evidence  pointing  that  way  may  be  men- 
tioned the  Monument  Creek  beds  of  Colorado,  while  an  example  of 
Cretacic  sandstones  of  this  type  is  found  in  the  Nubian  sandstone 
of  Egypt,  though  this  is  probably  not  of  this  character  throughout. 
Certain  parts  of  the  Dakota  sandstone  of  the  western  United  States 
and  of  the  Raritan  formation  of  the  east  also  must  be  mentioned. 
Other  examples  will  undoubtedly  be  found  on  closer  study.  In 
the  Jurassic  of  western  North  America  occurs  a  sandstone  of  great 
thickness  and  wide  areal  extent,  which  shows  in  a  wonderful  man- 
ner the  peculiar  type  of  cross-bedding  formed  by  migrating  sand 


OLDER    DUNE-LIKE    DEPOSITS 


571 


dunes.  This  is  the  White  Cliff  sandstone  of  southern  Utah,  the 
origin  of  which  as  a  subaerial  dune  sand  deposit  can  hardly  be 
questioned. 

The  Triassic  shows  many  examples  of  dune  sands,  commonly 
much  iron-stained,  though  these  are  generally  associated  with  fluvia- 
tile  and  sometimes  lacustrine  deposits.  They  have  been  recognized 
in  both  America  and  Europe.  In  the  Triassic  strata  of  England 
and  the  Elgin  sandstone  of  Scotland  this  eolian  origin  seems  to  be 
well  indicated. 

In  the  Palaeozoic  occur  many  deposits  which  bear  the  earmarks 
of  an  eolian  or  dune  origin.  Among  those  that  may  be  cited  in  this 
connection  are  the  white  dune  sands  beneath  the  Magnesian  lime- 
stone of  England  and  the  similar  beds  of  "Weissliegende"  in  Ger- 
many; the  Kanab  and  Colob  formations  (probably  Permic)  of 
southwestern  Utah  and  northwestern  Arizona ;  parts  of  the  Old  Red 
sandstone  of  Britain ;  and  the  Sylvania  and  St.  Peter  sandstones  of 
Siluric  and  Ordovicic  age,  respectively,  in  the  United  States.  The 
Sylvania  sandstone  may  be  taken  as  a  typical  example  of  this  kind 


FIG.   120.     Cross-bedding  in   Sylvania  Sandstone    (Siluric).      (After  Sherzer 
and  Grabau.)     Scale  i  :8o. 


of  deposit  (Sherzer  and  Grabau-45 :  72).  This  rock  consists  of 
well-rounded  grains  of  quartz,  of  nearly  uniform  size,  and  seldom 
carrying  over  3  per  cent,  impurities,  these  being  mainly  calcium  and 
magnesium  carbonates.  In  fineness,  uniformity  of  size,  roundness 
of  grain  and  purity  of  composition  it  outrivals  the  most  typical 
modern  desert  sands,  such  as  are  found  in  various  parts  of  the 
Libyan  and  Sahara  deserts.  Cross-bedding  of  the  eolian  type  is 
well  developed,  as  shown  by  some  of  the  accompanying  sketches 
(Figs.  119,  I2oj.  Altogether  this  deposit  ranges  in  thickness  up 
to  300  feet,  and  is  distributed  over  an  area  of  more  than  six  degrees 
east  and  west  longitude  and  four  degrees  north  and  south  latitude. 
It  may  be  regarded  as  one  of  the  best  examples  of  a  Palaeozoic 
dune  sand  deposit  known  to  us. 


572  PRINCIPLES    OF    STRATIGRAPHY 


VOLCANIC  DUST  DEPOSITS. 

As  has  been  shown  in  an  earlier  chapter  (II),  the  fine  dust  re- 
sulting from  explosive  eruptions  of  volcanoes  is  carried  far  and 
wide  over  the  surface  of  the  earth  and  becomes  a  part  of  many 
widespread  contemporaneous  deposits.  Of  the  18  cubic  kilometers 
(4.3  cubic  miles)  of  volcanic  dust  and  cinders  thrown  into  the  air 
on  the  explosion  of  Krakatoa  in  1883,  one-third  fell  at  a  distance 
of  more  than  15  kilometers  or  9.4  miles  from  the  seat  of  disturb- 
ance. At  a  distance  of  1,000  miles  from  the  volcano  ashes  still  fell 
inches  deep.  Shaler  has  estimated  that  not  less  than  300  cubic 
miles  of  fine  dust  have  been  discharged  by  the  Javanese  and 
Malayan  volcanoes  since  1770,  and  more  than  an  equal  quantity  of 
such  dust  has  been  thrown  into  the  air  by  other  volcanoes  of  the 
earth  during  the  same  period.  The  settling  of  this  material  all  over 
the  surface  of  the  earth  forms  an  important  addition  tp  the  eolian 
rocks  of  the  crust. 

In  character  this  volcanic  dust  consists  of  minute  angular  grains 
of  vitreous  or  glassy  material,  often  showing  by  their  curved  form 
that  they  are  parts  of  the  walls  of  glass  bubbles.  This  material  has 
been  recognized  in  deposits  of  various  ages  among  the  stratified 
series  of  the  earth's  crust.  Extensive  deposits  of  anemopyrolutytes 
and  pyrarenytes  have  been  found  in  the  Tertiary  of  South  America, 
especially  in  Patagonia,  where  the  remains  of  mammals  are  found 
in  it.  Sinclair  (47)  has  found  that  the  Bridger  (Eocenic)  beds  of 
Wyoming  are  largely  composed  of  such  material,  though  cross- 
bedded  fluviatile  deposits  of  sanidine  and  other  sands  are  likewise 
characteristic.  The  fine  pyrolutyte  of  the  Florissant  basin  is  an  ex- 
ample of  deposition  of  volcanic  dust  under  playa  lake  or  river  flood 
plain  conditions  with  the  entombment  of  many  remains  of  terrestrial 
organisms.  Pyrolutytes  and  pyrarenytes  are  common  in  many 
regions  of  the  earth,  but  the  conditions  of  their  deposition  are  not 
fully  understood  in  most  cases.* 

SPECIAL  INDICATORS  OF  EOLATION. 

Rocks  of  terrestrial  origin  are  not  infrequently  characterized  by 
the  presence  in  their  mass  of  wind-carved  pebbles  or  glyptoliths.f 
These  are  commonly  dreikanter,  and  they  indicate  that  for  a  time 
at  least  the  region  containing  them  was  above  sea-level  and  subject 

*See  further  under  pyroclastic  rocks,  Chapter  XII.       t  Woodworth,  533. 


CALCAREOUS    ANEMOLITHS  573 

to  the  sweep  of  the  prevailing  winds.  These  dreikanter  may  then  be 
buried  in  deposits  of  eolian,.fluviatile  and  even  marine  origin,  but 
only  in  the  first  case  are  they  likely  to  be  left  in  an  undisturbed 
position. 

Besides  being  found  in  abundance  in  desert  and  semidesert  areas 
of  to-day  (see  ante,  Chapter  II),  they  are  also  known  from  a 
number  of  older  deposits.  They  have  been  described  by  Walther 
from  the  pre-Cambric  Torridon  sandstone  of  Scotland,  and  they 
are  not  uncommon  in  the  basal  Cambric  Eophyton  sandstone  of 
Sweden.  At  the  other  end  of  the  scale  they  are  found  in  Pleisto- 
cenic  deposits  of  Germany  and  North  America,  where  in  some 
cases,  as  at  Cape  Cod,  Massachusetts,  they  are  buried  by  subse- 
quent fluviatile  and  eolian  deposits  in  the  position  in  which  they 
were  formed.  (Davis.)  They  have  also  been  found  in  the  Triassic 
beds  of  England,  where  wind-corraded  and  polished  surfaces,  and 
surfaces  showing  insolational  flaking  also  occur. 

Accumulations  of  pebble  beds,  especially  where  the  pebbles  are 
covered  with  desert  varnish,  may  in  some  cases  also  be  traced  to 
extensive  eolation,  which  removed  all  the  finer  material  and  subse- 
quently buried  the  residual  pebble  beds  under  new  accumulations 
of  eolian  sands  and  dust.  What  seem  to  be  pebbles  of  this  kind 
buried  by  dunes  of  oolites,  which  have  since  been  changed  to  iron 
appear  at  the  base  of  the  Siluric  section  in  Wisconsin. 


CALCAREOUS  AND  OTHER  NONSILICEOUS  EOLIAN  SANDS. 

Recent  and  Tertiary  Examples.  On  Bermuda,  where  siliceous 
material  is  wanting,  the  dunes  are  composed  entirely  of  calcareous 
material.  This  consists  in  part  of  fragments  of  shells  and  in  part  of 
coral  sand,  while  foraminiferal  shells  (Orbiculina,  etc.)  frequently 
make  up  a  considerable  portion  of  the  deposit.  The  older  dune 
sand  of  the  islands  has  been  consolidated  into  a  hard  rock  (anemo- 
calcarenyte,  Bermudaite),  which  is  locally  known  as  "sandstone/' 
though  nearly  pure  calcium  carbonate.  Shells  of  Helix  and  Livona 
are  enclosed  in  this  calcarenyte,  the  former  a  land  shell,  the  latter 
marine.  These  shells  of  Livona  in  some  cases  were  carried  into  the 
dune  sand  by  the  wind,  but  in  others  they  were  buried,  together 
with  Area,  Chama  and  Tellina,  by  the  dunes  which  advanced  over 
the  site  on  which  they  grew.  Below  the  beds  of  calcarenytt  are 
finer  layers,  some  of  them  calcilutytes,  and,  like  the  calcarenytes, 
they  generally  show  wind-drift  structure  and  fine  lamination.  Eol- 
ian limestones  composed  almost  wholly  of  oolite  grains  are  now 


574  PRINCIPLES    OF    STRATIGRAPHY 

forming  on  the  shores  of  Great  Salt  Lake  in  Utah,  where  oolites  are 
constantly  developing  through  the  activities  of  unicellular  algae. 
Eolian  limestones  in  which  the  grains  are  Foraminifera  and  par- 
ticles of  shells  may  also  be  deposited  by  the  wind  many  miles  in- 
land and  often  high  above  the  level  of  the  sea.  These  deposits  are 
stratified  and  cross-bedded  and  probably  more  common  than  gen- 
erally assumed,  since  they  are  usually  taken  for  marine  deposits. 
The  absence  of  marine  organic  remains  larger  than  those  trans- 
portable by  wind,  however,  indicates  their  eolian  origin,  while  the 
presence  of  land  animals  is  an  additional  piece  of  evidence.  Lime- 
stones of  this  type  have  been  described  from  the  coast  of  the 
Arabian  Sea  (Evans-i4:  $78-580),  where  they  constitute  the  Milio- 
litic  formation,  so  called  on  account  of  the  abundance  of  the  for- 
aminifer  Miliola.  The  Junagarh  limestone  overlying  the  Deccan 
trap  in  the  Kathiawar  Peninsula  of  western  India  is  a  typical  ex- 
ample of  this  kind  of  rock.  It  underlies  the  city  from  which  it 
takes  its  name,  at  a  distance  of  about  30  miles  from  the  sea,  and 
has  a  thickness  probably  exceeding  200  feet.  It  is  mainly  formed 
of  calcareous  particles  derived  from  shallow-water  organisms  of  re- 
cent types,  each  particle  being  ordinarily  surrounded  by  an  en- 
velope of  deposited  carbonate  of  lime,  the  whole  being  bound  to- 
gether by  a  later  cement  of  the  same  material.  Interspersed  with 
the  calcareous  grains  are  minute  mineral  fragments  derived  from 
the  igneous  rocks  of  the  neighborhood,  but  they  constitute  only 
from  6.5  to  12.5  per  cent,  of  the  whole.  The  limestone  is  divided 
by  horizontal  planes  into  tiers  3  to  4  feet  thick,  the  division  planes 
marking  decided  breaks  in  deposition.  Between  the  planes  the 
lamination  is  very  oblique  and  cut  off  abruptly,  both  above  and  be- 
low, by  the  major  division  planes.  Usually  the  inclination  is  differ- 
ent on  either  side  of  the  plane,  the  direction,  which  is  generally  to 
the  east,  remaining  constant,  or  varying  even  to  reversal.  The 
angle  of  inclination  with  the  horizontal  may  be  anything  up  to  30°, 
and  may  vary  from  point  to  point  of  the  same  division  of  the  rock, 
though  on  the  whole  it  is  rather  regular. 

In  other  parts  of  the  Kathiawar  Peninsula  similar  conditions  ex- 
ist, and  it  has  been  found  that  the  rock  is  purer  in  proportion  to 
its  distance  from  the  sea,  along  the  border  of  which  it  is  not  infre- 
quently mixed  with  much  siliceous  sand.  (Fedden-i5.)  Some- 
times, as  on  the  south  coast  of  the  peninsula,  the  beds  are  rubbly 
and  earthy f  and  in  them  have  been  found  two  specimens  of  Bulimus, 
two  of  Helix  and  one  of  Cyclotus.  On  the  coast,  at  Verawal,  the 
Miliolite  limestone  passes  laterally  into  an  open,  porous,  sandy  rock, 
made  up  very  largely  of  organic  fragments  and  minute  organisms, 


EOLIAN    LIMESTONES  575 

resembling  a  raised  beach  in  the  vicinity.  In  the  interior  the  "milio- 
lite"  is  stated  to  occur  "capriciously  in  the  gorges  of  the  hills  or  as 
patches  on  their  sides  like  remnants  of  a  snowdrift,"  while  .on 
Chotila  Hill  it  forms  a  fringe  around  the  truncated  top  at  a  height 
of  1,173  feet  above  sea-level.  Other  more  siliceous  deposits  of  this 
type  are  known  from  Cutch,  where  they  form  a  "concrete"  on  low 
ground  and  at  the  foot  of  the  hills  bordering  the  Rann,  with  strong, 
oblique  bedding  and  with  shells  of  the  land  snail  Buliminus. 

Limestones  of  the  Junagarh  type  are  also  well  developed  on  the 
southeastern  seaboard  of  Arabia,  overlying  the  nummulitic  lime- 
stone or  sometimes  resting  directly  on  the  granite.  These  form 
white-domed  hills  of  calcarenyte  of  unknown  thickness  and  from 
100  to  200  feet  above  the  level  of  the  sea,  extending  inland  as  far 
as  the  eye  can  reach.  On  the  sea  border  they  show  scarps  up  to  a 
hundred  feet  in  height.  The  rock  contains  hardly  a  fossil  larger 
than  the  size  of  the  grains  composing  it,  though  in  some  localities 
large  shells  of  Hippopus  and  Ostrea,  as  well  as  corals,  are  abun- 
dant in  this  rock  up  to  40  feet  above  sea-level,  indicating  former 
submergence  to  that  extent.  A  small  quantity  of  hyaline  quartz  and 
dark  specks,  probably  hornblende,  also  occur.  The  calcareous  par- 
ticles are  largely  remains  of  minute  Foraminifera.  ( Carte r-8  :jj, 
34.)  The  age  of  all  of  these  limestones  is  not  older  than  late  Plio- 
cenic ;  indeed,  some  of  them  are  forming  now  near  the  coast.  The 
Junagarh  limestone  is  believed  to  have  been  formed  from  the  ma- 
terial blown  inland  from  the  coast,  but  Evans  doubts  if  it  has  been 
carried  from  the  present  coast  30  miles  away.  He  holds  rather  that 
at  the  time  of  the  formation  of  this  rock  the  peninsula  stood  some 
150  feet  lower  than  at  the  present  day,  and  had  the  character  of  an 
island  or  group  of  islands. 

Microscopic  examination  of  the  foraminferal  shells  of  the 
Junagarh  limestone  by  Dr.  Frederick  Chapman  shows  that  they  are 
in  most  instances  worn  and  polished  apparently  by  eolian  action. 
At  30  miles  from  the  sea  the  common  or  frequent  forms  are  Milio- 
lina  trigonula  (Lam),  M.  cf.  oblonga  (Montagu),  Pulvinulina  re- 
panda  (F.  and  M.),  Nonionina  communis  (d'Orb),  Polystomella 
striatopunctata,  Amphistegina  lessonii  (d'Orb).  Other  rarer 
genera  are  Discorbina,  Truncatulina,  Rotalia  and  ( ?)  Operculina. 
Some  Ostracoda  were  also  present,  much  worn  and  polished. 

The  Montpelier  limestones  of  Jamaica  (Hill-23 :  737)  may  also 
belong  to  this  type.  They  have  a  thickness  of  500  feet,  and  are 
almost  entirely  composed  of  foraminiferal  remains,  especially  Orbi- 
toides,  Nummulinae,  and  Miliolidae,  all  shallow- water  forms.  There 
is,  however,  a  total  absence  of  macroscopic  fossils,  which,  if  the 


576 


PRINCIPLES    OF    STRATIGRAPHY 


deposit  is  marine  rather  than  eolian,  is  at  least  a  surprising  fact. 
Extensive  false-bedded  limestones  composed  almost  entirely  of 
comminuted  marine  shells  and  containing  bones  of  land  animals  in 
places  occur  near  Cape  Town  in  South  Africa,  and  belong  proba- 
bly to  this  type  of  deposit.  (Rogers  and  Schwartz-43.)  Wind- 
blown calcareous  deposits  of  almost  pure  foraminiferal  shells,  and 
consisting  of  subglobular  Miliolinae  and  inflated  Truncatulina  loba- 
tula,  have  been  found  on  the  Isthmus  of  Earawalla,  between  Dog's 
Bay  and  Gorteen  Bay,  on  the  southwestern  coast  of  Galway,  Ire- 
land. They  form  low  dunes  covering  an  area  1,000  yards  from 
northeast  to  southwest,  and  about  350  yards  from  bay  to  bay.  Land 
shells  occur  at  intervals,  but  very  few  if  any  marine  shells,  except 
such  as  appear  to  be  derived  from  kitchen  middens  in  the  vicinity, 


FIG.  121.  Cross-bedding  in  Jurrasic  oolites  of  Somersetshire,  England.  (After 
De  la  Beche.)  a,  a,  a,  diagonal  layers  of  broken  shells,  fish-teeth, 
pieces  of  wood,  and  oolite  grains,  lying  in  plane  of  diagonal  bed- 
ding, b,  b,  b,  b,  mud  layers. 

or  have  been  carried  up  by  birds  for  food.  The  surface  drift  in  the 
North  Atlantic,  together  with  local  currents,  carries  an  abundance 
of  Foraminifera  into  Dog's  Bay,  where  every  high  tide  spreads 
them  over  the  gently  sloping  strand,  together  with  small  Gas- 
tropoda. They  dry  rapidly  and  are  carried  landward  by  the  wind, 
the  whole  surface  sometimes  being  in  a  state  of  rolling  motion. 
Foraminifera,  Ostracoda,  fragments  of  shells,  etc.,  thus  travel 
across  the  isthmus,  sometimes  into  the  bay  on  the  opposite  side. 
These  organisms  are  not  surrounded  by  an  extra  coating  of  lime, 
as  in  the  case  of  the  Indian  examples,  probably  because  such  chem- 
ical deposition  of  lime  is  less  characteristic  of  cooler  climates. 

Wind-carried  Foraminifera  have  been  found  in  the  eastern 
desert  of  Egypt,  in  the  sands  obtained  near  the  foot  of  a  gully  in 
the  hills,  about  a  mile  west  of  the  Gulf  of  Jemsa,  on  the  western 
side  of  the  Red  Sea.  On  the  islands  in  the  Red  Sea  no  siliceous 
sand  is  to  be  found,  as  a  rule.  The  sands  are  calcareous,  and  are 
chiefly  formed  from  comminuted  fragments  of  corals  and  shells,  as 


EOLIAN    LIMESTONES 


577 


on  Gaysum  Island,  or  of  Foraminifera,  as  on  the  southern  side  of 
Gaysum  Island,  where  Orbitolites  complanata  is  the  predominant 
form. 

Older  Examples.  Some  of  the  Jurassic  oolites  of  Great  Britain 
appear  also  to  belong  in  the  category  of  wind-drifted  calcareous 
sands.  De  la  Beche  (3)  figures  a  pronounced  cross-bedding  struc- 
ture of  the  Forest  marble  (oolite)  of  Somersetshire,  here  repro- 
duced. (Fig.  121.)  The  diagonal  layers  are  "composed  of  broken 
shells,  fish  teeth,  pieces  of  wood  and  oolitic  grains,  sometimes  mere 
rounded  pieces  of  shells,  the  various  substances  lying  in  the  planes 
of  the  diagonal  layers,  and  presenting  every  appearance  of  having 
been  shoved  or  pushed  over  the  more  horizontal  surfaces  formed 


FIGS.  I22a  and  b.    Cross-bedding  of  uniform-grained  St.  Louis  limestone  (cal- 
carenyte),  south  of  St.  Louis,  Mo.     Scale  1:25. 

during  the  intervals  between  the  mud  deposits."  The  cross-bed- 
ding is  rather  more  regular  than  that  of  wind  deposits  generally, 
and  suggests  the  torrential  type.  De  la  Beche  states  that  the  Bath 
oolite  of  Somersetshire  is  likewise  of  this  type,  the  rounded  frag- 
ments being  drifted  together  with  the  true  oolite  grains.  Accord- 
ing to  Evans  (14:5^0),  the  grains  of  the  Great  Oolite  often  show  a 
worn  character,  suggesting  abrasion  by  the  wind,  and  he  holds  that 
the  false-bedded  oolites  which  succeed  the  Stonesfield  slates  are  not 
improbably  of  eolian  origin.  Personal  examination  of  a  number  of 
these  British  oolites  has  convinced  the  author  of  their  remarkable 
resemblance  to  wind-drifted  sands.  The  cross-bedding  figured 
above  (Fig.  122),  from  the  Mississippic  calcarenytes  of  Missouri, 
also  suggests  an  anemoclastic  origin  for  at  least  a  portion  of  this 
rock. 

Possible  application  to  the  chalk  beds.  The  remarkable  com- 
position and  the  structural  characters  of  the  White  Chalk  of  west- 
ern Europe  have  commonly  arrested  attention  and  given  rise  to 
speculation  regarding  its  origin  and  mode  of  deposition.  At  first 
it  was  thought  that  the  deep-sea  Globigerina  ooze  forms  a  modern 
analogue  of  this  deposit,  but  when  it  was  found  that  the  foraminif- 
eral  shells  composing  the  chalk  were  very  largely  of  shallow-water 


578  PRINCIPLES    OF    STRATIGRAPHY 

benthonic  forms  this  hypothesis  had  to  be  given  up.  Nor  would 
the  character  of  the  adjacent  deposits  bear  out  such  an  interpreta- 
tion. The  absence  of  stratification  in  some  parts  and  the  fineness, 
homogeneity,  and  uniform  character  of  the  deposit  give  it  a  loess- 
like  aspect.  The  fossil  echinoderms  and  other  macroscopic  organ- 
isms, which  are  found  at  intervals,  suggest  proximity  to  the  sea, 
with  occasional  inundations,  though  dead  echini  tests  might  readily 
be  blown  inland  as  well. 

The  layers  of  flints  in  the  chalk  have  a  similar  rude  horizontality 
to  that  assumed  by  the  Loessmdnnchen  in  Pleistocenic  structureless 
loess,  and  like  these  are  of  secondary  origin,  and  not  necessarily 
evidence  of  stratification.  Such  an  arrangement  may  express  rather 
the  periodic  stand  of  the  ground  water  as  suggested  by  Potonie. 
Where  regular  stratification  and  an  abundance  of  macroscopic  or- 
ganisms are  found,  a  submarine  origin  no  doubt  must  be  main- 
tained. 

Dunes  of  Gypsum.  A  remarkable  type  of  dune  sand  has  been 
described  from  New  Mexico.  This  is  the  white  sand  of  Otero 
county  which  forms  a  tract  of  dunes  of  nearly  pure  granular  gyp- 
sum covering  an  area  of  about  350  square  miles.  The  gypsum  sand 
is  derived  from  the  "ribs"  of  gypsum  which  rise  above  the  salt  flats 
in  successive  ridges.  These  gypsum  beds  belong  to  the  Red  bed 
series  of  Permic  age.  The  action  of  the  elements  soon  breaks  up 
the  exposed  gypsum  crystals  into  small  grains,  which  are  carried 
away  by  the  wind  and  piled  up  into  dunes.  The  salt  and  alkaline 
salts  forming  on  the  surfaces  of  the  salinas  are  also  driven  with  the 
gypsum,  but  on  account  of  their  solubility  do  not  remain  in  the 
dunes.  (Herrick-22.) 


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14.  EVANS,  JOHN  W.     1900.     Mechanically-formed  Limestones  from  Juna- 

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Geographische  Abhandlungen,  Band  IX,  Heft  I. 

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23.  HILL,  R.  T.     1899.     The  Geology  and  Physical  Geography  of  Jamaica. 

Bulletin  of  the  Museum  of  Comparative  Zoology  at  Harvard  College 
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24.  HOWE,    ERNEST.     1907.     Landslides    in    the    San    Juan    Mountains,  y 

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25.  HUNTINGTON,    ELLSWORTH.     1907.     Some    Characteristics   of   the 

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26.  KEYES,    CHARLES    R.     1908.     Geologic    Processes    and    Geographic 

Products  of  the  Arid  Region.     Geological  Society  of  America  Bulletin, 

Vol.  XIX,  pp.  570-575,  pis.  38-41. 
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the  Yorkshire  Geological  Society,  N.  S.,  Vol.  XVI,  pp.  15-20. 
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Formation?     American  Naturalist,  Vol.  XXXIII,  pp.  403-409. 

32.  McCONNELL,  R.  G.     1903.     Report  on  the  Great  Landslide  at  Frank, 

Alberta,  1903.  Annual  Report  of  the  Geological  Survey  of  Canada, 
Vol.  XV,  p.  34aa. 

33.  McGEE,  W.  J.     1891.     The  Pleistocene  History  of  North  Eastern  Iowa. 

Annual  Report  of  the  United  States  Geological  Survey,  Vol.  XI,  part  I, 
pp.  191-257- 

34.  MILLER,  W.  J.    1910.    Origin  of  the  Color  in  the  Vernon  Shales.    Bulletin 

of  the  New  York  State  Museum  of  Natural  History,  140.  6th  Report 
of  Director  for  1909,  pp.  150-156. 

35.  PALGRAVE,  W.  G.     1865.     Narrative  of  a  Year's  Journey  through  Central 

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36.  PASSARGE,  S.     1904.     Die  Kalahari.     Berlin. 

37.  PENCK,  ALBRECHT.     1894.     Morphologic  der  Erdoberflache,  Vol.  II., 

Stuttgart. 

38.  POOL,  RAYMOND  J.     1913.     Glimpses  of  the  Great  American  Desert, 

Popular  Science  Monthly,  Vol.  LXXX,  pp.  209-235. 

39.  PRZHEVALSKY,  N.  M.   (Prjevalsky).    1883.    Dritte  Reise  durch  central 

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of  Science,  3rd  series,  Vol.  XVII,  pp.  133-144. 

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South  African  Philosophical  Society,  Vol.  X,  pp.  427-436,  pi.  X. 

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45.  SHERZER,  W.  H.,  and  GRABAU,  A.  W.     1909.    The  Sylvania  Sandstone, 

Its  Distribution,  Nature  and  Origin,  Michigan  Geological  and  Bio- 
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CHAPTER   XIV. 

ORIGINAL    STRUCTURE    AND    LITHOGENESIS    OF    THE    CONTI- 
NENTAL HYDROCLASTICS. 

A  very  large,  perhaps  the  largest,  portion  of  the  stratified  elas- 
tics of  the  earth's  crust  consists  of  water-laid  deposits,  or  hydroclas- 
tics.  By  this  is  not  meant  that  they  were  deposited  in  standing 
water,  though  this  is  true  of  a  large  portion  of  them,  but  that  water 
was  influential  in  the  making  of  the  deposit.  They  therefore  include 
river-laid  elastics  as  well  as  those  formed  in  the  sea  or  in  lakes. 

Hydroclastic  rocks  may  be  divided  into  the  following  groups : 

1.  Stream  or  river-laid  elastics   (potamoclastics). 

2.  Lake  or  lacustrine  elastics  (limnoclastics). 

3.  The  Delta — a  transitional  deposit. 

4.  Marine  elastics  (haloclastics). 

Each  of  these  will  admit  of  a  number  of  subdivisions.  The 
potamoclastics  and  limnoclastics,  together  with  the  atmoclastics, 
anemoclastics,  pyroclastics,  and  autoclastics  belong  to  the  continen- 
tal or  terrestrial  type  of  elastics,  as  opposed  to  the  marine  or  halo- 
clastics. Seacoast  deltas  form  the  transition  from  the  one  to  the 
other.  The  continental  hydroclastics,  together  with  the  delta  de- 
posits, will  be  considered  in  this  chapter;  the  marine  hydroclastics 
being  reserved  for  the  next. 


RIVER-LAID   CLASTICS,   OR   POTAMOCLASTICS. 

All  along  the  river  course,  from  near  the  head  to  the  mouth, 
clastic  deposits  may  be  forming,  their  character  and  amount  vary- 
ing with  the  character  of  the  stream  and  its  environment.  Under 
the  latter,  the  kind  of  rock  material  and  climate  must  be  mentioned 
as  all-important  controlling  factors.  The  amount  of  weathered 
rock  material  available  for  transport  and  final  deposition  is  also 
of  the  greatest  importance.  We  may  consider  the  clastic  river 
deposits  under  the  following  headings: 

582 


RIVER-LAID    CLASTICS  583 

a.  Alluvial  fans. 

b.  Flood  plains. 

c.  The  playa — a  temporary  expanse  of  certain  rivers. 

Considering"  the  classes  of  streams  mentioned  in  Chapter  III 
(p.  129),  it  may  be  noted  that  the  deposits  of  consequents  and  inse- 
quents  are  essentially  alike,  those  of  overflow  streams  may  be 
neglected  as  insignificant,  but  deposits  of  glacial  streams,  from  their 
abundant  supply,  are  of  the  greatest  importance.  Only  the  residual 
clays  of  subterranean  streams  need  to  be  considered. 

a.  ALLUVIAL  FANS.  Wherever  the  debris-laden  stream  leaves 
its  steep  mountain  bed  and  debouches  upon  the  piedmont  belt,  or 
the  floor  of  a  large  valley,  it  changes  from  a  degrading  stream,  or 
one  just  at  grade,  to  an  aggrading  stream,  since  the  change  in  the 
angle  of  the  river  bed  brings  with  it  decreasing  velocity  of  the 
current.  In  its  steeper  development  the  alluvial  fan  grades  directly 
into  the  talus  and  other  atmoclastic  deposits  with  which,  indeed,  it 
forms  a  continuing  sedimentary  series,  the  river  portion  often  being 
difficult  to  separate  from  the  purely  atmoclastic  type. 

Form  and  Extent  of  Modern  Alluvial  Fans.  In  extent  alluvial 
fans  vary  from  an  area  of  only  a  few  square  feet  to  one  covering 
thousands  of  square  miles.  Small  alluvial  fans  are  best  described 
as  semi-cones  with  a  surface  slope  which  may  be  as  high  as  20° 
or  even  30°.  As  the  fan  increases  in  size  its  surface  angle  is 
lowered,  until,  in  the  very  large  deposits  of  this  type,  the  surface 
seems  almost  to  be  horizontal.  Small  cones  are  seen  to  rise  regu- 
larly toward  the  notch  in  the  hills  through  which  the  river  de- 
bouches, but  in  the  very  large  alluvial  fans  there  may  result  a  con- 
fluence of  many  adjoining  deposits,  which  will  obliterate  the  effects 
of  regularity.  On  all  large  fans,  whether  simple  or  confluent,  ero- 
sion channels  abound,  for  the  streams  building  the  deposits  divide 
near  the  head  of  each  fan  into  numerous  distributaries,  each  of 
which,  when  not  depositing,  will  be  eroding.  Thus  a  succession  of 
contemporaneous  erosion  surfaces  will  result,  and  later  beds  will 
be  deposited  on  the  eroded  surfaces  of  the  older.  In  this  manner 
the  effect  of  a  disconformity  may  be  repeatedly  produced  within 
the  depositional  unit,  and  such  apparent  disconformities  might  lead 
to  grave  misinterpretations  of  the  age  and  relationships  of  the  ad- 
joining beds.  Should,  by  subsidence,  the  sea  cover  such  an  alluvial 
fan  of  great  extent,  a  decided  break  would  appear  between  the  non- 
marine  and  marine  strata,  the  latter  gradually  encroaching  by  over- 
lap upon  the  eroded  surface  of  the  old  subaerial  fan. 

Among  the  large  alluvial  fans  or  dry  deltas  of  modern  times 


584  PRINCIPLES    OF    STRATIGRAPHY 

may  be  mentioned  that  of  the  Merced  in  California,  of  the  Garonne 
at  the  northern  base  of  the  Pyrenees,  the  delta  of  the  Cooper  River 
in  the  Lake  district  of  South  Australia,  the  great  flood  plain  delta 
of  the  Huang-ho  or  Yellow  River  of  China,  and  the  similar  but 
compound  Indo-Gangetic  delta  plain  of  northern  India. 

The  Merced  River  of  California  rises  in  the  Sierra  Nevadas  and 
carries  much  waste  down  their  steep  western  slopes.  Reaching  the 
broad  open  valley  of  California,  which  lies  between  the  Sierra  and 
the  Coast  range,  it  has  built  a  fan  which  at  present  has  a  radius 
of  about  40  miles.  This  consists  of  gravel  near  the  mountain,  and 
of  fine  silt  at  a  distance.  On  account  of  the  gentle  slope  of  the 
surface,  the  water  is  turned  readily  from  one  channel  into  the  other 
at  the  head  of  the  fan. 

"The  many  rivers  issuing  from  the  valleys  of  the  Sierra  Ne- 
vada and  the  Coast  range  upon  the  'Valley  of  California'  have 
formed  an  extensive  plain,  of  which  the  Merced  fan,  ...  is 
only  a  part.  The  successive  fans  are  so  broad  and  flat  that  their 
slightly  convex  form  can  hardly  be  recognized  without  the  aid  of 
surveying  instruments.  Nearly  all  the  streams  run  in  shallow  chan- 
nels, but  little  beneath  the  gently  sloping  surface  of  the  fans.  The 
fans  from  the  east  and  west  meet  in  a  broad,  flat-floored  trough." 


River-made  plains  of  this  type  are  formed  on  both  sides  of  the 
Alps.  Those  on-^the  south  have  begun  to  cut  valleys  into  the  old 
deposits,  while  those  on  the  north  have  cut  to  a  depth  of  1,000  feet, 
leaving  the  former  plain  as  a  series  of  ridges.  The  river  Po  flows 
eastward  between  the  broad  plain  built  by  the  rivers  from  the  high 
Alps  on  the  north,  and  the  narrower  one  built  by  the  streams  from 
the  lower  Apennines.  Where  it  enters  the  Adriatic  Sea  the  Po 
builds  a  normal  delta. 

While  the  material  of  this  river  plain  is  typically  a  subaerial 
deposit,  intercalated  marine  beds  are  not  wanting.  They  have  been 
reported  from  the  Venetian  region  where  they  represent  periodic 
encroachment  of  the  sea.  (Penck-4i.) 

One  of  the  most  extensive  of  modern  dry  deltas  is  that  of 
Cooper  Creek  in  the  Lake  district  of  South  Australia.  Its  area  is 
more  than  twice  that  of  the  Nile  delta,  its  length  being  nearly  185 
miles  and  its  width  over  170  miles.  The  water  in  the  river,  how- 
ever, is  abundant  only  after  strong  rains,  the.  various  distributaries 
being  changeable  canals  on  the  surface  of  the  delta.  (Peter- 
mann-43.) 

Even  larger  than  the  Cooper  Creek  alluvial  fan  is  that  of  the 
Huang-ho  or  Yellow  River  of  China.  Its  head  is  about  300  miles 


ALLUVIAL   FANS  585 

from  the  present  shore,  and  has  an  elevation  of  only  400  feet  above 
sea-level.  It  has  thus  an  average  fall  of  \y$  feet  per  mile,  a  slope 
so  gentle  that  it  k  imperceptible.  Along  the  coast  the  fan  extends 
from  near  Pekin  southward  for  about  400  miles  to  where  it  joins 
the  great  plains  of  the  Yang-tse-kiang,  being  interrupted,  however, 
by  the  mountainous  province  of  Shantung. 

Owing  to  the  very  gentle  slope  of  the  fan  the  overflow  at  its 
head  and  the  corresponding  diversion  of  a  distributary  will  result 
in  the  inundation  of  vast  areas.  The  mouth  of  the  river  has 
been  shifted  more  than  200  miles  north  or  south,  such  shiftings 
having  been  numerous  during  Chinese  history.  "The  flood  of  1887 
covered  an  area  estimated  at  50,000  square  miles,  immensely  fertile 
and  swarming  with  villages.  The  number  of  people  drowned  was 
at  least  a  million  and  a  greater  loss  followed  from  famine  and 
disease  caused  by  the  flood."  (Davis-i8:^po.)  Flood  plain  fans 
of  this  type  thus  furnish  excellent  examples  of  the  manner  of 
destruction  and  burial  by  river  silts  of  terrestrial  organisms,  and 
they  further  illustrate  how  peat  deposits  in  swamps  may  be  buried 
to  be  converted  in  the  course  of  time  into  coals.  The  material 
carried  by  the  Yellow  River  is  mostly  fine  silt  derived  from  the 
loess  in  the  interior,  which  from  its  color  gives  the  name  to  the 
river.  The  fineness  of  the  material  accounts  in  part  at  least  for 
its  very  gentle  slope,  for  it  can  be  carried  to  great  distances  before 
it  settles  out. 

Growing  steadily  but  slowly  seaward  it  is,  of  course,  inevitable 
that  marginal  marine  deposits  should  be  enclosed  in  the  growing 
fan.  Very  slight  depression  of  the  land  would  cause  a  partial 
flooding  by  the  sea,  with  accompanying  marine  deposits.  In  its  sea- 
ward growth  the  great  delta  has  annexed  the  former  rocky  island, 
which  is  now  the  Province  of  Shantung. 

The  Indo-Gangetic  alluvial  plain  is  an  example  of  a  river  plain 
formed  of  many  confluent  dry  deltas  and  carried  -forward  by  the 
two  great  rivers  of  northern  India — the  Indus  on  the  west  and  the 
Ganges,  with  the  tributary  Brahmaputra,  on  the  east.  Numerous 
small  streams  feed  these  rivers  from  the  south  slope  of  the  Hima- 
layas, carrying  an  abundance  of  coarse  and  fine  debris.  (Old- 
ham-4O.)  The  great  alluvial  plain  extends  over  an  area  of  about 
300,000  square  miles,  and  comprises  the  richest  and  most  populous 
portion  of  India.  It  varies  in  width  from  90  to  nearly  300  miles, 
and  entirely  separates  the  lower  peninsula  of  India  from  the  Hima- 
layas to  the  north.  It  rises  924  feet  above  the  sea  in  its  highest 
portion,  and  the  deepest  boring  has  located  these  deposits  at  a  depth 
of  nearly  a  thousand  feet  below  the  present  sea-level.  This  is  at 


586  PRINCIPLES    OF    STRATIGRAPHY 

Lucknow,  which  lies  approximately  midway  between  the  Indus  and 
the  Ganges  headwaters  and  about  370  feet  above  sea-level.  It 
abounds  in  gravels  and  conglomerates  near  the  slbping  borders,  but 
lutaceous  or  clayey  deposits,  more  or  less  arenaceous,  prevail  over 
much  of  the  plain,  especially  near  the  center,  with  only  subordinate 
deposits  of  sand,  gravel,  and  conglomerates.  Beds  of  blown  sand 
of  great  thickness  are  found  in  some  regions.  Pebbles  are  scarce 
at  a  distance  of  more  than  twenty  or  thirty  miles  from  the  enclosing 
hills.  Shells  of  river  and  marsh  molluscs  are  occasionally  found, 
and  calcareous  concretions  and  nodules  of  irregular  shape,  locally 
known  as  kankar,  are  frequent.  "The  more  massive  forms 
are  a  variety  of  calcareous  tufa,  which  sometimes  forms  thick  beds 
in  the  alluvium  and  frequently  fills  cracks  in  the  alluvial  deposits, 
or  in  older  rocks."  (Oldham-4o:^J7.)  Calcareous  tufas  also  form 
conglomerates  in  the  stream  beds  by  cementing  pebbles  derived  from 
the  hills.  In  the  clays  along  the  borders  and  in  the  shoals  of  the 
Jumna  River  a  great  variety  of  vertebrate  remains  has  been  found, 
including  elephant,  hippopotamus,  ox,  horse,  antelope,  crocodile, 
and  various  fish.  Borings  in  other  regions  revealed  the  presence  of 
peat,  forming  extensive  beds  to  a  depth  of  20  to  30  feet  below 
the  surface,  while  a  layer  of  stiff  blue  clay  15  feet  in  thickness  was 
found  10  feet  below  the  surface  at  Calcutta.  Clay  and  variegated 
sand  with  calcareous  concretions,  mica  and  small  pebbles  alternated 
to  a  depth  of  120  feet,  below  which  a  quicksand  was  found.  At 
152  feet  this  became  dark  and  coarse  of  grain  and  intermixed  with 
red  water-worn  nodules  of  hydrated  iron.  At  159  feet  a  stiff  clay 
was  found  which,  at.  163  feet,  became  friable  and  contained  much 
vegetable  and  ferruginous  matter.  Lower  still  fine  and  coarse  sands 
alternating  with  clays  occur,  while  at  340  feet  a  ruminant  bone 
was  found,  and  pieces  of  tortoise  shell  at  still  greater  depth.  Three 
hundred  and  ninety-two  feet  below  the  surface  pieces  of  coal,  such 
as  are  found  in  the  mountain  streams,  and  fragments  of  decayed 
wood  were  found  in  the  sand,  while  below  400  feet  sand  and 
shingle  of  fragments  of  primary  rocks  abounded.  The  borings 
also  showed  wood,  remains  of  terrestrial  mammals,  fluviatile  reptiles, 
and  fresh-water  molluscs.  No  traces  of  marine  fossils  have  been 
found.  The  presence  of  earthy  limestones  in  these  deposits  is  of 
especial  interest,  because  it  shows  that  limestones  do  not  necessarily 
indicate  lacustrine  or  marine  conditions.  As  already  noted,  in 
northern  Mexico  and  other  tropical  regions  of  America,  a  super- 
ficial crust  of  white  lime,  often  free  from  foreign  material,  is 
formed.  This  material,  called  tepetate,  has  been  dissolved  from 
the  limestones  of  the  surrounding  region,  transported  in  solution  by 


WASTE-FILLED    BASINS  587 

the    streams,    and    then    redeposited    by    evaporation.      (Hill   and 


Basins  Filled  by  River-Washed  Waste.  There  are  many  ex- 
amples of  great  basins  surrounded  by  mountains  and  filled  to  a 
certain  extent  by  the  waste  washed  from  the  mountains.  The 
larger  of  these  basins  are  generally  formed  by  tectonic  movements, 
the  process  being  a  downwarping.  An  example  of  such  a  valley 
holding  a  "waste  lake"  is  the  upper  Arkansas  valley,  back  of  the 
Front  Range  of  the  Rocky  Mountains.  As  the  basin  was  forming 
by  warping,  the  rivers  deposited  their  load  on  its  floor,  while  at  the 
same  time  the  outlet  of  the  Royal  Gorge  was  being  cut  through  the 
Front  Range.  The  plains  of  waste  within  the  basin  slope  forward 
from  the  mountainsides,  but  they  have  been  only  slightly  dissected 
so  far.  Another  excellent  example  is  found  in  the  Vale  of  Kash- 
mir, enclosed  by  the  front  and  middle  ranges  of  the  Himalayas  in 
northwest  India.  In  area  this  vale  equals  that  of  the  Connecticut, 
being  elliptical  in  form,  a  hundred  miles  long  from  southeast  to 
northwest,  and  forty  or  fifty  miles  broad.  It  is  formed  by  a  down- 
warping  between  two  lofty  mountain  ranges,  which,  for  the  most 
part,  have  very  steep  sides.  The  floor  of  the  valley  is  deeply 
filled  with  river-laid  waste,  coarse  near  the  mountains,  but  free 
from  pebbles  at  the  center.  Its  depth  is  measured  probably  by  thou- 
sands of  feet,  while  its  surface  elevation  is  more  than  5,000  feet 
above  sea-level.  Across  this  plain  meanders  the  Jhelam  River, 
which  escapes  by  a  deep  gorge  through  the  enclosing  mountains. 
Southern  Europe  furnishes  another  good  example  of  a  waste- 
floored  basin  in  the  oval  plain  of  Hungary,  which  has  a  diameter  of 
about  200  miles.  Gravelly,  sandy  and  loamy  materials  brought  by 
the  rivers  from  the  enclosing  mountains  have  formed  this  plain, 
which  rises  slightly  toward  the  mountains,  where  it  is  formed  of 
gravels,  while  the  level  center  is  a  fine  silt  plain,  resembling  an 
abandoned  lake  bottom.  The  Danube  and  its  tributaries  meander 
through  it  and  escape  by  the  deep  gorge  of  the  Iron  Gate  cut 
through  the  Transylvanian  Alps. 

A  somewhat  similar  basin  lies  in  southwestern  Wyoming, 
within  the  embrace  of  a  series  of  mountain  ranges,  the  Wasatch  on 
the  west,  the  Uinta  on  the  south,  and  the  Wind  River  Ranges  on 
the  north  and  east.  The  Green  River  flows  through  this  basin  and 
escapes  by  a  deep  canyon  through  the  Uinta  Mountains.  The 
original  deep  filling  of  waste  material  has  now  been  extensively 
trenched  by  the  rivers  and  converted  into  a  dissected  upland,  with 
valleys  cut  into  the  old  waste  deposit,  in  some  cases  a  thousand  feet 


588  PRINCIPLES    OF    STRATIGRAPHY 

deep.  Other  waste  basins  of  this  kind  are  found  in  Spain,  Italy, 
and  elsewhere. 

In  arid  regions  the  basins  often  have  an  inward  drainage  and 
are  filled  by  the  combined  atmoclastic  creep  and  the  river  wash. 
Fans  with  their  heads  rising  500  feet  or  more  above  their  bases 
and  extending  10  or  15  miles  outward  characterize  such  basins. 
The  water  of  the  stream  evaporates  or  sinks  into  the  ground  be- 
fore the  center  of  the  basin  is  reached.  When  such  fans  become 
confluent  they  form  huge  waste  plains  of  relatively  steep  grade, 
filling  the  valleys  and  partly  burying  the  mountain  slopes.  In  Utah, 
Nevada,  and  Arizona  depressions  of  great  depth  have  thus  been 
wholly  filled,  while  the  waste  mantle  backs  up  2,000  or  3,000  feet 
on  the  mountain  flanks. 

"A  great  part  of  Persia  consists  of  large  basins  enclosed  by 
mountains  and  without  outlet  to  the  sea.  Long  waste  slopes  stretch 
forward  5  or  10  miles  with  a  descent  of  1,000  or  2,000  feet,  stony 
near  the  mountain  flanks,  and  gradually  becoming  finer-textured 
and  more  nearly  level.  The  central  depressions  are  absolute  deserts 
of  drifting  sands,  with  occasional  saline  lakes  or  marshes. 

"Central  Asia  repeats  the  same  conditions  on  a  still  larger  scale. 
The  basin  of  eastern  Turkestan  includes  many  half  buried  ranges 
in  its  central  part.  It  is  quite  possible  that  some  ranges  are  com- 
pletely covered  with  waste.  Many  rivers  flowing  from  the  moun- 
tain rim  wither  on  their  way  toward  the  chief  central  depression ; 
only  the  largest  river  (Tarim)  reaches  it,  there  spreading  out  in 
Lob  (Lake)  Nor.  The  chief  settlements  are  near  the  border  of 
the  basin,  where  the  larger  rivers  come  out  from  the  mountains." 
(Davis-i8:ju.) 

The  deposits  of  these  regions  must  be  considered  as  in  part  at 
least  of  purely  atmoclastic  and  anemoclastic  origin. 

RIVER  FLOOD  PLAINS.  River  flood  plains  vary  enormously  in 
extent  as  well  as  in  the  character  of  the  material.  Streams  with 
relatively  steeply  sloping  beds  may  have  stony  flood  plains,  if  they 
are  abundantly  supplied  with  coarse  detritus  from  the  head  and 
sides.  The  flood  plain  of  the  Saco  in  the  Intervale  is  covered  with 
rounded  cobbles  and  boulders,  these  often  forming  a  regular  cobble- 
stone pavement.  The  stream  is  a  rushing  one,  and  in  flood  carries 
away  all  the  finer  material.  A  large  part  of  the  boulders  and 
cobbles  is  formed  of  the  granite  of  which  this  part  of  the  White 
Mountain  region  is  composed,  but  a  part  of  the  material  at  least 
is  derived  by  the  rehandling  of  flood-plain  deposits  formed  during 
the  preceding  flooded  stage  period  controlled  by  the  melting  ice  of 
the  glacial  period. 


FLOOD    PLAIN    DEPOSITS  589 

Flood  plains  of  streams  of  less  velocity  are  made  up  of  fine 
materials  left  by  the  river  when  it  overflows  its  banks.  As  most  of 
the  deposit  is  formed  near  the  river  the  banks  on  either  side  are 
higher  than  the  surface  of  the  plain  away  from  it,  there  being  thus 
a  gentle  slope  away  from  the  river.  In  this  way  the  natural  levees 
of  the  Mississippi  are  built,  which  rise  considerably  above  the  level 
of  the  "back  swamps"  on  either  side.  Here  the  slope  away  from 
the  river  east  or  west  is  5  or  10  feet  to  the  mile,  while  the  general 
southward  slope  of  the  entire  flood  plain  is  under  half  a  foot  to 
the  mile. 

A  striking  example  of  a  flood  plain  is  afforded  by  that  of  the 
Nile,  which  flows  from  a  well-watered  region  through  a  desert 
country  without  receiving  a  tributary  for  a  thousand  miles,  except 
a  few  small  wet  weather  streams.  Entrenched  beneath  the  desert 
uplands  this  flood  plain  holds  its  own  for  a  length  of  500  miles, 
and  maintains  a  width  of  from  5  to  15  miles,  broadening  on  the 
delta  to  over  100  miles.  The  annual  inundation  of  the  flood  plain 
is  caused  by  the  northward  movement  of  the  belt  of  equatorial  rains 
in  summer.  The  flood  begins  in  June  and  usually  rises  25  feet  or 
more  at  Cairo  in  the  late  summer  or  early  autumn.  The  annual 
addition  of  the  river  silt  causes  a  slow  rising  of  the  entire  flood 
plain  estimated  to  amount  to  4^  inches  a  century. 

This  region  furnishes  an  instructive  example  of  widely  varying 
contemporaneous  deposits  within  the  same  general  area.  On  the 
one  hand  occur  the  drifting,  cross-bedded,  well  rounded  and  pure 
quartz  sands  of  the  desert,  and,  on  the  other,  the  extremely  fine, 
well-stratified  muds  of  the  river  flood  plain.  Both  enclose  the  re- 
mains of  organisms  or  of  structures  built  by  man,  but  there  is  an  es- 
sential difference  between  the  remains  found  in  each  deposit.  Aside 
from  ruins  of  human  habitations  and  other  works  of  man,  only 
occasional  remains  of  animals  which  were  adapted  to  a  dry  climate 
are  preserved  in  the  desert  sands.  These,  on  the  whole,  will  be 
rare  because  burial  is  often  a  slow  process,  and  the  bones  of  the 
dead  creatures  will  crumble  unless  quickly  covered.  On  the  flood 
plain,  on  the  other  hand,  aquatic  organisms  abound,  giving  a 
totally  different  faunal  as  well  as  floral  association.  According  to 
the  rash  doctrine  of  the  persistence  of  lithologic  units,  recently 
advocated  by  some  geologists,  such  contemporaneous  deposits  would 
be  interpreted  as  of  different  ages. 

From  the  nature  of  deposits  on  river  flood  plains,  perfect  and 
often  very  fine  stratification  is  to  be  expected.  This  may  be  con- 
sidered as  characteristic  of  typical  flood  plains.  'The  plains  of  the 
Po  and  of  the  Ganges  and  the  great  fan  of  the  Huang-ho  are  very 


590 


PRINCIPLES    OF    STRATIGRAPHY 


largely  composed  of  fine  sediments;  the  proportion  of  fine  to  coarse 
materials  in  the  extensive  deposits  of  these  rivers  seems  to  be 
greater  than  it  is  in  many  of  the  so-called  lake  beds  of  the  west 
[of  North  America]."  (Davis-iQ  1361-362.) 

River  flood  plains  consisting  of  fine  material  are  especially 
adapted  for  receiving  the  transit  impression  of  organisms  as  well 
as  sun-cracks,  rain-drop  impressions,  etc.  Indeed,  almost  the  only 
known  modern  examples  of  such  structures  commonly  referred  to 
seashore  origin  are  found  on  river  flood  plains  or  on  the  surfaces 
of  the  playas. 

Another  feature  characterizing  many  river  flood  plains  is  the 
levelness  of  their  surfaces,  which  argues  well  for  the  close  approxi- 
mation to  horizontality  of  their  strata.  Many  minor  irregularities 


FIG.  123.     Torrential    type    of  cross-bedding ;   seen   in   modern   torrential    de- 
posits.    (After  Hobbs.) 

will,  of  course,  be  found,  such  as  shallow  channels,  filled  by  later 
deposits  and  other  evidence  of  contemporaneous  erosion. 

Cross-Bedding  of  Torrential  Sediments.  Whenever  sands  and 
gravels  are  spread  by  torrential  floods,  diagonal  or  cross-bedding  on 
a  large  scale  will  result.  Between  the  nearly  horizontal  layers  of 
finer  sands  or  gravels  occur  beds  inclined  at  a  nearly  uniform  and 
relatively  large  angle  with  the  enclosing  layers.  Successive  cross- 
bedded  strata  will  have  their  beds  slope  in  the  same  direction, 
which  is  that  of  the  stream  producing  them.  Such  a  type  of  cross- 
bedding  is  wholly  inconsistent  with  the  theory  of  wave  formation 
or  of  currents  in  a  body  of  water.  It  has  been  observed  in  modern 
torrential  deposits  (Hobbs~3i  '.291),  and  is  a  characteristic  feature 
of  many  ancient  sandstones  and  conglomerates,  the  torrential  origin 
of  which  it  indicates  (Fig.  123).  It  is  not  an  infrequent  structure 
in  the  torrential  deposits  of  the  terminal  moraine  on  Long  Island. 
(See  further,  Chapter  XVII.) 

Thickness  and  Composition  of  River  Deposits.     The  thickness 


TORRENTIAL    DEPOSITS  591 

of  river  deposits  is  practically  unlimited,  and  depends  on  the  source 
of  supply  of  material  and  the  depth  of  the  valley  in  which  it  is 
deposited.  Where  downwarping  of  a  piedmont  belt  occurs,  so  as 
to  form  a  geosyncline,  the  thickness  of  the  formation  may  become 
enormous.  Torrential  deposits  in  .Calabria,  Italy,  have  been  found 
1,500  feet  or  more  in  thickness  and  including  boulders  of  many 
petrographic  types,  often  exceeding  a  foot  in  diameter.  The  Al- 
hambra  formation  of  Spain  is  at  least  1,000  feet  thick  and  consists 
mainly  of  river  deposited  pebbles  distinctly  water  worn  and  varying 
in  size  from  a  fraction  of  an  inch  to  six  inches  or  more  "in  length. 
Some  of  the  partly  dissected,  but  still  unconsolidated  torrential 
deposits  fringing  the  Front  Range  of  the  Rocky  Mountain  region 
contain  boulders  many  feet  in  diameter.  Some  torrential  deposits 
may  be  entirely  composed  of  rounded  boulders  with  only  enough 
sand  and  fine  gravel  to  fill  the  interstices.  Portions  of  the  Old  Red 
sandstone  of  Scotland  furnish  splendid  examples  of  fossil  boulder 
beds  of  this  kind. 

The  Siwalik  formation  of  India  furnishes  an  excellent  example 
of  a  sub-recent  fluviatile  deposit  of  great  thickness.  It  skirts  the 
southern  border  of  the  Himalayas,  forming  the  Siwalik  Hills.  The 
strata  have  been  uplifted  by  the  latest  movement  in  this  region  and 
exposed  by  erosion.  The  thickness  of  the  formation  is  upward  of 
15,000  feet,  and,  except  at  the  base,  where  it  is  characterized  by 
passage  beds  from  the  underlying  marine  Sirmur  group,  it  is  of 
non-marine  origin  throughout.  In  age  it  is  said  to  range  from 
Miocenic  to  Quaternary,  though  most  of  it  belongs  to  the  Pliocenic. 
In  this  formation  "sandstone  immensely  predominates  .  .  . 
and  is  of  a  very  persistent  type  from  end  to  end  of  the  region  and 
from  top  to  bottom  of  the  series.  Its  commonest  form  is  indis- 
tinguishable from  the  rock  of  corresponding  age  known  as  Molasse 
in  the  Alps,  and  is  of  a  clear  pepper  and  salt  gray,  sharp  and  fine  in 
grain,  generally  soft,  and  in  very  massive  beds.  The  whole  Middle 
and  Lower  Siwaliks  are  formed  of  this  rock,  with  occasional  thick 
beds  of  red  clay  and  very  rare  thin,  discontinuous  bands  and 
nodules  of  earthy  limestone,,  the  sandstone  itself  being  sometimes 
calcareous  and  thus  cemented  into  hard  nodular  masses.  .  .  . 
In  the  Upper  Siwaliks  conglomerates  prevail  largely;  they  are  often 
made  up  of  coarsest  shingle,  precisely  like  that  in  the  beds  of  the 
great  Himalayan  torrents.  Brown  clays  occur  often  with  the  con- 
glomerate, and  sometimes  almost  entirely  replace  it.  This  clay, 
even  when  tilted  to  the  vertical,  is  indistinguishable  in  hand  speci- 
mens from  that  of  the  recent  plains  deposit ;  and  no  doubt  it  was 
formed  in  a  similar  manner,  as  alluvium.  The  sandstone,  too,  of 


592  PRINCIPLES    OF    STRATIGRAPHY 

this  zone  is  exactly  like  the  sand  forming  the  banks  of  the  great 
rivers,  but  in  a  more  or  less  consolidated  condition."  (Medlicott 
and  Blanford-38:5^.)  The  fossils  of  this  formation  are  of  fresh 
water  or  of  terrestrial  types  exclusively,  and  they,  as  well  as  the 
nature  of  the  deposit,  point  the-  continental  origin  of  this  forma- 
tion. 'The  mountain  torrents  are  now  in  many  cases  engaged  in 
laying  down  great  banks  of  shingle  at  the  margin  of  the  plains,  just 
like  the  Siwalik  conglomerates ;  and  the  thick  sandstones  and  sandy 
clays  of  the  Tertiary  series  are  of  just  the  same  type  of  form  and 
composition  as  the  actual  deposits  of  the  great  rivers."  (Medlicott 
and  Blanford.) 

In  the  Salt  Range  of  the  Punjab  these  alternating  gray  and 
greenish  sandstones  and  the  red  and  light  brownish  orange  clays 
"are  from  seventy  to  a  hundred  and  twenty  feet  in  thickness,  be- 
ing very  frequently  about  a  hundred  feet  each,  but  some  zones 
are  much  thicker."  (Wynne-62  :io8.) 

Depth  of  Compound  Continental  Deposits.  The  great  amount 
of  material  which  may  accumulate  in  deserts  as  the  product  of 
combined  creep,  torrential  and  eolian  deposit  is  seen  from  a  well 
boring  near  Ashkabad,  Turkestan  (Walther-57  1/05),  which  pene- 
trated sands,  clays  and  gravels  to  a  depth  of  666  meters  without 
finding  rock  bottom.  No  organic  remains  were  found,  and  the 
character  of  the  material  is  similar  to  that  of  the  surface  deposits 
of  the  Transcaspian  desert,  from  which  it  is  inferred  that  this  entire 
mass  of  over  2,000  feet  of  sediment  accumulated  under  climatic 
and  topographic  conditions  similar  to  those  now  prevailing. 

Chatter  or  Percussion  Marks.  A  characteristic  feature  of  many 
boulder  or  cobblestone  deposits  of  modern  time  as  well  as  of 
former  periods  is  the  presence  of  numerous  crescentic  chatter  or 
percussion  marks  on  the  finer  grained  and  well-rounded  pebbles, 
especially  porphyries,  quartzites,  and  the  like.  These  have  much 
the  form  and  size  of  impressions  made  by  the  end  of  a  finger  nail 
in  soft  clay,  and  are  due  to  the  violent  impact  of  one  rounded 
pebble  or  boulder  upon  another.  Such  marks  are  plentifully  pro- 
duced by  the  impact,  one  upon  another  of  the  hard,  fine-grained 
pebbles  used  for  grinding  in  the  revolving  cylinders  of  cement  mills 
and  other  works. 

Organic  Remains  in  Torrential  Deposits.  On  the  whole,  or- 
ganic remains  will  be  few  or  absent  in  coarse  torrential  deposits. 
Even  tough  masses  of  wood  will  be  shattered  and  completely  anni- 
hilated. As  a  result,  such  deposits  will  be  free  from  organic  re- 
mains, though,  of  course,  with  increasing  fineness  of  the  sediment 
the  possibility  of  the  preservation  of  such  remains  increases.  Since 


ORGANIC  REMAINS   IN    RIVER   DEPOSITS       593 

in  semi-arid  regions  violent  floods  arise  abruptly,  sweeping  down 
the  previously  almost  dry  river  beds,  and  converting  them  in  a 
few  minutes  into  raging  torrents,  it  is  apparent  that  organisms  may 
be  surprised  and  suddenly  overwhelmed  and  their  remains  entombed 
in  the  resulting  deposits  of  the  flood.  We  need  only  recall  such 
disasters  as  that  which  recently  befell  a  transcontinental  railroad 
where  the  sudden  flooding  of  a  previously  dry  wadi  swept  away 
a  trestle  and  its  load  of  cars,  these  with  their  luckless  passengers 
being  buried  in  the  sand  and  silt  of  the  lower  course  of  the  stream. 
The  many  unrecorded  entombments  of  cattle  and  other  creatures 
by  just  such  sudden  floods  would,  if  known,  form  adequate  illus- 
trations of  the  origin  of  many-fossiliferous  sandstones  of  the  past. 

One  of  the  chief  causes  of  the  destruction  of  animal  life  on 
plains  of  subaerial  deposition  is  found  in  the  periodic  droughts 
affecting  these  regions.  The  geologic  effects  of  such  droughts 
have  been  noted  in  many  tropical  countries,  especially  along  the 
west  coast  of  Africa,  in  India,  and  in  South  America.  Darwin 
(17)  has  described  the  "gran  seco"  or  great  drought  which  occurred 
between  the  years  1827  and  1830,  when,  in  the  northern  part  of  the 
province  of  Buenos  Ayres  (South  America)  and  the  southern  part 
of  St.  Fe,  vast  numbers  of  birds  and  animals  perished,  the  vegeta- 
tion withered  and  died,  and  the  brooks  became  dry,  until  finally 
the  whole  country  was  turned  into  a  dusty,  waterless  waste.  Dar- 
win writes :  "A  man  told  me  that  the  deer  used  to  come  into  his 
courtyard  to  the  well,  which  he  had  been  obliged  to  dig  to  supply 
his  own  family  with  water;  and  that  the  partridges  had  hardly 
strength  to  fly  away  when  pursued.  The  lowest  estimation  of 
the  loss  of  cattle  in  the  province  of  Buenos  Ayres  alone  was  taken 
at  one  million  head.  A  proprietor  at  San  Pedro  had  previously 
to  these  years  20,000  cattle,  at  the  end  not  one  remained. 

"I  was  informed  by  an  eye-witness  that  the  cattle  in  herds  of 
thousands  rushed  into  the  Parana,  and  being  exhausted  by  hunger 
they  were  unable  to  crawl  up  the  muddy  banks  and  thus  were 
drowned.  .  .  .  Without  doubt  several  hundred  thousand  ani- 
mals thus  perished  in  the  river :  their  bodies  when  putrid  were  * 
seen  floating  down  the  stream;  and  many  in  all  probability  were 
deposited  in  the  estuary  of  the  Plata.  All  the  small  rivers  became 
highly  saline,  and  this  caused  the  death  of  vast  numbers  in  particu- 
lar spots;  for  when  an  animal  drinks  of  such  water  it  does  not 
recover.  .  .  .  Subsequently  to  the  drought  of  1827  to  '32  a 
very  rainy  season  followed  which  caused  great  floods.  Hence  it  is 
almost  certain  that  some  thousands  of  the  skeletons  were  buried  by 
the  deposits  of  the  very  next  year."  Darwin  adds  very  pertinently, 


594  PRINCIPLES    OF    STRATIGRAPHY 

"What  would  be  the  opinion  of  a  geologist,  viewing  such  an  enor- 
mous collection  of  bones,  of  all  kinds  of  animals  and  of  all  ages, 
thus  embedded  in  one  thick  earthy  mass?  Would  he  not  attribute 
it  to  a  flood  having  swept  over  the  surface  of  the  land,  rather  than 
to  the  common  order  of  things?"  (Darwin-i7,  Chapter  vii.) 
These  droughts  are  of  frequent  occurrence  and  seem  to  show  an 
approximate  periodicity  of  about  fifteen  years. 

Distances  to  Which  Material  May  Be  Carried  by  Rivers.  Wade 
(55),  in  his  study  of  the  distribution  of  the  gravels  derived  from 
the  hills  of  igneous  rock  facing  the  western  border  of  the  Red 
Sea,  comes  to  some  interesting  conclusions  regarding  the  distance 
to  which  pebbles  may  be  transported  by  subaerial  agencies.  On  the 
eastern  side  of  these  ranges  the  fragments  have  traveled  only  a 
short  distance,  lying  still  in  the  plains  at  the  foot  of  the  hills.  On 
the  western  side  of  the  Red  Sea  ranges  the  gravels  appear  to  have 
been  carried  along  the  main  wadis  and  old  lines  of  drainage*  of  ten  to 
great  distances.  "The  pebbles  have  traveled  in  more  or  less  westerly 
directions  down  the  wadis,  into  the  important  north-and-south  wadi 
which  continues  the  line  of  the  Nile  north  from  Quena.  They  are 
abundant  for  some  distance  north  and  south  of  Quena.  Thence 
they  have  been  carried  northward  down  the  Nile  Valley.  .  .  . 
The  most  interesting  occurrences  of  the  rocks,  which  the  Survey 
geologists  say  'could  only  come  from  the  Red  Sea'  are  at  Heluan, 
a  few  miles  south  of  Cairo  .  .  .  and  in  the  Delta  itself,  where 
they  were  found  in  the  Royal  Society's  boring  at  Zagazig.  Thus 
these  rocks  have  been  river-borne  for  at  least  400  miles."  (Wade- 
55:^44.)  The  age  of  these  gravels  is  Pleistocenic. 

Extensive  deposits  of  apparently  river-borne  pebbles  are  found 
in  many  older  formations.  In  the  Trias  of  England  they  have  been 
found  300  miles  from  their  source.  The  Pottsville  conglomerate 
series  of  eastern  North  America  extends  northwestward  for  a  dis- 
tance of  400  miles  or  more,  the  pebbles  of  the  series  throughout  be- 
ing derived  from  the  Appalachians  on  the  southeast. 

Purity  and  Rounding  of  Fluviatile  Deposits.  On  the  whole,  the 
•  material  of  a  subaerial  fan  is  very  heterogeneous,  but  by  prolonged 
reworking  and  the  sorting  action  of  running  water  a  considerable 
assortment  into  kinds  as  well  as  sizes  of  grain  may  be  effected. 
In  dry  climates  the  disintegration  of  granitic  rocks  is  not  accom- 
panied by  extensive  decomposition.  Fresh  feldspar  crystals  will 
remain,  and  these  may  be  rounded  by  wind  attrition.  (Wade-55.) 
In  moister  climates,  on  the  other  hand,  feldspar  will  decay,  forming 
kaolin  or  laterite,  and  by  deflation  or  by  flotation  these  products  of 
finer  grain  will  be  swept  away. 


RIVER    PEBBLES  595 

Form  of  River  Pebbles.  Rudolf  Hoernes  (32)  has  recently 
insisted  upon  the  distinctive  characters  possessed  by  the  pebbles 
subject  to  prolonged  river  and  wave  transport.  According  to  him,  / 
river-borne  pebbles  are  always  flat,  and  more  or  less  wedge-shaped, 
owing  to  the  fact  that  the  current  merely  shoves  the  coarser  mate- 
rial along  its  bottom.  Marine  and  lacustrine  pebbles,  on  the  other 
hand,  are  rounded  or  roller-shaped,  because  the  waves  tend  to  roll 
the  material. 

Eduard  Suess  in  1862,  in  describing  the  fluviatile  Belvedere 
gravels  of  the  Vienna  district,  says,  in  effect  ($3:64,  65):  "A 
comparison  of  a  considerable  quantity  of  such  pebbles  shows  that 
they  conform  more  or  less  to  a  single  typical  form,  being  almost 
without  exception  sharpened  to  a  wedge-shaped  form  on  one  side. 
This  form  distinguishes  shoved  pebbles  from  rolled  pebbles;  it  is 
produced  by  the  pushing  along,  over  the  bottom,  of  the  rock  frag- 
ments by  the  current  of  the  stream.  Rolled  pebbles,  such  as  are 
moved  to  and  fro  by  the  surf  on  the  shore,  never  have  the  wedge- 
shaped  form,  but  a  uniformly  oval  or  cylindrical  ground  form." 
According  to  J.  Lorenz  von  Liburnau  (37:95,  96)  the  flat  river 
pebbles  suffer  chiefly  a  horizontal  rotation,  so  that  the  top  and 
bottom  of  the  pebbles  are  rubbed  against  the  overlying  and  under- 
lying ones,  while  at  the  same  time  the  edges  are  worn  off,  the  re- 
sult being  a  mass  of  flat,  worn  cakes  with  smooth,  rounded  edges. 

In  contradistinction  to  these  observations  and  deductions,  Penck 
emphatically  insists  upon  the  rolling  of  pebbles  on  the  stream-bed 
as  the  chief  method  of  river  transport.  Such  rolling  may  affect 
scattered  pebbles  or  the  entire  mass,  in  which  case  the  entire  sedi- 
ment on  the  river  bottom  is  in  motion,  the  individual  pebbles  roll- 
ing and  striking  against  one  another,  with  the  result  that  rounded 
pebbles  are  produced.  In  portions  of  the  Rhine  bed,  such  a  mass 
three  meters  in  depth  is  thus  moved  along.  (Penck— 41 1284.) 

It  is  extremely  doubtful  if  the  distinctions  made  by  Suess  and 
Hoernes  can  be  considered  of  more  than  local  applicability.  The ' 
character  of  the  rock  which  has  furnished  the  material  is  probably 
of  much  greater  significance,  as  pointed  out  by  Walther.  Thus,  on 
the  shores  of  Lake  Michigan,  where  the  bed  rock  is  a  uniform 
grained  limestone,  the  pebbles  are  chiefly  of  a  rounded  or  roller- 
shaped  character,  while  on  Lake  Erie,  where  the  cliffs  are  of  shale, 
flat  gravel  predominates,  except  where  glacial  deposits  have  formed 
a  local  source  of  supply.  Again,  on  a  relatively  steep  shore,  where 
wave-work  is  pronounced,  as  on  the  northern  Massachusetts  coast, 
the  pebbles  are  well  rounded  through  rolling,  while  on  a  shallow 
coast,  where  the  wash  of  the  waves  rushes  up  and  down  the  beach 


596  PRINCIPLES    OF    STRATIGRAPHY 

as  a  sheet  flood,  the  pebbles  are  more  often  merely  moved  back- 
ward and  forward  without  much  overturning,  or,  again,  the 
pebbles  are  scarcely  moved,  but  polished  and  worn  by  the  sand 
carried  back  and  forth  across  them. 

Pebbles  of  glacial  stream  deposits  are  always  rounded,  since 
in  such  deposits  only  the  more  massive  rocks  escape  destruction. 
The  pebbles  and  coarser  rocks  of  the  White  Mountain  streams  are 
all  well  rounded,  this  being  especially  well  shown  in  the  flood  plain 
of  the  Saco  River  at  Intervale.  Destruction  of  all  the  weaker 
type  of  rocks  by  prolonged  river  transport  is  also  imminent,  and 
this  is  especially  the  case  on  large  river  flood  plains  or  deltas. 
Prolonged  exposure  of  granitic  or  other  coarse-grained  igneous 
rocks  results  in  their  disintegration,  and  thus  by  a  process  of  assort- 
ing, the  pebbles  may  be  reduced  to  a  few  fundamental  lithologic 
types,  such  as  quartz,  porphyry,  etc.  There  are  many  older  quartz 
conglomerates  with  well-rounded  pebbles,  but  free  from  fossils, 
which  appear  to  represent  extreme  cases  of  concentration.  The 
Millstone  grit,  the  Pottsville  conglomerate,  and  the  Shawangunk 
and  other  conglomerates  are  almost  wholly  composed  of  quartz 
pebbles.  In  many  cases  these  quartz  pebbles  are  derived  from  vein 
quartz,  but  in  other  cases  they  are  probably  a  highly  indurated 
quartzite  in  which  the  individual  grains  have  become  obliterated. 

It  is  difficult  to  understand  how  extensive  conglomerates,  some- 
times many  hundreds  or  even  a  thousand  feet  in  thickness,  and 
composed  almost  entirely  of  quartz  pebbles  embedded  in  quartz 
sand,  can  have  originated.  If  the  material  of  the  pebbles  is  vein 
quartz,  an  enormous  destruction  of  rock  is  indicated,  since  veins 
form  only  a  small  portion  of  the  rock  mass  carrying  them.  If 
the  material  of  the  pebbles  is  an  older  quartzite,  the  problem  is 
less  difficult.  Again,  in  some  cases  the  pure  quartz  pebble  conglom- 
erates may  be  formed  of  the  reworked  gravels  derived  from  the  de- 
struction of  older  conglomerates.  Thus  the  pebbles  of  the  "yellow 
gravel"  of  the  coastal.plain  may  be  the  product  of  the  destruction 
of  the  formerly  much  more  extensive  Pottsville  conglomerate.  In 
this  connection  it  is  interesting  to  record  that  some  of  these 
pebbles  are  fossiliferous,  carrying  corals  of  Siluric  age.  This  may 
represent  a  silicified  limestone,  the  silica  thus  being  of  secondary 
origin.  Whether  any  such  origin  may  be  postulated  for  a  con- 
siderable portion  of  the  quartz  pebbles  is  doubtful. 

From  our  present  knowledge  of  the  subject,  it  seems  that 
no  constant  differences  can  be  ascertained  between  river  and  shore 
pebbles,  both  may  be  round  or  flat,  and  both  may  be  well  worn  or 
subangular,  and  form  part  of  a  mass  of  a  very  uniform  lithic  char- 


OVERLAP   OF    RIVER   DEPOSITS  597 

acter,  or  one  composed  of  a  heterogeneous  aggregate.  On  the 
whole,  destruction  of  all  but  the  resistant  quartz  seems  more  as- 
sured on  the  flood  plain  of  large  rivers  than  on  the  seashore;  and 
certainly  the  wide  transport  of  such  material  is  more  readily  ef- 
fected by  streams. 

The  sorting  action  of  streams  on  sands  has  already  been  dis-- 
cussed.  (Chapter  V,  p.  252.) 

Overlap  Relations  of  River  Deposits.  In  a  growing  subaerial 
river  delta,  the  later  formed  portions  will  progressively  overlap 
the  earlier  formed  parts,  coming  to  rest  upon  the  basement  beds, 
beyond  the  margin  of  the  older  beds  of  the  delta.  Since,  however, 
this  can  be  recognized  only  as  an  overlap  of  formations  of  definite 
chronologic  value,  and  not  an  overlap  of  continuous  beds,  this  sub- 
ject is  better  discussed  after  the  simpler  type  of  marine  overlap 
has  been  described.  The  general  theoretical  relationship  is  ex- 
pressed by  the  following  diagram  (Fig.  124),  from  which  it  will 
be  seen  that  the  principal  overlap  is  away  from  the  source  of  supply. 
There  may,  of  course,  be  a  slight  headward  overlap  due  to  aggrada- 


FIG.   124.     Diagram    showing    normal    non-marine    progressive    overlap,  each 

later  stratum  resting  upon  the  old  land  surface  beyond  the  edge 

of  the  preceding  one.     A  slight  headward  overlap  is  also  indi- 
cated. 

tion  of  the  upper  part  of  the  river  channels  as  the  grade  is  lowered. 
This,  as  a  rule,  will  be  slight  and  local  as  compared  with  the  over- 
lap at  the  other  end,  though  it  is  not  to  be  denied  that  at  times 
such  a  headward  overlap  may  be  considerable. 

Flood  Plains  of  Glacial  Streams.  These  are  of  exceptional 
character  owing  to  the  abundant  supply  of  detritus  as  well  as  water 
from  the  melting  ice.  As  already  pointed  out  in  Chapter  III,  p.  136, 
such  streams  when  overloaded  will  form  extensive  deposits  in  their 
valleys,  aggrading  these  to  a  considerable  depth.  Subsequent  change 
in  the  character  of  the  stream,  either  from  diminution  of  supply, 


598  PRINCIPLES    OF    STRATIGRAPHY 

from  increase  in  the  amount  of  water  by  sudden  melting,  or  from 
a  general  uplift  of  the  region,  will  cause  the  rivers  to  entrench 
themselves  in  the  old  flood  plains,  leaving  the  remnants  as  terraces 
on  either  side  of  the  valley.  Nearly  all  the  streams  coming  from 
the  glaciated  region  have  such  terraces,  which  mark  the  greater 
deposition  in  periods  preceding  the  present  one.  Examples  of 
deposits  'of  this  type  now  forming  are  seen  in  the  valleys  of  the 
streams  coming  from  the  Alaskan  and  other  glaciers. 

River  and  Flood  Plain  Deposits  from  Continental  Ice-Sheets. 
Several  types  of  such  deposits  are  recognized  and  are  noteworthy 
on  account  of  their  peculiarity;  among  these  are:  I.  the  torrential 
moraine,  or  kame ;  2.  the  frontal,  or  apron  plain ;  3.  the  esker ;  and, 
4.  the  glacial  sand  plain,  or  temporary  lake  delta.  The  essential 
characters  of  each  are  as  follows : 

1.  Torrential  moraine  or  kame  deposits.     These  are  irregular 
hills  of  semi-stratified  sands  and  gravels,  all  of  the  pebbles  being 
water   worn.     The   material   was   derived   from   the   ice   and   was 
dumped  by  the  rivers  in  front  of  the  ice-sheet.    These  deposits  are 
commonly  of  irregular  shape,  being  more  or  less  confluent  cones  of 
debris,  and  often  complicated  by  the  formation  of  kettle  holes  from 
the  melting  of  included  ice  blocks,  as  in  normal   moraines.     The 
topography  of  such  a  deposit,  when  extensive,  is  often  a  series  of 
knobs  and  basins. 

2.  The  frontal  or  apron  plain.    This  is  also  a  subaerial  deposit 
and  consists  of  the  material  carried  forward  from  the  glacial  mo- 
raine by  streams,  and  spread  as  a  veneer  or  mantle  over  the  older 
formations  in  front  of  the  ice.     Where  it  is  spread  over  a  coastal 
plain,  it  is  generally  of  uniform  thickness,  this  decreasing  from  the 
source  outward.     The  material  also  becomes  finer  away  from  the 
source  of  supply.     Kettle  holes  may  occur,  but  they  are  less  fre- 
quent than   in  the  kame  moraine.     Cross   channels  made  by  the 
streams  from  the  ice  are  not  uncommon  features.    Typical  examples 
of  such  apron  plains  are  found  south  of  the  moraine  on  Cape  Cod, 
and  in  similar  relations  to  the  moraines  on  Nantucket,   Martha's 
Vineyard,  and  Long  Island.    In  the  Cape  Cod  sections  of  this  apron 
plain  facetted  pebbles  or  dreikanter  have  been  found  in  place,  in- 
dicating wind  activity  and  further  proving  the  subaerial  origin  of 
this  deposit.     Such  wind  work  may  locally  modify  the  deposit,  sub- 
stituting wind  cross-bedding  for  the  horizontal  bedding  given  to 
them  by  the  water. 

Marine  fossils  may  be  locally  embedded  in  such  deposits  if 
they  are  formed  near  the  shore,  and  when  a  partial  subsidence  is 
succeeded  by  further  deposition  by  streams  from  the  ice.  A  fine 


GLACIAL   DEPOSITS  599 

example  is  shown  by  the  fossiliferous  layers  of  Sankaty  Head  on 
Nantucket,  which,  however,  lie  really  within  the  kame-moraine 
area  rather  than  in  the  present  apron  plain.  It  is  probable,  however, 
that  the  fossiliferous  beds  themselves  belong  to  an  earlier  apron 
plain,  for  it  is  known  that  the  Wisconsin  ice  sheet  advanced  over  this 
deposit  and  built  its  moraine  and  apron  plain  further  south.  (Wil- 
son-6o:/j.) 

3.  The  esker.  (Swedish  os,  pi.  osars.)  This  term  is  applied 
to  long,  narrow  ridges  of  sand  and  gravel  with  steeply  sloping  sides 
and  often  a  sinuous  outline.  The  summit  of  the  esker  is  generally 
a  narrow,  flat  space  between  the  sloping  sides,  the  cross-section  be- 
ing very  nearly  a  triangular  one.  The  eskers  of  the  last  glacial 
period  run  in  general  parallel  with  the  direction  of  the  ice  move- 
ment and  while  occurring  largely  perhaps  in  the  north  and  south 
valleys,  along  which  the  main  drainage  lines  from  the  ice  discharged, 
they  are  not  confined  to  these,  but  often  pass  indifferently  over  hills 
and  through  valleys.  In  height  they  rarely  exceed  100  feet,  but  in 
length  they  may  be  followed  for  tens  or"  in  rare  cases  even  hun- 
dreds of  miles.  Their  best  development  in  this  country  is  in  New 
England,  while  Scandinavia  and  Finland  furnish  some  of  the  best 
illustrations  in  the  Old  World. 

Eskers  may  be  formed  in  various  ways,  such  as  by  filling  of 
gorges  in  the  ice,  by  accumulation  of  debris  in  englacial  tunnels  and 
by  aggradation  of  their  bed  by  sub-glacial  streams.  (Grabau-23.) 
This  last  is  the  most  characteristic  method  of  formation.  Streams 
originating  under  the  ice  are  enclosed  in  a  tunnel  and,  being  under 
an  enormous  hydrostatic  pressure,  will  fill  this  tunnel  after  the 
.manner  of  the  water  in  a  city  main.  It  may  thus  be  forced  up- 
ward and  will  discharge  at  a  level  much  above  that  of  its  upper 
courses,  if  it  is  located  in  a  valley  sloping  against  the  ice  mass,  as  is 
so  often  the  case. 

Flowing  uphill,  such  a  stream  will  tend  to  erode  the  roof  of 
its  tunnel,  and  simultaneously  to  aggrade  its  bottom  in  the  higher 
(upstream)  parts.  As  the  stream  rises  in  the  ice  by  roof  erosion, 
the  floor  is  more  and  more  aggraded  until  this  filling  all  along  the 
line  has  reached  the  level  of  the  outlet,  or  risen  slightly  above  it. 
Melting  removes  the  supporting  walls  on  either  side  of  this  aggraded 
river-bed,  when  the  sides  will  slump,  giving  the  characteristic  lateral 
slopes  and  the  triangular  cross-section  to  the  esker.  At  points 
where  the  original  deposit  is  narrow,  so  much  material  will  be  in- 
volved in  the  slumping  to  give  the  proper  angle  of  repose  that  the 
surface  of  the  .esker  will  be  actually  lowered.  Thus  irregularities  in 
height  in  the  esker  are  readily  accounted  for.  (Woodworth-6i.) 


6oo  PRINCIPLES    OF    STRATIGRAPHY 

4.  Glacial  sand  plains.  Whenever  the  ice  holds  up  a  tempo- 
rary body  of  water  between  its  front  or  sides  and  the  margins  of 
the  valley  or  basin  in  which  it  lies,  opportunity  for  the  formation  of 
glacial  deltas  or  sand  plains  is  given.  These  may  be  formed  around 
the  margins  of  the  lake  by  streams  coming  from  the  land,  when 
they  partake  of  the  true  delta  to  be  described  beyond.  Such  deltas 
have  been  recorded  from  glacial  lakes  in  New  Jersey  and  else- 
where. The  marginal  sand  plains  of  the  Upper  Hudson  Valley 
were  deposited  in  lakes  bordering  the  ice  sheet  which  occupied 
the  center  of  that  valley.  Sand  plains  formed  at  the  front  of  the  ice 
of  material  carried  by  streams  from  the  ice  abound  in  New  Eng- 
land, especially  in  eastern  Massachusetts,  where  they  have  been 
fully  described.*  A  characteristic  feature  of  these  sand  plains  is 
their  correspondence  in  height  to  the  elevation  of  the  outlet,  which 
determined  the  level  of  the  temporary  lake.  Not  infrequently  a 
number  of  successive  sand  plains  is  formed  corresponding  to  a  suc- 
cession of  lake  levels  determined  by  progressive  uncovering  oHower 
outlets.  In  New  England  these  plains  are  generally  highest  in  the 
southern  portions  of  the  old  northward  sloping  valleys  and  become 
progressively  lower  toward  the  north.  In  Lake  Bouve,  an  extinct 
glacial  lake  in  the  Boston  Basin,  eight  series  of  such  sand  plains  are 
known,  each  series  lower  than  the  preceding  one  on  the  south. 
( Grabau-23  '.580. )  A  special  example  of  rather  striking  character 
is  seen  in  the  sand  plains  of  Wellfleet,  Eastham,  and  Truro  on  Cape 
Cod,  which  were  deposited  in  a  lake  held  in  an  embayment  in  the 
eastern  ice  lobe,  and  dammed  in  part  by  the  terminal  moraine  of 
that  ice  lobe,  across  which  the  discharge  of  the  waters  occurred. 
In  this  case  the  highest  series  of  plains  lies  between  the  two  lower 
series.  By  the  melting  of  the  ice  these  plains  were  left  without  any 
immediately  surrounding  land  barrier,  as  isolated  sand  masses  run- 
ning northward  into  the  ocean  from  the  eastern  end  of  the  terminal 
moraine.  (Grabau-24;  Wilson-6o  '.52-66,  pis.  34,  36,  37,  38.)  In 
form  the  isolated  sand  plain,  revealed  on  the  melting  of  the  ice 
and  the  drainage  of  the  temporary  lake,  consists  of  a  surface  slope 
which  is  gently  forward  from  the  center  of  origin ;  a  steeper  frontal 
or  delta  slope,  joining  the  surface  slope  abruptly,  and  having  a 
lobate  or  scalloped  outline,  and  a  still  steeper  back  slope  often  with 
concavities  between  sharp  cusps.  This  latter  surface  is  due  to 
slumping  after  the  supporting  ice  front  against  which  the  delta  was 
built  had  melted  away.  Its  slope,  therefore,  represents  the  angle 
of  repose  of  the  material  under  the  conditions  of  formation.  The 
gentle  surface  slope  represents  the  subaerial  part  of  the  delta,  while 

*  See  papers  by  Crosby,  Grabau,  Clapp,  etc.,  cited  in  Chapter  III. 


CONSOLIDATED    GLACIAL  DEPOSITS  601 

the  lobate  front  is  the  slope  of  the  front  of  the  original  delta  where 
the  oblique  frontal  layers  or  fore-set  beds  were  added.  The  loba- 
tion  is  due  to  the  division  of  the  stream  into  a  number  of  spreading 
fingers  or  distributaries,  each  of  which  builds  its  own  portion  of  the 
delta  forward.  In  section  it  will  be  seen  that  the  greatest  part  of 
the  sand  plain  is  composed  of  the  sloping  fore-set  beds,  which  are 
inclined  at  an  angle  of  20  or  more  degrees.  The  upper  ends  of 
the  fore-set  beds  are  abruptly  truncated,  and  on  these  truncated 
edges  rest  the  coarser,  nearly  horizontal,  top-set  beds  which  con- 
stitute the  subaerial  part  of  the  delta.  The  foot  of  the  fore-set 
beds  generally  rests  upon  a  thin  series  of  bottom-set  beds  of  finest 
material,  often  of  clay  or  rock  flour.  All  the  beds  are  well  stratified 
and  the  pebbles  are,  as  a  rule,  well  rounded. 

Consolidated  Sand  Plains.  Sand  plains  of  Pleistocenic  age  have, 
in  some  cases,  become  consolidated  so  as  to  form  a  rock  mass  of 
more  or  less  induration.  This  is  especially  the  case  where  many  of 
the  pebbles  are  of  limestone,  when  partial  solution  and  redeposition 
of  the  lime  in  the  interstices  will  occur.  A  typical  example  of 
such  a  consolidated  deposit  is  seen  on  the  banks  of  the  lower 
Niagara  River,  near  the  railroad  station  at  Lewiston,  New  York. 
Here  steep  fore-set  beds  are  seen  dipping  at  an  average  angle  of 
15-20  degrees  toward  the  south.  The  beds  are  sufficiently  well 
cemented  to  form  a  vertical  wall,  though  the  material  can  be  broken 
into  its  component  pebbles  by  blows  of  a  hammer.  The  deposit, 
which  is  perhaps  30  or  40  feet  thick,  appears  to  have  formed  in  a 
body  of  water  held  up  against  the  front  of  the  Niagara  escarpment 
by  an  ice  lobe  lying  a  short  distance  to  the  north.  Streams  from 
this  ice  lobe  supplied  the  pebbles  and  sand  which  built  up  the  delta. 

This  deposit  is  sufficiently  consolidated  to  resist  ordinary  erosion, 
and  river,  lacustrine,  or  even  marine  sediments  could  be  formed  over 
it  without  disturbing  it.  Indeed,  since  the  formation  of  this  deposit 
this  region  is  believed  to  have  been  invaded  by  the  sea  by  way  of  the 
Hudson,  Lake  Champlain,  and  the  St.  Lawrence,  but  this  was  not 
of  sufficient  duration  to  permit  the  formation  of  extensive  marine 
deposits.  It  is  easy  to  see,  however,  that  these  steeply  inclined 
delta  beds  of  coarse  material,  followed  by  marine  sediments,  such 
as  would  have  been  formed  had  the  sea  stood  here  longer,  and  this 
in  turn  by  lacustrine  deposits,  such  as  would  be  formed  if  the 
present  lake  should  expand,  would  give  a  complex  succession  of 
formations,  the  history  of  which  would  be  decipherable  only  with 
considerable  difficulty. 

The  NagelHuh  of  Salzburg.  (Crammer-13  '.325-334.)  The  city 
of  Salzburg  in  the  Austrian  province  of  the  same  name  and  close 


602  PRINCIPLES    OF    STRATIGRAPHY 

to  the  Bavarian  border  furnishes  a  remarkable  example  of  a  con- 
solidated conglomerate  or  pebble  rock  of  the  type  described.  This 
goes  by  the  name  of  Nagelfluh,  from  the  fact  that  where  the  rela- 
tively small  pebbles  have  fallen  out  of  the  matrix  a  depression 
like  that  made  ,by  the  head  of  a  nail  is  seen.  This  rock  appears 
in  several  large  erosion  remnants  within  the  city ;  one  of  them, 
the  Monchsberg,  rises  with  perpendicular  walls  (partly  artificial) 
and  is  pierced  by  a  tunnel  through  which  one  of  the  city  streets  is 
carried.  Other  remnants  are  the  neighboring  Rainberg,  and  the 
more  distant  hill  of  Hellbrunn.  All  of  these  are  evidently  part  of  a 
once  continuous  conglomerate  bed,  which  has  since  been  dismem- 
bered by  erosion.  The  cohesion  of  the  material  is  such  that  old 
crypts  hollowed  in  this  rock  and  used  in  the  third  century  as  places 
of  secret  worship  are  still  in  a  practically  unchanged  condition. 

The  walls  show  inclined  bedding  which  indicates  the  delta  char- 
acter of  these  deposits  (Penck-42  \i6i-i66).  According  to  the 
opinion  of  Penck,  Crammer,  and  others,  the  sand  and  pebbles  were 
washed  into  a  lake  which  occupied  the  Salzburg  basin  during 
post-glacial  time.  The  fact  that  the  Nagelfluh  rests  upon  a  glacial 
moraine,  as  determined  by  excavations  and  observations  on  natural 
and  artificial  exposures,  seems  to  indicate  that  this  deposit  is  of 
post-glacial  age,  though  other  observers  have  held  that  the  age 
of  the  deposit  might  be  greater,  perhaps  late  Tertiary. 

Nagelfluh  of  similar  character,  but  probably  of  greater  age,  is 
found  in  a  number  of  localities  in  South  Germany  and  elsewhere. 
In  some  cases,  as  in  Munich,  it  is  used  extensively  for  building 
purposes.  It  is,  of  course,  not  necessarily  true  that  all  conglomer- 
ates of  this  type  are  of  non-marine  origin,  though  most  of  them 
probably  are  river  deposits. 

PLAYAS  OR  TAKYRS  AND  SALINAS.  In  the  low,  flat-bottomed 
depressions  of  undrained  desert  basins  the  rivers  at  times  of  flood 
will  spread  out  into  extensive  shallow  lakes  of  temporary  existence. 
In  the  Great  Basin  region  of  western  North  America  one  such 
temporary  lake  reaches  a  length  of  about  100  miles  by  a  breadth  of 
12  to  15  miles,  but  with  the  water  scarcely  more  than  a  few  inches 
deep.  Here  the  fine  silt  of  the  river  is  deposited,  gradually  subsid- 
ing as  the  shallow  lake  evaporates.  After  complete  evaporation  a 
smooth,  hard-baked  surface  remains,  .marked  by  sun-cracks  and 
the  tracks  of  animals  which  visited  the  spot  before  complete  harden- 
ing of  the  mud  had  occurred.  Raindrop  impressions  likewise  re.- 
main  on  such  a  surface.  In  structure  the  material  is  beautifully 
and  finely  stratified,  as  may  be  seen  on  the  sides  of  the  sun-crack 
rifts.  This  constitutes  the  playa  of  the  American  deserts  (Mexico 


PLAYAS   AND    SALINAS  603 

and  the  southern  United  States),  the  takyr  or  schala  of  Asia,  or  the 
sebcha  of  Africa.  Russell  has  described  a  number  of  such  tempo- 
rary playa  lakes  from  the  western  United  States  (49:50).  He  finds 
them  a  characteristic  feature  of  the  greater  part  of  the  valleys  of 
Nevada,  the  largest  being  in  the  Black  Rock  Desert  in  the  north- 
western part  of  the  state.  It  forms  during  the  winter  months  and 
reaches  an  area  of  from  450  to  500  square  miles,  but  is  seldom  over 
a  few  inches  in  depth.  Often  after  storms  it  is  a  vast  sheet  of 
liquid  mud,  a  characteristic  of  many  playa  lakes.  In  a  few  hours 
or  a  few  days  the  water  of  the  lake  may  all  evaporate,  leaving  a 
hard,  dry  and  absolutely  barren  surface,  cracked  in  all  directions 
as  the  surface  contracts  in  drying.  "The  lake  beds  then  have  a 
striking  resemblance  to  tesselated  pavements  of  cream-colored  mar- 
ble, and  soon  become  so  hard  that  they  ring  beneath  the  hoof -beats 
of  a  galloping  horse,  but  retain  scarcely  a  trace  of  his  foot-prints." 
Around  the  margin  of  the  lakes  is  a  belt  of  plain  with  desert  vege- 
tation, the  transition  to  which  is  formed  by  a  marshy  tract  which 
in  summer  is  marked  by  an  abundant  efflorescence  of  salts. 

Mechanical  analysis  has  shown  that  the  material  of  the  playa 
may  be  100  per  cent,  clay,  and  that  laterally  it  will  gradually  pass 
through  the  addition  of  sands  into  the  surrounding  eolian  deposits. 
In  limestone  regions  where  siliceous  rocks  are  wanting  the  mate- 
rial of  the  playa  will  be  largely  lime  mud,  and  this  may  be  the 
origin  of  some  of  the  finely  bedded,  sun-cracked  calcilutytes  of  the 
American  Siluric,  where  the  percentage  of  lime  and  magnesium 
carbonates  is  seventy  or  less. 

If  the  playa  lake  exists  for  some  time  it  may  become  stocked 
with  certain  forms  of  organisms,  especially  types  whose  eggs  or 
larvae  can  be  transported  by  wind  or  by  birds.  The  small  crusta- 
ceans Estheria,  Daphnia,  and  Cypris  are  characteristic  of  desert 
lakes,  the  first  having  been  found  in  ponds  which  are  dry  for 
eleven  successive  months.  (Fischer,  quoted  by  Walther~57:p^.) 
When,  as  is  frequently  the  case,  salts  are  present  in  the  sediment, 
these  effloresce  on  the  surface,  and  from  their  hygroscopic  charac- 
ter keep  the  surface  of  the  playa  sufficiently  moist  to  prevent  the 
removal  by  the  wind  of  the  accumulated  material,  and  further  to 
catch  all  dust  particles  carried  across  the  surface  by  the  winds. 
Thus  the  surface  of  the  playa  becomes  dusted  over  with  a  fine  coat- 
ing of  sand  or  dust,  this  process  being  repeated  as  the  salts  rise  to  the 
surface  of  the  newly  added  layer.  Where  salt  is  present  in  great 
abundance  a  moist,  slippery  surface  with  incrustations  of  salt  re- 
sults, thus  forming  salinas.  When  wet,  their  surface  is  impassable, 
but  when  dry  a  crust  of  hard  salt  of  dazzling  whiteness  characterizes 


604  PRINCIPLES    OF    STRATIGRAPHY 

the  salina.  As  already  noted,  the  thickness  which  such  a  salt 
deposit  may  reach  is  practically  limited  only  by  the  depth  of  the 
basin  and  the  supply  of  the  salt. 

The  deeply  cleft  surface  of  the  dry  playa  is  not  infrequently 
buried  by  the  wandering  sands  of  the  desert,  while  the  rifts  between 
the  polygonal  blocks  are  filled  with  wind-blown  material,  or  the 
mud  of  the  next  succeeding  inundation,  and  so  preserved.  This  is 
made  possible  by  the  rapidity  with  which  the  playa  surface  becomes 
flooded,  a  case  being  on  record  where  a  lake  10  to  15  kilometers 
wide  and  of  immeasurable  length,  though  only  from  an  inch  and 
a  half  to  a  foot  in  depth,  came  into  existence  in  twenty  minutes. 
(Obrutschew,  quoted  by  Walther-57  :iio.)  It  must,  however,  be 
noted  that  the  dried  surface  of  the  playa  is  not  infrequently 
softened  on  being  wetted,  and  that  from  swelling  and  flowage  of 
the  mud  the  cracks  may  be  closed  again  before  they  are  filled.  In 
this  manner  many  mud-cracked  surfaces  are  again  obliterated. 
From  preliminary  experiments,  Barrell  concludes  (2:537-53^)  that 
"a  mud-cracked  loam  or  silty  clay,  even  when  the  sand  particles 
are  imperceptible  to  the  fingers,  is  an  unfavorable  material  for  the 
preservation  of  its  detailed  surface  features,  .  .  .  Upon  being 
wet  by  rain  the  rapid  swelling  and  disintegration  of  the  surface 
stratum  would  turn  the  surface  of  such  a  deposit  into  a  creamy 
mud.  .  .  ."  On  the  other  hand,  "a  pure  clay,  slowly  subsiding 
from  quiet  waters,  and  wet  sufficiently  long  to  become  compact 
upon  drying,  would  retain  its  mud  cracks  upon  rewetting,  either 
by  rain  previous  to  flooding  or  by  the  flood  waters  themselves." 
When  the  newly  deposited  layer  is  a  very  thin  one  it  will  curl  up 
like  shavings  on  drying  and  these  clay  shavings  will  be  blown  into 
the  sand  dunes,  where,  upon  subsequent  softening,  they  will  be 
compressed  into  clay  lentils  or  pebbles,  and  so  become  a  constituent 
part  of  an  otherwise  pure  sandstone. 

PRESERVATION  OF  FOOTPRINTS,  ETC.,  IN  SUB  AERIAL  DEPOSITS. 
Of  the  greatest  significance  is  the  relative  ease  with  which  tracks 
of  animals  are  preserved  in  desert  deposits.  The  scarcity  of  rain 
permits  their  almost  indefinite  retention  on  suitable  surfaces  with- 
out being  buried.  In  the  Sahara  desert  tracks  of  camels  made  in 
1877  were  still  perfectly  recognizable  in  1892  (Foureau-2i  :/75), 
the  interval  of  fifteen  years  having  altered  them  but  little.  Where- 
ever  ( Walther-57  :##)  a  temporary  accumulation  of  water  after 
a  desert  rain  attracts  the  varied  desert  fauna,  or  allows  animals 
living  on  the  border  of  the  desert  to  make  extended  excursions  into 
the  flooded  regions,  their  footprints  will  be  left  upon  the  impres- 
sionable surface  of  mud,  remaining  after  such  an  inundation.  These 


PALUDAL   AND    LACUSTRINE    CLASTICS         605 

will  in  time  be  covered  by  the  shifting  sands  of  the  desert  and  a 
relief  mold  will  be  produced  by  the  covering  sands.  Such  a  relief 
impression  will  be  more  readily  preserved  than  the  original  im- 
pression, which  may  be  destroyed  by  the  softening  of  the  clay 
surface  of  the  playa.  A  single  extensive  inundation  by  heavy  rains 
of  a  desert  surface  may  permit  a  wide  horizontal  migration  across 
this  surface  of  animals  which  never  before  and  never  after  entered 
this  region.  Thus  their  tracks  may  be  widely  preserved  in  a  single 
horizon  in  a  desert  formation,  like  those  of  Cheirotherium  in  the 
Upper  Buntsandstein  (Walther-57:<5'#),  even  though  the  animal 
lived  during  a  much  longer  time  period.  Repeated  floodings,  an- 
nually or  at  intervals  of  many  years,  will  permit  the  formation  of 
successive  track-bearing  layers,  by  animals  living  on  the  border  of 
the  desert.  This  mode  of  preservation  certainly  accords  best  with 
the  characters  of  the  tracks  found  in  such  formations  as  the  Newark 
sandstone  of  the  eastern  United  States,  whereas  the  frequent  as- 
sumption that  the  successive  track-bearing  beds  were  made  between 
tides  and  buried  by  the  sediment  brought  in  by  the  returning  tide 
does  not  allow  for  the  obliterating  effect  of  the  tide,  an  argument 
equally  applicable  to  stream-laid  deposits  upon  the  fresh  tracks. 
(Voigt-54:/<5d.) 

The  conditions  favoring  the  preservation  of  footprints  in  desert 
regions  militate  against  the  preservation  of  the  animals  themselves. 
For,  unless  the  body  is  buried  at  once,  it  is  sure  to  fall  a  prey  to 
the  desert  carnivora,  while  sun  and  wind  will  complete  the  destruc- 
tion of  what  remains.  This  explains  the  scarcity  of  remains  of  the 
animals  in  the  strata  which  contain  their  footprints. 

Other  Structural  Characters.  Ripple  marks  and  rill  marks, 
though  usually  regarded  as  typical  only  of  marine  formations,  are 
equally,  if  not  more,  characteristic  of  the  non-marine  deposits. 
Their  discussion  is,  however,  deferred  until  hydroclastic  sediments 
have  been  more  fully  discussed. 


NORMAL    PALUDAL    AND    LACUSTRINE    CLASTIC 

DEPOSITS. 

Clastic  deposits  in  swamps  (paludal  elastics)  are  of  relatively 
little  importance  except  when  associated  with  vegetal  deposits. 
These  latter  are  by  far  the  most  important,  the  elastics  being  subor- 
dinate and  confined  to  the  sediments  carried  in  by  wet  weather 
streams  and  rains,  or  the  dust  settling  out  of  the  air. 

Deposits  in  ponds  and  lakes,  on  the  other  hand,  i.  e.,  in  water 


606  PRINCIPLES    OF    STRATIGRAPHY 

bodies  free  or  nearly  so  from  growing  vegetation,  are  of  more 
significance,  since  they  add  a  decided  individualistic  note  to  the'ter- 
restrial  hydroclastic  series  with  which  they  are  commonly  asso- 
ciated. It  is  true  that  many  of  their  most  pronounced  characteris- 
tics are  due  to  peculiarities  in  the  composition  of  their  waters 
which  will  give  rise  to  deposits  of  special  chemical  character,  such 
as  have  been  discussed  in  preceding  chapters.  In  other  respects, 
again,  the  nature  of  the  sediment  is  not  very  different  from  that  of 
the  ocean,  except  in  so  far  as  the  absence  of  the  tides,  the  differ- 
ence in  composition  and  specific  gravity  of  the  water  and  the 
difference  in  size  of  the  water  body  influence  such  deposition.  The 
last  falls -practically  out  of  consideration  in  lakes  of  great  size,  such 
as  the  American  Great  Lakes. 

The  clastic  sediment  of  lakes  is  chiefly  derived  from  two 
sources,  that  resulting  from  the  erosion  of  its  shores  by  waves, 
and  that  brought  in  by  the  tributary  streams.  Erosion  is  very 
marked,  especially  in  the  larger  lakes,  such  as  Erie,  Ontario,  Huron, 
etc.,  and  the  product  is'  distributed  along  the  shore  as  shingle,  or 
heaped  up  into  storm  terraces,  as  on  Lake  Michigan.  Coarse  mate- 
rial is  seldom  carried  far  out  into  the  lake,  but  accumulates  along 
the  shores,  where  it  is  subject  to  constant  wave  attack.  The  finer 
sand  and  mud,  however,  resulting  from  such  wave  attack  are 
carried  out  from  shore  and  slowly  settle  all  over  the  lake  bottom 
and  sides.  This  also  happens  to  some  of  the  fine  slime  brought 
in  by  streams,  but  this  tends  for  the  most  part  to  sink  to  the  lake 
bottom.  The  coarsest  of  the  river-borne  sediments  will  build  up  a 
delta  at  the  shore,  but  the  finer  mud,  which  is  held  in  intimate  sus- 
pension in  the  stream  water,  is  carried  beyond  this  point.  Its 
presence  in  the  stream  water  renders  that  water  heavier,  and  it 
will,  therefore,  not  mingle  with  the  lighter  warm  water  of  the  sur- 
face of  the  lake,  but  will  sink  to  the  deeper,  cooler  and  denser 
strata.  Thus  a  mud-laden  stream  passing  into  a  lake  will  become 
submerged,  often  passing  along  the  lake  bottom,  and  occasionally 
forming  a  channel  there,  bounded  by  submerged  mud  banks  on 
either  side.  The  force  of  the  current  will  finally  be  dissipated  in 
the  deeper  waters  of  the  lake  and  the  sediment  will  slowly  sink  to 
the  bottom,  forming  horizontal  and  well-stratified  layers  of  mud- 
rock,  free  from  irregularity  of  bedding  and  of  uniformly  fine 
grain.  Mingled  with  sedime'nts  of  this  type  are  the  muds  which 
were  held  suspended  for  a  time  in  the  upper  waters  and  which 
settled  all  over  the  lake  bottom. 

With  the  seasonal  variation  in  the  strength  of  the  streams  there 
must  be  a  corresponding  variation  in  the  grain  of  the  sediment. 


LACUSTRINE    CLASTICS.     DELTAS  607 

Thus  when  the  current  is  powerful  and  surcharged  with  sediment 
slightly  coarser  material  may  be  carried  to  the  lake  bottom  than 
is  the  case  during  the  period  of  lessened  river  activity.  A  series  of 
annual  layers  is  thus  formed  which  in  any  given  case  may  serve  to 
measure  the  length  of  time  required  for  the  formation  of  the  de- 
posit. This  method  has  been  applied  by  Berkey  (8)  for  the  de- 
termination of  the  time  required  for  the  deposition  of  finely  bedded 
clays. 

DELTAS. 

Deltas  are  the  terminal  deposits  of  rivers,  and,  as  such,  have 
an  intimate  association  with  the  continental  elastics.  It  is  true,  of 
course,  that  a  part  of  the  delta  of  the  seacoast  is  of  submarine 
origin,  and  its  discussion  therefore  falls  more  essentially  under  the 
heading  of  marine  elastics.  Still,  deltas  are  peculiar  features  of 
relatively  limited  distribution,  and  m  no  way  represent  normal 
marine  conditions.  Indeed,  a  part  of  the  delta  is  always  typically 
non-marine,  and  the  place  of  the  delta  is  therefore  intermediate 
between  true  continental  and  marine  elastics.  Moreover,  deltas 
are  common  in  lakes,  these  belonging,  of  course,  entirely  to  the 
continental  division  of  the  hydroclastics. 

A  typical  delta  may  be  taken  as  one  that  is  built  into  a  body  of 
standing  water,  the  level  of  which  is  essentially  a  permanent  one. 
Subsequent  drainage  of  the  water  body  may  expose  the  delta  as 
we  have  seen,  but  all  such  changes  bring  the  delta-building  process 
to  an  end.  On  the  whole,  deltas  are  more  abundant  on  lakes  than 
on  the  seashore,  partly  because  lakes  are  not  subject  to  tidal  cur- 
rents and  fluctuation  of  level,  but  partly  also  because  wave  activity 
on  the  sea  coast  is  greater.  Fluctuation  in  level  due  to  tides  does 
not  necessarily  militate  against  delta  building,  as  is  shown  by  the 
Indus  delta,  which  is  built  where  the  tidal  range  is  10  feet,  while 
that  of  the  Ganges  is  built  into  a  sea  having  a  tidal  range  of  16 
feet.  Where  wave  action  is  strong,  however,  and  especially  where 
long  shore  transport  of  material  is  pronounced,  delta  building  is 
restricted.  Deltas  are  thus  the  triumph  of  river  deposition  over 
wave  and  current  destruction,  and  their  location  and  extent  will  be 
determined  by  the  relative  importance  of  the  opposing  processes. 
As  examples  of  typical  existing  deltas  on  the  sea  coast  may  be 
named  that  of  the  Nile,  on  the  Mediterranean;  of  the  Po,  on  the 
Adriatic;  the  confluent  deltas  of  the  Rhine  and  Meuse;  and  that 
of  the  Ems,  on  the  North  Sea ;  the  deltas  of  the  Lena  and  of  the 
Mackenzie,  on  the  open  Arctic  Ocean ;  those  of  the  Ganges,  Brah- 


6o8 


PRINCIPLES    OF    STRATIGRAPHY 


maputra  and  the  Indus,  on  the  Indian  Ocean ;  of  the  Niger  and  the 
Orinoco,  on  the  Atlantic  Ocean;  and  the  Mississippi  delta  on  the 
Gulf  of  Mexico.  Of  the  numerous  deltas  on  the  protected  waters 
of  Europe  and  Asia  may  be  mentioned  that  of  the  Danube  on  the 
Black  Sea,  the  Volga  on  the  Caspian,  and  those  of  the  Oxus  (Amu- 
darja)  and  the  Jaxartes  (Syr-darja)  on  the  Aral  Sea. 

Form  and  Rate  of  Growth  of  Deltas.  The^orm  of  the  deltas 
varies  greatly  from  the  typical  triangular  outline  resembling  the 
Greek  letter  delta  (A)  characteristic  of  the  Nile  delta  (the  type 
of  deltas;  Fig.  125)  to  the  long,  narrow  estuarine  filling  of  the 
Mackenzie  mouth,  on  the  one  hand,  and  the  very  broad,  but  short, 
cuspate  delta  of  the  Tiber,  or  the  still  narrower  strip-like  or  stunted 
delta  formed  by  the  Cavonne  on  the  Gulf  of  Taranto,  southern  Italy, 


FIG.   125.     The   Nile   Delta. 

on  the  other.  The  mouth  of  the  delta-building  river  may  advance 
singly  (unilobate)  without  dividing  into  distributaries,  as  is  nearly 
the  case  with  the  Ebro  on  the  northeast  coast  of  Spain,  or  it  may 
be  multilobate  with  the  distributaries  pushing  each  its  own  narrow 
lobe  forward,  which  may  even  become  a  finger-like  extension,  as 
in  the  remarkable  Mississippi  delta.  If  the  distributaries  are  nu- 
merous, they  may  form  a  network  of  streams,  as  on  the  Nile  delta, 
which  advances  by  a  continuous,  more  or  less  scalloped  front. 

In  size  the  deltas  of  the  present  day  vary  from  an  insignificant 
deposit  at  the  mouth  of  a  small  stream  to  areas  covering  many 
thousands  of  square  miles,  as  in  the  deltas  of  the  Nile,  the  Lena, 
and  the  Mississippi.  Confluent  deltas  of  several  streams  occur, 
making  irregular  deposits  with  many  lagoons,  as  in  the  Rhine- 
Meuse-Ems  delta;  while  deltas  building  on  a  coast  with  many 


CHARACTERISTICS    OF    DELTAS  609 

islands  may  gradually  annex  these  to  the  land  by  enclosing  them 
in  the  growing  delta.  The  hilly  province  of  Shantung  has  thus 
been  enclosed  in  the  great  delta  of  the  Huang-ho,  and  a  number 
of  small  islands  have  been  included  in  the  delta  of  the  Aspropota- 
mos  in  western  Greece. 

The  rate  of  growth  of  deltas  varies  greatly  and  is  often  con- 
siderable. Thus  the  Jaxartes  increased  by  13^4  square  miles  be- 
tween 1847  and  1900.  (Andrussow-i  :^p.)  The  delta  of  the  Rhone 
is  said  to  have  lengthened  more  than  26  kilometers  since  400  B.  C. 
The  southwest  pass  of  the  Mississippi  delta  grew,  according  to 
Captain  Talcot,  104  meters  in  length  in  1838,  the  south  pass  85 
meters,  the  northeast  and  southeast  passes  each  40  meters,  and  the 
pass  a  1'Outre  92  meters,  giving  an  average  of  80  meters  per  year 
for  each  pass.  While  this  holds  for  the  year  in  question,  it  is 
not  possible  to  consider  that  such  an  increase  occurs  in  all  years. 
Indeed,  often  one  year  destroys  what  is  built  in  the  preceding  year. 
The  Po  delta  has  increased  between  the  years  12001600  at  an  aver- 
age rate  of  25  meters  per  year,  but  from  1600  to  1804  its  rate  of 
increase  was  70  meters  per  annum.  One  of  the  most  rapidly  grow- 
ing deltas  is  that  of  the  Terek,  on  the  Caspian.  Within  a  period  of 
30  years  the  water  has  been  pushed  back  15  kilometers  by  the 
growth  of  the  delta,  which  increased  thus  at  the  rate  of  half  a 
kilometer  per  year.  The  other  extreme  is  shown  by  the  delta  of 
the  Danube,  which  at  one  of  its  mouths  is  not  over  4  meters  per 
year,  though  somewhat  more  rapid  at  another.  The  average  in- 
crease of  the  Nile  is  about  4  meters  'per  year,  while  the  delta  of 
the  Tiber  is  estimated  to  increase  at  the  low  rate  of  I  meter  per 
year.  According  to  Pumpelly,  the  Huang-ho  has  increased  on  the 
average  at  a  rate  of  30  meters  per  year  between  B.  C.  220  and 
A.  D.  1730. 

Thickness  or  Depth  of  Deltas.  (Credner-i4.)  The  depth  of 
delta  deposits  on  modern  sea  coasts  varies  greatly,  but  is,  on  the 
whole,  comparatively  slight.  Thus  the  mud  of  the  Nile  delta  is 
not  over  10  or  15  meters  thick.  It  rests  on  loose  sea  sand.  The 
delta  deposits  of  the  Rhine  have  a  thickness  of  60  meters,  those  of 
the  Rhone  over  100  meters.  In  the  Po  the  depth  averages  122 
meters,  though  near  Venice  172.5  meters  were  penetrated  without 
reaching  bottom.  The  delta  deposits  of  the  Ganges  and  Brahma- 
putra rest  on  older  sediments  and  average  only  20  meters  in  thick- 
ness. The  actual  delta  deposits  of  the  Mississippi  range  from  9.5 
to  1 6  meters  near  New  Orleans,  increasing  to  30  meters  at  the 
head  of  the  passes,  beyond  which  the  thickness  rapidly  increases. 
They  rest  throughout  on  a  stiff  blue  clay  of  earlier  age.  The  Rhone 


6io  PRINCIPLES    OF    STRATIGRAPHY 

delta  in  Lake  Geneva  has  a  thickness  of  180  to  275  meters  and  a 
length  of  nearly  two  English  miles. 

Delta  Slopes.  The  surface  of  the  delta  has  always  a  gentle 
slope,  this  being  steeper  in  the  smaller  deltas  than  in  the  larger  ones, 
and  steeper  also  in  the  deltas  of  coarse  material  than  in  those  of  fine 
silts.  The  frontal  slope  of  the  delta  is,  as  a  rule,  much  steeper, 
being  sometimes  as  high  as  25°  or  30°,  or  in  some  cases  even  35° 
in  the  small  deltas  of  Pleistocenic  and  modern  lakes.  In  the 
larger  deltas,  especially  those  on  the  sea  coast,  the  frontal  slope 
is  much  gentler.  The  strata  of  the  Rhone  delta  in  Lake  Geneva 
•are  so  slightly  inclined  that  they  almost  take  on  a  horizontal  atti- 
tude. The  total  thickness  of  this  delta,  180  to  275  meters,  is  dis- 
tributed over  nearly  2  miles.  The  frontal  slope  is  i  to  18.  A 
much  gentler  slope  is  seen  in  the  delta  of  the  same  stream  in  the 
Mediterranean,  where  the  rate  is  I  in  160,  the  depth  increasing 
from  4  to  40  fathoms  in  the  distance  of  6  or  7  miles  from  the  mouth 
of  the  stream. 

Deltas  of  small  lakes  often  show  a  steeper  inclination  for  the 
older  coarser  beds  than  for  the  finer  younger  ones.  Thus  the  delta 
of  the  Aar  in  the  Lake  of  Brienz  shows  near  the  shore  an  inclina- 
tion of  the  beds  amounting  to  30  degrees.  About  300  meters  from 
the  shore  the  grade  has  decreased  to  20  degrees,  while  at  the  ex- 
treme margin  of  the  present  delta,  1,100  to  1,200  meters  from  the 
shore,  the  beds  are  nearly  horizontal.  The  delta  of  the  Dundelbach 
in  the  southwest  angle  of  the  little  Lake  of  Lungern  in  Switzer- 
land shows  coarse  beds  near  the  margin,  sloping  at  an  angle  of  35 
degrees,  while  the  younger  layers  have  a  very  gentle  slope  only. 

The  Bird-foot  Delta  of  the  Mississippi.  The  lower  part  of 
the  Mississippi  delta  has  a  remarkable  form,  distinguishing  it 
from  all  other  modern  deltas.  From  Forts  Jackson  and  St.  Philip 
onward  for  a  distance  of  nearly  25  mile's  the  river  is  confined  in  a 
narrow  channel  or  "neck"  which  finally  divides  at  the  "Head  of  the 
Passes"  into  three  divergent  channels,  or  passes,  each  bordered 
by  low  banks  of  stiff  clay  and  forming  a  structure  resembling  a 
bird's  foot.  One  of  these  passes,  the  Pass  a  1'Outre,  divides  again 
into  the  North  Pass  and  the  Northeast  Pass.  The  other  two,  the 
South  Pass  and  the  Southwest  Pass,  continue,  as  single  narrow  fin- 
gers, the  latter  for  nearly  20  miles.  Some  distance  above  the  head 
of  the  passes  a  similar  channel,  the  Main  Pass,  extends  northward, 
and  still  farther  up  a  group  of  small  channels  diverges  from  the 
neck.  The  material  composing  the  banks  of  the  neck  and  the 
passes  is  wholly  unlike  ordinary  river  silt,  though  in  general  a  thin 
superficial  layer  of  this  occurs.  Primarily,  however,  the  banks 


THE    MISSISSIPPI    DELTA 


611 


consist  of  a  stiff  blue  clay  not  unlike  the  stiff  "Port  Hudson  clays" 
(Hilgard-29)  which  underlie  the  whole  delta.  Such  mud  is  brought 
to  the  surface  in  a  series  of  mud  volcanoes  or  mud-lumps  which, 
from  time  to  time,  arise  on  the  delta  surface.  These  are  believed  by 
Hilgard  to  be  formed  of  the  fine  mud  brought  down  by  the  river 
and  precipitated  outside  of  the  delta  by  flocculation.  Over  this 
liquid  mud  are  spread  the  river  sediments,  the  weight  of  which  and 
that  of  the  growing  marshes  and  their  pressure  upon  the  mud 


FIG.  126.  The  Mississippi  Delta.  At  the  "bird  foot"  the  passes  are  from 
,right  to  left:  North  Pass,  Northeast  Pass  (these  two  unite  to 
form  the  Pass  a  1'Outre),  South  Pass,  Southwest  Pass.  The 
Northeast  Pass  has  a  small  southern  branch,  the  Southeast  Pass 
(not  shown),  while  another  group  of  channels,  diverges  from  the 
"neck"  about  five  miles  above  the  "head  of  the  passes." 

layers  result  in  local  upheavals  and  formation  of  mud  lumps  or 
craters,  as  long  ago  suggested  by  Lyell.  Rod  soundings  in  such 
a  crater  have  reached  a  depth  of  24  feet,  but  no  solid  bottom. 
The  mud  flow  from  these  craters  varies  with  the  stages  of  the  river, 
becoming  much  more  lively  in  times  of  flood,  when  great  masses  of 
water,  or  of  silt  brought  down  by  the  river,  press  upon  the  layer 
of  liquid  mud.  Hilgard  believes  that  the  banks  of  the  neck  and  the 
passes  are  formed  of  the  disintegrated  and  redeposited  mud  from 
such  mud  lumps,  and  that  when  a  mud  lump  arises  in  the  channel, 
as  has  recently  occurred,  a  division  is  likely  to  take  place.  Hilgard 


612  PRINCIPLES    OF    STRATIGRAPHY 

testifies  to  the  tough,  resistant  character  of  this  clay,  which  when 
wet  is  almost  inerodable  by  pure  water.  (29.) 

Structure  and  Composition  of  the  Delta.  Theoretically  the  delta 
consists  of  bottom-set,  fore-set,  and  top-set  beds.  These  are  all 
well  developed  in  the  small  deltas  formed  in  Pleistocenic  time  in 
temporary  ice-dammed  lakes  and  now  open  to  examination  after 
the  draining  of  these  lakes.  In  the  deltas  on  the  sea  coast,  however, 
one  or  the  other  of  these  beds  is  often  absent,  or  two  may  merge, 
this  being  most  frequently  the  case  with  the  fore-set  and  bottom- 
set  beds. 

The  fore-set  beds  of  small  or  young  deltas  are  generally  steeply 
inclined,  as  already  noted.  This  is  especially  the  case  when  the 
supply  of  detritus  is  large.  As  the  delta  increases  in  size  the  later 
fore-set  beds  become  more  flattened  and  bend  over  at  the  bottom 
into  the  horizontal  bottom-set  beds.  The  upper  ends  of  the  fore- 
set  beds,  on  the  other  hand,  show  more  or  less  of  erosion  and 
across  their  truncated  edges  are  deposited  the  top-set  beds.  There 
may,  of  course,  be  at  times  a  bending  over  of  the  top-set  beds  into 
the  fore-set,  but  in  the  young  delta  the  contact  is  more  or  less  sharp. 
In  the  larger  deltas  of  fine  material,  on  the  other  hand,  the  top-set 
beds  may  be  more  or  less  continuous  with  the  fore-set,  and,  indeed, 
the  two  may  imperceptibly  grade  into  each  other,  without  even  a 
change  in  angle. 

The  top-set  beds  of  small  deltas  consist  of  the  coarser  material 
laid  down  in  nearly  horizontal  beds.  If  we  assume  that  the  normal 
delta  begins  as  a  subaqueous  detrital  cone  or  semi-cone  growing 
in  circumference,  it  is  apparent  that  fore-set  and  bottom-set  beds 
alone  exist  during  the  earlier  stages.  As  the  radius  of  the  cone 
increases,  its  summit  is  invariably  truncated  by  the  waves  and  by  the 
stream  itself,  which  carries  the  detritus  out  to  the  front  of  the  cone. 
Thus  a  level  plane  is  formed  partly  by  non-deposition  and  partly  by 
contemporaneous  erosion  truncating  the  fore-set  beds.  Its  surface 
will  be  to  some  extent  below  water  level,  the  depth  depending  on 
the  strength  of  the  wave  activity.  Upon  this  plane  will  be  deposited 
the  top-set  series  which  the  current  can  no  longer  carry  to  the  edge 
of  the  growing  delta.  The  top-set  series  will  continue  to  grow  in 
thickness  and  extent  as  the  delta  grows,  and  its  landward  part  will 
begin  to  emerge  and  become  subaerial.  The  extent  to  which  this 
subaerial  part  of  the  top-set  series  will  grow  is  determined  by 
the  strength  of  the  river  and  the  slope  which  it  can  control.  In 
smaller  deltas  the  frontal  angle  of  the  delta  is  also  the  junction 
between  top-set  and  fore-set  beds  and  marks 'the  extent  of  sub- 
mergence of  the  delta.  In  larger  deltas  the  top-set  beds  go  deeper. 


STRUCTURE   OF   DELTAS  613 

Examination  of  deltas  permanently  or  temporarily  laid  dry 
shows  that  the  structure  is  by  no  means  a  uniform  or  simple  one 
throughout.  Thus  the  delta  of  the  Dundelbach,  laid  open  to  obser- 
vation by  the  partial  drying  of  the  Lake  of  Lungern  into  which  it 
was  built,  showed  striking  variation.  Near  its  head  it  consists  of 
beds  of  coarse  and  fine  gravel,  sloping  at  an  angle  of  about  35 
degrees.  Large,  flat  rock  fragments  rest  with  their  surfaces  on 
the  inclined  gravel  layers,  and  a  bed  of  compressed  bituminous 
woods  and  leaves,  six  inches  in  thickness,  is  interbedded  with  these 
gravels  in  one  part  of  the  section.  In  general,  the  successive  in- 
clined layers  are  only  a  few  inches  thick;  and  this  thickness  does 
not  increase  toward  the  lower  end  in  the  coarser  layers.  In  the 
fine  mud  layers,  however,  there  is  an  increase  in  thickness  down- 
ward before  the  layers  bend  over  horizontally  at  the  bottom.  These 
finer  textured  layers  rest  gently  against  the  steeper,  coarser  ones, 
filling  especially  the  angle  between  the  steeper  layers  and  the  flat 
lake  bottom. 

The  numerous  (20  or  more)  well  borings  made  into  the  con- 
fluent deltas  of  the  Po,  Etch,  and  Brenta,  in  the  region  about 
Venice,  have  revealed  the  fact  that  the  structure  of  the  delta  is  an 
extremely  heterogeneous  one.  While  the  beds  are,  in  general, 
horizontal,  with  only  minor  undulations,  the  succession  is  scarcely 
the  same  in  any  two  of  the  bore  holes.  This  proves  that  the 
beds  of  the  delta  form  a  succession  of  lenticular  masses,  of  very 
limited  extent.  Only  two  sandy  layers,  carrying  water,  have 
proved  in  any  way  constant;  all  other  layers  quickly  wedge  out 
laterally.  (See  the  combination  of  profiles  given  by  Credner- 
14:  pi.  I,  Fig.  o.)  The  successive  layers  comprise  brown  clays 
alternating  with  yellowish  sands  with  lignites  and  occasionally 
layers  containing  marine  organisms.  The  series  includes  several 
beds  with  molluscan  remains.  Marine  molluscs,  especially  Cardi- 
acea,  abound  in  the  higher  fossiliferous  layers,  while  in  the  deeper 
beds  only  occurs  the  intermingling  with  these  of  fresh-water  types. 
In  some  wells  lignites  with  associated  land  snails,  such  as  Succinea, 
Pupa,  Helix,  etc.,  were  found.  Vegetable  material  occurs  at  four  suc- 
cessive horizons  in  the  Po  delta  down  to  a  depth  of  100  meters.  The 
material  is  the  same  as  that  now  forming  marshlands  on  the  coast 
of  the  Adriatic.  This  and  the  occurrence  of  the  land  snails  in  the 
lower  beds  would  suggest  subsidence  since  delta-building  began 
here.  The  borings  near  Venice  show  that  about  one-third  of  the 
material  making  up  the  upper  sixty  meters  of  the  delta  ground  con- 
sists of  lignite  and  peat. 

Quite  a  different  picture  from  this  is  presented  by  the  mud 


614  PRINCIPLES    OF    STRATIGRAPHY 

deposits  of  the  Nile.  At  low  water  these  are  visible  in  the  steep 
banks  which  then  rise  8  to  10  meters  above  water  level.  The  hard- 
ened Nile  mud  forms  a  series  of  horizontal  beds  varying  in  thick- 
ness from  a  few  inches  to  several  feet,  and  looks  more  like  an  an- 
cient stratified  series  than  like  a  modern  deposit.  The  material  of 
the  Nile  mud  is  a  more  or  less  uniformly  fine-grained  one,  the 
size  of  the  grains  varying  from  1/13  to  i/ioo  mm.,  rarely  reaching 
i/io  mm.  in  size.  It  is  a  unique  deposit  probably  not  paralleled  by 
any  other  modern  one  on  the.  face  of  the  earth.  An  analysis  of 
the  mud  (Clarke-i2 1481)  gave: 

SiO2 45.10 

A12O3 15-95 

Fe203 13-25 

MgO 2 . 64 

CaO 4.85 

K2O 1.95 

Na20 0.85 

S03 0.34 

H20 15.54 


100.47 

The  remarkable  fact  about  this  mud  is  its  high  iron  and  low  organic 
content,  though  some  analysts  have  found  the  finely  divided  or- 
ganic matter  as  high  as  5.53  per  cent,  or  even  7.9  per  cent.  Some 
analyses  show  an  admixture  of  barium  carbonate  over  wide  areas. 

In  other  deltas  the  organic  material  is  pronounced.  The  abun- 
dant admixture  of  leaves  and  more  or  less  lignitized  wood  in  some 
deltas  has  already  been  noted.  In  the  Po  delta  it  occurs  in  four 
successive  horizons.  In  the  Ganges  delta  such  deposits  are  found 
between  9  and  15  meters  in  depth,  together  with  carbonized  trunks 
of  trees  characteristic  of  the  region,  such  as  Heritiera  littoralis, 
which  abounds  in  the  lower  part  of  Bengal.  In  the  lower  Mississippi 
delta  driftwood  is  common,  the  logs  being  at  times  united  into 
floating  rafts.  Not  infrequently  erect  trunks  are  found  among 
these,  with  their  roots  spreading  in  all  directions,  as  if  while  grow- 
ing there  they  were  submerged  by  a  subsidence.  The  Mackenzie 
River  delta  likewise  contains  an  abundance  of  carbonized  drift- 
wood, and  this  is  true  of  many  other  deltas. 

More  striking,  however,  in  some  ways  is  the  abundance  of 
finely  divided  vegetable  matter  in  some  deltas.  Thus  the  mud 
of  the  Vistula  (Weichsel)  loses,  according  to  G.  Bischof  (9)  23.3 
per  cent,  on  ignition,  most  of  this  being  organic  material.  The 
clay  of  the  Vistula  delta  in  the  Bay  of  Dantzig  is  so  rich  in  or- 
ganic material  that  it  has  a  deep  black  color,  and  is  locally  known 


ORGANIC    REMAINS    OF    DELTAS  615 

as  pitch,  "pech."  The  bearing  of  this  fact  on  the  origin  of  some 
black  shales  will  be  considered  later. 

Organisms  of  the  Delta.  Marine  organisms  are  not  uncommon 
in  sea-coast  deltas,  but  they  are,  as  a  rule,  distributed  in  certain 
layers  only.  Lyell  has  explained  the  occurrences  of  marine  molluscs 
in  extensive  beds  between  the  fresh  water  layers  of  the  delta  as  due 
to  wave  work,  which  casts  masses  of  shells  upon  the  growing  delta 
surface.  In  some  parts  of  the  Rhone  delta  marine  and  fresh  water 
shells  alternate  in  the  deposit.  This  is  explained  by  Lyell  as  probably 
due  to  the  alternating  occupancy  of  lagoons  and  channels  on  the 
growing  delta  by  salt  or  by  fresh  water,  according  as  the  prevailing 
wind  or  other  causes  may  ordain.  As  already  noted,  the  delta  of 
the  Po  also  contains  fresh  water  organisms  associated  with  marine 
shells,  but  only  in  the  lower  beds,  while  upward  the  shell  deposits 
become  purely  marine.  Foraminiferal  shells  often  abound  in  mod- 
ern deltas.  Thus  the  Mississippi  mud  was  found  to  contain  an 
abundance  of  marine  Polygastrica  and  Phytolitharia  as  well  as 
fresh  water  Polythalamia.  Phytolitharia  also  abound  in  the  mud  of 
the  Nile.  Indeed,  the  range  of  foraminiferal  shell  material  in  the 
Nile  mud  is  from  4.6  to  10  per  cent.,  while  the  Ganges  carries  as 
high  as  12.4  or  even  25  per  cent,  of  foraminiferal  material. 

Other  animal  remains  have  been  found,  but  are  less  abundant. 
Remains  of  arthropods  occur  in  the  Po  delta  sometimes  in  close  as- 
sociation with  the  lignites.  Remains  of  river  animals  also  abound 
in  modern  deltas,  as  shown  by  the  presence  of  turtles  and  croco- 
dile remains  in  the  delta  deposits  of  the  Ganges  and  the  Zambesi. 
Terrestrial  vertebrate  remains  have  likewise  been  found  in  these 
deltas,  among  them  bones  of  recent  antelope,  buffalo,  lion,  hippo- 
potamus, and  other  mammals. 

Gaseous  Emanations  of  Deltas.  The  gradual  decomposition 
of  the  organisms  in  the  delta  deposits  gives  rise  to  gaseous  emana- 
tions which  either  escape  through  artificial  borings  in  the  delta  or 
find  natural  passageways  through  the  mud,  building  up  craters 
as  in  the  mud-lumps  of  the  Mississippi  delta.  The  numerous  bor- 
ings in  the  delta  of  the  Po  have  furnished  an  abundance  of  inflam- 
mable gas,  the  use  of  which  for  illuminating  purposes  has  actually 
been  attempted.  Sulphuretted  hydrogen  is  also  developed,  espe- 
cially where  sea  water  comes  in  contact  with  the  decaying  vege- 
table matter,  as  noted  in  the  case  of  marine  marshes  (see  ante, 
page  493).  In  the  mud-lumps  of  the  Mississippi  delta,  the  volume 
of  gas  emitted  is  between  1/20  and  1/30  that  of  the  mud  flow 
from  these  craters.  The  gas  is  probably  not  instrumental  in  these 
mud  eruptions,  but  merely  an  accompaniment  of  the  same. 


6i6  PRINCIPLES    OF    STRATIGRAPHY 

Cementation  of  Delta  Deposits.  The  delta  deposits  may  be 
compacted  merely  by  pressure,  or  the  component  particles  may  be 
bound  together  by  the  introduction  of  a  cement.  The  Rhone  delta 
contains  much  sandstone,  the  grains  of  quartz  being  bound  by  a 
calcareous  cement,  due  to  the  abundance  of  lime  in  the  stream. 
The  presence  of  numerous  limestone  pebbles  in  glacial  deltas  also 
becomes  a  source  of  lime  which  is  redeposited  among  the  pebbles 
and  cements  them.  Such  an  example  is  found  in  the  partly  con- 
solidated, gravels  of  the  Pleistocenic  delta  in  the  Ontario  basin  near 
Lewiston,  and  a  still  more  extensive  one  in  the  Nagelfluh  delta  of 
the  Salzburg  region  already  referred  to.  Cementation  by  infiltrated 
iron  oxides  also  occurs. 

Deposits  of  lime  are  especially  abundant  in  deltas  of  arid 
regions,  such  as  the  Volga,  the  Indus,  the  Nile,  and  the  Colorado. 
Extensive  deposits  of  massive  travertine  and  caliche  have  been 
formed  in  Arizona  and  New  Mexico.  Such  deposits  are,  how- 
ever, also  found  where  the  river  water  is  high  in  lime  content,  as 
in  the  Rhine  delta  and  in  the  Rhone  delta  already  mentioned.  In 
the  latter  case  the  approach  to  a  semi-arid  climate  over  the  delta 
in  the  mediterranean  is  a  further  factor  aiding  deposition  of  lime. 
The  silt  of  the  Rhine  delta  in  the  Lake  of  Constance  contains 
30.76%  of  CaCO3,  1.24%  MgCO3,  and  5.20%  FeCO3.  The  other 
principal  constituents  are  SiO2  50.14%,  A12O3  4.77%,  Fe2O3  2.69%, 
and  small  quantities  of  the  oxides  of  manganese,  magnesium,  cal- 
cium, potassium,  and  sodium. 

Modification  of  the  Delta  Surfaces.  The  chief  modifications 
suffered  by  the  delta  are  wave  and  wind  erosion,  and  the  forma- 
tion of  deposits  over  the  surface  of  the  delta.  Wind  erosion  affects 
the  surface  of  the  delta,  while  wave  erosion  occurs  around  the 
margin  of  the  delta  when  the  force  of  the  river  no  longer  is  able 
to  continue  construction.  It  is  common  on  a  sinking  coast,  as 
is  shown  by  the  encroachment  of  the  sea  on  the  deltas  bordering  the 
North  Sea.  Wave  erosion  may  also  become  effective  when  delta- 
building  has  practically  come  to  an  end  owing  to  the  decrease  of 
supply  incident  to  development  of  low  relief  with  old  age.  In  such 
a  case  the  sea  may  gradually  encroach  on  the  delta  and  plane  away 
the  upper  layers,  until  the  remaining  remnant  of  the  delta  is  wholly 
submerged,  when  normal  marine  sediments  may  succeed.  In  all 
such  cases  there  is  commonly  found  a  fringing  belt  of  dunes  at 
the  outer  margin  of  the  delta,  as  in  the  case  of  the  Rhine  delta. 
Such  dunes  may  also  be  formed  where  building  is  still  in  progress, 
as  in  the  Rhone  delta,  where  dunes  are  formed  between  the  two 
principal  mouths  of  the  stream.  Other  eolian  deposits  may  form 


MODIFICATION    OF   DELTA  617 

.»-*•» 

on  the  delta,  such  as  dust  brought  from  a  distance  and  wind- 
arranged  material  from  the  surface  of  the  delta  itself.  Additional 
river  deposits  in  the  form  of  natural  levees  may  be  built  by  the 
overflowing  river,  which  leaves  much  of  its  material  near  the  bank, 
which  is  thus  raised  above  the  surface  of  the  delta  on  either  side. 
The  floor  of  the  channel  may  also  be  raised  by  aggradation,  and 
the  river  thus  flows  at  a* level  much  higher  than  that  of  the  sur- 
rounding country.  Where  the  levees  are  artificially  raised  the 
river  bed  may  come  to  occupy  a  position  far  above  the  normal 
level  of  the  delta  or  flood  plain.  Thus  the  channel  of  the  Po  has 
been  elevated  in  this  manner  to  such  an  extent  that  it  is  said  to 
rise  above  the  tops  of  the  houses  in  the  town  of  Ferrara  (Le  Conte- 
36:^).  Where  the  sea  temporarily  floods  part  of  the  delta,  de- 
posits of  salt  may  occur,  as  in  the  Rann  of  Cutch  and  other  low- 
lying  delta  districts.  The  Nile  delta  is  likewise  characterized  by 
saline  deposits  along  the  coast,  due  to  evaporation  of  the  sea  water 
which  at  intervals  floods  the  surface.  Over  these  salt  beds  sand 
dunes  are  seen  to  wander.  Deposits  of  vegetal  material  in  swamps 
further  characterize  many  delta  surfaces.  Such  deposits  may  be 
marine  marsh  deposits  or  fresh  water  swamp  deposits,  or  both. 
Salt  and  gypsum  deposits  are  not  uncommon  on  the  lower  part  of 
the  deltas  in  arid  climates. 

Relation  of  Delta  Building  to  Crustal  Movements.  From  the 
known  relations  of  rivers  to  delta  building  it  would  appear  that 
periods  of  strong  river  activities  are  also,  as  a  rule,  periods  of 
pronounced  delta  formation,  while,  conversely,  periods  of  dimin- 
ished river  work  will  be,  on  the  whole,  periods  of  slow  and  com- 
paratively limited  delta  building.  In  general,  youthful  ungraded 
conditions  of  a  land  with  corresponding  high  relief  favor  delta 
building,  while  mature  or  graded  conditions  characteristic'of  regions 
of  low  relief  are  correspondingly  unfavorable  to  delta  building. 
There  are,  however,  modifying  circumstances  which  may,  to  a  cer- 
tain extent,  reverse  these  results,  but  as  a  general  working  proposi- 
tion they  may  be  confidently  accepted.  Furthermore,  conditions  of 
youth  and  high  relief  with  active  river  work  are  productive  of  an 
abundance  of  coarse  waste,  which  will  result  in  the  outward  and 
upward  building  of  deltas  with  strongly  contrasted  slopes  in  fore-set 
and  top-set  beds,  while  the  finer  waste  supplied  in  lesser  quantities 
by  a  region  of  relative  maturity  will  tend  to  build  outward  deltas 
of  gently  inclined  layers  and,  on  the  whole,  of  uniformity 
of  slopes  or  confluence  of  top-set,  fore-set,  and  bottom-set  beds. 
In  youthful  regions  of  much  waste  supply  the  subaerial  part  of 
the  delta  will  become  a  prominent  feature,  while  the  reverse  will 


6i8  PRINCIPLES    OF    STRATIGRAPHY 

be  true  in  regions  past  maturity  and  of  slight  supply  of  waste. 
It  is  thus  readily  conceivable  that  periods  of  intensive  and  extensive 
delta -building  may  alternate  in  the  earth's  history  with  periods 
during  which  deltas  are  of  relatively  insignificant  extent  and  the 
size  and  number  of  deltas  in  one  period  afford  no  criterion  by  which 
those  of  another  may  be  measure^. 

Effect  of  subsidence.  While  the  effect  of  stationary  sea-level 
will  be  the  rapid  outward  building  of  the  delta,  with  pronounced 
development  of  the  fore-set  beds,  slow  subsidence  will  result  in 
the  extensive  development  of  top-set  beds  and  a  restriction  in  the 
building  of  the  fore-set  beds.  If  the  subsidence  is  periodic  and 
interrupted,  the  sea  will  temporarily  encroach  on  the  delta,  and 
the  terrestrial  top-set  beds  will  be  covered  by  a  layer  of  marine 
sediments.  Continued  deposition  by  the  rivers  will,  however,  crowd 
back  the  sea,  and  renewed  building  of  top-set  beds  will  occur.  In 
this  manner  intercalated  marine  layers  will  be  formed  between  the 
terrestrial  deposits.  Such  layers  are  found  in  modern  deltas  as 
already  noted,  and  they  are  also  common  in  older  delta  deposits, 
where  they  are  generally  taken  as  indicating  the  marine  origin  of 
the  entire  formation.  That  they  have  no  such  value  is  clearly 
shown  by  their  relation  to  the  continental  beds  in  modern  delta 
deposits.  If  subsidence  were  slow  and  more  or  less  regular,  con- 
tinued deposition  by  rivers  would  tend  to  keep  the  sea  out  altogether, 
and  a  thick  deposit  of  top-set  beds  of  terrestrial  origin  would  result. 
Such  deposits  of  considerable  thickness  are  found  to  characterize 
the  larger  modern  deltas,  which  thus  appear  to  occupy  sites  of 
continued  subsidence.  Similar  conditions  prevailed  over  the  sites 
of  delta  deposits  of  Mesozoic  and  Palaeozoic  time,  resulting  in  the 
formation  of  continental  deposits  of  great  thickness. 

Subsidence  of  such  a  rate  as  to  be  in  excess  of  the  building 
power  of  the  streams  will  put  an  end  to  the  process  of  building  the 
deltas  and  result  in  their  final  submergence.  This  has  been  brought 
about  in  a  number  of  cases  where  former  deltas  and  parts  of 
deltas  are  now  below  sea-level.  In  earlier  geologic  periods  such 
complete  submergence  has  resulted  in  the  burial  of  the  delta  de- 
posit beneath  a  marine  series  of  greater  or  less  thickness.  Credner 
(14)  and  others  have,  indeed,  held  that  any  subsidence  is  detri- 
mental to  the  process  of  delta  building,  and  that  such  stuctures  are 
found  only  on  rising  or  at  least  stationary  coasts.  That  subsidence 
has,  however,  played  a  part  in  the  formation  of  modern  deltas  is 
shown  by  the  presence  in  most  of  them  of  terrestrial  remains  and 
peat  layers,  etc.,  which  now  lie  at  a  considerable  depth  beneath 
sea-level  (Fig.  127). 


DELTAS,    AND    CRUSTAL    MOVEMENTS 


619 


Effect  of  elevation.  Slight  elevation  of  the  delta  area  results 
in  the  destruction  by  erosion  of  the  top-set  series  in  the  upper  parts 
of  the  delta,  and  the  carrying  forward  of  the  material  to  be  added 
to  the  subaqueous  fore-set  series.  The  zone  over  which  continental 
deposition  takes  place  will  also  advance  seaward,  and  thus  terres- 
trial sediments  will  come  to  rest  on  marine  deposits.  Where  the  in- 
clination of  the  fore-set  beds  is  very  gentle  these  terrestrial  beds  may 
come  to  rest  upon  them  with  practically  no  change  in  dip.  Cessation 
of  elevation  or  reversal  of  movement  and  the  resumption  of  normal 
delta  building  will  result  in  the  deposition  of  a  new  terrestrial 
series  on  top  of  the  erosion  plane,  and  a  new  marine  series  on  top 
of  the  terrestrial  series  nearer  the  sea.  A  hiatus  and  discon- 
formable  relationship  will  thus  appear  between  the  two  members  of 
the  terrestrial  part  of  the  delta,  and  this  disconformity  will  be  re- 


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/V-..  L:_ L_  I    _i-  it.-      j :  i_7r^    •*"'  -^^^^^^g".-;  •  •<  •.-  =  •  .•  •  •  -._  •• ;  -. ,-  -  ..  ..  /  '.*»,•;!  ~:.  -  ~A  ,  *.*  • : 


,,  _       ..-.  ^ 

Conh'nental  delta   deposiKs.  ..F      ^v; 


»*E   ^  ^^^,^.^^^^-i 
~~&l     -=~      \#, 


~  *Vj?'~-  •-.'?:••::••»  =   ".^^^^^^m^^^ug^^^^^v-  :•.'..'.-,•.•  /(Y  :.:  •*''>'•'*  \'i'  '••  •.-•"^•'-.' 

FIG.  127.  Diagrammatic  section  of  a  seashore  delta,  showing  the  relation 
of  continental  and  submarine  deposits  in  a  region  of  fluctuating 
sea-level.  (After  Barrell.) 

placed  seaward  by  a  terrestrial  layer  interpolated  between  two 
marine  series.  If  the  delta  front  is  comparatively  steep  it  may, 
of  course,  happen  that  the  uplift  carries  the  erosion  to  the  top  of 
the  delta  front,  beyond  which  deposition  will  be  submarine.  In 
a  very  large  delta  slow  rising  will  result  in  the  slow  seaward  migra- 
tion of  the  zones  of  erosion  and  the  zone  of  terrestrial  deposition, 
the  lowering  of  the  upper  part  of  the  delta  by  erosion  progressing 
steadily,  while  at  the  same  time  the  zone  of  terrestrial  deposition 
extends  farther  and  farther  outward.  (Barrell-6.) 

Deltas  Merging  into  Desert  Deposits.  A  remarkable  combina- 
tion of  a  river  delta  with  desert  deposits,  on  the  one  hand,  and 
marine  deposits,  on  the  other,  is  shown  by  the  Colorado  on  the 
Arizona-California  and  Lower  California  boundary.  This  delta  was 
originally  built  into  the  Gulf  of  California,  the  head  of  which  was 
by  it  completely  severed  from  the  main  part  of  this  funnel  sea. 
The  cut-off  portion  dried  out  completely  under  the  influence  of 


620  PRINCIPLES    OF    STRATIGRAPHY 

the  drying  westerlies,  leaving  the  arid  Coahuila  basin  north  of  the 
delta,  the  central  portion  of  which  is  300  feet  below  sea-level ; 
while  southward  the  delta  enters  the  present  head  of  the  California 
Gulf.  Occasionally  a  northwest  distributary  of  the  Colorado,  the 
New  River,  carries  water  into  the  basin,  which  in  the  past  has 
filled  to  overflowing,  a  fresh  water  lake  being  thus  formed.  The  dry- 
ing up  of  this  left  saline  deposits  upon  the  lacustrine  beds,  and 
these,  together  with  the  eolian  and  occasional  river  deposits,  form  a 
complicated  series  of  sediments  succeeding  the  former  marine  de- 
posits of  the  region,  all  of  these  changes  being  brought  about 
without  any  change  in  the  sea-level.  A  moderate  subsidence  or  a 
partial  destruction  of  the  delta  would  let  the  sea  in  again,  and  thus 
marine  deposits  would  once  more  succeed  the  complicated  terres- 
trial series.  The  area  thus  affected  is  somewhere  in  the  neighbor- 
hood of  5,000  square  miles.  (Fig.  69,  Chapter  IX.) 


COLORS    OF    CONTINENTAL    CLASTICS. 

The  color  of  clastic  rocks  depends  to  a  very  large  degree  upon 
the  states  of  oxidation  of  its  iron  content,  and  the  absence 
or  abundance  of  carbon.  A  low  state  of  oxidation  gives  colors 
ranging  from  green  to  blue,  while  the  higher  states  of  oxidation 
are  marked  by  yellow,  orange,  brown,  or  red  colors.  According 
to  the  carbon  content,  the  color  may  vary  from  white,  when  no 
carbon  is  present,  through  various  shades  of  gray  to  black.  Abun- 
dant carbon  in  the  strata  will  prevent  oxidation  of  the  iron  and 
will  reduce  the  higher  oxides  to  the  lower.  Lack  of  carbon  favors 
high  oxidation. 

Sediments  deposited  on  land  or  in  very  shallow  waters  are 
especially  subject  to  oxidation,  unless  there  is  an  abundance  of 
organic  matter  present  to  prevent  such  oxidation.  In  moist  or 
pluvial  climates  with  a  moderate  amount  of  vegetation,  the  soil 
is  apt  to  be  bluish  from  the  prevention  of  a  high  degree  of  oxidation 
by  the  vegetation.  This  is  especially  true  where  the  vegetation  is 
intimately  associated  with  the  soil.  The  manner  in  which  this  is 
accomplished  on  the  western  side  of  Nicaragua  has  already  been 
referred  to  (p.  36).  Where  black  soils  are  formed,  as  on 
swampy  surfaces,  especially  on  low  alluvial  plains  or  peneplains, 
oxidation  is  likewise  prevented.  The  same  thing  is  true  of  delta 
deposits  rich  in  carbon.  Where,  however,  vegetation  is  extremely 
luxuriant  it  may  prevent  the  saturation  of  the  soil  with  moisture 
through  transpiration  and  likewise  prevent  a  satisfactory  commin- 


COLORS  OF   CONTINENTAL   CLASTICS  621 

gling  of  the  vegetation  with  the  soil.  In  such  cases  oxidation  may 
proceed  without  hindrance,  as  in  the  case  of  the  eastern  slopes  of 
Nicaragua,  where  red  soil  from  3  to  10  meters  deep  underlies  the 
dense  vegetation. 

In  seasons  of  dryness,  when  the  amount  of  vegetation  is  small, 
the  iron  of  the  sediments  of  deltas  and  alluvial  fans  may  become 
thoroughly  oxidized.  Where  dryness  prevails  for  most  of  the 
year,  and  where  vegetation  is  as  a  result  scanty,  such  oxidation 
may  be  especially  favored.  Thus  semiarid  or  even  desert  regions 
would  furnish  the  best  conditions  for  such  oxidation.  On  river 
flood  plains  there  is  always  sufficient  moisture  to  result  in  the 
formation  of  hydroxides  of  iron,  and  hence  the  colors  of  such 
deposits  will  range  from  yellows  to  ocher  and  brown.  It  is  only 
under  conditions  of  intense  heat  that  dehydration  will  result  with 
a  consequent  change  in  color  toward  the  reds.  Such  change  of 
color  may,  however,  take  place  as  the  result  of  aging  of  the  deposit, 
as  pointed  out  by  Crosby.  In  such  a  case  dehydration  is  virtually 
spontaneous,  and  "...  the  color  of  the  deposit,  so  far  as  it 
is  due  to  ferric  oxide,  is,  other  things  being  equal,  a  function  of  its 
geological  age."  "In  other  words,"  says  Crosby  further,  "the  color 
naturally  tends  with  the  lapse  of  time  to  change  from  yellow  to 
red;  and,  although  this  tendency  exists  independently  of  the  tem- 
perature, it  is  undoubtedly  greatly  favored  by  a  warm  climate." 

(150 

Barrell  (4:288)  holds  that  "a  still  more  potent  cause  exists 
Ir  .  .  in  the  dehydration  effected  by  the  great  increase  in  pres- 
sure and  moderate  rise  in  temperature  which  takes  place  upon 
the  burial  of  the  material  to  some  thousands  of  feet  beneath  later 
accumulations."  Under  such  pressure  the  tendency  would  be  for 
the  oxide  to  give  up  its  water  with  corresponding  reduction  in 
volume  (see  ante,  p.  177),  just  as  shales  are  formed  by  the  giving 
off  of  about  one-half  the  combined  water  by  the  silicate  of  alumina, 
and  this  at  temperatures  probably  often  far  below  boiling  point. 

It  is,  of  course,  necessary  that  organic  matter  should  be  absent 
from  such  a  deposit,  for  its  presence  would  prevent  oxidation  in 
the  first  place.  It  is  not  necessary  that  the  absolute  amount  of  iron 
should  be  very  large  to  affect  the  color  of  the  deposit.  The  bril- 
liant red  Vernon  shales  of  the  eastern  New  York  Siluric  carry 
only  2.25  per  cent,  of  ferric  iron  and  0.75  per  cent,  of  ferrous  iron 
(Miller-39).  The  chief  desideratum  is  that  the  iron  should  be  in 
an  extremely  fine  state  of  subdivision  and  intimately  disseminated 
or  diffused  through  the  mud  or  dust  deposits.  This  fine  division 
and  diffusion  of  the  iron  have  been  noted  by  Dawson  for  the  red 


622  PRINCIPLES    OF    STRATIGRAPHY 

Mississippic  beds  of  Nova  Scotia,  where  the  iron  has  "the  aspect 
of  a  chemical  precipitate  rather  than  of  a  substance  triturated  me- 
chanically" (20:^5).  The  same  thing  has  been  noted  by  Hilgard 
with  regard  to  the  red  tropical  soils,  where  the  percentage  of 
ferric  oxide  is  by  no  means  markedly  high,  but  where  the  oxide 
is  very  finely  diffused  throughout  the  mass. 

Finely  diffused  oxide  of  iron,  but  in  the  state  of  ferric  hydrate, 
is  the  coloring  agent  of  the  yellow  loess  of  China.  The  total  amount 
of  ferric  oxide  in  American  loess  ranges  from  2.50  per  cent  to  3.74 
per  cent.,  and  in  one  case  to  5.22  per  cent.,  while  a  limited  amount 
of  FeO  (from  0.12  to  1.02%)  is  also  present,  but  organic  carbon 
is  very  slight,  ranging  from  0.09  to  0.19  per  cent.  Dehydration  of 
the  iron  with  age,  especially  after  burial,  would  result  in  the  forma- 
tion of  fine-grained  red  deposits,  in  every  respect  similar  to  the 
Vernon  red  shales. 

The  red  Vernon  shales,  like  red  shales  and  sandstones  fre- 
quently, are  associated  with  salt  and  gypsum  deposits.  This  is 
an  indication  of  arid  conditions  during  the  deposition  of  the  muds 
from  which  these  shales  are  formed.  Salt  and  gypsum  deposits  of 
the  present  time  are  associated  with  gray  and  bluish-gray  muds 
and  it  is  only  by  subsequent  oxidation  and  dehydration  that  the 
red  color  is  produced. 

One  of  the  essentials  in  the  production  of  red  rocks  by  such 
subsequent  oxidation  and  dehydration  appears  to  be  the  virtual 
absence  of  organic  matter  which  would  prevent  oxidation.  Where 
the  ground  water  level  is  high  organic  matter  will  accumulate  and 
oxidation  is  prevented.  But  where  the  sands  and  muds  are  ex- 
posed to  circulating  air  in  dry  seasons,  with  a  low  ground  water 
level,  more  or  less  complete  oxidation  of  the  iron  will  take  place. 
Such  a  condition  is  found  in  delta  deposits  of  arid  regions,  as,  for 
example,  the  Nile  delta,  in  which  organic  matter  seems  to  be  of 
very  small  amount,  while  the  iron  content  is  comparatively  high. 
It  is  probable  that  the  Nile  mud  on  aging  would  take  on  a  red  color. 

There  is,  however,  another  factor  which  may  affect  the  change 
in  color,  and  that  is  the  lime  carbonate  content  of  the  deposit.  This 
is  high  in  many  delta  deposits  of  arid  regions  and  its  presence  may 
prevent  the  production  of  a  red  color  by  the  formation  of  complex 
silicates  of  lime,  iron,  and  alumina.  According  to  Ries  (4.7:6,  n) 
a  buff  or  cream  color  is  produced  if  clay  containing  three  times  as 
much  lime  as  iron  or  more  is  burned  into  bricks.  Magnesia  has 
the  same  coloring  effect  on  the  burned  ware  as  lime,  while  alkalies 
tend  to  turn  the  iron  red  into  a  brown.  As  the  Rhine  delta  in  the 
Lake  of  Constance  has  nearly  12  times  as  much  lime  carbonate  as 


COLORS   OF   CONTINENTAL   CLASTICS  623 

iron  oxide,  it  would  not  produce  red  bricks,  and  it  is  not  improb- 
able that  the  lime  would  have  the  same  effect  in  preventing  the 
formation  of  a  red  color  with  age. 

Alternation  of  Red  Beds  with  Those  of  Other  Colors.  This  is 
a  feature  often  found  in  older  formations  and  has  also  been  ob- 
served in  modern  continental  hydroclastics.  Huntington  (34:36^)  has 
described  such  deposits  of  pinkish  or  reddish  sandy  clays  and  sands 
alternating  with  whitish  or  greenish  clays  from  the  uplifted  and 
dissected  Pleistocenic  deposits  of  the  basin  of  Seyistan  in  eastern 
Persia.  These  layers  are  well  shown  in  cliffs  from  400  to  600  feet 
high,  exposed  by  recent  erosion.  The  red  beds  are  continuous  and, 
while  preserving  their  general  aspect  for  many  miles,  they  vary 
greatly  in  detail.  Wedging  out  layers  of  sand  or  even  gravel  occur, 
slight  erosion  disconformities,  occasional  ripple  marks,  worm-casts 
and  rain-drops  are  not  uncommon,  and  the  uniform  oxidation  of 
these  beds  indicates  long  exposure  to  the  air  under  conditions  of 
aridity.  This  is  further  shown  by  the  condition  of  the  modern 
delta  deposits  of  the  region,  of  which  the  subaerial  part  is  well 
drained  and  aerated  and  everywhere  of  a  light  brown  color.  On  the 
shores  of  the  modern  Lake  of  Seyistan,  where  the  clayey  beds  are 
saturated  with  water  and  subject  to  successive  floodings,  the  brown 
colors  are  replaced  by  light  colored  soils  with  black  bands.  The 
margin  of  the  present  lake  supports  a  dense  growth  of  reeds  and 
the  clay  deposits  on  its  bottom  are  greenish  and  white.  The  green- 
ish and  whitish  beds  of  the  dissected  older  deposits  correspond  to 
these  lake  sediments.  They  represent  subaqueous  deposits  formed 
during  the  greater  extent  of  the  lake,  and  in  continuity  and  uni- 
formity, as  well  as  color,  they  contrast  strongly  with  the  pink  and 
red  beds  formed  during  the  contraction  of  the  lake  as  subaerial 
sediments. 

Alternating  red  and  white  layers  of  this  type  are  characteristic 
of  the  Moencopie  formation  of  northern  Arizona  and  southern 
Utah,  a  deposit  of  Permic  age.  The  absence  of  fossils  and  the 
general  close  correspondence  between  these  beds  and  the  series 
exposed  in  the  dissected  basin  of  Seyistan  have  led  Huntington  to  the 
conclusion  that  both  have  a  similar  origin. 

Alternations  of  gray  and  green  sandstones  with  red  clays  are 
well  shown  in  the  Middle  Siwalik  group,  a  late  Tertiary  deposit 
exposed  in  the  foothills  of  the  Himalayas.  As  previously  noted, 
this  formation  represents  a  fluviatile  deposit,  of  the  type  now  form- 
ing over  the  Indo-Gangetic  plain.  A  corresponding  Devonic  ex- 
ample is  seen  in  the  Catskill  formation  of  eastern  New  York  and 
Pennsylvania,  where,  through  a  thickness  of  perhaps  5,000  feet, 


.  624 


PRINCIPLES    OF    STRATIGRAPHY 


there  is  a  constant  alternation  of  red  shales  and  greenish  sand- 
stones. The  physical  characteristics  of  the  deposit  and  the  absence 
of  marine  and  presence  of  land  and  fresh  water  organisms  show 
that  this  series  was  formed  under  fluviatile  conditions  similar  to 
those  of  the  Siwalik. 

Lateral  variation  in  color  is  also  a  frequent  feature  of  older 
deposits  and  can  be  explained  ^by  the  contemporaneous  beds  now 
forming  in  the  Seyistan  basin,  where  the  oxidized  subaerial  de- 
posits merge  laterally  into  the  unoxidized  subaqueous  or  lacustrine 
ones.  The  fossiliferous  Permic  limestones  and  shales  of  Kansas 
may  be  traced  southward  into  red  sandstone  and  shales  of  the 
same  age  in  Oklahoma,  the  latter  being  practically  unfossiliferous. 
These  red  clays  may  be  in  part  the  residual  clays  from  dissolved 
limestones  (Beede-7)  and  in  part  of  clastic  origin.  Their  high 
state  of  oxidation  suggests  widespread  subaerial  deposition  under 
sufficiently  arid  conditions  to  permit  the  free  influence  of  the 
atmosphere.  Lateral  variation  of  a  more  irregular  character  is 
shown  in  some  Mesozoic  clays,  such  as  the  Potomac  group  of  the 
Atlantic  coast,  and  the  Cretacic  Atlantosaurus  or  Como  beds  of 
Wyoming,  and  in  the  Tertiary  beds  of  the  Wind  River  and  Big- 
horn basins  and  elsewhere.  In  the  Wasatch  and  Wind  River 
clays  analyses  have  shown  the  iron  content  to  be  as  follows  f  Sin- 
clair and  Granger-52  11/5)  : 


Horizon 

Total  Iron 

Total  Iron 

Phase 

calculated  as 

Fe203 

FeO 

Fe2O3 

I. 

Mottled    (red  and  blue)    clay, 

Wind  River  

red 

8.16 

o.  19 

7.91 

blue 

6.67 

0.38 

6.24 

2 

Blue  clay,  Wasatch 

blue 

-J     T.A 

O    S2 

2.  77 

3- 

Red  clay,  Wasatch,  same  locality 

red 

4.82 

0.58 

4.18 

Sinclair  and  Granger  comment  on  these  analyses  as  follows :  "In 
all  the  samples  examined,  the  total  iron  in  the  red  clays  is  in  excess 
of  that  present  in  the  blue  by  1.48  per  cent,  to  1.49  per  cent.  The 
amount  of  ferrous  iron  in  the  blue  Wasatch  clay  is  less  than  that 
present  in  the  red,  while  in  the  mottled  Wind  River  clay  it  is 


COLORS   OF   CONTINENTAL   CLASTICS  625 

slightly  greater  in  the  blue  than  in  the  red  phase,  but  in  neither 
case  does  it  seem  possible  to  ascribe  the  blue  color  to  ferrous  oxide, 
as  this  substance  is  far  exceeded  in  amount  by  ferric  iron,  evidently 
occurring  in  the  blue  clay  in  some  other  form  than  ferric  oxide 
(hematite),  perhaps  as  a  hydrous  silicate.  In  the  Wasatch  clay 
the  red  contains  1.41%  more  Fe2O3  than  the  blue;  in  the  Wind 
River  clay  Fe2O3  in  the  red  phase  is  1.67%  greater  than  in  the  blue. 
If  this  excess  of  iron  is  present  in  the  form  of  hematite,  as  the  red 
color  seems  to  show,  it  is  possible  that  the  remaining  iron  in  the 
red  clay  may  be  in  the  same  form  as  in  the  blue  (a  hydrous  sili- 
cate?) and  that  the  blue  color  has  been  masked  by  the  red  pig- 
ment." 

'The  results  of  analysis  seem  to  show  that  the  blue  color  has 
not  been  derived  from  the  red  by  reduction  of  the  iron  as  ordinarily 
understood.  The  red  color  may  have  been  derived  from  the  blue  by 
conversion  of  the  hypothetical  silicate  into  carbonate  by  meteoric 
waters,  and  the  subsequent  oxidation  of  these  salts,  or  by  the  intro- 
duction of  iron  compounds  in  solution  and  their  concentration  and 
oxidation  possibly  under  drier  climatic  conditions  than  existed 
during  the  deposition  of  the  blue  clays.  We  favor  the  latter  alterna- 
tive and  regard  the  coloration  of  the  clays  as  a  phenomenon  con- 
trolled by  conditions  active  during  the  deposition  of  each  individual 
stratum  (red  or  blue,  as  the  case  may  be),  and  not  by  subsequent 
or  secondary  changes.  Under  the  arid  conditions  which  exist  at 
present  over  most  of  the  Wind  River  and  Bighorn  basins,  the 
blue  clays  show  no  tendency  to  weather  red.  The  layer  of  weath- 
ered mud-cracked  clay  on  the  surface  of  bad  land  slopes  cut  in  the 
blue  clays  is  yellow  from  the  hydrous  oxide,  limonite."  (  $2 :/ 15, 
116.) 

Original  Red  Color  of  Sediments.  Whatever  the  case  above 
mentioned  shows,  it  must  not  be  overlooked  that  some  sediments 
when  deposited  already  have  a  decidedly  red  color,  or  that  this  may 
be  acquired  before  burial.  Soils  washed  from  regions  of  extensive 
laterite  formation  will  be  deposited  as  red  sediments  either  on 
land  or  in  the  sea.  Such  sediments  may  be  carried  great  distances 
from  regions  where  they  are  formed  to  regions  where  their  pro- 
duction is  prohibited  by  the  local  climatic  conditions.  Russell  held 
that  the  red  sands  of  the  Newark  system  were  deposited  with  a 
coating  of  red  iron  oxide  formed  during  decomposition.  This  con- 
clusion may,  however,  be  questioned. 

Desert  sands  not  infrequently  have  their  grains  coated  with 
a  thin  deposit  of  iron  oxide  which  often  gives  the  sands  a  brilliant 
color,  as  in  the  case  of  the  carmine  sands  of  the  Nefud  desert  of 


626  PRINCIPLES    OF    STRATIGRAPHY 

northern  Arabia.  The  source  (57:^5)  of  the  iron  is  believed  to  be 
in  the  sand  itself,  as  shown  by  analysis,  the  coating  having  formed 
under  the  influence  of  the  sun's  heat,  as  the  desert  varnish  forms 
on  the  larger  pebbles  and  boulders.  This  latter,  however,  is 
subject  to  destruction  owing  to  the  size  of  the  fragments,  for 
Walther  has  observed  that  after  a  hea-vy  rain  this  brown  coating 
is  quickly  removed  by  the  impact  of  the  rock  masses.  In  like  man- 
ner a  coating  of  iron  oxide  on  sand  grains  subject  to  wind  trans- 
port must  be  destroyed,  and  this  probably  accounts  for  the  almost 
uniform  white  or  golden  color  of  desert  sands.  The  absence  of 
such  a  coating,  then,  on  the  pebbles  of  ancient  desert  gravels 
need  not  be  surprising,  and  the  yellow  or  white  color  of  gravel 
and  coarse  sand  beds  intercalated  between  red  deposits  may  not 
necessarily  indicate  great  climatic  differences,  but  may  result  rather 
from  the  destruction  of  the  color  coat  in  the  coarser  material. 


EXAMPLES    OF   OLDER   CONTINENTAL   HYDRO- 
CLASTICS. 

Examples  of  fluviatile  and  lacustrine  deposits  have  been  rec- 
ognized in  nearly  all  geological  horizons,  from  the  pre-Cambric  to 
the  present.  Not  all  stratigraphers  agree  in  regarding  the  forma- 
tions enumerated  below  as  of  unequivocally  non-marine  origin,  but 
the  more  obviously  fluviatile  and  glacial  formations  are  recognized 
as  such  by  most  recent  students  of  the  subject. 

CENOZOIC   OR  TERTIARY   EXAMPLES. 

Among  the  Tertiary  deposits  of  the  Great  Plains  regions  of  the 
western  United  States  are  many  beds  showing  stratification,  but 
composed  in  large  part  of  alternate  pebble  and  sand  beds,  with 
cross-bedding  structure  well  marked.  These  have  commonly  been 
classed  as  "lake  deposits,"  but,  as  Davis  (19:345)  has  shown,  these 
are  more  likely  deposits  made  by  running  water,  and  represent 
outwash  plains  or  alluvial  fans,  formed  by  the  streams  from  the 
mountains.  Some  of  these  deposits,  as  in  the  case  of  the  Vermillion 
Creek  beds  in  Wyoming,  consist  near  the  mountains  from  which 
they  have  been  derived  of  excessively  coarse  conglomerates  be- 
tween 3,000  and  4,000  feet  thick,  nearly  structureless,  lines  of 
stratification  being  rarely  perceived,  "The  blocks  of  which  the  con- 
glomerate is  chiefly  formed  range  from  the  size  of  a  pea  to  masses 
with  a  weight  of  several  tons  .  .  ."  (King-35  :j<5p.)  At  some 


TERTIARY  CONTINENTAL   HYDROCLASTICS     627 

distance  from  the  mountains  the  beds  consist  of  coarse  red  sand- 
stones interbedded  with  clays  and  arenaceous  marls.  In  the  Arapa- 
hoe  and  Denver  formations  of  Colorado,  basal  conglomerates  from 
50  to  200  feet  in  thickness  are  succeeded  by  arenaceous  clays,  and 
these,  in  turn,  are  followed  by  400  feet  of  eruptive  debris,  above 
which  are  again  conglomerates  and  sands  derived  from  the  moun- 
tains. Cross-bedding  and  wedging  out  of  layers  are  common,  show- 
ing a  considerable  current.  In  some  of  the  beds  "tree  stumps  in 
erect  position  with  roots  in  mud  layers  and  broken  trunks  in  sand 
or  gravel  .  .  ."  occur  (Cross-i6:id#)  and  contemporaneous 
lava  flows  are  interbedded  with  the  sediments. 

In  these  deposits  the  remains  of  terrestrial  vertebrates  are  fre- 
quently abundant,  while  fresh  water  animals  are  found  only  where 
temporary  bodies  of  water  existed.  Associated  with  typical  atmo- 
clastic  are  lacustrine  deposits,  often  rich  in  remains  of  fish  or 
other  fresh  water  animals,  and  eolian  deposits  (anemoclastics). 
Not  infrequently  the  atmoclastics  extend  out  covering  either  lacus- 
trine or  eolian  deposits. 

The  Eocenic  and  Oligocenic  deposits  of  the  Wind  River  and 
Bighorn  basins  in  Wyoming  have  already  been  referred  to.  These 
deposits  consist  of  clays  and  sands  often  well  banded  and  alternat- 
ing red  and  bluish  in  color,  of  arkose  sands,  and  of  conglomerates 
and  occasional  fine  tuffs  or  pyrolutytes.  They  contain  land  and 
river  vertebrates,  such  as  crocodiles,  turtles,  garpike,  Eohippus, 
Heptodon,  Lambdotherium,  etc.,  and  shells  of  Unio.  Microscopic 
as  well  as  macroscopic  study  of  the  deposits  has  shown  that  they 
are  derived  from  the  crystalline  or  other  rocks  of  the  enclosing 
mountains,  and  their  character  and  mode  of  occurrence  show  that 
they  were  either  wind  or  river  transported.  In  the  coarser  sand- 
stones and  arkoses  of  the  Wind  River  and  Bridger  ( ?)  beds, 
Archaean  granites  and  Palaeozoic  quartzites  are  readily  recognizable. 
"The  well-rounded  gravels,  found  in  some  of  the  arkoses,  point 
with  equal  certainty  to  running  water  as  the  transporting  agent, 
while  fluviatile  deposition  is  shown  by  the  frequent  channels  filled 
with  coarse  sandstone  which  cut  irregularly  across  the  finer  clays, 
by  the  frequent  interstratification  of  sandstone  lenses  with  the  clays 
and  by  the  presence  in  the  latter  of  fish,  crocodiles,  and  turtles, 
and  occasional  beds  of  Unios.  Local  swamps  are  indicated  by 
lignites  in  the  blue  clays  and  sandstones,  but  never  in  the  red 
clays." 

Sometimes  change  in  climate  or  steepening  of  grade  is  indi- 
cated by  coarsening  of  sediments  .  .  .  "for  instance,  the 
coarse,  frequently  cross-bedded  arkose  forming  the  lower  member 


628  PRINCIPLES    OF    STRATIGRAPHY 

of  the  so-called  Bridger  of  the  Beaver  Divide  appears  to  represent 
a  series  of  conjoined  alluvial  fans  spreading  out  over  the  banded 
clays  of  the  Wind  River,  but  it  is  not  possible  to  say  whether  the 
gravels  and  sands  were  transported  by  torrential  streams  under 
a  dry  climate  or  by  streams  whose  carrying  capacity  had  been  in- 
creased by  uplift."  (Sinclair  and  Grange r~52  :uj.)  The  fresh- 
ness of  the  feldspars  indicates  that  they  had  not  been  leached  by 
carbonated  waters,  such  as  might  be  expected  to  occur  if  they 
were  deposited  in  a  region  of  high  humidity.  This  also  suggests 
that  they  have  not  been  derived  from  the  parent  rock  by  ordinary 
weathering  processes,  but  rather  by  temperature  changes,  which 
shatter  the  minerals  without  affecting  their  freshness.  Altogether, 
the  deposits  suggest  dry,  not  necessarily  arid,  climate,  with  rapid 
changes  of  temperature  and  rapid  transportation  for  short  dis- 
tances and  burial  beyond  the  reach  of  carbonated  waters. 

The  clays  of  the  Wasatch  and  Wind  River  deposits  are  com- 
monly banded,  alternating  beds  of  red  and  blue-green  clay  or  of  red 
with  mottled  clay  occurring.  "The  red  clays  are  frequently  streaked 
with  blue-green  color  along  joint  cracks  or  are  traversed  by  anas- 
tomosing green  lines  along  what  may  have  been  the  courses  of 
roots.  The  beds  are  lenticular  in  shape,  varying  from  a  few 
inches  in  thickness,  with  little  horizontal  extent,  to  strata  from  18 
inches  to  50  feet  in  thickness,  traceable  sometimes  for  several 
hundred  yards  to  a  mile  or  more.  .  .  .  Lignite  is  never  found 
in  the  red  clays,  but  may  be  present  in  the  blue.  .  .  ."  The  fos- 
sils found  in  the  red  beds  are  always  fragmentary,  "the  more  re- 
sistant parts,  such  as  jaws  and  teeth,  predominating.  In  the  blue 
and  mottled  clays  associated  skeletons  ...  of  Coryphodon 
were  found."  (Sinclair  and  Granger-52  1114,  -f/5.)  The  microscope 
has  not  revealed  any  essential  difference  between  the  variously 
colored  clays. 

Sinclair  and  Granger  ascribe  the  color  banding  to  the  alternation 
of  moist  and  dry  climatic  conditions,  though  no  evidence  of  exces- 
sive aridity  has  been  found ;  the  fauna  of  the  red  and  blue  bands 
being  the  same.  "The  clays  cannot  owe  their  color  to  different 
sources  of  supply,  for  they  are  microscopically  the  same  and  the 
alternation  of  color  bands  is  too  regular  and  of  too  frequent  re- 
currence to  permit  this  inference.  The  red  clay  cannot  represent 
upland  oxidized  wash,  for  waters  swift  enough  to  carry  the  bone 
fragments  found  in  the  clay  would  also  transport  rock  fragments 
of  some  size,  and  these  are  not  found."  The  blue  clays  of  the 
Wasatch  are  sometimes  lignitic  and  often  afford  associated  skeletal 
remains,  and  this  suggests  that  they  were  formed  during  cycles 


TERTIARY   CONTINENTAL   HYDROCLASTICS     629 

of  more  abundant  rainfall,  when  the  surface  of  the  intermontane 
basin  was  prevented  from  drying  out  rapidly.  The  red  clays,  how- 
ever, appear  to  have  been  formed  "during  the  drier  cycles,  when 
the  carbonaceous  matter  of  decaying  plants  was  completely  oxidized, 
concentration  and  oxidation  of  iron  compounds  occurred,  and  ani- 
mal bones  exposed  at  the  surface  were  weathered  and  broken  be- 
fore entombment."  Conditions  of  this  kind  seem  to  have  been 
widespread,  as  shown  by  similar  color 'banding  in  the  Wasatch  in 
other  localities. 

In  the  Wasatch  formation  along  the  contacts  of  red  and  blue 
beds  or  in  many  of  the  red  beds  themselves  great  numbers  of 
fragmentary  jaws  and  scattered  teeth  of  vertebrates  have  been 
found.  The  clays  appear  to  represent  the  deposits  on  the  dry  basin 
floor  over  which  the  bones  of  these  creatures  were  scattered  and 
weathered  before  being  buried.  In  the  blue  clays  associated  skele- 
tons are  common.  These  are  the  remains  of  animals  which  were 
either  drowned  and  rapidly  covered  beneath  fluviatile  sediments  or' 
were  mired  in  the  soft  clays.  The  teeth  found  in  the  Wind  River 
area  usually  have  the  roots  worn  away  and  only  the  harder  enamel- 
covered  crowns  are  preserved.  The  Unio  beds  of  the  Wasatch  are 
always  of  limited  extent  and  seem  to  be  confined  to  the  blue  clays. 
The  lignite  layers  in  these  clays  are  usually  mere  dirt  bands,  but 
some  in  the  Wind  River  basin  have  considerable  thickness  (52:1/7). 

The  Oligocenic  beds  of  this  region  contain  limestone  deposits 
associated  with  wind-laid  volcanic  tuffs.  These  limestones,  which 
are  found  near  the  top  of  the  series,  are  a  spring  deposit  forming 
sheets  of  tufaceous  limestone,  or  layers  of  white  nodular  masses, 
calcareous  without,  but  containing  more  or  less  silica  within.  Worn 
quartz,  feldspar,  and  pink  granite  pebbles  are  sometimes  found  in 
the  limestone,  which  is  also  partly  replaced  by  silica  in  the  form 
of  opal  or  chalcedony.  No  fossils  have  been  found  in  the  lime- 
stone, which  appears  to  have  been  formed  under  relatively  dry 
climatic  conditions. 

These  Tertiary  deposits  on  the  eastern  slopes  of  the  Rockies 
have  thus  all  the  characteristics  of  deposits  formed  under  semiarid 
conditions.  These  conditions  prevail  to-day  in  this  region  under 
the  influence  of  the  westerly  winds,  which,  on  crossing  the  Coast 
Range,  where  they  leave  most  of  their  moisture,  become  still  drier 
on  crossing  the  Rockies.  Greater  elevation  of  the  mountain  ranges 
would  probably  increase  .the  aridity  of  the  Interment  basins  in  this 
region  and  so  reestablish  the  conditions  of  Tertiary  time. 

Hobbs  (31)  has  recently  described  a  typical  torrential  forma- 
tion of  great  thickness  from  southern  Spain.  This  ranges  in  age 


630  PRINCIPLES    OF    STRATIGRAPHY 

from  Miocenic  to  the  present.  Its  material  is  derived  from  the  crys- 
tallines of  the  Sierra  Nevada,  from  the  northern  flanks  of  which  it 
extends  for  twenty-five  miles,  and  locally  from  the  Triassic  dolo- 
mite of  the  Sierra  Harana  (Alhambra  formation).  The  formation, 
approaching  a  thousand  feet  in  thickness,  is  a  conglomerate  near 
the  mountains  with  pebbles  varying  "from  a  fraction  of  an  inch  to 
six  inches  or  more  in  length."  Within  the  various  stream  valleys 
local  peculiarities  of  rock  material  exist,  corresponding  to  the  pecu- 
liarities of  the  rocks  in  the  respective  headwater  branches  of 
these  streams.  At  a  distance  from  the  mountains  fine  material 
prevails,  much  of  it  of  a  loess-like  character,  indicating  wind  and 
playa-lake  deposition.  Floated  plant  material,  such  as  roots  and 
brushes,  appear  to  be  characteristic  of  some  of  the  finer  deposits. 
These  torrential  deposits  seem  to  be  intimately  related  to  the 
semiarid  conditions  of  the  interior  of  Spain,  caused  by  the  monsoon 
winds.  These  winds  blow  northward  from  the  Mediterranean  in 
summer,  crossing  the  Sierra  Nevada  and  leaving  much  of  their 
moisture  on  the  southern  slopes.  Descending  the  northern  slopes 
they  are  relatively  drying  winds  and  so  permit  the  formation  of 
these  periodic  torrential  deposits. 

Similar  torrential  deposits  of  great  thickness  and  ranging  in 
age  from  late  Tertiary  to  the  present  are  described  from  southern 
Italy  (31:^90).  A  marked  pross-bedding  structure,  already  re- 
ferred to  (Fig.  123),  so  similar  to  what  is  commonly  found  in  an- 
cient sandstones,  is  characteristic  of  many  of  these  deposits.  The 
Siwalik  formation  of  India  has  already  been  cited  as  a  subaerial 
deposit  of  similar  character  and  age.  It  is  of  great  interest  in  that 
it  reaches  the  enormous  thickness  of  15,000  feet.  Here  also  belongs 
in  part  the  Mollasse  of  the  Alps.  This  is  a  complex  series  of 
light-colored  sandstones  and  conglomerates  with  occasional  lime- 
stones, found  in  the  Alpine  forelands,  in  the  south  of  Germany  and 
in  Switzerland.  The  lower  part  of  the  Mollasse  is  of  Oligocenic  age 
and  begins  as  a  marine  series.  In  southern  Germany  this  reaches  in 
places  a  thickness  of  600  meters  (Bavaria)  and  is  followed  by  an 
immense  series  of  fresh  water  sands  and  conglomerates  approach- 
ing a  thousand  meters  in  thickness.  This  series  shows  in  part 
brackish  water  and  in  part  fluviatile  and  lacustrine  conditions.  The 
brackish  water  phase  contains  Cyrena,  Cerithium,  Cytherea,  etc., 
and  the  fresh  water  Limngeus,  etc.  Numerous  leaves  and  other 
remains  of  land  plants  (Cinnamomum,  Juglans,  Quercus,  Betula, 
Rhamnus,  etc.)  are  found  locally,  forming  what  is  known  as 
"Blattermollasse"  and  forming  occasional  beds  of  brown  coal, 
which  is  extensively  exploited  in  the  Bavarian  fore-Alps.  Red  sedi- 


TERTIARY    CONTINENTAL    HYDROCLASTICS     631 

ments  forming  the  "red  Mollasse"  are  frequent  in  the  upper  non- 
marine  part  of  the  Oligocenic  Mollasse,  especially  in  Switzerland, 
but  occur  also  in  upper  Swabia.  The  red  beds  are  generally  fol- 
lowed by  conglomerates  with  pebbles  ranging  in  size  from  that  of 
an  egg  to  that  of  a  man's  head  and  locally  kown  as  Nagelfluh. 
These  in  places  reach  a  great  thickness.  Away  from  the  Alps  the 
material  becomes  finer.  The  Miocenic  Mollasse  succeeding  this 
often  begins  with  calcareous  beds  to  a  large  extent  formed  of  the 
shells  of  the  land  snail,  Helix  rugulosa  (Rugulosa  limestones). 
This  is  followed  by  a  series  of  loose  sands,  glauconitic  sandstones 
and  conglomerates  (Nagelfluh)  several  hundred  meters  thick  in  the 
southern  part  of  the  region.  The  lower  part  of  this  series  is  again 
purely  marine,  but  the  upper  part  is  once  more  brackish  and  non- 
marine,  beds  containing  Cardium  sociale,  Melanopsis,  etc.,  marking 
the  brackish  portion ;  sands  with  Paludina,  Unio,  and  Chara  fruits, 
marking  the  lacustrine  and  fluviatile.  These  series  constitute  the 
Middle  Mollasse.  The  highest  beds  finally  forming  the  Upper 
Mollasse  of  Upper  Miocenic  age  are  again  wholly  non-marine. 
They  consist  of  sands,  clays,  marls,  occasional  thin  beds  of  brown 
coal,  local  volcanic  tuffs  and  especially  non-marine  limestones. 
These  so-called  Sylvana  limestones  consist  of  the  shells  of  the  land 
snails  Helix  sylvana  and  H.  inftexa,  of  those  of  the  pond  and  river 
snails  Planorbis,  Limnseus,  etc.  Bones  of  the  mastodon  also  occur. 
Other  beds  contain  an  abundance  of  the  shells  of  the  river  and 
lake  molluscs,  Unio,  Anodonta,  Limnseus,  Melania,  Melanopsis, 
etc.  Local  deposits  of  thin  marly  limestones  with  plant  (maple, 
poplar,  etc.)  and  insect  remains  also  occur,  as  in  the  celebrated  de- 
posit of  Oningen  on  the  Lake  of  Constance  (Bodensee)  and 
local  deposits  like  those  of  the  Steinheim  basin  with  its  sands 
filled  with  Planorbis,  Helix,  and  land  vertebrates.  Remains  of 
terrestrial  vertebrates  abound  in  all  of  these  deposits. 

Since  the  axis  of  the  Alps  is  parallel  to  the  direction  of  the  rain- 
bringing  winds,  both  sides  receive  an  abundant  rainfall,  though 
within  the  mountains  are  dry  valleys.  The  extensive  formation  of 
the  Mollasse,  partly  of  subaerial  origin  on  the  northern  side  of  the 
Alps,  suggests  a  different  condition  during  Tertiary  times,  so  as  to 
result  in  a  more  arid  condition  on  the  north,  or,  at  any  rate,  in  con- 
ditions which  would  favor  the  formation  of  extensive  alluvial  fans. 

MESOZOIC   EXAMPLES   OF    CONTINENTAL   HYDROCLASTICS. 

The  Potomac  Formation  of  the  Atlantic  coast  of  North  America 
represents  a  series  of  delta  and  flood  plain  deposits  comparable 


632  PRINCIPLES    OF    STRATIGRAPHY 

to  those  of  the  Huang-ho  and  the  Indo-Gangetic  plain.  Extensive 
torrential  deposits  are  absent  here,  the  series  being  composed  mainly 
of  sands  and  clays.  The  series  goes  back  to  late  Jurassic  or  early 
Comanchic  time,  and  comprises  four  'main  divisions,  the  Patuxent, 
Artindel,  Patapsco,  and  Raritan.  The  organic  remains  in  these 
deposits  are  chiefly  land  plants,  while  the  remains  of  a  land  fauna 
have  also  been  found.  No  marine  organisms  are  known  except  in 
the  upper  part  of  the  series,  the  Magothy  formation  of  New  Jer- 
sey, which,  however,  also  contains  land  plants.  Above  this  series 
lie  sands  and  clays  with  an  Upper  Cretacic  marine  fauna.  These 
deposits  were  spread  upon  a  broad  coastal  belt  by  rivers  coming 
from  the  region  of  Palaeozoic  and  older  strata  on  the  northwest, 
where  peneplanation  was  in  progress.  The  sea  margin  at  this  time 
must  have  been  some  distance  farther  to  the  east  than  the  present 
coast.  The  rivers  were  numerous  and  more  or  less  evenly  spaced, 
so  as  to  produce  a  continuous  series  of  confluent  deltas  which  ex- 
tended from  Massachusetts  to  the  Gulf  of  Mexico.  Landward  the 
subdivisions  of  this  series  are  separated  by  erosion  disconformities, 
marking  periodic  upwarpings,  but  seaward  they  become  thicker, 
and  the  disconformities  probably  disappear.  Somewhere  east  of 
the  present  coast  line  these  deposits  probably  pass  into  a  continu- 
ous marine  series,  now  submerged. 

The  fluviatile  origin  of  these  deposits  is  suggested  by  the  dis- 
continuity of  the  strata,  beds  and  lenses  of  clay  and  gravel  occurring 
in  sand  and  vice  versa.  Many  of  the  clays  are  strongly  variegated 
in  color,  the  state  of  oxidation  of  the  iron  varying  both  horizontally 
and  vertically,  while  concentrated  segregations  of  the  iron  also  oc- 
cur. Such  variable  conditions  for  oxidation  exist  on  river  flood 
plains,  but  not  in  lakes  or  on  the  sea  bottom.  The  abundant  plant 
remains,  which  by  their  character  show  little  transportation,  as 
well  as  the  absence  of  marine,  brackish  or  even  lacustrine  organ- 
isms, strongly  indicate  fluviatile  -conditions,  as  do  also  the  bones 
of  dinosaurs,  turtles,  and  crocodiles. 

The  Arundel  formation  appears  to  have  been  deposited  within 
stream  valleys  eroded  in  the  Patuxent,  and  in  this  formation  gyp- 
sum has  been  found.  This  suggests  greater  aridity  during  the 
period  of  deposition  of  this  formation  than  during  the  time  the 
more  widely  spread  sands  and  clays  of  the  other  divisions  accumu- 
lated. In  the  Raritan  formation  feldspathic  sands  occur,  further 
suggesting  an  increase  in  aridity,  while  lignitic  quartz  sands  alter- 
nating with  highly  oxidized  sands  testify  to  a  variety  of  conditions. 
Some  of  the  quartz  sands  show  the  characteristics  of  dune  deposits. 
Upward  the  occurrence  of  lignites  with  Teredo  borings  marks  the 


MESOZOIC  CONTINENTAL  HYDROCLASTICS      633 

beginning  of  marine  invasion,  the  river  building  processes  being 
overcome  by  the  invading  forces  of  the  sea.  (See  further, 
Barrell-6.) 

The  Red  Beds  of  North  America.  The  Red  Beds  of  the  Rocky 
Mountain  region 'and  the  similar  red  sandstones  of  the  Newark 
formation  of  the  eastern  United  States  are  now  generally  recognized 
as  subaerial  deposits,  in  part  of  fluviatile  and  in  part  of  eolian 
origin,  with  subordinate  lacustrine  and  rarely  estuarine  conditions. 
The  source  of  the  western  red  beds  was  the  old  Palseocordilleran 
chain  of  mountains  formed  at  the  end  of  the  Palaeozoic,  and 
extending  northwestward  from  Arizona  to  northern  California. 
On  the  Pacific  side  of  this  chain  marine  Triassic  and  Jurassic  beds 
were  forming,  while  east  of  the  range  a  series  of  alluvial  fans  ac- 
cumulated, these  being  now  in  part  represented  by  the  Red  beds. 
Their  highly  oxidized  character  indicates  that  accumulation  was 
under  semi-arid  climatic  conditions,  such  as  would  prevail  with  a 
westerly  wind  sweeping  over  a  mountain  chain  of  sufficient  height 
to  deprive  it  of  most  of  its  moisture.  That  vegetation,  neverthe- 
less, existed  in  some  parts  of  the  mountain  slopes  is  shown  by 
the  abundance  of  the  petrified  woods  preserved  in  these  deposits, 
into  which  they  were  probably  carried  by  torrential  streams.  Ac- 
cording to  Williston  and  Case  (59)  the  upper  Red  beds,  from 
Lander,  Wyoming,  on  the  north  to  New  Mexico,  Kansas,  and  Texas, 
on  the  south,  range  from  five  hundred  to  possibly  a  thousand  feet 
in  thickness  and  are  ''barren  or  almost  barren  measures  character- 
ized by  light  colors  of  the  sandstone,  often  of  eolian  origin,  and 
more  or  less  interspersed  or  capped  with  massive  beds  of  gypsum." 
It  may  be  added,  however,  that  some  authors  still  hold  to  the  ma- 
rine theory  of  origin  of  these  beds.  (See,  especially,  Henning-28.) 

Vertebrate  fossils  of  Triassic  (Keuper)  age  are  reported  from 
all  along  the  line  of  outcrop,  chiefly  comprising  phytosaurs  and 
labyrinthodonts,  closely  agreeing-  with  species  from  the  European 
Keuper.  Some  of  the  lower  Red  beds  of  the  southern  and  western 
region  are  of  Permic  age,  and  indicate  the  earlier  commencement 
of  this  type  of  sedimentation. 

Triassic  Red  Beds  of  Eastern  North  America  and  of  Europe. 
The  Newark  series  is  likewise  best  regarded  as  forming  local 
remnants  of  a  combination  of  widespread  alluvial  fans,  river  flood 
plain,  and  eolian  deposits,  derived  from  the  Appalachians  to  the 
west  and  built  out  toward  the  east  on  the  low  coastal  plain,  or  into 
depressions,  and  under  conditions  of  semi-aridity  which  permitted 
pronounced  oxidation  of  the  sediments.  The  beds  themselves 
abound  in  shrinkage  cracks,  raindrop  impressions  and  animal  foot- 


634  PRINCIPLES    OF    STRATIGRAPHY 

prints.  Fish  remains  and  shells  of  Estheria  are  found  in  inter- 
calated black  shales,  and  terrestrial  plant  remains  are  not  uncom- 
mon in  some  sections.  Much  feldspar  occurs  and  this  together 
with  the  oxidation  of  the  iron  compounds  indicates  the  relative 
aridity  of  the  climate.  Intrusive  sheets  and  lava  flows  characterize 
the  northern  development,  and  coal  beds  the  southern.  Barrell 
and  Kummel  have  brought  forward  evidence  in  the  sediments  that 
a  part  of  the  material  in  Connecticut  and  in  New  Jersey  was  de- 
rived from  the  east  as  well  as  from  the  west.  They  therefore 
consider  the  deposits  as  formed  in  large  basins  bounded  by  faults, 
rather  than  accumulations  on  a  coastal  plain  surface.  Until  re- 
cently the  Triassic  deposits  of  eastern  North  America  were  inter- 
preted as  estuarine  accumulations  (Russell-48;  Chamberlin  and 
Salisbury-n),  but  the  detailed  study  of  the  physical  characters 
of  the  rocks  has  developed  the  evidence  which  shows  them  to  be  con- 
tinental deposits  (Barrell-5).  Similarly  the  corresponding  Triassic 
deposits  of  northern  and  western  Europe,  the  New  Red  sandstone 
of  England  and  the  Bunter  Sandstein  and  Keuper  of  Germany  had 
been  regarded  as  estuarine,  tidal,  or  lake  deposits  (Reade-46), 
but  their  subaerial  origin,  as  sediments  deposited  by  rivers  chiefly 
from  the  mountains  of  that  period  on  the  south  and  west,  is  being 
more  generally  recognized.  On  the  Continent  the  material  was 
chiefly  derived  from  the  old  Vindelician  mountain  range  which 
existed  where  now  is  the  valley  of  the  Danube  and  separated  the 
Alpine  Triassic  sea  from  the  North  German  lowlands.  According 
to  Brauhauser  (Fraas-22:5/j)  the  pebbles  of  the  Lower  Bunter 
sandstein  of  Schramberg  are  not  worn  by  rolling,  but  the  pebbles 
of  the  conglomerate  forming  the  base  of  the  Middle  Bunter  are 
well  rounded  and  their  size  decreases  from  southeast  to  northwest. 
The  material  is  derived  from  the  crystallines  and  from  the  Rothlie- 
gende  of  the  Permic.  Wind-cut  facetted  pebbles  also  occur,  but 
they  have  been  more  or  less  worn-  by  subsequent  reworking.  Wal- 
ther  (58:79)  speaks  of  middle  and  eastern  Europe  in  Lower 
Triassic  time  as  a  huge  desert  area  supplied  with  variable  detritus 
by  streams  from  the  mountains  on  the  south  and  west,  and  covered 
by  endless  dunes,  interspersed  with  ponds,  and  once  at  least  by 
a  large  relict  sea.  Clastic  material  accumulated  to  a  depth  of  400  to 
600  meters,  after  which  the  sea  invaded  the  region  from  the  east 
and  .the  marine  Muschelkalk  was  deposited.  An  earlier  temporary 
and  partial  invasion  of  the  sea  is  suggested  by  fossiliferous  hori- 
zons. The  Keuper  marks  a  return  to  continental  sedimentation, 
which  in  Switzerland,  France,  and  England  was  uninterrupted. 
At  the  beginning  widespread  sandstones  (Schilf sandstein)  were 


PALEOZOIC   DELTA   DEPOSITS  635 

formed,  these  being-  interpreted  as  flood  plain  and  delta  deposits. 
(Fraas-22:5/<5).  The  upper  sandstone  (Stubensandstein)  has  been 
interpreted  as  probably  in  part  a  fluviatile  and  in  part  an  eolian 
formation,  the  sandstones  representing  an  accumulation  on  a  flat 
piedmont  area  at  the  foot  of  the  actively  eroded  Vindelician  moun- 
tain chain.  The  extensive  variegated  clays  of  the  Keuper  have 
been  regarded  by  Lang  and  others  as  marine  sediments,  but 
Philippi  (44:465),  Fraas  (22:5/7),  and  Walther  (58)  consider 
them  rather  as  aerial  sediments  especially  of  eolian  origin,  repre- 
senting a  sort  of  loess-like  accumulation.  This  interpretation  is 
suggested  by  the  manner  of  occurrence  in  these  sediments  of  the 
skeletons  of  phytosaurians,  aetosaurians,  land  turtles,  and  laby- 
rinthodonts,  with  occasional  dinosaurs,  all  lacking  evidence  of  tran- 
sport or  destruction  by  aquatic  animals  such  as  might  be  expected  if 
the  remains  were  carried  into  the  sea.  The  prevailing  color  of 
these  sediments  is  red  except  where  they  were  subsequently  re- 
worked by  water,  and  here  a  gray  color  predominates. 


PALEOZOIC  DELTA  DEPOSITS. 

These  are  numerous,  especially  in  North  America,  where  a 
whole  series  has  been  determined.  Thus  the  entire  Coal  Measure 
series  and  Permic  of  eastern  North  America  chiefly  consist  of  river 
deposits  with  only  occasional  incursions  of  the  sea.  The  Pottsville 
conglomerate  at  the  base  of  the  series  is  an  especially  good  ex- 
ample. It  was  deposited  from  two  centers,  one  in  east  central 
Pennsylvania,  the  other  in  southern  Virginia.  From  these  points 
outward  the  beds  progressively  overlap  away  from  the  source  of 
supply,  and  apparently  upon  an  old  land  surface,  there  being  in 
these  sections  no  marine  equivalents.  The  Pocono  sandstone  is  a 
similar  deposit,  and  between  it  and  the  Pottsville  lies  the  Mauch 
Chunk  red  shale,  a  deposit  of  river  flood  plain  and  eolian  origin 
during  a  period  of  relative  aridity  (Barrell-3).  Still  earlier  in  the 
Devonic  a  similar  deposit,  the  Catskill,  was  formed  progressively 
replacing  a  marine  formation  (Chemung)  westward  (Grabau-25). 
The  Oneonta  (Portage)  sandstone  of  New  York  and  the  upper 
Hamilton  or  Ashokan  formation  is  interpreted  as  of  the  same  char- 
acter. Still  earlier  in  the  Devonic  the  Esopus  grit  represents  the 
characters  of  a  sea-level  delta  built  westward  by  a  stream  debouch- 
ing near  northern  Pennsylvania.  The  Gaspe  sandstone  of  eastern 
Canada  likewise  represents  a  Devonic  dry  delta  deposit.  Still 
earlier  in  the  Siluric  and  Ordovicic  similar  dry  deltas  were  built 


636  PRINCIPLES    OF    STRATIGRAPHY 

to  the  northwest  by  streams  from  an  old  Appalachian  continent, 
these  deposits  sometimes  replacing  marine  sediments  westward, 
at  others  building  out  upon  a  dry  land  or,  in  one  case  at  least,  a 
desert  area.  (Grabau-27).  * 

A  remarkable  feature  of  these  deposits  is  the  repeated  succes- 
sion upon  light  colored  pebble  deposits,  with  evidence  of  torrential 
origin,  of  finer  red  sediments  with  characters  suggesting  flood  plain 
and  eolian  origin.  Such  are  in  the  Ordovicic  the  light  Bald  Eagle 
conglomerate  followed  by  the  red  Juniata  shales,  in  the  Siluric  the 
Shawangunk  conglomerate  followed  by  the  red  Longwood  shales, 
in  the  Devonic  the  Hamilton  and  Oneonta  sands  followed  by  the 
Catskill  red  beds,  in  the  Mississippi  the  Pocono  conglomerate  and 
sandstone  followed  by  the  red  Mauch  Chunk  shale.  This  succes- 
sion seems  to  indicate  conditions  which  permitted  easterly  winds 
to  sweep  across  a  more  or  less  elevated  land  mass  (Appalachia), 
where  they  were  deprived  of  much  of  their  moisture,  thus  creating 
semi-arid  conditions  on  the  west  of  this  land  mass.  Moderate 
aridity,  with  periodic  torrential  rainfalls  and  swollen  streams 


APPALACHIA  '   1 1' I  ""'I'/ 1  //////// 


.//'//' ' ' 

FIG.   128.     Hypothetical  section  of  Appalachia  in  Palaeozoic  time  to  show  the 
possible   arrangement   of  the   winds,  and  the  corresponding  de- 


posits. 

forming  alluvial  fans  of  pebbles,  seems  to  have  existed  repeatedly, 
but  in  each  case  was  followed  by  drier  conditions  such  as  would 
be  produced  by  a  renewed  elevation  of  the  land,  and  the  consequent 
deposition  in  the  lee  of  the  land  mass  of  highly  oxidized  sands  and 
dust  as  river  flood  plain  and  eolian  formations,  which  are  now  seen 
in  the  red  beds.  The  conditions  favoring  such  deposition  are  illus- 
trated in  the  preceding  diagram  (Fig.  128). 

Deposits  of  a  similar  character  are  found  in  the  Old  Red  sand- 
stone of  western  Europe,  and  the  Siluric  deposits  of  the  north 
of  England  and  the  south  of  Scotland  also  show  much  evidence  vof 
deltaic  origin. 

One  of  the  most  striking  examples  of  a  seashore  delta  of 
Upper  Devonic  age  seems  to  be  represented  in  the  black  shale  of 
Ohio,  Michigan,  and  western  New  York.  To  be  sure  this  has  also 
been  interpreted  as  a  deep  sea  deposit,  but  its  peculiarities  all  point 


PALAEOZOIC   DELTA    DEPOSITS  637 

to  a  delta-like  origin,  represented  to  a  certain  degree  by  the  modern 
deposits  at  the  mouth  of  the  Mississippi.  The  abundance  of  spores 
of  rhizocarp-like  plants,  represented  to-day  by  fresh  water  plants, 
the  presence  of  tree  trunks,  and  especially  the  thinning  away  east- 
ward and  southward,  and  their  interpolation  between  normal  shal- 
low water  marine  sediments,  all  point  to  the  delta  origin  of  these 
shales. 

NOTE: — For  a  full  discussion  of  the  Early  Palaeozoic  delta  deposits  of  Eastern 
North  America,  see  Grabau,  27. 


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53.  SUESS,  E.     1882.     Der  Boden  der  Stadt  Wien. 

54.  VOIGT,  F.  S.     1836.     Weitere  Nachrichten  tiber  die  Hessberger  Thier- 

fahrten.     Neues  Jahrbuch  fur  Mineralogie,   u.  s.  w.     1836,  pp.  166-174. 

55.  WADE,  ARTHUR.     1911.     Observations  on  the  Eastern  Desert  of  Egypt. 

Quarterly  Journal  of  the  Geological  Society  of  London,  Vol.  LXVII, 
pp.  238-262,  pis.  13-16. 

56.  WALTHER,  J.    1893-94.     Einleitung  in  die  Geologie  als  Historische  Wis- 

senschaft. 

57.  WALTHER,   J.     1900.      Das   Gesetz   der  Wustenbildung   in  gegenwart 

und  Vorzeit.     Ed.  I  (Ed.  II,  1912). 

58.  WALTHER,  J.     1910.      Die  Bunte  Sandwuste.     Lehrbuch  der  Geologic/ 

von  Deutschland.  Kapitel  13,  pp.  79-82.  Die  Keuperzeit — ibid.,  Kapi- 
tel  15,  pp.  87-90. 


640  PRINCIPLES    OF    STRATIGRAPHY 

59.  WILLISTON,  SAMUEL  W.,  and  CASE,  E.  C.     1912.     The  Permo-car- 

boniferous  of  Northern  New  Mexico.     Journal  of  Geology,  Vol.  XX, 
pp.  3-12. 

60.  WILSON,  J.  HOWARD.     1906.     The  Glacial  History  of  Nantucket  and 

Cape  Cod,  Chapter  IV;  Columbia  University  Press,  Geological  Series, 
Vol.  I. 

61.  WOODWORTH,  J.  B.     Some  Typical  Eskers  of  Southern  New  England. 

Boston  Society  of  Natural  History  Proceedings,  Vol.  XXVI,  pp.  197-220. 

62.  WYNNE,   A.   B.     1878.       The   Geology  of  the   Salt  Range  in    Punjab. 

Memoirs  Geological  Survey  of  India,  Vol.  XIV,  p.  608. 


CHAPTER   XV. 

STRUCTURAL  CHARACTERS  AND  LITHOGENESIS  OF  THE 
MARINE  HYDROCLASTICS. 

Marine  hydroclastics  are  accumulating  in  nearly  every  portion 
of  the  ocean  to-day,  and  their  fossil  representatives  are  among  the 
most  widespread  of  the  geological  formations.  They  are  most  abun- 
dantly developed  in  the  littoral  portion  of  the  seas,  including  the 
epicontinental  seas,  but  also  occur  in  the  abyssal  regions.  In  gen- 
eral, we  may  classify  the  material  with  reference  to  its  source,  either 
as  terrigenous  or  land-derived,  or  as  oceanic  or  derived  from  purely 
marine  deposits.  The  latter  group  is  essentially  limited  to  the 
regions  around  coral  reefs  or  other  organic  deposits,  and  so  has  a 
marked  uniformity  of  petrographic  character.  Viewed  as  a  whole, 
marine  elastics  are  nearly  always  well  stratified,  and  they  are  as  a 
rule  fossiliferous.  Indeed,  it  may  be  seriously  questioned  if  marine 
elastics  are  ever  wholly  free  from  organic  remains,  though  for  con- 
siderable distances  off  certain  shores  organisms  may  be  so  rare  as 
to  escape  detection.  Thus  Kindle  (54)  reports  dredging  off  the 
coast  of  Alaska  for  a  hundred  miles  or  more  along  the  shore,  with- 
out finding  any  organic  remains  whatever.  This  of  course  does  not 
prove  their  absence,  but  only  indicates  their  scarcity,  and  indeed  at 
another  point  of  the  same  coast  organisms  were  abundant.  More- 
over, such  dredging  affects  only  the  surface  layers  of  the  sea  floor, 
and  does  not  prove  the  absence  of  remains  in  somewhat  deeper 
layers. 

It  is  perfectly  well  known  that  marine  organisms  migrate  with 
the  seasons,  and  that  at  a  certain  locality,  where  life  was  abundant 
during  one  season,  it  is  almost  entirely  absent  in  another,  the  or- 
ganisms having  migrated  into  deeper  water.  What  is  true  of  sea- 
sons is  also  true  of  longer  periods,  some  regions  formerly  well 
stocked  with  organisms  being  barren  for  years  at  a  time,  after 
which  a  return  of  the  fauna  takes  place.  Such  migration  up  and 
down  the  ocean  floor  is  often  determined  by  factors  difficult  to  as- 

641 


642  PRINCIPLES    OF    STRATIGRAPHY 

certain.  In  the  Alaskan  case  it  may  be  due  to  the  abundance  of  cold 
water  carried  in  from  the  land  by  the  melting  of  the  glaciers,  which, 
as  shown  by  Tarr  (92),  has  recently  become  very  marked  through 
changes  which  also  caused  an  advance  of  the  glaciers  in  certain  lo- 
calities. Portions  of  the  glaciers  hitherto  protected  by  debris  or 
otherwise  have  been  suffering  ablation  during  July  and  early 
August  at  a  rate  sufficient  to  lower  the  ice  surface  four  inches  a 
day. 

While  marine  fossils  are  as  a  rule  a  reliable  indication  of  the 
marine  origin  of  a  given  series  of  elastics,  this  is  the  case  only  when 
the  fossils  are  generally  distributed  throughout  the  mass,  or  when 
there  is  no  other  positive  indication  of  a  non-marine  origin.  As  has 
already  been  shown,  eolian  limestones  composed  almost  wholly  of 
marine  organisms  are  forming  at  the  present  time,  and  have  formed 
in  the  past.  Fossils  weathering  out  from  a  marine  series  may  be 
incorporated  in  the  next  overlying  continental  formation,  as  in  the 
case  of  the  Eocenic  and  other  fossils  of  the  rocks  forming  the  floor 
of  the  Libyan  desert,  which  are  included  in  the  overlying  desert 
sands.  Marine  organic  remains  may  be  carried  inland  by  winds,  by 
birds  or  in  some  other  manner,  and  thus  become  incorporated  in 
terrestrial  formations.  Finally,  deposits  of  terrestrial  character  may 
be  at  intervals  submerged  by  a  momentary  encroachment  of  the  sea, 
as  in  the  case  of  the  Po,  the  Rhine  and  other  deltas,  with  the  result 
that  intercalated  marine  sediments  are  formed.  Or,  again,  the  sea 
may  invade  a  large  territory  previously  the  theater  of  terrestrial 
deposition,  and  by  reworking  the  upper  layers  of  the  continental  de- 
posits, or  in  some  cases  the  entire  mass,  may  impress  upon  it  lo- 
cally a  marine  character.  This  has  been  the  case  with  the  St.  Peter 
sandstone,  largely  an  eolian  formation;  with  the  upper  part  of  the 
Sylvania  sandstone  of  similar  origin ;  with  the  Dakota  and  ap- 
parently also  with  the  Potsdam  sandstone,  which,  in  many  sections, 
still  shows  characters  pointing  to  torrential  or  eolian  origin  of  a 
considerable  portion  of  the  rock. 

It  should  of  course  also  be  emphasized  that  the  reverse  is  likely 
to  hold,  namely,  that  absence  of  marine  fossils  is  not  an  absolute  in- 
dication of  the  non-marine  character  of  a  formation,  though  absence 
over  a  very  large  area  may  probably  be  taken  as  a  fairly  certain 
guide.  The  physical  characters  of  the  rocks  and  their  relationships 
must  be  taken  into  careful  consideration.  Among  the  negative  char- 
acters of  marine  elastics  are :  the  absence  of  mud  cracks,  rain  prints, 
footprint  impressions,  rill  marks,  etc.,  though  all  of  these  may 
occur  in  the  shore  zone. 


MARINE    HYDROCLASTICS 


643 


SUBDIVISIONS   OF  THE  AREAS   OF   MARINE  DEPOSI- 
TION.    TYPES  OF  MARINE  DEPOSITS. 

The  following  districts  and  zones  or  regions  of  deposition  of 
clastic  material  may  be  recognized  in  the  sea : 

1.  The  Littoral  District,  or  that  ranging  from  the  shore  to  the 
edge  of  the  continental  shelf,  that  portion  of  mediterraneans  corre- 
sponding to  this,  and  the  whole  of  the  bottoms  of  epicontinental 
seas.     Deposits  formed  here  are  "littoral  deposits,"  and  they  are 
among  the  most  varied  of  their  kind.    The  littoral  district  is  divisi- 
ble into  the  shore  zone  between   tides  and  the  permanently  sub- 
merged shallow  water  or  neritic  zone*    (Flachsec),  extending  to 
the  isobath  of  200  meters. 

2.  The  Bathyal  District  (Renevier)  is  that  district  lying  between 
the  outer  limit  of  the  neritic  zone,  i.  e,,  the  2OO-meter  line,  and  ap- 
proximately the  isobath  of  goo,  or,  in  round  numbers,  1,000  meters. 
It  represents  the  steep  slope  from  the  edge  of  the  continental  shelf 
to  the  point-  of  decreasing  angle  of  slope.     This  comprises  only^  the 
upper  portion  of  Penck's  aktic  region,  which  extends  to  the  mean 
sphere  level  of  2,400  meters  below  sea-level  (see  Chapter  I).     (Fig. 
i,  P-  8.) 

3.  The  Deep  Sea  or  Abyssal  District.    This,  according  to  Penck 
and  others,  begins  at  the  2,4OO-meter  line,  but  so  far  as  deposition  is 
concerned  begins  practically  at  the  i,ooo-meter  isobath. 

A  general  classification  of  oceanic  sediments,  including  all  types, 
was  made  by  Murray  and  Renard  (62: 186),  as  follows: 


Murray  and  Renard' s  Classification  of  Marine  Deposits. 


i.  Deep-sea  deposits  beyond 
100  fathoms .  . 


2.  Shallow- water  deposits  be- 
tween low-water  mark  and 
100  fathoms 

3.  Littoral  deposits  between 
high  and  low- water  marks . 


Red  clay 
Radiolarian  ooze 
Diatom  ooze 
Globigerina  ooze 
Pteropod  ooze 
Blue  mud 
Red  mud 
Volcanic  mud 
Coral  mud 

f  Sand,  gravels, 
{      muds,  etc. 

Sands,  gravels, 
muds.  etc. 


I.  Pelagic  deposits  form- 
ed in  deep  water  re- 
moved from  lancf 


1 1. 'Terrigenous  deposits 
formed  in  deep  and 
shallow  water,  mostly 
close  to  land 


*  Haug  (43 :86)  and  others  have  shown  a  tendency  to  use  neritic  in  the  sense 
in  which  littoral  is  here  used,  restricting  that  term  to  the  shore  zone  or  inter- 
cotidal  region.  The  use  here  advocated  seems  the  most  serviceable. 


644  PRINCIPLES    OF    STRATIGRAPHY 

Otto  Kriimmel  (55 : /5<?)  has  made  a  threefold  division  of 
marine  sediments;  modifying  the  classification  of  Murray  and 
Rehard  as  follows : 

Krummel's  Classification  of  Marine  Deposits. 

I.  LITTORAL  OR  NEAR  LAND  DEPOSITS. 

1.  Strand  or  shore  deposits. 

2.  Shelf  (shallow  water)  deposits: 

Each  comprises  boulder,  gravel,  sand,  and  mud  deposits,  which  according 
to  their  source  are  clastic,  volcanic,  biogenic,  chemical  (halmyrogenic)  and 
glacial. 

II.     HEMIPELAGIC  OR  DEEP  SEA  TERRIGENOUS  DEPOSITS. 

1.  Blue  and  red  mud  (including  volcanic  mud). 

2.  Greensand  and  green  mud. 

3.  Lime  sand  and  lime  mud: 

(Subdivisions  as  under  littoral.) 

III.     EUPELAGIC  DEPOSITS  DISTANT  FROM  LAND. 

A.  Epilophic  deposits  (formed  on  the  submarine  ridges  and  swells). 

(a)  Calcareous  deep  sea  ooze. 

1.  Globigerina  ooze. 

2.  Pteropod  ooze 

(b)  Siliceous  deep  sea  ooze. 

3.  Diatomaceous  ooze. 

B.  Abyssal  deposits: 

4.  Deep  sea  red  clay 

5.  Radiolarian  ooze 

Since  diatomaceous  oozes  have  been  found  at  depths  of  5,000- 
6,000  meters,  and  Globigerina  ooze  is  sometimes  found  in  depths 
greater  than  that  where  red  clay  accumulates,  the  subdivisions  of  the 
Eupekgic  deposits  as  given  by  Krummel  are  hardly  satisfactory 
(Philippi-fx)).  Andree  (4)  suggests  dividing  Krummers  Group 
III  into  calcareous  and  noncalcareous  (siliceous),  the  former  com- 
prising Globigerina  ooze,  with  Pteropod  ooze  as  a  facies,  the  latter 
diatomaceous  ooze,  and  the  deep-sea  red  clay  with  the  radiolarian 
ooze  as  a  facies  of  the  latter.  This  entire  class,  with  the  exception 
of  the  red  clay,  has  been  discussed  under  organic  deposits  or 
biogenics  (Chapter  X). 

The  distinction  between  areas  of  deposition  and  types  of  de- 
posits'must  be  clearly  kept  in  mind.  The  former,  as  we  have  seen, 
comprise  (i)  the  littoral  district,  with  its  two  zones,  (a)  the  shore 
and  (b)  the  neritic  zones;  (2)  the  bathyal  district  and  (3)  the 
abyssal  district.  Oceanic  deposits  must  be  classified  first  as  to  their 


CLASSIFICATION    OF   MARINE   DEPOSITS        645 

origin  and  next  as  to  their  mode  of  occurrence.    Thus  we  may  -make 
the  following  classification,  taking  oceanic  deposits  as  a  whole : 

A  New  Classification  of  Marine  Deposits. 

I  MARINE  HYDROGENICS  (HALMYROGENIC    deposits)    or    chemical    precipitates 

from  the  sea  water.     (These  have  been  fully  discussed  in  Chapter  IX.) 

II  MARINE  BIOGENICS  or  organic  deposits  of  marine  origin 
A     Benthonic  or  living  on  sea  bottom 

1  Littoral — originating  in  littoral  district 

a     Shore  zone 

(1)  autochthonous  or  growing  in  situ 

(2)  allochthonous  or  cast  up  from  deeper  water 
,    b     Neritic  or  shallow  water  zone 

(1)  autochthonous — growing  in  situ 

(2)  allochthonous — transported,  usually  from  shore  zone 

2  Bathyal 

(1)  autochthonous 

(2)  allochthonous — transported,  usually  from  littoral  zone 

3  Abyssal 

1 i )  autochthonous 

(2)  allochthonous — transported  from  the  littoral  or  bathyal 
regions 

B  Pelagic  or  living  in  the  open  ocean  and  its  extension  into  the  shore 
indentations,  either  as  plankton  or  nekton.  (See  Chapter  XXVII.) 
These  may  settle  in  the  Littoral,  Bathyal  or  Abyssal  districts,  remain- 
ing either  in  place,  or  more  or  less  rearranged  or  worked  over,  especially 
in  shallow  water  whence  they  may  be  cast  on  shore  and  even  blown 
inland. 

III  MARINE  CLASTICS.     Fragmental  material  worn  off  by  or  in  the  sea 

A    Hydrcclastics — worn  off  or  rearranged  by  the  sea  waves  or  currents 

1  Terrigenous  or  land-derived 

a     from  continent  including  continental  islands 
b     from  oceanic  islands  exclusive  of  coral  reefs,  and  other  organic 
deposits 

2  Thalassigenous ;  or  sea- derived 

a    organic  lime  sand  and  mud  derived  from  coral  reefs,  from 

nullipore  reefs,  shell  deposits,  etc. 

b     derived    from    halmyrogenic    or    chemical    deposits.     Clastic 
material  derived  by  destruction  by  waves  of  chemical  deposits 
formed  by  the  sea  (not  known).     Chemically  formed  marine 
oolites  when  worn  by  waves  may  come  under  this  head 
B     Bioclastics:  rock  material  broken  up  by  marine  organisms 

Marine  bioclastics.     These  may,  according  to  the  source  from  which 
the  material  was  originally  derived,  be  classed  as 

1  Terrigenous,  from  continents  and  islands 

2  Thalassigenous,  from  coral  reefs,  etc. 

IV  MARINE  DERELICTS,  or  stragglers  from  other  realms.     These  may  be  de- 

posited in  the  Littoral,  Bathyal  or  Abyssal  districts 
A     Land-derived,  either  from  continents  or  islands 
I     Terrestrial,  derived  from  the  land 


646  PRINCIPLES    OF    STRATIGRAPHY 

a  Organic:  land  plants  or  animals  floating  out  to  sea  or  rafted 
seaward  (as  under  b)  and  deposited  in  the  Littoral,  Bathyal 
or  Abyssal  districts.  (Microorganisms  blown  out  to  sea  with 
the  dust  would  also  be  classed  here.) 

b  Inorganic:  rocks,  sand,  gravel,  etc.,  rafted  from  land  and  deposit- 
ed in  the  Littoral,  Bathyal  or  Abyssal  districts.  According  to 
the  method  of  transport  we  have: 

(1)  plant  rafted:  rocks,  etc.,  held  by  roots  of  floating  trees  etc. 

(2)  animal  rafted:  stones  in  stomachs  of  modern  sharks,  and 
.     seals,  and  of  Jurassic  Mystriosaurus  and  Plesiosaurus  as 

well  as  in  the  stomachs  of  many  land  animals  which  may 
float  out  to  sea 

(3)  ice  rafted:  by  icebergs  and  floating  ice  cakes 

(4)  wind  rafted:  wind-blown  dust  or  sand,  and  volcanic  ma- 
terial brought  from  the  land 

(5)  ship  rafted:  substances  carried  out  by  ships  or  man-made 
rafts  and  cast  overboard  or  deposited  on  the  foundering 
of  the  ship 

(6)  carried  into  the  sea  by  slipping  or  gliding 

2  Aquatic:  derived  from  the  rivers  and  estuaries.     This  would  comprise 
chiefly  river  animals  and  plants  which  have  been  carried  out  to  sea 

3  Derived  from  adjacent  higher  zone  by  gliding  or  thrusting 
B     Atmospherically  derived 

Since  the  chief  atmogenic  solids,  snow  and  hail,  have  only  a  temporary 
existence,  deposits  from  this  source  may  be  neglected.  Rare  cases 
of  organisms,  such  as  seabirds,  which  spend  most  of  their  lives  in  the 
air,  might  perhaps  be  included  here,  but  they  may  as  well  be  classed 
with  terrestrial  derelicts 

C     Meteoric — of  Extratelluric  origin 

Here  belong  the  cosmic  dust  and  the  meteorites 

D     Of  Subcrustal  Origin 

This  includes  volcanic  eruptions  beneath  the  sea  and  on  the  coast, 
so  that  both  pyrogenics  and  pyroclastics  flow  or  are  projected  into 
the  sea.  The  direct  pyroclastics  merge  of  course  into  the  wind-trans- 
ported pyroclastics 


DISCUSSION  OF  THE  MARINE  CLASTICS. 

In  the  following  pages  the  clastic  deposits  will  be  discussed  with 
reference  to  the  regions  in  which  they  are  deposited.  Lacustrine 
elastics  will  be  repeatedly  used  for  parallel  illustrations. 

THE  LITTORAL  DISTRICT  AND  ITS  DEPOSITS. 

The  term  littoral  zone  is  frequently  restricted  to  the  part  be- 
tween high  and  low-water  mark,  i.  e.,  the  shore,  while  the  term 
neritic  has  recently  come  into  use  for  that  portion  between  low 
water  and  the  edge  of  the  continental  shelf.  The  term  littoral  dis- 


LITTORAL   DEPOSITS  647 

trict  is,  however,  best  applied  to  all  that  part  of  the  sea  above  the 
deep-sea  portion,  i.  e.,  approximately  above  the  hundred-fathom  line. 
This  is  in  conformity  with  usage  of  the  term  in  bionomics  (Ort- 
mann-63  15),  where  the  littoral  fauna  and  flora  are  those  occupying 
the  sea  bottom  within  the  illuminated  region.  It  is  in  this  sense 
that  the  term  littoral  will  be  used  throughout  this  book,  while  the 
littoral  zone  or  the  zone  between  high  and. low  water  will  be  re- 
ferred to  as  the  shore. 

Littoral  deposits  are  found  between  the  edge  of  the  continental 
shelf  and  the  high-water  edge  of  the  shore.  In  the  shore  zone  they 
grade  imperceptibly  into  continental  deposits,  through  the  zone  of 
the  strand,  while  at  the  outermost  margin  of  the  littoral  district  they 
grade  into  abyssal  deposits.  Around  the  margins  of  oceanic  islands 
the  littoral  belt  is  of  greater  or  less  width,  according  to  the  slope  of 
the  submerged  portion  of  the  island. 

It  is  within  the  littoral  district  as  here  denned  that  by  far  the 
largest  proportion  of  clastic  material  is  deposited.  It  is  here  also 
that  the  bulk  of  the  hydrogenic  and  the  biogenic  deposits  of  the  sea 
is  formed. 


The  Shore  Zone  (Inter  Co-tidal  Zone ;  Littoral  Zone 
in  Restricted  Sense). 

The  separation  of  the  shore  zone,  or  that  portion  between  high 
and  low-water  mark,  from  the  portion  of  the  littoral  district  never 
uncovered,  is  of  very  little  significance  from  the  lithogenetic  point 
of  view,  however  much  its  import  biologically.  For,  although  this 
zone  is  the  focus  of  the  destructive  activity  of  the  waves,  their  work 
is  not  limited  to  this  portion.  It  is  known  that  wave  work  is  very 
effective  at  a  depth  of  thirty  feet,  while  at  sixty  it  has  still  an  in- 
fluence upon  the  bottom  deposits.  In  fact  on  a  gently  sloping  coast, 
the  destructive  work  of  the  waves  is  found  in  the  deeper  water 
away  from  the  shore,  rather  than  in  the  shore  zone.  Neither  has 
the  shore  a  distinctive  type  of  sediment;  not  even  the  pebbly  sedi- 
ment is  confined  to  it,  but  occurs  also  at  a  distance  from  shore ;  nor 
are  sands,  muds  or  even  organic  deposits  excluded  from  the  shore, 
the  sands  and  muds  being  often  more  characteristic  than  the  peb- 
bles. As  for  organisms,  only  stationary  or  attached  types  dis- 
criminate between  the  shore  and  the  permanently  submerged  zone, 
and  among  these  certain  ones  do  not  make  an  absolute  distinction. 
The  shore  zone  is,  however,  of  significance  in  this  respect,  that 
characters  typical  of  continental  deposits,  such  as  mud  cracks,  rain- 


648  PRINCIPLES   OF    STRATIGRAPHY 

prints,  footprints,  etc.,  can  be  impressed  upon  the  exposed  sedi- 
ments, and  preserved  under  favorable  circumstances. 

Since  the  magnitude  of  tides  varies  with  the  moon's  phases,  the 
exact  limit  of  the  shore  zone  is  never  fixed.  During  spring  tides  the 
zone  encroaches  upon  the  strand,  that  indefinite  zone  just  above 
high  water,  while  the  ebb  succeeding  will  lay  bare  portions  of  the 
zone  generally  submerged.  On  lakes  the  shore  zone  practically  dis- 
appears (it  would  be  wrong,  however,  to  say  that  there  is  no  littoral 
district  on  the  lakes)  unless  the  seiche  is  to  be  considered  as  equiva- 
lent to  the  tides. 

Fades  of  the  Shore  Zone.  The  shore  zone  may  represent  one 
or  more  of  a  variety  of  fades,  or  types  of  material,  none  of  which 
can  be  considered  as  strictly  confined  to  it.  The  most  typical  facies 
of  the  shore  zone  are:  i,  the  rocky  cliff  facies;  2,  the  bouldery 
facies;  3,  the  gravelly  facies;  4,  the  sand  facies;  5,  the  mud  flat 
facies,  and  6,  the  organic  facies.  Each  of  these  facies  has  its  dis- 
tinct physical  and  organic  characters. 


i.  Rocky  cliff  facies. 

This  is  most  significant  from  the  point  of  view  of  bionomics,  as 
will  be  more  fully  discussed  in  a  later  chapter.  Erosion  is  active 
here,  and  coarse  fragments  are  broken  from  the  cliff  and  accumu- 
late as  a  submarine  talus  and  boulder  pavement.  Where  rock  accu- 
mulation takes  place,  a  rudaceous  phase  will  be  found  next  to  the 
cliff,  the  material  of  the  rock  fragments  being  that  of  the  cliff  from 
which  they  are  derived.  Since  in  such  cases  the  rock  fragments 
broken  from  the  cliff  may  fall  into  water  sufficiently  deep  to  prevent 
much  attrition  of  the  fragments,  the  resultant  rudyte  may  be  a 
breccia,  the  fragments  being  in  the  main  angular.  Examples  of 
such  cliff  rudytes  are  found  in  the  St.  Croix  formation  of  the 
Dalles  region  of  the  Wisconsin  River,  and  in  the  Lake  Superior 
sandstone  of  Marquette,  Michigan.  Some  of  these  may  of  course 
be  old,  subaerial  talus  slopes  reworked  by  the  transgressing  sea. 
This  appears  to  be  the  case  with  the  basal  Mid-Devonic  limestones 
(Dundee)  of  Michigan  and  western  Ontario.  (See  Chapter  XIII.) 


2.     Bouldery  facies. 

Where  a  rock  cliff  fronts  the  waves,  the  fragments  broken  from 
the  cliff  by  the  frost  and  by  the  sea  are  generally  ground   into 


FACIES    OF    THE    SHORE    ZONE  649 

pebbles,  sand  and  mud,  unless  the  water  at  the  foot  of  the  cliff  is 
sufficiently  deep  to  render  the  force  of  the  waves  ineffective.  Thus 
boulders  will  seldom  accumulate  in  such  numbers  as  to  make  a 
boulder  beach  at  the  foot  of  a  cliff,  since  the  destruction  of  the  cliff 
proceeds  with  sufficient  slowness  to  allow  the  reduction  of  most  of 
the  fragments  to  pebbles  or  smaller  particles.  If,  however,  the  sea 
eats  into  a  morainal  or  other  bouldery  deposit,  as  is  the  case  of  many 
portions  of  the  New  England  and  Long  Island  coast  of  the  North 
Atlantic,  a  heavy  boulder  beach  arranged  in  the  form  of  a  pave- 
ment by  the  close  approximation  of  the  boulders  through  wave  and 
shore-ice  work  will  result.  In  like  manner,  when  the  sea  en- 
croaches upon  an  old  subaerial  talus  heap,  a  boulder  beach  may  be 
formed,  the  waves  being  able  to  round  off  and  arrange  the  boulders, 
but  not  to  destroy  them.  The  boulders  themselves  become  a  natu- 
ral barrier,  against  which  the  waves  beat  themselves  to  pieces  with- 
out accomplishing  much  erosional  work.  Where  the  tides  are  ex- 
ceptionally high,  as  in  the  Bay  of  Fundy,  the  boulders  broken  from 
the  cliffs  by  the  frost  and  insolation  will  be  rolled  and  worn  at  high 
tide,  but  the  power  of  the  waves  is  too  small,  and  the  time  during 
which  the  boulders  are  subject  to  their  influence  too  short,  to  pro- 
duce any  other  results.  Here  the  accumulation  of  boulders  is  really 
to  be  compared  with  a  subaerial  talus,  which  is  periodically,  but  for 
a  short  time  only,  exposed  to  wave  activity.  On  the  whole,  boulder 
beaches  other  than  those  due  to  erosion  o£  drift  deposits  are  of  com- 
paratively rare  occurrence,  and  the  same  thing  may  be  said  of  an- 
cient marine  boulder  beds.  It  is  doubtful  if  many  such  existed, 
most  of  the  boulder  beds  of  former  geologic  epochs  being  probably 
of  continental  origin.  That  boulders  of  even  moderate  size  may 
for  a  long  time  remain  entirely  unmoved  by  the  waves  is  shown  on 
the  east  coast  of  Scotland,  where  the  boulders  and  ledges  are  cov- 
ered by  living  Acmaea  or  by  extensive  growth  of  sea  weeds.  Even 
delicate  sea  anemones  are  found  attached  to  these  boulders,  often  in 
such  a  position  that  a  slight  movement  of  the  boulders  would  grind 
them  to  pieces.  In  other  cases  the  boulders  and  pebbles  are  en- 
crusted by  a  growth  of  Lithothamnion  or  Melobesia.  It  sometimes 
happens  that  in  certain  zones,  or  areas,  the  waves  are  able  to  move 
the  boulders,  with  the  result  that  there  they  are  entirely  bare  of 
either  vegetation  or  animal  covering. 

3.     Gravel  fades. 

By  far  the  greater  part  of  the  present  shore  lines  of  the  world  is 
sandy  or  gravelly,  the  former  predominating.    Gravelly  beaches  or 


650 


PRINCIPLES    OF    STRATIGRAPHY 


beaches  of  cobbles  or  shingles  are  chiefly  characteristic  of  steeply 
sloping  and  exposed  rocky  shores,  where  the  finer  product  of  ero- 
sion is  carried  by  the  undertow  to  deeper  water,  the  coarser  alone 
remaining.  The  character  of  the  pebbles  will  of  course  partake  of 
that  of  the  cliff  from  which  they  are  formed,  those  derived  from 
the  more  easily  shattered  rock,  as  well  as  the  most  difficult  to  grind 
to  powder,  predominating.  Thus  on  the  north  shore  of  Massachu- 
setts felsite  pebbles  predominate,  on  Lake  Michigan  limestone  peb- 
bles, and  on  the  shore  of  Lake  Erie  flat  shale  pebbles.  These  peb- 
bles are  often  piled  up  into  extensive  terraces,  especially  after  heavy 
storms.  These  terraces  may  show  on  section  a  rude  and  irregular 
bedding,  but  the  regular  cross-bedding  (torrential  type)  found  in 
many  old  conglomerates  was  not  formed  in  this  manner. 


FIG.  129.  Diagram  illustrating  the  deposits  in  the  littoral  district  of  the  sea. 
At  the  shore  gravelly  and  sandy  fades  occur,  these  shading  off 
seaward  into  lutaceons,  and,  finally,  calcareous  sediments.  The 
latter  are  derived  from  the  coral  reef  C.  R.,  i.  e.,  they  are  thalassi- 
genous,  while  the  others  are  terrigenous.  The  overlapping  of 
the  formations  is  also  shown. 


Organic  remains  in  pebble  beds.  On  the  beach,  where  the  peb- 
bles undergo  much  movement,  most  organic  remains,  such  as  shells, 
bones,  etc.,  are  rapidly  destroyed.  Nevertheless,  they  are  occa- 
sionally preserved,  as  is  shown  by  the  occurrence  of  worn  shell 
fragments  even  in  the  high  gravel  terraces. 

That  organic  remains  are  common  in  older  boulder  and  pebble 
beds  has  been  the  experience  of  many  geologists,  though  some  of 
the  so-called  conglomerate  beds  are  due  to  causes  other  than  those 
active  on  sea  beaches.  A  comparatively  modern  example  of  a  pebble 
and  sand  beach  now  abandoned  by  a  slight  elevation  of  the  coast 
is  found  in  eastern  Scotland.  Near  Goldspie  on  the  Moray  Firth, 
the  lower  of  the  elevated  beach  lines  abounds  in  entire  shells  of 
Acmsea  and  other  shore  forms,  as  well  as  in  worn  fragments  of 
this  and  other  shells.  Boulders  up  to  the  size  of  six  inches  or  more, 


FACIES    OF    THE    SHORE    ZONE  651 

and  well  worn,  are  found  in  this  beach.    Other  examples  no  doubt 
occur  in  other  sections  of  this  coast  and  elsewhere. 

Boulder  beds  of  Tertiary  age  are  not  uncommon.  In  the  Mi- 
ocenic  of  the  Vienna  Basin,  some  of  the  best  preserved  pelecypocl 
and  gastropod  shells  are  found  in  a  boulder  bed  with  pebbles  up  to 
six  inches  or  more  in  diameter,  and  well  rounded.  The  Cretacic 
boulder  beds  of  South  Germany  and  of  Sweden  are  other  examples. 
In  the  former  well-worn  boulders  up  to  several  feet  in  diameter 
constitute  the  deposit,  while  among  them  abound  fragments  and  en- 
tire individuals  of  brachiopods,  pelecypods  and  other  organisms 
often  in  a  remarkable  state  of  preservation.  In  the  Dresden  region 
pothole-like  hollows  are  found  in  the  old  porphyries  with  a  depth 
of  20  feet  or  more,  and  these  are  filled  with  a  coarse  boulder  con- 
glomerate of  Cretacic  age,  the  individual  boulders  often  a  foot  or 
more  in  diameter,  and  well  worn.  Among  these  boulders  sponges, 
oysters  and  other  organisms  occur  in  abundance.  In  Scania  and 
elsewhere  an  Upper  Cretacic  conglomerate  of  pebbles  and  boulders 
worn  or  angular  contains  •Belemnites  and  other  fossils  of  that 
period,  many  of  them  showing  no  wear.  One  of  the  most  striking 
examples  of  such  a  conglomerate  is  found  on  the  present  eastern 
coast  of  Sutherland,  North  Scotland,  near  the  village  of  Helms- 
dale.  The  formation  occurs  as  a  coastal  strip,  largely  eroded  by  the 
present  sea,  and  forming  a  series  of  low-lying  skerries  exposed  at 
low  water.  The  age  of  the  formation  is  Jurassic,  but  it  is  almost 
wholly  composed  of  large  and  small  fragments  of  Caithness  flags 
(Lower  Old  Red  sandstone),  some,  of  the  fragments  reaching  the 
astonishing  length  of  20  feet  or  more.  The  larger  fragments  lie  in 
irregular  positions,  their  stratification  planes  dipping  in  all  direc- 
tions, and  they  resemble  in  every  respect  the  fragments  now  found 
at  the  foot  of  the  cliffs  of  these  flags  on  the  exposed  Caithness 
coast.  Among  the  fragments  and  firmly  embedded  in  the  con- 
glomerate and  breccia  matrix  are  worn  heads  of  coral  (Isastrea), 
shells,  Belemnites  and  other  Jurassic  organisms.  Many  of  the 
smaller  organisms  have  apparently  escaped  all  wear. 


4.     Sandy  fades. 

Sand  is  by  far  the  most  typical  material  of  the  shore  zone,  on 
lakes  as  well  as  on  the  seashore.  To  a  large  extent  the  sand  con- 
sists of  quartz  grains,  since  this  is  the  least  destructible  constitu- 
ent of  rocks.  In  regions  of  purely  calcareous  sources  of  sand,  as  in 
the  Bermudas,  and  on  many  coral  reef  islands,  the  sand  is  largely  or 


652  PRINCIPLES    OF    STRATIGRAPHY 

wholly  composed  of  grains  of  calcium  carbonate,  with  or  without 
magnesium. 

As  Shaler  has  pointed  out,  the  sand  of  the  seashore  is  com- 
pacted into  a  resistant  mass  by  the  films  of  water  which  separate 
the  grains  and  which  are  held  in  position  by  capillary  attraction. 
Whoever  has  walked  on  wet  beach  sand  has  noted  the  difference  in 
firmness  between  the  wet  and  dry  sands,  the  former  often  con- 
stituting a  hard,  level  floor.  On  such  a  surface  the  force  of  the 
waves  is  spent;  the  sands  will  retain  their  original  angular  charac- 
ter, since  the  dividing  film  of  water  acts  as  a  cushion,  which  pre- 
vents the  mutual  attrition  of  the  grains.  Thus  the  grains  of  beach 
sand  are  normally  angular  and  with  fresh  surfaces,  and  this  type  of 
sand  should  be  looked  for  in  normal  marine  sandstones.  (Shaler- 
88.)  Shaler  cites  as  an  example  of  marine  sands  protected  in  this 
manner  from  wearing,  the  sand  of  northern  Florida  .  .  .  "which 
has  traveled  southward  from  the  region  beyond  Cape  Hatteras" 
.  ;  .  and  which  "is  not  more  rounded  than  much  which  is  in  the 
inner  or  landward  dunes  of  the  coast  within  sound  of  the  ocean 
waves."  (88:151.) 

When,  through  drying,  the  binding  films  of  water  are  destroyed, 
the  sands  become  loosened  and  are  then  readily  shifted  about  by 
the  wind,  accompanied  by  mutual  attrition  of  the  grains.  Here, 
then,  no  permanent  structural  features  are  formed.  '  Both  rill  and 
ripple  marks  left  on  the  retreat  of  the  tide  are  either  obliterated  by 
the  wind  or  washed  away  by  the  returning  tide,  owing  to  the  non- 
coherency  of  the  material.  An  exception  to  this  seems  to  be  the 
wave  mark  on  a  very  gently  sloping  sand  beach,  and  the  hollows  ex- 
cavated behind  pebbles  or  shells  by  the  return  of  the  wave  on  such 
a  beach.  Examples  of  these  are  known  from  the  Upper  Medina 
sandstone  in  western  New  York,  and  in  other  formations.  (Fair- 
child-32.) 

Marine  arkoses.  Accumulation  of  feldspathic  sands  on  the  sea 
coast  and  their  incorporation  in  marine  strata  are  effected  under  a 
peculiar  combination  of  circumstances  such  as  exist  to-day  in  the 
Gulf  of  California,  as  described  by  McGee  (57).  The  granitoid 
rocks  of  this  region  are  subject  to  disintegration  under  the  arid 
climatic  conditions,  due  to  the  interception  of  the  Westerlies  by  the 
coast  ranges.  Decomposition  is  practically  absent,  the  disintegrated 
material  being  transported  by  sheet  floods.  These  result  from  ex- 
ceptional thunderstorms,  accompanied  by  sudden  and  extensive  pre- 
cipitation. Part  of  the  material  is  carried  into  the  Gulf  and  there 
assorted  by  the  waves,  the  coarsest  and  cleanest  material  being  de- 
posited at  the  salients  of  the  coast,  while  in  the  reentrants  much 


FACIES    OF    THE    SHORE    ZONE  653 

finely  comminuted  material  is  deposited  with  the  coarse  quartz  and 
feldspar.  Quartz- feldspar-mica  sandstones  are  thus  produced 
under  conditions  permitting  the  entombment  of  marine  organisms. 
Sorting  of  sands  and  gravels  by  waves.  The  conditions  under 
which  waves  accomplish  sorting  of  sands  and  gravels  according  to 
size  and  material  are  given  by  Bailey  Willis  (105:481)  as  the  fol- 
lowing : 

(a)  Vigorous  wave  action,  accompanied  by  strong  undertow. 

(b)  Prolonged   transportation  in  consequence  of  deep  water 

and  continuous  currents. 

(c)  Moderate  volume  of  sediments. 

On  the  other  hand,  the  conditions  under  which  sorting  is  not  or 
but  slightly  accomplished  are,  according  to  Willis : 

(a')     Feeble  or  diffused  wave  action. 

(b')     Concentrated  deposition. 

(c')     Excessive  volume  of  sediment. 

In  general,  with  a  given  amount  of  loose  materials  to  work 
upon,  the  waves  will  accomplish  sorting  in  proportion  to  their 
strength  and  the  strength  of  the  undertow.  The  finest  material  will 
be  carried  out  farthest,  while  only  the  coarsest  material  will  be  left 
behind.  Where  the  material  is  all  of  one  kind,  as,  for  example, 
quartz  sand,  the  sorting  will  be  entirely  according  to  size,  while 
variation  in  the  mineralogical  character  of  the  material  may  lead  to 
a  sorting,  according  to  the  specific  gravity  as  well.  Thus  quartz 
sands  may  be  entirely  washed  free  from  mica  and  clay  particles, 
while  garnet  and  magnetite,  two  characteristic  accompaniments  of 
sands  derived  from  many  igneous  or  metamorphic  rocks,  will  segre- 
gate through  the  washing  out  of  all  quartz  grains. 

This  sorting  according  to  size  and  specific  gravity  is  best  accom- 
plished if,  in  addition  to  the  strong  wave  movement  which  stirs 
up  the  sediment,  strong  currents  exist  which  can  transport  the  ma- 
terial for  long  distances. '  The  smallest  and  lightest  material  may 
thus  be  carried  much  farther  away  from  the  point  where  the 
coarsest  is  dropped,  the  separation  being  thus  most  pronounced. 
In  this  respect  the  separation  by  currents  will  be  analogous  to  the 
separation  of  sediments  by  wind.  A  water  current  of  a  given 
velocity  is  equaled  in  carrying  power  only  by  a  wind  current  of  28 
times  that  velocity  (Udden-o^rj/p),  but  wind  currents  exceeding 
average  ocean  currents  in  velocity  by  very  much  more  than  that  are 
characteristic  of.  many  regions,  especially  in  the  upper  atmosphere. 
Thus  material  projected  or  carried  into  the  air  stands  a  much  better 


654  PRINCIPLES    OF    STRATIGRAPHY 

chance  of  sorting  than  does  material  in  the  sea.  Moreover,  material 
dropped  by  one  air  current  may  be  picked  up  again  by  another, 
while  sands  dropping  in  deeper  water  below  the  reach  of  the  cur- 
rents are  more  likely  to  be  left  undisturbed  by  them. 

If  the  amount  of  supply  of  detritus  is  great,  sorting  will  be  im- 
peded. Flocculation,  or  the  gathering  together  of  particles,  will  oc- 
cur, the  coarser  carrying  down  with  them  the  finer.  Flocculation  is 
less  marked  in  wind-transported  material,  where  the  load  is  always 
much  less  per  unit  of  bulk  of  the  carrier  than  in  most  waters,  and 
for  this  reason  also  the  sorting  by  wind  is  more  pronounced  than 
that  by  water.  Udden  thinks  that  under  ordinary  circumstances 
this  difference  is  nearer  i  to  100,000  than  i  to  1,000.  (99:^5".) 
The  slope  of  the  sea  bottom  (Willis-io5  :  484)  is  also  a  determining 
factor  in  the  transportation  of  material  by  marine  currents.  Where 
the  slope  is  a  gentle  one,  sand  may  be  carried  for  200  miles  or 
more,  as  on  the  Atlantic  coast  of  the  United  States,  where  the  conti- 
nental plateau  is  covered  with  sands  to  its  outer  rim.  The  trans- 
porting current  here  is  the  undertow,  assisted  by  tides.  Since, 
however,  the  force  of  the  undertow  is  largely  determined  by  the 
strength  of  .the  waves,  it  follows  that  in  circumscribed  and  very 
shallow  seas  no  such  extensive  transportation  is  possible.  Where 
the  slope  is  a  steep  one,  as  en  the  west  coast  of  South  America,  the 
force  of  the  undertow  is  dissipated,  though  pebbles  and  sand  will 
more  readily  move  down  the  slope.  As  a  rule,  the  distance  to  which 
sands  are  transported  in  such  a  case  is  limited. 

Organic  remains  in  marine  and  lacustrine  sands.  These  are  gen- 
erally common,  especially  in  the  sea,  though  areas  free  from  such 
remains  are  known,  as  in  the  case  of  the  Alaskan  coast,  already 
cited.  Such  absence  is,  however,  due  to  purely  local  causes.  Even 
in  the  beach  sands  organic  remains  abound.  Everywhere  along  our 
coasts  shells  in  numbers,  and  crustacean  and  echinoderm  tests  to  a 
lesser  degree  are  buried  in  the  sands  of  the  beach,  and  in  those 
just  below  the  low-water  line.  In  the  neritic  zone  animal  life  of  all 
kinds  abounds  on  the  sandy  bottoms  (see  Chapter  XXVIII). 
Abandoned  shores  of  lakes  and  of  the  sea  also  are  rich  in  organic 
remains.  The  higher  beaches  of  the  late  Pleistocenic  stages  of  the 
Great  Lakes  contain  numerous  shells  of  fresh- water  mollusca,  and 
so  do  the  sands  of  the  old  shore  lines  of  Niagara  and  other  rivers. 
So  abundant  are  shells  and  other  organisms  in  the  sands  of  the 
modern  sea  coast  that  their  entire  absence  from  older  sandstones 
must  be  looked  upon  as  indicative  of  conditions  of  deposition  other 
than  normal.  It  is  begging  the  question  to  assume  the  subsequent 
removal  of  such  remains  either  by  solution  or  otherwise,  for  even 


FAClES    OF    THE    SHORE    ZONE  655 

though  percolating  waters  should  dissolve  away  the  shells  a  mold 
or  impression  of  the  same  will  remain,  which  no  agent  short  of 
metamorphism  can  obliterate,  and  that  not  always.  The  abundance 
of  organic  remains  in  sandstones  of  all  kinds  and  colors  and  of  all 
ages  shows  that  there  are  no  inherent  characteristics  in  sand  which 
prevent  the  preservation  of  such  remains.  In  practically  all  cases 
when  organic  remains  or  their  impressions  are  wanting  in  sand- 
stones, we  have  a  right  to  assume  that  they  were  not  present  at  the 
time  of  formation  of  the  deposit.  Such  absence  suggests  a  sub- 
aerial  rather  than  subaqueous  origin -for  the  deposit,  and  as  such  it 
should  be  considered  unless  other  unmistakable  characteristics  point 
to  a  subaqueous  (marine  or  lacustrine)  origin.  (For  application  to 
basal  beds  see  Pumpelly-75  :<?//.) 


5.     Muddy  fades. 

This  generally  occurs  in  intimate  association  with  an  organic 
facies  in  the  shore  zone.  Where  sands  accumulate  in  sheltered  mar- 
ginal lagoons,  plants  (eel  grass)  and  animals  commonly  contribute 
their  remains  to  enrich  and  color  the  mud.  Salt  marshes  are  the 
normal  successors  of  the  mud  flat,  the  organic  element  here  being 
in  the  ascendency..  (See  ante,  Chapter  XI.)  The  purely  inorganic 
structures  of  such  a  mud  flat  are,  in  addition  to  stratification,  the 
mud  cracks,  rain  prints  and  rill  marks,  and  the  tracks  and  trails  of 
animals  frequenting  the  shore.  During  very  high  spring  tides  ex- 
tensive portions  of  a  very  flat  shore  may  be  covered  with  a  layer  of 
mud,  which  on  the  retreat  of  the  tide  may  become  marked  by  mud 
cracks  and  footprint  impressions.  Since  such  areas  will  be  uncov- 
ered for  a  fortnight,  the  clay  may  become  sufficiently  hardened  to 
permit  the  permanent  preservation  of  the  mud  cracks.  It  must, 
however,  be  borne  in  mind  that  when  the  mud  deposit  made  by 
one  inundation  is  comparatively  thin,  as  is  apt  to  be  the  case,  this 
layer  will  on  drying  curl  up  into  shaving-like  masses  and  be  blown 
away  by  the  wind.  While  under  exceptional  conditions  the  mud 
cracks,  rill  marks  and  tracks  formed  in  the  shore  zone  may  be-  pre- 
served, such  preservation  is  far  from  being  characteristic. 

Flocculation  and  the  conditions  of  mud  deposits.  The  formation 
of  mud  deposits  at  the  mouths  of  great  rivers  emptying  in  the  sea, 
as  in  the  case  of  the  Mississippi,  is  favored  by  the  presence  of  the 
salt  in  the  sea  water.  Flocculation,  or  the  drawing  together  of 
particles,  takes  place  much  more  extensively  in  salt  than  in  fresh 
water,  and  as  a  result  such  particles  will  sink  more  quickly  in  sea 


656 


PRINCIPLES    OF    STRATIGRAPHY 


water  than  in  lakes.     Experiments  (Brewer-n  :  168)  have  shown 
that  clay  which  had  been  in  suspension  in  fresh  water  for  thirty 


FIG.  130.  Diagram  showing  the  lateral  shading  off  of  the  clastic  sands  and 
pebbles  into  calcareous  deposits  without  intervening  muddy 
phase.  The  successive  formations  a,  b,  and  c  change  shoreward 
into  arenytes.  An  apparently  continuous  sand  bed ;  a-c  is  thus 
produced  resting  upon  the  old  land  surface. 

months  had  not  settled  out  as  clearly  as  the  same  clay  from  a  solu- 
tion of  common  salt  in  less  than  thirty  minutes.  These  results  have, 
however,  been  questioned  by  Wheeler  (103),  who  gives  the  accom- 
panying table,  showing  the  rate  of  settlement  in  the  two  media : 


Table  Showing  Rate  of  Settlement  of  Solid  Matter  in  Fresh  and 

Salt  Water. 


No. 

i 

2 

'  3 
4 
5 
6 

7 
8 
9 
IO 

ii 

I2T 

13 

14 

No.  of 

grains 
to  a 
lineal 
inch 

Material 

Time  taken 
to  settle 

Water 
clear 

Ft. 
per 
minute 

Remarks 

Fresh 

Salt 

Fresh 

Salt 

m. 

sec. 

m. 

sec. 

h. 

m. 

h. 

m. 

5 

10 
20 

20-60 

IOO 
200 

300 

1,400 
•   500 
1,000 
2,000 

600 

1,500 
1,  600 
1,440 

Small  pebbles  

0 

I  • 
Tl 

0.50 
0.42 

0.21 

o.  13 

5.04 
2.4O 

Water  not 
discolored 
do 
do 
do 
do 
do 
do 
do 
Water  scarcely 
discolored 
Water  turbid 
do 
do 
do 
do 
do 
do 
do 

Small  pebbles 

Coarse  sand    

o 

A 

'5° 

o 

Sand  

o 

IO 

o 

Sand 

o 

25 

Whiting  

12 

o 

Plaster  of  Paris 

5 

0 

12 
2 

8 
33 

18 
i? 
24 

o 

4.5 

0 
0 
0 
0 
0 
0 
0 
0 

o 
15 

2 

9 

28 

2 

18 
IS 
0 

45 

o 
o 
o 

0 

40 

o 
o 

22 

o 
o 

3 
o 

I 
7 

0 
IO 

I 
o 

10 

i 

30 

6 

0 
0 

15 

0 

30 
43 

0 

22 
O 
O 
I 
0 

9 
I 

0 

i 

0 

0 
33 
30 

1  8 

0 

o 
30 

I  .20 

O.7O 
O.42 

O.  II 
0.22 
0.46 
0.4O 

0.35 

Warp  Trent  

(Fine  warp,  Dutch  river). 
Silt,  salt  marsh  
Warp  marsh 

(Alluvium,  Boston  Dock) 
(Alluvium,  River  Parrett) 
Tilbury  Basin 

Brick  clay  

Boulder  clay  

The  phenomena  of  flocculation  have  been  attributed  to  chemical 
reaction,  but  seem  to  find  a  better  explanation  in  the  forces  of  at- 


FACIES    OF    THE    SHORE    ZONE  657 

traction  or  tension  existing  among  the  fine  particles  of  a  solid  in 
suspension.  These  forces  are  modified  by  the  existence  of  the  salt 
in  the  solution.  (Whitney-iO4;  Clarke-2O.)  According  to  the  ex- 
periments of  G.  Bodlander  (10),  the  sodium  chloride  of  the  sea 
water  is  not  so  important  in  this  respect,  other  salts,  especially  mag- 
nesium chloride,  being  more  active.  Carbon  dioxide,  which  abounds 
in  sea  water,  also  rapidly  clears  it  of  suspended  clay  particles,  but 
temperature  changes  seem  to  be  of  little  significance  in  this  re- 
spect. (Krummel-55 :  152-214.)  Even  in  sea  water,  however,  the 
finest  particles  do  not  settle  out  completely  after  several  weeks  of 
rest. 

Terrigenous  muds   extend   from  the   shore  to   abyssal   depths. 
They  will  be  more  fully  considered  under  the  neritic  zone. 


6.     Organic  fades. 

This  consists  of  the  eel  grass  and  peat  marsh  areas  of  the  sea 
coast  and  of  the  rush  and  swamp  borders  of  lakes  and  ponds.  The 
characteristics  of  these  have  been  fully  described  in  previous  chap- 
ters, and  need  not  be  dwelt  upon  here  at  length.  Extensive  mussel 
beds  such  as  are  forming  in  many  places  on  our  sea  coast  may  also 
be  classed  here,  though  these  are  as  a  rule  intimately  associated 
with  the  muddy  facies  of  the  flats.  Shallow-water  coral  and  Litho- 
thamnion  growths  are  other  examples  of  this  facies,  which  belongs 
with  the  lithogenic  rather  than  the  lithoclastic  division. 


Subaqueous  SoliUuction. 

The  movement  or  gliding  of  rock  material  when  saturated  with 
water,  which  under  subaerial  conditions  is  called  solifluction  (see 
Chapter  XIII),  also  takes  place  under  subaqueous  conditions.  Ar- 
nold Heim  proposed  to  distinguish  this  mode  of  movement  as  sub- 
solifluction  (47:141).  Such  movements  have  occurred  in  many 
regions  of  the  world,  both  on  lakes  and  on  the  seashore,  but  only  a 
few  cases  have  been  fu^ly  investigated.  Among  these  are  the  glidings 
which  in  1875  and  again  in  1877  affected  the  village  of  Horgen  on 
the  Lake  of  Zurich  (Switzerland),  and  the  one  which  took  place 
in  the  village  of  Zug  on  the  Zuger  See  in  the  Canton  of  Zug 
(Zoug),  north  central  Switzerland.  Both  of  these  were  described 
by  Professor  Albert  Heim  and  others  in  special  publications,  and 
summarized  by  Arnold  Heim  in  1908  (47:  136). 


658  PRINCIPLES    OF    STRATIGRAPHY 

The  village  of  Horgen  is  situated  on  the  southern  shore  of  the 
Lake  of  Zurich.  The  shore,  which  is  here  composed  of  the  sand- 
stones and  marls  of  the  Mollasse,  was  covered  originally  by  sand, 
gravel  and  clay  in  the  upper  part;  and  this,  near  the  shore,  was  un- 
derlain by  soft  muds,  which  extended  lakeward,  covering  the  rocks 
to  the  center  of  the  lake.  On  the  ground  thus  underlain  with  soft 
mud  rests  a  part  of  the  railroad,  which  skirts  the  southwestern  shore 
of  the  lake  (Zurichseebahn),  the  Horgen  station  being  built  close 
to  the  shore.  A  sea  wall  was  built  and  the  surface  raised  a  slight 
amount  (0.4  to  0.6  meter)  by  filling-in,  but  prior  to  this  a  number 
of  buildings  and  a  stone-cutting  yard  were  removed,  so  that  on 
the  whole  the  excess  of  loading  was  slight.  On  February  9,  1875, 
when  the  filling  in  was  nearly  complete,  the  new  sea  wall  and  the 
filled  area  suddenly  sank  for  a  length  of  135  meters,  the  lake  along 
the  line  of  the  railroad  reaching  a  depth  of  7  meters.  The  examina- 
tion showed  that  a  part  of  the  bottom  layer  of  soft  mud  had  slid 
lakeward,  so  that  the  more  resistant  overlying  sand  and  gravel  beds 
came  to  rest  upon  the  rock  surface.  The  gliding  continued  until 
the  mud  layers  had  completely  bared  the  rock  slopes  for  a  distance 
of  nearly  300  meters  lakeward.  The  most  pronounced  of  these 
glidings  occurred  on  June  12,  1875,  this,  however,  affecting  mainly 
the  sublacustrine  mud  layers.  By  filling  in  a  part  of  the  sunken  area 
and  carrying  the  railroad  line  farther  inland,  the  construction  was 
completed  and  the  line  opened  for  traffic  September  20,  1875.  The 
following  day  was  one  of  heavy  rains,  and  on  the  morning  of  the 
22nd  fissures  began  to  open  in  the  made  land,  the  new  wall  began 
to  crack,  and  suddenly  a  part  of  the  wall,  85  meters  long,  and  the 
station  lands  and  tracks  to  a  width  of  23  meters  sank  beneath  the 
inrushing  lake  waters.  Just  before  noon  a  second  subsidence  took 
place,  a  third  one  followed  early  in  the  afternoon,  and  others  fol- 
lowed on  the  23rd  and  24th  of  September.  The  total  area  which 
thus  disappeared  beneath  the  water  of  the  lake  had  a  length  of  204 
meters  and  a  width  of  48  meters,  with  an  area  of  6,560  square  me- 
ters. Subsequent  glidings  occurred  in  October  and  November. 

The  gliding  began  on  the  steeper  slopes  at  a  distance  from 
shore,  and  was  then  transferred  shoreward.  The  first  effect  of  the 
gliding  of  February  9  was  the  lowering  of  the  outer  slope  from 
31  per  cent,  to  27  per  cent.,  but  the  gliding  of  June  12  caused  the 
complete  baring  of  the  rock  for  a  distance  of  150  meters  or  more, 
and  a  change  of  grade  back  to  30  per  cent,  or  31  per  cent.,  and 
even  a  higher  one  farther  lakeward.  This  became  even  more  pro- 
nounced in  the  glidings  of  September  and  later.  The  total  extent 
of  the  glidings  was  450  meters,  and  the  material  was  carried  out  to 


SUBAQUEOUS    GLIDINGS  659 

a  depth  of  125  meters.  The  affected  part  of  the  coast  extended 
from  Horgen  to  Kapfnach,  a  distance  of  1.5  km.  The  material  was 
spread  over  the  lake  bottom,  raising  it  from  I  to  3  meters.  In  Oc- 
tober, 1877,  another  small  portion  (the  Sustplatz)  subsided 
(Frankfurter  Zeitung,  Beilage  zu  No.  304,  1877),  showing  that 
movements  are  not  ended.  More  recent  glidings  if  they  occurred 
have  not  come  to  our  notice. 

The  village  of  Zug  has  a  similar  record.  As  early  as  1435,  on 
March  4th,  26  houses  on  the  "Niederen  Gasse,"  in  the  old  part  of 
the  village,  slipped  into  the  lake,  60  persons  perishing  at  the  time. 
In  1593  the  level  of  the  lake  was  lowered  by  drainage,  and  further 
subsidences  occurred.  On  July  5,  1887,  three  successive  portions 
of  the  shore  fell  into  the  lake,  submerging  more  than  20  houses. 
The  material  which  slid  into  the  sea  consisted  of  sandy  mud,  a  delta 
built  by  the  Lorze  when  the  lake  stood  at  its  higher  level.  A  broad 
stream  of  mud  flowed  into  the  sea,  300  meters  from  the  point  of 
fracture,  to  a  depth  of  23  meters,  under  the  lake  level,  and  then  con- 
tinued outward  to  a  distance  of  about  1,020  meters  from  shore  and 
a  depth  of  45  meters  below  lake  level  as  a  broad  mud  flow  150  to 
250  meters  wide  and  from  i  to  4  meters  high.  The  -gliding  began 
in  the  lakeward  region,  and  migrated  landward,  as  in  the  case  of 
headward-growing  streams.  The  remarkable  fact  here  is  that  the 
average  grade  of  the  surface  along  which  the  gliding  has  taken 
place  from  the  break  to  the  end  of  the  mud  stream,  a  distance  of 
1,020  meters,  was  only  4.4  per  cent.  The  earlier,  smaller  move- 
ment extended  for  only  about  500  meters  into  the  lake  and  over  a 
grade  of  6  per  cent.  The  same  rule  thus  seems  to  hold  for  the 
subaquatic  as  for  the  subaerial  solifluction,  namely,  the  larger  the 
moving  mass  the  smaller  the  average  slope  on  which  it  moves. 

Many  similar  though  less  instructive  glidings  have  taken  place 
on  the  Swiss  lakes,  among  them  those  of  Montreux-Veytaux  on 
Lake  Geneva  ( Schardt-85  ;  86).  Nathorst  has  also  described  simi- 
lar subaquatic  glidings  in  Sweden. 

In  1895  or  thereabouts  movements  of  this  type  occurred  at 
Odessa,  where  several  buildings  slid  into  the  Black  Sea.  The  dis- 
tance to  which  this  mass  was  carried  is  unknown,  but  it  was  on  a 
much  larger  scale  than  that  at  Zug. 

Submarine  glidings  of  this  type  are  probably  common,  but  no 
measurements  are  made  of  them.  Such  glidings  are  often  indicated 
on  the  steeper  slopes  by  the  breaking  of  the  cables.  In  no  case, 
however,  have  the  magnitude  and  extent  of  the  glidings  been  ascer- 
tained, though  dislocations  by  faulting  are  known  (see  page  890). 

It  is  of  course  evident  that  material  thus  sliding  down  a  sub- 


66o 


PRINCIPLES    OF    STRATIGRAPHY 


marine  surface  must  be  piled  up  to  some  extent  in  the  deeper  areas 
where  it  comes  to  rest.  As  the  result  of  such  gliding  the  strata  must 
suffer  much  deformation,  especially  if  they  are  at  all  consolidated. 
Such  deformations  have  all  the  characters  of  orogenic  disturbances 
due  to  lateral  pressure,  and  indeed  it  has  been  suggested  that  some 
extensive  mountain  folds  and  overthrusts  may  have  originated  in 
this  manner.  These  deformations  will  be  more  fully  discussed  in 
Chapter  XX^ 

Accessory  Features  of  Subaqueous  Gliding.  Among  the  ac- 
cessory features  produced  by  subaqueous  and  especially  submarine 
solifluctions,  we  may  mention  in  addition  to  the  deformations  al- 
ready noted,  and  to  be  more  fully  discussed  in  a  later  chapter,  the 
following  phenomena  : 


FIG.  131.  Diagram  illustrating  the  changes  in  stratification  due  to  subaquatic 
gliding.  In  the  shore  section  strata  are  eliminated,  while  farther 
out  duplication  occurs.  (After  Heim.) 


I.  Increase  of  the  strata  in  the  lower  regions  where  the  shore 
material  is  carried  by  gliding,  and  where  strata  are  thus  repeated  by 
the  superposition  of  portions  of  the  same  strata  upon  one  another. 
2.  Reduction  of  the  number  of  strata  in  the  zone  affected  by  the 
gliding  where  the  ends  of  the  strata  are  thus  removed,  and  on  the 
deposition  of  subsequent  beds  a  local  disconformable  relation  is  pro- 
duced with  hiatus  signifying  no  appreciable  time  interval.  3.  Su- 
perposition of  older  on  younger  beds.  Thus  at  Zug,  the  mass  which 
slid  into  the  sea  was  more  than  99  per  cent,  formed  during  the 
former  high-water  period  of  the  lake,  and  came  to  rest  by  gliding 
upon  the  deposits  formed  since  the  present  water  level  was  estab- 
lished (Fig.  131).  4.  Displacement  of  facies.  Thus  at  Zug  gravel 
and  even  coarse  blocks  were  carried  by  gliding  into  the  region  where 
they  would  otherwise  be  absent.  In  submarine  solifluction  shore 
sediments  may  be  carried  out  to  the  neritic  belt,  or  the  latter  into 
abyssal  regions.  A  shore  breccia  may  thus  come  to  lie  among  off- 
shore marine  sediments.  5.  Destruction  of  life.  The  benthonic  and  to 


NfiRITIC  DEPOSITS  66 1 

some  extent  also  the  pelagic  life  will  be  destroyed  by  such  glidings 
and  the  distribution  of  the  fauna  will  be  altered.  Such  a  case  has 
been  noted  in  connection  with  the  rock  slide  at  Elm.  Such  dis- 
turbance might  result  in  the  sudden  destruction  of  the  entire  ben- 
thonic  fauna,  young  and  old  alike,  all  stages  being  found  together. 
Above  the  mass  of  material  which  caused  this  destruction  may  come 
a  stratum  carrying  only  remains  of  planktonic  organisms  without 
sedentary  benthos,  which  would  return  only  after  a  while.  (Heim- 


The  Permanently  Submerged  or  Neritic  Zone  (Flachsee,  Shallow 
Water  or  Thalassal  Zone). 

This  zone  extends  from  the  low-water  line  of  the  shore  zone,  a 
somewhat  variable  line,  to  the  edge  of  the  continental  shelf.  Sev- 
eral provinces  of  more  or  less  importance  may  be  recognized,  chief 
of  which  are : 

1.  The  estuary. 

2.  The  marginal  lagoon. 

3.  Epicontinental  seas  and  mediterraneans. 

4.  The  ocean  littoral. 

i.  The  Estuary.  This  is  the  point  of  meeting  place  of  the 
terrestrial  and  marine  realms.  It  receives  on  the  one  hand  the  sedi- 
ments and  other  material  brought  by  the  rivers  from  the  land,  and 
on  the  other  it  admits  the  waters  of  the  sea,  which  for  a  time  at 
least  modify  the  character  of  the  deposit.  Alternately  the  waters  of 
the  land  and  of  the  sea  predominate,  as  a  result  of  which  the  de- 
posits formed  in  the  estuary  will  have  characteristics  typical  of  both. 
As  a  good  example,  we  may  consider  the  estuary  of  the  La  Plata  in 
South  America.  This  has  a  length  of  125  miles,  and  receives  the 
water  of  the  Parana  and  Uruguay  rivers.  The  currents  of  these 
rivers  thus  come  into  periodic  contention  with  the  tides  from  the 
Atlantic.  (Willis— 105  ://pz.)  Where  the  power  of  the  tidal  wave 
balances  that  of  the  rivers,  no  current  exists,  a  condition  which  may 
continue  for  hours.  (Revy-8i :  <?p,  jo.)  Here  at  from  10  to  20 
miles  above  the  mouth  of  the  estuary,  the  material  held  in  sus- 
pension is  dropped,  as  a  result  of  which  submerged  banks  are  form- 
ing, which  eventually  grow  into  islands.  The  current  during  both 
flood  and  ebb  tide  is  swifter  in  the  deep  channels  than  in  shallow 
portions  of  the  estuary,  hence  deposits  made  during  flood  tide  will 
be  more  copious  over  the  shallows  than  in  the  deeper  channels, 


662 


PRINCIPLES    OF    STRATIGRAPHY 


which  latter  are  also  more  subject  to  scour  during  the  ebb  tide. 
The  shallows  thus  become  tide  flats,  which  later  are  raised  rush- 
grown  islands,  thus  restricting  the  water  within  narrow  channels. 
The  original  length  of  the  La  Plata  was  325  miles,  but  about  two- 
thirds  of  this  has  been  filled  up  in  the  manner  described.  Where 
material  of  different  sizes  is  brought  by  the  rivers  into  the  estuary 
the  coarser  will  be  dropped  when  the  current  is  first  checked  by  the 
rising  tide,  the  finer  following  when  the  checking  is  complete. 
During  the  scouring  of  the  bottom  at  ebb  tide  much  of  the  fine 
material  may  be  carried  away  again.  (Willis-iO5  :  492.) 

The  floor  of  the  Hudson  has  in  many  places  been  built  up  by 
mud  deposits  to  such  an  extent  that  extensive  mud  flats  are  laid 


FIG.  132.  Diagram  illustrating  the  relationship  between  subsidence  and  the 
growth  of  estuarine  deposits.  A,  bar  and  lagoon  (barachois)  on 
a  young  coast;  B,  estuarine  deposits  covered  by  transgressing 
sea  on  subsiding  coast.  The  bar  and  lagoon  rest  on  terrestrial 
deposits  and  not  on  the  old  crystalline  base.  (After  Barrell.) 


bare  at  low  tide,  a  hundred  or  more  miles  above  its  mouth,  while 
the  channel  over  much  of  this  distance  is  comparatively  shallow. 
The  rock  bottom  of  the  Hudson,  on  the  other  hand,  is,  in  places,  as 
in  the  Highlands,  more  than  600  feet  below  tide  level.  It  is  proper 
to  note,  however,  that  a  part  of  the  filling  of  this  channel  is  proba- 
bly glacial,  only  the  upper  hundred  feet  on  the  average  being  river 
silt. 

The  estuary  of  the  Severn  (Sollas-89)  may  serve  as  another 
example.  The  tidal  channel  of  this  river  is  notorious  for  its  mud. 
"At  high  tide  it  is  filled  with  a  sea  of  turbid  water,  thick  and 
opaque  with  tawny-colored  sediment;  as  the  tide  ebbs  a  broad  ex- 
panse of  shining  mud  flats  is  revealed  fringing  the  coast;  but  so 
like  is  the  water  to  the  mud  that,  seen  from  a  distance,  it  is  often 
hard  to  tell  where  the  sea  ends  and  the  shore  begins.  It  is  the 
same  with  its  tributaries,  the  Wye,  the  Usk,  Ely  and  Rhymney  on 


ESTUARINE    DEPOSITS  663 

the  Welsh  side,  the  Avon,  Yeo,  Parrot  and  others  on  the  English 
coast."     (Sollas-Sgid//.) 

The  origin  of  this  mud  has  been  a  subject  of  much  dispute.  In 
part  no  doubt  it  is  supplied  by  the  rivers  which  have  a  catchment 
basin  of  9,193  square  miles  (English),  but  much  is  also  produced 
by  the  Waves  washing  the  shores  of  the  estuary.  The  water  in  the 
tidal  portion  of  the  Severn  Channel  flows  up  and  down  twice  daily 
at  the  rate  of  from  6  to  12  miles  an  hour,  a  velocity  much  greater 
than  that  required  to  move  along  large  boulders  of  rocks.  As  a 
result  scouring  of  the  channel  occurs  in  many  places.  The  devel- 
opment of  the  currents  has  been  described  by  Mr.  W.  R.  Browne 
(13)  :  "In  ordinary  tidal  channels  such  as  the  Avon  below  Bristol, 
the  course  of  events  during  an  ebb  seems  to  be  as  follows.  At  first 
the  slope  of  the  surface  is  exceedingly  small  (in  the  Avon  it  was 
about  ij/2  feet  in  7*4  miles),  and,  while  the  velocity  at  the  surface 
is  considerable,  it  diminishes  rapidly  from  thence  downward,  and 
at  some  distance  from  the  bottom  becomes  nil.  This  continues  for 
about  two-thirds  of  the  ebb,  the  surface  velocity  increasing  up  to  a 
certain  point,  and  then  becoming  nearly  constant.  During  all  this 
time  not  only  is  no  scour  going  on  at  the  bottom,  but,  if  the  waters 
be  muddy,  an  actual  deposition  of  silt,  is  taking  place.  At  this  time, 
after  about  two-thirds  of  the  ebb,  the  water  has  fallen  about  three- 
quarters  of  its  total  height,  the  slope  of  its  surface  has  considera- 
bly increased,  and  the  conditions  approximate  to  those  of  an  ordi- 
nary river.  The  bottom  layers  of  the  water  then  spring  suddenly 
into  motion,  the  surface  velocity  diminishes  steadily  as  the  tidal 
waters  disappear,  until  it  assumes  the  normal  rate  of  the  low-water 
flow.  During  this  period  a  scour  of  the  bottom  is  of  course  going 
on ;  but,  as  this  velocity  is  not  much  higher  than  in  the  subsequent 
period  of  low- water  flow,  the  rate  of  scour  will  not  be  much  greater ; 
and  the  actual  scour  will  be  insufficient  to  compensate  for  the 
amount  of  deposit  from  the  tidal  waters  which  has  taken  place,  not 
only  during  the  period  of  high  water,  but  also  during  the  first  two- 
thirds  of  the  ebb.  It  must  follow,  therefore,  that  the  scouring  effect 
of  the  tide  is  little  or  nothing,  and  the  observed  incapacity  of  tidal 
flows  to  sweep  away  the  silt  they  have  deposited  is  amply  and  satis- 
factorily explained." 

Sollas  thinks  that  eventually  much  of  the  silt  will  find  its  way 
t)ut  to  sea,  owing  to  the  constant  outward  pressure  of  the  normal 
river  current.  As  a  part  of  the  material  is  carried  seaward  from 
the.  constant  mass  moved  back  and  forth,  new  material  is  supplied  by 
the  rivers. 

The  material  of  this  estuarine  mud  consists  of  "a  variable  qnan- 


664  PRINCIPLES    OF    STRATIGRAPHY 

tity  of  fine,  argillaceous  granules,  small,  angular  fragments  of  color- 
less transparent  quartz  containing  numerous  minute  included  cavi- 
ties, a  few  similar  fragments  of  flint,  siliceous  fragments  of  a 
glauconite  green  color,  minute  crystals  of  quartz  of  the  ordinary 
form,  minute  prisms  of  tourmaline  highly  dichroic  and  similar  in 
form  to  macroscopic  prisms  of  schorl,  and  minute  rhombohedra  of 
calcite."  Materials  of  organic  origin  also  occur,  such  as  coccoliths 
and  rarely  coccospheres,  both  of  the  ordinary  cyatholith  type  so 
common  in  adjacent  seas  and  in  the  Atlantic  ooze;  further,  For- 
aminifera,  including  Miliola,  Textularia,  several  species,  Nonionina 
crassula,  Polystomella  umbilicata,  Rotalia  sp.,  Spirillina  sp.,  etc., 
more  rarely  spicules  of  Alcyonaria,  fragments  of  echinoderm  skele- 
tons and  minute  spines;  and  triradiate  spicules  of  calcisponges, 
probably  Sycandra.  "Most  of  the  Foraminifera  are  quite  empty, 
glassy  and  transparent;  but  some  contain  a  brownish,  soft  granu- 
lar material;  and  in  one  instance  a  small  Rotaline  form  was  ob- 
served partially  replaced  by  pyrites."  (90-  6*4-)  The  siliceous  or- 
ganic remains  comprise  chiefly  sponge  spicules,  very  rarely  Radi- 
laria,  and  a  variable  quantity  of  diatoms.  The  remains  of  other 
organisms  found  in  the  mud  are  all  of  marine  types,  though  they 
occur  on  the  banks  of  rivers  at  a  great  distance  from  a  truly  marine 
area. 

In  the  muds  of  the  rivers  above  the  limit  of  tidal  influence,  only 
spicules  of  fresh-water  sponges  and  diatoms  were  found  (Spongilla 
fluviatilis),  foraminifera  and  other  marine  organisms  being  absent. 
Nor  were  any  of  these  organisms  derived  from  the  Mesozoic 
strata  through  which  these  rivers  flow.  The  organic  remains  of  the 
modern,  as  well  as  the  older,  muds  of  the  Severn  estuary  were  ap- 
parently all  derived  from  the  Bristol  Channel,  which  is  the  further 
enlargement  of  the  Severn  estuary  and  along  the  shores  of  which 
from  10  to  15  miles  west  of  the  Severn  estuary  marine  life  abounds. 
The  older  alluvial  deposits  of  the  Severn  estuary  have  a  maximum 
thickness  of  about  50  feet.  These  comprise  in  descending  order : 


a     More  sandy  zone  5  to  7  feet 
Zone  i.     Upper  clay     \  b    More    argillaceous    zone,     with    disseminated 

vegetable  matter  7  to  8  feet  ± 
Upper  peat,  I  to  2  feet  6  inches 

Zone  2.     Lower  clay 

Lower  peat,  i  to  4  feet 

Zone  3.     Sands  and  mud 
Gravel 
Triassic  sandstones 


ESTUARINE    DEPOSITS  665 

The  gravel  contains  glacial  pebbles  and  rolled  boulders  up  to  a 
cubic  foot  in  size.  It  is  not  always  present.  The  mud  is  a  marine 
or  tidal  deposit  like  the  blue  clay  which  replaces  it  elsewhere,  and 
from  which  it  differs  chiefly  in  being  nearly  or  quite  free  from 
clay.  There  seems  to  be  a  gradual  transition  from  coarse  at  the 
bottom  to  fine  at  the  top.  Some  of  the  sands  contain  fragments  of 
a  bryozoan,  and  many  chips  of  pelecypod  shells,  including  a  small 
Avicula.  Foraminifera,  spines  of  echinoderms  and  sponge  spicules 
also  occur.  In  a  section  through  Caldicot  Marsh  near  Portskewet, 
fifty  feet  deep,  a  bed  of  marl  was  encountered  10  feet  above  the 
base,  which  contained  a  mixture  of  fresh  and  brackish  water  shells, 
such  as  Limnsea,  Planorbis,  Scrobicularia  piperata  and  Cardium 
edule.  Diatoms  are  common  in  it,  and  also  remains  of  Chara. 
A  similar  bed  occurs  near  Cardiff,  about  19  miles  farther  south.  It 
occurs  at  the  same  depth.  Altogether  the  beds  of  zone  3  repre- 
sent a  normal  estuarine  deposit,  with  a  fauna  and  flora  both  brack- 
ish and  fresh. 

The  lower  part  of  zone  2  has  remains  of  forest  trees  associated 
with  it.  It  is  covered  by  blue  clay  with  Foraminifera  and  other 
marine  organic  remains,  indicating  a  subsidence.  The  upper  Peat 
bed,  sometimes  the  only  one,  "consists  of  various  plant  remains,  in- 
cluding leaves  and  roots  of  yellow  flags  and  spores  and  mycelia  of 
fungi,  while  its  upper  surface  is  strewn  with  trunks  and  branches  of 
trees,  oak,  fir,  and  birch  being  the  chief.  The  fir  still  retains  its 
bark,  and  the  heartwood,  when  cut,  is  often  found  to  have  pre- 
served its  original  color.  Some  of  the  wood  has  been  bored  by 
some  kind  of  beetle."  (go  1621.)  The  peat  is  very  pure,  though 
containing  occasional  sand  grains,  Foraminifera  or  sponge  spicules. 
It  often  contains  an  abundance  of  spherules  of  iron  pyrites,  and 
sometimes  the  vegetable  cells  are  filled  with  it,  these  occupying  the 
place  of  the  departed  protoplasm  within  the  resistant  cell  walls. 
The  origin  of  this  pyrite  is  similar  to  that  of  coast  marshes  or 
swamps  in  general.  When  the  salt  water  comes  in  contact  with  the 
decaying  vegetable  matter  a  series  of  reactions  occurs,  which  will 
end  in  the  formation  of  iron  pyrites.  The  upper  clay  contains 
Foraminifera,  sponge  spicules  and  other  marine  organisms,  besides 
disseminated  vegetal  material. 

2.  The  Marginal  Lagoon  or  Barachois.  These  names  are  ap- 
plied to  the  water  bodies  cut  off  from  the  main  portion  of  the  sea 
by  the  formation  of  barrier  beaches.  So  long  as  the  lagoon  is  not 
filled  in  by  silt  and  organic  deposits,  it  belongs  to  the  neritic  zone 
of  the  littoral  district.  The  process  by  which  it  is  converted  into 


666  PRINCIPLES    OF    STRATIGRAPHY 

tidal  flats  and  marshes  has  already  been  sketched.  (See  Chapter 
XL)  It  need  only  be  noted  here  that  the  deposits  accumulating 
in  the  lagoon  are  the  finer  sands  and  muds  brought  by  the  tidal 
currents,  and  the  sands  blown  across  from  the  beach.  Though 
stratification  may  be  well  marked  in  these  lagoon  deposits,  the  evi- 
dence of  agitation  by  waves  or  currents  is  slight.  Cross-bedding 
structure  is  not  characteristic  of  such  deposits,  but  ripple  marks, 
of  the  oscillation  type,  i.  e.,  symmetrical,  sharp  crests  with  broad, 
rounded  troughs,  may  be  formed.  A  characteristic  feature  of  these 
deposits  is  the  presence  of  the  eel  grass  leaves  which  penetrate  the 
strata  in  a  vertical  direction,  having  been  instrumental  in  the  pre- 
cipitation around  them  of  the  suspended  material,  through  a  check- 
ing of  the  velocity  of  the  current.  In  the  last-formed  deposits  of 
the  lagoons  organic  matter  will  predominate  and  peat  beds — the 
coal  of  the  future — mark  the  transition  through  the  shore  zone  to 
terrestrial  conditions.  Of  older  deposits  of  this  type  the  Low- 
ville  limestone  has  already  been  cited.  This  is  a  formation  of  fine 
lime  mud  deposited  around  vertical  stems  or  branches  of  a  marine 
organism,  probably  not  a  plant,  however.  Thus  the  resulting  calci- 
lutyte  is  penetrated  by  numerous  vertical  tubules,  now  largely  oc- 
cupied by  crystalline  calcite,  and  producing  on  the  bedding  planes 
the  so-called  bird's-eye  structure  which  gave  the  formation  its  orig- 
inal name. 

3.  Epicontinental  Seas  and  Mediterraneans.  Tho'se  portions  of 
the  littoral  district  which  extend  into  the  land  as  arms  or  partly 
enclosed  embayments  of  no  great  depth,  without  being  estuaries  of 
great  rivers,  are  of  considerable  importance  to  the  stratigrapher, 
since  epicontinental  seas  of  this  type  were  very  characteristic  of 
many  geologic  epochs.  Their  chief  significance  is,  however,  a  faunal 
one,  since  sedimentation,  except  in  special  cases,  does  not  differ 
much  from  that  upon  the  continental  shelf.  Nearly  landlocked  epi- 
continental seas  within  pluvial  districts,  such  as  Hudson  Bay  or  the 
Baltic  Sea,  do  not  differ  appreciably  from  the  littoral  belt  of  the 
open  ocean,  but  where  such  enclosed  seas  occur  in  arid  climates  the 
greater  density  and  increased  salinity  of  their  waters  will  influence 
perceptibly  not  only  the  fauna  and  flora,  but  also  the  deposits.  If 
the  intracontinental  sea  of  the  arid  or  semiarid  climate  is  a  med- 
iterranean, i.  e.,  if  its  center  extends  to  depths  much  greater  than 
its  outlet,  the  peculiarities  of  the  deposits  will  be  emphasized.  The 
Black  Sea  forms  an  instructive  example  of  the  conditions  found  in 
an  almost  completely  enclosed  water  body  of  great  depth  in  a  semi- 
arid  region.  According  to  Andrussow  (5;  2i:?oo),  the  superficial 


MARINE    LITTORAL  667 

water  layer,  of  about  125  fathoms,  has  a  less  salinity  and  density 
than  the  deeper  water,  being  largely  renewed  by  the  fresh  water 
of  the  drainage.  The  heavier  lower  water  is  derived  from  the 
Mediterranean  by  way  of  the  richly  saline  Marmora  and  yEgean 
seas,  requiring  about  1,700  years  for  its  renewal.  Vertical  cur- 
rents are  slight  on  account  of  the  greater  density  of  the  deeper 
water,  and  hence*  these  lower  waters  have  not  sufficient  oxygen  to 
support  animal  life.  Sulphuretted  hydrogen  is  separated  out,  prob- 
ably through  the  agency  of  sulphobacteria,  in  the  deeper  water ;  be- 
ginning at  100  fathoms,  with  33  c.c.  of  H2S  per  100  liters  of  water 
until,  at  500  fathoms,  570  c.c.  of  H2S  per  100  liters  of  the  water  are 
separated.  Below  this  the  increase  is  less^rapid.  As  the  H2S  in- 
creases, the  sulphates  of  the  water  decrease,  and  carbonates  and 
FeS  are  separated  out. 

The  sediments  of  the  Black  Sea  comprise  sandy  detritus  to  a 
depth  of  20  fathoms,  below  which  occurs  gray,  blue,  sticky  mud 
rich  in  Modiola  phaseolina  to  the  loo-fathom  line.  In  the  great 
depths  occurs  a  very  fine,  sticky,  black  mud  with  rich  separation  of 
FeS,  abundant  remains  of  planktonic  diatoms,  and  shells  of  young 
pelecypods,  which  have  descended  to  this  depth  on  completion  of 
their  early  pelagic  existence  (mero-planktonic  stage).  Besides  the 
black  is  a  dark-blue  mud  with  less  FeS,  but  a  richer  separation  of 
CaCO3  in  minute  grains,  this  lime  often  constituting  thin  banks, 
while  pelagic  diatoms  are  likewise  abundant.  Clarke  (21  :  201}  has 
suggested  the  possible  origin  of  some  of  the  Upper  Devonic  black 
shales  of  New  York  (Portage)  under  similar  conditions,  but  this  is 
a  much  mooted  question.  Pompeckj  (71  :  43  et  seq)  has  interpreted 
the  black  Posidonia  bronni  shales  of  the  Jurassic  of  Regens- 
burg,  Bavaria,  as  deposits  of  this  type.  It  is,  however,  difficult  to 
understand  how  such  a  region  can  furnish  conditions  for  the  per- 
fect preservation  of  the  saurians  of  that  period,  so  that  in  some 
cases  even  the  skin  of  the  animals  is  intact. 

4.  The  Ocean  Littoral,  or  the  Neritic  Zone.  This  is  the  most 
widely  distributed  littoral  belt  at  the  present  time.  Its  deposits  vary 
considerably,  according  to  distance  from  shore,  depth  of  water  and 
relation  to  currents.  In  general  a  seaward  gradation  in  the  texture 
of  the  material  from  coarse  to  fine  is  observable,  sands  being  found 
near  shore  (though  often  extending  out  for  great  distances),  while 
muds  are  formed  further  offshore  and  in  specially  protected  places. 
In  the  Arabian  Sea  muds  are  carried  from  700  to  800  miles  from 
land,  owing  to  the  nature  of  the  ocean  currents.  Calcareous  accu- 
mulations are  typical  of  this  region,  especially  those  formed  around 
coral  reefs.  These  have  been  fully  described  above. 


668 


PRINCIPLES    OF    STRATIGRAPHY 


DEPOSITS  OF  THE  BATHYAL  DISTRICT. 

«  < 

On  the  whole  the  deposits  of  this  region,  which  nominally  lie  be- 
tween 200  and  900  meters  or  between  100  and  500  fathoms,  are  con- 
tinuous with  those  of  the  neritic  zone  on  the  one  hand,  and  with 
those  of  the  abyssal  on  the  other.  The  following  deposits  seem  to 
be  most  characteristic  of  this  district,  though  extending  into  both  of 
the  adjoining  ones: 


Table  Showing  Kinds  and  Distribution  of  Bathyal  Deposits. 


Clastic  deposits 

Mean  depth 

Area  covered 
in  square  miles 

in  fathoms 

in  meters 

I 

2 

3 

4 
5 
6 

7 
8 

Blue  mud  

1,411 
623 
513 
449 
i,033 
243 
740 
176 

2,397 
1,140 
920 

821 
1,889 
444 
i,353 
322 

14,500,000 

100,000 

850,000 
600,000 

2,556,800 

Red  mud 

Green  mud  

Green  sand 

Volcanic  mud.  . 

Volcanic  sand  

Coral  mud 

Coral  sand  

The  table  on  page  669,  taken  from  Clarke's  Data  of  Geochemistry 
(2ob:^65p),  gives  the  analysis  of  the  terrigenous  and  volcanic  muds 
and  the  green  sands:  i,  Blue  mud  dried  at  110°  (Brazier);  2, 
red  mud  dried  at  100°  (Hornung)  ;  3,  green  mud  dried  at  110° 
(Brazier)  ;  4,  green  sand  dried  at  110°  (Brazier)  ;  5,  volcanic  mud 
dried  at  110°  (Brazier). 

Three  types  of  land-derived  muds  are  found  in  the  modern  sea 
away  from  the  shore.  These  are  the  blue,  the  red  and  green  muds. 

The  Blue  or  Slate-Colored  Mud.  This  is  the  most  widely  dis- 
tributed, extending,  according  to  Murray  and  Renard,  over  an  area 
of  14,500,000  square  miles.  It  covers  the  floors  of  the  shallow  sea 
to  the  edge  of  the  continental  shelf,  as  well  as  the  floor  of  the  entire 
polar  sea.  The  greatest  depth  at  which  it  was  observed  by  the 
Challenger  was  5,120  meters.  In  the  Gulf  of  Naples  it  begins  at 
a  depth  of  15  meters,  where  in  contact  with  the  sea  water  it  gen- 


BATHYAL   DEPOSITS 


669 


TABLE  OF  ANALYSES  OF  MUDS  OF  TERRIGENOUS  AND  VOLCANIC 

ORIGIN. 


(i) 
Blue  mud 

(2) 

Red  mud 

(3) 
Green  mud 

(4) 
Green  sand 

(5)  . 
Volcanic 
mud 

Ignition  
SiO2                

5.60 
64.20 

6.  02 
31  66 

3-30 

^I    27 

9.10 

2Q    7O 

6.22 
•\A     12 

A12O3  

IV  55 

9.21 

4.08 

TI    2S 

Q    22 

Fe2O3 

8  *8 

452 

12    72 

5O5 

I  ^    A6 

MnO2 

trace 

CaO  

2.  .  SI 

25.68 

O.  1O 

O   22 

I    44 

MgO 

O   2S 

2    O7 

O    12 

O    IT. 

O    22 

Na2O  .. 

I    6^ 

K2O  

I  .  V* 

CaCO3  

2.94 

46.  16 

4Q   46 

12    22 

Ca3P2O8  
CaSO4  

i-39 

O   42 



0.70 

o  s8 

trace 
i  07 

trace 
o  27 

MgCO3 

.,       o   76 

O    S7 

2    O2 

o  8^ 

SO3   . 

O   27 

CO2  

17   11 

Cl  

2.46 

Total  

IOO   OO 

IOI   98 

IOO   OO 

IOO   OO 

IOO   OO 

LessO  =  Cl  

0.87 
IOI.  II 

erally  has  a  red  or  brown  color,  due  to  iron  oxide  or  hydrate,  and 
when  dried  its  color  is  gray  or  brown  from  the  oxidation  of  its  con- 
tained iron  sulphides.  Pure  clay  often  constitutes  only  a  small  pro- 
portion of  this  mud  (though  ranging  from  16  to  97  per  cent.),  and 
the  lime  content  may  be  as  high  as  35  per  cent.  Quartz  is  a  char- 
acteristic constituent.  This  is  the  type  of  mud  which  has  in  the  past 
given  rise  to  most  of  the  marine  shales  and  slates. 

The  Red  Mud.  This  is  much  more  restricted  -in  its  distribution 
than  either  the  blue  or  green.  It  is  found  opposite  the  mouths  of 
tropical  rivers,  such  as  the  Amazon  and  the  Yang-tze-Kiang,  and  is 
derived  from  the  red  laterite  or  residual  soil  of  the  tropical  coun- 
tries. Its  percentage  of  pure  clay  varies  from  28  to  68,  and  its 
lime  content  varies  from  6  to  60  per  cent. ;  glauconite  is  absent,  but 
quartz  is  characteristic.  The  red  mud  closely  resembles  the  red  mud 
of  the  deep  sea,  which  has,  however,  a  different  origin,  being  proba- 
bly in  large  part  the  product  of  decay  of  volcanic  material  which 
has  settled  to  this  depth.  Muds  of  this  kind  may  easily  preserve  an 


670  PRINCIPLES    OF    STRATIGRAPHY 

abundance  of  shells  and  other  remains  of  marine  organisms.  Since 
they  are  formed  opposite  the  mouths  of  great  rivers,  which  may 
sweep  terrestrial  organisms  into  the  sea,  such  remains  may  also  be 
expected  in  these  deposits. 

The  Green  Mud.  This  ranges  in  depth  from  180  to  2,300  meters 
(99  to  1,250  -|-  fathoms),  and  may  contain  as  much  as  56  per  cent, 
of  lime.  In  shallower  depths  this  green  mud  passes  into  greensands. 
The  percentage  of  clay  in  the  green  mud  varies  from  24  to  48. 
Glauconite  is  one  of  the  chief  constituents  of  both  the  greensands 
and  green  muds. 

Greensand.  This  is  essentially  the  mineral  glauconite,  an  impure 
hydrous  silicate  of  iron  and  potassium.  Clarke  states  that,  "accord- 
ing to  the  best  analyses,  glauconite  probably  has  when  pure  the 
composition  represented  by  the  formula  Fe"'  KSi,O,.--aq.,  in  which 
some  iron  is  replaced  by  aluminum,  and  other  bases  partly  replace 
K."  This  is  forming  in  the  present  ocean  near  the  "mud  line" 
around  continental  shores.  It  is  never  pure,  but  contaminated  by 
alteration  products  and  other  substances,  and  hence  its  composition 
varies  widely.  In  the  present  ocean  it  is  chiefly  formed  on  the  in- 
terior of  foraminiferal  shells,  and  it  is  believed  that  the  decompos- 
ing organic  matter  in  these  shells  is  responsible  for  its  formation. 
According  to  Murray  and  Renard  (62:3.83),  the  shell  is  partly 
filled  with  fine  silt  or  mud,  and  upon  this  the  organic  matter  will 
act.  "Through  intervention  of  the  sulphates  contained  in  the  sea 
water,  the  iron  of  the  mud  is  converted  into  sulphide,  which  oxi- 
dizes later  to  ferric  hydroxide.  At  the  same  time  alumina  is  re- 
moved from  the  sediments  by  solution,  and  colloidal  silica  is  lib- 
erated. The  latter  reacts  upon  the  ferric  hydroxide  in  presence  of 
potassium  salts  extracted  from  adjacent  minerals,  and  so  glauconite 
is  produced."  (Clarke-2ob  -.402.)  The  constant  association  of  the 
glauconite  shells  with  the  debris  of  rocks  in  which  potassium-bear- 
ing minerals  such  as  orthoclase  and  muscovite  occur  seems  to  sus- 
tain this  view  of  Murray  and  Renard  of  the  origin  of  glauconite. 

Glauconite  may,  however,  form  under  other  conditions  than 
those  now  obtaining  in  the  glauconite  region  of  the  present  oceans. 
L.  Cayeux  (15)  has  shown  that  in  certain  instances  glauconite  has 
formed  subsequent  to  the  consolidation  of  the  rocks  in  which  it 
occurs.  Cayeux  shows  that  this  mineral  can  also  form  without  the 
intervention  of  organisms. 

While  glauconite  of  the  present  sea  and  in  the  sedimentary  rocks 
is  crystalline  (monoclinic,  La  Croix),  having  a  definite  cleavage, 
though  not  crystal  form,  the  mineral  caladonite  of  nearly  identical 
composition  is  earthy  in  texture  and  never  granular.  This  is  a  de- 


GREENSANDS  671 

composition  product  of  augite  in  various  basaltic  rocks,  and  may  be 
identical  with  glauconite  (Clarke).  Another  mineral  of  similar 
appearance  is  greenalite,  found  in  the  iron-bearing  rocks  of  the 
Mesabi  range  of  Minnesota.  It  is  free  from  potassium,  the  iron 
being  practically  all  in  the  ferrous  state  (Leith-56:  240),  while  in 
glauconite,  where  potassium  is  an  essential  constituent,  the  iron  is 
mainly  in  the  ferric  state.  Cayeux  has  also  observed  that  glau- 
conite is  frequently  present  in  arable  soils,  in  all  conditions  from 
perfect  freshness  to  complete  alteration  into  limonite,  to  which 
Clarke  remarks  that  the  formation  of  the  species  is  perhaps  "one 
of  the  modes  by  which  potassium  is  withdrawn  from  its  solution  in 
the  ground  water."  (20^:494.)  "Probably,  in  all  their  occur- 
rences," says  Clarke,  "the  final  reaction  is  the  same,  namely,  the 
absorption  of  potassium  and  soluble  silica  by  colloidal  ferric  hy- 
droxide. In  the  ocean  these  materials  are  prepared  by  the  action  of 
decaying  animal  matter  upon  ferruginous  clays  and  fragments  of 
potassium-bearing  silicates.  In  the  sedimentary  rocks,  where  glau- 
conite appears  as  a  late  product,  the  action  of  percolating  waters 
upon  the  hydroxide  would  account  for  its  formation.  In  igneous 
rocks  the  hydroxide  is  derived  from  augite,  or  perhaps  from  olivine, 
and  percolating  waters  again  come  into  play.  Thus  the  various  pro- 
ductions of  glauconite  and  caladonite  become  the  results  of  a  single 
process,  which  is  exactly  equivalent  to  that  in  which  .potassium  com- 
pounds are  taken  up  by  clays."  (20^:4^4.) 

Greensands  are  found  in  nearly  all  formations  from  the  Cambric 
to  the  present,  and  often  constitute  a  predominant  element  of  the 
formation,  as  in  the  Cretacic  Greensands  of  England  and  America. 
Analyses  of  the  mineral  from  different  horizons  show  on  the  whole 
a  close  correspondence  in  composition,  there  being,  however,  a  stead- 
ily decreasing  percentage  of  potash  from  the  older  to  the  more  re- 
cent. In  the  table  on  page  672,  the  average  composition  of  various 
glauconites  is  given :  (a)  from  the  Lower  Ordovicic  of  Minnesota, 

(b)  from  the  Cretacic  .Greensands  of  Wooburn,  Antrim,  Ireland, 

(c)  from  the  Cretacic  Greensand  marls  of  Hanover  County,  Vir- 
ginia, (d)  modern  oceanic  glauconite,  mean  of  four  analyses  from 
Challenger  dredgings   (analyses  b,  c,   d  quoted  from  Clarke-2ob : 

494)- 

The  mechanical  composition  of  typical  greensand  marls  (Nave- 
sink)  of  the  Cretacic  of  New  Jersey  has  been  determined  by 
Prather  (73: 162 ;  74)  to  be  as  follows: 

Fine  clay  (settling  out  of  suspension  in  water  in  the  course  of 
from  i  to  24  hours),  14.41  per  cent. ;  sand,  almost  wholly  composed 
of  pure  glauconite,  pyrite,  shell  fragments  and  Foraminifera  (set- 


672 


PRINCIPLES    OF    STRATIGRAPHY 


Table  of  Analyses  of  Glauconite  from  Various  Horizons. 


(a) 
Ordovi- 
cic 

(b) 
Cretacic 
Ireland 

(c)  ; 
Cretacic 
Virginia 

(d) 
Modern 
oceanic 

SiO2 

48.  18 

40.00 

51  .56 

53.61 

A12O3                     

6.97 

13.00 

6.62 

9.56 

Fe9CK 

16.81 

15.  16 

21  .46 

FeO                                  

27.08 

10.  17 

8.33 

1.58 

MnO 

trace 

MgO                                       

i  .97 

0.95 

2.87 

CaO 

I    07 

o  62 

I    IQ 

Na2O 

i  .25 

2.16 

1.84 

0.42 

K2O  

7.40 

8.21 

4.  15 

3-49 

H2O 

8  75 

6    IQ 

IO.  \2 

5.96 

Total 

OQ   6^ 

100  48 

OQ  ct; 

IOO.  ^4 

tling  out  of  suspension  in  water  in  five  minutes  or  less),  85.59  per 
cent.  A  sample  from  a  lower  bed  of  the  same  formation  (Nave- 
sink)  gave  clay  as  above  8.18  per  cent.;  sand,  composed  about 
equally  of  pure  glauconite  and  of  rounded  grains  of  quartz,  with 
some  mica,  91.82  per  cent. 

Many  grains  of  glauconite  represent  internal  molds  of  forami- 
niferal  shells,  though  frequently  further  enlargement  of  these  molds, 
after  the  solution  of  the  shell,  produces  irregular  glauconite  nodules. 
W.  B.  Clark  (17:  238 ';  18)  believes  that  the  New  Jersey  glauconites 
were  formed  in  much  the  same  manner  as  the  modern  glauconites 
of  the  ocean,  but  Prather  (74:509)  points  out  some  objections  to 
this  interpretation,  and  cites  evidence  of  shallow-water  conditions 
during  the  accumulation  of  these  glauconite  sands.  He  finds  that 
the  casts  of  Foraminifera  are  the  exception.  The  greensand  grains 
of  the  Lower  Ordovicic  dolomites  of  Minnesota  are  regarded  by 
Hall  and  Sardeson  (42 :  186}  as  having  their  origin  "in  the  chem- 
ical conditions  of  the  mingled  mineral  matters  of  the  including 
rocks.  .  .  ."  and  not  in  the  chemical  changes  within  foraminiferal 
shells.  (See  Hunt-49 :  joj ;  50 : 196,  309  551:  257.)  Though  mod- 
ern glauconite  deposits  are  chiefly  confined  to  depths  at  or  for  some 
distance  below  the  100- fathom  line,  the  frequent  association  of  this 
mineral  with  typical  littoral  deposits,  and  in  formations  containing 
a  littoral  fauna,  indicates  that  in  the  past  it  may  have  formed  in 


BATHYAL   DEPOSITS  673 

shallower  water  sufficiently  removed  from  the  shore  to  prevent  ex- 
cessive detrital  deposition. 

The  secondary  origin,  through  erosion  of  older  greensand  de- 
posits and  redeposition  of  the  material  in  shallow  water,  must  also 
be  considered.  Such  deposits  are  forming  at  the  present  time  by 
the  erosion  of  the  Cretacic  greensands  of  the  Atlantic  coastal  plain. 
Andree  (3  '.381)  holds  that  this  may  have  been  the  origin  of  green- 
sand  lenses  in  the  Neocomien  sandstones  of  northwest  Germany 
(Teutoburger  Wald,  especially  the  Oswing).  The  lower  Cenoma- 
nien  deposits  of  greensands  (Essener  Greensand)  of  northwestern 
Germany  are  other  examples  of  such  deposits  formed  near  shore, 
passing  laterally  near  Mons  into  a  shore  conglomerate  with  rich 
fauna. 

Greensand  is  to-day  found  sporadically  on  the  shallow  ocean 
floor  under  the  Gulf  Stream  in  depths  of  only  a  few  hundred 
meters.  ( Pourtales-72  :  jp/. ) 

The  decomposition  of  glauconite  produces,  according  to  L. 
Cayeux,  ferric  hydroxide  and  pyrite,  but  other  alteration  products 
may  also  result.  Thus  the  bright-red  "Redbank"  sands  of  the  New 
Jersey  Cretacic  seem  to  owe  their  color  to  the  decomposition  of  the 
glauconite  mingled  with  the  quartz  grains  of  the  deposit.  This  de- 
composition may  be  due  to  the  more  porous  character  of  these  sands, 
but  that  it  was  not  produced  under  present  climatic  conditions  is 
shown  by  the  bright-red  tints  which  indicate  a  prolonged  period  of 
subjection  to  dehydrating  agencies. 


Deposits  on  Lee  Banks  and  on  the  Edge  of  the  Continental  Shelf. 

Where  ocean  currents  carrying  fine  silt  pass  from  shoals  to  deep 
water,  the  checking  of  the  current  resulting  causes  a  deposition  of 
more  or  less  of  the  silt.  (Willis-io5 : 497.)  Thus  on  the  lee  of  a 
submerged  ridge  a  bank  of  silt  will  form,  the  structure  of  which  is 
probably  that  of  the  delta,  the  successive  additions  being  at  a  com- 
paratively steep  angle.  The  Gulf  Stream  crosses  several  shoals  or 
submerged  terraces,  and  deposits  of  the  type  mentioned  are  formed 
in  the  lee  of  these.  "The  steepest  slope  of  the  Gulf  of  Mexico  from 
the  looth  to  the  2,oooth- fathom  line  is  in  the  position  of  a  lee-bank 
northwest  of  the  Yucatan  plateau.  .  .  .  The  Blake  plateau,  over 
which  the  Gulf  Stream  sweeps  north  of  the  Bahamas,  is  clean,  hard 
limestone,  but  a  lee-bank  of  mud  and  ooze  is  forming  on  its  short, 
steep  slope  into  deep  water."  (105  :  497-) 

A  similar  type  of  deposit  is  forming  on  the  edge  of  the  conti- 


674  PRINCIPLES    OF    STRATIGRAPHY 

nental  plateau  off  the  Atlantic  coast  of  North  America.  The  pla- 
teau or  shelf  itself  is  covered  with  shore-derived  arenaceous  de- 
posits. Dredgings  from  these  were  examined  by  Bailey  Willis,  who 
states  that  they  "are  indeed  finer  near  the  eastern  edge,  yet  are  dis- 
tinctly granular  and  incoherent." 

The  black  muds  of  the  Ordovicic  with  their  world-wide  distri- 
bution of  graptolites  seem  to  offer  an  older  illustration  of  this  type 
of  sedimentation.  The  graptolites  are  often  arranged  so  as  to  in- 
dicate current  action,  and  it  appears  that  these  muds  (Deep  Kill, 
Norman's  Kill,  Utica)  were  distributed  by  these  currents  and  de- 
posited on  the  ocean  floor  under  their  pathway. 


ABYSSAL  DEPOSITS. 

In  the  abyssal  district  of  the  ocean,  beyond  the  one  thousand- 
meter  line,  current-borne  detrital  material  is  relatively  unimpor- 
tant. Terrestrial  material  borne  by  currents  is  not  unknown,  how- 
ever, as  in  the  case  of  the  deep-sea  vegetal  deposits  already  referred 
to.  Even  rock  waste  is  carried  by  currents  to  realms  of  greater 
depths  where  these  are  not  far  from  shore,  while  terrestrial  material 
carried  by  floating  icebergs  or  rocks  held  by  the  roots  of  floating 
trees  or  sea  weeds  may  come  to  be  deposited  at  any  depth.  Among 
other  deposits  of  the  littoral  district  which  pass  over  into  the  abys- 
sal, greensand  has  already  been  noted,  as  extending  to  a  depth  of 
700  fathoms.  The  characteristic  deposits  of  this  district,  exclusive 
of  the  marine  derelicts,  may  be  divided,  according  to  their  origin, 
into  the  pelagic  and  the  terrigenous.  To  these  must  be  added  the 
meteoric  or  extra-terrestrial  materials,  and  the  subcrustal  or  vol- 
canic. 

Abyssal  Deposits  of  Pelagic  Origin. 

Pelagic  deposits  are  those  which  have  descended  to  the  bottom 
from  the  pelagic  district  of  the  ocean,  i.  e.,  the  upper  hundred- 
fathom  layer  of  water  of  the  open  ocean.  They  comprise  chiefly 
the  shells  and  skeletal  parts  of  pelagic  animals  and  plants,  such  as 
Foraminifera,  radiolaria,  pteropods,  ostracods  and  diatoms,  the 
shells  and  other  hard  parts  of  pelagic  molluscs,  and  the  skeletal 
parts  of  fish,  especially  the  teeth  of  selachians,  and,  further,  the 
ear  bones  of  whales,  and  other  hard  parts  of  this  as  well  as  other 
pelagic  vertebrates.  The  young  stages  of  organisms,  such  as  mol- 
luscs, brachiopods  and  echinoderms,  may  also  be  included  in  these 


ABYSSAL   DEPOSITS  675 

deposits.  The  former  group  may  be  termed  the  holopelagic  group, 
since  it  comprises  organisms  permanently  at  home  in  the  pelagic 
district,  while  the  latter  may  be  termed  the  meropelagic  group,  com- 
prising types  at  home  in  the  pelagic  district  during  part  of  their 
lives  only. 

Foraminifera,  ostracods  and  pteropod  shells  are  calcareous,  and 
these  form  the  chief  source  of  the  lime  deposits  of  the  deep  sea. 
Foraminiferal  oozes  of  the  modern  sea  generally  abound  in  the 
shells  of  Globigerina,  hence  the  term  Globigerina  ooze  is  ap- 
plied to  them.  It  should  be  emphasized,  however,  that  the  For- 
aminifera of  this  ooze  are  pelagic  species,  i.  e.,  types  which  float  in 
the  pelagic  district  of  the  open  ocean.  This  point  is  often  over- 
looked in  interpreting  former  foraminiferal  oozes  as  deep-sea  de- 
posits. Thus  it  has  been  shown  repeatedly  that  the  Foraminifera 
of  the  chalk  are  largely  of  littoral  types  with  only  such  pelagic  ad- 
ditions as  might  be  expected  from  the  fact  that  the  pelagic  district 
really  overlaps  the  littoral.  Nevertheless  the  chalk  is  commonly 
compared  with  the  modern  Globigerina  ooze,  and  referred  to  abys- 
sal deposits,  whereas  the  Foraminifera  composing  it  point  rather  to 
a  littoral  origin. 

The  great  purity  of  deep-sea  oozes  of  pelagic  origin  is  due  to 
the  fact  that  the  amount  of  terrigenous  material  settling  here  is 
relatively  slight.  Thus  in  tropical  seas,  in  depths  of  600  fathoms 
or  less,  pelagic  shells  of  carbonate  of  lime  often  constitute  80 
per  cent,  to  90  per  cent,  of  the  deposit.  With  increasing  depth, 
however,  the  percentage  of  carbonate  of  lime  decreases,  though  the 
surface  conditions  are  the  same.  Thus  at  2,000  fathoms  the  lime 
is  less  than  60  per  cent.,  at  2,400  fathoms  30  per  cent,  and  at  2,600 
fathoms  10  per  cent.  (Chamberlin  and  Salisbury-i6: 382),  while 
below  this  lime  is  generally  absent.  The  most  rapid  falling  off  of 
the  percentage  of  lime  carbonate  is  below  2,200  fathoms,  while  be- 
tween 2,400  and  2,600  fathoms  the  floor  of  the  ocean  is  covered 
with  red  clay.  The  explanation  generally  given  for  this  decrease 
in  the  percentage  of  carbonate  of  lime  is  the  greater  power  of  solu- 
tion of  the  deeper  waters,  owing  either  to  the  great  pressure  under 
which  it  exists  or  to  the  abundance  of  CO2  in  it  derived  from  emana- 
tions from  the  sea  floor,  or  to  both  causes.  (For  other  factors  in- 
fluencing this,  see  Philippi-69.)  The  red  clay  of  the  deeps  has 
been  regarded  as  the  insoluble  residue  left  on  solution  of  these 
shells,  a  not  unlikely  source  for  at  least  a  part  of  this  deposit. 

Radiolaria  and  diatom  shells  are  siliceous,  and  often  constitute 
extensive  deposits  in  the  modern  oceans.  Diatoms  are,  however, 
not  confined  to  salt  water,  but  occur  in  fresh  water  as  well.  Ex- 


676  PRINCIPLES    OF    STRATIGRAPHY 

tensive  beds  of  diatoms  are  known  in  various  older  deposits  both 
marine  and  lacustrine.  Characteristic  examples  are  found  in  the 
coastal  plain  strata  of  eastern  North  America,  where  a  single  bed 
underlying  the  city  of  Richmond,  Virginia,  has  a  thickness  of  18 
feet.  Beds  of  fossil  Radiolaria  of  considerable  thickness  are  also 
known  from  older  deposits,  the  most  famous  being  the  "Barba- 
does  earth"  and  the  "Tripolite,"  though  this  name  is  often  applied 
to  diatomaceous  or  other  siliceous  earths. 

Abyssal  Deposits  of  Terrigenous  Origin. 

Among  these  may  first  be  noted  the  terrigenous  matter  carried 
to  great  distances  by  the  currents,  especially  opposite  the  mouths  of 
great  rivers.  Thus  terrigenous  deposits  are  carried  out  for  a  thou- 
sand miles  opposite  the  mouth  of  the  Amazon.  The  fine  coral  mud, 
found  around  oceanic  coral  islands,  often  making  the  water  milky 
for  miles,  may  settle  to  the  more  moderate  depths  of  the  abyssal 
region  around  these  islands.  Characteristic  deep-sea  deposits  of 
continental  origin  are  the  blue,  green  and  red  clays  already  referred 
to,  the  greensand  in  the  upper  portion  and  the  deposits  of  drift  logs 
and  leaves,  such  as  were  dredged  by  the  Blake  and  the  Albatross  in 
the  Caribbean  and  off  the  west  coast  of  America.  The  most  abun- 
dant deep-sea  deposits  of  terrestrial  origin  are  volcanic  ejecta- 
menta,  especially  the  finer  volcanic  ashes  which  are  spread  far  and 
wide  by  wind  currents  and  eventually  settle  on  sea  and  land  alike. 
Even  fragments  of  pumice,  dropped  on  the  surface  of  the  ocean 
and  floated  until  they  become  waterlogged,  are  characteristic  of 
deep-sea  deposits.  Volcanic  glass  and  lapilli  are  likewise  found  in 
the  deep-sea  deposits,  some  of  these  probably  originating  from  sub- 
marine volcanoes.  It  is  believed  that  much  of  the  red  clay  which 
covers  the  deeper  ocean  floor  is  a  result  of  the  decomposition  of 
such  volcanic  material.  This  floating  volcanic  debris  is  often  classed 
as  pelagic,  but  it  is  evident  that  it  has  nothing  in  common  with  the 
true  pelagic  material.  It  may  for  convenience  be  classed  as  pseudo- 
pelagic,  in  which  class  also  may  be  included  the  leaves,  tree  trunks, 
etc.,  which  have  'floated  out  from  the  land  (pseudoplankton)  and 
come  to  rest  on  the  bottom  of  the  deep  sea.  All  of  these  are  strictly 
terrestrial,  only  the  holopelagic  and  meropelagic  types  being  truly 
marine. 

The  Red  Clay. 

The  red  clay  of  the  deep  sea  is  distributed  over  an  area  aggre- 
gating 51,500,000  square  miles,  and  occurs  in  depths  below  2,400  to 


ABYSSAL   DEPOSITS 


677 


2,600  fathoms.  It  contains  much  volcanic  debris,  besides  the  bones 
of  mammals,  zeolitic  crystals  and  spherules  of  extra-terrestrial  ori- 
gin. As  already  noted,  the  solution  of  the  pelagic  shells  in  deeper 
water  liberates  a  minute  quantity  of  such  red  clay,  but  a  consid- 
erable part  also  appears  to  be  derived  by  decomposition  of  volcanic 
dust.  The  clay  is  generally  rich  in  Radiolaria;  indeed  these  have 
been  regarded  as  forming  merely  a  phase  of  the  red  clay  deposit  of 
the  deep  sea,  they  seldom  if  ever  occurring  quite  pure. 


Analyses  of  Deep-Sea  Deposits. 

The  following  analyses  quoted  from  Clarke  (2oa— 436)  give  (a) 
the  composition  of  the  red  clay  from  23  analyses.  Others  have 
given  a  carbonate  of  lime  content  as  high  as  60  per  cent.  Added  to 
this  are  analyses  of  (b)  radiolarian  ooze,  (c)  diatom  ooze,  (d) 
Globigerina  ooze,  average  of  21  analyses,  (e)  Globigerina  ooze  very 
high  in  carbonate,  and  (f)  pteropod  ooze.  All  samples  dried  at 
110°.  Soluble  and  insoluble  portions  in  analyses  a,  b  and  d  are  not 
separated  in  the  table. 


Table  of  Analyses  of  Deep-Sea  Deposits. 


a 

b 

c 

d 

e 

f 

Red  clay 

Radio- 
larian 

Diatom 
ooze 

Globi- 
gerina 

Globi- 
gerina 

Ptero- 
pod 

ooze 

ooze 

ooze 

ooze 

Ignition 

4    5O 

7  41 

5    ^O 

7  QO 

i  40 

2    OO 

SiO2     

62  10 

56.02 

67.92 

•U  .71 

1.36 

3    65 

A12O3  

16.06 

10.52 

o.  55 

II  .  IO 

0.65 

0.80 

Fe2O3 

ii  81 

14.  OQ 

o  ^o 

7   O"* 

o  60 

1    06 

MnO2  

o  55 

1   2T, 

trace 

CaO  

0.28 

O.  ^9 

0.41 

MgO    . 

o  50 

O  25 

O    12 

CaCO3  

0.92 

3.89 

19.29 

37-51 

92.54 

82.66 

Ca3P2O8  

0.19 

1-39 

0.41 

2.80 

0.90 

2.44 

CaSO4  

0.37 

0.41 

0.29 

0.29 

0.19 

o-73 

MgCO3  

2    7O 

i   50 

I    n 

i  i^ 

0.87 

0.76 

Insoluble*.  .  .  . 

4.72 

1.49 

3-90 

IOO.OO 

IOO.OO 

100.00 

100.00 

IOO.OO 

IOO.OO 

*  Contains  silica,  alumina,  and  ferric  oxide  not  separated. 


678  PRINCIPLES    OF    STRATIGRAPHY 


Older  Deposits  That  Have  Been  Considered  of  Deep-sea  Origin. 

•  The  question,  Are  there  any  deep-sea  deposits  among  the  sedi- 
ments in  the  older  geological  series,  has  been  variously  answered 
in  the  past.  Sir  John  Murray  held  that  abyssal  sediments  were  not 
represented  among  the  known  sediments,  except  perhaps  in  such 
instances  as  the  radiolarian  ooze  of  Barbados.  Chalk  has  in  the 
past  frequently  been  cited  as  an  example  of  a  deep-sea  deposit  of 
Cretacic  time,  and  this  opinion  is  still  defended  by  some.  (Supan- 
91:  #55.)  There  seems  to  be,  however,  a  growing  recognition  of 
the  fact  that  this  formation  is  of  comparatively  shallow-water  ori- 
gin, the  organisms  composing  it  being  benthonic  rather  than  pelagic. 

Many  older  radiolarian  cherts  or  radiolarites  have  been  referred 
to  deep-sea  origin.  Their  almost  constant  interpolation  between 
beds  of  shallow-water  origin  has,  however,  thrown  doubt  upon  this 
interpretation.  Of  comparatively  deep-water  origin  are  believed  to 
have  been  the  massive  limestones  of  the  Trias  of  the  eastern  Alps 
and  of  some  of  the  Jurassic  deposits  of  the  Alpine  region.  This 
applies  especially  to  the  Aptychus  beds  of  the  Upper  Jurassic,  some 
of  which  seem  to  have  no  other  remains  than  the  operctila  of  am- 
monite shells,  the  so-called  Aptychi.  These  opercula  are  believed 
to  have  sunk  to  the  bottom  on  the  death  and  decay  of  the  pelagic 
ammonite,  while  the  shell  continued  to  float  and  eventually  was  de- 
posited in  other  sediments  of  generally  shallower  water  origin. 

Whether  these  deposits  will  eventually  prove  to  have  such  an 
origin,  or  whether  they,  too,  may  not  be  of  shallow-water  origin, 
must  for  the  present  remain  undecided. 

In  North  America  the  black  muds  of  the  Upper  Devonic  have 
been  regarded  as  of  deep-water  origin  (Clarke-2i),  but  formed 
under  conditions  similar  to  those  obtaining  in  the  Black  Sea.  The 
same  origin  has  been  suggested  by  Pompeckj  (71)  for  the  dark 
Liassic  shales  with  saurian  remains  found  in  Wiirttemberg  and  in 
England.  In  both  cases,  however,  the  deposits  may  with  equal  if 
not  greater  certainty  be  classed  as  of  shallow-water  origin. 


Concretions  of  the  Deep  Sea. 

Concretions  are  a  characteristic  feature  of  the  deep  sea.  Though 
not  clastic,  they  may  be  noted  here  for  the  sake  of  completeness. 
Foremost  among  these  are  manganese  concretions,  which  are  widely 
distributed  on  the  abyssal  ocean  floor.  Sometimes  they  occur  in 


ABYSSAL   DEPOSITS  679 

heaps  of  small  grains  or  lumps.  They  range  in  depth  to  over  8,000 
meters,  being  especially  abundant  in  the  Pacific.  They  are,  how- 
ever, also  found  in  shallow  water,  as  in  the  case  of  the  deposits 
formed  in  Loch  Fyne  in  Scotland.  (Buchanan.)  The  mineral  is 
generally  the  hydrous  oxide,  and,  according  to  Murray,  is  a  product 
of  disintegration  of  the  volcanic  rocks  found  so  abundantly  in  these 
deeper  waters.  The  manganese  and  iron  derived  from  the  vol- 
canics  are  at  first  in  the  form  of  carbonate,  after  which  they  become 
altered  to  the  oxide.  The  concretions  commonly  contain  fragments 
of  pumice  or  lapilli  or  a  bone  or  other  organic  structure  as  a  nucleus. 
(See  also  Chapter  IX.)  Besides  the  manganese  concretions  there 
are  concretions  of  other  minerals,  of  which  barium  is  one. 


Cosmic  Deposits  in  the  Deep  Sea. 

Fine  particles  with  a  metallic  interior  often  magnetic  are  found 
in  the  deeper  water  deposits.  These  have  been  interpreted  as  cosmic 
dust,  the  product  of  meteoric  showers.  Chamberlin  and  Salisbury 
( 16 : 381-2)  state  that  the  number  of  meteorites  which  enter  the 
atmosphere  daily  has  been  estimated  at  from  1 5,000,000  to  20,- 
000,000,  and  that  if  on  the  average  each  weighs  10  grains  (a  high 
estimate),  the  total  amount  of  extra-terrestrial  matter  reaching  the 
earth  yearly  would  be  5,000  to  7,000  tons,  of  which  about  three- 
fourths  on  the  average  would  fall  into  the  sea.  At  this  rate  it  would 
take  some  fifty  billion  years  to  cover  the  sea  bottom  with  a  layer 
one  foot  in  thickness. 


Submarine  Volcanic  Deposits. 

Deposits  formed  on  the  floor  of  the  ocean  by  submarine  volcanic 
eruptions  probably  constitute  an  important  part  of  the  deep-sea 
deposits.  Not  all  of  the  widely  distributed  volcanic  material,  how- 
ever, found  in  the  deep  sea  is  the  product  of  submarine  volcanic 
eruptions ;  a  large  part  of  the  pumice,  lapilli  and  volcanic  glass  and 
dust  is  derived  from  terrestrial  volcanoes,  and  is  carried  to  the  deep 
sea  by  flotation  on  the  surface  of  the  ocean,  or  as  wind-borne 
dust,  or  as  both.  The  Hawaiian  Islands  represent  the  result  of 
prolonged  submarine  volcanic  eruptions,  and  the  accumulation  of 
the  material  in  the  vicinity,  until  they  rose  to  the  present  height  of 
the  sea-level.  For  the  general  subject  of  submarine  eruptions,  see 
Thoulet  (94).  (See  also  Chapter  XXII.) 


68o  PRINCIPLES    OF    STRATIGRAPHY 


INTERRUPTIONS  OF  MARINE  SEDIMENTATION. 

It  is  generally  assumed  that  deposition  in  the  deep  sea  is  rela- 
tively constant  and  not  subject  to  interruptions  of  any  but  acci- 
dental character.  Under  this  latter  may  be  classed  the  appearance 
of  submarine  volcanoes,  which  will  act  in  a  twofold  manner  by  dis- 
turbing the  waters  of  the  bottom  of  the  sea  and  creating  currents 
which  will  stir  up  and  sweep  away  sediment  previously  accumu- 
lated, and,  second,  by  forming  a  new  series  of  deposits,  as  well  as 
creating  new  slopes  and  regions  of  deposition.  Seismic  disturbances 
likewise  cause  interruptions  of  sedimentation  and  rearrangement  of 
sediments. 

In  the  lesser  depths  of  the  ocean,  however,  the  currents  of  the 
surface  will  to  a  certain  extent  also  affect  the  bottom  sediment. 
This  is  partly  due  to  their  ability  to  sweep  away  loose  material 
even  in  considerable  depths  and  partly  to  their  influence  in  pre- 
venting sedimentation.  As  already  noted  in  Chapter  V  in  narrow 
passages,  the  currents  may  be  effective  at  considerable  depths. 
Agassiz  states  "that  the  bottom  of  the  Gulf  Stream  along  the  Blake 
plateau  is  swept  clean  of  slime  and  ooze,  and  is  nearly  barren  of 
animal  life."  (i  :  <?5p.)  This  effect  is  felt  to  a  depth  of  1,281  me- 
ters. According  to  Verrill,  the  floor  of  the  ocean  beneath  the  Gulf 
Stream  in  depths  of  150  to  600  meters,  and  at  a  distance  of  100  to 
200  km.  from  land,  is  covered  with  fine  sand,  mostly  quartz,  some 
feldspar,  mica  and  magnetite,  fragments  of  shells,  etc.,  coral  and 
rhizopods.  Fine  mud  is  absent  and  is  even  scarce  in  depths  of 
1,000  meters,  having  apparently  been  carried  away  by  the  Gulf 
Stream.  A  current  of  more  than  7  mm.  per  second  at  the  bottom 
can  stir  up  and  move  shell  particles  of  0.12  mm.  or  less  in  diameter 
and  be  quite  effective  in  transporting  mud  particles.  Currents  of 
3  mm.  per  second  can  carry  along  Globigerina  ooze.  Measure- 
ments on  the  Gulf  Stream  have  shown  a  velocity  of  about  31  mm. 
per  second  at  a  depth  of  910  m.  west  of  the  Bermudas.  In  1,100 
m.  depth,  however,  no  measurable  velocity  was  shown. 

As  already  noted  (Chapter  V),  the  passages  between  the  several 
islands  of  the  Canary  group  have  their  bottoms  kept  clean  by  the 
tidal  currents  rushing  through  them.  These  currents  are  effective 
to  a  depth  of  2,000  meters.  On  the  submarine  banks  in  the  neigh- 
borhood of  these  islands  the  denuding  effect  of  the  tidal  currents  is 
felt  to  considerable  depths.  On  the  Seine  bank  only  hard  rock  bot- 
tom was  found  in  depths  of  less  than  200  meters.  In  greater  depths, 
down  to  964  meters,  only  coarse  sand  was  found.  Only  in  the 


INTERRUPTIONS   OF   MARINE   SEDIMENTATION    681 

depths  exceeding  1,500  and  2,000  meters  is  an  accumulation  of  the 
fine  Globigerina  ooze  possible. 

In  the  passes  between  the  islands  of  the  Indian  Archipelago,  the 
Siboga  expedition  found  mostly  "hard  bottom,"  the  sounding  in- 
struments bringing  up  only  broken-off  rock  fragments,  or  impres- 
sions of  a  rock  bottom.  In  exceptional  cases  coarse  sand  was 
found.  Since  these  depths  extend  to  1,500  meters,  it  is  probable  that 
we  have  here  a  prevention  of  sedimentation  by  the  removal  of  the 
particles  before  they  reach  the  bottom,  rather  than  any  effect  of 
eroding  work  of  the  current  at  such  depth.  (Weber-ioi  :  187.} 
Compensatory  currents,  such  as  those  formed  in  the  Roman  Med- 
iterranean by  greater  evaporation,  also  affect  sedimentation.  In  the 
case  mentioned  the  Gibraltar  current  flows  in  at  the  surface,  while  a 
deeper  current  passes  out  beneath,  affecting  the  lower  30  meters  of 
the  water  in  the  pass.  Currents  due  to  melting  ice  also  affect  sedi- 
mentation. The  diatoms  of  the  Antarctic  region  settle  only  north 
of  the  region  of  drift  ice  (Philippi).  In  addition  to  the  oceanic 
and  the  tidal  currents,  the  upward  currents,  which  bring  the  colder 
water  of  the  depths  to  the  surface,  are  effective  agents  in  modifying 
deposition.  All  such  currents  are  further  effective  in  determining 
the  facies  of  the  sediment,  and  abrupt  changes  from  one  to  another 
type  of  sediment  may  often  be  due  to  them. 

It  thus  appears  that  sedimentation  on  the  sea  bottom  is  unequal 
in  extent  and  that  the  surface  of  more  elevated  ridges,  or  areas 
subject  to  current  scour,  may  remain  free  from  sediment,  while  this 
is  accumulating  all  around.  Cases  of  interruption  of  the  continuity 
of  sediments  referable  to  such  causes  are  not  unknown  from  the 
older  rocks.  A  good  example  is  found  in  the  Upper  Siluric  beds 
of  the  Helderberg  Mountains  in  eastern  New  York.  Near  the  city 
of  Kingston  a  submarine  ridge  of  folded  and  eroded  sandstones  of 
Mid-Ordovicic  age  projected  above  the  general  bottom  of  the  late 
Siluric  sea,  and  was  kept  free  from  the  deposits  accumulating  all 
around  it.  Thus  the  Rosendale  waterlimes  and  the  Wilbur  lime- 
stone are  wanting  over  the  Kingston  ridge,  but  present  all  around 
at  a  distance  of  a  few  miles.  Only  the  upper  part  of  the  Cob- 
bleskill  limestone  is  deposited  upon  the  ridge,  which  became  buried 
in  the  deposits  accumulating  around  it,  to  which,  however,  the 
ridge  itself  did  not  contribute  any  material.  These  deposits,  how- 
ever, accumulated  in  shallow  water,  as  lime  muds  derived  by  the 
erosion  of  a  not  too  distant  limestone  shore.  The  shallow  water  is 
indicated  by  the  abundance  of  mud  cracks  at  several  levels.  The  ab- 
sence of  the  Credneria  beds  and  of  the  carinata-quader  (sand- 
stone) in  the  vicinity  of  Dresden  (Plauenscher  Grund)  has  also 


682  PRINCIPLES    OF    STRATIGRAPHY 

been  referred  to  the  existence  of  elevated  ridges  and  cliffs  in  the 
Cretacic  sea  in  that  vicinity,  on  which  coarse  boulders  formed  the 
only  loose  material,  while  around  were  accumulating  finer  sedi- 
ments. ( Petrascheck-65  :  26  et  seq.,  Fig.  45.) 

It  further  appears  that  interruption  of  sedimentation  and  even 
contemporaneous  erosion  are  processes  which  may  be  active  in  the 
moderate  depths  of  the  ocean,  especially  between  depths  of  200  and 
900  meters,  i.  e.,  in  the  bathyal  zone  of  the  sea.  Such  an  interrup- 
tion may  give  rise  to  a  distinct  hiatus,  as  well  as  a  variation  in  thick- 
ness of  sediments.  It  is  not  improbable  that  some  of  the  breaks  in 
the  geological  series  referred  to  subaerial  erosions  and  the  forma- 
tion of  disconformities  may  be  due  to  the  processes  outlined  above. 
That  such  is  frequently  the  case  may  perhaps  be  questioned,  though 
much  emphasis  is  laid  upon  it  by  some  stratigraphers  and  students 
of  Pakeogeography.  (Bailey  Willis-io6;  107.) 

The  numerous  breaks  in  the  Alpine  Jurassic  limestone  series 
have  been  regarded  by  Neumayr  and  others  as  examples  of  dis- 
continuous deposition  without  the  occurrence  of  periods  of  dry  land 
and  erosion.  Currents  are  believed  to  have  been  the  disturbing 
agent.  From  the  Rhsetic  upward  irregularities  in  the  distribution 
of  the  sediment  are  of  increasing  frequency  and  extent ;  these  are 
partly  due  to  variations  in  the  sea-level,  partly  to  tectonic  move- 
ments of  the  suboceanic  floor,  and  partly  to  the  periodic  want  of 
material  for  sedimentation  (Diener).  In  part  these  breaks  may 
also  be  due  to  oceanic  or  tidal  currents.  (Andree-3.) 

Stratigraphic  gaps  are  numerous  in  the  geological  formations  of 
North  America,  but  it  remains  still  to  be  determined  which  of  these, 
if  any,  are  due  to  contemporaneous  erosion,  or  to  prevention  of 
deposition  by  currents,  etc.  Some  of  the  gaps  in  the  Ordovicic 
limestones  of  the  Appalachians  may  be  explained  in  this  manner. 
When  the  great  limestone  series  of  the  Palaeozoic  of  western 
North  America  are  more  fully  investigated,  evidences  of  such  intra- 
formational  gaps  may  be  found. 


PERSISTENCE  AND  VARIATION  IN  THICKNESS  OF  MARINE  STRATA. 

One  of  the  familiar  phenomena  confronting  the  field  geologist 
is  the  enormous  variation  in  the  thickness  of  strata  when  traced 
from  point  to  point.  For  this  variation  several  explanations  are 
available.  In  the  first  place,  it  often  happens  that  a  given  series  of 
great  thickness  is  in  other  regions  represented  by  only  a  fraction 
of  the  formation,  this  being  due  to  the  occurrence  of  a  constantly 


VARIATIONS    OF    MARINE    SEDIMENTS          683 

widening  hiatus  between  the  adjacent  formations.  Thus  it  appears 
that  the  Lower  Ordovicic  series  of  eastern  North  Ameriea  is  repre- 
sented by  some  2,500  feet  of  limestones  in  central  Pennsylvania, 
while  only  about  400  feet  are  found  in  the  Mohawk  Valley  of  New 
York.  This  diminished  series,  however,  represents  only  the  lowest 
part  of  the  Pennsylvania  deposits,  the  entire  middle  and  upper  part 
being  absent.  Upon  these  beds  rests  a  series  of  limestone  2,500 
feet  thick  and  representing  the  Middle  Ordovicic,  but  this  again  is 
represented  by  less  than  100  feet  in  the  Mohawk  Valley.  This 
time,  however,  it  is  the  upper  part  of  the  Middle  Ordovicic  which 
is  present.  Thus  the  gap  in  the  Mohawk  Valley  cuts  out  all 
but  the  lowest  of  the  Lower  Ordovicic  and  all  but  the  highest  of 
the  Middle  Ordovicic.  Southward  the  gap  becomes  less  by  the  ap- 
pearance of  higher  members  of  the  subjacent  and  lower  members 
of  the  superjacent  series.  This  is  perhaps  the  most  frequently  ap- 
plicable explanation  of  the  differences  in  thickness  of  marine 
formations  of  similar  lithologic  character.  In  the  next  place,  there 
is  variation  in  thickness  due  to  variation  in  character  of  the  sedi- 
ment. Formations  of  different  lithic  composition  may  show  great 
variation  in  thickness  due  to  original  difference  in  deposition.  Thus 
a  sandy  series  is  likely  to  be  much  thicker  than  a  shale  series  into 
which  it  passes  and  which  was  formed  during  the  same  period. 
Again,  sediments  of  two  kinds  from  separate  sources  may  over- 
lap, and  so  one  may  thin  away  as  the  other  thickens.  This  is  espe- 
cially the  case  where  continental  sediments  overlap  a  marine  series 
of  the  same  age  or  vice  versa.  The  Catskill  and  Chemung  series  of 
the  Upper  Devonic  of  the  eastern  United  States  is  a  case  in  point. 
The  Catskill  continental  beds  are  thick  in  the  east,  but  die  away 
westward,  while  beneath  the  thinning  cover  of  this  series  the  marine 
Chemung  increases  progressively  from  nothing  in  the  east  until  it 
alone  fills  the  interval  in  western  New  York.  But  even  the  marine 
series  may  overlap  in  this  manner.  Thus  the  Black  shales  of  Port- 
age time  are  thickest  in  Ohio,  and  wedge  out  eastward  in  New  York 
and  Pennsylvania.  Their  place  is  taken  by  the  sandy  Portage  beds 
which  have  their  source  in  the  east  and  grow  thinner  toward  the 
west. 

The  third  cause  of  differences  in  thickness  is  local  variation 
in  the  regions  of  sedimentation.  A  relatively  shallow  and  stationary 
area  of  the  sea  bottom  may  experience  little  sedimentation,  while  a 
slowly  subsiding  area  may  receive  a  great  supply  of  sediment  of  es- 
sentially similar  character.  The  Moscow  shale  of  the  Middle  De- 
vonic of  western  New  York  is  a  good  example  of  this.  In  the 
Genesee  Valley  region  its  thickness  is  about  250  feet,  while  on  Lake 


684  PRINCIPLES    OF    STRATIGRAPHY 

Erie  it  is  only  17  feet.  Still  further  west  in  Canada  the  thickness  in- 
creases again  to  over  a  hundred  feet.  The  17  feet  of  shales  in  the 
Lake  Erie  section  apparently  represent  the  250  feet  of  the  eastern 
section,  but  owing  to  lack  of  accumulation,  probably  because  the  wa- 
ter remained  shallow  and  currents  were  active,  the  amount  of  de- 
posit was  slight.  That  this  shallow  area  seems  to  have  formed  a 
barrier  between  the  eastern  and  western  faunas  is  indicated  by  their 
diversity. 

In  contradistinction  to  this  marked  variation  is  the  persistence 
in  thickness  of  the  underlying  Encrinal  or  Morse  Creek  *  limestone. 
This  bed  is  only  about  2  feet  thick,  but  it  has  been  traced  almost  con- 
tinuously from  western  Ontario  (Thedford)  to  the  Genesee  Valley, 
a  distance  of  over  200  miles,  and  throughout  the  extent  it  retains  its 
lithic  character,  thickness  and  uniformity  of  organic  content.  (Gra- 
bau-39.) 

COMPREHENSIVE  FORMATIONS. 

• 

Under  this  title  may  be  grouped  deposits  which  apparently 
without  break  continued  over  long  periods  of  time.  That 
such  exist  has  frequently  been  observed,  though  many  appar- 
ent lithic  units  have  been  found  to  consist  of  several  members 
separated  by  disconformities.  The  Hunton  limestone  of  Okla- 
homa was  formerly  believed  to  be  a  unit,  extending  without  break 
from  the  Niagaran  to  the  Oriskanian.  It  is  now  known  to  consist 
of  at  least  four  distinct  and  disconformable  members  separated  by 
great  time  gaps  (Reed-8o).  The  Durness  limestone  of  northern 
Scotland,  believed  to  range  from  Lpwer  Cambric  to  Ordovicic,  is 
now  known  to  consist  of  a  basal  member  of  Lower  Cambric  age, 
separated  by  a  hiatus  and  disconformity  from  the  Lower  Ordovicic, 
the  Middle  and  Upper  Cambric  being  wanting.  (Grabau~4O.)  That 
such  comprehensive  formations  occur,  nevertheless,  is  shown  by  the 
deposits  on  the  floor  of  the  modern  deep  sea,  where  teeth  of  Ter- 
tiary sharks  (Carcharodon)  occur  side  by  side  with  remains  of  or- 
ganisms now  living.  Here  sedimentation  is  so  slow  that  the  time 
interval  since  the  Tertiary,  when  these  sharks  died,  has  not  been 
sufficient  to  completely  bury  their  teeth. 

So  far,  however,  no  such  comprehensive  sediments  are  known 
from  the  older  geological  formations,  though  a  commingling  of  or- 
ganisms of  various  geological  horizons  is  not  uncommon.  This 

*  The  "Encrinal  Limestone"   of  western  New  York  is  not  the  same  as  the 
Tichenor  of  central  New  York. 


COMPREHENSIVE   FORMATIONS  685 

may  be  due  to  a  weathering  out  of  the  fossils  of  an  older  forma- 
tion and  their  incorporation  in  the  deposits  of  a  later  one,  as  in  the 
case  of  the  Ordovicic  fossils  included  in  the  base  of  the  overlying 
Mississippic  black  shale  in  Tennessee,  or  again  fossils  of  an  older 
formation  may  be  washed  out  along  the  shore  and  incorporated  in 
the  new  deposit.  Thus  Miocenic  oyster  shells  on  the  Atlantic  coast 
serve  as  a  basis  for  attachment  of  modern  oysters,  and  are  buried 
with  these  in  the  modern  deposits. 

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travaux  chimiques  des  Pays-Bas,  Vol.  XIX,  pp.  222-294. 

91.  SUPAN,  ALEXANDER.     1911.     Grundziige  der  physischen  Erdkunde. 

5te  Auflage,  Leipzig,  Veit  &  Co. 

92.  TARR,  RALPH  S.     1907.     Recent  Advance  of  Glaciers  in  Yakutat  Bay 

Region,  Alaska.  Bulletin  of  the  Geological  Society  of  America,  Vol. 
XVIII,  pp.  257-286. 

93.  THOULET,  J.     1900.      Fixation  des  argiles  en  suspension  dans  1'eau  par 

les  corps  poreux.  Comptes  Rendus,  des  Stances  de  1'Acad^mie  des 
Sciences,  Paris.  130,  p.  1639. 

94.  THOULET,     J.     1903.     Les    volcans    sous-marins.     Revue    des    Deux 

Mondes.     73  annee,  5feme  pe"riode,  t.  XIII,  livrc  3,  I,  II,  pp.  61 1-624. 


690  PRINCIPLES    OF    STRATIGRAPHY 

95.  THOULET,    J.     1906.     Le   calcaire   et   1'argile   dans   les  fonds  marins- 

Comptes  Rendus,  des  Seances  de  1' Academic  des  Sciences,  Paris.     142, 

PP-  738-739. 

96.  THOULET,    J.     1908.     Etude    comparee    des    fonds  marins  anciens  et 

actuels.     Annales  des  Mines,  10  series,  t.  XIII,  p.  236. 

97.  THOULET,  J.     1910.     Instructions  pratiques  pour  1'etablissement  d'une 

carte  bathymetrique-lithologique  sous-marine.  Bulletin  de  1'Institut 
Oceanographique  de  Monaco,  Nr.  169. 

97a.  THOULET,  J.  1911.  Carte  bathy-lithologique  de  la  c6te  du  Golfe  du 
Lion  entre  1'embonchure  de  la.  T6t  et  Gruissan.  Comptes  Rendus  des 
Seances  de  1' Academic  des  Sciences,  Paris:  152,  pp.  1037-1038. 

98.  TORNQUIST,  AL.     1909.     Ueber  die  Wanderung  von  Blocken  und  Sand 

am  ost-preussischen  Ostseestrand.  Schriften  der  physisch-okonomischen 
Gesellschaft,  pp.  79-88,  taf.  I,  II. 

99.  UDDEN,  J.  A.     1894.     Erosion,  Transportation  and  Sedimentation  Per- 

formed by  the  Atmosphere.     Journal  of  Geology,  Vol.  II,  pp.  318-331. 

100.  VERNON-HARCOURT,  L.  F.     1900.     Experimental  Investigations  on 

the  Action  of  Seawater  in  Accelerating  the  Deposit  of  River-silt  and  the 
Formation  of  Deltas.  Minutes  of  the  Proceedings  of  the  Institute  of 
Civil  Engineers,  Vol.  CXLII,  pp.  272-287.  London. 

101.  WEBER,    M.      1900.      Die    niederlandische    "Siboga"    Expedition    zur 

Untersuchung  der  Marinen  Fauna  und  Flora  des  Indischen  Archipels. 
Petermann's  Geographische  Mittheilungen,  Vol.  XLVI,  p.  187. 

102.  WEULE,  K.     1896.     Zum  Problem  der  Sedimentbildung.     Annalen  der 

Hydrographie,  Bd.  XXIV,  pp.  402-413. 

103.  WHEELER,   W.    H.-    1902.     The   Sea   Coast.     New   York,    Longmans, 

Green  &  Co. 

104.  WHITNEY,     MILTON.     1892.     Some    Physical    Properties    of    Soils. 

United  States  Department  of  Agriculture,  Bulletin  No.  4. 

105.  WILLIS,     BAILEY.     1893.     Conditions    of     Sedimentary     Deposition. 

Journal  of  Geology,  Vol.  I,  pp.  476-520. 

1 06.  WILLIS,  B.     1910.    Principles  of  Palaeogeography.        Science  N.  S.,  Vol. 

XXXIII,  Feb.  18,  1910,  pp.  246-251. 

107.  WILLIS,  B.     1911.     The  Influence  of  Marine  Currents  on  Deposition  in 

Continental  Seas.     Abstract,  Science,  N.  S.,  Vol.  XXXIII,  pp.  313-314. 

108.  WORTH,  R.  H.     1899.     The  Bottom-deposits  of  the  English  Channel 

from  the  Eddystone  to  Start  Point,  near  the  Thirty-fathom  Line.  Trans- 
actions of  the  Devonshire  Association  for  the  Advancement  of  Science, 
Vol.  XXXI,  pp.  356-375. 


CHAPTER   XVI. 
CHARACTERS  AND  LITHOGENESIS  OF  THE  BIOCLASTIC  ROCKS. 

Bioclastic  rocks  consist  of  fragments  of  older  rocks  which  have 
been  broken  by  the  mechanical  activities  of  organisms.  Among 
these  man  is  the  most  active,  and  he  is  undoubtedly  the  greatest 
producer  of  bioclastic  rocks.  To  distinguish  this  type  the  name  of 
artificial  elastics  is  applied  to  it,  and  as  examples  concrete  and  other 
artificial  stone  may  be  mentioned.  These  need  not  be  more  fully  dis- 
cussed, though  their  variety  is  great  and  their  characters  manifold. 

There  are  also  other  organisms  which  in  a  more  or  less  effec- 
tive way  render  rocks  clastic  and  so  furnish  the  material  from 
which  new  rocks  may  be  formed.  Chief  among  these  are  the  great 
herds  of  vertebrates  of  the  plains  and  steppes  and  the  even  larger 
animals  of  former  geological  periods. 

Pechuel-Loesche  (7:^5)  describes  the  destruction  of  the  land 
surface  through  the  immense  herds  of  cattle  which  he  had  wit-- 
nessed  in  Herero  land,  German  Southwest  Africa.  He  says  in  ef- 
fect: "In  extensive  manner  these  animals  aid  in  the  leveling  of 
many  land  areas.  As  the  dryness  increases,  the  herds  of  grazing 
cattle  become  more  numerous  around  the  last  of  the  sparsely  dis- 
tributed water  bodies.  Thousands  and  tens  of  thousands  of  the 
large  and  the  small  animals  overrun  for  miles  the  surrounding 
country  for  days,  weeks  and  months.  Through  countless  hoof- 
beats  the  ground  is  loosened,  and  so  furnishes  enormous  masses  of 
dust,  while  at  the  same  time  all  inequalities  are  trampled  down  and 
destroyed.  The  inclined  surfaces  would  be  furrowed  by  numerous 
rain-water  gullies,  if  these  were  not  constantly  destroyed  by  the 
hoofs  of  the  roaming  animals,  and  if  it  were  not  for  the  fact  that 
the  rain  water  is  constantly  guided  along  the  paths  formed  by  the 
animals  going  to  and  from  the  water  in  long  lines  ranged  one  be- 
hind the  other.  Furthermore,  the  cover  of  dust  prevents  to  an  as- 
tonishing degree  the  penetration  of  the  short,  heavy  downpour  of 
rain  into  the  deeper  strata." 

Where  herds  abound,  the  surface  of  the  country  is  a  compara- 

691 


692 


PRINCIPLES    OF    STRATIGRAPHY 


tively  level  plain,  but  where  herds  are  absent,  as  in  the  regions  be- 
tween Karibib,  the  Otyipatura  and  the  Erongo,  infested  by  the  Hot- 
tentot robber  hordes,  the  country  is  much  dissected  by  rain-water 
streams. 

Passarge  thinks  that  it  is  not  too  much  to  attribute  to  the  de- 
structive force  of  the  great  herds  of  vertebrates  in  semiarid  regions 
the  principal  role  in  the  lowering  of  great  regions  and  the  produc- 
tion of  gently  inclined  plains  free  from  river  furrows,  with  rem- 
nants of  higher  monadnocks  such  as  the  Inselberge  of  the  Kalahari 
(Passarge^:  730-131). 

What  is  true  of  the  modern  herds  of  vertebrates  must  have  been 
equally  true  of  the  great  herds  of  mammals  of  Tertiary  time,  and 


sfc 


FIG.  133.     White  ants'  nests  of  earth  in  Matto  Grosso,  on  the  plains  of  the 
upper  Paraguay.     (After  Branner.) 

perhaps  to  an  even  greater  extent  of  the  gigantic  saurians  of  the 
Mesozoic.  Certain  it  is  that  by  their  activities  these  creatures  have 
furnished  an  immense  supply  of  material  to  the  winds,  which  would 
carry  it  to  other  regions  and  deposit  it  as  new  sediment.  Burrow- 
ing mammals  such  as  the  prairie  dog,  rabbit,  mole,  badger,  wood- 
chuck,  gopher  and  ground  squirrel  are  also  very  active  in  tunneling 
the  upper  layers  of  the  soil  and  in  transferring  material  from  below 
to  the  surface.  The  beaver  may  also  be  mentioned  in  this  connec- 
tion as  a  destructive  as  well  as  a  constructive  agent. 

The  manner  in  which  fish,  feeding  on  corals  and  nullipores,  pro- 
duce fine  coral  sand  and  mud  has  already  been  noted.  In  like 
manner  Crustacea  are  known  to  be  active  in  breaking  up  the  skele- 
tons of  echinoderms  and  other  organisms,  thus  producing  lime  sand. 
Sponges  and  algae  riddle  shells  and  even  rocks,  forming  winding 
passageways,  which  render  these  masses  more  liable  to  destruction 
by  waves  and  other  agencies.  Similarly  certain  mollusca,  Pholas, 


LITHOGENESIS    OF   THE    BIOCLASTIC   ROCKS    693 

Saxicava,  etc.,  bore  into  solid  rocks  or  into  heavy  shells,  thus  aid- 
ing in  the  destruction  of  the  mass.  To  a  certain  extent  this  is  also 
true  of  some  echini. 

Earthworms  are  active  agents  in  loosening  and  rearranging  the 
soil  particles,  and  to  a  certain  extent  in  destroying  the  rock  masses. 
According  to  Darwin,  in  many  places  over  50,000  earthworms  are 
at  work  in  a  single  acre  of  soil.  The  amount  of  material  which 
they  transport  to  the  surface  each  year  was  estimated  by  Darwin  to 
be  over  18  tons  per  acre.  (4.)  The  lugworms  or  lobworms, 
crawling  through  the  sands  along  the  shore,  are  similarly  active  in 


FIG.    134.     Mound   of  white  ants   in  the  laterite   region  of   Africa.      (After 
Branner.) 

working  over  the  soil.  They  leave  behind  casts  of  sand,  and  the 
amount  of  soil  they  work  over  has  been  estimated  to  be  sometimes 
as  much  as  3,147  tons  per  acre.  (Davison-5 : 491.)  Ants  and 
termites  are  also  important  agents  in  the  rearrangement  of  the  soils, 
especially  in  tropical  regions,  where,  according  to  Branner,  they 
"are  vastly  more  important  as  geologic  agents  than  the  earthworms 
of  temperate  regions."  (i :  i^2\  253.)  In  Brazil  the  ants  excavate 
chambers  and  galleries,  which  radiate  and  anastomose  in  every  di- 
rection, and  into  these  they  carry  great  quantities  of  leaves.  The 
mounds  resulting  from  these  excavations  are  often  from  15  to  30 
meters  long,  from  3  to  6  meters  across  and  from  one-third  to  over 
one  meter  high,  and  contain  tons  of  earth.  In  the  forests  the 


694  PRINCIPLES    OF    STRATIGRAPHY 

mounds  are  sometimes  14  feet  high  (4^  meters),  and  from  10  to 
30  feet  (3  to  9  meters)  in  basal  diameter.  They  are  often  so  close 
together  that  their  bases  touch  each  other.  Branner  has  estimated 
(3:^9)  that  in  an  area  of  10,000  square  meters  on  which  53 
mounds  occurred  the  amount  of  earth  brought  up  by  ants  and  built 
into  mounds  would  cover  the  area  with  a  layer  22.25  centimeters  in 
thickness. 

The  termites'  nests  rise  to  3^  meters  in  height,  and  may  be  3 
meters  in  basal  diameter.  They,  too,  are  often  closely  set,  those 
along  the  upper  Paraguay  being  not  over  3  meters  apart.  (Fig. 

I33-) 

A  comparison  of  the  work  of  earthworms  and  ants  gave  the 
following  result  (Branner-3 : 495).  Total  weight  of  earth  brought 
to  the  surface  in  100  years  over  I  hectare  (10,000  square  meters)  : 

By  worms  in  England  (Darwin-4),  2,598,500  kilograms. 

By  ants  in  Brazil  (Branner-3),  3,226,250  kilograms. 

The  work  of  ants  on  the  soil  and  subsoil  is  summarized  by 
Branner  as  follows  (3:494)  : 

Directly : 

1.  "By  their  habits  of  making  underground  excavations  that 
radiate  from  a  central  nucleus  and  often  aggregate  several  miles 
in  length. 

2.  "By  opening  the  soil  to  the  atmospheric  air  and  gases. 

3.  "By  bringing  to  the  surface  large  quantities  of  soil  and  sub- 
soil. 

4.  "By  introducing  into  their  subterranean  excavations  large 
quantities  of  organic  matter,  which  must  yield  acids  that  affect  the 
soil  and  the  subjacent  rocks. 

5.  "By  using  these  excavations  for  habitations  and  the  pro- 
duction of  gases  that  attack  the  soil  and  its  contained  minerals." 

Indirectly. 

6.  "By  the  periodic  passage  and  circulation  of  meteoric  waters 
through  their  extensive  tunnels. 

7.  "By  affecting  the  availability  of  the  soil   for  agricultural 
purposes. 

8.  "By  affecting  the  habitability  of  the  land  by  man. 

9.  "By  the  destruction  of  crops. 

10.  "By  the  consumption  (by  the  termites)  of  dead  plants  and 
of  timbers  and  lumber  used  in  houses  and  for  the  manufacture  of 
furniture,  machinery,  etc." 

In  temperate  regions  ants  are  less  active,  though,  according  to 
Shaler,  they  transfer  annually  half  a  centimeter  of  material  from 
the  subsoil  to  the  surface,  in  certain  fields  in  Massachusetts.  (8.) 


LITHOGENESIS    OF   THE    BIOCLASTIC   ROCKS    695 

Plants  also  are  destroyers  of  rocks,  though  their  work  is  nor- 
mally very  slow.  Lichens  growing  on  smooth  rock  surfaces  will 
eventually  roughen  them  by  appropriating  some  of  the  material. 
Roots  of  higher  plants  often  penetrate  into  the  rock,  especially 
limestones,  to  an  astonishing  extent.  In  sandstones  they  have  been 
found  to  penetrate  several  meters.  Growing  saplings  in  fissures 
tend  to  disrupt  the  rock  masses.  Finally  bacteria  abound  in  the 
upper  soil  layers  (2l/2  millions  have  been  estimated  in  a  cubic  cen- 
timeter of  soil  in  the  surface  layers),  and  these  are  active  agents 
in  modifying  the  soil. 

It  thus  appears  that  the  work  of  organisms  is  by  no  means  a 
negligible  factor,  and  will  in  the  course  of  time  produce  important 
results.  Of  these  organisms  man  is  of  course  the  most  important, 
and  it  is  not  going  too  far  to  say  that  on  the  whole  he  is  the  most 
powerful  geological  agent  at  work  in  modifying  the  surface  of  the 
land. 

BIBLIOGRAPHY  XVI. 

1.  BRANNER,  JOHN  C.     1896.     Decomposition  of  Rocks  in  Brazil.     Bulletin 

of  the  Geological  Society  of  America,  Vol.  VII,  pp.  255-314. 

2.  BRANNER,    J.    C.     1900.     Ants   as   Geological   Agents   in    the   Tropics. 

Journal  of  Geology,  Vol.  VIII,  pp.  151-153. 

3.  BRANNER,  J.  C.     1910.     Geologic  Work  of  Ants  in  Tropical  America. 

Bulletin  of  the  Geological  Society  of  America,  Vol.  XXI,  pp.  449-496. 

4.  DARWIN,    CHARLES.     1883.     The    Formation    of    Vegetable    Mould. 

D.  Appleton  &  Co.,  New  York,  pp.  1-313. 

5.  DAVISON,   CHARLES.     1891.     Work   Done  by   Lobworms.     Geological 

Magazine,  3d  Ser.,  Vol.  VIII.,  pp.  489-493. 

6.  PASSARGE,   SIEGFRIED.     1911.      Die  pfannenformigen  Hohlformer  der 

sudafrikanischen  Steppen.     Petermann's  Mittheilungen  LVII,  pt.  ii,  pp. 
130-135- 

7.  PECHUEL-LOESCHE.     1884.     Das  Ausland. 

8.  SHALER,  NATHANIEL  S.     1892.     Effects  of  Animals  and  Plants  on  Soils. 

In  "The  Origin  and  Nature  of  Soils, "  U.  S.  Geological  Survey,  I2th  Annual 
Report,  pt.  I,  pp.  219-345  (268-287). 


CHAPTER   XVII. 
SUMMARY  OF  ORIGINAL  FEATURES  OF  CLASTIC  ROCKS. 

We  may  now  summarize  the  various  structural  features  of  clas- 
tic rocks  which  were  formed  at  the  time  these  rocks  were  deposited 
and  which  therefore  serve  as  guides  in  the  determination  of  the 
mode  of  origin  of  the  rocks  possessing  them.  In  dealing  with  each 
feature  separately  it  will  be  possible  to  indicate  the  extent  to  which 
it  is  characteristic  of  one  or  the  other  of  the  types  of  clastic  rocks 
so  far  discussed. 

We  may  treat  these  characters  under  the  following  headings : 

1.  Stratification. 

2.  Cross-bedding. 

3.  Beach  cusps. 

4.  Wave  marks. 

5.  Rill  marks. 

6.  Mud  cracks  (sun  cracks  or  desiccation  fissui'es). 

7.  Clay  galls. 

8.  Clay  boulders  and  pebbles. 

9.  Rain  prints. 

10.  Ripple  marks. 

11.  Impressions  made  by  animals  in  transit. 

12.  Application   of   these   structures   in   determining   position   of 

strata. 

13.  Rounding  and  sorting  of  sand  grains,  and  wearing  of  pebbles. 
"14.     Characteristics  of  inclusions  in  sand  grains, 

15.  Organic  remains. 

16.  Concretions  (partly  secondary). 

17.  Secretions  (secondary). 

Nearly  all  of  these  structural  characters  have  been  generally  con- 
sidered as  preeminently  if  not  exclusively  characteristic  of  marine 
or  lacustrine  hydroclastics.  From  the  foregoing  discussion,  how- 
ever, it  will  appear  that  many  of  them  are  far  from  being  the  ex- 
clusive features  of  these  types  of  deposits.  In  fact,  it  may  be  said 

696 


STRATIFICATION  697 

that,  with  the  exception  of  the  beach  cusps,  the  wave  marks  and 
the  clay  pebbles,  they  are  characteristic  of  subaerial  deposits,  while 
some  of  them,  such  as  cross-bedding,  desiccation  fissures,  rain  prints 
and  footprints,  are  almost  exclusively  confined  to  the  formations 
other  than  marine  or  lacustrine.  The  most  pronounced  of  the  char- 
acters enumerated,  stratification,  is  also  of  frequent  occurrence  in 
the  endogenetic  formations. 

Concretions  are  only  occasionally  original  structures,  being  for 
the  most  part  secondary.  Secretions  are  always  of  secondary  char- 
acter, but  they  are  included  here  for  the  sake  .of  comparison  with 
concretions  which  belong  here  in  part. 

i.  STRATIFICATION.  In  its  broadest  sense  ( Walther-23  \6so 
et  seq.)  stratification  is  the  arrangement  of  rock  masses  in  layers 
or  strata,  each  one  of  which  was  at  one  time  the  latest  deposit,  and 
the  top  of  each  stratum  was  successively  the  top  of  the  lithosphere 
at  that  point.  Stratification  thus  defined  occurs  in  all  rocks,  which 
are  deposited  in  successive  layers.  Thus  a  series  of  lava-flows  will 
show  stratification,  each  flow  representing  a  distinct  stratum.  These 
volcanic  strata  are  often  steeply  inclined,  as  is  also  the  case  in 
clastic  strata  along  the  margins  of  coral  reefs  or  in  the  alluvial  fan 
or  talus  heap. 

Among  the  pyrogenic  rocks  stratification  is  produced  where 
lava  streams  of  different  composition  succeed  each  other,  or  where 
streams  of  the  same  composition  are  separated  by  an  interval,  dur- 
ing which  the  surface  of  the  earlier  one  either  hardened  or  became 
altered  to  some  extent,  or  again  was  covered  by  a  layer  of  clastic 
material,  before  the  second  flow  occurred.  Atmogenic  snow  ice  or 
glacial  ice  becomes  stratified  when  the  succeeding  deposits  of  snow 
are  separated  by  intervals  during  which  the  older  layer  solidified  or 
was  covered  by  a  thin  layer  of  dust  or  by  other  clastic  material. 
False  stratification  is  often  produced  in  this  rock  by  the  formation 
of  shearing  planes,  along  which  some  of  the  subglacial  detritus  is 
carried  up  into  the  ice.  Hydrogenic  and  biogenic  rocks  may  also 
be  stratified,  this  being  brought  about  by  cessation  of  deposition, 
by  change  in  the  material,  through  interposition  of  elastics,  or  by 
alternation  in  deposition  of  different  classes  of  endogenetic  ma- 
terials. Examples  of  this  are  shown  in  the  alternation  of  layers  of 
gypsum  and  salt,  or  in  the  intercalation  of  layers  of  potash  and 
other  salts  between  the  beds  of  ordinary  rock  salt.  The  numerous 
intercalated  silt  layers  of  the  salt  deposits  of  the  Bitter  Lakes  of 
Suez  further  serve  as  an  illustration.  While  stratification  is  thus 
not  confined  to  the  clastic  rocks,  it  finds  its  most  typical  expression 
in  this  group.  All  clastic  deposits  may  be  stratified,  this  stratifi- 


698 


PRINCIPLES    OF    STRATIGRAPHY 


cation  being  due  to  change  in  material,  to  change  from  one  type  of 
clastic  to  another,  or  to  alternation  of  clastic  with  endogenetic  de- 
posits. The  most  typical  development  of  stratification  is  in  the 
water-laid  elastics  (hydroclastics),  and  especially  in  those  laid  down 
in  standing  water.  Before  considering  the  various  kinds  of  stratifi- 
cation, however,  we  must  first  have  a  clear  conception  of  the  mean- 
ing of  the  term  stratum. 

Definition  of  Stratum.  The  current  definitions  of  the  term 
stratum  vary  greatly,  as  will  be  seen  from  the  following  quotations : 
(a)  "A  layer  of  rock;  a  portion  of  a  rock  mass  which  has  so  much 
homogeneity  and  is  so  separated  from  the  rock  that  lies  over  and 
under  it  that  it  has  a  character  of  its  own."  (Century  Diction- 
ary.) (b)  "The  term  stratum  is  sometimes  applied  to  one  layer 
and  sometimes  to  all  the  consecutive  layers  of  the  same  sort  of 


FIG.  135.  A  mass  of  stratified  rocks 
bounded  by  joint  faces  and  iso- 
lated by  erosion.  The  strata  are 
inclined  but  appear  horizontal  in 
one  section. 


FIG.  136.  Stratified  chalk  penetrated 
by  pipes  of  sand  and  gravel. 
Kent,  England.  (Prestwich.) 


rock."  (Chamberlin  and  Salisbury,  Geology-i :  464.)  (c)  "Strata 
or  Beds  are  layers  of  rock  varying  from  an  inch  or  less  up  to  many 
feet  in  thickness.  A  stratum  may  be  made  up  of  numerous  laminae, 
if  the  nature  of  the  sediment  and  the  mode  of  deposit  have  favored 
the  production  of  this  structure  .  .  .  [it]  .  .  .  may  be  one  of  a 
series  of  similar  beds  in  the  same  mass  of  rock,  as  where  a  thick 
sandstone  includes  many  individual  strata,  varying  considerably  in 
their  respective  thicknesses;  or  it  may  be  complete  and  distinct  in 
itself,  as  where  a  band  of  limestone  or  iron  stone  runs  through  the 
heart  of  a  series  of  shales." 

"The  smallest  subdivisions  of  the  Geological  Record  are  lam- 
inae, a  number  of  which  may  make  a  stratum,  seam  or  bed.  As  a 
rule,  a  stratum  is  distinguishable  by  lithological  rather  than  palae- 
ontological  features."  (Geikie-Textbook,  4th  ed.-i:<5j5;  2:860.) 

(d)  "In  the  description  of  a  formation  the  term  stratum  (from 


STRATIFICATION  699 

the  Latin  for  bed,  strata  in  the  plural)  is  used  for  each  section  of 
the  formation  that  consists  throughout  of  approximately  the  same 
kind  of  rock  material.  Thus,  if  shale,  sandstone  and  limestone  suc- 
ceed one  another  in  thick  masses,  each  is  an  independent  stratum. 
A  stratum  may  consist  of  an  indefinite  number  of  beds,  and  a  bed 
of  numberless  layers.  But  the  distinction  of  layer  and  bed  is  not 
always  obvious."  (Dana-Manual,  5th  ed.-p/.) 

(e)  Schichten  nennt  man  plattenformige  Lagen  welche  "... 
durch  parallele  Flachen  begranzt  werden,  bei  weiter  Ausdehnung 
in  der  Regel,  nur  geringe  Dicke  besitzen,  und  das  Product  successiver 
Ubereinanderlagerung  bilden."      (Credner-Elemente,  8th  ed.,-^5.) 

(f)  "The  material  between  two  planes  of  stratification  forms 
a  stratum  or  bed,  though  if  the  deposit  be  very  thin  it  is  known  as 
a  lamina,  and  the  planes  are  spoken  of  as  planes  of  lamination  (no 
hard  and  fast  line  can  be  drawn  between  strata  and  laminae;  sev- 
eral of  the  latter  usually  occur  in  the  space  of  an  inch)."     (Marr- 
Principles  of  Stratigraphical  Geology-^/.) 

From  the  foregoing  definitions  it  will  be  seen  that  there  is  a 
considerable  diversity  of  opinion  regarding  the  value  of  the  term 
stratum.  We  may  gain  a  clearer  concept  if  we  consider  it  in  the 
light  of  its  origin.  Continuous  deposition  under  the  same  condi- 
tions will  produce  a  deposit  nearly  uniform  throughout,  and  of  a 
thickness  commensurate  with  the  rate  of  deposition,  the  length  of 
time  and  the  coarseness  of  the  material.  A  sudden  change  in  con- 
ditions will  bring  about  an  abrupt  change  in  the  character  of  the 
material  deposited.  It  may  be  coarser,  or  it  may  be  finer  in  grain,  or 
it  may  be  of  a  wholly  different  composition.  Variation  in  grain, 
or  texture,  unless  an  abrupt  change  occurs,  is  indicative  of  only 
minor  changes  in  physical  condition  of  the  region.  But  variation  in 
the  composition  of  the  material  denotes  a  change  of  some  magni- 
tude. This  being  the  case,  a  decided  change  in  the  composition  of 
the  material  ought  to  be  considered  a  change  in  strata,  while  a 
change  in  texture,  unless  it  be  a  great  one,  should  be  considered  as 
of  minor  value,  and  therefore  should  constitute  a  subdivision  of  the 
stratum  into  layers.  The  great  changes  in  texture  which  may  con- 
veniently be  regarded  as  of  stratum  value  are  those  from  one  to 
the  other  of  the  three  primary  textural  divisions  of  the  clastic  rocks, 
namely,  lutaceous,  arenaceous  and  rudaceous.  Thus  a  rudyte  fol- 
lowing an  arenyte  may  well  be  considered  a  distinct  stratum.  But 
the  change  from  a  fine  arenyte  to  a  coarse  one  or  vice  versa  is  bet- 
ter regarded  as  a  change  in  layers.  Where  deposition  is  continu- 
ous, while  increase  in  the  force  of  the  currents  and  increase  in  the 
coarseness  of  the  deposit  are  progressive,  an  arenyte  may  gradually 


700  PRINCIPLES    OF    STRATIGRAPHY 

pass  upward  into  a  rudyte,  whereupon  the  distinction  of  strata  is 
a  matter  of  judgment.  In  such  cases  the  stratum  of  arenyte  ter- 
minates with  a  layer  of  rudaceous  arenyte  where  the  arenaceous 
material  still  predominates,  while  the  stratum  of  rudyte  begins  with 
a  layer  of  arenaceous  rudyte,  in  which  the  rudaceous  material  has 
become  most  prominent. 

A  change  in  composition  is  not  always  of  sufficient  magnitude 
to  warrant  separation  into  a  new  stratum.  Thus  a  stratum  of 
silicarenyte  or  pure  quartz  sandstone  may  have  interbedded  layers 
of  ferruginous,  argillaceous,  calcareous  or  glauconite  material, 
where  this  material  is  only  of  sufficient  quantity  to  produce  a  variety 
of  the  sandstone.  Where,  however,  a  calcarenyte  or  a  clay  rock 
(argillutyte)  succeeds  to  a  silicarenyte,  a  new  stratum  is  produced. 
Where  deposition  is  continuous,  but  the  supplied  material  changes 
in  composition,  a  gradation  from  a  pure  silicarenyte  to  a  pure  cal- 
carenyte may  occur,  without  break  of  continuity.  In  this  case,  as 
in  the  case  of  the  gradation  in  texture,  the  line  of  division  between 
the  two  strata  must  be  drawn  on  the  relative  preponderance  of  ma- 
terials. The  stratum  of  silicarenyte  will  terminate  with  a  layer  of 
calcareous  silicarenyte,  while  the  stratum  of  calcarenyte  will  begin 
with  a  layer  of  siliceous  calcarenyte. 

While  gradations  as  here  discussed  are  not  of  uncommon  occur- 
rence, in  the  more  familiar  type  of  stratification  the  strata  abruptly 
succeed  each  other.  Thus  a  stratum  of  limestone,  clastic,  organic  or 
chemical  and  frequently  composed  of  only  one  layer,  may  be  inter- 
calated between  strata  of  shales.  Again  strata  of  limestones  are 
separated  by  strata  of  carbonaceous  clay  or  by  sandstones,  the  sep- 
arating strata  in  many  cases  being  mere  films.  In  such  cases  the 
stratum  of  clayey  material  is  represented  by  only  one  lamina.  Not 
infrequently  strata  of  clastic  limestones  (calcarenytes)  are  sepa- 
rated by  a  thin  stratum  of  organic  limestone  in  a  single  layer,  and 
generally  containing  an  admixture  of  clayey  matter.  A  decided 
change  in  color  may  readily  serve  as  a  basis  for  division  into  strata, 
since  such  change  generally  indicates  a  marked  change  in  physical 
conditions  during  deposition.  Thus  a  black  shale  succeeding  a  gray 
or  bluish  one  marks  a  change  in  conditions  of  deposition.  A  change 
from  a  gray  to  a  red  sandstone  likewise  indicates  physical  changes 
from  conditions  preventing  to  those  permitting  extensive  oxidation, 
as  elsewhere  discussed.  Finally  the  occurrence  or  indications  of  de- 
cided physical  breaks,  such  as  erosion  surfaces  and  disconformities, 
serves  to  separate  distinct  strata. 

Types  of  Stratification.  Walther  (23:631)  recognizes  two 
kinds  of  stratification,  direct  and  indirect.  The  former  is  produced 


STRATIFICATION— CROSS-BEDDING  701 

when  the  changes  in  sedimentation  produce  differences  in  the  strata, 
as  when,  for  example,  volcanic  ashes  are  deposited  upon  a  lava 
flow,  or  when  fine  clay  deposits  are  succeeded  by  deposits  of  sands 
from  a  rising  flood,  or  when  in  the  deep  sea,  after  continuous 
deposition  of  Globigerina  ooze,  a  bionomic  change  brings  about  a 
deposition  of  diatomaceous  oozes.  Here  each  stratum  corresponds 
to  the  physical  change  which  brought  about  the  change  in  deposi- 
tion. When,  however,  a  rearrangement  of  the  sediment  of  the 
shallow  sea  occurs,  owing  to  the  agitation  of  this  sediment  by  the 
waves,  a  secondary  separation  of  materials  results,  which  was  not 
dependent  on  original  changes  in  sedimentation.  Thus  a  mixed 
sand  may  be  assorted  into  layers,  according  to  grain,  or  a  pebbly 
deposit,  charged  originally  with  sand,  may  be  separated  into  a 
stratum  of  conglomerate  and  one  of  sand.  Again,  a  deposit  of 
mixed  foraminiferal  and  pteropodan  shells  may  be  separated  into 
two  strata,  one  of  Foraminifera,  tfre  other  of  pteropods,  on  account 
of  the  difference  in  their  specific  gravities.  The  cases  just  cited 
constitute  what  Walther  has  termed  indirect  stratification.  Some- 
times it  finds  expression  in  layers,  sometimes  in  strata.  The  re- 
markable alternation  of  pure  limestone  and  calcareous  clays  in  the 
Cincinnati  series  of  the  Ordovicic  of  Ohio,  etc.,  has  been  explained 
in  this  manner  as  indirect  stratification.  The  sharp  assortment  of 
the  material,  the  abruptness  of  contact  and  freedom  from  grada- 
tions would  seem  to  indicate  that  this  interpretation  is  correct. 
(Perry-i8.) 

Stratification  is  often  indicated  only  by  the  arrangement  of 
pebbles,  mica  scales,  or  of  fossils  in  interrupted  horizontal  lines, 
within  a  single  stratum  or  even  a  single  bed.  The  arrangement  of 
the  flints  in  the  chalk  suggests  the  stratification  of  this  deposit,  a 
single  stratum  appearing  often  of  exceeding  thickness,  while  the 
material  is  of  uniform  texture,  thus  exhibiting  no  lamination.  The 
same  thing  is  true  of  the  Losspuppchen  or  concretions  of  the  loess, 
but  in  this  case  it  is  not  always  the  stratification  which  is  indicated 
by  them,  but  lines  of  permeability,  which  have  no  direct  relation  to 
stratification.  This  may  possibly  be  the  case  also  in  some  flint  layers 
of  the  chalk,  as  already  suggested. 

2.  CROSS-BEDDING.  This  is  most  readily  seen  in  elastics  of  an 
arenaceous  texture,  though  rudytes  sometimes  show  it  on  a  large 
scale.  It  consists  of  an- arrangement  of  the  grains  in  diagonal  lay- 
ers with  reference  to  the  plains  bounding  the  strata.  Originally 
these  laminae  may  have  been  deposited  at  a  considerable  angle  from 
the  horizontal.  Above  and  below,  these  oblique  layers  are  bounded 
by  the  planes  of  stratification,  and  they  are  commonly  truncated  on 


702  PRINCIPLES    OF    STRATIGRAPHY 

their  upper  surfaces.  Successive  beds  may  have  their  oblique  lam- 
inae inclined  at  different  angles  or  in  different  directions,  and  hori- 
zontal layers  may  rest  upon  the  truncated  edges  of  inclined  layers, 
thus  simulating  unconformity.  This  oblique  lamination  may  range 
in  magnitude  from  beds  a  millimeter  or  less  in  thickness  to  strata 
having  a  thickness  of  a  hundred  feet  or  more.  In  such  a  case  the 
deposit  was  generally  formed  as  a  delta  in  a  standing  body  of  water, 
with  strong  currents  flowing  in  and  depositing  the  sands  or  pebbles 
on  the  growing  delta  front.  Oblique  beds  formed  in  this  manner 
are  known  as  "fore-sets,"  and  are  generally  truncated  at  the  top  by 
the  currents,  which  deposit  horizontal  beds  or  "top-sets,"  generally 
of  coarser  material,  upon  the  truncated  upper  edges.  Basally  the 
fore-set  beds  will  either  rest  upon  or  directly  merge  into  the  bot- 
tom-set beds,  which  are  made  of  finer  material,  mostly  clay  and  silt. 
The  angle  of  the  fore-set  beds  generally  decreases  outward,  the 
last  fore-sets  of  a  large  delta  being  fine  and  less  steeply  inclined 
than  the  older  ones  (see  ante,  p.  610).  Small  deltas  were  formed 
in  numerous  localities  toward  the  end  of  the  last  glacial  epoch  in 
standing  bodies  of  water  along  the  ice  front.  Their  structure  can 
readily  be  examined  in  many  sand  pits.  Several  types  of  cross- 
bedding  may  be  distinguished. 

a.  Delta  Type.    This  type  of  cross-bedding,  already  noted,  con- 
sists essentially  of  a  single  bed  of  diagonal  layers  bounded  below 
and  above  by  nearly  horizontal  beds.    It  appears  to  be  characteristic 
of  deltas  deposited  in  a  standing  body  of  water.     Whether  or  not 
this  type  is  also  characteristic  of  deltas  formed  on  the  sea  coast 
depends  on  the  strength  and  magnitude  of  the  tides.     It  is  evident 
that  only  one  series  of  fore-set  beds  will  be  formed  in  any  given 
delta,   and  that  relatively   stationary   conditions   alone   permit  the 
formation    of  the  delta.     If,  after  the  building  of  a  delta  in  a  lake, 
a  rise  in  the  water  level  should  occur,  a  new  delta  might  be  built  up 
over  the  old  one,  and  thus  the  resulting  formation  would  show  two 
sets  of  diagonal  beds,  separated  by  horizontal  beds,  the  top  sets  of 
the  first  and  the  bottom  beds  of  the  second.    Such  a  superimposition 
of  two  deltas  is,  however,  difficult  to  conceive  of  on  a  subsiding  sea 
coast  where  subsidence  is  accompanied  by  transgression,  and  con- 
sequent transference  of  the  zone  of  delta  building. 

b.  Cross-bedding  of  Torrential  Deposits.     Superimposition   of 
obliquely  bedded  strata  is,  however,  eminently  characteristic  of  tor- 
rential deposits.     Each  succeeding  deposit  will  be  characterized  by 
fore-set  and  top-set  beds,  and  the  number  of  such  superimposed 
strata  is  chiefly  dependent  on  the  frequency  of  recurrence  of  the 
torrents.     The  length  of  the  fore-set  bed  formed  by  a  river  on  dry 


CROSS-BEDDING  703 

land  is  of  course  much  less  than  that  of  a  delta  fore-set.  Most 
likely  a  greater  length  than  six  feet  is  rare,  while  probably  by  far 
the  greater  number  fall  below  a  foot  in  length.  The  angle  which 
the  fore-set  beds  make  with  the  horizontal  varies  proportionately 
to  the  coarseness  of  the  material,  but  in  any  given  case  it  is  ap- 
proximately uniform.  Moreover,  the  angle  of  the  fore-sets  of  suc- 
cessive strata  is  as  a  rule  similar  and  in  the  same  direction,  while  the 
dividing  top-set  beds  are  parallel  in  the  successive  strata.  Thus  a 
section  of  a  torrential  deposit  will  show  a  succession  of  obliquely 
bedded  strata,  separated  and  bounded  above  and  below  by  strata, 
which  make  a  high  angle  with  them,  are  parallel  to  each  other,  and 
originally  represented  the  surface  slope  of  the  deposit.  The  inclina- 
tions of  the  laminae  of  the  successive  cross-bedded  strata  are  uni- 
form, and  the  laminae  all  slope  in  the  same  direction.  This  is  the 
type  of  cross-bedding  found  in  many  ancient  sandstones,  and  it 
seems  to  be  highly  improbable  that  any  such  structure  could  be 
produced  by  agents  working  on  the  sea  coast.  (Fig.  123.) 

c.  Cross-bedding  of  Eolian  Deposits.  Such  regularity  of  cross-  i/ 
bedding  as  is  found  in  both  lacustrine  and  torrential  deposits  is, 
however,  not  characteristic  of  eolian  deposits.  In  these  the  laminae 
when  oblique  show  no  uniformity  of  slope  or  direction  within  either 
the  same  stratum  or  successive  strata.  Nor  are  the  dividing  laminae 
parallel  to  each  other.  Cross-bedding  of  eolian  deposits  is  brought 
about  in  the  following  manner :  A  sand  dune  in  its  structure  shows 
a  series  of  concentric  shells  of  sand  consisting  of  alternating  coarse 
and  fine  layers.  This  is  a  feature  characteristic,  according  to 
Forchhammer  (9:7),  of  every  dune  of  the  Jutland  coast,  and  in- 
ferentially  of  the  majority  if  not  of  all  sand  dunes.  Toward  the 
side  of  the. wind  the  dune  layers  have  an  angle  of  5°,  while  on  the 
lee  side  the  angle  is  as  high  as  30°.  The  stratification  is  shown 
chiefly  by  the  varying  coarseness  of  the  grains  composing  succes- 
sive layers,  this  being  determined  by  the  variable  strength  of  the 
winds,  to  which  the  dune  owes  its  origin.  If  through  a  change  of 
the  conditions  which  built  up  the  dune,  i.  e.,  change  in  the  force  or 
the  direction  of  the  wind  or  in  the  amount  of  the  sand  supplied, 
or  through  other  causes,  the  dune  begins  to  migrate,  a  part  of 
its  basal  portion  may  remain  behind,  as  the  truncated  base  of  the 
dune,  while  upon  this  truncated  surface  a  new  dune  may  accumu- 
late, which  in  turn  will  meet  with  the  same  fate,  leaving  its  basal 
portion  behind.  Successive  portions  of  this  kind  will  eventually 
produce  a  bed  of  sand  in  which  the  cross-bedding  is  of  extreme 
irregularity  and  inconstancy.  (Fig.  137.)  (Walther-22: 7/5 
[519].)  Huntington  (15)  has  shown  that  a  characteristic  feature" 


704  PRINCIPLES    OF    STRATIGRAPHY 

of  such  cross-bedding  is  the  tangency  of  the  layers  at  the  base,  while 
at  the  top  erosion  has  sharply  truncated  them. 

This  type  of  cross-bedding  is  not  infrequently  met  with  in 
arenytes  among  the  strata  of  all  ages.  The  Medina  sandstone 
(Siluric)  of  western  New  York  affords  some  excellent  examples 
of  this  type,  and  it  is  highly  probable  that  the  beds  showing  this 
structure  were  originally  wind-laid  deposits.  Other  excellent 
examples  of  such  cross-bedding  are  shown  in  the  Sylvania  sand- 
stone (Upper  Siluric)  of  Ohio,  Michigan  and  Canada  (Figs. 
119,  120)  and  in  the  White  Cliff  sandstones  (Jurassic)  of  the  Kanab 
Plateau  and  in  the  La  Platte  sandstone  (Jurassic)  of  Utah.  Cal- 
carenytes,  too,  sometimes  show  this  structure,  as  noted  above,  for 
the  Junagarh  limestone  of  India  and  for  other  modern  deposits 
recognized  as  wind-laid.  The  cross-bedding  of  the  Somersetshire 
oolite  (Forest  marble),  referred  to  above  (Fig.  121),  appears  also 
to  be  indicative  of  the  eolian  origin  of  this  rock.  Excellent  exam- 


FIG.  137.     Eolian  cross-bedding  as  found  in  desert  sands.     (After  Walther.) 

pies  of  this  type  of  bedding  in  a  heavy-bedded,  non-siliceous  lime- 
stone (calarenyte)  have  been  observed  by  the  author  in  the  cut 
through  the.  Warsaw  (Mississippic)  limestone  on  the  Missouri  Pa- 
cific Railroad,  south  o£  St.  Louis,  Missouri.  This  is  reproduced  in 
Figs.  I22a  and  b,  on  page  577.  Compare,  also,  Figs.  13,8,  139. 

Comparison  of  Types.  A  comparison  of  the  three  types  of 
cross-bedding,  i.  e.,  the  delta,  the  torrential  and  the  eolian,  will  show 
the  distinctive  character  of  each,  namely :  uniformly  sloping  fore- 
set  beds  in  one  series  and  generally  on  a  large  scale,  for  delta  de- 
posits; uniform  fore-set  beds  of  small  size  and  in  successive  but 
similar  series  separated  by  horizontal  deposits,  for  torrential  de- 
posits ;  and  oblique  beds,  variable  in  angle  and  slope  within  the  same 
and  successive  series  commonly  without  horizontal  dividing  beds, 
for  eolian  deposits.  While  these  types  grade  into  each  other  where 
the  deposits  meet  or  overlap,  it  is  not  known  that  any  one  type  of 
cross-bedding  is  produced  by  another  agent.  Thus  the  torrential 
type  of  cross-bedding  cannot  be  readily  conceived  of  as  formed  in 
wthe  sea,  and  the  same  may  be  said  of  the  eolian  type.  The  bedding 
of  a  sand  bar  may  perhaps  show  something  analogous  to  the  wind- 


CROSS-BEDDING 


705 


formed  cross-bedding,  but  conditions  for  the  preservation  of  such 
are  perhaps  seldom  realized.  Gilbert  has  described  the  mode  of 
formation  of  cross-bedding  through  the  shifting  of  ripples  on  the 


FIG.  138.  Crosfc-bedding  of  the  Eolian  type  (Orange  sand  or  La  Fayette 
Formation),  Mississippi  Central  Railroad,  Oxford,  Miss.  (After 
Hilgard.) 

sea  floor,  due  to  a  current  accompanying  oscillatory  movements.  He 
considers  "that  sediment  may  be  added  to  a  rippled  surface  without 
any  disturbance  of  the  pattern,  but  that  there  is  usually  a  coinci- 
dent gradual  bodily  shifting  of  the  pattern  in  some  direction." 


FIG.  139.     Ledges  of  sandstone  near  Colorado  Springs,  showing  Eolian  cross- 
bedding. 

"The  shifting  of  the  ripple  profile  during  the  accumulation  of  the 
sediment  makes  the  accumulation  unequal  on  the  two  sides  of  the 
trough  (figure  3),  and,  if  the  ratio  of  shifting  to  deposition  exceeds 
a  certain  amount,  there  is  deposition  on  only  one  side  of  the  trough 
and  erosion  on  the  other."  (Gilbert-i2 :  ijp,  Figs.  3-4-}  In  this 
case  two  sets  of  oblique  planes  are  produced,  one  due  to  deposi- 
tion, the  other  to  erosion,  the  latter  representing  the  progress  of  the 


7o6  '  PRINCIPLES    OF    STRATIGRAPHY 

profile  of  the  troughs  along  certain  tangents.  The  tangent  planes 
are  often  nearly  horizontal,  in  which  case  the  cross-bedding  would 
approach  in  appearance  the  torrential  type.  The  absence  of  divid- 
ing strata  would,  however,  readily  distinguish  it.  Cross-bedding  of 
this  type  has  been  observed  by  Gilbert  in  the  Medina  sandstone  of 
western  New  York,  and  referred  to  wave  work. 

"When  the  waves  from  a  new  direction  act  on  a  surface  already 
rippled,  they. produce  a  new  pattern,  which  at  first  combines  with 
the  old  one,  but  eventually  obliterates  it.  The  troughs  of  the  new 
pattern  are  formed  in  part  by  excavation  from  ridges  of  the  old,  and 
the  lamination  associated  with  the  old  ridges  is  truncated,  so  that 
the  new  lamination  is  unconformable."  (12:140,  Fig.  5.)  Sev- 
eral such  unconformities  may  succeed  each  other,  and  Gilbert 
holds  that  the  irregular  cross-bedding  of  the  Medina  sandstone, 
referred  to  above  as  perhaps  of  eolian  origin,  was  produced  in  this 
manner.  It  may  be  doubted,  however,  if  ripples  of  a  sufficient  mag- 
nitude to  produce  such  a  structure  are  ever  produced  under  water, 
and  still  more  if  when  produced  they  are  accompanied  by  such 
rapid  deposition  as  the  case  would  seem  to  require.  For,  as  Gil- 
bert has  pointed  out,  the  formation  of  large  ripples  requires  great 
waves,  and  therefore  broad  and  deep  water  bodies,  and  in  such 
deposition  of  sands  is  not  extensive.  On  the  whole,  the  structure  de- 
scribed conforms  much  more  nearly  to  the  observed  structure  of 
anemoclastic  deposits.  It  may  also  be  questioned  if  the  ripple  cross- 
bedding  on  a  small  scale  may  not  with  equal  or  perhaps  greater 
facility  be  produced  by  the  wind  alone.  It  would  seem  that  shift- 
ing wind  ripples,  which  are  sand  dunes  on  a  small  scale,  would  pro- 
duce the  same  structure  that  shifting  sand  dunes  produce  on  a 
larger  scale. 

Strata  which  show  the  irregular  type  of  cross-bedding  must  be 
carefully  scrutinized  for  other  evidence  of  eolian  activity  as  well 
as  for  evidence  of  marine  or  fluviatile  origin.  The  occurrence  in 
the  rock  of  scattered  marine  organisms  is  no  conclusive  evidence 
of  the  marine  origin  of  the  formation,  unless  it  can  be  shown  that 
the  organisms  in  question  lived  where  found  or  at  least  were  car- 
ried there  by  currents  of  water  and  not  by  wind. 

3.  BEACH  CUSPS.  (Johnson-i6.)  Beach  cusps  are  triangular 
ridges  extending  across  the  beach  generally  at  right  angles  to  the 
shore  front.  When  most  typically  developed  the  beach  cusp  has  the 
form  of  an  isosceles  triangle  with  its  base  parallel  to  the  beach,  but 
at  its  upper  edge,  and  its  apex  near  the  water.  The  cusp  may  be 
broad,  approaching  in  form  an  equilateral  triangle,  but  more  gen- 
erally it  is  long,  narrow  and  extremely  acute,  the  sides  sometimes 


BEACH    CUSPS  707 

appearing  almost  parallel.  'The  cusps  may  constitute  the  serrate 
seaward  side  of  a  prominent  beach  ridge,  or  may  occur  as  isolated 
gravel  hillocks  separated  by  fairly  uniform  spaces  of  smooth,  sandy 
beach.  They  may  be  sharply  differentiated  from  the  rest  of  the 
beach,  or  may  occur  as  gentle  undulations  of  the  same  material  as 
the  beach  proper,  and  so  be  scarcely  discernible  as  independent 
features."  "A  cusp  may  rise  from  an  inch  or  less  to  several  feet 
above  the  general  level  of  the  beach.  Many  are  relatively  low  and 
flat,  others  high  and  steep-sided.  Sometimes  the  highest  part  is 
comparatively  near  the  apex;  at  other  times  the  highest  part  is  far 
back,  and  from  it  a  long,  sloping  ridge  trails  forward  toward  the 
water.  As  a  rule,,  the  cusps  appear  to  point  straight  out  toward 
the  water — that  is,  the  axis  of  the  cusp  is  at  right  angles  to  the 
shore  line — and  neither  side  of  a  cusp  is  steeper  than  the  other,  ex- 
cept where  oblique,  wind-made  waves  have  eroded  one  side  only." 
(Johnson— 16:  605-606.)  The  material  of  the  cusp  varies  from  the 
finest  sand  to  the  coarsest  cobblestone,  there  being  no  necessary 
relationship  between  the  size  of  the  cusp  and  the  size  of  the  material 
composing  it.  Gravel  cusps  are  often  found  on  sandy  beaches,  the 
cusps  being  always  built  of  the  coarser  material  of  the  beach.  In 
size  cusps  vary  from  a  length  of  8  or  12  inches  to  30  feet  or  more. 
The  distance  between  cusps,  measured  from  crest  to  crest,  ranges 
on  small  ponds  from  less  than  a  foot  to  two  feet  or  more.  On  sea 
beaches  they  may  be  less  than  10  feet  apart,  while  those  built  by 
large  storm  waves  may  be  100  feet  apart  The  spacing  is  fairly 
regular,  though  in  some  cases  there  seems  to  be  irregularity  in 
spacing,  as  shown  by  Jefferson.  (Johnson-i6.)  Compound  cusps 
are  also  occasionally  formed. 

Various  theories  have  been  propounded  to  explain  the  origin 
of  beach  cusps ;  for  a  review  of  these  the  reader  is  referred  to  the 
paper  by  Johnson,  where  a  reference  to  the  bibliography  is  also 
found.  Johnson's  theory,  and  the  one  best  supported  by  the  facts, 
is,  concisely  stated,  ''that  selective  erosion  by  the  swash  develops 
from  initial,  irregular  depressions  in  the  beach,  shallow  troughs  of 
approximately  uniform  breadth,  whose  ultimate  size  is  proportional 
to  the  size  of  the  waves,  and  determines  the  relative  uniform  spac- 
ing of  the  cusps,  which  develop  on  the  intertrough  elevations." 
(16:620.) 

Fossil  Beach  Cusps.  Beach  cusps  on  old  shore  lines  are  known 
especially  from  the  Medina  sandstone  of  western  New  York.  They 
were  described  by  Gilbert  (12)  as  giant  ripples,  but,  as  suggested 
by  Branner  (3)  and  by  Fairchild  (7),  they  are  undoubted  examples 
of  ancient  beach  cusps.  The  spacing  of  these  cusps  varies  from 


708  PRINCIPLES    OF    STRATIGRAPHY 

10  to  30  feet,  and  their  height  from  6  inches  to  3  feet.  Fairchild 
has  found  crests  80  feet  apart,  but  it  is  not  certain  that  all  such 
structures  are  referable  to  cusps. 

4.  WAVE  MARKS.    On  shallow  coasts  the  advancing  waves  slide 
up  onto  the  shore  after  breaking,  forming  the  "swash."    After  the 
retreat  of  the  wave,  its  furthermost  advance  is  found  to  be  marked 
by  a  fine,  wavy  line,  corresponding  in  outline  to  that  of  the  water's 
edge,  and  composed  of  fine  particles  of  mica,  fragments  of  seaweed, 
fine  sand  grains  and  other  matter  light  enough  to  be  carried  along 
by  the  water.    Numerous  wave  lines  of  this  character  may  generally 
be  seen  on  a  shore  of  the  type  noted.     In  exceptional  cases,  as  in 
the  Medina  sandstone  of  New  York,  these  are  finely  preserved  after 
the  consolidation  of  the  rock,  appearing  often  as  perfect  as  on  the 
unconsolidated  beach.     (Fairchild-7.) 

5.  RILL  MARKS.    The  water  running  off  after  each  swash,  or  on 
the  retreat  of  the  tide,  frequently  cuts  rills  into  the  surface  of  the 
beach.    These  rills  represent  a  river  system  in  miniature,  and  gen- 
erally  consist  of  a  number  of   small,   quickly   widening  channels, 
which  join  a  trunk  channel  at  a  very  oblique  angle,  and  which  are 
in  turn  joined  by  other  branches  at  an  oblique  angle. 

A  different  type  of  rill  marks  is  found  where  small  streams  de- 
bouch upon  a  flat,  sandy  or  clayey  plain.  Here  the  waters  of  the 
stream  will  divide  into  innumerable  fingers  and  fingerlets,  the  re- 
verse of  the  river-system  type.  Thus  before  the  water  sinks  into 
the  ground  or  runs  off,  a  series  of  channels,  branching  more  and 
more  in  their  lower  courses,  have  been  produced.  These  channels 
are  reproductions  on  a  small  scale  of  the  large  channels  spreading 
over  the  subaerial  deltas  at  the  debouchure  of  desert  streams. 

After  the  dying  out  of  the  streamlets  which  produced  the  rills, 
the  conditions  are  generally  favorable  for  the  preservation  of  these 
in  the  hardening  mud,  and  through  covering  by  wind-drifted  sand  or 
flood  deposits.  On  the  shore  conditions  for  the  preservation  of  rill 
marks  are  less  favorable,  since  the  succeeding  wave  will  generally 
destroy  the  marks  left  by  the  run-off  preceding.  Occasionally,  how- 
ever, such  a  preservation  may  occur.  In  either  case,  the  filling  mud 
or  sand  will  on  hardening  show  the  relief  of  the  original  rill,  re- 
producing the  minutest  channel  as  a  raised  ridge.  These  relief 
structures  greatly  resemble  branching  stems  of  plants  and  have 
sometimes  been  described  as  such..  (Rogers,  Lesquereux,  New- 
berry.) 

Water  flowing  down  the  beach  is  often  checked  locally  by  peb- 
bles or  shells  lying  partly  buried  on  the  beach.  In  such  cases  the 
water  flowing  down  on  either  side  of  the  obstruction  will  excavate 


RILL-MARKS;    MUD    CRACKS  709 

characteristic  depressions,  or  the  water  falling  over  the  obstruction 
will  gully  the  surface  for  a  short  distance  below.  Examples  of 
these  are  found  in  the  Medina  sandstone. 

6.  MUD-CRACKS,  SUN-CRACKS  OR  DESICCATION  FISSURES. 
When  lutaceous  deposits  are  exposed  by  the  retreat  of  the  tide,  or 
by  the  shrinking  or  disappearance  of  a  playa  lake  or  a  pond,  or  by 
the  uncovering  of  the  flood-plain  of  a  river,  the  drying  which  they 
undergo  will  result  in  the  formation  of  polygonally  arranged  cracks, 
and  a  gentle  concaving  of  the  upper  surfaces  of  the  polygons  thus 
bounded.  When  the  desiccated  layers  of  mud  are  thin,  they  will 
often  curl  up  like  wood  shavings,  and  may  be  blown  away  by  the 
wind.  When  on  reflooding  of  the  surface  or  by  the  deposition  of 
wind-blown  material,  these  cracks  are  filled  in  by  deposits  of  the 
same  or  different  material,  the  polygons  will  remain  more  or  less 
perfectly  outlined.  This  desiccation  fissure,  sun-crack,  mud-crack, 
prismatic,  or  paving  block  structure,  as  it  is  variously  called,  is 
found  not  only  in  clayey  rocks,  but  also  in  fine  calcilutytes,  like 
those  of  the  Helderberg  mountains  (Rondout  waterlimes),  the 
Solnhofen  beds  (Marsh),  the  Cincinnati  limestones  (Perry-i8),  and 
in  many  other  lutaceous  deposits.  They  testify  to  the  exposure 
of  these  deposits  before  they  were  solidified.  (For  a  full  dis- 
cussion of  this  subject  see  Barrell-i.) 

Playa  Surface.  Taking  the  areas  of  mud-crack  formation  in 
the  order  of  their  magnitude,  the  playa  surface  would  probably 
stand  first.  Here  the  entire  surface  for  hundreds  of  square  miles 
becomes  mud-cracked,  often  to  considerable  depth,  on  the  complete 
drying  up  of  the  temporary  playa  lake.  Here,  too,  the  conditions 
for  the  preservation  are  most  favorable.  Not  only  is  the  exposure 
a  long  one,  often  the  greater  part  of  the  year,  or  for  many  years, 
and  for  much  of  the  time  to  intense  heat,  but  the  chances  of  proper 
burial  are  much  greater.  Wandering  sand  dunes  may  thus  preserve 
the  record,  dust  deposits  may  fill  the  fissures,  or,  at  the  next  flood, 
sands  or  mud  may  be  swept  into  them.  In  fact,  the  playa  or  takyr 
seems  to  be  the  ideal  surface  for  mud-crack  record,  and  one  is 
tempted  to  refer  most  mud-cracked  strata  to  such  an  origin.  Cer- 
tainly where  fossil  mud-cracks  penetrate  a  formation  to  the  depth 
of  ten  feet,  as  is  the  case  in  the  upper  Shinarump  (Jura-Triassic) 
shales  of  Utah  (Gilbert-n  :  p),  it  is  difficult  to  believe  that  they 
could  be  formed  under  other  conditions  than  those  permitting  pro- 
longed exposure  such  as  is  found  only  in  the  playas  of  the  desert, 
where  ten  years  or  more  may  elapse  between  rainfalls. 

Permanent  Lake  Surface.  Much  less  extensive,  and  of  minor 
significance,  are  the  sun-cracked  areas  which  come  into  existence 


710  PRINCIPLES    OF    STRATIGRAPHY 

around  permanent  lake  bodies  as  the  result  of  periodic  shrinking 
of  the  lake  after  a  flooding  of  the  adjacent  lands.  Such  mud- 
cracked  areas  will  be  exposed  for  long  periods  of  time  and  so  re- 
semble the  flood  plains  of  rivers.  They  at  best,  however,  form  but 
a  narrow  marginal  belt  around  the  lake  and  the  beds  characterized 
by  them  would  grade  laterally  into  fresh  water  lake  beds  in  which 
remains  of  fresh  water  organisms  are  found.  The  mud  cracks  of 
the  Tertiary  lake  beds  of  Florissant  may  be  of  this  type. 

River  Flood  Plains.  Next  in  importance  to  the  playa,  and 
perhaps  even  rivaling  it  in  extent,  is  the  river  flood  plain.  "Here 
after  a  great  flood  extensive  areas  may  be  laid  bare  and  be  sub- 
jected to  desiccation  and  cracking  during  the  long  period  of  expo- 
sure before  the  next  flood.  Since,  in  the  lower  reaches  of  rivers, 
the  material  spread  out  by  the  flood  is  of  the  nature  of  a  fine  silt, 
the  conditions  for  the  formation  of  the  mud-cracks  are  fully  satis- 
fied. Here,  too,  preserval  of  the  mud-crack  record  is  readily  ac- 
complished by  the  filling  of  the  fissures  by  the  sediment  of  the  next 
flood. 

The  mud-cracked  flood  plain  deposit  would  differ  from  the  playa 
deposit  in  the  more  frequent  presence  of  carbonaceous  material,  since 
vegetation  is  an  accompaniment  of  river  courses,  but,  as  a  rule, 
absent  from  the  playa,  or  found  only  around  the  margin.  Aquatic 
animals,  too,  should  be  more  characteristic  of  the  flood-plain  than 
of  the  desert  deposit,  and  would  especially  characterize  the  old 
stream  channels  dissecting  the  flood  plain,  and  recognizable  in  the 
fossil  state  by  the  lines  of  coarser  sediment — the  filling  of  these 
channels — which  traverse  the  finer  deposits. 

The  Shore  Zone.  The  shore  zone  between  high  and  low  water 
also  may  furnish  conditions  favorable  for  the  formation  of  mud- 
cracks.  This  is  especially  the  case  where,  as  in  the  Bay  of  Fundy, 
the  tide  recedes  very  far,  and  where  large  tracts  remain  exposed 
during  the  fortnightly  interval  between  high  spring  tides.  Along 
the  margins  of  estuaries  broad  mud-flats  are  often  exposed,  and 
here  shrinkage  cracks  may  form  between  tides.  The  time  of  expo- 
sure of  all  but  the  highest  parts  of  the  shore  zone,  is,  however,  too 
short  to  allow  of  a  sufficient  hardening  of  the  mud-cracked  area 
to  enable  it  to  resist  the  softening  and  destroying  effects  of  the 
returning  tide.  Moreover,  in  modern  mud  flats  of  this  type,  or- 
ganisms exist  in  great  numbers,  so  that  we  would  expect  to  find 
mud-cracked  rocks  which  are  formed  on  the  shore  to  be  more  or 
less  fossiliferous. 

On  the  whole,  mud-cracks  are  much  more  characteristic  of  con- 
tinental deposits,  especially  of  the  playa  and  flood  plain,  than  of 


CLAY  GALLS;  CLAY  BOULDERS       711 

the  seashore.  Only  under  exceptional  conditions  can  we  expect 
the  preservation  of  extensive  mud-cracked  surfaces  of  the  sea- 
shore. Moreover,  the  formation  of  great  littoral  deposits  must 
be  accompanied  by  a  subsidence  of  the  sea-floor,  and  a  consequent 
landward  transgression  of  the  seashore  with  its  .attendant  phe- 
nomena. The  migration  of  the  shore  zone  would  thus  bring  about 
a  transference  of  the  zone  of  mud-crack  formation,  so  that  we 
could  hardly  expect  to  find  a  thick  marine  formation  with  repeated 
horizons  of  mud-cracked  layers  unless  we  assumed  that  the  subsi- 
dence was  so  gradual  a  one  that  deposition  kept  pace  with  it. 

7.  CLAY  GALLS   (THON-GALLEN).     When  the  mu.d  layers  on 
the  playa  surface  or  on  the  river  flood  plain  are  very  thin,  drying 
will  cause  them  to  curl  up  into  masses  resembling  shavings.     Such      / 
curly  mud  shavings  occur  on  river  flood  plains  exposed  to  a  hot  sun, 
and  they  may  also  under  favorable  conditions  be  formed  on  the 
seashore,  as  in  the  case  of  the  coast  of  the  Red  Sea   (Walther- 

23  '-847) ,  When  thoroughly  dry  these  shavings  may  be  blown  by 
the  wind  into  neighboring  sand  dunes  in  which  they  become  buried. 
Subsequent  softening  of  the  clay  when  the  sand  dune  is  saturated 
with  water,  as  in  the  rainy  seasons,  will  bring  about  a  compression 
of  the  clay-shaving  into  a  thin,  flat  pellet  of  clay  which  will  lie 
embedded  in  the  sand  parallel  to  the  stratification.  Such  clay  pel- 
lets, called  Thon-gallen,  or  clay  galls,  are  common  in  sandstones 
of  subaerial  origin,  especially  in  red  sandstones.  They  may/  indeed, 
be  regarded  as  practically  positive  evidence  of  a  subaerial  origin 
of  the  rock  containing  them,  though  these  rocks  may  be  seashore 
dunes  or  formed  far  inland.  . 

8.  CLAY   BOULDERS.      Clay   boulders    formed    of    plastic   clay 
rolled  about  by  the  waves  are  not  uncommon  occurrences  on  the  sea- 
shore.    They  have  been  recorded  by  Walther    (23:847)   and  by 
O.  Fraas  (10:^77)  from  the  coast  of  the  Red  Sea.    On  the  coasts 
mentioned  they  represent  the  clay  deposited  during  the  previous 
high  tide,  which  on  exposure  at  low  tide  dries  and  breaks  up  into 
fragments.     These  are  rolled  into  balls  by  the  returning  tide  and 
incorporated  in  the  later  sediment,  where  they  have  the  appearance 

of  concretions.  Examples  of  such  structures  seem  to  occur  in  the  J 
Dev9nic  calcilutytes  of  Michigan,  where  rounded  balls  of  a  darker 
color  are  included  in  lighter  bedded  deposits  of  similar  character. 
The  author  has  observed  the  formation  of  clay  boulders  on  the 
coast  of  Scotland.  Here  fragments  of  glacial  clays  broken  from 
the  cliffs  are  rolled  about  by  the  waves  and  fashioned  into  pebbles 
and  boulders  of  elongate  but  well-rounded  outline.  Where  these 
are  rolled  over  a  pebble  beach,  the  hard  pebbles  are  pressed 


712  PRINCIPLES    OF    STRATIGRAPHY 

into  the  clay  ball  which  then  assumes  the  appearance  of  a  worn 
conglomerate  fragment.  As  such  it  may  be.  embedded  in  the  suc- 
ceeding formation.  Frass  (10)  records  such  boulders  with  shell 
fragments  for  pebbles,  from  the  Jurassic  of  Spitzbergen. 

9.  RAIN  PRINTS.  Partly  dried  clay  surfaces  and  to  some  ex- 
tent those  of  other  lutaceous  deposits,  when  exposed  to  a  short, 
sharp  rain,  will  receive  the  impressions  made  by  the  striking  rain 
drops.  When  the  rain  drops  strike  obliquely  a  low  rim  around  part 
of  the  impression  shows  where  the  mud  was  displaced  more 
strongly,  and  therefore  the  side  away  from  that  from  which  the 
rain  slanted.  Thus  the  more  pronounced  marking  is  always  on  the 
obtuse  side  of  the  intersection  of  the  surface  and  the  path  of  the 
rain  drop.  A  replica  in  relief  of  this  impression  is  found  on  the 
under  side  of  the  layer  of  mud  spread  next  above.  This  feature  is 
eminently  characteristic  of  continental  mud  deposits,  its  preserva- 
tion on  the  sea  coast  being  a  matter  of  doubtful  probability.  Im- 
pressions apparently  of  this  character  have,  however,  been  re- 


FIG.  140.     Plan  of  Eolian  rip-    FIG.    141.     Diagram   showing   direction   of 
pie-marks     in     fine     sand.  currents  and  vortices  in  the  formation 

(After  Walther.)  of  ripple-marks.     (After  Darwin.) 

ported  from  the  marine  (shallow  water)  limestones  of  the  Cin- 
cinnati region.  (Perry-i8:  j^p,  Fig.  i.) 

10.  RIPPLE  MARKS.  These,  are  rhythmic  undulations  or  waves 
of  the  sand  due  either  to  the  motion  of  the  air  or  of  the  water. 
Two  types  of  ripples  are  recognized:  i.  Current  ripples,  formed 
by  the  wind  on  the  surface  of  sand  dunes,  etc.,  or  by  currents  of 
water  in  shallow  basins;  and  2.  Oscillation  ripples,  formed  by  the 
vortices  of  water  in  the  sands  at  the  bottoms  of  shallow  stationary 
water  bodies. 

"A  current  of  water  flowing  over  a  bed  of  sand  reacts  on  any 
prominence  of  the  bed.  An  eddy  or  vortex  is  created  in  the  lee  of 
the  prominence,  and  the  return  current  of  this  vortex  checks  travel- 
ing particles,  causing  a  growth  of  the  prominence  on  its  down- 
stream side.  At  the  same  time  the  upstream  side  is  eroded,  and  the 
prominence  thus  travels  downstream.  It  is  a  subaqueous  dune.  Its 
upstream  slope  is  long  and  gentle ;  its  downstream  slope  is  short  and 
steep."  ( Gilbert-i 2  :IJ7.)  The  natural  mold  of  this  type  of  ripple 


RIPPLEMARKS  713 

will  be  difficult  to  distinguish  from  the  original  ripple,  though  the 
directions  of  the  slopes  will  be  reversed.  A  careful  examination, 
however,  will  show  that,  whereas  the  surfaces  of  the  normal  cur- 
rent ripple  are  gently  convex,  those  of  the  mold  will  be  gently 
concave. 

Oscillation  ripples  are  produced  .  .  .  "by  the  to-and-fro 
motion  of  the  water,  occasioned  by  the  passage  of  wind  waves. 
During  the  passage  of  a  wave  each  particle  of  water  near  the 
surface  rises,  moves  forward,  descends,  and  moves  back,  describing 
an  orbit  which  is  approximately  circular.  The  orbital  motion  is 
communicated  downward,  with  gradually  diminishing  amplitude. 
Unless  the  water  is  deep  the  orbits  below  the  surface  are  ellipses, 
the  longer  axes  being  horizontal,  and  close  to  the  bottom  the  ellipses 
are  nearly  flat,  so  that  the  water  merely  swings  forward  and  back. 
It  is  in  this  oscillating  current,  periodically  reversed,  that  the 
sand-ripples  are  formed.  A  prominence  occasions  vortices  alternat- 
ing on  its  two  sides,  and  is  thereby  developed  in  a  systematic  way, 
with  equal  slopes  and  a  sharp  apex.  There  is  a  strong  tendency  to 
produce  the  mole  laterally  into  a  ridge,  the  space  between  ridges  is 
definitely  limited  by  the  interference  of  vortices,  and  in  time  there 
results  a  regular  pattern  of  parallel  ridges  equally  spaced."  (Gil- 
bert-12.)  In  the  center  of  the  oscillation  ripple  a  low  sharp  ridge 
is  frequently  found  which  bn  the  mold  is  represented  by  a  groove. 
(Van  Hise-2i  :  720.)  See,  further,  the  discussion  by  Darwin  (6)  of 
the  movements  and  vortices  involved  in  ripple  formation  (Fig.  141). 

The  amplitude  of  the  water  oscillations  and  their  frequency  con- 
trol the  size  of  the  resulting  ripples,  as  has  been  shown  by  experi- 
ment. The  depth  of  the  water  has  a  direct  bearing  upon  the  ampli- 
tude of  the  wave  and  therefore  upon  the  size  of  the  ripple.  No 
definite  law  has,  however,  been  worked  out  as  yet. 

According  to  Siau,  who  studied  the  ripple-marks  of  the  haven 
of  St.  Giles,  on  the  English  Channel,  their  crests  are  distant  from 
30-45  cm.  at  a  depth  of  20  meters,  while  their  troughs  are  from 
8-10  cm.  below  their  crests,  and  contain  heavier  basaltic  gravel. 
At  greater  depths  their  size  diminishes.  The  greatest  depth  at 
which  they  were  observed  was  188  meters.  (Hunt-i4.) 

In  cross-section  the  oscillation  ripple  presents  regular  concavi- 
ties divided  by  sharp  ridges,  and  a  faint  central  ridge  in  many  cases. 
This  type  is  distinguished  from  the  mold  of  the  current  ripple 
chiefly  by  the  asymmetry  of  the  concavity  of  the  latter,  one  side 
being  shorter  and  steeper  than  the  other  in  the  mold  of  the  cur- 
rent ripple.  The  central  ridge  when  present  is  likewise  a  charac- 
teristic feature.  A  mold  of  the  oscillation  ripple  would  show 


PRINCIPLES    OF    STRATIGRAPHY 


gently  rounded  or  convex  ridges  often  with  a  groove  on  top,  and 
separated  by  sharp  depressions.  This  mold  is  distinguished  from 
the  normal  current  ripple  mainly  by  its  symmetry.  In  the  desert, 
wind  ripples  of  all  dimensions  and  of  great  variety  of  form  occur. 
They  vary  in  width  from  2  'cm.  or  less  to  a  meter  or  more.  Some- 
times they  are  sharp  angled,  at  others  round.  They  generally 
occur  in  long  parallel  series,  often  branching  repeatedly,  the 
branch  running  parallel  to  the  main  stem.  (Walther-22  :  5^5  [179] .) 
(Figs.  140,  142.) 

The  width  and  height  of  the  ripple-mark  are  dependent  on  the 
size  of  the  grain  of  sand  and  the  strength  of  the  wind.  Uniform 
currents  will  produce  an  elongation  of  the  ripple  which  always 
extends  at  right  angles  to  the  direction  of  the  wind.  (Hunt-i4.) 
In  many  respects  the  arrangement  of  wind  ripples  and  of  sand 


FIG.  142.     Plan  of  Eolian  ripple-marks  in  coarse  desert  sand.     (After  Wal- 
ther.)      (Compare  with  Fig.  140.) 

dunes  in.  deserts  is  very  similar,  the  former  being  reduced  replicas 
of  the  latter. 

In  the  distribution  of  the  material  of  the  wind  ripple,  there 
appears  also  to  be  a  distinctive  character,  in  that  the  coarser  mate- 
rial is  found  on  the  crest  of  the  ripple,  instead  of  in  the  trough,  as 
in  subaqueous  ripples. 

ii.  IMPRESSIONS  OF  ANIMALS  AND  PLANTS  IN  TRANSIT.  Ani- 
mals walking  or  crawling  over  a  surface  of  mud  or  sand  commonly 
leave  characteristic  impressions.  Plants  rafted  along  by  the  wind 
or  waves,  and  medusae  floating  and  dragging  their  tentacles,  also 
make  characteristic  markings,  though  these  are  not  always  readily 
determinable.  All  such  markings  are  depressions,  and  they  will 
be  reproduced  in  relief  on  the  under  side  of  the  next  overlying 
stratum.  Occasionally  the  burrows  of  certain  animals  will  be 
marked  by  elevations  or  knobs.  These  structures  will  be  dis- 
cussed in  their  biological  relations  in  the  chapter  on  fossils,  and 
they  are  mentioned  here  only  to  complete  the  survey  of  minor 
original  features  of  sediments. 


ROUNDING  AND  SORTING  OF  SAND  GRAINS    715 

As  to  their  occurrence,  it  may  be  repeated  that  footprints  of 
terrestrial  animals  are  best  preserved  in  the  clays  of  the  desert 
playas,  and  the  flood-plains  of  rivers,  while  those  formed  on  the 
seashore  are  commonly  obliterated  again  by  the  action  of  the  re- 
turning tide  and  the  waves.  Tracks  and  burrows  of  worms,  and 
trails  of  molluscs  and  Crustacea,  on  the  other  hand,  point  more  gen- 
erally to  a  seashore  or  the  borders  of  interior  tideless  seas,  or,  again, 
more  rarely  to  river  flood-plains. 

12.  APPLICATION    OF    THESE    STRUCTURES    IN    DETERMINING 
POSITION  OF  STRATA.     The  importance  of  discriminating  between 
the  original   structure  as   here  described   and   its   reproduction  in 
reverse,  in  the  overlying  stratum,  will  be  appreciated  when  it  is 
considered  that  strata  often  stand  vertical,  and  are  even  overturned. 
The  determination  of  the  upper  and  lower  surfaces  of  the  strata 
may  be  the  only  means  for  recognizing  the  superposition  of  the 
strata  of  a  region.    In  all  cases,  the  surface  on  which  the  structure 
(ripple-mark,  impression,  etc.)   was  originally  made  is  the  upper 
surface  of  the  stratum,  while  the  surface  having  a  reverse  repro- 
duction of  the  structure    (raised   footprint,  mold  of   ripple-mark, 
etc.)  is  the  lower  surface  of  that  stratum. 

13.  ROUNDING  AND  SORTING  OF  SAND  GRAINS  AND  WEARING 
OF  PEBBLES.     This  subject  has  already  been  discussed  in  previous 
sections,  but  may  be  briefly  summarized  here.     Sand  grains  under 
o.i  mm.  in  diameter  will  not  be  rounded  by  wave  action  upon  the 
coast,   for  they  are  held  in  suspension,  and,  moreover,  capillarity 
provides  the  adjacent  grains  with  a  separating  cushion  of  water 
which  prevents  mutual  attrition.     Larger  grains  may  under  favor- 
able conditions  be  rounded  by  the  waves.     They  are  even  better 
situated  in  this  respect  in  river  beds.     The  most  efficient  agent  of 
all  in  the  rounding  of  grains  is  the  wind,  as  it  it  is  also  the  most 
efficient  sorting  agent. 

Pebbles  are  rounded  largely  by  the  action  of  running  water 
and  by  waves.  That  the  wind  is  able  to  do  work  in  this  direction 
is  shown  by  the  rounded  pebbles  of  the  Hamada  or  stony  desert, 
where  water  activity  is  absent.  It  has  been  repeatedly  asserted  that 
there  is  a  decided  difference  in  form  between  pebbles  of  river  bot- 
toms and  those  of  the  shore.  The  former  are  said  to  be  typically 
flat,  from  the  fact  that  they  are  shoved  along  on  the  bottom  of 
the  stream,  while  the  latter  are  rounded  because  they  are  rolled  about 
by  the  waves.  The  reverse  has  also  been  held.  Until  more  detailed 
observations  on  modern  shores  and  river  bottoms  are  made,  no 
such  general  criterion  can  be  accepted.  As  a  matter  of  fact,  flat 
pebbles  abound  on  many  shores  where  the  material  from  which 


7i6  PRINCIPLES    OF    STRATIGRAPHY 

they  are  derived  is  a  thin-bedded  rock  or  tends  to  split  into  thin 
layers.  Here  the  pebbles  are  shoved  up  the  beach  and  dragged 
back,  rolling  being  seldom  seen.  Pebbles  formed  from  angular 
fragments,  on  the  other  hand,  are  rolled  about  on  the  beach. 
Thus  it  appears  that  the  original  form  of  the  material  is  of  more 
significance  than  the  agent  active  in  the  rounding. 

14.  CHARACTERISTICS  OF  INCLUSIONS  IN  SAND  GRAINS.  In 
tracing  the  source  of  the  quartz  grains  in  sands  and  sandstones 
Mackie  (17)  has  advocated  the  use  of  inclusions  found  in  the 
quartz  or  their  absence.  He  divides  the  inclusions  into: 

(1)  Regular  inclusions^  of  quartz,  chlorite,  muscovite,  bio- 

tite,  rutile,  apatite,  zircon,  garnet,  magnetite,  titanifer- 
ous  iron,  etc.  Characteristic  of  the  quartz  of  schists. 

(2)  Acicular,  or  fine  needle-like  inclusions  of  doubtful  min- 

eral, capable  of  being  subdivided  according  to  arrange- 
ment of  the  needles.  Characteristic  of  granites. 

(3)  Irregular  inclusions,  mostly  fluid  lacunae  with  or  with- 

out gas  bubbles.  Characteristic  of  granites,  but  more 
readily  subject  to  disruption  by  changes  in  tempera- 
ture or  to  crushing  than  the  others,  and,  hence,  di- 
minishing in  proportion  with  the  age  of  the  forma- 
tion, and  the  repeated  reworkings  of  the  grains. 

The  absence  of  inclusions  in  quartz  suggests  vein  quartz  as  the 
source,  or  the  quartz  of  schists.  After  a  determination  of  the  in- 
clusions in  the  quartz  grains  of  the  crystallines  which  might  have 
furnished  the  sands  of  the  Rothes  Burn,  and  the  determination  of 
the  percentage  of  feldspar,  garnet,  staurolite,  mica,  hornblende, 
chlorite  and  magnetite  in  the  sands  of  this  stream,  together  with 
the  inclusions  in  the  quartz  grains,  Mackie  concludes  that  23%  of 
the  sand  was  derived  from  granite,  57%  from  schist,  and  20% 
from  diorite.  The  matrix  of  the  Lower  Old  Red  conglomerate  of 
Gollachy  Mill^  was  in  like  manner  determined  as  derived  20% 
from  granite,  77%  from  schist,  and  3%  from  diorite  and  volcanics. 
In  these  analyses  the  feldspar  was  divided  between  the  granite 
schist  and  diorite,  the  garnet,  staurolite,  mica,  chlorite  and  the 
quartz  with  regular  inclusions  and  without  inclusions  were  referred 
to  schists,  while  the  hornblende  and  magnetite  were  referred  to 
diorite.  Analyses  of  the  sand  grains  of  successive  members  of 
both  the  lower  and  upper  Old  Red  Sandstone  showed  that,  during 
the*  process  of  erosion  of  the  lands  supplying  the  material  of  this 
formation  in  northern  Scotland,  different  sand-supplying  forma- 


INCLUSIONS;    ORGANIC   REMAINS  717 

tions  were  uncovered,  the  first  or  highest  of  which  supplying  mate- 
rial for  the  oldest  beds  was  non-granitic. 

From  the  nature  of  the  inclusions  Berkey  has  been  enabled 
to  determine  that  the  quartz  grains  of  the  St.  Peter  sandstone  were 
derived  from  the  gneisses  and  granites  of  the  Canadian  Old  Land, 
and  that  the  Sylvania  sands  were  most  probably  derived  from  the 
older  St.  Peter  sands,  with  which  they  agree  in  all  respects. 

15.  ORGANIC  REMAINS.  Abundant  remains  of  marine  organ- 
isms are  generally  a  good  criterion  for  the  marine  origin  of  the 
strata  containing  them.  There  are,  however,  important  exceptions 
to  this.  Thus  the  foraminiferal  limestones  of  India  and  South 
Africa  are  formed  as  eolian  deposits  upon  dry  land,  and  often  at  a 
distance  from  the  shore,  though  the  remains  themselves  are  all 
of  marine  types.  Marine  types  may  also  be  included  in  a  terrestrial 
deposit  as  a  result  of  derivation  from  older  marine  strata  by 
weathering  or  erosion.  Again  shells  of  marine  organisms  may  be 
carried  inland  by  birds  and  other  animals  (including  man)  and 
become  embedded  in  later  deposits.  Man-made  shell  heaps  are 
generally  recognizable  by  the  presence  in  them  of  human  imple- 
ments as  well  as  evidence  of  fire,  but  shells  carried  inland  by  birds 
are  not  readily  recognizable  as  such.  The  occurrence  of  organisms 
of  marine  types  in  relict  seas  distant  from  the  coast  must  be  con- 
sidered. This  subject  will  be  more  fully  discussed  in  a  subsequent 
chapter. 

Occasional  intercalation  of  marine  layers  in  delta  formations 
otherwise  of  non-marine  origin  must  also  be  noted  here.  Such 
intercalations  have  been  used  to  prove  the  marine  origin  of  an  en- 
tire formation,  the  bulk  of  which  is  most  probably  of  terrestrial 
origin. 

Fresh  water  and  terrestrial  organisms  when  exclusively  found 
in  a  formation  indicate  a  continental  origin.  But  such  remains 
may  be  as  characteristic  of  fluviatile  as  of  lacustrine  deposits  and 
often  more  so.  Thus  the  remains  of  land  vertebrates  and  of  plants 
in  a  formation  indicate  more  commonly  river,  flood-plain,  swamp, 
or,  in  the  case  of  the  vertebrates,  steppe  deposits,  the  remains  being 
embedded  in  the  river  muds  or  covered  by  blown  sands.  Abundant 
remains  of  fresh  water  molluscs,  Crustacea,  etc.,  of  Chara  and  other 
fresh  water  plants,  indicate  a  lacustrine  or  paludal  origin  of  the 
formation  containing  them. 

Terrestrial  organisms,  especially  plants,  may  also  be  carried  out 
to  sea  and  so  become  embedded  in  marine  formations.  The  same 
thing  is  true  of  river-inhabiting  fish,  Crustacea,  and  Mollusca.  The 
extent  of  such  transportation  is  generally  determinable,  as  shown 


;i8  PRINCIPLES    OF    STRATIGRAPHY 

by  David  White  (24),  by  the  degree  of  injury  suffered  by  the 
perishable  parts,  such  as  bark,  leaves,  etc.  Seeds  and  spores  of  river 
plants,  such  as  the  water  ferns  or  rhizocarps.  may  also  be  carried 
out  to  sea  and  buried  in  normal  marine  sediments.  Their  occur- 
rence, however, 'always  suggests  a  river-borne  origin  for  the  mud 
in  which  they  are  found,  as  in  the  case  of  the  Genesee  and  Portage 
muds  of  the  Devonic  in  which  occur  the  spore  cases  of  the  water 
fern  Protosalvinia,  mingled  with  marine  organisms. 

16.  CONCRETIONS.  Concretions  are  segregations  of  mineral 
matter  which  grow  in  size  by  addition  externally,  internally  or  in- 
terstitially.  From  the  point  of  view  of  their  origin  and  relation- 
ship to  the  enclosing  rocks,  two  types  .may  be  distinguished  :  ( i ) 
those  forming  as  contemporaneous  accumulations,  afterward  buried 
by  clastic  or  other  strata,  and  (2)  those  forming  within  the  strata 
after  their  deposition.  This  second  group  clearly  belongs  to  the 
secondary  structures  of  rocks. 

Concretions  of  calcium  carbonate,  of  barite,  of  manganese,  and 
concretions  composed  of  fragmental  material  cemented  by  phos- 
phate of  lime  are  among  the  first  group,  forming  at  the  present 
time.  The  phosphate  concretions  are  most  characteristic  of  the 
shore  zone,  while  the  manganese  concretions  are  common  in  the 
deep  sea.  The  latter  (Walther-23  :  701)  are  most  abundant  in  the 
Pacific  between  767  and  8,183  meters,  and  in  the  Indian  and 
Antarctic  Oceans  between  2,926  and  4,754  meters  depth.  In  the 
Atlantic  Ocean  they  are  found  between  767  and  5,211  meters  depth, 
chiefly  in  the  neighborhood  of  volcanic  islands. 

These  concretions  commonly  constitute  the  uppermost  layer  of 
the  lithosphere  in  the  deep  sea,  and  they  are  gradually  buried  by 
the  accumulation  of  fine  muds.  Not  infrequently  they  constitute 
the  foundation  on  which  corals  or  other  sedentary  benthonic  organ- 
isms gain  a  foothold,  and  such  a  concretion  in  moderately  deep 
water  may  serve  as  the  nucleus  about  which  a  coral  reef  is  built  up. 
Chemically  formed  oolites  and  pisolites  should  be  mentioned  under 
contemporaneous  concretions.  These  have  been  fully  discussed 
in  a  preceding  chapter. 

The  secondarily  formed  concretions,  or  those  growing  within 
the  strata,  and  therefore  of  later  age,  are  represented  by  clay-stone 
concretions,  so  characteristic  of  shale  and  clay  beds,  and  readily 
recognized  as  belonging  to  this  secondary  type  by  the  fact  that  the 
stratification  lines  are  seen  to  pass  through  them.  Large  examples 
of  these  are  found  in  Devonic  and  later  lutaceous  deposits.  They 
have  not  infrequently  grown  about  fossils.  Many  of  these  also 
show  the  septarium  structure  as  described  below.  The  Losspiippchen 


CONCRETIONS  719 

and  "Lossmannchen,"  of  the  German  loess,  the  "Marlekor"  and 
"Nakkebrod"  of  similar  Swedish  deposits,  the  "Kankar"  of  India, 
and  the  clay  iron  stones  of  the  British  Carbonic  shales  are  other 
examples  of  concretions  of  this  type. 

According  to   their  method  of  growth   concretions   have  been 
divided  by  Todd  into  four  types  (20)  : 

1.  Accretions. 

2.  Intercretions. 

3.  Excretions. 

4.  Incretions. 

Accretions  grow  regularly  and  steadily   from  the  center  out- 
ward by  successive  additions  of  materials.     This  type'  of  concre- 


FIG.   143.     Concretion   (accretion)   of  clay  stone,  Connecticut  Valley.     (After 
Gratacap.) 

tion  will  be  solid  from  the  center  and  if  of  subsequent  growth  will 
include  or  enmesh  particles  of  the  rock  in  which  it  forms  without 
any  considerable  disturbance  of  it.  The  stratified  structure  may 
also  be  preserved  in  accretions,  unless  by  crystallization  a  radiate 
structure  is  produced.  Examples  of  this  type  are  the  remarkable 
concretions  of  the  postglacial  clays  of  the  Connecticut  Valley. 
(Sheldon-i9.)  (Fig.  143.) 

The  radial  structure  due  to  crystallization  is  well  developed  in 
the  large  spherical  concretions  of  the  Devonic  black  shales  of  Kettle 
Point,*  Ontario,  and  of  Michigan.  From  their  fibrous  structure 
they  are  not  infrequently  mistaken  for  petrified  wood.  (Daly-5.) 

Intercretions  grow  by  accretion  on  the  exterior  and  by  inter- 
stitial addition,  causing  a  circumferential  expansion  and  resultant 
cracking  and  wedging  apart  of  the  interior  of  the  concretion.  The 
cracks  widen  toward  the  center  and  are  commonly  filled  by  mineral 

*  So  named  from  the  resemblance  of  partly  exposed  concretions  to  inverted 
kettles. 


720  PRINCIPLES    OF    STRATIGRAPHY 

matter,  chiefly  calcite,  the  accumulation  of  which  helps  to  widen 
and  extend  these  internal  fissures.  Concretions  of  this  type  are 
familiarly  known  as  septaria.  from  the  fact  that  when  they  have 
been  worn  on  the  surface  the  veins  sometimes  weather  in  relief, 
and  thus  produce  a  septate  structure.  Often,  however,  the  veins  are 
depressed.  These  concretions  are  sometimes  thought  to  be  petri- 
fied turtles,  and  in  many  localities  are  known  by  the  name  of 
"turtle  stones."  They  are  abundant  in  the  Devonic  shales  of 
eastern  North  America  and  in  the  Cretacic  beds  of  the  interior, 
while  the  Jurassic  of  western  Europe  is  famous  for  its  remarkably 
beautiful*  examples. 

Excretions  are  centripetal  concretions  "consolidation  progress- 
ing inward  from  the  exterior."  (Dana-Mawwa/,  4th  ed. — p#.) 
They  are  represented  by  nodular  shells  of  sand  cemented  by  iron 
oxide,  and  generally  filled  by  more  or  less  unconsolidated  sand  or 
contain  other  shells  of  cemented  sand.  Todd  holds  that  normal  ac- 
cretions or  intercretions  of  ferrous  carbonate,  on  coming  in  contact 
with  waters  charged  with  carbon  dioxide  and  oxygen,  will  begin  to 
dissolve  and  a  shell  of  ferric  -hydroxide  will  form  on  its  surface  by 
precipitation.  The  iron  carbonate  of  the  portion  of  the  concretion 
within  this  shell  will  similarly  be  dissolved  and  reprecipitated  as 
ferric  hydrate,  a  second  shell  thus  being  added  on  the  interior  of  the 
first.  The  impurities  of  sand  or  clay  in  the  original  concretion  re- 
main behind,  in  a  loose  condition.  Thus  while  the  actual  thickening 
of  the  shell  is  on  the  inside,  and  the  growth,  therefore,  from  without 
inward,  the  molecular  movement  of  the  iron  salts  is  froim  within 
outward,  i.  e.,  from  the  core  of  the  original  concretion  to  the  inner 
wall  of  the  shell.  When  the  process  is  completed  a  loose  mass  of 
sand  or  other  impurities  alone  remains  behind,  or,  if  the  original  con- 
cretion was  free  from  impurities  or  nearly  so,  the  resultant  excre- 
tion may  be  hollow.  Excretions  formed  within  ferruginous  sand- 
stones are  of  ten 'the  cause  of  puzzling  hollow  cavities. 

Incretions.  These  are  cylindrical  concretions  with  a  hollow 
core.  Todd  infers  that  these  originate  where  the  walls  of  a  cavity, 
like  the  cylindrical  tube  left  by  a  decayed  root  in  the  sand  or  clay, 
serve  as  the  nucleus  for  deposition.  The  iron  is  drawn  from  the 
surrounding  material  and  moves  inward  to  the  center,  where  it 
is  added  to  the  central  cylinder,  which  grows  in  thickness  outward 
by  the  addition  of  successive  shells  on  the  exterior,  until  the  sur- 
rounding matrix  is  depleted. 

Minute  concretions  of  this  type  are  common  in  the  loess.  They 
consist  of  carbonate  of  lime,  and  resemble  clay  pipe  stems  in  size 
and  form. 


SECRETIONS  721 

17.  SECRETIONS.  Secretions  are  deposits  formed  on  the  walls 
of  cavities  in  rocks,  the  first  layer  being  the  outer  one  of  the  secre- 
tion. A  constant  supply  of  material  may  bring  about  the  filling 
of  the  cavity,  as  in  veins  and  agate  geodes,  while  the  cutting  off  of 
the  supply  results  in  the  production  of  hollow  geodes,  lined  with 
crystals. 

All  secretions  are  secondary  rock  structures,  and  they  are  men- 
tioned in  this  chapter  merely  for  convenience  in  comparison  with 
concretions.  Of  the  latter,  incretions  and  excretions  are  secondary 
structures,  and  the  same  is  true  largely  if  not  wholly  of  intercre- 
tions.  Accretions  are,  however,  extensively  represented  by  con- 
temporary concretions,  though  many  kinds  of  true  accretions  are 
also  formed  secondarily  in  strata  of  various  kinds. 


BIBLIOGRAPHY    XVII. 

1.  BARRELL,  JOSEPH.     1906.     Relative  Geological  Importance  of  Con- 

tinental,  Littoral  and  Marine  Sedimentation,  Part  III.  Journal  of 
Geology,  Vol.  XIV,  pp.  524-568. 

2.  BERKEY,  CHARLES  P.     1906.     Paleogeography  of  Saint  Peter  Time. 

Geological  Society  of  America,  Bulletin,  Vol.  XVII,  pp.  229-250. 

3.  BRANNER,    JOHN    C.     1901.     Origin    of    Ripple    Marks.     Journal    of 

Geology,  Vol.  IX,  pp.  535~536- 

4.  CANDOLLE,    CASIMIR   DE.       1883.      Rides  formus  a  la  surface  du 

sable  depose"  au  fond  de  1'eau  et  autres  phenomenes  analogues.  Archives 
des  Sciences  Physiques  et  Naturelle,  Geneve.  No.  3,  Tome  IX,  pp. 
241-278. 

5.  DALY,  REGINALD  A.     1900.     The  Calcareous  Concretions  of  Kettle 

Point,  Lambton  County,  Ontario.  Journal  of  Geology,  Vol.  VIII,  pp. 
135-150. 

6.  DARWIN,  GEORGE  H.      1883.      On  the  Formation  of  Ripple  Mark/ 

in  Sand.  Proceedings  of  the  Royal  Society  of  London,  Vol.  XXXVI,  pp. 
18-43. 

7.  FAIRCHILD,  HERMAN  L.      1901.      Beach    Structure   in   the   Medina/ 

Sandstone.     American  Geologist,  Vol.  XXVIII,  pp.  9-13,  pis.  II-IV. 

8.  FLEMING,  J.  A.     1902.     Waves  and  Ripples  in  Water,  Air  and  ^Ether. 

London.  ' 

9.  FORCHHAMMER,   G.     1841.     Geognostische   Studien,  am   Meeresufer. 

Neues  Jahrbuch  fur  Mineralogie,  etc.,  pp.  1-38,  t.  III. 

9a.  FOREL,  F.  A.  1883.  Les  Rides  de  Fond  e"tudius  dans  le  lac  Le"man. 
Archives  des  Sciences  Physiques  et  Naturelles,  Geneve,  (3.)  Tome  X, 
pp.  39-72. 

10.  FRAAS,  O.     1872.     Heuglin's  geologische  Untersuchungen  in  Ost  Spitz- 

bergen.  Petermanns  geographische  Mittheilungen,  Bd.  XVIII,  pp.  275- 
277. 

11.  GILBERT,  G.  K.     1877.     Report  on  the  Geology  of  the  Henry  Mountains. 

United  States  Geographical  and  Geological  Surveys  of  the  Rocky  Moun- 
tain Region. 


722'  PRINCIPLES    OF    STRATIGRAPHY 

12.  GILBERT,    G.  K.     1899.     Ripple   Marks   and   Cross-bedding.     Bulletin, 

of  the  Geological  Society  of  America,  Vol.  X,  pp.    135-139,  pi.  XIII 
5  %s. 

13.  GRABAU,    AMADEUS   W.     1907.     Types   of   Cross-bedding  and  Their 

Stratigraphic  Significance.  Science,  N.  S.~,  Vol.  XXV,  pp.  295-296. 

J  14.     HUNT,  A.  R.     1882.     On  the  Formation  of  Ripple  Mark.        Proceedings 

of  the  Royal  Society  of  London,  Vol.  XXXIV,  pp.  1-18. 

15.  HUNTINGTON,  ELLSWORTH.  1907.  Some  Characteristics  of  the 
Glacial  Period  in  Non-Glaciated  Regions.  Geological  Society  of  America, 
Bulletin,  Vol.  XVIII,  pp.  35i~388,  9  pis.,  16  figs. 

]  16.  JOHNSON,  DOUGLAS  W.  1910.  Beach  Cusps.  Geological  Society  of 
America  Bulletin,  Vol.  XXI,  pp.  599-624  (with  review  of  previous  litera- 
ture on  Beach  Cusps). 

17.  MACKIE,  WILLIAM.      189^.     The  Sands  and  Sandstones  -of  Eastern 

Moray.     Edinburgh  Geological  Society  Proceedings,  Vol.  VII,  pp.  148- 
172. 

18.  PERRY,  NELSON  W.     1889.     The  Cincinnati  Rocks.     What  was  their 

Geological  History?    American  Geologist,  Vol.  IV,  pp.  326-336,  2  pis. 
xj  19.     SHELDON,    J.    M.    ARMS.     1900.     Concretions    from    the    Champlain 

Clays  of  the  Connecticut  Valley.     Boston,  1900. 
x\  20.     TODD,  J.  E.     1903.     Concretions  and  Their  Geological  Effects.    Bulletin 

of  the  Geological  Society  of  America,  Vol.  XIV,  pp.  353-360. 

21.  VAN  HISE,  CHARLES  R.     1896.     Principles  of  North  American  Pre- 

Cambrian  Geology.   U.  S.  Geological  Survey,'  i6th  Annual  Report,  Pt.  I, 
pp.  581-872,  pis.  CVIII-CXVII. 

22.  WALTHER,  JOHANNES.     1891.     Die  Denudation  in  der  Wuste.     Ab- 

handlungen  der  koniglich-kaiserlichen  Gesellschaft  der  Wissenschaften. 
Mathematische-Physische  Klasse,  Bd.  XVI,  pp.  345-570  (1-225). 

23.  WALTHER,  J.      1894.      Die  Auflagerungsflachen  und  die  Entstehung  der 

Schichtung,  pp.  620-641,  and  other  chapters  in  Einleitung  in  die  Geologic 

Jals  Historische  Wissenschaft,  3  Teil.     Lithogenesjs  der  Gegenwart. 
24.     WHITE,  DAVID.     1911.     Value  of  Floral  Evidence  in  Marine  Strata  as 
•    Indicative  of  Nearness  to  Shores.     Geological  Society  of  America  Bulle- 
tin, Vol.  XXII,  pp.  221-227. 


CHAPTER   XVIII. 
OVERLAP  RELATIONS  OF  SEDIMENTARY  FORMATIONS. 

Overlap,  or  the  extension  of  one  formation  beyond  the  other, 
is  a  structural  feature  of  the  greatest  significance  in  stratigraphy. 
Two  kinds  of  overlap  may  be  recognized,  the  irregular  and  the 
regular  or  progressive.  The  irregular  overlap  of  strata,  resulting 
from  sudden  changes  of  physical  conditions,  is  more  of  the  nature 
of  an  accidental  feature,  and  belongs  rather  to  the  general  subject 
of  unconformity  of  formations.  While  its  recognition  is  of  great 
importance  in  establishing  the  progress  of  events,  it  has  not  the 
stratigraphic  significance  of  the  other  type. 

PROGRESSIVE    OVERLAP. 

Under  this  term  we  include  the  regular  overlapping  of  suc- 
cessive formations  due  either  to  a  normal  transgressive  movement 
or  to  a  regular  regressive  movement.  According  as  we  deal  with 
marine  or  non-marine  sediments  we  have  (Grabau-3)  :  (A)  The 
marine  progressive  or  (B)  the  non-marine  progressive  overlaps. 
The  former  are  the  more  varied  in  type  and  will  be  discussed  first. 

A.  MARINE  PROGRESSIVE  OVERLAP.  We  may  dis- 
tinguish two  types  of  marine  progressive  overlap:  i.  Normal 
transgressive  overlap,  due  to  a  progressively  encroaching  sea ;  and, 
2.  Regressive  or  retreatal  overlap,  due  to  a  progressively  retreating 
sea.  Generally  a  regressive  movement  is  both  preceded  and  fol- 
lowed by  a  transgressive  movement,  so  that  as  a  result  of  this 
compound  progressive  overlap  a  complex  type  of  structure  comes 
into  existence. 

The  progress  of  deposition  of  the  clastic  sediments  on  a  normal 
shelving  seashore  is  controlled  by  two  factors :  namely,  the  rate  of 
supply  of  material,  and  the  rate  and  direction  of  change  in  the  rela- 
tive position  of  sea-bottom  and  sea-level.  According  to  the  varia- 
tion of  one  or  both,  sedimentation  will  vary. 

723 


724  PRINCIPLES    OF    STRATIGRAPHY 

Three  relations  of  land  and  sea  may  be  recognized : 

1.  Subsiding  land  block  or  rising  sea-level. 

2.  Stationary  sea-level. 

3.  Rising  land  block  or  falling  sea-level. 

Each  of  these  conditions  is  further  complicated  by  variation  in 
the  rate  of  subsidence,  or  elevation,  and  the  rate  of  supply  of  detri- 
tal  material.  In  general,  rising  sea-level  produces  transgressive 
movements,  except  where  the  supply  of  detritus  is  excessive,  when 
stationary  or  regressive  movements  are  produced.  Stationary  and 
falling  sea-level  produce  regressive  movements. 


I.     RISING  SEA-LEVEL  OR  POSITIVE  DIASTROPHIC  MOVEMENT. 

A  subsiding  land  block  or  rising  sea-level  may  be  either  of  local 
or  of  world-wide  effect.  Its  cause  may  be  diastrophic  movements,  or 
the  gentle  displacement  of  the  water  by  the  accumulation  of  sedi- 
ment on  the  ocean  floor.  Such  rising  of  the  sea-level  produces  a  con- 
tinuous transgression  of  the  sea  upon  the  land,  i.  e.,  a  landward  mi- 
gration of  the  shore-line.  The  rate  of  migration,  other  things  being 
equal,  varies  inversely  as  the  steepness  of  the  slope  of  the  coast. 
Thus  a  slight  depression  of  a  very  gentle  shore  will  cause  a  great 
transgression  of  the  sea,  while  even  a  considerable  depression  of  a 
steep  or  vertical  coast  may  produce  little  or  no  transgression.  In  the 
following  discussions,  the  slope  of  the  land  surface  affected  by  the 
transgression  will  be  considered  as  a  gentle  one,  such  as  is  pro- 
duced by  a  period  of  prolonged  erosion  of  an  old  land  surface. 

Wilson  (9:776*;  Rutot-7)  has  tabulated  the  possible  relationship 
between  the  rate  of  depression  of  the  land  (rise  of  the  sea-level) 
and  the  rate  of  supply  of  detritus,  as  follows : 

Rate  of  /-_.->  Rate  of 

Depression          Uniform  *r~ j^f -7^  Uniform        supply  of 

detritus 


Variable  ^ £ ^Variable 


The  simplest  conditions  are  those  in  which  the  rate  of  depression 
and  the  rate  of  supply  are  both  uniform.  These  alone  will  be  con- 
sidered; the  variable  conditions  of  either  one,  or  of  both  factors, 
will  produce  corresponding  variations  of  the  norm  to  an  almost 
unlimited  degree. 


TRANSGRESSIVE    OVERLAP  725 

With  uniform  rates  of  both  subsidence  and  supply,  three  cases 
may  be  considered : 

a.  Rate   of   depression   is   equal   to   the   rate   of   supply   of 

detritus. 

b.  Rate  of  depression  exceeds  rate  of  supply. 

c.  Rate  of  depression  is  exceeded  by  rate  of  supply. 

The  first  case  would  result  in  the  production  of  relatively  stationary 
conditions,  if  the  shore-line  were  bounded  by  a  vertical  face,  when 
a  uniform  regular  amount  of  detritus  equaling  the  amount  of  sub- 
sidence would  produce  a  constant  depth  of  water.  With  a  shelving 
shore,  on  the  other  hand,  a  uniform  regular  transgressive  move- 
ment would  occur,  with  a  regular  and  uniform  change  in  the  char- 
acter of  the  deposit  at  any  given  point.  The  second  case  will  pro- 
duce a  rapid  transgressional  movement  with  a  less  normal  suc- 
cession of  formations,  while  the  third  will  produce  either  stationary 
or  retreating  coast-line,  coupled  with  an  increasing  amount  of 
subaerial  deposition. 

i.     Transgressive  Movements. 

a.  Rate  of  Depression  Equals  Rate  of  Supply.  Under  these 
conditions  a  uniform  and  progressive  overlapping  of  each  later 
layer  over  all  the  preceding  ones  takes  place.  Each  layer  has  a 
rudaceous  or  coarsely  arenaceous  texture  at  the  shore,  and  grades 
seaward  into  finer  arenaceous  and  ultimately  lutaceous  material. 
If  the  shore  is  composed  of  old  crystalline  rocks,  the  rudytes  and 
arenyte,s  resulting  from  their  destruction  will  be  largely , siliceous, 
while  the  lutytes  will  be  argillaceous  and  more  or  less  micaceous. 
The  coarse  shoreward  ends  of  the  beds,  when  viewed  in  their 
ensemble,  will  appear  as  a  single  coarse  bed  resting  upon  the  old 
land.  From  the  consideration  of  its  origin,  however,  it  will  be 
seen  that  no  two  portions  of  the  bed  along  a  line  transverse  to 
the  seashore  will  be  of  the  same  age,  each  seaward  portion  will 
be  younger  than  that  lying  next  to  it  nearer  the  land.  Thus  the 
formation  line,  limiting  the  basal  conglomerate  or  sandstone,  will 
run  diagonally  upward  through  the  planes  of  synchronous  deposi- 
tion. The  basal  bed  is  not  generally  a  conglomerate,  for  where 
the  sea  transgresses  upon  an  old  land  which  has  long  been  subject 
to  subaerial  disintegration  a  basal  sandstone  will  be  produced,  since 
there  is  not  coarse  material  enough  to  form  pebbles.  When  de- 
composition has  gone  on  for  a  long  time  prior  to  the  transgression 
of  the  sea,  and  when  the  decomposed  material  is  subjected  to  a 


726  PRINCIPLES    OF    STRATIGRAPHY 

thorough  sorting  by  the  encroaching  waters,  a  nearly  pure  -silicar- 
enyte  may  come  to  rest  directly  upon  the  eroded  surface  of  the 
crystalline  old  land.  This  is  finely  shown  in  the  basal  Palaeozoic 
contact  in  portions  of  the  Front  Range  of  the  Rocky  Mountains, 
where  a  nearly  pure  quartz  sandstone  rests  on  an  almost  perfectly 
even  erosion  surface  of  granite.  (Crosby-2.)  Where  atmospheric 
agencies  have  been  sufficiently  active  to  disintegrate  a  granite 
surface,  without,  however,  reducing  the  feldspar  to  clay,  the  basal 
sandstone  will  be  a  feldspathic  arenyte  or  arkose.  Again  examples 
are  known  where  decomposition  has  affected  the  underlying  crystal- 
line old  land  to  a  considerable  extent,  but  where  little  sorting  of 
material  was  accomplished  by  the  transgressing  sea,  so  that  the 
basal  bed  is  a  highly  argillaceous  arenyte.  The  contact  of  this  with 
the  underlying  crystalline  basement  rock  will  in  consequence  not 
be  a  sharp  one,  the  crystalline  rock  grading  through  a  decomposed 
zone  into  the  overlying  sandstone.  An  example  of  this  indefinite 
type  of  contact  is  seen  on  Presque  Isle  near  Marquette,  Michigan, 
where  the  Lake  Superior  sandstone  passes  downward  into  a  rock 
produced  by  the  consolidation  of  the  undisturbed  disintegrated  sur- 
face of  the  basal  peridotite. 

A  consideration  of  the  progressive  landward  migration  of  the 
coarser  deposits  under  uniform  conditions  will  lead  to  the  recogni- 
tion that  the  changes  in  any  given  bed,  from  the  shore  seaward, 
will  be  exactly  duplicated  by  the  changes  in  a  given  vertical  sec- 
tion from  the  base  upward.*  For  it  will  be  seen -that  the  coarse 
bed  deposited  directly  upon  the  old  sea-floor  of  crystalline  rock  is 
succeeded  upward  by  a  somewhat  finer  bed,  since  the  zone  of  dep- 
osition of  the  coarse  material  has,  by  the  continuous  subsidence, 
migrated  further  landward.  Thus,  as  shown  in  the  annexed  figure 
(Fig.  144),  the  lowest  coarse  deposits  of  bed  (a)  which  form  the 
shore  zone  of  that  bed  are  succeeded  vertically  by  the  finer  deposits 
of  bed  (b)  made  at  a  somewhat  greater  distance  from  the  new 
shore.  At  this  new  shore  (of  bed  b)  coarse  deposits  are  accumu- 
lating, but  they  are  beyond  the  belt'of  the  former  deposition  of 
coarse  material.  Again  a"n  advance  of  the  shore  to  c  transfers 
the  shore  belt  of  coarse  (rudaceous)  deposition  in  the  same  direc- 
tion and  by  the  same  amount.  Consequently  the  belt  of  arenaceous 
deposits  of  bed  c  is  likewise  transferred  shoreward  and  comes  to 

*  The  variation  in  texture  of  deposits  due  to  storms  and  the  corresponding 
change  in  the  power  of  waves  and  currents  discussed  in  a  preceding  chapter, 
are  here  left  out  of  consideration,  since  they  will  at  best  produce  only  minor 
variations  in  the  strata.  The  present  discussion  deals  with  formations  on  a  large 
scale. 


TRANSGRESSIVE   OVERLAP 


727 


rest  on  the  belt  of  rudaceous  deposits  of  bed  b,  just  as  the  arenace- 
ous deposits  of  that  bed  come  to  rest  on  the  rudaceous  deposits  of 
bed  a.  In  like  manner  the  lutaceous  deposits  of  bed  c  come  to 
rest  on  the  arenaceous  deposits  of  bed  b,  just  as  the  lutaceous 
deposits  of  bed  b  come  to  rest  on  the  arenaceous  belt  of  bed  a. 
Two  sections,  then,  made  at  I  and  II,  will  show  precisely  the  same 
succession  in  coarseness  and  kind  of  material  from  the  bottom  up, 
the  only  difference  being  that  in  section  II  the  lutaceous  bed  is  much 
thicker  than  in  section  I.  Erosion,  however,  may  remove  so  much 
of  the  lutaceous  beds  of  section  II  as  to  equalize  the  amount  in 
the  two  sections.  It  would,  of  course,  be  incorrect  to  consider  each 
lithic  unit  in  section  I  to  be  of  the  same  age  as  the  corresponding 
lithic  unit  in  section  II,  for,  although  there  is  a  similar  lithic  suc- 
cession, bed  a,  and  the  lower  portion  of  bed  b  are  unrepresented  in 


Section  I.  Section  II. 

FIG.  144.  Diagram  showing  regular  marine  progressive  overlap  on  an  old 
land  surface.  A  basal  sandstone  occurs  everywhere,  this  grading 
upward  and  seaward  into  lutaceous  deposits.  At  section  I  the 
series  comprises  beds  b  and  c  only,  but  at  section  II  beds  a-c  are 
present. 

section  I.  In  general,  it  is  safe  to  assume  that  in  a  case  of  this 
kind,  where  continuous  transgression  on  a  uniformly  shelving  shore 
has  taken  place,  the  basal  bed  of  the  section  farther  up  the  old  shore 
is  of  later  age  than  the  corresponding  lithic  bed  of  the  section 
farther  seaward.  There  are  many  cases  where  relationships  of  this 
type  must  be  considered  in  the  correlation  of  strata. 

We  have  so  far  considered  only,  siliceous  detrital  material  de- 
rived from  an  old  land  composed  of  crystalline  or  other  siliceous 
rocks.  We  must  now  consider,  in  addition  to  these,  the  organic 
rocks  and  their  clastic  derivations,  which  play  so  important  a  role 
in  the  sedimentary  series  accumulating  on  the  sea  bottom.  As 
noted  in  an  earlier  chapter,  purely  biogenic  stratified  deposits  are 
formed  by  the  accumulation  of  the  various  organic  oozes  on  the 
sea-floor,  such  as  foramini feral,  radiolarian,  diatomaceous  or  ptero- 
podan.  Where  clastic  sediments  are  accumulating  very  slowly, 
as  at  a  distance  from  shore,  these  organic  oozes  may  constitute 
an  important  part,  if  not  most,  of  the  sediment.  In  such  cases,  the 
ooze  being  a  calcareous  one,  the  clay  and  other  lutaceous  beds 


728 


PRINCIPLES    OF    STRATIGRAPHY 


forming  in  quieter  water  will  shade  off  into  calcareous  sediments, 
and  may  even  be  entirely  replaced  by  limestones  of  this  type. 
Where  coral  reefs  or  shell  heaps  are  forming  off  shore,  the  clastic 
derivations  of  these  will  become  commingled  with,  and  shade  off 
into,  the  terrigenous  sediments  near  shore.  As  explained  in 
Chapter  X,  the  coarsest  fragments  will  remain  near  the  reef,  the 
calcarenytes  coming  next,  and  shading  off  into  the  finest  calcilutytes. 
These  calcilutytes  may  be  gradually  replaced  shoreward  by  siliceous 
or  argillaceous  lutytes,  or  they  or  the  calcarenytes  may  grade  di- 
rectly into  the  silicarenytes.  Where  this  latter  occurs,  we  have  a 
seaward  change  from  pure  quartz  sand  (silicarenyte),  through  cal- 
ciferous  sandstone  (calcareous  silicarenyte)  and  siliceous  calca- 
renytes to  pure  calcarenytes.  This  change  is  probably  more 
often  observed  in  the  Palaeozoic  series  than  the  change  from  siliceous 
to  argillaceous  sediments.  (Fig.  145.) 


FIG.  145.  Diagram  showing  regular  marine  progressive  overlap;  a  basal 
sandstone  is  present,  but  this  grades  upward  and  seaward  into 
calcareous  deposits.  The  differences  between  sections  A  and  C 
are  readily  seen. 


Older  examples.  The  type  of  overlap  here  described  seems  to 
have  been  by  far  the  most  general  as  recorded  in  both  Palaeozoic 
and  Mesozoic  deposits.  An  illustration  is  seen  in  the  basal  Ordo- 
vicic  sandstone  of  Ontario,  which  on  Lake  Huron  lies  at  the  base 
of  the  Chazy  series,  but  farther  northeast  is  basal  Trenton.  The 
basal  Cambric  sandstone  of  Sweden  also  varies  in  age  from  Lower 
to  Upper  Cambric,  though  there  is  probably  a  series  of  unre- 
corded intervals  during  which  retreat  and  erosion  took  place  with- 
out the  deposition  of  a  basal  sandstone  by  the  readvancing  sea. 
From  the  evidence  of  the  dreikanter  and  other  structural  features 
it  is  known  that  this  basal  bed  represents  an  old  residual  sandy 
covering  of  terrestrial  origin,  subsequently  encroached  upon  by  the 
sea.  It  is  not  improbable  that  wherever  basal  sandstones  occur, 
extending  upward  through  such  a  long  series,  as  the  entire  Cam- 
bric in  which  there  are,  moreover,  stratigraphic  breaks,  these  sand- 


EXAMPLES   OF  TRANSGRESSIVE   OVERLAP      729 

stones  are  older  continental  deposits  slightly  reworked  by  an  ad- 
vancing sea.  This  appears  also  to  be  the  case  in  the  Cambric  of 
North  America.  The  basal  Cambric  sandstones  and  conglomerates 
of  the  southern  Appalachian  region  underlie  the  Olenellus-bearing 
shales  and  limestones,  while  those  of  the  Oklahoma  and  Ozark 
regions  underlie  beds  generally  referred  to  the  Middle  Cambric. 
Finally,  in  the  upper  Mississippi  Valley  the  St.  Croix  sandstone 
series  actually  contains  in  its  upper  portion  the  Cambro-Ordovicic 
transition  fauna.  In  many  cases  this  northern  "Potsdam"  sand- 
stone shows  evidence  of  continental  origin  in  pre-ma"rine  time  by 
the  occurrence  of  well-marked  torrential  cross-bedding  in  parts 
which  apparently  have  not  been  reworked.  In  the  North  American 
Cambric  there  are  numerous  distinct  breaks,  the  magnitude  of 
which  is  not  yet  fully  ascertained,  except  that  it  is  now  generally 
recognized  that  above  the  Middle  Cambric  there  is  a  hiatus  corre- 
sponding to  nearly  the  whole  of  the  Upper  Cambric  of  the  Atlantic 
coast.  These  breaks  are,  as  a  rule,  not  marked  by  retreatal  inter- 
calated sandstones.  Further  examples  of  overlap  involving  large 
portions  of  a  system  are  shown  in  the  North  American  Palaeozoic 
by  the  entire  absence  of  the  Lower  Cambric  at  St.  John,  New 
Brunswick,  where  the  basal  marine  elastics  belong  to  the  Middle 
Cambric,  while  only  30  miles  northeastward,  at  Hanford  Brook, 
the  Lower  Cambric  (Etcheminian)  has  a  thickness  of  1,200  feet. 
In  Cape  Breton  this  thickness  measures  several  thousand  feet.  The 
well-known  fact  that  the  Cambric  of  Bohemia  begins  with  the 
Paradoxides  beds  of  Middle  Cambric  age,  while  Lower  Cambric 
beds  occur  in  western  Europe,  shows  a  pronounced  eastward  trans- 
gression of  the  Cambric  sea  in  Europe  with  corresponding  overlap 
of  formations. 

The  'basal  Mesozoic  sandstone  of  the  Texas  and  Mexico  re- 
gions furnishes  another  typical  example  of  a  rising  basal  bed  in  a 
transgressive  series.  In  central  Mexico  this  basal  .sandstone  lies 
beneath  Upper  Jurassic  limestones ;  on  the  Tropic  of  Cancer  it 
has  risen  into  the  base  of  the  Comanchic;  on  the  Texas-Oklahoma 
line  it  has  risen  through  the  Lower  Comanchic  (Trinity)  and  lies 
at  the  base  of  the  Fredericksburg  or  Middle  Comanchic;  and, 
finally,  in  central  Kansas  it  has  passed  up  to  near  the  base  of  the 
Upper  Comanchic  or  Washita  series.  There  are,  however,  one  pro- 
nounced (Paluxy)  and  several  smaller  sandstone  members  inter- 
calated in  the  limestone  series,  and  these  mark  either  shoaling  or 
an  actual  emergence  of  the  sea-bottom. 

In  this  case,  as  in  the  Cambric,  the  basal  sands  are  most  prob- 
ably of  continental  origin  reworked  by  the  transgressing  Coman- 


730 


PRINCIPLES    OF    STRATIGRAPHY 


chic  sea.  These  basal  sands  indicate  by  their  purity  a  distant  source 
and  long  transportation,  and  the  time  interval  during  the  Triassic 
and  early  Jurassic  periods  was  ample  to  make  possible  an  extended 
accumulation  of  widespread  river  and  eolian  sands  derived  in  large 
part  from  the  crystallines  of  the  Canadian  and  western  uplands, 
added  to  no  doubt  by  contributions  from  uncovered  Palaeozoic  and 
older  sediments.  A  striking  case  of  change  in  lithic  character  with 
progress  of  transgression  is  seen  in  the  Cretacic  series  of  south- 
east England  and  in  that  of  northeast  Ireland  and  the  west  of 
Scotland  (Mull  and  Morvern).  (Fig.  146.)  In  both  cases  the  series 
begins  with  basal  conglomerates,  followed  by  sands,  clays,  and 


FIG.  146.  Diagram  showing  overlap  and  change  in  lithic  character  of  the 
Cretacic  formations  of  England  and  Ireland,  from  southeast  to 
northwest. 

greensands.  This  is  followed  by  (2)  Glauconite  sands  and  marls, 
then  by  (3)  marls  and  Greensand  chalk,  passing  into  glauconitic 
and  argillaceous  chalk,  and,  finally,  by  (4)  pure  white  chalk.  In 
England  the  basal  series  (i)  rests  on  the  Weald  clays,  and  is  of 
Aptien  age,  while  in  Ireland  it  rests  on  Lias  and  is  of  Cenomanien 
age.  In  Scotland  it  also  is  of  Cenomanien  age.  The  next  lithic 
series  (No.  2)  is  of  Albien  (Gault)  age  in  England,  but  of  Turonien 
age  in  Ireland.  The  succeeding  marls  and  Greensand  chalk  (No.  3) 
are  of  Cenomanien  age-  in  England,  but  of  lower  Senonien  age  in 
Ireland.  Finally,  the  white  chalk  of  England  begins  in  the  Turo- 
nien, but  in  Ireland  and  Scotland  it  occurs  only  in  the  upper  Seno- 
nien. This  illustrates  not  only  the  progressive  overlap  of  the  forma- 


OVERLAP    ON    PENEPLAIN  731 

tions,  but  also  the  progressive  overlap  of  facies  in  the  same  direc- 
tion. 

b.  Rate  of  Depression  Exceeds  Rate  of  Supply.  Under  these 
conditions  there  will  be  a  rapid  transgression  of  the  sea,  and  the 
meager  supply  of  detritus  will  be  spread  thinly  over  the  sea-floor, 
or,  if  the  depression  is  a  rapid  one,  in  many  places  deeper  water 
deposits  may  accumulate  upon  the  original  old  land  surface.  Such 
cases  are  known  and  are  probably  less  infrequent  than  one  is  led 
to  suppose  from  the  scattered  observations  available  in  the  litera- 
ture. Wilson  (8  '.148)  cites  the  case  of  a  calcareous  conglomerate 
of  Black  River  age,  carrying  angular  quartz  fragments,  molds  of  a 
Cameroceras  and  fragments  of  crinoid  stems,  which  rests  directly 
upon  the  Archaean  red  granite  near  Kingston  Mills,  Ontario.  From 
the  basin  of  the  Moose  River,  Devonic  corals  have  been  reported, 
with  their  bases  attached  to  an  Archaean  abyssolith.  (Parks-6  -.188.) 
As  under  normal  conditions  of  transgression,  with  an  equivalent 
supply  of  detritus,  the  change  in  lithic  character  is  a  gradual  one 
from  coarse  at  the  base  to  fine  at  the  top,  so,  in  any  rapid  or  sudden 
transgression,  we  would  expect  to  find  an  abrupt  change  from 
coarse  material  to  fine,  or  from  near-shore  to  off-shore  deposits. 
Conversely,  where  we  find  a  sudden  change  from  coarse  beds  be- 
low to  fine  beds  above,  we  may  postulate  a  sudden  relative  change, 
either  a  sudden  transgression  or  a  sudden  diminution  in  the  supply 
of  material.  Sometimes  a  sudden  transgression  will  transfer  the 
shore  zone,  from  which  much  of  the  detrital  material  is  supplied, 
from  one  lithic  formation  to  another,  when  the  character  of  the 
deposit  will  change.  Thus  an  abrupt  change  of  sea-level  may 
transfer  the  shore  from  a  broad  outcropping  belt  of  quartz  sand- 
stones to  a  parallel  belt  of  limestones,  the  sandstones  being  covered 
by  the  encroaching  sea.  As  a  result,  the  deposition  of  quartz  sands 
may  cease,  and  fine  calcareous  muds  derived  from  the  erosion  of 
limestones  may  be  deposited  upon  the  coarse  quartz  sands  without 
transition.  Such  a  change  appears  to  have  taken  place  in  eastern 
North  America  in  late  Siluric  time,  effecting  a  change  from  the 
Salina  silicarenytes  (Binnewater  sandstones)  to  the  fossiliferous 
limestones  and  water-limes  (Rosendale  cement)  which  overly  them. 

Where  transgression  takes  place  over  an  old  peneplain  surface, 
on  which  residual  soil  has  accumulated  during  the  long  period  of 
exposure,  this  ancient  soil  may  be  incorporated,  without  much 
change,  as  a  basal  bed.  Where  the  soil  is  lutaceous,  especially 
where  it  is  a  residual  clay  containing  much  carbonized  vegetable 
material,  as  in  the  case  of  an  old  swamp-covered  surface,  a  black 
carbonaceous  mud  will  constitute  the  basal  layer,  which  is  sue- 


732 


PRINCIPLES    OF    STRATIGRAPHY 


ceeded  upward  by  other  beds  of  fine-grained  terrigenous  material 
or  by  limestones  derived  from  organic  sources.  Such  a  black 
basal  shale  may  also  result  from  the  washing  of  the  residual  black 
soil  from  the  surface  of  the  plain  into  the  shallow  encroaching 
sea.  In  any  case,  the  basal  black  shale  will  rise  diagonally  across 
the  planes  of  synchroneity,  and,  although  it  will  constitute  a  lithic 
unit,  it  is  not  a  stratigraphic  unit,  but  made  up  of  the  shale  ends 
of  a  successive  series  of  deeper  water  formations.  This  relation- 
ship is  shown  in  the  following  diagram.  (Fig.  147.)  An  example 
of  this  type  of  basal  bed  is  found  in  the  Eureka  (Noel)  black  shale 
of  the  Mississippi  Valley.  This  formation  rests  generally  upon 
eroded  Ordovicic  strata,  the  contact  being  a  disconformable  one. 
Upward  it  passes  into  limestones,  which  in  southwestern  Missouri 


/~  **/  0  »7(Bl ,L  /^wJLSJbJ 


FIG.  147.     Diagram  of  overlap  of  marine  strata  on  basal  black  shale  in  south- 
western Missouri  and  northern  Arkansas. 

are  of  Chouteau  age,  the  shale  itself  carrying  Kinderhook  fossils, 
while  in  northern  Arkansas  it  is  succeeded  by  limestone  carrying 
Burlington  fossils.  The  same  relationship  exists  in  the  southern 
Appalachian  region,  where  the  black  shale  has  risen  into  the  base 
of  the  Keokuk,  if  not  higher.  (Grabau~3.) 


T2.     Regressive  Movements. 

c.  Rate  of  Depression  Is  Exceeded  by  Rate  of  Supply.  In  this 
case  accumulation  will  go  on  so  fast  as  to  fill  in  the  shallow  shore 
zone,  when  the  coarse  material  begins  to  extend  seaward,  progres- 
sively overlapping  the  off-shore  deposits  in  a  seaward  direction. 
We  will  thus  have  a  gradual  change  in  the  character  of  the  sedi- 
ment from  the  lutaceous  material  at  the  bottom  to  arenaceous  and 
sometimes  coarser  terrigenous  material.  This  material  will  all  be 
land-derived,  and,  as  it  is  deposited  rapidly,  not  a  very  thorough 
sorting  can  generally  be  expected.  As  the  shore  migrates  seaward, 
subaerial  deposits  may  accumulate  above  it.  (Wilson-p: 


REGRESSIVE    MOVEMENTS  733 

Local  temporary  increase  in  the  rate  of  supply  may  be  due  to 
causes  not  readily  determinable,  but  widespread  and  persistent 
changes  must  be  regarded  as  indicative  of  climatic  change.  Be- 
fore we  accept  such  a  climatic  change,  however,  as  the  cause  of  a 
seaward  migration  of  terrigenous  deposits  we  must  satisfy  our- 
selves, if  possible,  that  the  migration  in  question  is  not  due  to  a 
change  in  the  rate  of  subsidence,  the  climatic  conditions  and,  there- 
fore, the  rate  of  supply  of  detritus  remaining  the  same.  For  it  is 
evident  that  a  gradual  diminution  of  the  rate  of  subsidence  would 
produce  practically  the  same  results  as  a  corresponding  increase 
in  supply. 

II.     STATIONARY   SEA-LEVEL. 

When  the  supply  of  detritus  continues  uniformly,  while  the 
sea-level  remains  stationary,  a  regression  of  the  seashore  will  take 
place,  but  at  a  faster  rate  than  would  be  the  case  if  subsidence 
still  continued,  though  at  a  diminished  rate.  The  shore  zone  would 
creep  out  over  the  deeper  water  deposits,  the  transition  from  the 
one  to  the  other  being  rather  more  abrupt  than  in  the  case  of  a 
slowly  subsiding  sea-floor.  On  the  whole,  however,  stationary 
conditions  produce  a  change  of  sediment  differing  in  degree  only 
from  that  incident  upon  a  diminution  in  the  rate  of  subsidence. 


III.     FALLING   SEA-LEVEL. 

The  falling  sea-level  or  rising  land  block  is  accompanied  by  a 
continuous  regression  of  the  seashore,  and  a  consequent  seaward 
migration  of  the  shore  zone  with  its  attendant  deposits.  If  the 
emergence  is  not  too  fast  the  waves  will  be  able  to  remove  much 
of  the  formerly  deposited  shore  detritus  and  carry  it  seaward  into 
the  shoaling  off-shore  districts.  Thus  a  bed  of  sand  or  conglom- 
erate will  advance  seaward  over  the  finer  off-shore  deposits,  com- 
ing to  rest  upon  these  often  without  transition  beds.  Further- 
more, the  continuous  movement  of  the  clastic  shore  derivatives 
will  tend,  in  the  coarser  material,  to  a  perfect  rounding  off  of  the 
pebbles,  and  in  general  to  a  destruction  of  all  but  the  most  resistant 
materials.  Thus  a  much  washed-over  sandstone  or  conglomerate 
may  come  to  consist  entirely  of  quartz,  constituting  a  pure  silica- 
renyte  or  silicirudyte.  It  is  probably  not  saying  too  much  that  all 
pure  quartz  elastics,  derived  from  a  complex  crystalline  old  land, 
and  resting  abruptly  upon  a  clayey  or  calcareous  off-shore  deposit, 


734 


PRINCIPLES    OF    STRATIGRAPHY 


represent  the  seaward  spreading  shore  zone  of  a  rising  sea-floor, 
unless  they  are  referable  to  continental  deposits. 


Characteristics  of  Regressive  Deposits. 

As  the  retreat  of  the  sea  from  the  land  may  under  normal  condi- 
tions be  considered  a  process  occupying  a  greater  or  less  amount 
of  time,  it  is  evident  that  deposition  at  a  distance  from  shore  need 
not  be  interrupted.  Thus,  while  within  the  zone  of  retreat  for  any 
given  time  period,  no  sedimentation  will  occur,  such  sedimentation 
may,  nevertheless,  go  on  at  a  regular  rate  beyond  this  zone.  In 
other  words,  a  certain  thickness  of  off-shore  deposits  must  be 
considered  the  depositional  equivalent  of  a  given  time  period, 
which  in  the  shore  zone  is  represented  by  a  given  amount  ot  re- 


FIG.  148.  Diagram  illustrating  regressive  overlap  (off-lap)  and  the  forma- 
tion of  a  sandstone  of  emergence  Or-v)  into  which  the  shore- 
ends  of  the  successive  members  of  the  retreatal  series  (a-d) 
grade. 

treat.  Thus  it  is  brought  about  that  each  successive  formation  of 
the  retreatal  series  extends  shoreward  to  a  less  extent  than  the 
preceding  one.  As  each  formation  or  bed  passes  shoreward  into 
a  coarser  clastic  it  is  evident  that  the  shore  ends  of  all  the  forma- 
tions deposited  during  the  retreat  will  together  constitute  a  stratum 
of  sandstone  or  conglomerate  which  in  age  rises  seaward,  since  in 
that  direction  it  is  progressively  composed  of  the  ends  of  higher 
and  higher  formations.  These  relationships  are  shown  in  Fig.  148, 
where  it  will  be  noted  that  the  diagonal  rise  of  the  shore-formed 
stratum  is  from  the  shore  seaward,  whereas  in  transgressive  move- 
ments the  shore-formed  stratum  or  basal  bed  rises  diagonally  land- 
ward. In  the  series  shown  in  the  diagram,  the  beds  a-d  were  suc- 
cessively laid  down  during  the  retreat  of  the  sea  from  A  to  B. 
Each  later  formed  bed  comes  to  an  end  before  it  has  reached  the 
shoreward  end  of  the  preceding  one,  and  each  formation  grades 
from  a  clayey  or  calcareous  character  landward  into  silicoarena- 
ceous  character.  Thus  b  reaches  landward  to  a  less  extent  than  a, 
the  shore  end  of  which,  composed  of  quartz  sands,  remains  ex- 


REGRESSIVE    DEPOSITS  735 

posed.  The  shore  end  of  b  is  also  composed  of  quartz  sands,  since 
during  the  formation  of  b  the  shore  has  migrated  seaward.  In  like 
manner  c  does  not  entirely  cover  b,  and  d  does  not  wholly  cover 
c,  each  ending  .in  a  sand  facies.  Thus  the  sand  ends  of  all  the  beds 
will  be  exposed  at  or  just  above  sea-level,  and  constitute  a  continu- 
ous sand  formation,  which,  however,  is  not  of  the  same  age  at 
any  two  points  along  a  line  transverse  to  the  direction  of  the  shore. 
Such  a  sand  formation  will,  however,  be  mapped  as  a  unit,  and  re- 
ceive a  formational  name.  If  the  basal  portion  of  such  a  sand  for- 
mation is  fossiliferous,  it  will  contain  in  a  seaward  direction  the 
fossils  of  successively  higher  formations.  Thus  the  portion  of  the 
sandstone  formation  x,  y  in  Fig.  148  will  at  x  contain  the  fossils 
of  formation  a,  and  at  3;  the  fossils  of  formation  d,  while  -between 
these  points  it  will  contain  the  fossils  of  b  and  c,  where  it  forms 
the  end  of  these  respective  formations.  When  the  land  is  suffi- 
ciently elevated  during  the  retreat  of  the  sea,  stream  erosion  will 
set  in  and  the  material  left  by  the  retreating  sea  may  be  removed 
by  the  streams.  Furthermore,  if  elevation  of  the  land  is  responsible 
for  the  retreat  of  the  sea,  the  streams  coming  from  this  higher 
land  will  bring  more  detritus,  and  hence,  where  erosion  is  not 
going  on,  deposition  by  rivers  will  further  elevate  the  surface  of 
the  emerging  coastal  plain.  The  same  thing  is  true  also  if  the 
regressive  movement  is  due  to  an  increase  in  the  supply  of  detrital 
material.  In  either  case,  pebbles  and  sands  derived  through  the 
erosion  of  the  old  land  or  of  old  conglomerates  and  sandstones 
may  be  carried  out  for  great  distances  over  this  emerging  surface, 
while  wind-assorted  sands,  with  their  grains  rounded  and  pitted 
from  attrition,  may  also  accumulate  over  this  surface.  The  peculiar 
structures  of  both  torrential  and  eolian  sands,  i.  e.,  cross-bedding, 
ripples,  etc.,  may  thus  be  incorporated  in  this  retreatal  sandstone. 
Remains  of  land-plants  and  of  land  and  fresh  water  animals  may 
readily  be  entombed  in  the  deposits  thus  accumulating  upon  the 
flat  plain  of  retreat,  and  even  coal  beds  may  form  and  become  em- 
bedded in  sandstones  the  bases  of  which  vary  in  age  from  place 
to  place. 

Burial  of  Retreatal  Sandstones  by  Subsequent  Transgressive 

Movements. 

When  the  regressive  movement  of  the  shore  has  come  to  an 
end,  and  transgressive  changes  recommence,  the  upper  portions  of 
these  migratory  shore  deposits  may  be  worked  over  once  more,  and 
now  partake  of  the  character  of  a  basal  sandstone  or  conglomerate. 


PRINCIPLES    OF    STRATIGRAPHY 


As  the  shore  zone  advances  landward,  finer  deposits  will  be  laid 
down  over  the  coarser  basal  bed  and  thus  the  transgressive  portion 
of  such  a  sandstone  or  conglomerate  will  pass  diagonally  across  the 
planes  of  synchroneity.  The  deposit  resulting  by  the  time  the 
shore  zone  has  returned  to  its  former  position  will  therefore  be 
a  composite  formation  including  within  it  a  hiatus,  which  may  rep- 
resent a  considerable  time  interval,  but  is  not  recognizable  by  any 
structural  character.  The  encroaching  sea  will  work  over  the  sand 
dune  deposits  and  thus  water-laid  sandstone  beds,  composed  of 
rounded  translucent  quartz  grains  and  well  stratified,  will  result. 
In  the  upper  part  of  these  worked-over  sandstones  marine  shells 
and  other  remains  may  be  included,  the  age  o<f  which  changes 
shoreward,  since  the  transgressive  portion  of  this  sandstone  repre- 
sents successively  the  ends  of  higher  and  higher  formations,  after 
the  manner  of  a  true  basal  sandstone  of  a  transgressive  series. 


FIG.  149.  Diagram  showing  the  relationship  of  the  strata  in  five  successive 
sections,  in  a  compound  regressive-transgressive  series.  The 
intercalated  sandstone  x  y  encloses  the  hiatus.  (See  Fig.  150.) 

The  recognition  of  an  intercalated  shore  formation  of  great 
areal  extent  between  off-shore  sediments  as  the  product  of  combined 
regressive  and  transgressive  movement  must  be  based  on  a  com- 
parison of  sections  taken  at  intervals  over  the  entire  area  covered 
by  the  formation  in  question.  Such  sections  will  show  the  inter- 
calated shore  formation  (sandstone  or  conglomerate)  to  be  in 
more  or  less  intimate  association  with  the  lower  beds  of  the  under- 
lying formation  and  the  higher  beds  of  the  overlying  formation  at 
their  shoreward  ends,  but,  away  from  the  shore,  higher  members  of 
the  lower  formation  and  lower  members  of  the  higher  formation 
will  progressively  appear  until  near  the  line  of  farthest  retreat 
both  lower  and  upper  formation  will  be  complete,  while  beyond  that 
the  intercalated  bed  will  gradually  lose  its  shore  character  and 
merge  with  the  enclosing  formations.  This  character  of  the  sec- 
tions is  shown  in  the  preceding  diagram  (Fig.  149).  Formation 
A,  consisting  of  divisions  J  to  4,  and  formation  B,  consisting  of 


COMPOUND   OVERLAP 


737 


divisions  a  to  d,  are  both  complete  in  section  5,  which  marks  the 
farthest  limit  of  retreat  of  the  sea.  Bed  x,  the  intercalated  shore 
formation,  fades  away  in  this  section.  In  section  4  all  the  members 
of  both  formations  -are  represented,  but  divisions  4  and  a  are  not. 
complete,  while  the  intercalated  bed  x  is  prominent.  In  section  3, 
divisions  4  and  a  are  wanting,  and  in  section  2,  divisions  j  and  b  are 
likewise  wanting.  In  section  I,  finally,  all  except  the  lowest  divi- 
sion (/)  of  formation  A,  and  the  highest  (d)  of  formation  B,  are 
missing.  It  would  be  obviously  wrong  to  correlate  division  /  of  sec- 
tion I  writh  the  whole  of  formation  A  as  exposed  in  section  5,  or 
division  d  of  section  I  with  the  whole  of  formation  B  of  section  5. 
Yet  such  correlations  have  not  infrequently  been  made  in  the  past. 
In  each  of  the  above  sections  the  intercalated  sandstone  or  con- 
glomerate may  be  intimately  related  to  both  overlying  and  underly- 
ing formations,  and  contain  tjieir  fossils.  Such  a  relation  would 


FIG.  150.  Diagram  of  a  compound  regressive-transgressive  series,  showing  the 
seaward  decrease  of  the  hiatus  between  the  upper  and  lower 
part  of  the  series.  (See  Fig.  149.) 

show  that  the  actual  hiatus  is  represented  by  the  middle  part  of  the 
intercalated  bed,  which  middle  part  may  not  infrequently  be  repre- 
sented by  continental  deposits.  Yet  so  intimate  are  the  physical  re- 
lationships between  the  bottom,  middle  and  top  of  the  intercalated 
formation  that  a  separation  into  more  than  one  formation  is  im- 
possible. Thus  in  section  I  the  intercalated  formation  x  may  have 
all  the  characters  of  a  formational  unit  or  a  single  stratum,  and  may 
grade  upward  into  division  d  and  downward  into  division  I,  so  that 
to  all  appearance  continuous  deposition  obtained  in  this  locality.  If 
the  respective  ages  of  divisions  d  and  /  are  recognized,  formation  x 
will  be  likely  to  be  considered  the  depositional  equivalent  of  divi- 
sions 2  to  4  and  a  to  c  of  section  5.  Such  is  indeed  the  fact,  except 
that  the  central  portion  of  x,  the  terrestrial  portion,  whether  repre- 
sented by  continental  deposits  or  an  unrecognizable  erosion  plane, 
represents  all  but  the  upper  fraction  of  division  c,  and  the  lower  of 
division  2.  The  hiatus  or  stratigraphic  break  thus  represented  in 


738 


PRINCIPLES    OF    STRATIGRAPHY 


the  middle  portion  of  the  intercalated  formation  is  a  constantly  de- 
creasing one  from  section  I  to  section  5.  In  each  section  it  covers 
the  interval  of  time  between  the  emergence  of  the  sea  bottom  at  that 
point  during  the  regressive  movement  and  its  resubmergence  during 
the  succeeding  transgressive  movement.  This  relationship  may  be 
expressed  in  the  preceding  diagram.  (Fig.  150.)  The  following 
diagrammatic  sections  (Fig.  151)  show  the  relation  of  a  series  of 
strata  recording  a  transgressive  movement  followed  by  a  regressive 
and  again  by  a  transgressive  movement,  x-z  is  the  basal  sandstone 
bed  of  the  transgressive  series,  x-y  the  intercalated  sandstone  of  the 


FIG. 


151.  Diagram  showing  the  relationships  of  the  strata  In  a  transgressive- 
regressive-transgressive  series.  Basal  sandstone  x  £  and  inter- 
calated sandstone  x  y  are  both  present. 


regressive-transgressive  series.  Beds  i  to  3  are  the  first  series  of 
transgressive  formations,  beds  4  to  7  the  regressive  formations,  and 
beds  8  to  12  the  second  series  of  transgressive  formations. 


EXAMPLES  OF  INTERCALATED  SANDSTONES  FROM  THE  PALAEOZOIC 
AND  MESOZOIC  FORMATIONS  OF  NORTH  AMERICA. 

The  Saint  Peter  Sandstone.  This  is  an  exceedingly  pure  quartz 
sandstone  of  rounded,  well-worn  and  pitted  grains  of  nearly  uni- 
form size  in  any  given  region.  It  is  widely  distributed  in  central 
North  America,  lying  generally  between  a  member  of  the  Chazyan 
and  one  of  the  Beekmantownian  formations  of  the  Ordovicic.  In 
Minnesota  it  lies  beneath  the  upper  beds  of  the  Stones  River  (Up- 
per Chazyan),  grading  upward  into  and  containing  some  of  its 
characteristic  fossils  in  the  upper  layers.  Its  base  rests  upon  lower 
Beekmantown  (Shakopee),  into  which  it  also  grades  in  many  sec- 
tions, though  in  others  it  forms  a  sharp  contact  or  even  rests  on  an 


INTERCALATED    SANDSTONES 


739 


erosion  plane  of  the  dolomite.  Where  conformable  it  may  contain 
lower  Beekmantown  fossils.  Sometimes  the  lower  beds  are  slightly 
disturbed,  while  the  upper  ones  do  not  partake  of  such  disturbance. 
This  indicates  an  interval  of  time  after  the  deposition  of  the  lower 
beds,  during  which  they  were  disturbed,  and  after  which  the  higher 
strata  were  deposited  upon  them.  Southward,  higher  members  of 
the  Beekmantown  series  come  in  beneath  the  Saint  Peter  sandstone 
and  lower  members  of  the  Chazyan  above  it.  In  the  Arbuckle 
Mountains  the  upper  bed  (here  known  as  the  Simpson  formation) 
is  about  2,000  feet  thick,  while  the  Beekmantown  below  the  Saint 
Peter  is  of  similar  thickness.  This  sandstone  thus  has  all  the  char- 
acteristics of  a  regressive-transgressive  sandstone  intercalated  be- 
tween limestones,  and  may  be  regarded  as  a  typical  example.  (Gra- 
bau-3;  4.)  (Fig.  152.) 


FIG.  152.  Diagram  representing  the  Cambric,  Lower  Ordovicic  (Beekman- 
town), and  Middle  Ordovicic  (Chazyan)  formations,  and  the 
compound  transgressive-regressive-transgressive  overlaps  between 
Oklahoma  and  Minnesota.  The  intercalated  sandstone  is  the 
Saint  Peter. 

The  Dakota  Sandstone.  This  sandstone  of  Mid-Cretacic  age  has 
essentially  the  same  relation  to  the  enclosing  calcareous  strata  as  has 
the  Saint  Peter.  It  contains,  besides,  an  abundant  flora  of  terres- 
trial plants,  so  that  its  value  as  a  record  of  complete  emergence  be- 
comes even  greater.  In  southern  Kansas  this  sandstone  lies  at  the 
top  of  the  Fredericksburg  division  of  the  Comanchic,  while  in  Texas 
it  lies  on  top  of  the  Washita  or  LTpper  Comanchic.  In  either  case 
there  is  commonly  a  gradation  from  the  limestones  and  shales  to 
the  sandstones.  The  top  of  this  sandstone  passes  upward  into  the 
marine  Eagle  Ford  formation  in  Texas,  while  further  north,  in 
Colorado  and  the  Dakotas,  it  grades  into  the  much  later  Benton 
beds. 

B.  NONMARINE  PROGRESSIVE  OVERLAP.  This  term 
is  applied  to  the  large  structure  normally  produced  during  the 
formation  of  a  great  fan  or  subaerial  delta,  from  the  wash  carried 
by  the  streams  from  the  mountains  and  deposited  upon  the  plains 
adjoining.  Such  a  subaerial  fan  will  of  course  grow  in  extent  year 


74o 


PRINCIPLES    OF    STRATIGRAPHY 


by  year,  and  in  so  growing  the  latest  deposits,  whether  derived  from 
the  mountain  or  whether  obtained  through  the  reworking  of  the 
previously  deposited  portion,  will  as  a  rule  extend  further  out  into 
the  plain  than  did  those  of  previous  periods  of  deposition.  In  other 
words,  each  later  formation  will  overlap  the  previous  ones  by  a 
margin  commensurate  with  the  increase  in  the  size  of  the  fan,  and 
beyond  the  margin  of  the  previously  formed  bed  it  will  come  to  rest 
directly  upon  the  floor  of  the  plain.  This  overlapping  of  later 
formed  over  earlier  ones  will  of  course  be  a  progressive  one  if  .the 
growth  is  continuous.  The  essential  point  of  difference  between  this 
type  of  overlap  and  that  formed  in  a  transgressing  sea  is  that  in 
the  subaerial  fan  the  formations  will  primarily  overlap  one  another 
away  from  the  source  of  supply  of  the  material,  while  in  the  ma- 
rine progressive  overlap  the  overlap  is  toward  the  source  of  supply 
of  the  material.  The  following  diagrams  will  illustrate  this  differ- 


FIG.  153.  Diagrams  illustrating  the  relationship  of  the  strata  in  nonmarine 
progressive  overlap  (a)  and  marine  progressive  overlap  (b). 
The  source  of  the  material  in  each  case  is  on  the  left. 

ence,  the  source  of  supply  in  each  case  being  on  the  left.  (Figs. 
153,  a,  b.)  It  should,  however,  be  noted  here  (Barrell— i)  that  at 
the  head  of  the  delta  an  overlap  toward  the  source  of  supply  may 
occur,  since  with  the  aggradation  of  the  delta  plain  and  the  conse- 
quent lowering  of  the  river  grade  deposition  may  commence  farther 
upstream.  Such  effects  are  seen  in  interior  basins,  where  the  upper 
beds  extend  farther  toward  the  mountains  from  which  the  material 
has  been  derived.  It  appears  to  be  shown  also  in  the  case  of  the 
Newark  formation,  where  the  upper  beds  extend  farther  north, 
overlapping  the  lower  ones.  (Kummel-5  '.48.)  It  may,  however, 
be  questioned  whether  headward  overlapping  of  the  formations  is 
ever  of  marked  character,  since  it  is  necessarily  confined  to  the 
stream  channels  supplying  the  detritus  and  probably  does  not  spread 
greatly  in  a  lateral  direction.  In  any  case  it  cannot  be  compared  in 
extent  and  importance  with  the  overlap  on  the  margin  of  the  fan, 
which  is  always  away  from  the  source  of  supply. 

The  coarsest  material  of  the  subaerial  fan  will  of  course  be  de- 
posited near  the  head  of  the  delta.     Finer  material  may  be  carried 


NONMARINE   TRANSGRESSIVE   OVERLAP        741 

out  for  hundreds  of  miles  across  such  a  delta,  as  is  abundantly 
shown  by  the  delta  plains  of  the  Indus  and  Ganges  and  of  the 
Huang-ho  River.  Occasionally  pebbles  well  rounded  may  be  car- 
ried out  to  great  distances,  and  this  is  especially  true  of  the  well- 
rounded  pebbles  derived  from  older  conglomerates.  When  the  sur- 
face of  the  delta  has  become  very  flat,  drainage  obstructions  may 
take  place,  in  which  case  swamps  and  the  deposit  of  carbonized 
plant  remains  will  form.  Thus  a  fossil  delta  of  this  type  may  in- 
clude coal  seams,  the  tops  of  which  may  again  be  eroded,  or  covered 
with  a  moderately  coarse  river  deposit. 

An  essential  feature  of  this  type  of  overlap  in  purely  nonmarine 
sediments  is  the  relation  which  the  beds  have  to  the  surface  on 
which  the  overlapping  edges  rest.  If  this  is  an  old  land  surface, 


N.VM 


FIG.  154.  Diagram  showing  the  westward  overlap  of  the  various  members  of 
the  Pottsville  series  of  eastern  North  America,  upon  the  old 
erosion  surface  of  pre-Pottsville  age; the  surface  of  supply  is  in 
the  southeast. 

*.  e.,  without  contemporaneous  sediments  of  .a  marine  origin,  the 
evidence  of  the  nonmarine  origin  of  this  overlapping  series  is  com- 
plete. For  it  is  manifestly  inconceivable  that  clastic  sediment  will 
be  carried  across  a  body  of  water  and  be  deposited  upon  the  oppo- 
site shore  in  such  a  relationship  as  to  suggest  marine  transgressive 
overlap. 


THE   POTTSVILLE   SERIES,   A   TYPICAL   EXAMPLE  OF   NONMARINE 
PROGRESSIVE  OVERLAP.     (Fig.  154.) 

This  is  a  deposit  of  quartzose  elastics,  consisting  for  the  most 
part  of  rounded  quartz  pebbles  embedded  in  a  matrix  of  sand.  In 
the  eastern  area  the  conglomerate  is  coarsest,  the  pebbles  often 
reaching  a  diameter  of  several  inches.  They  consist  also  of  a 
greater  variety  of  material,  but  westward,  where  the  pebbles  are 
smaller,  scarcely  any  but  those  of  quartz  remain.  Several  distinct 
coal  beds  with  associated  shales  occur,  making  identification  of 


742 


PRINCIPLES    OF    STRATIGRAPHY 


horizons  possible.  The  formation  is  thickest  in  the  eastern  Appa- 
lachians and  thins  away  westward  by  failure  of  the  lower  beds  and 
overlap  of  the  higher.  The  lowest  beds  are  found  in  two  localities  in 
the  eastern  area,  near  Pottsville,  Pennsylvania,  and  in  the  Poca- 
hontas  region  of  West  Virginia  and  Virginia.  From  these  two  cen- 
ters the  deposits  spread  northward,  westward  and  southwestward, 
each  later  division  overlapping  the  preceding  ones,  until  in  western 


FIG.  155.     Diagram  showing  replacing  overlap  of  a  nonmarine  series  over  a 
marine  one. 

Pennsylvania  and  Ohio  only  the  highest  members  of  the  series  are 
present.  Since  the  source  of  these  beds  can  only  be  in  the  eastern 
Appalachians,  where  alone  rocks  capable  of  furnishing  such  ma- 
terial exist,  the  overlap  becomes  one  away  from  the  source  of  sup- 
ply. Such  an  overlap  might  perhaps  be  produced  under  water  if 
the  overlapping  marine  sediments  belonged  to  a  spreading  sub- 
marine delta.  In  this  case  the  beds  would  become  increasingly  finer 
around  the  periphery  of  the  submerged  delta,  and  they  would  merge 


FIG.  156.  Diagram  showing  the  relationship  of  the  nonmarine  Catskill  and 
the  marine'  Chemung  in  eastern  North  America.  A  Devonic  ex- 
ample of  replacing  overlap. 

into  deposits  of  purely  marine  origin.  Nor  would  the  delta  be  of  a 
size  comparable  to  that  of  the  Pottsville,  which  by  its  character,  its 
coal  beds  and  its  overlap  relations  is  shown  to  be  of  subaerial  ori- 
gin. There  are  to  be  sure  one  or  more  reported  horizons  of  marine 
faunas,  a  brachiopod  fauna  having  been  found  in  the  middle  Potts- 
ville (Horsepen)  as  far  north  as  Sewell,  on  New  River.  If  these 
organisms  really  indicate  marine  conditions  and  not  secondary  in- 
clusions, this  can  only  mean  a  momentary  invasion  of  the  delta 
area  from  a  neighboring  arm  of  the  sea.  Naiadites  and  "Spirorbis" 
have  been  found  in  the  Lower  Lykens  division  of  the  anthracite 


REPLACING  OVERLAP 


743 


region  of  Pennsylvania,  but  these  organisms  do  not  necessarily  in- 
dicate marine  conditions. 

REPLACING  OVERLAP.     This  type  of  overlap  occurs 


c. 


when  a  series  of  clastic  sediments  of  terrestrial  origin  replaces  a 
typical  oceanic  or  thalassic  series,  or  where  continental  elastics  re- 


FIG.  157.  Diagram  showing  «the  westward  replacing  overlap  of  the  Utica 
shale  on  the  Trenton  limestone,  both  being  marine  formations, 
but  one  (the  Utica)  terrigenous  and  the  other  thalassigenous. 

place  those  formed  in  the  sea  (Fig.  155).  The  latter  is  associated 
only  with  a  retreating  seashore,  and  the  overlapping  of  the  nonma- 
rine  beds  does  not  take  place  on  the  old  land  surface,  but  upon  previ- 
ously deposited  and  all  but  contemporaneous  marine  beds.  Along 
the  border  line  the  two  will  blend,  and  it  will  appear  as  if  the  non- 

Appalaehlan  Reffl«n 


interior  Region 


Continental  S«rl« 


FIG.  158.  Diagram  showing  replacing  overlap  of  terrigenous  marine,  fol- 
lowed by  continental  sediments  on  the  east  over  marine  lime- 
stones, etc.,  on  the  west. 

marine  series  overlay  the  marine  series,  though  in  reality  it  is  a  case 
of  replacement  of  the  one  by  the  other.  A  typical  example  of  such 
a  progressive  replacement  is  seen  in  the  Catskill  sandstone,  which 
as  a  nonmarine  formation  spread  westward  from  its  centers  of  ori- 
gin, of  which  it  appears  there  were  at  least  two.  The  correspond- 


744  PRINCIPLES    OF    STRATIGRAPHY 

ing  marine  beds  are  the  Chemung  sandstones  and  shales,  which  may 
be  regarded  as  the  submerged  continuations  of  the  Catskill  beds. 
Oscillatory  conditions  are  indicated  by  occasional  intercalations  of 
the  marine  between  the  nonmarine  layers.  In  the  eastern  area  the 
series  is  represented  wholly  by  the  nonmarine  Catskill;  in  the 
western  it  is  represented  wholly  by  the  marine  Chemung.  Between 
these  extremes  marine  Chemung  is  always  overlain  by  nonmarine 
Catskill.  These  relationships  are  shown  in  the  diagram  on  page 
742.  (Fig.  156.) 

This  type  of  overlap,  though  away  from  the  source  of  supply, 
is  not,  however,  limited  to  nonmarine  deposits.  It  may  likewise  be 
shown  by  a  spreading  clastic  shore  deposit,  which  gradually  re- 
places a  limestone  of  neritic  origin  without  actual  emergence  of  the 
zone  of  shore  deposits  occurring.  Or  a  current-borne  type  of  ter- 
rigenous sediment  may  progressively  replace  a  limestone  of  neritic 
origin.  Examples  of  such  replacement  .are  found  in  the  changing 
facies  of  the  Trenton  limestones,  which  (Grabau-4)  are  gradually 
replaced  westward  by  the  spreading  Utica  *  type  of  deposit,  which 
is  of  near-shore  and  probably  shallow-water  origin.  This  is  illus- 
trated in  the  diagram  on  page  743  (Fig.  157).  A  combination  of 
this  type  and  the  replacing  by  sediments  of  continental  origin  is 
shown  in  Figure  158  on  page  743,  involving  the  Upper  Ordovicic 
and  Lower  Siluric  deposits  of  eastern  North  America. 


BIBLIOGRAPHY  XVIII. 


1.  BARRELL,   JOSEPH.     1912.     Criteria   for   the   Recognition   of   Ancient 

Delta  Deposits.      Geological  Society  of  America  Bulletin,  Vol.  XXIII, 
PP.  377-446. 

2.  CROSB Y,  WILLIAM  O.  1899.     Archaean-Cambrian  Contact  near  Manitou, 

Colorado.     Bulletin  of  the  Geological  Society  of  America,  Vol.  X,  pp. 
141-164. 

3.  GRABAU,  AMADEUS  W.     1906.     Types  of  Sedimentary  Overlap.     Bulle- 

tin of  the  Geological  Society  of  America,  Vol.  XVII,  pp.  567-636. 

4.  GRABAU,  A.  W.     1910.     Physical  and  Faunal  Evolution  of  North  America 

During   Ordovicic,    Siluric   and   Early   Devonic  Time.     In  "Outlines  of 
Geological  History,"  etc.,  Chapter  IV.    t 

5.  KUMMEL,  HENRY  B.       1898.     .Annual  Report  of  the  State  Geologist 

of  New  Jersey  for  1898.     New  Jersey  Geological  Survey. 

6.  PARKS,  WILLIAM  ARTHUR.     1899.     The  Nipissing-Algoma  Boundary 

(Ontario).     Ontario  Bureau  of  Mines,  Vol.  VIII,  pp.  175-196. 

*  Using  this  term  in  its  broader  sense,  in  which  it  is  practically  equivalent 
to  the  whole  of  the  Trenton. 


BIBLIOGRAPHY    XVIII  745 

7.  RUTOT,  A.     1883.     Les  Phenomenes  de  la  Sedimentation  Marine.     Etudies 

dans  leur  Rapports  avec  la  Stratigraphie  regionale.       Bulletin  du  Muse"e 
Royal  d'histoire  naturelle  de  Belgique,  Tome  II,  pp.  41-83. 

8.  WILSON,  A.  W.  G.     1901.     Physical  Geology  of  Central  Ontario,  Canadian 

Institute  Transactions,  Vol.  VII,  pp.  139-186. 

9.  WILSON,  A.  W.  G.     1903.     The  Theory  of  the  Formation  of  Sedimentary 

Deposits.     Canadian  Record  of  Science,  Vol.  IX,  pp.  112-132. 


CHAPTER   XIX. 
METAMORPHISM  OF  ROCKS/ 

GENERAL  DEFINITIONS.  The  term  metamorphism,  from  the 
Greek  /utera,  interchange,  and  fiop<£?7  form  (+ism),  has  been 
applied  to  the  process  of  alteration  of  rock  masses  in  any  manner 
whatsoever.  The  product  of  such  metamorphism  is  metamorphic 
rock,  often  an  entirely  new  substance  so  far  as  form  and  other 
physical  characters  are  concerned.  It  is  true  that  the  term  is  sel- 
dom used  in  the  comprehensive  sense,  metamorphism  being  gener- 
ally considered  as  brought  about  by  the  agencies  of  heat  and  pres- 
sure, due  to  contact  with  heated  bodies,  or  from  being  subject  to 
dynamic  disturbances.  There  can  be  no  question,  however,  that 
these  are  only  special  phases  of  metamorphism,  and  that  they  can- 
not be  separated  genetically  from  the  more  quiet  processes  of  altera- 
tion to  which  rocks  are  subject  under  ordinary  physical  conditions. 
As  such,  the  weathering  of  rocks  must  be  included.  Metamorphism 
may  bring  about  a  change  in  one  or  more  of  the  following  charac- 
ters :  composition,  texture,  structure.  The  change  in  composition 
may  be  chemical  alteration  or  mineralogical  change,  new  minerals 
appearing  in  a  rock  as  a  result  of  metamorphism,  and  old  minerals 
may  disappear.  Texture  may  be  changed  completely,  as  from  compact 
limestone  to  crystalline  marble,  or  special  textures,  characteristic  of 
metamorphic  rocks,  may  be  produced,  such  as  cataclastic ,  parallel 
orientation,  etc.  Original  structures,  such  as  flow  structure,  stratifi- 
cation, etc.,  may  be  obliterated  and  new  ones  produced,  such  as 
cleavage,  fissility,  joints,  slatiness,  schistosity  and  gneissosity  (Van 
Hise-34). 

THE  FORCES  PRODUCING  METAMORPHISM.  The  forces  at  work 
in  the  production  of  metamorphism  are  given  by  Van  Hise  (34:45) 
as:  I,  chemical  energy;  2,  gravity;  3,  heat  and  light;  while  the 
agents  through  which  these  work  upon  the  rocks  are:  (a)  gases, 
(b)  liquids,  and  (c)  organic  compounds.  Organic  compounds  are 
mainly  active  in  the  surface  belt  where  weathering  of  rocks  takes 

746 


METAMORPHISM  747 

place,  but  gaseous  and   liquid  solutions  *   are  agents  everywhere 
present  and  active,  within  the  known  crust  of  the  earth. 

THE  REGIONS  OF  METAMORPHISM.  The  regions  where  meta- 
morphism  of  various  kinds  takes  place  are  classified  by  Van  Hise 
(34:4^),  according  to  depth,  as  follows: 

I.  The  zone  of  katamorphism,  or  that  zone  in  which  simple 
compounds  are  produced  from  more  complex  ones,  comprising  (a) 
the  belt  of  weathering,  extending  from  the  surface  to  the  level  of 
ground  water,  and  (b)  the  belt  of  cementation,  extending  from  the 
ground-water  level  to  the  next  zone. 

II.  The  zone  of  anamorphism,  or  that  zone  in  which  complex 
compounds  are  produced  from  simple  ones. 

Characteristics  of  the  Zones  of  Mefamorphism.  The  belt  of 
weathering  is  the  region  of  rock  destruction;  the  belt  of  cementation 
is  the  region  of  rock  construction  and  the  zone  of  anamorphism  the 
region  of  rock  reconstruction.  The  zone  of  katamorphism  is  also  the 
zone  of  fracture  of  rocks,  where  openings  may  exist.  Van  Hise  has 
calculated  that  the  maximum  depth  of  this  zone  cannot  be  greater 
than  12,000  meters,  and  in  most  cases  is  probably  much  less.  The 
zone  of  anamorphism  also  corresponds  to  the  zone  of  rock  flowage, 
where  the  pressure  is  greater  than  the  strength  of  the  rocks,  and 
deformation  will  take  place  without  fracture,  but  with  rock  flowage, 
which  will  not  permit  the  existence  of  empty  pore  spaces. 

Recent  experiments  on  rock  flowage  made  by  Professors  F.  D. 
Adams  (2)  and  L.  V.  King  (21)  at  McGill  University,  Montreal, 
have  shown  that  cavities  can  exist  at  much  greater  depths  than 
10,000  meters.  They  placed  cylinders  of  granite,  with  holes  bored 
through  them,  in  a  testing  machine,  and  subjected  them  for  seventy 
hours  to  a  pressure  of  96,000  pounds  per  square  inch  at  a  temper- 
ature of  550°  C.  After  the  experiment  it  was  found  that  the  hole 
was  unchanged.  The  pressure  obtained  corresponded  to  that  occur- 
ring at  a  depth  of  .about  15  miles,  but  the  temperature  was  that  esti- 
mated to  prevail  in  the  earth's  crust  at  a  depth  of  only  eleven  miles. 

*  Solutions  have  been  defined  as  "homogeneous  mixtures  which  cannot  be 
separated  into  their  constituent  parts  by  mechanical  means"  (Ostwald).  They 
may  consist  of  gases  mingled  with  other  gases,  with  liquids  or  with  solids,  of 
liquids  mingled  with  liquids  or  with  solids,  and  of  solids  mingled  with  solids. 
"The  solutions  resulting  from  these  various  combinations  may  be  gases,  liquids, 
or  solids  or  partly  two  or  all."  (Van  Hise~34:5p).  The  gases  important  in 
rock  alteration  are  oxygen  (O2)  sulphur  (Ss  to  S2)  water  vapor  (H2O),  ammonia 
(NH3),  carbon  dioxide  (CO2),  sulphurous  oxide  (SO2),  boric  acid  (H3BO3),  hydro- 
chloric acid  (HC1)  and  hydrofluoric  acid  (HF).  The  liquid  solutions  are  all 
water  solutions. 


748  PRINCIPLES    OF    STRATIGRAPHY 


KINDS  OF  METAMORPHISM. 

Metamorphism  is  always  a  complex  problem,  but  according  to 
the  dominant  forces  three  distinct  types  have  generally  been  recog- 
nized, viz.,  static,  contactic  (contagic),  and  dynamic.  Static  meta- 
morphism  is  that  process  of  alteration  which  goes  on  without  the 
interference  from  without  of  forces  producing  deformation,  or  the 
invasion  of  heat  from  contact  with  a  molten  mass.  It  is  essentially 
an  endogenetic  process,  being  concerned  only  with  those  forces  uni- 
versally active  within  the  mass.  These  include  chemical  energy, 
gravitative  rearrangement  within  the  rock  mass  and  the  pressure 
due  to  its  own  mass,  as  well  as  the  pressure  resulting  from  the 
crystallization  of  the  mass.  Further,  the  influence  of  heat  caused 
by  these  changes  within  the  mass — but  not  invading  heat  (or  cold) 
from  without — and  the  influence  of  the  omnipresent  water  and  gases 
within  the  rock  mass.  This  complex  activity  is  essentially  metaso- 
matic  and  includes  in  reality  two  quite  distinct  processes :  the  de- 
struction of  rock  masses  by  the  atmosphere  and  water  and  the 
construction  and  reconstruction  of  rocks  by  the  processes  going  on 
within  the  mass. 

The  process  of  weathering  has  been  dealt  with  at  length  in 
earlier  chapters;  there  remain  for  present  consideration  only  the 
constructive  and  reconstructive  processes  of  metamorphism.  To 
the  static  phases  of  these  processes  of  alteration  the  name  diagenesis 
has  been  applied  by  Johannes  Walther,  the  name  itself  having  been 
used  first  by  Gumbel  in  1868  in  his  "Geognostische  Beschreibung 
des  ostbayerischen  Grenzgebirges"  for  the  more  general  processes 
of  metamorphism.  Andree  has  proposed  to  restrict  the  term  to  those 
molecular  and  chemical  transformations  which  the  sediment  under- 
goes under  the  influence  of  the  medium  in  which  it  was  deposited, 
and  to  which  it  is  still  subject  after  separation  from  this  medium, 
through  the  ordinary  circulating  or  vadose  waters,  in  so  far  as  these 
do  not  contain  any  foreign  substances  in  solution,  i.  e.,  such  sub- 
stances as  are  derived  from  outside  of  the  sediment.  He  would 
include  as  chief  of  these  changes:  recrystallization,  formation  of 
concretions,  lithification  and  desalinification.  In  so  far  as  this 
restriction  excludes  changes  due  to  percolating  thermal  waters  or 
waters  bearing  mineral  solutions,  changes  which  may  affect  locally 
parts  of  various  rock  formations,  this  restriction  seems  .warranted. 
Such  changes  are  to  be  classed  under  the  heading  of  contact  meta- 
morphism and  are  to  be  placed  either  with  thermic  metamorphism 
or  are  to  be  considered  separately  as  hydrometamorphism.  The 


KINDS    OF    METAMORPHISM  749 

name  contact  metamorphism  is  applied  here  to  the  reconstruction  of 
rocks  due  to  contact  with  ( I )  heated  masses  such  as  igneous  bosses, 
dikes,  sills,  etc.  (thermic  metamorphism  or  pyrometamorphism)  ;  (2) 
mineralizing  waters,  or  the  alteration  produced  in  the  rock  walls  by 
the  rising  of  heated  or  acidulated  waters  through  fissures  (hydro- 
metamorphism).  Since  such  fissures  are  generally  closed  shortly 
after  by  the  formation  of  veins,  no  pronounced  or  extended  altera- 
tion is  produced  in  the  wall  rock.  Finally,  (3)  vapors  bearing  or 
acting  as  mineralizers  in  passing  through  rock  masses  also  produce 
profound  local  changes  which  would  come  under  the  same  general 
heading  of  contact  metamorphism  (atmometamorphism).  If  the 
rock  undergoes  any  change  in  character,  when  in  contact  with  a 
glacier  or  ice  cover,  this  too  is  to  be  classed  as  thermometamor- 
phism,  while  contact  with  a  heated  meteoric  body  would  also  belong 
here.  In  all  cases  this  is,  therefore,  to  be  regarded  as  a  contact 
metamorphism.  Grabau  (16)  has  suggested  for  this  process  the 
name  cethobalUsm,  from  aW6s,  fire,  and  /?oAAo>,  to  strike,  which 
though  emphasizing  the  heat  element  may,  nevertheless,  be  expanded 
to  cover  all  contact  cases.  Rocks  altered  in  this  manner  would  be 
designated  aethoballic  rocks.  The  essential  of  such  changes  is  that 
they  are  local. 

Dynamic  metamorphism  is  a  term  restricted  to  the  reconstruction 
processes  initiated  by  tectonic  movements,  such  as  faulting,  thrust- 
ing, gliding  or  folding  of  rocks.  Since  it  generally  affects  extensive 
regions,  it  is  also  called  regional  metamorphism,  as  contrasted  with 
the  local  contact  metamorphism.  The  essential  causes  here  are  the 
pressure  due  to  the  tectonic  movements,  and  the  motion  accompany- 
ing them,  the  result  being  a  crushing,  shearing  and  rearrangement 
of  the  component  particles  of  rock,  and  often  a  recrystallization.  A 
secondary  factor  is  the  heat  developed  during  this  movement.  The 
alterations  duevto  impact  with  meteoric  bodies,  whether  hot  or  cold, 
must  also  be  classed  here,  and  it  is  not  improbable  that  in  the  past 
they  have  played  a  considerable  role.  Finally,  it  must  be  consid- 
ered whether  the  normal  changes  supposed  to  go  on  in  the  zone  of 
flowage,  under  the  immense  pressure  of  the  superincumbent  rocks, 
do  not  in  reality  belong  under  the  division  of  dynamic  metamor- 
phism. Grabau  (16)  has  proposed  the  term  symphrattism  from 
o-v/A<£paTTo>,  to  press  together,  for  this  type  of  metamorphism,  and 
for  the  rocks  of  this  type  he  suggests  the  term  symphrattic  rocks. 

As  has  been  repeatedly  emphasized,  especially  by  Johannes  Wal- 
ther,  metamorphic  rocks  of  all  kinds  are  naturally  classed  with  the 
rocks  from  which  they  are  derived,  and  not  as  a  separate  class. 


750  PRINCIPLES    OF    STRATIGRAPHY 


STATIC  METAMORPHISM  OR  DIAGENISM. 

Of  the  diagenetic  processes  affecting  rocks  the  following  may  be 
especially  considered :  (I)  lithification,  (II)  recrystallization,  (III) 
dolomitization,  (IV)  replacement  of  limestone  by  silica,  etc.,  (V) 
desalinification,  (VI)  formation  of  concretions,  (VII)  hydratioo 
and  dehydration. 

I.     LITHIFICATION  OR  INDURATION. 

The  lithification  of  a  rock  is  not  restricted  to  diagenetic  proc- 
esses, but  may  be  greatly  aided  if  not  altogether  caused  by  the 
other  processes  of  metamorphism,  especially  the  dynamic  ones.  Nor 
is  lithification  a  natural  result  of  aging,  for  time  has  little  or  no 
influence  as  a  primary  factor,  though  it  may  become  important 
when  lithification  is  primarily  due  to  some  other  factors.  As  ex- 
amples may  be  cited  the  still  unconsolidated  early  Palaeozoic  sands 
and  clays  of  the  undisturbed  plains  of  Russia,  and  the  much  meta- 
morphosed Eocenic  rocks  of  the  Alps,  or  of  the  Coast  Range  of 
California.  In  the  last  two  cases  cited,  the  alteration  of  the  rocks 
is  of  course  due  to  the  dynamic  disturbances  which  have  affected 
them,  but  consolidation  by  purely  diagenetic  processes  of  recent 
sediments  is  not  unknown.  Thus  the  consolidation  of  the  coral 
sand  of  Bermuda  furnishes  a  good  example  of  a  lithified  rock  of 
modern  origin,  .while  the  Nagelfluh  of  Salzburg,  Austria,  and  other 
districts  illustrates  the  solidification  of  a  clastic  deposit  of  Pleisto- 
cenic  origin.  (See  Chapter  XIV,  p.  601.) 

Lithification  takes  place  with  varying  rapidity  in  rocks  of  dif- 
ferent origin.  Thus  pyrogenic  rocks,  lavas  or  intruded  masses 
solidify  comparatively  rapidly  through  cooling.  This  results  either 
in  congelation  into  an  amorphous  mass  or  in  crystallization — wholly 
or  in  part.  Water  solidifies  with  extreme  rapidity  by  crystalliza- 
tion when  subjected  to  the  proper  reduction  of  temperature.  Snow 
crystals  (atmogenic  rocks)  solidify  somewhat  more  slowly  from 
granular  neve  into  glacier  ice,  a  typical  process  of  diagenetic  meta- 
morphism, though  involving  to  a  certain  extent  recrystallization. 
The  same  method  of  solidification  probably  affects  most  hydrogenic 
rocks.  Organic  rocks  are  solidified  at  the  time  of  their  formation, 
except  organic  oozes  and  granular  organic  rocks  (pulverites,  granu- 
lites,  etc.),  which  may  be  combined  into  masses  much  as  clastic 
rocks  are.  The  lithification  of  clastic  rocks  is  due  to  pressure- 
cohesion,  to  cementation,  or  to  recrystallization. 


DIAGENESIS;    LITHIFICATION  751 

The  methods  of  lithification,  not  confined  to  diagenetic  processes, 
however,  may  thus  be  tabulated : 

1.  Congelation — in  amorphous  bodies. 

2.  Crystallization — chiefly  in  pyrogenic  rocks. 

3.  Recrystallization — chiefly   in  atmogenic  and   hydrogenic 

rocks. 

4.  Welding  or  pressure  cohesion — chiefly  in  clastic  rocks. 

5.  Cementation — chiefly  in  clastic  and  organic  rocks. 

Igneous  rocks  solidify  by  congelation  into  an  amorphous  glass 
(obsidian,  etc.)  or  by  crystallization.  Atmogenic  snow  crystals  con- 
solidate into  firn  and  glacier  ice  by  a  process  of  recrystallization, 
when  the  smaller  crystals  are  destroyed  to  the  gain  of  the  larger 
ones.  This  is  also  true  of  granular  hydrogenic  rocks  such  as  rock 
salt  and  gypsum.  Hydrogenic  rocks  are  also  solidified  through 
cementation  by  precipitated  material  of  the  same  kind.  Biogenic 
rocks  are  usually  consolidated  by  the  precipitation  of  calcium  car- 
bonate under  the  influence  of  decaying  organic  matter  and  the  for- 
mation of  ammonium  carbonate. 

Sphserites,  granulites  and  pulverites,  of  whatever  origin,  are  gen- 
erally consolidated  by  the  same  agents  which  consolidate  the  clastic 
strata. 

LITHIFICATION  OR  INDURATION  OF  CLASTIC  ROCKS.  Under  this 
heading  will  also  be  included  the  granular  or  pulverulent  endoge- 
netic  substances.  The  two  chief  methods  are  :  ( I )  Pressure-cohe- 
sion, or  welding,  and  (2)  cementation.  Recrystallization,  especially 
through  secondary  enlargement,  also  consolidates  loose  material,  but 
is  more  common  in  rocks  already  lithified.  Though  distinct  proc- 
esses, they  seldom  if  ever,  occur  wholly  alone,  both  welding  and 
cementation  generally  taking  place  at  the  same  time,  though  in 
unequal  amount.  Recrystallization  may  accompany  these  processes. 

i.  Welding.  (Van  Hise-34:  595-597,  670-671.)  This  is  a  proc- 
ess of  mechanical  consolidation  caused  either  by  the  pressure  of 
superincumbent  rocks  or  by  tectonic  movements.  This  pressure  re- 
sults in  bringing  closely  together  the  particles  of  which  the  rocks 
are  composed.  If  water  is  present,  this  is  squeezed  out,  while  the 
mineral  particles  are  mechanically  readjusted  with  reference  to  one 
another.  The  particles  will  cohere,  because  they  are  brought  so 
close  together  by  the  pressure  that  they  are  within  the  limit  of 
molecular  attraction  of  one  another.  This  takes  place  especially  in 
the  zone  of  anamorphism,  where  the  pressures  in  all  directions  are 
greater  than  the  crushing  strength  of  the  rocks,  and  hence  sufficient 
to  bring  the  particles  within  the  sphere  of  molecular  attraction. 


752  PRINCIPLES    OF    STRATIGRAPHY 

The  depth  at  which  this  occurs  varies  with  the  rock  substances, 
being  comparatively  moderate  for  plastic  substances  like  coal  and 
clay,  and  much  greater  for  refractory  rocks  like  quartzites,  etc. 
(Van  Hise-34:  671.} 

While  universal  within  the  zone  of  anamorphism,  welding  is  not 
unknown  in  the  belt  of  cementation  of  the  zone  of  katamorphism. 
Here  especially  the  lutaceous  sediments  are  affected,  the  arenaceous 
and  coarser -elastics,  especially  when  the  particles  are  of  uniform 
size,  having  too  few  points  of  contact  for  welding  to  occur.  Thus 
quartz  sandstone  of  nearly  uniform  grain  may  become  slightly  co- 
herent by  incomplete  welding,  with  cementation  weak  or  absent,  and 
so  constitute  a  "free-stone,"  so  called  on  account  of  the  ease  with 
which  it  is  quarried  and  cut.  Many  of  the  British  cathedrals  and 
abbeys,  and  some  Continental  ones  as  well,  are  built  of  rocks  of 
this  type,  rocks  which  from  their  uniformity  of  grain  and  ready 
response  to  the  gravers'  tools  made  possible  the  elaborate  carvings 
which  adorn  these  structures.  In  not  a  few  cases  this  rock  seems 
to  have  been  formed  by  the  induration  of  former  wind-blown  sands. 
The  slight  cohesion  of  the  round  and  uniform-grained  Sylvania 
sandstone  (Siluric)  of  Michigan,  Ohio  and  Canada,  and  of  the 
scarcely  more  coherent  Saint  Peter  sandstone  of  the  United  States 
furnishes  examples  of  cases  where  induration  has  scarcely  been 
effected,  though  what  there  is  may  probably  be  referred  to  welding 
processes.  This  is  seen  in  the  fact  that  these  sandstones  are  almost 
absolutely  free  from  foreign  matter,  which  might  act  as  a  cement, 
while,  except  in  rare  cases,  secondary  silica  has  not  been  deposited. 

Cohesion  may  occur  in  lutaceous  sediments  without  complete 
exclusion  of  water.  Thus  Becker  (7:157)  has  shown  that,  "when 
the  films  of  water  between  the  particles  become  very  thin,  they  may 
become  an  important  factor  in  the  coherence  of  the  rocks.  The 
molecular  attraction  of  the  water  films  and  the  adjacent  particles, 
or  their  adhesion,  and  the  cohesion  of  the  molecules  of  the  films 
may  be  sufficient  to  give  the  rocks  a  certain  amount  of  strength." 
(Van  Hise-34 : 506. )  Thus  muds  and  silts  welded  in  this  manner 
may  have  a  marked  coherence. 

The  squeezing  out  of  the  water,  in  whole  or  in  part,  the  rear- 
rangement of  particles,  and  the  partial  compression  of  the  particles 
themselves  result  in  a  reduction  of  volume.  Thus  a  considerable 
reduction  in  the  thickness  of  a  formation  may  occur.  Fossil  shells 
or  other  organisms  in  such  a  formation  may  be  pressed  flat  or 
crushed  unless  previously  altered  so  as  to  be  resistant.  The  gener- 
ally flattened  or  crushed  character  of  brachiopods  and  other  shells  in 
Palaeozoic  shales  are  good  illustrations.  If,  however,  a  resistant 


DIAGENESIS :     LITHIFICATION  753 

structure,  such  as  a  calcareous  or  other  concretion,  exists  in  the 
rock,  this  will  resist  compression  more  than  the  enclosing  mud,  and 
so  the  layers  of  the  latter  may  assume  an  upward  or  downward 
curving  attitude  arching  over  or  under  the  concretion,  or,  if  the 
latter  is  large,  end  abruptly  against  it,  sometimes  with  the  occur- 
rence of  slickensided  surfaces  on  the  exterior  of  the  concretion. 
Stylolites  also  belong  in  this  category  of  pressure  structures.  They 
will  be  more  fully  discussed  beyond. 

That  rocks  are  ordinarily  under  great  strain  from  lateral  and 
vertical  pressure  has  been  shown  by  the  fact  that  when  the  pressure 
is  relieved,  as  in  quarrying,  expansion  takes  place,  while  upward 
bucklings  of  the  quarry  floor  are  also  frequently  observed.  (Niles— 
24;  25  ;  Johnston-2o;  Cramer-o,;  10.) 

The  further  phenomena  resulting  from  pressure  will  be  more 
fully  discussed  under  symphrattism  or  dynamo-metamorphism. 

2.  Cementation.  This  is  accomplished  by  the  deposition,  in  the 
pores  of  the  rock  mass  and  between  the  particles,  of  a  substance 
which  will  bind  them  together.  The  material  is  brought  in  solution 
by  the  percolating  rain  or  ground  water,  and  may  be  derived  from 
a  distance,  from  immediately  adjoining  formations,  or  from  the 
formation  in  question  itself.  Thus  the  calcareous  sands  of  the 
dunes  on  Bermuda  are  cemented  by  the  rain  water  which  percolates 
through  them  and  which  dissolves  some  of  the  lime  only  to  redeposit 
it  elsewhere  in  the  same  formation.  The  oolite  grains  of  Gran 
Canaria  in  the  Canary  Islands  are  cemented  by  lime  deposited  by 
the  sea  water  which  is  instrumental  in  forming  these  oolite  grains. 
This,  as  in  the  similar  cementation  of  organic  lime  accumulations, 
on  coral  reefs,  etc.,  is  brought  about  by  the  separation  from  the 
water  of  additional  lime,  through  the  decay  of  the  organic  matter 
and  the  formation  of  ammonium  carbonates  in  the  warm  waters, 
this  chemical  reacting  with  the  lime  salts  in  solution  in  the  sea 
water.  Pleistocenic  gravels  are  often  cemented  by  the  lime  derived 
from  a  partial  solution  of  the  limestone  pebbles  which  they  contain 
or  which  are  found  in  an  overlying  gravel  or  sand.  Examples  of 
this  are  not  uncommon  in  limestone  regions.  The  great  Pleisto- 
cenic Nagefluh  deposit  of  the  Salzburg  region  is  an  example  of  the 
cementation  of  a  deposit  in  this  manner  never  buried  under  younger 
formations.  The  pebbles  and  grains  of  the  rock  are  so  firmly 
cemented  that  the  galleries  and  crypts,  cut  into  the  formation  and 
dating  back  to  the  third  century,  are  still  perfectly  preserved. 
Pleistocenic  delta  deposits  exposed  near  Lewiston,  New  York,  and 
formed  when  the  ice  front  rested  near  the  Niagara  escarpment,  and 
before  Lake  Iroquois  came  into  existence,  have  become  consolidated 


754  PRINCIPLES    OF    STRATIGRAPHY 

by  lime  cementation  so  as  to  form  a  fairly  cohesive  rock,  showing 
well  the  oblique  bedding  of  the  fore-set  beds. 

The  porosity  of  the  rock  is  an  important  factor  in  aiding  cemen- 
tation. Other  things  being  equal,  the  more  porous  rocks  will  have  a 
better  chance  of  cementation.  Thus  the  Columbian  gravels  (Pleis- 
tocenic)  of  the  Raritan  Bay  region  in  New  Jersey  are  frequently 
cemented  into  a  hard  pebbly  rock,  the  yellowish  well-worn  quartz 
pebbles  being  embedded  in  a  deep  brown  sandstone  cemented  by 
iron  oxide,  the  whole  resembling  a  giant  peanut  brittle.  The  under- 
lying Cretacic  strata,  on  the  other  hand,  are  unconsolidated  except 
where  locally  some  of  the  sands  are  bound  together  by  iron  oxide. 
Certain  layers  in  the  Monument  Creek  Tertiary  sandstone  of  Colo- 
rado Springs  are  strongly  cemented  by  iron  oxide,  while  the  re- 
mainder of  the  sandstone  mass  is  free  from  such  cement.  As  a 
result,  monuments  are  carved  by  the  wind  out  of  these  rocks,  the 
iron-cemented  layers  forming  the  capping  stones  of  these  monu- 
ments. In  the  Miocenic  deposits  of  Baden,  near  Vienna,  the  shell- 
bearing  pebble  beds  are  often  cemented  by  lime  into  a  fairly  re- 
sistant rock,  while  the  clays  are  entirely  unconsolidated. 

The  principal  minerals  deposited  between  the  particles  of  a  rock 
to  form  a  cement  are  lime,  iron  and  silica.  Silica  may  be  in  the 
form  of  a  colloidal  cement,  but  in  quartz  sandstone  it  is  far  more 
often  deposited  in  such  a  way  as  to  have  optical  and  crystallographic 
continuity  with  the  silica  of  the  grain  it  surrounds.  This  secondary 
enlargement  of  a  quartz  grain,  forming  more  or  less  perfect  crystals 
which  interlock  closely,  is  not  an  uncommon  thing  and  may  result 
in  the  formation  of  a  hard  and  strongly  indurated  rock.  Neverthe- 
less, such  close  cohesion  of  new  grown  crystals  does  not  always  take 
place,  and  the  mass  will  fall  to  pieces  at  the  blow  of  a  hammer, 
leaving  a  mass  of  angular  quartz  crystals  which  only  under  the 
microscope  show  that  they  represent  the  secondary  development  by 
addition  of  the  originally  more  or  less  well-rounded  quartz  grains. 
This  is  not  an  uncommon  source  of  angular  quartz  grains. 

Van  Hise  mentions  as  the  most  important  cementing  substances : 
silica,  iron  oxide  and  aluminum  oxide,  among  the  oxides;  calcite, 
dolomite  and  siderite  among  the  carbonates,  both  hydrous  and 
anhydrous  silicates,*  and  marcasite  and  pyrite  among  the  sulphides. 
(Van  Hise-34:  621-622.) 

The  Keweenawan  sandstone  of  Lake  Superior  may  be  cited  as  a 
case  in  which  the  cementation  is  largely  due  to  the  deposition  of 

.  *  Among  the  hydrous  silicates  are:  (i)  zeolites  and  prehnite;  (2)  chlorites; 
(3)  epidotes;  (4)  serpentine  and  talc.  Among  the  anhydrous  silicates  are  feld- 
spars, hornblende  and  mica. 


DIAGENESIS :     RECRYSTALLIZATION  755 

feldspar  upon  worn  grains  of  that  mineral,  the  old  and  new  mineral 
being  in  optical  continuity.  (Van  Hise-32.)  The  sandstone  con- 
tains both  orthoclases  and  plagioclases,  and  both  are  enlarged  by 
deposition  of  new  material  in  optical  continuity  with  the  old.  Horn- 
blende has  also  been  found  to  be  secondarily  enlarged  in  old  volcanic 
tuffs. 

Quart  zites  and  Novaculites. 

When  quartz  sandstones  are  so  completely  cemented  by  second- 
ary silica,  whether  deposited  independently  or  in  optical  continuity 
with  the  original  quartz  grains,  that  the  rock  will  break  across  the 
original  grains  rather  than  between  them,  the  rock  is  called  a 
quartzite.  If  the  original  grain  of  the  quartz  rock  was  a  luta- 
ceous  one,  the  result  01  this  excessive  induration  is  a  novaculite. 


Lithification  of  Clastics  Largely  a  Supramarine  Process. 

Since  lithification  of  elastics  by  cementation  and  recrystallization 
requires  the  active  circulation  of  ground  water,  it  is  apparent  that 
it  is  chiefly  effective  after  the  deposits  in  question  have  been  lifted 
above  sea-level,  if  they  originally  were  marine.  This  is  not  entirely 
true  for  processes  of  recrystallization,  which  may  go  on  even  be- 
neath sea-level. 

II.     RECRYSTALLIZATION. 

Recrystallization  of  the  mineral  constituents  may  affect  all  rocks, 
and  occur  under  static,  dynamic  or  contactic  conditions.  As  a  proc- 
ess of  diagenism  it  often  produces  marked  results,  though  these 
are  never  carried  to  the  extremes  which  are  attained  when  it  acts 
as  a  process  of  symphrattism.  When  it  takes  place  in  unconsoli- 
dated  material  it  may  become  a  method  of  lithification,  but  it  is 
more  commonly  found  in  rocks  already  consolidated  by  one  or  the 
other  method.  As  a  method  of  change  from  a  less  stable  to  a  more 
stable  form  of  mineral  it  is  of  the  greatest  importance.  Thus  the 
original  less  stable  forms  of  CaCO3,  aragonite,  ktypeit,  found  in 
marine  oolites  and  organic  deposits,  are  changed  to  the  more  stable 
form  calcite.  (See  Chapter  IX.)  In  the  case  of  organic  remains  so 
altered,  the  finer  structural  features  are  commonly  lost. 

Recrystallization  is  especially  effective  in  the  more  soluble  rocks, 


756  PRINCIPLES    OF    STRATIGRAPHY 

such  as  limestones,  gypsum  and  salt,  though  the  secondary  enlarge- 
ment of  quartz  crystals  in  reality  also  belongs  here.  Gypsum,  anhy- 
drite, rock  salt  and  granular  snow  are  other  substances  easily  sub- 
ject to  recrystallization.  In  this  process  the  smaller  particles  are 
commonly  dissolved  and  their  material  added  to  the  larger  ones. 
In  the  zone  of  katamorphism,  solution  and  redeposition  are  going 
on  throughout  the  limestone  with  the  result  that  the  entire  mass  is 
gradually  recrystallized.  This  may  affect  both  loose  aggregates  of 
calcite  grains  which  thereby  become  consolidated,  and  it  may  affect 
indurated  limestones  which  are  then  gradually  altered  toward  the 
condition  of  marble.  True  marble  is  probably  formed  only  under 
the  influence  of  dynamic  forces,  but  many  recrystallizations  come 
close  to  approaching  this  state. 

It  is  often  assumed  that  recrystallization  has  affected  most  of 
the  older  Palaeozoic  limestones,  because  of  their  lack  of  organic 
remains,  which,  it  is  argued,  are  destroyed  by  recrystallization.  It 
may  be  questioned  whether  organic  remains  are  ever  destroyed  by 
ordinary  recrystallization,  though  there  is  no  doubt  of  this  when 
recrystallization  under  dynamic  influences  goes  on.  In  the  case  of 
many  of  the  older  Palaeozoic  limestones,  however,  the  absence  of 
organic  remains  is  a  primary  character.  Many  of  these  limestones 
were  deposited  as  lime  muds  and  silts  derived  from  the  erosion  of 
still  older  limestones,  and  without  the  direct  participation  in  their 
formation  of  lime-secreting  organisms. 

Rock  salt  deposits  on  recrystallization  tend  to  become  coarser, 
as  in  the  case  of  the  Polish  deposits.  The  same  is  true  for  gypsum, 
which  sometimes  crystallizes  out  into  masses  of  large  dimensions. 
The  largest  found  up  to  date  in  Utah  measured  in  some  cases  150 
cm.  in  greatest  dimension.  When  deeply  buried,  gypsum  loses  its 
water  under  the  influence  of  pressure  and  recrystallizes  into  anhy- 
drite. This  brings  with  it  a  decrease  of  volume  of  38%. 

An  important  point  for  consideration  lies  in  the  fact  that  recrys- 
tallization is  favored  by  pressure.  The  greater  the  pressure,  the 
more  likely  is  the  deformation  to  be  accomplished  by  recrystal- 
lization. 

Pressure  Phenomena  Due  to  Recrystallization. 

In  rocks  of  homogeneous  character  and  fine  grain,  recrystalliza- 
tion may  have  a  deformative  effect  on  the  original  structure  lines 
and  not  infrequently  upon  the  enclosing  strata.  This  is  especially 
well  seen  in  the  salt  deposits  of  undisturbed  regions,  such  as  the 
Zechstein  salt  of  north  Germany  and  the  Salina  salt  of  New  York. 


DIAGENESIS:     ENTEROLITHIC    STRUCTURE      757 

In  the  former,  where  the  enclosing  rocks  are  undisturbed,  the 
layers  of  brightly  colored  bittern  salts  and  of  gypsum  often  show 
a  remarkable  flexuous,  sinuous  or  disrupted  character  not  unlike  a 
structure  produced  by  strong  compressive  strains  during  tectonic 
deformation.  That  such  deformation  is  not  tectonic  can  often  be 
shown  by  the  undisturbed  character  of  the  enclosing  sandstones  and 
shales.  Thus,  in  the  Salina  deposit  of  central  New  York,  some  of 
the  alternating  salt  and  gypsum  layers  occasionally  show  a  pro- 
nounced flexing  and  overfolding,  while  others  are  wholly  undis- 
turbed. This  is  well  shown  in  the  following  illustration  reproduced 
from  Everding  (Fig.  159)  and  representing  the  endolithic  deforma- 


FIG.  159.  Section  of  the  potash  layers  of  the  Berlepsch  shaft  near  Stassfurt. 
Scale  i  :35.  The  vertically  lined  beds  are  carnallite ;  the  beds 
with  horizontal  dashes  are  rock  salt;  the  deformed  layers  (white) 
are  kieserite.  (After  Everding.) 


tion  of  the  potash  layers  in  the  Berlepsch  salt  shaft  near  Stassfurt. 
Here  the  rock  salt  and  the  carnallite  are  apparently  undisturbed, 
while  the  kieserite  bands  within  the  carnallite  layers  show  most 
pronounced  distortions  in  different  directions.  "The  forces,"  says 
Arrhenius  in  this  connection,  "which  have  brought  about  this  pecu- 
liar deformation,  are  evidently  of  very  local  character,  and  con- 
fined to  the  respective. carnallite  layers."  Arrhenius  concludes  that 
tectonic  forces  cannot  be  the  cause  which  produced  these  deforma- 
tions. (Arrhenius-4.) 

From  the  resemblance  of  the  distorted  layers  to  the  convolutions 
of  an  intestine,  this  structure  has  come  to  be  known  in  German 
scientific  literature  as  "Gekrose"  structure,  a  name  first  applied  by 
Koken  in  1900.  (22.)  The  English  equivalent  of  this  term,  pro- 


758 


PRINCIPLES    OF    STRATIGRAPHY 


posed  by  me  some  time  ago,  and  first  used  in  print  by  Harm  (18), 
is  enterolithic  structure. 

What  is  believed  by  many  to  represent  extreme  cases  of  defor- 
mation due  to  endogenetic  causes  is  found  in  the  remarkable  salt 
domes  of  Louisiana  and  eastern  Texas,  and  of  North  Germany,  es- 
pecially in  middle  and  northern  Hanover  and  Brunswick,  extending 
as  far  as  the  Elbe.  Similar  occurrences  are  reported  from  Tran- 
sylvania, on  both  sides  of  the  Pyrenees,  and  from  southern  Algeria 
(Fig.  160). 

These  "salt  domes''  are  elliptical  in  section,  with  folded,  often 
much  distorted  layers  of  salt,  gypsum,  and  in  some  sections  potash 
salts,  which  rise  through  the  enclosing  strata,  deforming  them,  and 
maintaining  a  plug-like  relation  to  them.  It  is  true  that  some  writers 


FIG.  160.     Section  and  ground  plan   of  a   salt  dome   in  the    Moros   Valley, 
Hungary.     (After  Lamprecht  in  Fiirer's  Salzbergbau.) 

(Stille,  papers  cited  by  Hahn-i?)  have  explained  these  relation- 
ships as  due  to  repeated  foldings,  but  the  consensus  of  opinion 
(Hahn-i7)  seems  to  be  that,  while  some  folding  has  undoubtedly 
occurred  in  certain  places,  the  main  force  was  the  endogenetic  one 
due  to  the  crystallizing  force  of  the  salts  and  to  metasomatic  proc- 
'esses.  (Arrhenius-4.) 

Enterolithic  structure  is  also  a  frequent  occurrence  in  fine- 
grained limestones  or  dolomites.  A  remarkably  fine  example  is 
seen  in  the  basal  "hydraulic"  limestones  of  the  Lockport  series  of 
Siluric  age,  in  a  section  opened  by  the  canyon  of  Niagara.  The 
strata  are  finely  shown  along  the  railroad  bed  on  the  right  bank  of 
the  canyon.  This  structure  is  equally  well  developed  (Fig.  161)  in 
the  Upper  Muschelkalk  of  the  Neckar  Valley,  in  Wiirttemberg,  Ger- 
many (Koken-22),  and  will  probably  be  recognized  in  other  forma- 
tions. The  essential  feature  is  here,  as  pointed  out  by  Hahn,  that 
the  deformation  is  in  all  directions,*  not  in  certain  ones,  as  would 

*  The  multi-  gyro-  and  a-polar  deformations  of  Lachmann. 


DIAGENESIS:     ENTEROLITHIC    STRUCTURE      759 

be  the  case  in  tectonic  or  in  gliding  deformations.  Thus  deforma- 
tion is  shown  in  whichever  direction  the  section  of  the  formation  is 
cut,  nor  is  there  any  evidence  of  slickensiding,  such  as  is  to  be 
expected  if  the  deformation  is  tectonic. 

Koken,  who  described  the  disturbed  layers  of  the  Upper  Mus- 
chelkalk  of  the  Neckar  Valley  in  detail,  and  originated  the  name 
Gekrosekalk  for  them,  held  that  the  folding  and  wrinkling  were  due 
to  vertical  pressure  of  overlying  rocks  upon  the  still  plastic  layers. 
He  notes,  however,  that  the  folds  are  notably  sharp  and  their  limbs 
are  thickened  as  is  the  case  in  deformations  formed  by  swelling 


Myophoria  Gpl_dfussi 


FIG.  161.     Enterolithic  structure  in  the  Upper  Muschelkalk  (Gekrosekalk)  of 
the  Neckar  Valley  in  Wiirttemberg,  Germany.     (After  Koken.) 

masses,  such  as  gypsum,  but  not  through  horizontal  pressure.  While 
it  is  not  difficult  to  conceive  that  mere  vertical  pressure  on  still 
plastic  layers  can  produce  deformation  of  these  layers,  it  is  not 
quite  clear  what  should  cause  the  retention  of  plasticity  in  some 
layers  and  not  in  others.  The  deformed  Muschelkalk  layers  are 
bluish,  argillaceous  calcilutytes,  much  like  the  similarly  deformed 
layers  of  the  Niagara  section.  In  both  cases  internal  pressure  due 
to  crystallization  seems  to  have  been  an  active  agent  in  the  deforma- 
tion of  the  rock. 


III.       DOLOMITIZATION  OF  LIMESTONES. 

The  change  of  limestones  into  dolomites,  or  dolomitization,  has 
occurred  in  all  geologic  ages  and  is  in  progress  to-day.     (Pfaff-26.) 


760  PRINCIPLES    OF    STRATIGRAPHY 

True,  not  all  dolomites  are  of  secondary  origin,  some  being  no  doubt 
deposited  as  dolomite  rock  in  the  beginning.  Among  dolomites  of 
secondary  origin  we  may  distinguish  those  derived  by  the  clastation 
and  redeposition  of  older  dolomites  and  those  due  to  the  replace- 
ment of  limestones.  Only  the  latter  class  belongs  here,  but  the 
dolomites  of  clastic  origin  deserve  brief  attention.  Here  belong 
the  many  well-bedded,  fine  and  uniformly  grained  rocks  with  few 
or  no  fossils  which  abound  in  many  Palaeozoic  and  later  forma- 
tions. As  a  typical  example  may  be  mentioned  the  Monroe  (Upper 
Siluric)  dolomites  of  Michigan,  Ohio  and  Ontario,  which  have 
most  probably  been  derived  by  the  destruction  of  the  older  Niagaran 
dolomites  and  deposited  as  dolomitic  sand  and  mud.  This  is  prob- 
ably the  origin  of  most  of  the  fine-grained,  well-bedded  dolomites 
which,  from  the  fact  that  they  contain  scattered  fossils,  are  seen 
not  to  be  the  product  of  alteration  of  limestone. 

When  limestones  and  dolomites  are  found  interstratified,  the 
successive  beds  being  sharply  differentiated  from  one  another,  this 
seems  to  be  most  satisfactorily  explained  as  a  primary  difference  in 
the  materials  deposited.  Suess  (31,  11:262)  regards  this  altera- 
tion in  the  Plattenkalke  as  due  to  alternate  chemical  precipitation 
of  dolomites  and  limestones,  but  in  practically  all  rocks  of  this 
type  a  clastic  origin  of  the  deposit  must  be  postulated.  In  other 
words,  the  beds  are  calcilutytes,  some  of  them  pure,  others  mag- 
nesian,  the  mud  being  derived  alternately  from  calcareous  and  mag- 
nesian  sources.  Or,  again,  the  limestones  may  be  of  organic  origin, 
while  the  enclosed  dolomites  are  of  terrigenous  origin,  being  derived 
from  the  erosion  of  dolomites  forming  a  portion  of  the  land,  and 
such  alternation  would  have  no  more  significance  than  alternations 
of  limestones  (of  thalassigenous  origin)  and  shales  (of  terrigenous 
origin).  The  possibility  of  secondary  separation  of  a  mixture  of 
lime  and  dolomite  grains  by  agitation  of  the  water  and  the  unequal 
settling  according  to  specific  gravity  must  not  be  overlooked. 

Secondary  dolomites  due  to  diagenetic  alteration  processes  may 
originate  either  before  or  after  the  original  limestones  are  raised 
above  the  sea-level.  ( Steidtmann-3o. )  Such  alteration  may  be 
primarily  a  process  of  leaching,  either  under  the  sea  by  sea  water 
or  by  the  ground  water  circulating  through  the  upper  zones  of  the 
earth's  surface.  By  leaching  out  of  the  lime  the  proportion  of  the 
original  magnesian  content  is  greatly  increased.  Such  differential 
leaching  is  due  to  the  fact  that  calcium  carbonate  is  several  times 
as  soluble  as  magnesium  carbonate  as  first  shown  by  Bischoff.  When 
it  occurs,  one  result  is  the  rendering  porous  of  the  altered  rock, 
which,  if  under  pressure,  may  actually  collapse.  The  process  of 


DIAGENESIS :     DOLOMITIZATION  761 

alteration  may  on  the  other  hand  be  one  of  secondary  replacement 
of  calcium  by  magnesium.  Such  replacement  in  the  sea  had  appar- 
ently taken  place  in  the  case  of  coral  rock  reported  by  Dana  (12: 
jpj)  from  the  elevated  reefs  of  Makatea  Island  in  the  Pacific;  this 
rock  contained  38.7%  °f  magnesium  carbonate,  whereas  such  rock 
usually  contains  less  than  i%.  Similar  alterations  have  been  re- 
ported by  others,  thus  Branner  (8:26 4)  found  6.95%  of  magnesia, 
equivalent  to  14.5%  MgCO3,  in  reef  rock  of  Porta  do  Mangue, 
Brazil;  the  corals  of  the  reef  containing  only  from  0.2  to  0.99% 
of  MgO.  Similarly  Skeats  (28)  reports  analyses  of  modern  coral 
rock  from  the  Pacific  with  43.3%  of  MgCO3.  Such  alterations 
have  also  been  reported  from  Funafuti,  the  deep  boring  on  which 
showed  16.4%  MgCO3  at  a  depth  of  500  feet,  16%  MgCO3  at  640 
feet,  with  much  smaller  but  variable  percentages  above  and  below. 
A  boring  at  Key  West  showed  the  highest  percentage  of  MgO 
(6.7%)  at  a  depth  of  775  feet,  the  percentage  of  CaO  at  that  depth 
being  46.53%.  At  a  depth  of  25  feet  and  1,400  feet  the  two  minima 
occurred  (0.29%  and  0.30%  respectively).  » 

Metasomatic  replacement  through  the  agency  of  ground  water 
is  also  an  active  means  by  which  dolomites  are  produced.  In  some 
cases  it  is  less  effective  than  submarine  replacement,  principally 
because  sea  water  carries  more  magnesium  than  is  found  in  such 
underground  circulation.  Where  such  magnesia  is  supplied,  how- 
ever, as  in  regions  of  decomposing  magnesium-bearing  rocks,  this 
ground  water  replacement  may  be  very  effective.  The  magnesia 
is  of  course  obtained  from  the  belt  of  weathering  where  it  occurs 
as  carbonate  in  older  dolomites,  etc.,  or  as  silicate  in  crystalline 
rocks  and  minerals  (garnet,  staurolite,  tourmaline,  chondrodite, 
chlorite  and  the  zeolites,  etc.).  The  silicates  are  subject  to  carbona- 
tion  (see  ante,  pp.  35,  178),  and  the  carbonate  then  passes  into  solu- 
tion and  is  carried  downward  to  the  belt  of  cementation,  when,  on 
coming  in  contact  with  limestones  poor  in  magnesia,  replacement 
takes  place. 

Local  dolomitizations  also  occur,  as  for  example  at  Aspen,  Colo- 
rado, where  hot  magnesian  spring  waters  rising  through  the  lime- 
stone locally  alter  it  to  dolomite.  These  are,  however,  not  dia- 
genetic,  but  belong  to  the  division  of  contact  metamorphisms.  In 
general  limestones  which  have  suffered  orogenic  disturbances  are 
more  commonly  altered  to  dolomites  than  those  not  so  disturbed. 
Thus  (Van  Hise-34:#o/)  the  Tertiary  limestones  of  the  Coast 
Range  of  California  and  of  the  Alps  are  more  strongly  magnesian 
than  the  undisturbed  limestones  of  the  same  age.  This  is  due  to 
the  fact  that  disturbed  and  shattered  strata  of  mountain  regions 


762  PRINCIPLES    OF    STRATIGRAPHY 

offer  better  access  to  waters  bearing  magnesium,  through  the  agency 
of  which  the  replacement  is  brought  about.   - 

The  replacement  of  calcite  by  dolomite  involves  a  contraction  of 
12.30%.  Dolomites  due  to  alteration  will  thus  show  a  high  degree 
of  porosity  unless  they  have  been  subjected  to  compression  during 
orogenesis.  Such  porosity  is  shown  in  the  early  Palaeozoic  dolo- 
mites of  the  Mississippi  Valley,  and  also  in  the  Siluric  and  the 
Devonic  dolomites  of  Michigan,  Ohio  and  Canada.  When  the  rock 
is  under  pressure,  as  in  the  zone  of  anamorphism,  mashings  and 
recrystallizations  close  the  openings.  It  is  also  highly  probable  that 
pressure  promotes  dolomitization,  since  this  means  a  decreasing 
volume,  a  result  favored  by  pressure. 


IV.     REPLACEMENT  OF  LIMESTONES  BY  SILICA,  IRON  OXIDE,  ETC. 

Metasomatic  replacement  of  limestone  by  silica  is  a  familiar 
phenomenon.  In*  most  cases  the  replacement  affects  chiefly  certain 
parts  of  the  limestones  which  by  their  structure  seem  best  suited  to 
such  replacement.  Such  are  the  shells,  corals  and  other  organic 
remains  embedded  in  Palaeozoic  or  younger  limestones  where  the 
enclosing  matrix  generally  remains  unaffected,  though  the  fossil 
may  be  completely  replaced.  Oolitic  limestones  also  suffer  replace- 
ment by  silica  and  in  them  often  the  steps  of  replacement  are  shown 
by  the  decrease  in  lime  and  the  increase  in  silica.  A  mass  of  such 
siliceous  oolite  occurs  in  the  lower  Palaeozoic  rocks  of  central 
Pennsylvania,  where  it  covers  an  area  of  about  40  square  miles, 
with  scattered  extensions  over  a  much  wider  area.  Locally  the 
oolite  passes  into  chert.  These  siliceous  oolites  have  bee'n  regarded 
as  originating  in  rising  hot  springs  containing  silica  in  solution 
(Wieland-36:<?<fe),  but  others  (Moore-23;  Brown)'  hold  that 
they  represent  replacements  of  originally  calcareous  oolites.  This 
explanation  is  fully  borne  out  by  the  analysis,  and  the  incomplete- 
ness of  the  replacement  in  many  cases.  (See 'also  Ziegler-37.) 

Replacement  of  limestone  by  iron  oxide  is  also  a  frequent  occur- 
rence. In  the  basal  Siluric  beds  of  Wisconsin,  oolites,  which  from 
their  character  and  appearance  were  most  probably  calcareous  -in 
the  first  place,  have  been  changed  to  iron  oxide  (hematite).  The 
so-called  Clinton  iron  ore  seems  to  be  an  example  of  metasomatic 
replacement  of  limestones,  for  here  the  organic  fragments  (brachi- 
opod  shells,  Bryozoa,  etc.)  are  replaced  by  iron  oxide.  In  the  Gen- 
esee  gorge  at  Rochester  the  steps  in  replacement  could  formerly  be 
observed,  these  being  shown  by  the  progressive  increase  in  iron 


DESALINIFICATION ;    CONCRETIONS  763 

oxide  and  a  corresponding  decrease  in  calcium  carbonate.  It  is 
true  that  these  deposits  have  been  regarded  as  formed  directly  in 
lagoons  and  cut-offs  (Smyth-29)  along  the  sea  coast  of  the  time, 
the  iron  being  brought  by  the  wash  from  the  crystalline  old  land. 
This  theory  has,  however,  been  discarded  by  some  recent  students  of 
the  subject  in  favor  of  the  older  replacement  theory. 

The  replacement  of  calcareous  bodies  of  organic  origin  by  iron 
pyrites  and  other  mineral  substances  will  be  more  fully  discussed 
in  a  later  chapter. 

V.    DESALINIFICATION. 

Among  other  diagenetic  processes  of  importance  may  be  men- 
tioned the  desalinification  of  old  marine  sediments.  As  already 
noted,  the  amount  of  salt  absorbed  by  marine  sediments  varies 
greatly,  chiefly  in  proportion  to  their  pore  space.  (Gerbing-i5  : 85, 
118.)  After  these  sediments  are  raised  into  the  zone  of  circulating 
ground  water,  a  slow  removal  of  these  salts  takes  place.  Under 
arid  climatic  conditions,  as  already  noted,  this  may  go  on  more 
rapidly,  and  the  leached  salt  may  be  redeposited  in  salinas  and 
desert  salt  basins. 


VI.     FORMATION  OF  CONCRETIONS. 

This  has  already  been  discussed  at  some  length  in  a  previous 
chapter  (see  pp.  718-720)  and  need  be  dwelt  on  only  briefly  here. 
Percolating  waters  carrying  lime,  silica  or  other  substances  in  solu- 
tion will  deposit  these  in  the  strata  at  favorable  localities,  forming 
concretions  of  lime,  of  clay-iron-stones,  or  of  silica.  The  first  are 
common  in  calcareous  shales,  often  growing  to  large  size,  with  a 
corresponding  deformation  of  the  enclosing  layers,  through  the 
pressure  of  the  growing  concretion.  Not  infrequently  the  concre- 
tions become  confluent,  forming  a  concretionary  limestone  bed. 
The  nucleus  of  the  concretion  is  very  often  some  organic  fragment 
or  a  shell.  In  the  Champlain  clays  of  Cumberland,  Ontario,  entire 
specimens  of  fish  are  common.  Fish  remains  are  found  in  similar 
concretions  of  the  glacial  and  post-glacial  clays  of  Norway,  16 
species  having  been  recognized  so  far. 

The  common  types  of  concretion  in  the  Mesozoic  and  rakeozoic 
shales  are  the  septaria  already  described.  These  are  often  of  great 
size,  examples  10  feet  in  diameter  occurring  in  the  Devonic  of  New 
York.  They  not  infrequently  contain  a  fish  bone  as  a  nucleus, 


764  PRINCIPLES    OF    STRATIGRAPHY 

while  the  smaller  ones  commonly  have  a  goniatite  shell  at  the  center. 
Frequently  the  stratification  of  the  enclosing  beds  on  either  side 
appears  to  be  continuous  through  the  concretion,  while  the  beds 
above  and  below  are  arched,  owing  to  the  pressure  caused  by  the 
growing  septarium.  Some  of  this  arching  may  be  due  to  the  com- 
pression of  the  shale  around  the  resistant  septarium. 

Calcareous  clay  stones  are  also  common  in  the  loess,  where  they 
are  known  as  Losspuppen  or  Lossmannchen,  by  the  Germans,  as 
Fairy  stones  by  the  Scots,  and  as  Imatra  stones  by  the  Finlanders. 
They  form  in  parallel  lines,  giving  the  deposit  the  appearance  of 
stratification,  though  the  original  bedding  may  have  been4  quite 
diverse.  The  lines  of  concretions  mark  rather  the  successive  levels 
of  ground  water  than  any  structural  features  of  the  rock  itself. 

Claystone  concretions  of  very  regular  form  are  found  in  the 
Champlain  clays  of  the  Connecticut  Valley,  while  clay-iron-stones 
enclosing  ferns,  insects,  crustacean  and  other  remains,  occur  in  the 
Carbonic  shales  of  Grundy  County,  Illinois,  the  fossil-bearing  con- 
cretions of  Mazon  Creek  having  become  famous  on  account  of  their 
well-preserved  organic  remains. 

A  special  form  of  calcareous  concretion  is  known  from  the  black 
Devonic  shales  of  Michigan  and  Ontario,  being  especially  abundant 
at  Kettle  Point,  Lake  Huron.  These  are  spherical,  or  nearly  so, 
and  are  composed  of  radiating  crystals  of  calcium  carbonate,  which, 
growing  outward,  crowd  the  enclosing  strata  until  they  curve  about 
the  concretion.  The  structure  resembles  that  of  a  fibrous  wood, 
and  fragments  are  not  infrequently  mistaken  for  "petrified"  wood. 
Their  manner  of  occurrence,  growth  and  significance  is  fully  dis- 
cussed by  Daly  (n). 

Concretions  of  iron  pyrite  and  ef  marcasite  are  forming  in  many 
strata.  Sometimes  these  are  globular  masses  composed  of  crystals 
of  pyrite,  at  other  times  they  have  a  radial  structure.  Generally 
some  object  of  organic  origin  forms  the  nucleus  around  which  the 
concretion  grows.  In  the  Cretacic  clays  of  New  Jersey  pyrite  con- 
cretions are  forming  around  fragments  of  lignite,  all  stages  of  in- 
crustation and  replacement  being  observable. 

Siliceous  concretions  are  common  in  calcareous  formations. 
Thus  flints  characterize  chalk,  and  chert  layers  abound  in  many 
limestones.  Flints  may  occur  in  continuous  layers  in  massive  chalk 
beds  in  which  their  arrangement  alone  indicates  stratification.  As 
in  the  case  of  the  concretions  in  the  loess,  these  lines  of  flints  need 
not  have  a  necessary  relation  to  the  original  stratification. 

In  many  cases,  however,  the  flints  formed  around  a  siliceous 
sponge  oV  some  other  organism  which  acted  as  a  nucleus  to  attract 


CONTACT   METAMORPHISM  765 

the  silica  in  solution.  Here  the  flints  mark  the  original  distribution 
of  the  organic  remains  in  the  strata.  The  source  of  the  silica  is  to  be 
found  in  the  organic  structures  of  silica  scattered  through  the  mass 
of  the  chalk.  These  are  dissolved  by  the  circulating  waters  and 
redeposited  around  the  organic  nucleus. 

Chert  concretions  occupy  the  same  relation  to  limestone  that 
flints  do  to  chalk.  They  too.  are  derived  from  the  organic  silica 
enclosed  in  the  deposit,  and  redeposited  in  favorable  places.  Con- 
fluent concretions  of  chert  produce  a  more  or  less  continuous  chert 
bed  such  as  is  common  in  the  Devonic  limestones  of  eastern  North 
America.  Chert  concretions  may  enclose  organic  remains,  but  they 
do  not  necessarily  form  around  a  visible  nucleus.  Van  Hise  holds 
that  the  heavier  chert  bands  are  formed  first  by  the  original  segre- 
gation of  siliceous  organisms  and  the  subsequent  enrichment  by 
silica-bearing  ground  waters  of  these  siliceous  strata. 


VII.     HYDRATION  AND  DEHYDRATION. 

Hydration,  or  the  union  with  water  of  originally  anhydrous  de- 
posits, may  produce  profound  results.  Thus  anhydrite  is  changed 
to  gypsum  with  a  corresponding  swelling  of  the  entire  mass  (see 
ante,  p.  177)  and  the  production  of  deformative  structures.  Dehy- 
dration of  gypsum,  on  the  other  hand,  produces  a  corresponding 
shrinking  of  the  entire  mass. 


CONTACT   METAMORPHISM    OR  ^THOBALLISM. 

I.  Pyrometamorphism.  When  rocks  come  in  contact  with 
heated  igneous  masses,  as  a  result  of  subterranean  intrusions,  or  of 
surface  flows,  they  are  more  or  less  altered,  especially  along  the 
contact,  this  alteration  gradually  decreasing  in  intensity  away  from 
the  igneous  mass,  until  its  effect  has  been  entirely  lost.  Such  a 
phase  of  the  contact  metamorphism  may  be  called  igneo-  or  pyro- 
metamorphism.  It  is  especially  manifested  in  the  formation  of 
new  minerals  along  the  contact  zone  and  in  the  introduction  of 
mineral  substances  from  the  igneous  mass.  A  zonal  arrangement 
is  commonly  formed,  different  alteration  products  arising  at  dif- 
ferent distances  from  the  igneous  mass.  Effects  are  felt  by  both 
the  intruded  and  the  intruding  (or  overflowing)  rock;  the  former 
is  exomorphic,  the  second  endomorphic.  The  exomorphic  effect 
from  contact  with  dry  heat  is  first  of  all  a  raising  of  the  temper- 


766  PRINCIPLES    OF    STRATIGRAPHY 

ature  of  the  country  rock  adjacent  to  the  igneous  mass,  such  rise 
in  temperature  reaching  even  fusion  point.  Three  stages  of  influ- 
encing the  country  rock  are  recognized :  baking,  fritting,  and  vitri- 
fication. As  a  result  of  baking,  induration  of  unconsolidated  ma- 
terial will  occur  without  fusion.  Hydrous  minerals  are  dehydrated 
with  a  corresponding  change,  such  as  limonite  to  hematite,  gypsum 
to  anhydrite,  etc.  From  carbonates  the  CO.,  is  given  off,  changing 
limestone  and  dolomites  to  lime  and  magnesium  oxides,  respectively, 
which  have  a  caustic  reaction.  Volatile  gases  are  driven  off,  as  in 
the  case  of  coal  which  is  changed  to  coke. 

Fritting  is  partial  fusion,  carried  to  the  point  where  the  silica 
begins  to  act  on  the  bases,  forming  an  imperfectly  melted  or  fritted 
mass.  Vitrification  results  from  complete  fusion,  the  mass  being 
transformed  into  a  glass. 

The  effects  of  pyrometamorphism  on  clastic  rocks  are  various. 
"Sandstones  are  decolorized  and  often  fritted  to  a  glistening  enamel, 
like  a  porcelainic  mass;  where  the  cement  is  of  a  calcareo-argilla- 
ceous  nature,  this  is  melted  into  a  glass ;  clay  and  mud  are  con- 
verted into  porcelainite  or  brick,  with  marked  change  of  color  in 
many  cases ;  tuffs  and  phonolites  are  so  far  vitrified  as  to  acquire  a 
character  resembling  that  of  obsidian;  brown  coal  is  altered  into 
seam  coal  or  anthracite,  and  these  in  other  cases  into  a  substance 
more  resembling  graphite,  while  in  others  (probably  under  less 
pressure)  the  coal  is  converted  into  coke;  a  prismatic  structure  is 
developed  not  only  in  clays  and  marls,  but  even  in  sandstones,  in 
brown  coal,  in  seam  coal  and  in  dolomite;  limestones  are  altered 
into  crystalline  marble,  often  with  complete  effacement  of  their 
stratification  and  even  of  all  traces  of  their  fossils ;  the  finer  varieties 
of  grauwacke  and  its  associated  shales  are  converted  into  horn- 
stone,  as  in  the  classical  region  of  the  Brocken."  (Irving-iQ:  /<5.) 
The  effects  of  dry  heat  are  very  limited  in  extent,  usually  penetrat- 
ing the  rocks  only  for  a  short  distance.  Where  hydro-  and  gaseo- 
(atmo-)  metamorphism  are  also  active,  as  is  almost  universally  the 
case  in  pyrometamorphism,  the  alterations  will  be  more  extensive 
and  widespread.  The  endomorphic  effects,  or  those  on  the  igneous 
mass  itself,  are  largely  confined  to  a  more  rapid  solidification  and 
hence  the  production  of  finer  crystallization  along  the  contact,  owing 
to  the  chilling  effect  of  the  cool  wall  rock.  The  presence  of  water 
in  the  latter,  of  course,  contributes  to  a  much  modified  result,  as 
already  indicated  in  an  earlier  chapter  (p.  312). 

2.  Hydrometamorphism.  Contact  with  rising  waters,  whether 
hot  or  cold,  carrying  mineralizers,  produces  the  second  type  of  con- 
tact metamorphism  to  which  the  term  hydrometamorphism  may  be 


HYDRO-   AND    ATMOMETAMORPHISM  767 

applied.  As  already  noted,  waters  carrying  magnesium  locally  alter 
limestone  into  dolomites.  Sulphuretted  springs  on  the  Sinai  Penin- 
sula and  at  several  points  along  the  west  coast  of  the  Red  Sea  alter 
coral  limestones  to  gypsum,  and  silica-bearing  waters  locally  alter 
many  reef  limestones  into  siliceous  rocks,  as  in  the  Upper  Devonic 
coral  reef  limestones  of  Grund  in  Harz  and  elsewhere. 

The  greatest  amount  of  alteration  is,  however,  produced  by  the 
highly  heated  waters,  given  off  by  the  igneous  rock,  or  accompany- 
ing the  intrusion.  Here  must  be  classed  all  the  phenomena  of 
secondary  enrichment  of  the  wall  rocks  of  fissures,  by  the  rising 
waters,  though  the  actual  deposits  in  the  fissures  themselves  are  to 
be  classed  as  hydrogem'c  rocks.  The  subject  is  too  special  to  be 
pursued  here  at  greater  length.  The  student  is  referred  to  the  cur- 
rent works  on  ore  deposits  and  to  Van  Hise's  Treatise  on  Meta- 
morphism.  The  work  of  geysers  and  hot  springs  not  directly  asso- 
ciated with  volcanic  intrusions,  in  so  far  as  it  affects  the  wall  rock, 
must  also  be  classed  here'.  The  deposits  formed  by  these  agencies, 
however,  are  hydrogenic  deposits. 

3.  Atmometamorphism.  Contact  with  rising  vapors  and  gases, 
as  in  solfataras,  fumaroles,  etc.,  constitutes  a  third  type  of  contact 
metamorphism,  to  which  the  term  gaseo-  or  atmometamorphism  may 
be  applied.  In  its  broadest  sense  the  weathering  of  rocks  in  con- 
tact with  the  great  gas  envelope  of  the  earth,  the  atmosphere,  also 
belongs  here,  having  the  same  relation  to  the  intrusion  of  gases  as 
the  surface  flow  has  to  the  intruded  igneous  masses.  Practically, 
however,  we  may  confine  gaseous  metamorphism  to  the  work  of  hot 
vapors  and  gases  emitted  in  connection  with  volcanic  activity  and 
always  accompanying  pyrometamorphism.  Such  effects  are  visible 
to-day  in  solfataras  and  fumaroles  where  the  alteration  of  the  wall 
rock  is  proceeding  at  a  rapid  rate. 

The  high  temperature  of  the  vapors  and  their  high -content  of 
active  chemical  agents  make  their  work  of  alteration  much  more 
effective  than  the  work  of  water  solution  would  be.  The  work  of 
the  gases  at  very  high  temperature  is  called  fumarolic,  while  the 
work  of  the  gases  at  lower  temperature  is  solfataric. 

The  most  important  gases  active  in  the  fissures  of  the  rock  are : 
water  vapor,  sulphurous  oxide  (SO2),  chlorine  (CL),  hydrochloric 
acid  (HC1),  hydrofluoric  acid  (HF1),  hydrosulphuric  acid  (H2S), 
sulphuric  acid  gas  (SO3),  carbon  dioxide  (CCX),  oxygen  (O2)  and 
hydrogen  (H2).  Nitrogen  is  of  course  an  abundant  but  essentially 
useless  gas,  and  boric  acid  (H3BO3)  is  sometimes  plentiful.  Among 
the  processes  going  on  in  atmometamorphism  are  the  common  ones 
of  oxidation,  hydration  and  carbonation.  The  last  produces  sodium 


;68  PRINCIPLES    OF    STRATIGRAPHY 

carbonate,  which  is  abundant  at  times.  Chlorinization  results  in  the 
formation  of  NaCl,  KC1,  NH4C1,  Fed,,  CuCL,  MnCL  and  other 
chlorides.  By  the  action  of  sulphuric  acid  alums  are  formed,  of 
which  the  potash  and  soda  alums  are  the  most  abundant.  Gypsum 
is  formed  by  the  action  of  the  calcium-bearing  compounds  and  sul- 
phuric acid,  this  latter  also  forming  Glauber's  salts,  sodium  sul- 
phate and  potassium  sulphate.  The  hydrosulphuric  acid  acting  upon 
various  compounds  forms  sulphides,  and  so  in  turn  each  acid  acting 
upon  the  rocks  forms  compounds  of  various  kinds. 

These  activities  are  of  course  not  always  sharply  isolated.  In- 
deed, solfataric  and  fumarolic  actions  are  a  common  accompaniment 
of  igneous  activity  and  thus  the  alteration  of  the  rocks  is  a  com- 
plex of  pyro-,  hydro-  and  atmometamorphism. 

4.  Biometamorphism.  A  change  in  the  rock  due  to  contact  with 
organisms,  or  biometamorphism,  is  of  little  effect,  when  we  remem- 
ber that  the  change  must  be  produced  by  the  physiological  activities 
of  the  organism.  Thus  the  changing  of  clay  into  bricks  by  baking 
is  not  primarily  an  organic  process,  though  directed  by  man.  It  is 
a  case  of  pyrometamorphism,  even  though  the  heat  is  artificially 
supplied.  Disintegration  of  rocks  by  growing  organisms  is  perhaps 
their  only  significant  metamorphic  activity. 


DYNAMIC  OR   PRESSURE   METAMORPHISM,   OR 
SYMPHRATTISM. 

When  rocks  are  subjected  to  erogenic  disturbances,  their  internal 
structure  will  be  affected  by  the  movement  and  pressure,  and  to 
some  extent  by  the  heat  developed  by  these  processes.  The  effect 
in  slight  deformations  is  often  confined  to  the  planes  of  gliding 
along  which  deformation  has  taken  place.  Here  smooth  gliding  sur- 
faces or  slickensides  are  formed,  often  with  the  development  of  a 
thin  layer  of  mineral  matter,  and  marked  by  striations  and  flutings 
which  indicate  the  direction  of  motion.  Extreme  polishing  some- 
times results  from  such  movements.  Here  belong  the  glacial  stria- 
tions and  groovings  which  are  slickensides  on  a  large  scale. 

The  development  of  a  mineral  coating  on  the  polished  surface 
of  the  gliding  plain  may  be  the  direct  result  of  the  energy  liber- 
ated by  the  gliding  process,  or  it  may  be  the  secondary  deposit  in 
the  fissure,  when  the  surface  of  the  mineral  will  take  on  the  cast 
of  the  striated  surface.  Hematite,  chlorite,  calcite,  pyrite  and  other 
minerals  have  been  active  in  such  wise.  In  some  cases,  however, 
the  mineral  may  have  been  deposited  in  the  fissure  before  slipping 


DYNAMIC  METAMORPHISM  769 

took  place.     In  such  a  case,  the  effect  of  movement  is  seen  on  the 
mineral. 

In  general,  when  extensive  dynamic  disturbances  take  place, 
resulting  in  crushing  and  mashing  of  the  rocks,  new  minerals  and 
new  structures  are  developed.  The  former  are  numerous ;  among 
the  latter  are  cleavage,  fissility,  and  schistosity. 

Different  types  of  rocks  suffer  different  alterations  under  the 
influence  of  the  mass-mechanical  motion  characteristic  of  symphrat- 
tism.  A  few  of  these  alteration  products  may  be  mentioned,  but 
the  student  is  referred  to  special  treatises  on  the  subject  for  more 
detailed  information. 

When  coarse,  clastic  rocks,  or  rudytes,  are  subjected  to  dynamic 
metamorphism,  there  will  generally  result  a  recrystallization  and 
granulation,  and  the  development  of  schistose  structure.  This  is 
especially  the  case  in  the  matrix  in  which,  owing  to  its  great  range 
in  composition,  a  large  variety  of  minerals  may  be  developed.  A 
schist  conglomerate  or  conglomerate  schist  is  produced,  generally 
with  the  pebbles  flattened  and  elongated  and  more  or  less  granulated 
and  recrystallized.  With  extreme  movement,  the  pebbles  may  be 
flattened  into  laminae  or  changed  into  a  variety  of  minerals  accord- 
ing to  their  original  composition.  A  quartz  pebble  may  thus  be 
drawn  out  into  a  lamina  of  granulated  quartz,  often  only  as  thin  as 
cardboard  or  even  as  paper.  Granite  pebbles  may  be  transformed 
into  a  micaceous  lamina  with  quartz  and  feldspar  grains.  The  ma- 
terial of  the  original  pebble  may  become  more  or  less  commingled 
with  the  matrix  so  that  the  outline  of  the  pebble  disappears  and 
finally  all  trace  of  the  conglomeratic  character  is  lost,  the  mass 
being  a  schist  with  laminae  of  varying  composition  interspersed. 
The  matrix  may  become  progressively  slate,  schist  and  foliated 
schist,  the  particles  at  first  winding  in  and  out  among  the  pebbles, 
but  becoming  more  parallel  as  the  pebbles  disappear. 

Impure  arenytes  and  lutytes  may  suffer  changes  similar  to  those 
of  the  matrix  of  rudytes.  Clastic  gneisses  and  schists  are  thus 
produced,  or  exogneisses  and  exoschists,  since  they  are  derived  from 
exogenetic  rocks.  They  are  distinguished  from  endogneisses  and 
endoschists,  or  those  produced  from  endogenetic  (chiefly  pyrogenic) 
rocks,  by  the  parallel  orientation  of  their  mineral  particles,  which 
gives  cleavage  to  the  rock.  This  structure  is  almost  if  not  quite 
universal  with  the  schists  and  gneisses  derived  by  the  metamorphism 
of  sedimentary  rocks,  but  is  commonly  lacking  in  schists  and 
gneisses  produced  from  igneous  rocks. 

The  alteration  of  other  sedimentary  rocks  by  dynamic  meta- 
morphism may  be  briefly  reviewed.  Thus  quartz  sandstone  changes 


770  PRINCIPLES    OF    STRATIGRAPHY 

to  quartzite  and  then  to  quartzite  schist ;  arkoses  into  arkose  schists, 
and  arkose  gneisses ;  grits  into  graywackes,  graywacke  slates,  gray- 
wacke  schists  and  graywacke  gneisses,  and  shales  or  lutytes  into 
lutyte  schists  and  lutyte  gneisses  (pelite  schists  and  pelite  gneisses). 
Limestones  are  changed  to  marble  and  soft  coals  to  anthracites  and 
graphites.  In  general,  pure  sediments  are  the  least  altered,  while 
mixed  sediments  are  likely  to  produce  the  greatest  variety  of  new 
minerals  under  metamorphism. 


.    The  Terms  Slate,  Schist  and  Gneiss. 

The  term  slate,  though  generally  used  as  a  lithological  term, 
is  strictly  applied  only  as  a  structural  one.  A  slate  is  a  metamor- 
phic  rock  of  a  lutaceous  texture  and  homogeneous  character,  split- 
ting into  parallel  leaves,  and  whose  mineral  particles  are  for  the 
most  part  so  small  as  to  be  invisible  to  the  naked  eye.  ( See,  further, 
Chapter  XX.)  A  schist  has  been  defined  as  "a  rock  possessing  a 
crystalline  arrangement  into  separate  folia."  (Geikie-i4: 178.)  A 
typical  schist  has  its  cleavable  minerals  arranged  in  the  same  way 
and  like  one  another  and  large  enough  to  be  for  the  most  part 
visible  to  the  naked  eye.  Mica  is  the  most  important  cleavage- 
making  mineral,  and  the  most  typical  schist  is  one  composed  of 
quartz  and  mica  scales,  a  quartz  mica  schist,  more  commonly  spoken 
of  as  a  mica  schist. 

Van  Hise  has  urged  the  use  of  the  term  schist  in  a  purely 
structural  sense,  much  as  the  terms  shales  and  slate  should  be  used. 
This  is  in  strict  accord  with  the  definition  by  Geikie  given  above. 
In  mineral  composition  and  in  origin  schists  may  vary  greatly. 
Thus  we  may  have  the  ordinary  quartz  mica  schist,  which  contains 
quartz  and  mica  in  about  equal  proportions.  Hornblende  schists 
are  schists  containing  hornblende  and  some  other  minerals,  generally 
feldspar.  Thus  we  may  have  a  hornblende  plagioclase  schist.  If 
the  origin  of  the  schist  is  known  this  may  be  indicated  in  the 
name,  as  arkose  schist,  silicirudyte  schist,  or  if  derived  from  an 
igneous  rock  such  as  gabbro  it  becomes  a  gabbro  schist.  Both  com- 
position and  origin  may  be  indicated,  as  in  the  name  mica-quartz- 
feldspar-arkose-schist. 

In  certain  petrographic  circles,  especially  the  German  ones,  the 
term  schist  was  applied  to  rocks  not^only  having  a  schistose  struc- 
ture, but  also  a  definite  composition.  Thus  quartz  was  considered 
essential  in  the  formation  of  a  schist  and  was  assumed  to  be  pres- 
ent. We  thus  had  mica  schists,  hornblende  schists,  chlorite  schists, 


SLATE;    SCHIST;    GNEISS     ,  771 

etc.,  in  which  the  other  mineral  was  supposed  to  be  quartz.  If 
feldspar  was  present,  the  rock  was  called  a  gneiss.  (Rosenbusch- 
27.)  The  structural  use  of  the  term  seems,  however,  to  be  the 
preferable  one. 

Gneiss  was  originally  defined  as  a  banded  or  foliated  rock  hav- 
ing essentially  the  composition  of  granite,  i.  e.,  quartz,  feldspar  and 
mica  or  hornblende.  The  quartz  and  feldspar  were  taken  as  dis- 
tinctive minerals  and  the  others  added  as  qualifying  prefixes.  Thus, 
mica  gneiss  meant  a  schistose  or  foliated  rock,  consisting  of  quartz, 
feldspar  and  mica;  and  hornblende  gneiss,  the  same  combination 
with  hornblende  added  or  replacing  the  mica.  Such  gneisses  were 
supposed  to  be  metamorphic  derivatives  of  granites.  Since,  how- 
ever, many  rocks,  to  which  the  name  gneiss  has  been  commonly 
applied,  prove  not  to  have  the  composition  above  given,  the  petro- 
graphic  use  of  the  name  must  be  abandoned  in  favor  of  the  struc- 
tural use,  or  the  use  of  the  term  gneiss  as  well  as  schist  must  be 
very  much  restricted.  Van  Hise's  proposition  to  use  the  term  as 
a  purely  structural  one  seems  to  be  the  most  satisfactory  solution, 
and  accordingly  we  may  define  gneiss  as  a  banded  metamorphic 
rock  in  which  crystalline  structure  has  been  developed  and  in  which 
the  bands  are  petrographically  unlike  one  another  and  consist  of 
interlocking  mineral  particles.  The  bands  in  different  gneisses  are 
of  variable  thickness,  ranging  from  a  fraction  of  a  centimeter  to 
many  centimeters  (Van  Hise).  There  may  also  be  a  similar  varia- 
tion and  range  in  thickness  of  the  different  bands  of  the  same  gneiss. 
Thus  the  fundamental  distinction  between  gneiss  and  schist  is  the 
banded  character  of  the  former  as  compared  with  the  homogeneous 
character  of  the  latter.  This  homogeneous  character  is  still  more 
strongly  expressed  in  the  slates  in  which  the  cleavable  mineral  par- 
ticles are  not  visible  as  they  are  in  the  schists. 

Gneiss  may  be  derived  either  from  igneous  or  from  sedimentary 
rocks.  When  derived  from  igneous  rocks  the  parallel  arrangement 
of  the  mineral  particles  which  results  in  cleavage  is  more  often 
lacking. 

General  Terms  for  Metamorphic  Rocks. 

Two  terms  have  come  into  use  for  general  designation  of  meta- 
morphism  in  rocks.  These  are  meta  and  apo.  Meta  is  used  as  a 
prefix  to  any  rock  name  and  designates  that  the  rock  has  been 
altered  without  stating  how  or  to  what  degree.  Thus  we  may  say 
meta-arenyte,  meta-shale,  meta-granite,  meta-diofite,  etc.  Rocks 
already  metamorphosed  to  a  certain  degree  may  undergo  a  second 


772  PRINCIPLES    OF    STRATIGRAPHY 

set  of  changes  producing  meta-graywackes,  meta-quartzite,  etc. 
Here  the  rock  was  first  metamorphosed  to  a  graywacke  or  a  quartz- 
ite,  after  which  a  second  set  of  alterations  occurred. 

Apo  is  used  as  a  prefix  for  rocks  in  which  metasomatic  changes 
have  taken  place  without  entire  loss  of  original  texture  or  structure. 
Thus  a  devitrified  rhyolite  is  an  apo-rhyolite.  (Bascom-5.)  This 
name  applies  especially  to  rocks  which  have  undergone  diagenetic 
alterations  without  loss  of  structure,  though  the  chemical  and  min- 
eral composition  may  differ  greatly  from  those  of  the  original  rock. 
The  term  is  useful  to  call  attention  to  the  original  rock  from  which 
the  new  rock  is  derived.  Thus  quartzite  is  an  apo-arenyte,  gray- 
wacke an  apo-grit,  etc.  When  new  structures  are  produced  we 
obtain  slates,  schists  or  gneisses. 


Variation  in  Metamorphism  of  Strata. 

In  a  given  series  of  metamorphosed  strata  a  change  may  often 
be  noted  in  the  intensity  of  the  metamorphism  as  one  passes  from 
point  to  point.  This  change  may  be  along  the  strike  of  the  strata 
or  across  it.  In  the  first  case,  it  is  generally  gradual,  the  pro- 
foundly metamorphosed  strata  of  one  region  passing  gradually  into 
the  slightly  metamorphosed  equivalent  of  another.  Thus  the  three 
unconformable  series  of  strata,  the  Archaean,  the  Lower  Huronian 
and  the  Upper  Huronian,  are  so  closely  mashed  and  altered  in  the 
western  part  of  the  Marquette  district  of  Michigan  as  to  appear 
completely  conformable  and  suggest  an  inseparable  series.  In  trac- 
ing the  formations  to  the  less  metamorphosed  central  and  eastern 
parts  of  the  district,  the  three  unconformable  series  are  readily 
recognizable  as  well  as  the  original  character  of  the  formations. 

The  change  in  the  degree  of  metamorphism  across  the  strike  is 
generally  more  abrupt.  "Thus  the  rocks  at  the  crown  of  an  arch 
or  at  the  bottom  of  a  trough  may  be  only  partly  metamorphosed, 
while  the  same  formations  on  the  limbs  of  the  folds  may  be  pro- 
foundly metamorphosed,  this  being  due  to  the  difference  in  the 
amount  of  shearing  in  different  parts  of  the  folds,  or  to  the  dying 
out  or  change  in  character  of  orogenic  movements  across  the 
strike."  (Van  Hise-33  :  598-600.}  This  change  is  well  illustrated 
in  the  Hudson  River  series,  which  in  the  Hudson  Valley  is  prac- 
tically unaltered,  but  eastward  across  the  strike  in  the  Taconic 
range  becomes  schists  and  gneisses,  while  in  Vermont  and  parts  of 
eastern  New  York  the  series  changes  to  roofing  slates. 


METAMORPHISM  773 

Age  of  Metamorphic  Rocks. 

Rocks  of  all  ages  may  become  metamorphosed,  but  it  may  be 
stated  for  a  restricted  region  that  the  metamorphosed  rocks  of  that 
region  are  generally  older  than  the  non-metamorphosed  rocks. 
Strictly  considered,  this  should  apply  only  to  symphrattic  rocks, 
since  later  rocks  may  be  affected  by  an  intrusive  sheet  or  laccolith, 
the  effect  dying  out  upward  and  downward  and  thus  not  being 
noticeable  in  older  and  younger  strata.  Or  a  set  of  folded  strata 
may  be  locally  affected  by  intrusions  which  are  visible  in  the  newer 
and  not  in  the  older  strata.  Again  different  strata  are  differently 
affected  by  the  heat  of  a  dike  which  cuts  all  of  them,  and  some  in 
the  middle  of  the  series  may  be  much  altered,  while  lower  strata 
may  be  less  readily  altered.  Even  symphrattic  rocks  are  not  equally 
altered  throughout,  some  very  resistant  strata  being  scarcely  af- 
fected by  the  agents  which  strongly  metamorphose  others. 

While  metamorphism  is  undoubtedly  most  marked  in  pre-Cam- 
bric  and  in  early  Palaeozoic  rocks,  it  is  also  known  in  rocks  of  later 
age,  as  shown  by  the  metamorphic  gold-bearing  slates  of  Jurassic  age 
in  the  Sierra  Nevada  and  in  Sonora,  and  the  Eocenic  marble  of  the 
Himalayas.  See  further,  Correlation  by  Regional  Metamorphism, 
Chapter  XXXII. 


BIBLIOGRAPHY   XIX. 

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Question  of  the  Depth  of  the  Zone  of  Flow  in  the  Earth's  Crust.  Journal 
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2.  ADAMS,  F.  D.,  and  COKER,  ERNEST  G.      1906.    An  Investigation  into 

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CHAPTER   XX. 
DEFORMATION    OF    ROCK    MASSES. 

Having  in  the  preceding  chapters  dealt  at  length  with  the  subject 
of  rock  formation,  or  Litho  gene  sis,  we  must  next  turn  our  attention 
to  the  subject  of  rock  deformation  or  Orogenesis,  i.  e.,  the  making 
of  mountain  structures. 

As  the  result  of  rock  deformation  a  number  of  distinct  struc- 
tural features  come  into  existence,  some  of  which  have  already 
been  noted  in  the  preceding  chapters.  Deformation  may  be  classed 
as  endogenetic  or  exogenetic,  i.  e.,  produced  by  internal  or  external 
causes,  respectively.  Internal  causes  are  diagenetic,  such  as  chemi- 
cal change,  recrystallization,  etc.,  while  external  causes  include 
pressure  and  motion  due  to  gravity,  to  tectonic  disturbances,  etc. 
The  following  types  of  deformation  may  be  considered : 

I.  Endogenetic. 

1.  Endolithic  brecciation. 

2.  Enterolithic  structure. 

3.  Contractive  joints  (prismatic)   (basaltic). 

II.  Exogenetic. 

A.     Gravitational  Deformations. 

a.  Structures  Due  to  Movement. 

4.  Intraformational  brecciation. 

5.  Gliding  deformations. 

6.  Surface  deformation  through  creep. 

b.  Structures  Due  to  Compression. 

7.  Squeezed-out  strata. 

8.  Shaliness. 

9.  Slatiness. 

c.  Of  Complex  Origin. 

10.  Pressure  sutures  and  stylolites. 

11.  Cone-in-cone  structure. 

776 


TYPES    OF    DEFORMATION  777 

B.  Tectonic  or  Orogenic  Deformation. 

12.  Tectonic  joints. 

13.  Earthquake  fissures. 

14.  Slaty  cleavage. 

15.  Fissility. 

16.  Schistosity. 

17.  Gneissoid  structure. 

1 8.  Folding — Anticlines,  synclines,  isoclines,  fan  folds,  mono- 

clines, etc. 

19.  Domes  and  basins. 

20.  Faulting. 

C.  Contact  Deformations. 

21.  Prismatic  structure. 

22.  Insolation  joints. 

D.  Complex  Structures  Partly  Due  to  Deformation. 

23.  Metamorphism. 

24.  Disconformity  and  unconformity. 

ENDOGENETIC  DEFORMATIONS. 

i.  Endolithic  Brecciation.  This  term  is  applied  to  brecciation 
of  strata  caused  by  forces  acting  from  within  the  mass,  such  as 
crystallization  and  especially  swelling  or  hydration,  as  in  the  case 
of  gypsum,  etc.  In  this  last  case  it  is  only  the  extreme  of  entero- 
lithic  structure.  Similar  structures  are  produced  by  contraction  of 
the  rock  mass  on  drying  and  the  disruption  into  blocks  or  cakes 
which  are  subsequently  enclosed  by  later  deposits  and  form  an  endo- 
static  rudyte.  Examples  of  such  have  recently  been  described  by 
Hyde  (11:400-408)  from  the  Coal  Measures  of  Ohio.  Beds  of 
fresh-water  limestone  intercalated  in  the  series  and  deposited  in  a 
playa  lake  were  subject  to  periodic  drying,  as  a  result  of  which  the 
surface  for  several  acres  was  broken  up  into  polygonal  blocks  of 
various  sizes,  the  surfaces  of  which  were  frequently  covered  by 
the  shells  of  the  animals  killed  in  the  drying  of  the  lake.  The 
fragments  seem  to  have  been  exposed  for  a  while  to  weathering 
and  were  then  covered  by  a  second  flooding.  Where  the  covering 
deposits  were  muds,  the  limestone  fragments  form  a  striking  series 
of  pebbles  in  a  lutaceous  matrix  and  often  weather  out  in  relief. 
Many  intraformational  conglomerates  may  have  such  an  origin. 
Such  breccias  are  of  course  closely  similar  to  intraformational  brec- 
cias due  to  gliding  movements  as  described  under  Section  4. 


PRINCIPLES    OF    STRATIGRAPHY 


2.  Enterolithic  Structure.  This  has  already  been  discussed  in 
the  preceding  chapter.  In  so  far  as  it  can  be  shown  that  this  struc- 
ture is  a  purely  diagenetic  one,  brought  about  by  the  swelling  of 
the  mass  either  through  crystallization  or  hydration,  it  properly 
belongs  to  endogenetic  deformations.  If,  on  the  other  hand,  it 
should  be  proven  that  enterolithic  structure  in  some  rocks  is  pro- 
duced by  the  pressure  of  the  overlying  mass  and  the  consequent 
creep  and  rearrangement  of  the  particles  under  pressure,  such  de- 
formation must  be  classed  under  the  gravitational  section  of  the 
exogenetic  class. 

The  important  distinction  between  enterolithic  and  other  de- 
formations, such  as  folding  under  lateral  pressure,  or  gliding  in  a 
given  direction,  lies  in  the  fact  that  the  enterolithic  structure  folds 
in  all  directions — is  apolar  or  multipolar  instead  of  unipolar. 


FIG.  162.  Diagram  illustrating  the  formation  of  contraction  joints  and  of 
desiccation  fissures.  The  normal  form  is  hexagonal,  but,  as 
shown  in  the  left-hand  member,  an  irregular  pentagonal  form  is 
developed  when  one  side  is  suppressed. 

3.  Contraction  Joints — Basaltic  Jointing.  This  is  seen  in  the 
formation  of  mud  cracks  in  lutaceous  sediments  such  as  clay  or 
argillo-calcareous  mud  and  in  the  development  of  prismatic  jointing 
in  cooling  basalt  and  other  igneous  rocks.  In  the  latter  case  the 
prisms  always  form  at  right  angles  to  the  enclosing  surface,  such 
as  the  upper  and  lower  surface  of  a  sill  or  laccolith,  when  the  prisms 
will  be  vertical  or  curved,  or  the  lateral  walls  of  a  dike,  when  the 
prisms  will  be  horizontal.  The  prevalence  of  six-sided  forms  in 
these  prisms  suggests  that  the  crystallizing  force  centers  about 
equidistant  points  in  the  magma,  each  of  which  will  draw  an  equal 
amount  of  the  surrounding  matrix  toward  it  from  all  sides.  This 
results  in  other  equally  spaced  points  between  these  around  which 
the  tension  in  all  directions  is  greatest.  Since  the  points  around 
which  attraction  takes  place  are  all  equally  distant  from  one  an- 


ENDOGENETIC   DEFORMATION  779 

other,  they  form  the  apices  of  a  series  of  equilateral  triangles  and 
the  points  around  which  the  greatest  tension  is  focused  will  be  the 
centers  of  these  triangles.  The  smallest  number  of  cracks  about 
these  central  points  which  will  relieve  the  tension  in  all  directions  is 
three.  If  these  cracks  are  symmetrically  arranged  about  the  point, 
the  angle  between  any  two  of  them  is  120°,  which  is  the  angle 
between  the  two  sides  of  a  hexagonal  prism.  As  shown  in  the 
diagram  (Fig.  162),  this  uniform  contraction  about  equidistant 
points  will  result  in  the  formation  of  a  set  of  uniform  hexagonal 
prisms.  Unequal  development  or  failure  of  the  cracks  to  develop 
about  one  of  the  points  may  lead  to  five-sided  or  other  irregular 
prisms. 

Drying  mud  will  in  like  manner  cause  a  development  of  a  series 
of  prisms  which  typically  are  hexagonal,  but  from  lack  of  homo- 
geneity of  the  material  through  unequal  drying,  or  from  some  other 
cause,  are  frequently  irregular  polygons.  The  prisms  are  seldom 
very  high,  though  in  exceptional  cases  the  cracks  may  penetrate  to 
a  depth  of  ten  feet.  In  general  a  fraction  of  an  inch  is  the  usual 
height  of  the  dried  mud  prisms,  the  sides  of  which  are  slightly 
raised,  giving  a  concave  surface.  (See  ante,  Chapter  XVII.) 

Prismatic  jointing  is  also  sometimes  found  in  undisturbed  hydro- 
genie  rocks.  Examples  of  these  occur  in  some  gypsum  beds  of  the 
Paris  Basin.  It  is  quite  probable  that  this  structure  is  due  to 
pressure  exerted  by  hydration  of  anhydrite  and  so  belongs  to  the 
diagenetic  processes. 


DEFORMATIONS  DUE  TO  EXTRANEOUS  CAUSES— 
EXOGENETIC  DEFORMATIONS. 

This  type  may  be  divided  into  (A)  Gravitational,  (B)  Orogenic, 
and  (C)  Contactic. 

A.     GRAVITATIONAL  DEFORMATIONS. 
a.     Structures  Due  to  Movements. 

4.  Intraformational  Brecciation.  This  has  already  been  dis- 
cussed in  the  chapter  on  Autoclastic  rocks,  but  is  again  mentioned 
here  as  a  structural  feature.  It  is  probably  in  all  cases  an  extreme 
of  the  next  type,  and  so  may  be  considered  in  connection  with  that 
subject.  Here  belong  the  edgewise  conglomerates  of  many  lime- 
stone formations. 


780  PRINCIPLES    OF    STRATIGRAPHY 

5.  Subaquatic,  Gliding-deformation.  Offshore  deposits  of  sedi- 
ments on  a  gently  sloping  sea  or  lake  bottom  may  suffer  from  time 
to  time  deformation  of  the  surface  layers  through  gliding  or  slip- 
ping down  the  gently  inclined  sea  floor.  Such  deformation  has 
been  repeatedly  observed  in  modern  deposits.  The  best  known 
modern  examples  are  those  which  affected  the  village  of  Horgen 
on  the  lake  of  Zurich  in  1875,  and  the  village  of  Zug  in  1887.  Both 
of  these  have  already  been  described  in  Chapter  XV,  p.  658.  The 
most  remarkable  fact  about  the  gliding  in  Zug  was  that  it  took  place 
on  an  average  grade  of  6%  (3°  26'),  while  the  larger  and  more 


FIG.    163.     Folding    accompanying    subaquatic    gliding    in    Miocenic    marl    of 
Oeningen — natural  size.     (After  Heim.) 

pronounced  movement  occurred  on  a  grade  as  low  as  4.4%  (a 
trifle  over  2°  31').  The  material  which  thus  slid  into  the  lake 
was  brecciated  and  folded  with  overfolds,  overthrusts,  reversals  of 
layers,  excessive  strata,  etc.,  and  furnishes  an  excellent  guide  to 
the  interpretation  of  similar  movement  in  the  past.  Among  the 
chief  points  in  which  these  folds  differ  from  those  produced  diage- 
netically  by  swelling  of  gypsum,  or  by  pressure  of  overlying  masses, 
is  that  they  are  of  the  nature  of  normal  folds  due  to  lateral  com- 
pression and  so  show  movement  in  one  direction  only,  whereas  in 
the  case  of  the  other  deformations  movements  in  several  directions 
are  shown.  Furthermore,  the  axes  of  the  folds  are  thickened  in 
the  gliding  as  in  normal  tectonic  folds,  instead  of  the  limbs,  as  is 
the  case  in  folds  due  to  swelling. 


GLIDING  DEFORMATIONS  781 


Examples  of  fossil  subaqueous  soliftuction. 

A.  Miocenic  sublacustrine  glidings  of  Oeningen.  The  Miocenic 
marls  of  Oeningen,  noted  for  their  wonderful  remains  of  insects, 
etc.,  show  in  the  midst  of  these  beds  a  strongly  folded  layer,,  lying 
between  horizontal  beds  of  the  same  character.  These  foldings  are 
so  pronounced  that  they  inevitably  suggest  lateral  compression  as 
the  cause  of  their  production,  yet  the  entirely  undisturbed  charac- 


FIG.    164.      Folding   accompanying   subaquatic   gliding   in    Miocenic   marl   of 
Oeningen.     One-half  natural   size.      (After   Heim.) 


ter  of  the  enclosing  strata  forbids  such  an  assumption.  Another 
feature  which  indicates  gliding  is  the  independence  of  the  folded 
beds  from  the  basal  beds,  against  which  the  limbs  commonly  abut 
directly.  The  axes  of  the  folds  are  notably  thickened,  while  the 
limbs  are  thinned  by  compression  exactly  as  in  tectonic  folding. 
(Figs.  163,  164.) 

B.  Jurassic  deformations  of  this  type  are  known  from  the 
Solnhofen  Plattenkalke,  where  the  so-called  distorted  layer  (krumme 
Lage)  furnishes  a  good  example.  The  zone  has  a  thickness 
of  i  to  1.5  meters,  and  in  it  are  found  all  the  phenomena  of 
folding,  including  folds  5  meters  in  length.  Here  the  glidings  took 
place  in  the  periodically  submerged  lagoons  within  the  reefs  and  the 


782  PRINCIPLES    OF    STRATIGRAPHY 

calcareous  nature  of  the  material  probably  insured  a  partial  cemen- 
tation before  the  gliding  took  place.     (See  Fig.  95,  p.  440.) 

C.  Triassic  examples  are  known  from  the  Muschelkalk  of  Ger- 
many, especially  the  Main  region,  but  not  all  of  the  disturbances 
found  in  this  formation  and  so  fully  described  by  Reis  (20)  belong 


FIG.  165.     Deformation    due    to    subaqueous    gliding,    Muschelkalk,    Franken 
(Germany)    1 150.      (After  Reis.) 

here.  The  enterolithic  structure  described  by  Koken  (13)  from  the 
Neckar  Valley  must  certainly  be  removed  from  this  category  of 
deformation  due  to  submarine  glidings. 

D.  Devonic  examples  of  this  class  have  been  figured  by  Sir 
Wm.  Logan  from  the  Cape  Bon  Ami  limestones  of  Lower  Devonic 
age  from  Gaspe  (Logan-i5 :  jp^)  where  in  division  4  and  less 


FIG.  166.     Deformation    due    to    subaqueous    gliding,    Muschelkalk,    Franken 
(Germany)  1 150.     (After  Reis.)  ^ 


than  400  feet  above  the  base  of  the  entire  series  is  a  bed  seven 
feet  thick  made  up  of  several  thin  layers  of  limestone  and  limestone 
shale  and  presenting  a  series  of  wrinkles  or  contortions  from  which 
the  overlying  and  underlying  beds  are  free. ',  The  series  now  dips 
at  an  angle  of  24°  southwest.  The  folding  in  some  cases  has  been 
so  intense  as  to  cause  a  brecciation  of  the  limestone  beds.  (Fig.  167.) 


GLIDING  DEFORMATIONS 


783 


E.  Ordovicic  examples  of  this  type  are  beautifully  exposed  in 
the  walls  of  the  gorge  of  East  Canada  Creek  at  Trenton  Falls, 
N.  Y.  Here  there  are  at  least  three  such  disturbed  zones,  one  well 


FIG.  167.  Corrugated  limestone  beds,  showing  the  effects  of  subaqueous 
gliding.  Gaspe  limestone,  Canada.  Scale  about  i  :20O.  (After 
Logan.) 

shown  below  the  Lower  or  Sherman  Falls,  one  just  below  the  High 
Falls  (now  replaced  by  a  high  dam),  and  a  third  higher  up.  All  of 
these  show  a  wonderful  series  of  folds  and  overthrusts,  the  zones 
varying  in  thickness  up  to  4  meters,  and,  as  is  to  be  expected,  dying 


FIG.  168.  Deformation  due  to  sub-  FIG.  169.  Deformation  due  to  sub- 
aqueous gliding,  Trenton  lime-  aqueous  gliding,  Trenton  lime- 
stone, Trenton  Falls,  N.  Y.  1 175.  stone,  Trenton  Falls,  N.  Y.  i  :ioo. 
(After  Hahn.)  (After  Miller.) 

out  after  a  while,  though  traceable  for  some  considerable  distance. 
The  upper  and  lower  layers  are  not  disturbed,  but  absolutely  nor- 
mal, not  even  showing  evidence  of  excessive  compression.  The 
layers  involved  in  the  folding  are  not  always  the  same,  sometimes 
they  are  granular  limestones  with  abundant  organic  remains,  but 


784  PRINCIPLES    OF   STRATIGRAPHY 

more  often  they  are  calcilutytes.  The  fossils  are  often  broken,  but 
no  recrystallization  occurs;  the  appearance  is  such  as  would  be 
expected  from  the  result  of  gliding  of  a  mass  of  imperfectly  lithi- 
fied  lime  mud.  The  overlying  layers  have  all  the  characters  of 
normal  deposits  on  the  deformed  layers,  there  being  thus  a  struc- 
tural unconformity,  though  without  a  hiatus.  (Figs.  168,  169.) 
These  disturbances  at  Trenton  Falls  have  been  variously  explained, 
the  general  conclusions  of  geologists  being  either :  ( i)  that  they  were 
truly  tectonic — lateral  pressure  having  resulted  in  the  folding  of 
certain  strata  while  others  took  up  the  thrust  without  deformation, 
or  (2)  that  they  were  due  to  squeezing  out  of  certain  layers  under 
the  weight  of  the  overlying  rock  masses.  Both  explanations  are 
unsupported  by  the  detailed  characteristics  of  the  folds  and  their 


FIG.  170.     Edgewise     conglomerate,     Beek-       FIG.    171.     Section    across    the 
mantown     limestones,     Center    county,  two  interlocking  stylolites, 

Pennsylvania.     (After  Hahn.)  shown    in    Fig.    172,    much 

reduced.     (After  Wagner.) 

relationship  to  the  enclosing  layers.  The  recognition  of  these  layers 
as  gliding  surfaces,  analogous  to  the  Horgen-Zug  occurrences,  and 
comparable  to  the  Oeningen  folds,  is  to  the  credit  of  Dr.  F.  Felix 
Hahn,  at  that  time  curator  in  Palaeontology  in  Columbia  Univer- 
sity. (Hahn-/.) 

F.  A  Cambric  or  earlier  example  of  such  movements  seems  to 
be  indicated  by  the  folded  layers  of  the  Biri  limestone  of  Mjosen, 
Norway,  described  by  Rothpletz  (21).  This  limestone  contains 
certain  layers  "which  are  deformed  in  a  singular  manner  without 
the  enclosing  layers  partaking  of  such  deformation.  It  appears  as 
if,  during  the  tilting,  these  layers  had  not  enough  stability,  and 
collapsed  within  themselves,  so  that  between  the  more  stable  layers 
there  occurred  a  movement  in  which  the  enclosing  strata  had  no 
part."  (Rothpletz-2i  :  28.)  The  characters  of  these  foldings  seem 
in  every  way  analogous  to  those  of  the  younger  formations  de- 
scribed. 


INTRAFORMATIONAL   CONGLOMERATES         785 

Finally,  it  should  be  mentioned  that  in  the  unconsolidated  deposit 
of  the  Pleistocenic  such  deformations  occur,  though  some  of  them, 
no  doubt,  are  due  to  glacial  thrust.  The  deformation  of  the  Ter- 
tiary beds  of  Martha's  Vineyard  may  possibly  belong  to  this  cate- 
gory. 

Deformation  through  gliding  may  result  in  complete  brecciation 
of  the  deformed  layers.  The  fragments  may  lie  in  all  positions,  as 
in  the  case  of  ordinary  "intraformational  conglomerates,"  or  they 
may  consist  of  thin  cakes,  many  of  which  in  the  gliding  process  have 
assumed  a  vertical  position  in  the  mass.  This  forms  the  so-called 
"edgewise  conglomerate"  common  in  the  Ordovicic  limestones  of 
the  Appalachian  region.  The  characteristics  of  all  these  forma- 
tions seem  to  point  to  rather  shallow  water  as  the  place  of  deposi- 
tion of  these  strata,  and  the  possible  periodic  exposure  and  partial 
hardening  of  the  surface  layers.  A  different  explanation  has,  how- 
ever, been  given  for  these  by  Seely  and  amplified  by  Brown  (i). 

6.  Surface  Deformation  Due  to  Creep.    As  already  noted  (p. 
543),  vertical  strata,  especially  of  a  shaly  or  slaty  character,  are 
subject  to  deformation  in  portions  of  their  exposed  ends  by  the 
creep  of  the  surface  soil  down  a  sloping  hillside  composed  of  thin 
strata.    A  bending  in  the  direction  of  movement  is  generally  found 
to  occur  after  a  while.     Such  deformation  is  of  slight  importance, 
and  is  probably  never  preserved  in  the  older  rocks. 

b.     Deformations  Due  to   Vertical  Pressure  of  Overlying  Rock 

Masses. 

7.  Squeezing  Out  of  Layers.     This  may  occur  in  cases  where 
certain  beds  are  especially  susceptible  to  such  deformation.     Fine- 
grained, homogeneous  strata  seem  to  be  most  readily  affected  in  this 
way.    An  enterolithic  structure  similar  to  that  produced  by  swelling 
masses   (gypsum,  salt)   is  thus  produced,  the  effect  being  similar 
whether  the  pressure  originated  from  the  swelling  of  the  mass  itself 
or  from  the  weight  of  the  overlying  rock.    Koken  believes  that  the 
enterolithic   structure   in   the   Muschelkalk   of   the   Neckar   Valley 
(Gckrosekalke)   is  due  to  vertical  pressure  and  squeezing  out  of 
these  layers.     (Ante,  Fig.  161.) 

8.  Shaliness  is  the  property  of  lutaceous  rocks,  rich  in  clay,  to 
split  with  concave  or  "shelly"  surfaces  in  a  general  way  parallel  to 
the  bedding  planes.    The  structure  is  a  secondarily  derived  one,  due 
to  vertical  pressure  and  the  character  of  the  rock.     It  seems  to  be 
best  developed  in  calcareous  shales.     That  it  is  a  secondary  struc- 
ture is  shown  by  the  fact  that  the  splitting  will  sometimes  pass 


786 


PRINCIPLES    OF    STRATIGRAPHY 


across  a  fossil,  a  part  of  which  remains  with  either  portion  of  the 
split  mass. 

9.  Slatiness.  This  term  is  applied  to  the  structure  developed  by 
many  siliceous  and  carbonaceous  argillutytes  of  splitting  into  thin 
layers  or  plates  parallel  to  the  bedding  and  with  essential  regularity 
of  surfaces  similar  to  true  slaty  cleavage.  The  Genesee  and  Black 
Portage  shales  of  New  York,  the  Black  Shale  of  Ohio  and  Michigan 
and  others  of  their  kind  show  this  feature  well.  It  is  shown  in  the 
undisturbed  Jurassic  lutytes  of  Wtirttemberg,  which  are  split  into 
slate  blocks  to  all  appearance  comparable  to  slates  from  disturbed 


FIG.  1.72.     Stylolite  from  Trigonodus  limestone  (Muschelkalk)  of  Frauenthal. 
Three-quarters  natural  size.      (After  Wagner.)      (See  Fig.  171.) 

regions.  Finally  a  certain  slatiness  is  observed  in  the  Plattenkalke 
of  the  Upper  Jura  in  the  Solnhofen  region,  where  layers  are  split 
thin  enough  for  roofing  slate  purposes. 

In  all  these  cases  the  region  is  undisturbed,  and  the  slaty  struc- 
ture is  parallel  to  the  bedding.  It  is  apparently  developed  as  the  re- 
sult of  pressure  of  the  overlying  rock  masses,  and,  when  exposed 
to  erosion,  it  is  developed  by  the  weather  in  the  same  way  that 
slaty  cleavage  is  developed  by  the  weather. 

c.     Of  Complex  Origin. 

10.  Pressure  Sutures  and  Stylolites*  In  massive  limestones 
are  not  infrequently  found  irregular  sutures  or  seams,  which  pene- 

*  For  a  recent  comprehensive  survey  of  the  subject  together  with  discussion 
of  all  the  theories  of  origin  advanced,  and  reference  to  literature,  see  Wagner-24. 


PRESSURE  SUTURES  AND  STYLOLITES          787 

trate  the  rock  usually  in  a  direction  parallel  to  the  bedding  planes. 
These  sutures  (Drucksuturen  of  the  Germans)  range  from  a 
scarcely  visible  size  to  projections  an  inch  or  more  in7  length.  They 
interlock  on  opposite  sides  in  a  most  complicated  manner,  which 
has  led  to  their  comparison  with  the  sutures  of  a  skull  (Vanuxem). 
Such  sutures  have  been  found  in  limestones  of  widely  varying  geo- 
logical ages  and  in  different  parts  of  the  world.  They  seem  to  pass 
by  gradation  into  the  true  stylolite  structures  which  generally  occur 
in  the  same  or  in  similar  limestone  beds.  Stylolites  generally  occur 
along  a  horizontal  plane  of  separation^  and  consist  of  flutes  and 
slickensided  columns  of  limestone,  varying  in  length  up  to  4  inches 
or  more,  and  in  diameter  up  to  two  or  more  inches  and  projecting  al- 
ternately from  the  upper  and  from  the  lower  layer  at  right  angles. 
At  the  end  of  each  column  is  usually  a  cap  of  clay,  which  weathers 
out  in  the  cliff,  leaving  hollow  cavities.  That  these  structures  are 
due  to  pressure  is  suggested  by  the  fact  that  the  fracture  line  often 
passes  across  recognizable  organic  remains,  the  two  parts  of  which 
are  displaced  in  opposite  sides  of  the  fracture  plane.  The  structure 
thus  resembles  minute  faulting,  the  flutings  on  the  sides  of  the  col- 
umn being  analogous  to  the  slickensides  formed  at  the  fault  planes. 
Stylolites  are  often  mistaken  for  corals  or  other  organic  remains. 
Not  infrequently  a  shell  or  other  fossil  remains  caps  the  stylolite, 
and  determines  the  outline  of  the  fluted  column. 

Ordinary  pressure  work  has,  however,  not  taken  place  here, 
for  nowhere  is  there  any  evidence  of  deformation  of  the  beds  by 
crowding  or  compression  above  the  columns,  which  project  from 
one  face  of  the  suture  into  the  hollows  of  the  other.  In  other 
words,  if  the  interlocking  of  the  notch-like  projections  were  due  to 
simple  compression  before  or  after  solidification,  then  wherever  a 
hollow  occurs  there  should  be  evidence  above  and  around  that  hol- 
low of  compression  and  movement  to  crowd  away  the  material  so  as 
to  produce  that  hollow. 

That  the  structure  was  produced  after  the  solidification  of  the 
rock  is  shown  by  the  fact  that  the  surfaces  of  separation  are  sharp, 
that  the  sides  are  striated  and  that  all  evidence  of  massive  deforma- 
tion or  squeezing  is  wanting.  The  most  satisfactory  theory  yet  ad- 
vanced to  explain  these  remarkable  structures  is  that  they  are  the 
result  of  unequal  solution  along  sutures  or  fracture  planes.  If  solu- 
tion takes  place  on  the  concave  surfaces  of  both  the  upper  and  lower 
face  of  the  fracture,  the  result  must  be  the  production  of  a  series  of 
tooth-like  projections  from  both  sides  of  the  fissures,  which,  owing 
to  the  pressure  of  the  overlying  rock,  interpenetrate  more  and  more 
as  room  is  macje  by  solution.  In  other  words,  the  rock  opposite  the 


788 


PRINCIPLES    OF    STRATIGRAPHY 


end  of  each  tooth-like  projection  is  dissolved  away — the  hollows  are 
deepened,  and  thus  the  teeth,  by  gliding  under  pressure,  penetrate 
deeper  and  deeper  into  the  opposite  bed,  while  at  the  same  time 
they  become  longer  by  the  deepening  of  the  hollows  which  surround 
and  isolate  them.  The  residual  clay,  left  on  solution,  comes  to  rest 
as  a  cap  on  the  top  of  the  stylolite,  protecting  this  top  from  solu- 
tion. 

It  is  not  necessary  that  the  suture  or  dividing  plane  should  be 
irregular  to  begin  with.  Unequal  solution  on  opposite  sides  of  the 
plane  is  sure  to  occur,  since  rocks  are  seldom  so  homogeneous  that 
all  parts  are  equally  soluble.  Such  irregularity  once  produced,  it 
will  continue  to  be  augmented,  for  the  greatest  amount  of  pressure 


FIG.  173.  Sketch  of  a  portion  of  a  limestone  face  of  white  Jura  j8  in  Tal- 
heim,  showing  stylolites.  (After  Wagner.)  The  spaces  result- 
ing (black)  are  filled  with  calcite.  (After  Wagner.)  (Much 
reduced.) 

will  occur  where  the  rocks  on  opposite  sides  come  in  contact.  The 
projecting  mass,  especially  if  it  is  crowned  by  a  fossil  which  is  less 
readily  soluble  than  the  enclosing  rock,  generally  suffers  the  least 
solution,  while  the  hollow  opposite  into  which  it  presses  suffers 
the  largest  amount  of  solution.  The  protecting  cap  of  clay  also 
helps  this  process.  The  sides  of  the  growing  teeth  are  free  from 
pressure,  so  solution  is  absent  here,  and  deposition  even  may  oc- 
cur. (Figs.  171-173.) 

The  length  of  the  individual  stylolite  tooth  serves  as  a  fair  meas- 
ure of  the  amount  of  material  removed  by  solution  from  both  sides 
of  the  fracture  plane. 

ii.  Cone  in  Cone.  This  is  a  structure  sometimes  found  in 
lutaceous  rocks,  particularly  in  calcareous  or  ferruginous  argil- 
lutytes.  It  consists  of  a  number  of  crenulated  or  corrugated  conical 


TECTONIC    DEFORMATION  789 

layers  one  within  the  other.  In  the  beds  they  are  seen  to  consist  of 
two  sets  interlocking  from  opposite  sides,  the  top  and  bottom  of  the 
beds  affected  being  formed  by  the  bases  of  the  two  sets  of  cones. 

Professor  Marsh  (16)  has  suggested  that  this  structure  is  the 
result  of  concretions  forming  under  pressure.  It  has  also  been 
held  that  crystallization  of  the  calcium  carbonate  in  the  bed  is  re- 
sponsible for  the  formation  of  this  structure. 


B.    TECTONIC  OR  OROGENIC  DEFORMATIONS. 

Of  late  the  term  tectonic  has  come  to  be  more  specially  applied 
in  geology  to  larger  rock  structures,  due  to  disturbances  such  as  ac- 
company and  bring  about  the  formation  of  mountains.  In  other 
words,  orogenic  disturbances  have  come  to  be  considered  the  chief 
causes  in  the  production  of  tectonic  features.  Lateral  pressure 
seems  to  be  the  chief  active  agent  responsible  for  such  deformation, 
but  it  is  by  no  means  certain  that  the  products  of  such  lateral  com- 
pression are  always  distinguishable  from  those  of  vertical  compres- 
sion by  the  superincumbent  strata. 

The  various  types  of  tectonic  deformation  will  be  considered,  be- 
ginning with  tectonic  jointing. 


d.     Deformation  Resulting  in  Fractures  and  Related  Structures. 

12.  Joints.  Rocks  separated  into  more  or  less  regular  blocks  by 
natural  fissures  are  said  to  be  jointed.  Joints  may  be  due  to  shrink- 
age on  cooling,  or  on  desiccation,  forming  shrinkage  joints,  already 
discussed,  or  they  may  be  caused  by  folding  or  other  tensile  stresses, 
giving  tension  joints,  or  finally  they  may  be  due  to  compression  on- 
folding,  forming  compression  joints.  Both  tension  and  compression 
joints  frequently  occur  together.  In  tension  joints  the  surfaces  will 
be  rough  if  the  rock  is  arenaceous  or  rudaceous  and  the  grains 
weakly  held.  If  the  rock  is  lutaceous  or  otherwise  a  strong,  tolera- 
bly homogeneous  rock,  the  fracture  will  be  smooth  and  sharply  cut. 
Faulting  and  slickensiding  may  develop  along  such  joints  when  sub- 
jected to  pressure,  and  deposit  of  mineral  matter  will  take  place 
along  the  joint  surfaces. 

Daubree  (3)  has  shown  by  experiments  with  glass  plates  that, 
if  a  brittle  stratum  is  subjected  to  torsion,  when  the  limit  of  elas- 
ticity is  reached  it  will  break,  with  two  sets  of  parallel  fractures 
forming  nearly  a  right  angle  with  each  other  (Figs.  174,  175). 


790 


PRINCIPLES    OF    STRATIGRAPHY 


Crosby  (2)  has  shown  that,  if  a  shock  were  sent  through  the  strata 
before  this  limit  was  reached,  the  fracture  would  be  produced  in  a 
similar  manner.  The  shock  may  be  produced  by  the  giving  way 
of  the  first  portion  of  the  bed,  in  which  torsion  has  been  carried 
beyond  the  resisting  strength  of  the  bed,  or  it  may  have  extraneous 
causes. 

The  slight  amount  of  torsion  required  in  a  brittle  bed  is  easily 
accounted  for  by  differential  uplift  of  the  bed.     It  may  be  illus- 


FIG.  174.  Illustration  of  Daubree's 
method  of  breaking  a  sheet  of 
glass  by  torsion  to  produce  inter- 
secting joints. 


FIG.  175.  Arrangement  of  fractures 
in  glass  plate  broken  by  torsion. 
(Daubree.) 


trated  by  the  torsion  produced  in  a  large  sheet  of  stiff  cardboard 
lifted  slightly  by  one  corner. 

Compression  joints  are  produced  in  the  folding  of  rocks.  Simply 
folded  rocks  will  have  joints  in  two  planes  at  right  angles  to  each 
other.  Joints  of  this  kind  are  closely  related  to  fissility,  which  is 
distinguishable  only  by  the  greater  number  and  closer  approxima- 
tion of  the  shearing  planes.  'The  same  compression  might  produce 
fissility  along  one  set  of  shearing  planes  and  joints  along  another." 
(Van  Hise-23 : 671.) 

Minor  characteristics  of  joint  faces. 

Feather  fracture.  This,  as  shown  by  Woodworth  (26),  is  char- 
acteristic of  the  joint  surfaces  of  certain  fine-grained  phyllites  or 


JOINTS  791 

siliceous  lutytes.  It  consists  of  a  "delicate  tracery  of  feathery  lines 
diverging  from  a  roughly  outlined  axis,  which  traverses  the  face  of 
the  joint  block  in  a  plane  parallel  with  the  stratification.  When  the 
axis  of  the  feather  fracture  departs  from  this  plane  it  becomes  sinu- 
ous." (Woodworth-26.) 

Dendritic  markings.  These  are  formed  on  the  joint  planes  of 
fine-grained  rocks,  and  are  due  to  the  arborescent  deposit  of  earthy 
oxide  of  manganese  or  of  iron.  They  may  be  compared  to  the 
plumose  frost  traceries  on  window  panes.  In  the  so-called  land- 
scape marble,  this  deposit  has  penetrated  the  entire  rock,  and  is  seen 
on  all  polished  sections.  Dendrites  of  iron  pyrites  and  other  min- 
erals are  also  known.  Not  infrequently  they  are  mistaken  for 
vegetable  impressions. 

Widening  of  joints. 

Joints  of  tectonic  origin  may  be  widened  by  separation  of  the 
blocks,  by  solution  or  erosion  of  their  sides,  and  in  other  ways.  The 
Olean  conglomerate  on  the  hills  of  southwestern  New  York  fur- 
nishes a  good  illustration  of  widening  of  joints  by  separation  of  the 
blocks.  Here  huge  masses  40  feet  in  height  and  of  similar  basal 
dimensions  have  been  formed  in  the  coarse  conglomerate,  and  the 
blocks  have  in  many  cases  slid  far  enough  apart  to  open  passage- 
ways between  them.  These  street-like  passageways  between  the 
blocks  have  given  the  region  the  name  of  Rock  City.  The  gliding  of 
the  masses  is  favored  by  the  soft,  clayey  strata  underlying  and  by 
the  constant  erosion  which  is  going  on  on  the  hillsides. 

Joints  in  limestones  are  commonly  widened  by  solution  of  the 
wall  rock,  which  when  continued  long  enough  will  produce  cavern- 
like  passages  and  eventually  caves.  The  peculiar  character  of  the 
Karst  regions  of  the  world  is  accounted  for  by  such  solution. 
(See  ante,  p.  133.)  Not  infrequently  partly  widened  fissures  are 
filled  with  clay,  sand,  gravel  or  other  substances  from  above,  con- 
stituting a  clastic  "dike."  Sandstone  dikes  are  especially  common, 
though  not  always  originating  in  solution  fissures  (see  beyond). 
Fissures  thus  filled  are  common  in  most  modern  limestone  masses, 
covered  by  drift  deposits.  A  remarkable  example  of  a  Devonic  fis- 
sure in  Niagaran  limestone,  filled  with  fossiliferous  Upper  Devonic 
shales,  has  been  described  by  Weller  from  Illinois  (25). 

Widening  of  joint  fissures  by  erosion  is  of  common  occurrence. 
The  most  active  agent  is  often  the  wind,  which  cuts  away  at  the 
sides  of  the  prism  produced  by  the  joints,  and  narrows  it  until  only 
a  pillar,  isolated  from  its  neighbor,  remains  behind.  All  stages  of 


792  PRINCIPLES  OF  STRATIGRAPHY 

such  erosion  along  joint  cracks  may  be  seen  in  the  Tertiary  sand- 
stone of  Monument  Park,  Colorado,  where  in  the  ledges  the  begin- 
nings of  this  erosion  work  are  seen,  while  scattered  through  the  park 
are  numerous  isolated  stone  pillars,  generally  capped  by  a  fer- 
ruginous block  of  greater  resistance,  the  last  remnants  of  an  ex- 
tensive formation  which  formerly  covered  the  entire  region. 

13.  Earthquake  Fissures.  A  well-known  phenomenon  accom- 
panying more  or  less  violent  seismic  disturbances  is  the  opening  of 
fissures  in  the  rock  by  the  tearing  asunder  of  the  mass.  Such  fis- 
sures may  remain  open  or  be  filled  subsequently  by  the  washing  into 
them  of  surface  material,  or  they  may  be  filled  at  the  time  of  forma- 
tion by  material  violently  injected  into  them  from  above.  Recent 
fissures  have  been  described  by  Whimper  and  others.  (See  Chapter 
XXIII.)  Examples  of  such  fissures  are  sometimes  found  in  the 
fossil  state.  Thus  the  Upper  Siluric  limestones  and  dolomites  of 
western  New  York  and  Ontario  are  traversed  by  vertical  fissures, 
which  show  evidence  of  violent  disruption,  and  into  these  fissures 
sands  representing  the  Oriskany  period  were  injected.  These  sands 
apparently  rested  on  the  old  erosion  surface  of  the  Siluric  limestone 
before  the  shock  came.  The  shock  was  a  pre-Middle  Devonic  one, 
for  Middle  Devonic  (Onondaga)  strata  rest  upon  this  mass  without 
showing  any  evidence  of  being  affected  by  the  shock.  One  of  the 
best  examples  of  this  group  has  been  described  from  the  cement 
quarries  of  North  Buffalo. 

"The  total  depth  of  the  fissure  as  now  exposed  with  its  filling 
of  sandstone  is  in  the  neighborhood  of  10  feet.  The  dike  is  squarely 
cut  off  at  the  top,  where  the  Onondaga  limestone  rests  on  its  trun- 
cated end  and  on  the  limestones  flanking  it.  The  Onondaga  lime- 
stone is  entirely  unaffected  by  the  dike,  being  evidently  deposited 
after  the  formation  and  truncation  of  this  remarkable  mass  of  sand- 
stone. The  width  of  the  fissure  is  scarcely  anywhere  over  2  feet, 
but  lateral  offshoots  extend  for  many  feet  into  the  walls  of  Bull- 
head [and  Bertie]  limestone.  These  offshoots  or  rootlets  of  the 
dike  are  irregular,  commonly  narrow,  and  often  appear  as  isolated 
quartz  masses  in  the  Bullhead  or  Waterlimes,  the  connection  with 
the  main  dike  not  being  always  observable.  Such  masses  of  sand- 
stone have  been  noted  at  a  distance  of  20  or  30  feet  from  the  main 
dike.  They  are  always  small.  The  dike  itself  has  been  traced  for 
more  than  30  feet  in  an  east  and  west  direction  in  the  sloping  walls 
of  the  quarry.  The  walls  of  this  ancient  fissure  are  very  irregular, 
angular  masses  of  the  limestone  projecting  into  the  quartz  rock, 
while  narrow  tongues  of  sandstone  everywhere  enter  the  limestone. 
Extensive  brecciation  of  the  limestone  has  occurred  along  the  mar- 


SLATY  CLEAVAGE  793 

gin,  and  the  sandstone  there  is  filled  with  angular  fragments  of  the 
limestone,  which  show  no  traces  of  solution,  or  wear  by  running 
water.  These  limestone  fragments  are  themselves  frequently  in- 
jected with  tongues  of  the  quartz  sand.  The  nature  of  the  contact 
between  the  quartz  and  the  limestone,  the  trituration  of  the  latter, 
and  the  inclusion  of  individual  grains  of  quartz  sand  in  a  triturated 
mass  of  limestone,  the  presence  of  cavities  along  the  contact  filled 
with  recrystallized  calcite,  the  presence  of  elongated  limestone 
"streamers"  in  the  quartz  mass  near  the  contact,  all  "point  to  a 
cataclysmic  origin  of  the  fissure  .  .  .  and  a  more  or  less  violent  in- 
jection of  the  sand.  ...  It  seems  also  certain  that  the  fissure  was 
formed  after  the  deposition  of  a  considerable  mass  of  sand  over 
the  .  .  .  limestone,  and  that  the  formation  of  the  fissure  and  the  in- 
jection of  sand  from  above  occurred  simultaneously.  In  no  other 
way  can  we  account  for  the  inclusion  of  horses  of  the  wall  rock, 
often  of  considerable  size,  and  the  injection  of  the  sand  into  all  the 
fissures  and  crevices;  nor  can  we  readily  explain  on  any  other  hy- 
pothesis the  trituration  of  the  limestone  along  the  borders,  which 
clearly  indicates  a  violent  contact  between  the  sand  and  the  already 
consolidated  limestone.  The  supposition  that  the  fissure  is  due  to  a 
violent  disruption  of  the  wall  ...  is  further  borne  out  by  the  nu- 
merous minute  faults  which  occur  in  the  Waterlimes  in  the  vicinity 
of  the  fissure  and  elsewhere."  (Grabau-5  :  360-361.) 

14.  Slaty  Cleavage.  Slaty  cleavage  (Leith-i4)  is  the  property 
of  strata  to  split  or  "cleave"  along  certain  planes  which  as  a  rule 
have  no  relation  to  the  planes  of  stratification.  This  property  is 
especially  well  developed  in  argillutytes,  resulting  in  the  formation 
of  "slates,"  from  which  the  term  slaty  cleavage  has  been  derived. 
Slate  is  therefore  a  structural  term,  and  has  no  lithic  significance, 
except  in  so  far  as  the  structure  is  best  developed  in  the  clastic 
rocks  of  lutaceous  texture,  and  generally  in  part  at  least  of  argil- 
laceous composition.  This  rock  structure  has  been  explained  as 
"due  to  the  arrangement  of  the  mineral  particles  with  their  longer 
diameters  or  radial  cleavage,  or  both,  in  a  common  direction,  and 
that  this  arrangement  is  caused,  first  and  most  important,  by  paral- 
lel development  of  new  minerals;  second,  by  the  flattening  and 
parallel  rotation  of  old  and  new  mineral  particles,  and,  third, 
and  of  least  importance,  by  the  rotation  into  approximately  paral- 
lel positions  of  random  original  particles."  (Van  Hise-23 :  635.) 
(See  also  page  770.) 

The  original  cause  of  these  changes  is  the  lateral  compression  of 
the  rocks  due  to  orogenic  disturbances.  Cleavage  may  be  considered 
as  separation  of  the  laminae,  potentially  developed  in  the  rock.  The 


794  PRINCIPLES    OF    STRATIGRAPHY 

actual  cleavage  or  splitting  is  subsequently  developed  by  the  frost, 
or  other  atmospheric  agent,  or  by  the  hand  of  man. 

Coarse-grained  rocks  are  seldom  affected  by  cleavage.  Lime- 
stones likewise  offer  great  resistance  to  compression,  and  are  not 
generally  cleaved.  Thus  cleavage  may  often  be  developed  in  a 
stratum  of  argillaceous  lutytes,  while  adjoining  arenytes  or  calcare- 
ous beds  will  be  unaffected.  This  sometimes  gives  rise  to  the  ap- 
pearance of  an  unconformity. 

Cleaved  strata  commonly  have  their  original  bedding  structure 
obliterated.  Only  in  exceptional  cases  are  the  bedding  planes  pre- 
served, when  the  strata  are  differently  colored  or  when  a  change 
in  texture  occurs.  In  such  cases  ribbon  slates  or  banded  slates  are 
produced.  In  cleaved  fossiliferous  strata  the  fossils  may  sometimes 
be  detected  on  the  weathered  surfaces  of  the  bedding  plane,  the 
position  of  which  they  indicate.  A  very  general  distortion  of  the 
fossils  accompanies  the  formation  of  cleavage,  so  that  in  many  cases 
the  remains  are  no  longer  recognizable. 

Unless  the  relation  of  cleavage  to  the  bedding  is  detected,  an  er- 
roneous conception  of  the  structure  of  a  country  is  obtained.  Strata 
which  are  strongly  cleaved  generally  appear  to  be  vastly  thicker 
than  they  really  are,  and  unconformities  are  sometimes  considered 
to  exist  between  strata  where  in  reality  the  bedding  planes  are  per- 
fectly concordant.  If,  however,  a  formation  with  slaty  cleavage  is 
overlain  by  one  without  such  structure,  although  of  a  composition 
which  would  permit  its  development  as  readily  as  would  the  under- 
lying rock,  a  discordance  of  relation  is  indicated,  though  in  the  ab- 
sence of  other  evidence  this  is  not  fully  demonstrated.  (Van  Hise- 
23:7**.) 

15.  Fissility  is  the  structure  found  in  some  rocks,  "by  virtue  of 
which  they  are  already  separated  into  parallel  laminae  in  a  state  of 
nature."     It  thus  differs  from  cleavage,  where  this  separation  is 
only   potential.    Fissility   belongs   in   the   zone   of    fracture,   while 
cleavage  belongs  in  that  of  flowage.     Both  occur  and  grade  into 
each  other  in  the  zone  of  combined  fracture  and  flowage. 

16.  Schistosity.     This  structure  is  the  result  of  intense  meta- 
morphism  under  pressure,  and  is  characterized  by  the  development 
of  planes  of  cleavage  due  to  the  presence  of  large,  cleavable  par- 
ticles.    It  is  essentially  comparable  to  slaty  cleavage,  except  that 
metamorphism  has  gone  farther  and  the  rock  has  become  crystal- 
line.    Schistosity  may  be  developed  in  rocks  of  many  kinds,  both 
clastic  and  igneous.     Foliation  is  another  term  applied   to   these 
rocks. 

The  structure  is  essentially  due  to  recrystallization  of  the  rock 


DEFORMATION   BY   FOLDING  795 

on  mashing.  It  is  often  not  apparent  in  fresh  rocks,  but,  as  in  the 
case  of  slaty  cleavage,  is  developed  on  exposure  to  the  atmosphere. 
17.  Gneissoid  Structure.  This  structure,  like  schistosity,  re- 
sults from  intense  mashing  and  recrystallization  of  rocks  subjected 
to  symphrattic  metamorphism.  Gneissoid  structure  is  essentially 
characterized  by  banding,  the  bands  being  of  unlike  composition. 
The  mineral  particles  also  interlock  so  that  the  cleavage  is  much  less 
perfect  than  in  schists.  Usually  it  is  parallel  to  the  banding,  but 
this  is  not  always  the  case.  Gneissoid  structure  may  be  developed 
in  igneous  and  in  clastic  rocks.  In  the  former  case  we  have  granite- 
gneisses,  diortite-gneisses,  etc.,  in  the  lattc£  arenyte  or  sandstone 
gneisses,  rudyte  gneisses  or  conglomerate  gneisses,  etc. 


e.     Deformations  Due  to  Folding,  and  to  Folding  and  Erosion. 

1 8.  Folding.  Rock  folds  are  among  the  most  conspicuous  and 
easily  recognized  tectonic  features.  They  vary  greatly  in  magni- 
tude, from  the  minute  wrinkles  formed  in  the  axes  of  larger  folds, 
to  those  whose  limbs  are  many  miles  apart.  In  regions  of  erosion 
generally  only  a  part  of  the  fold  is  found,  the  folded  strata  having 
been  truncated  and  cut  down  until  only  portions  of  the  limbs  re- 
main. In  this  way  the  appearance  of  tilted  strata  is  produced,  these 
tilted  strata  being,  however,  only  the  remnants  of  great  folds. 

The  form  of  folds  is  very  variable,  but  it  has  been  possible  to 
select  a  number  of  distinct  types,  of  which  the  others  are  variants. 
These  distinct  types  are  (a)  anticline,  (b)  synclines,  (c)  isoclines, 
(d)  fan  folds,  and  (e)  monoclines.  Compound  anticlines  are 
anticlinoria  and  compound  synclines  are  synclinoria. 

(a)  Anticlines.     In  this  type  the  sides  or  limbs  of  the  fold 
typically  slope  away,  from  the  plane  of  the  axis  on  either  side.    The 
sloping  portions  are  known  as  the  limbs  of  the  anticline,  and  the 
amount  of  slope  as  compared  with  the  horizontal  is  the  angle  of  dip. 
All  folds  are  wrinkles  in  the  earth's  crust,  and  if  followed  far 
enough  along  the  axis  they  will  die  out.    The  amount  of  inclination 
of  the  axis  of  the  fold,  also  measured  from  the  horizontal,  is  called 
the  pitch.     Every  anticlinal  axis  pitches  in  two  directions,  i.  e.,  to- 
ward the  two  ends  of  the  folds.    A  short  anticline  in  which  the  two 
axes  are  of  approximately  equal  length  is  a  dome. 

(b)  Synclines.    When  the  limbs  of  the  fold  dip  toward  the  axis 
a  trough  fold  or  syncline  is  produced,:  the  axis  of  which  pitches  to- 
ward the  center  of  the  fold.     A  short  syncline,  in  which  the  two 
axes  are  of  nearly  equal  length,  is  a  basin. 


796 


PRINCIPLES    OF    STRATIGRAPHY 


Anticlines  and  synclines  may  be  either  symmetrical  or  asym- 
metrical, according  as  the  limbs  are  equal  in  length  and  inclination, 
or  unequal.  Anticlines  may  be  erect  or  recumbent.  In  the  latter 
case  one  limb  of  the  anticline  is  overfolded,  and  the  strata  compos- 
ing it  are  overturned. 


FIG.    176.      Anticlinal    fold    near    St 
Abbs  Head,  Scotland.     (Geikie.) 


FIG.  177.  Two  anticlines  enclosing  a 
s  y  n  c  1  i  n  e  truncated  above. 
(Geikie.) 


(c)  Isoclines.  When  the  limbs  of  a  fold  are  parallel  an  isocline 
is  produced.  The  limbs  of  such  a  fold  may  stand  vertically  or  they 
may  be  inclined.  In  the  latter  case  some  portion  of  the  strata  in- 
volved will  always  be  overturned,  i.  e.,  their  original  surface  now 


FIG.    178.      Synclinal    fold   near    Banff,    Scotland.      (After    Geikie.) 

lies  below.     Nearly  horizontal  isoclines  are  produced  by  overfolds 
and  underfolds. 

In  a  region  of  isoclinal  folds,  the  most  important  problem  con- 
fronting the  stratigrapher  is  the  recognition  of  the  repetition  of 
strata  and  the  proper  relationship  between  them.  It  is  evident  that 
a  succession  of  strata,  such  as  is  shown  in  Fig.  179,  a,  may  be  inter- 


ISOCLINAL  FOLDS 


797 


preted  as  all  belonging  to  one  limb  of  a  fold,  and  therefore  repre- 
senting a  continuous  series,  or  as  representing  one  or  more  isoclinal 
folds.  According  to  the  first  interpretation,  the  sediments  have 
great  thickness,  and  there  is  a  recurrence  of  similar  beds,  while, 
according  to  the  second  interpretation,  the  series  is  much  thinner 
and  the  recurrence  of  beds  is  only  apparent,  there  being  an  actual 
repetition  of  the  same  beds.  The  problem  is  often  a  difficult  one  to 
solve,  and  depends  upon  the  identification  of  the  similar  beds  as 
parts  of  the  same  bed.  A  knowledge  of  the  degree  of  folding  char- 
acteristic of  the  region  in  question  and  a  knowledge  of  the  charac- 
ters and  thicknesses  of  the  formations  involved  in  other  and  undis- 


123       4      4      321      123443 


FIG.  179.     Isoclinal  strata,  showing  repetition  of  strata  (a)  and  two  methods 
of  reconstructing  them  (b,  c). 

turbed  regions  will  often  serve  to  settle  the  question.  If  more  than 
two  kinds  of  beds  are  involved,  the  order  of  repetition  will  often 
give  a  clue  to  the  original  condition.  Thus  in  a  closely  folded  dis- 
trict, the  strata  within  the  same  fold  will  be  repeated  in  inverse 
order,  as  shown  in  Fig.  179,  a. 

This  generally  is  conclusive  evidence  of  repetition  by  folding.  If 
this  point  is  settled,  the  next  question  is:  Which  bed  is  the  upper 
and  which  is  the  lower  of  the  series?  If  the  character  of  the  folds 
can  be  determined  by  inspection,  the  proper  relation  will  at  once 
appear,  for  if,  when  beds  4  and  4  come  in  juxtaposition,  they  pre- 
sent the  upper  ends  of  the  fold,  i.  e.,  they  are  parts  of  an  anticline, 
bed  4  is  the  oldest  and  originally  the  lowest  of  the  series  (Fig. 
179,  &). 

If,  however,  the  two  limbs  of  the  folded  bed  4  join  below  the 


798  PRINCIPLES    OF    STRATIGRAPHY 

surface  in  a  concave  or  synclinal  fold,  bed  4  is  the  youngest  of  the 
series,  and  formerly  overlay  all  the  others.  When  the  actual  type 
of  folding  cannot  be  observed,  an  examination  of  the  beds  them- 
selves will  often  reveal  their  relationships.  Thus,  if  bed  3  shows 
normal  ripple  marks,  footprints  or  other  markings  (see  Chapter 
XVII)  on  the  surface  of  any  layer  facing  bed  2,  it  is  evident  that 
the  surface  of  3  next  to  bed  2  was  the  upper  surface  of  that  bed, 
and  that  the  strata  are  related,  as  in  Fig.  179,  b,  bed  3  being  older 
than  bed  2.  If,  however,  bed  3  shows  on  the  side  of  its  layers 
facing  bed  2  the  natural  molds  or  reverse  impressions  of  the  mark- 
ings named,  it  is  evident  that  that  is  the  lower  side  of  the  bed,  and 
that  3  therefore  overlies  2  and  is  younger,  as  shown  in  Fig.  179,  c. 
(d)  Fan  folds.  In  regions  of  sharp  folding  a  fan  type  of  fold 


FIG.   180.     Generalized  section  of  the  fan  fold  of  the  central  massif  of  the 
Alps.     (After  Heim.) 

may  be  produced,  in  which  the  limbs  of  the  arch  dip  toward  each 
other  for  a  certain  distance.  Here  the  lower  or  concave  portions  of 
the  fold  are  pressed  inward  with  the  result  that  the  beds  at  the  cen- 
ter of  the  fold  are  squeezed  out  or  pinched.  This  type  of  fold  is 
characteristic  of  the  Alps  and  other  strongly  folded  districts  (Fig. 
180). 

(e)  Monoclines.  Typically  a  monocline  is  a  part  of  an  anti- 
cline, cut  off  by  faulting  or  erosion.  Simple  monoclines  are  those 
in  which  the  strata  have  no  further  continuation.  Thus  the  Front 
Range  of  the  Rocky  Mountains  is  flanked  by  a  series  of  simple 
monoclines,  all  of  which  face,  with  their  erosion  slopes,  the  crys- 
talline axis  of  these  mountains.  In  many  cases  the  continuation  of 
these  folds  is,  however,  on  the  opposite  side  of  the  crystalline  axis. 
The  Blue  Ridge  extending  from  New  Jersey  for  the  entire  length 
of  the  Appalachians  is  a  variable  series  of  eastward  facing  mono- 
clines. The  Appalachians  themselves  are  for  the  most  part  com- 
posed of  complementary  monoclines,  these  representing  the  oppo- 
site limbs  of 'anticlines  with  the  axis  opened  by  erosion.  Simple 


ANTICLINORIA ;   SYNCLINORIA;  GEOSYNCLINES    799 

flexures  of  strata  are  sometimes  spoken  of  as  monoclines,  but  these 
are  in  reality  strongly  asymmetrical  anticlines.  They  may  be  spoken 
of  as  monoclinal  flexures,  but  should  not  be  spoken  of  as  monoclines. 
(Figs.  181-183.) 


FIG.  181.  A,  recumbent  isoclinal  fold,  with  over-  and  underfolds.  B,  mono- 
cline due  to  faulting.  C,  corresponding  monoclines,  due  to  ero- 
sion of  an  anticline. 

Anticlinoria  and  synclinoria.  When  a  succession  of  anticlines 
has  such  a  relationship  as  to  make  a  large  anticline,  it  is  called  an 
anticlinorium.  The  central  massif  of  the  Alps  may  be  taken  as  an 
illustration.  In  like  manner  a  large  synclinal  fold  composed  of  a 
succession  of  minor  folds  is  a  synclinorium.  Such  a  condition  exists 


FIG.  182.     A  simple  monoclinal 
flexure. 


FIG.    183.     The   same  passing  into  a 
fault. 


in  the  Mount 'Grey lock  massif  of  western  Massachusetts.     (Figs. 
184,  185.) 

Geosyncline  and  foredeep.  The  term  "geosyncline"  was  pro- 
posed by  Dana  for  the  long  trough  which  formed  to  the  east  of  the 
Appalachian  old  land  during  Palaeozoic  time.  In  this  trough  some 


8oo  PRINCIPLES    OF    STRATIGRAPHY 

40,000  feet  of  strata,  partly  of  marine  and  partly  of  continental 
origin,  were  deposited.  It  is  evident  that  there  must  have  been  a 
gradual  downbending  of  the  old  land  to  permit  this  extensive  series 
of  deposits  to  accumulate.  This  depression  should  not,  however,  be 
regarded  as  primarily  of  tectonic  origin.  It  is  much  more  likely 
that  it  represented  the  slow  sinking  of  the  crust  under  loading  and 
that  its  formation  was  due  to  the  progressive  reestablishment  of 
isostatic  equilibrium.  The  foredecps,  which  are  situated  off  the 
continental  margins,  are  probably  of  a  different  character.  Here 
we  have  in  general  downward-bending  troughs,  next  to  the  land 
mass,  where,  however,  there  is  no  great  amount  of  deposition.  Such 
down-war-ping  of  a  part  of  the  ocean  bed  may  well  be  regarded  as 


FIG.  184.     Anticlinorium.     Generalized  section  in  the  Alps.     (After  Heim.) 

of  tectonic  origin,  serving  to  relieve  the  accumulating  stresses  in 
the  earth's  crust.  An  examination  of  the  ocean  bottom  charts  will 
locate  the  existing  foredeeps.  (See  further,  Chapter  XXIII.) 


Relation  of  dip,  strike  and  outcrop. 

Dip  has  already  been  defined  as  the  inclination  of  the  strata  from 
the  horizontal.  Strike  may  be  defined  as  the  compass-bearing  of  the 
line  of  intersection  which  the  stratum  in  question  makes  with  a  hori- 
zontal plane.  It  may  also  be  spoken  of  as  the  compass-bearing  of 
the  edge  of  the  inclined  bed  when  cut  off  by  a  horizontal  plane. 
The  direction  of  strike  is  determined  by  compass,  with  reference  to 
the  true  north  and  south  line,  i.  e.,  the  meridian.  A  wrong  direc- 
tion is  often  furnished  by  the  outcrop  of  the  stratum  on  a 
sloping  surface.  If  the  slope  of  the  surface  and  the  dip  of 
the  strata  are  in  the  same  direction,  varying  only  in  amount,  or  if 
the  slope  and  dip  are  in  exactly  opposite  directions,  no  difference 
will  be  observed  between  outcrop  and  strike.  (Fig.  i86a.)  Again, 
if  the  strata  stand  vertically,  no  difference  will  be  observed  between 


RELATIONS   OF  DIP,  STRIKE  AND   OUTCROP    801 

outcrop  and  strike  (Fig.  i86b),  no  matter  what  the  surface  slope. 
In  all  other  cases,  however,  the  outcrop  on  a  sloping  surface  will 
differ  in  direction  from  the  true  strike  of  the  strata,  and  is  apt  to 
mislead  unless  this  fact  is  borne  in  mind.  In  general,  it  may  be 
said  that  the  lines  made  by  the  intersection  of  inclined  strata  with 
a  sloping  surface  have  their  down-slope  end  deflected  in  the  direc- 
tion of  the  dip  of  the  strata.  (Fig.  i86c.)  If  the  dip  is  vertical, 
this  deflection  will  not  alter  the  direction.  If  the  lines  of  inter- 


FIG.    185.     Synclinorium.     Mt.   Greylock,   Mass.      (After  Dale.) 

section  run  at  right  angles  to  the  slope  of  the  surface,  there  is  no 
down-slope  end,  and  hence  no  deflection.  (Fig.  i86a.)  Again,  it 
should  be  stated  that  the  true  strike  and  the  true  dip  are  always  at 
right  angles  to  each  other,  and  any  slope  whose  intersection  with  the 
inclined  stratum  makes  a  line  at  right  angles  to  the  line  of  dip  must 
show  the  true  strike  in  the  outcrops  in  its  surface.  (Fig.  i86a.) 

In  the  diagram,  Fig.  i86c,  the  inclined  plane,  A  B  C  C'  A'  has  its 
outcrop  and  strike  coinciding  where  cut  by  the  horizontal  surface 


FIG.   i86a. 


K         C*        W 

FIG.  i86b. 


FIG.   i86c. 


E  F  G  H,  but  where  cut  by  the  inclined  surface  D  E  H  I  the  out- 
crop is  deflected  toward  the  down-dip  side.  It  is  evident  from  com- 
parison with  Fig.  i86b  that  any  vertical  plane,  as  A  B  X  Y  Z,  whose 
intersection  with  the  horizontal  surface  coincides  with  that  of  the  in- 
clined plane  A  B  C  C'  A',  will  intersect  the  inclined  surface  along  a 
line  B  X  continuous  with  the  line  A  B  and  having  the  same  com- 
pass direction.  This  is  evidently  the  true  strike,  and  the  angle 
X  B  C  marks  the  angle  of  deflection  from  this  direction  of  the  in- 
tersection of  the  inclined  plane  on  the  sloping  surface,  i.  e.,  the 


802 


PRINCIPLES    OF    STRATIGRAPHY 


angle  of  deflection  of  the  strike.     Its  projection  on  a  horizontal 
plane  is  the  angle  Y'  X'  Y. 

The  amount  of  deflection  of  the  strike,  by  a  sloping  surface,  may 
be  seen  by  the  following  consideration:  Given  a  stratum  dipping 
due  west,  at  an  agle  of  45  degrees,  a  horizontal  surface  intersecting 
this  will  show  the  true  strike  due  north  and  south.  Given  a  second 
surface,  whose  intersection  with  the  horizontal  surface  is  at  right 
angles  to  the  strike,  i.  e.,  due  east  and  west  in  the  given  case*,  and 
which  also  intersects  the  inclined  plane.  If  this  surface  is  tilted  to 
the  vertical,  i.  e.,  if  the  beds  are  seen  in  vertical  section  at  right 
angles  to  the  strike  of  the  inclined  bed,  the  outcrop  or  intersection 
of  this  stratum  with  the  surface  will  coincide  with  the  dip,  i.  e.,  the 


B 


FIG.  187. 


line  of  outcrop  as  marked  by  compass  direction  has  been  deflected 
90°  by  a  tilting  of  the  surface  to  the  extent  of  90°.  If  the  surface 
is  tilted  45°,  the  line  of  intersection  as  marked  by  compass  direc- 
tion will  evidently  lie  halfway  between  the  two  or  N.  45°  E.  by  S. 
45°.  (Fig.  187.)  Thus  in  the  model  the  shaded  bed  A  C 
H  F  is  inclined  at  45°  from  the  horizontal,  while  the  surface  A  B 
C  D  is  also  inclined  45°  from  the  horizontal,  but  in  a  direction  at 
right  angles  to  that  of  the  bed  A  C  H  F,  i.  e.,  its  intersection  with 
the  horizontal  surface  is  at  right  angles  to  the  strike  of  the  bed. 
Thus,  by  construction,  X  Y  =  X  C '  =  X  D,  hence  A  X,  being  the 
diagonal  of  the  square  A  D  X  Y,  makes  an  angle  of  45°  with 
D  X  E  and  with  the  direction  of  C  H.  It  is  evident  that  the  line  of 
intersection  C  H  between  the  inclined  bed  and  the  horizontal  surface 
B  C  H  G  is  the  true  strike.  It  is  also  the  strike  of  the  vertical  bed 
C  H  E  D.  The  line  C  D,  the  intersection  of  this  vertical  plane  with 


RELATION   OF   DIP,   STRIKE   AND   OUTCROP     803 

the  sloping  surface  A  B  C  D,  has  the  same  compass  direction  as 
C  H,  and  hence  represents  the  true  strike.  The  line  A  C,  however, 
the  intersection  between  the  surface  A  B  C  D  and  the  plane  A  C 
H  F,  is  deflected  45°  from  that  direction,  since  its  direction  corre- 
sponds to  that  of  the  line  A  X,  the  diagonal  of  the  square  A  D  X  Y. 

With  a  constant  surface,  as  given,  and  sloping  at  45°,  the  out- 
crop of  a  vertical  stratum  will  have  no  deflection  from  the  line  of 
strike.  As  the  stratum  becomes  inclined  from  the  vertical  the  down- 
slope  end  will  be  deflected  in  the  direction  of  dip,  a  degree  for  every 
degree  of  departure  of  the  dip  from  90°.  When  45°  of  dip  are 
reached  the  deflection  will  be  45°.  With  decreasing  dip,  i.  e.,  its 
approach  to  o°,  the  deflection  will  approach  90°,  which  is  reached 
when  the  strata  are  horizontal.  When  the  slope  of  the  postulated 
surface  is  other  than  45°  the  deflection  of  the  strata  must  be  calcu- 
lated. Designating  the  dip  of  the  stratum  by  6,  the  angle  of  inclina- 
tion of  the  sloping  surface  from  the  horizontal  by  <£  and  the  deflec- 
tion of  the  outcrop  by  i^,  we  have  tan  $  =  cot  0  tan  <j>  or  ^  = 
tan-i  (cot  0  tan  <£). 

It  sometimes  happens  that  only  the  outcrop  of  inclined  strata  is 
visible  on  the  surface  of  a  region,  the  angle  of  dip  not  being  ascer- 
tainable.  In  such  a  case  the  angle  of  deflection  ( ^ )  can  often 
be  measured  directly  by  taking  a  reading  of  the  true  strike  on  a 
horizontal  portion  of  the  surface  and  another  of  the  apparent  strike 
on  a  sloping  surface,  where  the  intersection  with  the  horizontal  is 
at  right  angles  with  the  strike.  The  angle  of  slope  of  this  surface 
(<f>)  must  also  be  read  by  the  clinometer.  Thus  with  the  values  of 
two  terms  of  the  equation  ascertained  the  third  or  angle  of  dip 
(0)  may  be  readily  found  by  the  formula  tan  6  =  tan  <£  cot  ^  or 
0  =  tan- !  (tan  <£  cot  ^). 

An  example  may  further  illustrate  this :  Given  an  inclined 
stratum  of  which  the  true  strike  as  shown  by  the  intersection  with  a 
horizontal  surface  is  N.  10°  E.,  while  the  apparent  strike  on  an  in- 
clined surface  of  the  postulated  direction  of  slope  is  N.  30°  W.,  the 
angle  of  deflection  of  outcrops  between  horizontal  and  inclined  sur- 
face, i.  e.,  \J/,  is  therefore  40°.  The  angle  of  slope  of  the  inclined 
surface  may  be  assumed  as  30°.  Thus  the  dip  is:  tan  0  -  -  tan 
30°  cot  40°  or  0.6882608;  /.  0  —  about  34°  32'.  The  direction  of 
dip  is  to  the  east,  since  the  deflection  was  to  the  west.* 

The  above  formulas  apply  only  to  the  case  where  the  inclined 
surface  intersects  the  horizontal  along  a  line  at  right  angles  to  the 
true  strike,  i.  e.,  when  the  directions  of  slope  of  the  inclined  strata 
and  surface  are  at  right  angles  to  each  other.  When  the  direction 
of  slope  of  surface  varies  from  this,  the  amount  of  deflection  will 


804 


PRINCIPLES    OF    STRATIGRAPHY 


increase  or  decrease  according  as  the  direction  varies  toward  or 
away  from  that  of  the  inclined  strata.  Thus  the  more  nearly  the 
direction  of  slope  of  the  inclined  surface  approaches  that  of  the 
inclined  strata,  the  more  nearly  will  the  amount  of  deflection  ap- 
proach 90  degrees,  while  the  more  the  direction  of  slope  approaches 
the  opposite  of  that  of  the  strata  the  more  nearly  will  the  true  strike 
be  approached.  The  following  formulas  will  serve  in  such  a  case. 
In  Fig  188. 


Let  A  D  represent  the  outcrop  of  a  stratum  along  a  sloping  hill- 
side. 

D  B  represent  the   dip  of  the   stratum. 

a  =outcrop  dip,  or  the  angle  CAD  made  by  the  line  of  out- 
crop A  D  with  a  horizontal  plane  obtained  by  placing  the 
clinometer  on  the  line  of  outcrop  A  D. 

j8  =  the  angle  of  dip  of  the  stratum,  B  D  K  or  C  B  D  in 
diagram. 

y  =  the  angle  by  which  the  outcrop  is  shifted  by  the  slope  of  the 
hill  (ACE). 


mi.        •  tan  a 

Then  sm  y  =         — 5   or  y 


and  tan  ft  = 


tari/8 
tana 
sin  y 


sn 


or  £  =  tan 


/  tan  a' 


!    / tan  a 


sin 


an  a\ 
iny/ 


*  It  should  be  noted  that,  as  viewed  from  above,  the  deflection  is  in  the 
direction  of  the  dip,  but,  as  viewed  from  below,  looking  up  the  plane,  the 
deflection  is  in  the  opposite  direction.  This  must  be  borne  rn  mind  when 
the  compass  direction  is  read;  that  on  a  northward  sloping  plane  will  be 
read  from  above,  that  on  a  southward  sloping  plane  from  below. 


RELATION   OF   DIP,    STRIKE   AND   OUTCROP     805 

The  following  method  is  given  by  Keilhack  (12:65,  6<5)  f°r  the 
determination  of  the  true  dip  and  strike  when  observations  are  pos- 
sible only  on  vertical  cliffs  or  quarry  walls  (Fig.  189)  : 

Given  two  dip  observations  on  vertical  quarry  walls,  one  of  65°, 
on  a  wall,  the  compass  alignment  of  which  is  N.  45°  W.,  and  one 
of  45°  on  a  wall,  the  alignment  of  which  is  N.  65°  E.  Draw  two 
lines  at  a  b  and  a  c,  the  former  at  an  angle  of  N.  45°  W.,  and  the 
latter  N.  65°  E.,  so  that  they  intersect  in  the  point  a.  At  the  point  a 
erect  perpendiculars  to  a  b  and  a  c.  Lay  off  equal  distances  on  these 
from  a,  locating  the  points  e  and  d,  respectively.  At  d  lay  off  the 


FIG.  189. 


complement  of  the  angle  observed  on  the  wall  represented  by  a  c, 
that  is,  the  complement  of  45°,  which  is  45°.  At  e  lay  off  the  com- 
plement of  the  angle  observed  on  the  wall  represented  by  the  line 
a  b,  that  is,  the  complement  of  65°,  which  is  25°.  Complete  the 
right  angle  triangles  by  continuing  the  hypothenuses  until  they  meet 
the  lines  a  c  and  a  b,  at  f  and  g,  respectively.  Join  f  g  by  a  line 
which  represents  the  true  strike  of  the  strata,  which  if  a  c  and  a  b 
are  properly  oriented  can  be  readily  measured.  Drop  a  perpendicu- 
lar a  h  from  a  to  f  g.  This  is  the  direction  of  dip  toward  either 
a  or  h,  as  the  case  may  be.  Erect  a  perpendicular  to  a  h  at  a,  and 
lay  off  the  length  a  d  (=a  e),  on  it,  locating  point  i.  Connect  i  and 
h,  then  the  angle  i  h  a  is  the  angle  of  true  dip.  This  will  be  readily 
understood  if  the  three  shaded  triangles  are  bent  at  right  angles  to 


806  PRINCIPLES    OF   STRATIGRAPHY 

the  plane  of  the  paper,  either  up  or  down,  until  the  three  sides  a  d, 
a  e  and  a  i  coincide  with  the  apices  of  all  three  (d  e  i),  meeting  in  a 
common  point.  The  triangles  a  d  f  and  a  e  g  would  then  represent 
the  walls  of  which  the  original  dip  measurements  were  made,  the 
angles  in  each  case  being  represented  by  the  angles  a  f  d  and  a  g  e, 
respectively.  A  plane  resting  on  the  three  hypothenuses  would  rep- 
resent the  inclined  stratum. 


Strike  as  affected  by  pitching  axis  of  folds,. 

As  long  as  the  axis  of  an  anticline  or  syncline  continues  hori- 
zontal, the  outcrops  of  the  -beds  exposed  by  planing  off  the  summit 
of  the  fold  in  a  horizontal  surface  will  be  in  the  form  of  parallel 
bands,  the  lowest  appearing  at  the  center  and  the  repetition  of  the 


a  b  .: 

FIG.  190.     a,  Eroded  anticline  with  horizontal  axis,     b,  Eroded  anticline  with 
pitching  axis,  showing  resulting  outcrops  of  strata. 

beds  being  in  the  same  order, from  the  center  outward  in  both  direc- 
tions.    (Fig.  190,  a.) 

When  the  axis  of  the  fold  is  inclined  the  strike  of  the  strata  on 
opposite  sides  of  the  axial  plane  will  converge  and  finally  meet.' 
(Fig.  190,  b.)  In  an  anticlinal  fold  the  inner  strata  are  the  older; 
in  a  synclinal  fold  the  inner  strata  are  the  younger. 

Folding  as  indication  of  unconformity. 

In  a  complexly  folded  region  an  unconformity  may  sometimes 
be  detected  between  two  formations  not  actually  seen  in  contact  by 
the  fact  that  the  lower  formation  is  folded  much  more  strongly 
than  the  upper  one.  In  this  case  it  is  apparent  that  the  lower  forma- 
tion was  folded  and  truncated  before  the  upper  one  was  deposited, 
after  which  both  were  again  folded.  (See  Fig.  191.) 


THE  APPALACHIAN  FOLDS  807 


The  trend  of  the  Appalachian  folds. 

The  Appalachians  furnish  a  good  example  of  an  extended  line  bf 
folding  formed  at  approximately  the  same  time,  i.  e.,  the  end  of 
the  Palaeozoic.  They  show  a  remarkable  series  of  curves  of  varying 
size,  which;  with  reference  to  the  land,  may  be  called  convex  or 
land  lobes,  when  they  bulge  seaward,  and  concave  or  sea  lobes, 
when  they  extend  back  into  the  land.  (See  the  map,  Fig.  192.) 
Beginning  in  the  southwest,  we  have  the  following: 


FIG.  191.  Diagrams  showing  the  steps  by  which  complexly  folded  strata  are 
produced.  A — C,  deposition,  folding  and  truncation  of  first  series ; 
D — F,  deposition,  folding  and  erosion  of  second  series,  the  fold- 
ing and  erosion  also  affecting  the  first  series. 

1.  Louisiana  sea  lobe,  extending  from  Texas  to  central  Mis- 
sissippi with  the  apex  near  Little  Rock,  Arkansas,  and  with  proba- 
bly a  subordinate  .land  lobe  at  McAlester  in  Oklahoma. 

I  a.     Mississippi  land  lobe,  extending  through  northern  Missis- 
sippi and  "northwestern  Alabama. 

2.  Birmingham  sea  lobe,  a  small  lobe  in  central  Alabama. 
2a.    Rome  land  lobe  with  a  moderate  curve. 

3.  Knoxville  sea  lobe,  with  its  apex  looping  around  the  Knox- 
jville  area. 

3a.    Alleghany  land  lobe — along  the  main  line  of  the  Alleghany 
Mountains  of  Virginia.  ' 

4.  Pennsylvania  sea  lobe,  a  marked  lobe  with  the  apex  in  cen- 
tral Pennsylvania,  the  trend  changing  to  nearly  east. 

4a.    New  York  land  lobe,  the  apex  being  near  New  York  City. 

5.  Champlain  sea  lobe,  east  of  the  Adirondacks. 


8o8  PRINCIPLES    OF    STRATIGRAPHY 

5a.    Maine  land  lobe,  along  the  northwesern  boundary  of  Maine 

6.  Gaspe  sea  lobe,  a  pronounced  lobe,  the  trend  actually  chang- 
ing to  southeast  (40°). 

6a.  Cape  Breton  land  lobe,  the  change  of  trend  being  near  Syd- 
ney, Cape  Breton,  the  trend  again  turning  northeastward  and  con- 
tinuing thus  through  Newfoundland. 

19.  Domes  and  Basins.  Domes  are  shortened  anticlinal  struc- 
tures with  the  dip  of  the  strata  away  from  the  center  in  all  direc- 
tions or  quaquaversal.  These  dips  may  vary  greatly  in  different 
domes.  In  some  cases  they  are  so  low  as  to  be  scarcely  or  not  at 
all  perceptible  (Cincinnati  dome)  ;  in  others  they  may  be  45°  or 
over  (Black  Hills  dome).  Many  of  the  low-dipping  domes  are 
perceptible  as  such  only  by  the  erosion  which  has  removed  their 
central  portion,  often  leaving  a  topographic  depression.  Such  low 
domes  have  also  been  called  parmas,  after  one  of  the  low  east  and 
west  ranges  which  project  from  the  western  side  -of  the  .Urals 
(which  have  a  north-south  trend),  and  which  are  formed  by  gently 
folded  strata,  the  folds  dying  out  in  the  plains. 

Basins  are  the  reverse  of  domes,  the  strata  all  dipping  toward 
the  center.  As  a  rule,  basins  are  composed  of  gently  dipping  strata 
only  so  that-their  basin  character  is  recognized  only  by  the  rimming 
outcrops  of  the  lower  strata  after  erosion  (Michigan  basin,  Paris 
basin,  etc.).  Between  two  basins  lies  generally  a  more  sharply 
marked  anticline,  while  between  two  domes  a  pronounced  syncline 
often  occurs.  Sometimes  the  basin  structure  is  ascertained  by  the 
location  by  borings  all  over  the  area  of  the  summit  (or  bottom)  of 
a  certain  formation,  such  as  a  coal  bed  or  a  marked  sandstone. 
Thus  the  basin  structure  of  Iowa  is  beautifully  brought  out  by  the 
series  of  contours  connecting  areas  of  equal  depression  beneath  the 
surface  of  the  summit  of  the  St.  Peter  sandstone.  (Iowa  Geol. 
Survey,  Vol.  VI,  p.  316,  map.) 

Eastern  North  America  is  marked  by  a  number  of  distinct  basins 
and  domes,  many  of  which  are  indicated  by  the  outcrops,  while 
others  are  recognized  only  from  their  general  relationship  and  the 
occurrence  of  separating  anticlines  or  synclines.  All  of  these  basins 
and  domes  owe  their  final  character  to  the  Appalachian  folding,  but 
"some  of  them  apparently  existed  during  much  of  Palaeozoic  time. 
The  accompanying  map  (Fig.  192)  shows  the  location  of  these 
domes  and  basins.  It  will  be  observed  that  the  outermost  basins 
are  generally  embraced  by  convex  lobes  of  the  Appalachian  system, 
while  the  concavities  of  that  system  are  opposite  domes  or  opposite 
anticlines  separating  basis.  (See  also  Ruedemann-22 ;  Willis-3O.) 

The  principal  basins  so  far  determined  are  in  the  northeast,  the 


FIG.  192.  Map  of  North  America,  showing  the  sinuous  trend  of  the  Ap- 
palachian folds  (see  text)  and  the  domes  and  basis.  A=Alle- 
ghany  basin ;  AM=:Alabama-Mississipf>i  basin ;  I=/ott'a  basin ; 
I]=Illinois  basin;  J=Jamcs  Bay  basin;  IJ=St.  Lawrence  basin 
(Montreal,  etc.);  M=Michigan  basin;  N=New  York  basin; 
O=0klahoma  basin;  o=Ottawa  basin;  Q=Quebcc  basin.  The 
line  or  lines  between  basins  represent  anticlines.  The  domes 
are:  The  Adirondack;  west  of  this  the  Ontario;  north  of  this  the 
North  Ontario;  southwest  of  this  the  Wisconsin  dome.  In  the 
southern  area  are:  the  Cincinnati,  the  Nashville,  and  the  Ozark 
domes. 


8io  PRINCIPLES    OF    STRATIGRAPHY 

St.  Lawrence,  the  Quebec,  the  Ottawa,  and  the  New  York. 
The  Frontenac  axis  separates  the  last  two  basins,  and  joins 
the  Adirondack  dome  to  the  Ontario  dome.  Northwest  of  the  lat- 
ter is  the  North  Ontario  dome,  the  Temiscaming  syncline  separat- 
ing the  two.  To  the  north  of  this  is  the  James  Bay  Basin.  Next 
southward  of  this  series  is  the  Alleghany  basin,  embraced  by  the 
Alleghany  land  lobe  of  the  Appalachians  on  the  east.  Northwest  of 
this  is  the  Michigan  basin,  these  two  being  separated  by  the  Toledo 
anticlinals.  Northwest  of  the  Michigan  basin  is  the  Wisconsin 
dome,  which  is  separated  from  the  North  Ontario  dome  by  the  deep 
Superior  synclinals.  Southwest  of  the  Wisconsin  dome  is  the  Iowa 
basin,  and  southeast  of  this  the  Illinois  basin,  with  the  Keokuk  anti- 
cline between.  The  Illinois  and  Michigan  basins  are  separated  by 
the  Kokomo  anticline.  The  Cincinnati  dome  is  enclosed  by  the  Illi- 
nois, Michigan  and  Alleghany  basins,  and  south  of  it  is  the  smaller 
Nashville  dome,  with  small  basins  on  either  side.  The  southern 
tier  is  formed  by  the  Alabama-Mississippi  basin  in  the  embrace  of 
the  Mississippi  land  lobe,  the  Ozark  dome,  and  the  Oklahoma  basin. 


f.     Deformations  Due  to  Dislocation  of  Strata.    Faulting. 

20.  Faults.  "A  fault  is  a  fracture  in  the  rock  of  the  earth's 
crust  accompanied  by  a  displacement  of  one  side  with  respect  to 
the  other  in  a  direction  parallel  with  the  fracture."  (Reid,  etc.-i8; 

19.) 

<CA  closed  fault  is  one  in  which  the  two  walls  of  a  fault  are  in 
contact." 

"An  open  fault  is  one  in  which  the  two  walls  of  a  fault  are  sep- 
arated. The  same  fault  may  be  closed  in  one  part  and  open  in 
another." 

"A  fault  surface  is  the  surface  of  fracture.  It  is  rarely  plane, 
but  where  it  is  without  notable  curvature  over  any  area  it  may  be 
called  a  fault  plane  for  that  area. 

"A  fault  line  is  the  intersection  of  a  fault  surface  with  the 
earth's  surface." 

"The  shear  zone:  When  a  fault  is  made  up  of  a  number  of 
slips  on  closely  spaced  surfaces,  the  section  of  the  earth's  crust  con- 
taining these  minor  faults  is  called  'shear  zone.'  This  name  would 
also  apply  to  the  brecciated  zone,  which  characterizes  some  faults." 

"A  horse  is  a  mass  of  rock  broken  from  one  wall  and  caught  be- 
tween the  walls  of  the  fault.  (Fig.  1933.) 


FAULTS 


811 


"The  fault  strike  is  the  direction  of  the  intersection  of  the  fault 
surface,  or  the  shear  zone,  with  a  horizontal  plane."  The  same  pre- 
cautions apply  here  as  in  the  case  of  the  strike  of  the  strata  on  a 
sloping  hillside.  (See  p.  800.)  The  term  "trend"  would  be  bet- 
ter and  would  avoid  confusion. 

"The  fault  dip  is  the  inclination  of  the  fault  surface,  or  shear 
zone,  measured  from  a  horizontal  plane.  It  is  never  greater  than 
90°." 

<(The  hade  is  the  inclination  of  the  fault  surface  or  shear  zone, 
measured  from  the  vertical ;  it  is  the  complement  of  the  dip."  Hade 
is  to  be  preferred  to  dip  to  avoid  confusion  with  dip  of  strata.  (See 
beyond.) 

"The  hanging  wall  is  the  upper  wall  of  the  fault."  It  generally 
overhangs  the  vertical. 

"The  foot  wall  is  the  lower  wall  of  the  fault."  It  generally  pro- 
jects footwise  at  the  base. 


FIG.    1933.     A  horse. 

In  stratified  rocks  faults  may  be  parallel  in  strike  to  the  strike  of 
the  strata,  when  they  are  called  strike  faults,  or  the  strike  may  be 
approximately  at  right  angles  to  the  strike  of  the  strata,  when  they 
are  called  dip-faults.  The  bedding  fault  is  a  special  type  of  strike 
fault,  in  which  the  fault  plane  and  bedding  plane  coincide.  Be- 
tween the  strike  faults  and  the  dip  faults  are  many  directions  giving 
oblique  faults.  When  the  general  structure  of  a  region  is  consid- 
ered, the  faults  may  be  called  longitudinal,  when  their  strike  (or 
trend)  is  parallel  to  this  structure,  or  transverse,  when  it  is  across 
the  structure. 

The  slip  of  a  fault  is  the  displacement  on  the  fault  surface.  The 
net  slip  is  the  actual  amount  of  movement  between  points  on  the 
opposite  walls  originally  in  contact.  The  strike  *  slip  (trend-slip) 

*  Strike  and  dip  here  refer  to  the  strike  and  dip  of  the  fault,  not  of  the  strata. 
Trend  and  hade  would  be  better. 


812  PRINCIPLES    OF    STRATIGRAPHY 

is  the  component  of  the  slip  parallel  with  the  strike,  and  the  dip- 
slip  (hade  slip)  the  component  parallel  with  the  dip.  Thus  (in 
Fig.  193!))  a  b  is  the  net  slip,  a  c  the  strike-slip  and  b  c  the  dip- 
slip. 

The  shift  is  the  relative  displacement  of  the  rock  masses  outside 
of  the  zone  of  displacement,  and  is  used  when  there  are  many  minor 
slips  making  up  the  shear  zone  or  when  the  strata  in  the  neighbor- 
hood of  the  fault  are  bent.  It  is  the  relative  displacement  which 
would  exist  had  there  been  only  one  slip  of  the  same  magnitude  as 
the  combined  minor  slips. 


Features  shown  in  section  of  faults. 

Throw  is  the  vertical  displacement  of  the  strata,  as  seen  in  sec- 
tions, even  if  the  slip  is  inclined,  d  e  in  the  figures  (No.  194,  A  B) 


A  B 

FIG.  194.     Sections  of  faults:   A,  with  dip  of  fault  plane  across  strata;   B, 
with  dip  of  fault  plane  in  same  direction  as  dip  of  strata. 

Heave  or  horizontal  throw  is  the  horizontal  displacement  of 
srrata  seen  in  section,  as  e  g  in  the  figures  (No.  194,  A  B). 

Stratigraphic  throw.  This  is  the  distance  between  the  two  parts 
of  a  disrupted  stratum  measured  at  right  angles  to  the  plane  of  the 
stratum,  (a  b,  Fig.  194,  A  B.) 

The  Stratigraphic  heave,  or  dip  throw,  is  the  displacement  of 
the  strata  in  section  in  .the  direction  parallel  to  the  strata,  as  c  b  in 
Fig.  194,  A  B.  In  Fig.  A  it  signifies  shortening  and  overlapping  of 
the  strata,  in  Fig.  B,  lengthening  by  separation  of  the  strata. 


SURFACE  APPEARANCE  OF  FAULTS 


Features  shown  in  surface  appearance  of  faults,  i.  e.,  map  features 

of  faults. 

These  features  are  seen  in  strike  and  oblique  faults.  In  the 
former  the  apparent  horizontal  displacement  or  offset  is  measured 
along  the  fault  line,  and  is  the  same  as  the  actual  horizontal  dis- 
tance between  the  ends  of  the  corresponding  strata  (a  b).  (Fig. 
195  A.)  This  is  the  same  as  the  trend-slip,  but  is  probably  never  or 
but  seldom  the  actual  or  net  slip.  In  oblique  faults  the  offset  is 


A.    Map  of    StriKe     Fault 


gap 


Plan    or     Map   of 
oblla/ue     Fault 


offset 


D.  Plan  or  Map  of 
oblique    Fault 

FIG.    195.     Map   or   surface   views   of   faults. 

measured  at  right  angles  between  the  two  ends  of  the  disrupted 
strata,  as  (a  b)  in  Figs.  195  B  and  C,  where  the  trend-slip  is 
marked  by  a  c.  In  Fig.  B,  the  strata  are  disrupted  and  pulled  apart ; 
the  distance  thus  separated  is  the  gap.  In  Fig.  C  the  ends  are 
pushed  past  each  other,  making  an  overlap,  c  b. 


Classification  of  faults. 

Faults  have  been  classified  with  reference  to  direction,  as  strike 
(and  bedding),  dip  and  oblique  faults.  With  reference  to  their 
movements,  they  may  be  classified  into  normal  and  reverse  faults, 


8i4 


PRINCIPLES    OF    STRATIGRAPHY 


and  with  reference  to  the  force  producing  them  they  may  be 
classified  as  gravity  and  thrust  faults. 

With  reference  to  direction.  The  classification  with  reference  to 
direction  has  already  been  in  part  explained.  It  includes  strike 
faults,  dip  faults  %nd  oblique  faults,  with  reference  to  the  strata. 
With  reference  to  each  other,  they  may  be  parallel,  intersecting  or 
radial,  the  last  when  radiating  roughly  from  a  point.  With  refer- 
ence to  a  geological  region  whether  raised  or  depressed  (geologi- 
cally, but  not  necessarily  topographically),  they  may  be  peripheral, 
when  running  along  the  periphery  of  the  geological  formation,  or 
cross-faults  when  they  cut  across  it. 

With  reference  to  movement.  Movement  is  relative.  If  the 
stratum  of  the  hanging  wall  in  any  given  section  is  lower,  it  is 
designated  a  normal  fault.  If  the  stratum  of  the  hanging  wall  is 
higher,  it  is  a  reverse  fault. 


FIG.  196. 


With  reference  to  cause.  In  most  cases  normal  faults  probably 
mean  a  tension  and  a  down-sinking  of  the  hanging  wall,  accom- 
panied by  an  elongation  of  that  part  of  the  crust.  In  this  case  the 
normal  fault  would  also  be  a  gravity  fault.  In  like  manner  the  re- 
verse fault  generally  implies  an  upward  movement  of  the  hanging 
wall  with  consequent  foreshortening  of  the  crust  by  overlapping 
under  pressure.  In  such  a  case  the  reverse  fault  is  also  a  thrust 
fault.  Under  certain  conditions,  however,  a  gravity  fault  may  in 
section  show  the  conditions  of  a  reverse  fault  (Figs.  196,  A  B),  for, 
though  the  hanging  wall  has  slipped  down,  owing  to  the  oblique 
character  of  the  displacement  and  the  dip  of  the  strata,  the  beds 
seem  actually  to  have  slipped  up  over  each  other. 

In  like  manner  a  thrust  fault  may  in  section  show  the  charac- 
ters of  a  normal  fault,  the  ends  of  the  strata  on  the  hanging  >vall 
being  actually  lower  than  on  the  foot  wall.  This  is  shown  in  Figs. 
197,  A  B. 


FAULTED   STRUCTURES 


Terms  applied  to  rock  masses  formed  by  or  bounded  by  faults — but 
not  topographically  distinguishable  from  surrounding  masses. 

1.  A  horst  is  a  mass  geologically  elevated  relatively  to  the  sur- 
rounding region  and  separated  from  it  by  faults. 

2.  A  fault  basin  is  a  region  geologically  depressed  relatively  to 
the  surrounding  region  from  which  it  is  separated  by  faults. 

3.  A  fault  block  is  a  mass  bounded  on  at  least  two  opposite 
sides  by  faults.     It  may  be  geologically  elevated  or  depressed  rela- 
tively to  the  adjoining  region,  or  it  may  be  geologically  elevated 


relatively  to  the  region  on  one  side  and  depressed  relatively  to  that 
on  the  other. 

4.  A  fault  ridge  is  a  relatively  elongated  fault  block  lying  be- 
tween two  faults  with  roughly  parallel  trends. 

5.  A  fault  trough  is  a  relatively  depressed  (geologically)  fault 
block  lying  between  two  faults  with  roughly  parallel  trends. 


Terms  applied  to  the  topographic  expression  of  faults. 

1.  Fault  scarp — a  scarp  or  cliff  presenting  the  original  surface 
form  of  the  displacement. 

2.  Graben,  or  fault  scarp  valley — a  long,  narrow  topographic 
depression,  the  surface  expression   of  a  new   fault  trough.     Ex. 
Rhine  Graben ;  Purgatory  Chasm,  near  Sutton,  Mass.    It  is  bounded 
on  both  sides  by  fault  scarps  facing  inward. 


8i6  PRINCIPLES    OF    STRATIGRAPHY 

3.  Fault  scarp  ridge — a   topographic   ridge  bounded   by   two 
roughly  parallel  fault  scarps  which  face  outward  or  toward  the  sur- 
rounding low  country. 

4.  Fault  scarp  block — a  topographic  block  bounded  on  all  sides 
by  outward  facing  fault  scarps. 

5.  A  tilted  block — a  topographic  block  bounded  on  all  but  one 
side  by  fault  scarps  facing  outward.     The  excepted  side  may  be 
faced  by  the  fault  scarp  of  another  tilted  block. 

6.  A  fault  scarp  basin — a  topographic  basin  bounded  on  all 
sides  by  fault  scarps  facing  inward. 

7.  A  complex  scarp  basin — a  topographic  basin  bounded  on 


FIG.    198.     A   fault-line  valley. 


most  of  its  sides  by  fault  scarps  facing  inward,  but  bounded  by 
warpings  or  in  other  ways  on  one  or  more  sides. 


Secondary  features  due  to  erosion. 

1.  Fault-line  scarp.     (Davis-4.)     This  is  the  fault  scarp  resur- 
rected in  the  second  cycle  of  erosion,  after  the  obliteration  of  the 
original    fault   scarps.      This   may    face   either   way   and   may   be 
greater  or  less  than  the  original  fault  scarp.    If  it  faces  in  the  same 
direction  as  the  original  fault  scarp  it  is  resequent;  if  in  the  opposite 
direction  it  is  obsequent. 

2.  Fault-line  valley — a  valley  cut  out  along  an  old  fault-line 
after  the  obliteration  of  the  original  fault  scarp.     (Fig.  198.) 

3.  The  graben  and  fault  scarp  basin,  the  fault  scarp  ridges, 
fault  scarp  block  and  tilted  block  may  all  be  destroyed  by  erosion 
and  then  resurrected  in  the  second  cycle  of  erosion.     Such  cases 
may   be   designated    by    prefixing   the    word    erosion — an   erosion 
graben,  erosion   fault  scarp  basin,  erosion   fault   scarp  ridge,   etc. 
See,  further,  Davis  (4)  and  Hobbs  (Qa)  ;  also  Chapter  XXI. 


REPETITION   AND   ELIMINATION   OF   STRATA    817 


Stratigraphic  significance  of  faults. 

From  the  Stratigraphic  viewpoint,  strike  faults  are  of  the  great- 
est importance,  for  they  often  lead  to  a  duplication  of  strata  or  to 
the  elimination  of  certain  beds.  Many  mistakes  in  stratigraphy  have 
been  made  because  of  the  nonrecognition  of  such  faults.  The  Og- 
den  quartzite,  for  example,  regarded  as  a  distinct  formation  in  the 
western  Ordovicic,  has  been  shown  to  be  a  repetition  of  a  lower 
formation  due  to  overthrust.  In  the  Helderberg  region  of  New 
York,  near  Kingston,  duplication  by  overthrust  has  led  to  the  con- 
fusion of  the  stratigraphy.  The  overthrust  New  Scotland  beds 
were  originally  described  as  the  Upper  Shaly  (Port  Ewen),  and  the 
higher  formation  was  held^to  have  the  same  fossils  as  the  lower  one. 

In  discussing  the  effects  of  strike  faulting  on  the  apparent  suc- 
cession of  strata,  eight  principal  cases  may  be  considered : 

A.  Gravity  faults.     (Figs.  199,  A-G.) 

1.  Dip  of  fault  plane  with  dip  of  strata,  but  at  greater  angle. 
(Fig.   A.)      In   this  case  elimination   of   beds   will  take 
place. 

2.  At  smaller  angle.     In  this  case  repetition  of  beds  will 
take  place.     (Fig.  B.) 

3.  Dip  of  fault  planes  against  dip  of  strata.     In  this  case 
repetition  of  beds  will  result.     (Figs.  C-E.) 

4.  Dip  of  fault  plane  vertical  (hade  o).     The  "down  dip" 
portion  descends.    In  this  case  elimination  of  beds  results. 
(Fig.  F.) 

5.  The  "up  dip"  portion  descends.     In  this  case  repetition 
results.     (Fig.  G.) 

B.  Thrust  faults.     (Figs.  199,  H-J.) 

6.  Dip  of   fault  plane  with  dip  of   strata,  but  at  greater 
angle,  repetition  results.     (Fig.  H.) 

7.  Dip  at  smaller  angle — elimination  results.     (Fig.  I.) 

8.  Dip  of  fault  plane  against  dip  of  strata.     In  this  case 
elimination  of  strata  results.      (Fig.  J.) 

A  consideration  of  the  diagram,  Figs.  A  to  J,  will  show  that 
the  plane  of  faulting  cuts  the  inclined  strata  so  as  to  leave  a  portion 
which  is  limited  below  by  the  fault-plane,  but  may  extend  indefi- 
nitely upward  except  as  limited  by  the  earth's  surface.  This  por- 
tion may  be  called  the  "tip-dip"  end  of  the  strata  (see  the  fig- 
ures). The  other  part  is  limited  above  by  the  fault  plane,  and  may 
extend  indefinitely  downward.  This  is  the  "down-dip"  end  (d)  of 


8i8 


PRINCIPLES    OF    STRATIGRAPHY 


the  strata.  When  the  fault  plane  cuts  the  obtuse  angle  between  the 
strata  and  the  surface,  i.  e.,  when  its  dip  is  greater  than  that  of  the 
strata,  the  "up-dip"  end  lies  on  that  side  (to  the  right  of  the  plane 
in  the  figures).  When  it  cuts  the  acute  angle,  i.  e.,  dips  at  a  less 
angle  than  the  strata,  the  up-dip  end  lies  on  the  acute  side  (left  side 
of  the  fault  plane  in  the  figures).  With  the  part  thus  oriented,  the 


21  23456  12  1  2  3456 


FIG.   199.     Sections   showing  the  effects  of  strike  faults   in   eliminating  beds 
(A,  F,  I  and  J)   and  in  repeating  beds   (B,  C,  E,  G,  and  H). 

general  law  may  be  stated  that,  if  the  "up-dip"  end  moves  down,  we 
have  repetition  of  strata,  while,  if  the  up-dip  end  moves  up,  elimi- 
nation of  strata  results.  Conversely,  when  strata  are  repeated  or 
eliminated,  the  up-dip  end  must  be  assumed  as  having  moved  either 
down  or  up.  If  the  angle  of  the  fault  plane  is  ascertained,  the  fault 
will  appear  to  be  either  thrust  or  gravity,  according  to  the  greater 
or  less  angle  of  inclination  of  the  fault  plane,  as  compared  with  the 


RELATIONSHIPS    OF   ROCK    STRUCTURES        819 

strata,  and  the  repetition  or  elimination  of  the  strata.  The  general 
rule  can  be  easily  ascertained  at  any  time  by  a  consideration  of  the 
simple  case  shown  in  Figs.  F-G.  There  it  will  be  readily  seen  that, 
when  the  tip-dip  end  is  moved  up,  elimination  results,  and  when 
it  is  moved  down  repetition  occurs,  or,  to  put  it  the  other  way,  when 
the  down-dip  end  moves  up  repetition  occurs,  but  when  the  down- 
dip  end  moves  down  elimination  occurs.* 


Faults  as  indications  of  unconformity. 

If  in  two  superposed  formations  of  similar  character  and  sus- 
ceptibility to  faulting  the  lower  is  more  complexly  faulted  than  the 
upper,  the  indications  are  that  the  lower  was  faulted  before  the 
upper  was  deposited  upon  it,  and  that  then  the  two  formations  are 
unconformably  related. 

Relation  of  folds,  faults,  cleavage,  fissility  and  joints. 

Van  Hise  has  emphasized  the  close  relationships  existing  be- 
tween these  structures,  which  may  in  general  be  considered  as  dif- 
ferent manifestations  of  the  same  forces — thrust  and  gravity — act- 
ing upon  heterogeneous  rocks  under  varying  conditions.  When  rocks 
are  under  less  weight  than  their  ultimate  strength,  while  being  rap- 
idly deformed,  they  will  break,  with  the  formation  of  crevices,  of 
joints,  faults,  brecciations  or  fissility,  as  a  result  of  extensive  frac- 
turing. Such  rocks  are  then  regarded  as  being  in  the  zone  of  -frac- 
ture. When  rocks  are  buried  to  such  a  depth  that  the  weight  of  the 
superincumbent  strata  exceeds  their  ultimate  strength,  they  will 
flow  as  plastic  material  under  deforming  strains  and  folding  with- 
out fracture  results.  The  depth  at  which  this  takes  place  marks 
the  position  of  the  zone  of  plasticity  and  flowage.  The  depth  at 
which  flowage  occurs  varies  with  the  character  of  the  rock.  For 
soft  shales,  Van  Hise  estimates  that  probably  500  meters  or  less  of 
overlying  strata  will  prevent  the  formation  of  crevices  and  fractures 
to  any  considerable  extent,  while  for  the  strongest  rocks  a  depth 
of  perhaps  10,000  meters  is  required  to  reach  this  condition.  Cleav- 
age normally  belongs  in  this  zone.  Between  these  two  is  the  zone 
of  combined  fracture  and  plasticity.  In  this  zone  all  the  structures 
occur  together  in  complex  relationship.  Folds  may  pass  into  faults 
and  faults  into  folds.  Fissility  and  cleavage  occur  side  by  side. 

*  This  may  be  condensed  into  the  slogan — cfown,  down,  out. 


820  PRINCIPLES    OF    STRATIGRAPHY 

Downward  probably  most  faults  pass  into  flexuresj  these  flexures 
dying  out  at  still  greater  depth.  Van  Hise  thinks  that  5,000  meters 
is  a  possible  depth,  at  which  important  faults  disappear,  though 
some  may  extend  to  the  depth  of  a  number  of  miles.  Others,  how- 
ever, regard  the  necessary  depth  as  very  much  less. 


C.     CONTACT  DEFORMATIONS. 

Under  this  heading  may  be  placed  changes  in  the  rock  mass  as 
a  whole,  produced  by  contact  with  a  deforming  agent.  The  deform- 
ing force  is  heat  or  cold,  and  the  agents  conveying  the  former  are 
igneous  masses  (intruded  or  extruded),  hot  waters  or  gases,  and 
the  direct  rays  of  the  sun.  Heating  rock  masses  by  any  of  these 
agents  results  in  expansion  of  the  rock.  The  agents  conveying  cold 
are  glaciers  and  the  cold  atmosphere.  Their  action  on  the  rocks 
results  in  contraction.  The  chief  structures  produced  by  these 
agents  singly  or  in  conjunction  are  prismatic  jointing  and  insola- 
tion joints. 

21.  Prismatic  Jointing  Due  to  Contact  with  Igneous  Masses. 
When  igneous  masses  come  in  contact  with  sedimentary  rocks  a 
prismatic  structure  is  not  infrequently  developed.  This  has  been 
noted  in  clays,  marls,  sandstones,  brown  coal,  seam  coal  and  even 
in  dolomites.  Beautiful  examples  of  this  structure  are  found  in  the 
coal  seams  of  Ayrshire. 

In  all  cases  of  prismatic  jointing  thus  produced,  the  columns 
diverge  perpendicularly  from  the  surface  of  the  igneous  mass  which 
caused  the  alteration.  When  the  latter  is  vertical,  the  columns  are 
horizontal ;  when  it  undulates,  the  columns  follow  its  curvation.  It 
is  most  probable  that  this  structure  is  developed  as  the  result  of 
expansion  of  the  heated  rocks.  That  such  structure  can  develop 
under  pressure  due  to  expansion  is  shown  by  an  experiment  in 
which  prismatic  structure  is  formed  in  a  box  of  powdered  starch, 
stored  for  some  time  in  a  moist  region.  The  swelling  of  the  starch 
exerts  a  pressure  in  all  directions  against  the  sides  of  the  enclosing 
box,  and  after  a  time  a  series  of  prismatic  columns  is  developed 
which  radiate  from  the  center  outward,  being  at  right  angles  in 
most  cases  to  the  enclosing  walls.  Prismatic  structure  produced  by 
swelling  seems  also  to  have  occurred  in  nature,  as  is  shown  in  the 
gypsum  beds  of  the  Paris  Basin  (probably  originally  deposited  in 
part  at  least  as  anhydrite),  where,  as  observed  by  Jukes,  some  beds 
are  divided  from  top  to  bottom  by  vertical  hexagonal  prisms.  If 
this  structure  is  due  to  swelling  on  hydration,  as  in  the  case  of  the 


DISCONFORMITY  UNCONFORMITY  821 

starch  cited,  it  belongs  properly  under  the  subject  of  diagenetic  al- 
terations. Thus  there  are  at  least  three  ways  in  which  prismatic 
structure  is  produced: 

1.  Contraction  and  shrinking,  on  cooling  or  drying. 

2.  Expansion  and  pressure  by  heating  from  without. 

3.  Expansion  and  pressure  by  swellings  from  hydration. 

22.  Insolation  Joints.  '  These  are  joints  produced  in  massive 
rocks,  such  as  granite,  etc.,  by  the  alternate  expansion  and  contrac- 
tion to  which  they  were  subjected  under  the  diurnal  heating  and 
cooling.  Such  joints  are  parallel  to  the  surface  subjected  to  change 
in  temperature,  and  are  close  together  in  the  outer  portion  of  the 
mass,  but  farther  apart  at  a  depth.  They  serve  an  excellent  pur- 
pose in  quarrying  operations,  which  in  such  rocks  would  be  more 
difficult  otherwise. 


D.     STRUCTURES  IN  PART  DUE  TO  DEFORMATION  AND  IN  PART  TO 

EROSION. 

23.  Disconformity  and  Unconformity.  Strata  separated  by  an 
unrepresented  time  interval  are  generally  spoken  of  as  unconforma- 
bly  related.  Two  types  of  such  unconformable  relation  may  be  rec- 
ognized, the  stratic  where  the  stratification  of  the  formation  on  both 
sides  of  the  plane  of  nonconformity  is  parallel  or  nearly  so,  and 
the  structural,  where  the  two  sets  of  strata  are  inclined  at  a  greater 
or  less  angle  with  reference  to  each  other. 

For  the  first  type,  in  which  no  folding  of  the  older  set  of  strata 
is  involved,  the  term  dis conformity  has  been  proposed  (Grabau— 6: 
534))  with  the  corresponding  limitation  of  the  term  unconformity  to 
the  second  type,  or  that  in  which  folding  plus  erosion  of  the  first  set 
of  strata  precedes  the  formation  of  the  second  set. 

Crosby  (2a)  has  called  attention  to  the  unsatisfactory  character 
of  the  prefix  dis,  since  it  means  divergence  rather  than  parallelism. 
He  prefers  to  divide  unconformity  into  para-unconformity  (parun- 
conformity) — the  disconformity  of  Grabau,  and  clino-unconformity 
(clinunconformity)  for  the  angular  type  with  discordant  strata. 
Heim  (9)  had  previously  proposed  the  term  paenaccordanz  for 
approximate  conformity  with  the  strata  nearly  parallel.  This,  as 
Crosby  says,  is  not  quite  the  equivalent  of  the  parunconformity, 
which  implies  crustal  oscillation,  rather  than  deformation,  whereas 
Heim's  term  suggests  rather  gradation  between  true  conformity  or 
accordan2f  and  unconformity  or  discordant. 


822 


PRINCIPLES    OF    STRATIGRAPHY 


Disconformity  (Par unconformity,  Paenaccordanz).  When  strata 
are  elevated  without  folding  or  other  disturbances,  and  subjected 
to  a  prolonged  period  of  erosion,  after  which  their  truncated  edges 
are  covered  by  other  strata,  either  marine  or  nonmarine,  a  stratic 
unconformity  or  disconformity  (parunconformity,  paenaccordanz) 
is  produced.  Here  a  hiatus,  measured  by  the  length  of  time  during 
which  the  lower  strata  were  exposed  to  erosion,  plus  the  amount 
worn  away  during  this  exposure,  separates  the  two  series.  While 
this  hiatus  measures  the  unrepresented  strata  it  must  be  borne  in 
mind,  however,  that  it  does  not  represent  the  length  of  time  dur- 
ing which  deposition  was  interrupted  in  the  region  in  question. 
The  amount  of  nondeposition  can  be  determined  only  when  the 


E 

b 

a 

a 

A 

I 

B 

FIG.  200.     Diagrams  illustrating  the  development  of  disconformities. 

amount  of  erosion  during  the  elevation  of  the  region  is  known. 
We  may  assume  two  locations  A-B,  where  elevation  may  occur  or 
some  other  changes  by  which  deposition  continued  uninterruptedly 
at  B,  while  erosion  replaced  it  at  A.  (Fig.  200,  I-IV.)  Under  as- 
sumed conditions  a  formation  c,  equal  in  thickness  to  formation  a, 
may  be  deposited  at  B,  while  b  is  eroded  at  A.  If  later  deposition 
becomes  uniform  again  in  both  localities,  d  will  rest  conformably  on 
c  at  locality  B,  but  disconformably  on  a  at  A.  The  hiatus  at  locality 
A  comprises  formations  b  and  c,  but  the  actual  time  interval  is  meas- 
ured only  by  the  deposition  of  formation  c  at  locality  B.  In  this 
case  the  erosion  at  A  was  assumed  to  equal  the  amount  of  deposi- 
tion at  B,  and  hence  the  hiatus  at  A  represents  twice  the  amount  of 
the  time  interval  involved,  as  developed  at  B. 

If  erosion  at  A  exceeds  deposition  at  B,  then  the  hiatus  at  A 
representing  a  definite  time  interval  will  be  greater  than  twice  the 
depositional  equivalent  of  that  time  interval  at  B,  by  an  amount  pro- 
portional to  the  excess  of  erosion  over  deposition.  If  erosion  at  A 


DISCONFORMITY  823 

is  exceeded  by  deposition  at  B,  then  the  hiatus  at  A  will  be  smaller 
than  twice  the  depositional  equivalent  by  a  corresponding  amount. 
When  the  amount  of  erosion  is  zero  at  A,  the  hiatus  will  be  repre- 
sented by  the  deposit  at  B  above,  when  formation  d  will  rest  discon- 
formably  on  b  at  A,  instead  of  resting  on  a.  (Fig.  200,  IV.) 

The  disconformity  at  A  may  be  scarcely  indicated  in  the  strata, 
and,  if  it  were  not  for  the  fact  that  formations  elsewhere  found 
intercalated  between  the  two  strata  (as  at  B)  are  missing  here,  the 
disconformity  would  not  be  recognized  at  all.  Very  many  such  dis- 
conformities  exist  in  our  formations,  but  few  of  them  are  readily 
recognized  on  account  of  the  parallelism  of  the  strata.  Sometimes 
an  erosion  interval  and  the  subsequent  encroachment  of  the  sea  are 
indicated  by  the  existence  of  a  basal  conglomerate  in  the  later 
formation,  which  includes  fragments  of  the  earlier  one.  In  some 
cases,  where  a  rapid  transgression  of  the  sea  took  place,  or  where 
fine,  residual  soil  on  the  old  surface  is  but  slightly  reworked,  such 
basal  rudytes  may  be  wanting;  and  the  two  formations  follow  ap- 
parently with  perfect  conformity  upon  each  other.  This  is  the 
case  with  the  black  Chattanooga  shale,  where  it  rests  upon  the 
Rockwood  clays  in  the  Appalachians.  The  hiatus  here  comprises 
the  whole  of  the  Devonic  and  part  of  the  Siluric  as  well,  yet  the 
contact,  though  abrupt,  appears  like  a  conformable  one.  Careful 
examination  should,  however,  reveal  in  such  cases  a  more  or  less  im- 
perfect upper  surface  of  the  lower  bed,  where  some  traces  of  ero- 
sion are  still  visible.  When  this  upper  surface  is  an  undoubted 
deposition  surface,  i.  e.,  when  it  shows  no  traces  of  erosion  what- 
ever, and  when  furthermore  the  succeeding  beds  show  no  evidence 
of  derivation  from  the  underlying  bed,  the  existence  of  a  discon- 
formity may  be  doubted. 

Examples  of  contacts  where  disconformities  have  been  assumed, 
but  are  not  supported  by  evidence  of  erosion,  are  the  contact  be- 
tween the  pyritiferous  Brayman  shale  and  basal  Siluric  sandstone 
(Binnewater)  in  the  Schoharie  region,  and  the  Oriskany-Esopus 
contact  in  the  Helderbergs  of  eastern  New  York.  In  the  former 
case  the  Brayman  shales  are  known  to  be  of  Salina  age,  while  the 
sandstones  on  which  they  rested  were  regarded  as  of  Lorraine  age. 
There  is,  however,  no  evidence  of  a  hiatus  comprising  most  of  the 
Siluric  between  these  two  formations,  the  basal  arenyte  being  too 
intimately  related  to  the  shale  and  of  the  same  age.  The  hiatus, 
known  to  exist  in  this  region,  occurs  at  a  lower  level,  unless,  in- 
deed, as  has  recently  been  suggested  by  Ruedemann  and  others,  the 
Brayman  shale  is  Upper  Ordovicic.  The  Oriskany-Esopus  contact 
of  the  Helderbergs  also  has  the  aspect  of  a  conformable  one.  This 


824 


PRINCIPLES    OF    STRATIGRAPHY 


conformity  if  fully  established  has  even  a  more  far-reaching  signifi- 
cance. Where  a  marine  formation  is  abruptly  succeeded  by  a  con- 
tinental formation,  the  existence  of  a  possible  hiatus  between  the 
two  must  be  taken  into  consideration.  Recently  the  tendency  has 
manifested  itself  in  certain  quarters  to  greatly  multiply  the  number 


FIG.  201.     Basal   Palaeozoic   sandstone   resting  unconformably   upon   gneisstiid 
granite,   Williams    Canyon,    Colorado.      (After   Hayden.) 

of  disconformities.  (Ulrich-22a.)  In  many  cases  the  apparent 
absence  of  a  formation  between  two  others  is  merely  due  to  a 
change  in  facies  so  that  the  formation  is  actually  present,  but  in  a 
different  lithic  or  faunal  facies  or  both. 

Unconformity  (Clinunconformity,  Discordanz).  (Figs.  201-202.) 


FIG.  202. 


Unconformity  at   Siccar    Point,    Scotland,     a  a,   Ordovicic  strata, 
d,  d,  d,  Old  Red  Sandstone.     (After  Lyell.) 


The  structural  unconformity  is  readily  recognized  and  the  one 
generally  detected  wherever  it  occurs.  This  type  of  uncon- 
formity involves  the  folding  of  the  older  strata,  and  the  subsequent 
erosion  of  the  folds  followed  by  the  deposition  of  the  later  strata 
upon  the  eroded  edges  of  the  older  beds.  This  type  of  unconformity 


UNCONFORMITY 


825 


may  often  become  complicated  by  further  folding  and  erosion,  when 
the  complex  relationship  shown  in  Fig.  191  is  produced. 

In  all  cases  of  structural  unconformity  a  considerable  time  in- 


FIG.  203.     Cross-section  of  the  Aletschhorn,  showing  inverted  unconformity 
of  schists  upon  the  laccolithic  crystallines.     (After  Baltzer.) 

terval  remains  unrecorded.  This  is  measured  by  the  amount  of 
folding  and  erosion  which  the  strata  have  undergone.  In  this  cir- 
cumstance it  is  often  the  case  that  the  last  deposited  strata  prior  to 
the  time  that  folding  and  erosion  commenced  were  folded  down  to 


it  j^  ,    •;.  •.-..•••. 


Griinschiefer 


Gran  it 


FIG.  204.     Detail  of  the  peak  of  the  Aletschhorn.     i,  dragging  of  greenslate 
at  granite  contact;  2,  infolding  of  greenslate  into  the  granite. 

such  an  extent  that  they  were  preserved  from  complete  removal  by 
erosion.  Especially  is  this  the  case  when  the  folding  has  been  so 
intensive  as  to  place  the  strata  in  parallel  positions,  i.  e.,  isoclinal 
folding.  In  this  case  the  actual  time  interval,  during  which  no 
deposition  went  on  in  the  region  in  question,  may  be  determined  by 
a  comparison  of  the  ages  of  the  youngest  stratum  in  the  folded 


J 


826  PRINCIPLES    OF    STRATIGRAPHY 

series  with  that  of  the  first  stratum  unconformably  overlying  the 
series. 

Unconformities  and  disconformities  are  often  suggested  by  the 
occurrence  of  dikes  of  igneous  material  in  the  lower  rocks,  which 
do  not  penetrate  the  upper  beds.  Stronger  folding  or  faulting  in  the 
lower  than  in  the  upper  series  also  suggests  an  unconformity,  as 
shown  below.  As  a  unique  example  of  an  indicated  disconformity 
may  be  cited  the  sandstone  dikes  rilling  fissures  in  the  Siluric  lime- 
stones of  western  New  York  and  Canada,  the  overlying  beds  being 
wholly  unaffected  by  these  fissures  and  dikes  because  a  later  de- 
posit. Faulting  affecting  a  lower  set  of  strata,  but  not  a  higher  one, 
also  indicates  a  disconformable  relationship,  and  a  hiatus  represent- 
ing a  sufficient  time  interval  to  allow  for  the  removal  of  the  fault 
scarps  of  the  lower  series. 

The  appearance  of  an  inverted  unconformity,  where  the  later 
strata  end  abruptly  against  the  older  ones,  may  be  produced  by  in- 
tense folding  of  the  rocks  of  a  complex  region,  as  shown  in  the 
figures  of  the  structure  of  the  Aletschhorn  on  page  825.  (Figs.  203- 
204.) 

Conformable  or  accordant  strata  may  also  show  a  variety  of  as- 
pects. Crosby  has  shown  that  on  the  Atlantic  coastal  plain  of  North 
America,  the  strata  wedge  out  landward.*  This  wedging  conformity, 
where  the  formations  are  thinner  in  one  locality  than  in  the  other, 
though  fully  represented,  Crosby  has  called  spheno conformity,  and 
its  correlative,  where  the  strata  are  of  uniform  thickness,  he  calls 
piano  conformity.  If  contemporaneous  faulting  of  the  older  series 
goes  on  with  the  deposition  of  the  newer,  fractoconformity  is  pro- 
duced. 

BIBLIOGRAPHY  XX. 

1.  BROWN,  THOMAS  C.     1913.     Notes  on  the  Origin  of  Certain  Paleozoic 

Sediments,  Illustrated  by  the  Cambrian  and  Ordovician  Rocks  of  Center 
County,  Pennsylvania.     Journal  of  Geology,  Vol.  XXI,  pp.  232-250. 

2.  CROSBY,  WILLIAM  O.     1893.     The  Origin  of  Parallel  and  Intersecting 

Joints,  American  Geologist,  Vol.  XII,  pp.  368-375. 

2a.  CROSBY,  W.  O.  1912.  Dynamic  relation  and  terminology  of  strati- 
graphic  conformity  and  unconformity.  Journal  of  Geology,  Vol.  XX, 
No.  4,  1912,  pp.  289-299. 

3.  DAUBREE,  AUGUSTE.     1879.     Etudes  synthetiques  de  Geologic  Ex- 

perimentale,  pp.  300-374. 

4.  DAVIS,  WILLIAM  M.     1913.     Nomenclature  of  Surface  Forms  on  Faulted 

Structures.     Bulletin  of  the  Geological  Society  of  America,  Vol.  XXIV, 
pp.  187-216. 

*  A  part  of  this  is  no  doubt  due  to  actual  breaks  in  the  series,  which  disappear 
seaward. 


BIBLIOGRAPHY    XX  827 

5.  GRABAU,    AMADEUS    W.      1900.     Siluro-Devonic    Contact    in    Erie 

County,  New  York.  Bulletin  of  the  Geological  Society  of  America, 
Vol.  XI,  pp.  347-376. 

6.  GRABAU,  A.  W.     1905.     Physical  Characters  and  History  of  Some  New 

York  Formations.     Science,  N.  S.,  Vol.  XXII,  pp.  528-535. 

7.  HAHN,  F.  FELIX.     1912.     Untermeerische  Gleitung  bei  Trenton'  Falls 

(Nord  Amerika)  und  ihr  Verhaltniss  zu  Ahnlichen  Storungsbildern. 
Neues  Jahrbuch  fur  Mineralogie,  etc.  Beilage  Band  XXXVI,  pp.  1-41, 
Taf.  I-III,  1912. 

8.  HEIM,   ARNOLD.     1908.     Ueber    rezente    und   Fossile  Subaquatische 

Rutschungen  und  deren  Lithologische  Bedeutung.  Neues  Jahrbuch  fur 
Mineralogie,  etc.,  1908,  pt.  II,  pp.  136-157. 

9.  HEIM,  ARNOLD.     1908.     Die  Nummuliten-  und  Flysch-bildungen  der 

schweizer  Alpen  (discusses  Accordanz,  Discordanz,  Paen-accordanz). 
Abhandlungen  der  schweizerischen  Palaeontologischen  Gesellschaft, 
XXXV,  1908,  p.  173. 

9a.  HOBBS,  WILLIAM  H.      1911.      Repeating  Patterns  in  the  Relief  and  in  y 
the   Structure   of  the   Land.      Bulletin  of  the  Geological   Society  of 
America,  Vol.  XXII,  pp.  123-176,  pis.  7-13. 

10.  HOW,   JOHN  ALLEN.     1913.     Joints.     Encyclopedia  Britannica,    nth>/ 

edition,  Vol.  XV,  pp.  490-491. 

11.  HYDE,  J.  E.     1908.     Desiccation  conglomerates  in  the  Coal  Measures-^/ 

limestone  of  Ohio.     American  Journal  of  Science,  Vol.  XXV,  pp.  400—408. 

12.  KEILHACK,    KONRAD.     1908.     Lehrbuch    der    Praktischen    Geologic, 

2te  auflage,  Stuttgart. 

13.  KOKEN,  E.    1902.    Ueber  die  Gekrosekalke  des  Obersten  Muschelkalkes 

am  Unteren  Neckar.  Centralblatt  fur  Mineralogie,  etc.,  1902,  pp.  74 
et  seq. 

14.  LEITH,  C.  R.     1905.     Rock  Cleavage.     Bulletin  of  the  U.  S.  Geological 

Survey,  no.  239. 

15.  LOGAN,  SIR  W.     1863.     Geology  of  Canada,  1863,  pp.  391  et  seq. 

16.  MARSH,  OTHNIEL  C.     1868.     On  the  origin  of  the  so-called  lignites 

or  epsomites.  Proceedings  of  the  American  Association  for  the  Advance- 
ment of  Science,  Vol.  XVI,  pp.  135-143. 

17.  MILLER,  W.  J.     1909.     Geology  of  the  Remsen  Quadrangle.     New  York 

State  Museum  Bulletin  126,  1909. 

18.  REID,  H.  F.;  DAVIS,  W.  M.;  LAWSON,  A.  C.;  and  RANSOME,  F.  L. 

1912.  Proposed  Nomenclature  of  Faults.     Advance  Publication,  Geo- 
logical Society  of  America,  Bulletin  24. 

19.  REID,  H.  F.;  DAVIS,  W.  M.;  LAWSON,  A.  C.,  and  RANSOME,  F.  L. 

1913.  Report  of  the  Committee  on  the  Nomenclature  of  Faults.     Geo- 
logical Society  of  America  Bulletin,  Vol.  XXIV,  pp.  163-186. 

20.  REIS,    OTTO    M.     1909.     Beobachtungen    ueber    Schichten-folge    und 

Gesteins-ausbildungen  in  der  fnmkischen  Unteren  und  Mittleren  Trias. 
I.  Muschelkalk  und  Untere  Lettenkohle.  Geognostische  Jahreshefte, 
Bd.  XXII,  1909  (1910),  pp.  1-285,  plates  I-XI. 

21.  ROTHPLETZ,   A.     1910.     Meine  Beobachtungen  ueber  den  Sparagmit 

und  Birikalk  am  Mjosen  in  Norwegen-Sitzungsbericht.  K.  bayrischen 
Akademie  der  Wissenschaften,  Mathematisch-Naturwissenschaftliche 
Klasse,  Bd.  XV,  1910,  65  pages  and  maps. 

22.  RUEDEMANN,  RUDOLF.     1910.     On  the  Systematic  Arrangement  in 

the  elements  of  the  Palaeozoic  platform  of  North  America.  New  York 
State  Museum  of  Natural  History,  Bulletin  140,  pp.  141-149. 


1 


828  PRINCIPLES    OF    STRATIGRAPHY 

22a.  ULRICH,  E.  O.     Revision  of  the  Palaeozoic  Systems.        Bulletin  of  the 
Geological  Society  of  America,  Vol.  XXII,  pp.  281-680. 

23.  VAN  HISE,  CHARLES  R.     1904.    A  Treatise  on  Metamorphism.    United 

States  Geological  Survey,  Monograph  XL VI I. 

24.  WAGNER,   GEORG.     1913.     Stylolithen  und  Druck-suturen.      Geolog- 

ische  und  Palaeontologische  Abhandlungen   (Koken),  N.  P.,  Band  XI 
(XV),  Heft  2,  pp.  101-127,  taf.  X-XII.     (With  literature.) 

25.  WELLER,  STUART.     1899.     A   Peculiar  Devonian   Deposit  in  North- 

eastern Illinois.     Journal  of  Geology,  Vol.  VII,  pp.  483-488. 

26.  WOOD  WORTH,  J.  B.     1896.     On  the  fracture  system  of  joints,  with 

remarks  on  certain  great  fractures.     Boston  Society  of  Natural  History 
Proceedings,  Vol.  XXVII,  pp.  163-183,  pis.  1-5. 

Supplementary . 

27.  BOHM,    A.      (Edler  von  Bohmersheim)  1910.      Abplattung  und  Gebirgs- 

bildung.     Leipzig  und  Wien;  p.  83. 

28.  POKELS,  F.     1911.     Aenderungen  der  Rotationsgeschwindigkeit  der  Erde 

als  geologischer  Faktor.      Geologische  Rundschau,  Band  II,  pp.  141- 
144. 

29.  TAYLOR,  F.  B.     1885.    On  the  Crumpling  of  the  Earth's  Crust.    American 

Journal  of  Science.     3rd  ser.,  Vol.  XXX,  pp.  259-277. 

30.  WILLIS,  BAILEY.     1907.     A  Theory  of  Continental  Structure  Applied 

to    North    America.      Geological  Society  of  America.       Bulletin  Vol. 
XVIII,  pp.  388-412. 


CHAPTER   XXI. 

THE  PRINCIPLES  OF  GLYPTOGENESIS,  OR  THE  SCULPTURING 
OF  THE  EARTH'S  SURFACE. 

During  every  geological  period  the  complementary  processes  of 
erosion  and  deposition  were  in  evidence,  sometimes  the  one  pre- 
dominating and  sometimes  the  other.  Deposition  added  material 
to  the  crust  locally,  erosion  removed  it  elsewhere.  The  results  of 
erosion  in  terms  of  form  are  the  relief  features,  and  the  process 
viewed  from  this  angle  is  a  process  of  sculpturing.  The  genesis  of 
land  forms  is  thus  in  large  part  a  genesis  by  sculpturing  or  glypto- 
genesis* 

At  all  times,  wherever  land  existed,  erosion  produced  its  charac- 
teristic forms,  controlled  to  a  large  degree  by  the  character  of  the 
material  on  which  the  forces  of  erosion  were  at  work.  Many  of 
the  old  erosion  forms  were  buried  beneath  accumulations  of  new 
rock  material,  and  were  thus  preserved  in  a  fossil  form.  Where 
much  deformation  and  alteration  of  the  rocks  has  since  occurred, 
those  older  land  forms  may  have  become  unrecognizable.  •  Never- 
theless, in  many  cases  they  are  still  in  part  preserved,  and  from  a 
study  of  modern  types  we  may  gain  a  sufficient  insight  into  the  order 
of  the  development  to  enable  us  to  reconstruct  ancient  examples 
from  partly  preserved  remains. 

THE  CYCLE  OF  EROSION.  It  is  needful  at  the  outset*  for  us  to 
have  a  clear  conception  of  the  entire  cycle  of  erosion  as  expressed 
in  land  forms.  Beginning  with  the  young  or  newly  formed  land, 
which  may  be  a  recently  emerged  coastal  plain,  a  dome,  anticline, 
fault  block,  etc.,  the  development  of  a  drainage  system  as  outlined 
in  Chapter  III  brings  with  it  a  progressive  sculpturing  and  the  pro- 
duction of  a  series  of  topographic  features,  which  carries  the  land- 
scape through  all  stages  of  youthfulness  to  maturity  and  on  toward 
old  age.  With  the  completion  of  the  cycle  in  a  moist  climate  the 
condition  of  a  peneplain  is  reached,  when  the  region  is  worn  down 
to  essential  uniformity,  with  but  little  elevation  above  sea-level. 

*  From  7Xu7rr6s,  carved,  and  ytvKuru,  origin 

829 


830  PRINCIPLES    OF    STRATIGRAPHY 

The  encroaching  sea  may  finish  this  surface  into  an  almost  abso- 
lutely level  plane  of  marine  planation.  In  an  arid  climate  a  more  or 
less  sloping  plane  (chonoplain)  or  a  series  of  planes  will  be  formed 
in  the  old  age  of  the  landscape,  these  depending  for  their  character, 
slope,  and  elevation  on  the  forces  controlling  the  local  base  level 
of  erosion. 

After  the  cycle  has  thus  been  completed,  a  new  one  may  be  inau- 
gurated by  an  uplift  of  the  land  or  lowering  of  the  sea-level  or  other 
base-level  of  erosion  or  by  a  climatic  change,  etc.  Thus  a  second 
cycle  of  erosion  will  be  inaugurated  which,  if  left  undisturbed,  will 
continue  to  its  end,  and  a  second  peneplain  or  chonoplain  is  pro- 
duced. The  cycle  may  at  any  time,  however,  be  interrupted  by  a 
premature  rejuvenation,  the  earlier  cycle  remaining  thus  incomplete. 

Considering  the  principal  land  forms  resulting  from  land  sculp- 
ture, we  may  first  note  the  characteristics  of  immature  stages,  and 
later  on  those  of  the  completed  cycle.  Strata  unaffected  by  orogenic 
disturbances  will  be  considered  first,  and  later  on  those  which  have 
suffered  deformation.  The  types  to  be  discussed  include  the  forms 
resulting  from  the  normal  sculpturing  of  i.  the  coastal  plain,  2.  the 
monoclinal  strata,  3.  the  dome,  4.  the  anticline,  5.  the  basin,  and  6. 
the  syncline.  Faulted  structure  (7)  will  be  briefly  noted,  and  after 
this  the  peneplain  (8)  will  be  considered  more  at  length. 


A.     EROSION  FEATURES  IN  UNDISTURBED  STRATA, 
i.     THE  COASTAL  PLAIN. 

The  submerged  deposits  on  the  continental  or  island  margin,  of 
which  the  sub-coastal  plain  is  composed,  represent  most  typically  a 
series  of  clastic  sediments,  in  part  land-derived  and  in  part  thalas- 
sigenous  or  derived  from  organic  or  biogenic,  rarely  chemical,  de- 
posits formed  in  the  sea.  Stratification  is  well  developed,  and  the 
phenomenon  of  progressive  overlap  is  generally  well  marked.  Re- 
gressive phenomena,  accompanied  by  landward  erosion  and  seaward 
retreat  of  shore  features,  and  transgressive  phenomena  accompanied 
by  overlap  of  the  upper  beds  of  later  formations  on  the  eroded 
surfaces  of  earlier  ones,  are  all  commonly  represented  in  the  struc- 
ture of  the  sub-coastal  plain.  When  this  is  elevated  into  a  coastal 
plain  by  epeirogenic  movements,  or  into  a  mountain  by  orogenic 
disturbances,  these  structures  will  to  a  greater  or  less  extent  influ- 
ence the  erosion  topography  induced  upon  these  surfaces. 

The  coastal  plain  has  normally  a  gentle  dip  seaward,  while,  close 


THE    COASTAL    PLAIN 


831 


to  the  margin  of  the  old  land,  the  upper  thin  edges  of  the  last  de- 
posited layer,  provided  continuous  subsidence  precedes  the  elevation 
of  the  coastal  plain,  lap  over  the  earlier  layers  and  rest  directly 
upon  the  old  land.  These  overlapping  edges  of  the  strata  are  gen- 
erally the  first  to  be  removed  again,  and  in  their  place  will  appear  a 
shallow  valley  running  parallel  to  the  upper  edge  of  the  coastal  plain, 
the  inner  lowland  of  the  normal  coastal  plain  erosion  topography. 
Dissection  of  the  Coastal  Plain.  Streams  originating  upon  the 
coastal  plain  as  the  "run-off"  of  the  rain  and  snow-fall,  continue 
down  the  slope  of  the  surface  to  the  sea  in  more  or  less  parallel 
lines,  and  with  more  or  less  directness,  according  to  the  angle  of 
slope.  These  consequent  streams,  together  with  the  extended  conse- 
quents, i.  e.,  the  old  streams  of  the  old  land,  now  extended  across 
the  coastal  plain  to  the  new  sea  margin,  will  incise  more  or  less 


fcor 

FIG.  205.     The  emerged  coastal  plain  with  the  youthful  consequent  streams 
bearing  a  few  simple  insequents. 

parallel  channels  across  the  coastal  plain.  When  these  channels  are 
cut  down  to  the  level  of  the  "ground  water,"  they  will  be  supplied 
by  springs  with  a  permanent  stream,  whereupon  down-cutting  may 
proceed  at  an  accelerated  pace.  Along  the  margin  of  the  main 
streams,  lateral  tributaries  will  begin,  and,  cutting  headward,  will 
soon  diversify  the  original  channel  of  the  streams.  These  lateral 
branches  are  the  "insequent"  streams  of  the  physiographer,  since 
they  are  not  consequent  upon  a  constructional  slope.  Insequent 
streams,  furthermore,  cut  their  channels  backward  from  the  edge  of 
a  stream,  and  only  deepen  their  channels  as  the  channels  of  the  con- 
sequents to  which  they  are  tributary  are  deepened.  Consequent 
streams,  on  the  other  hand,  cut  their  channels  downward,  headward 
extension  being  generally  a  secondary  mode  of  growth.  Near  the 
old  land  the  insequents  will  remove  the  feather  edges  of  the  coastal 
plain  strata,  as  indicated  above,  and  here  will  come  into  existence  a 
stripped  belt,  expressed  topographically  in  a  broad,  shallow  valley, 
the  inner  lowland,  containing  the  enlarged  insequents,  now  more 


832  PRINCIPLES    OF    STRATIGRAPHY 

generally  spoken  of  as  the  subsequents.  This  inner  lowland  is 
bounded  on  one  side  by  the  stripped  slope  of  the  old  land  and  on 
the  other  by  the  cut  edges  of  the  coastal  plain  strata.  If  these  latter 
contain  resistant  members  of  limestone  or  sandstone,  they  will  pre- 
sent an  escarpment  or  cliff  of  some  steepness.  As  the  inner  lowland 
is  widened  and  deepened  the  cliff  increases  in  height  because  lower 
and  lower  members  of  the  coastal  plain  series  are  discovered  by 
the  removal  of  the  overlapping  higher  members.  This  will  con- 
tinue until  the  consequent  has  reached  a  condition  of  grade,  and  so 
will  arrest  further  deepening  of  the  channels  of  its  tributaries. 
Beyond  this  point  the  cliff  will  be  gradually  lowered,  through  con- 
tinued backward  pushing,  until  the  plane  of  erosion  and  the  sloping 


FIG.  206.  The  same  coastal  plain  as  shown  in  Fig.  205.  After  dissection 
and  the  formation  of  the  cuesta;  the  broad  inner  lowland  is 
occupied  by  the  subsequents. 

surface  of  the  coastal  plain  intersect  near  the  seashore,  when  the 
condition  of  peneplanation  is  reached. 

The  topographic  element  produced  by  the  dissection  of  the 
coastal  plain  is  known  as  the  cuesta.  Its  main  elements  are  the 
"inface"  or  cliff  facing  the  old  land,  and  the  gentle  outward  slope 
conforming  to  the  slight  inclination  of  the  coastal  plain  strata,  and 
formed  by  its  top  member.  Between  the  cuesta  and  the  old  land  is 
the  stripped  belt  or  inner  lowland,  occupied  by  the  subsequent 
stream.  This  is  tributary  to  the  consequent  stream,  which  dissects 
the  cuesta  transversely.  (Figs.  205,  206.) 

Deposition  in  dissected  coastal  plain.  A  moderately  dissected 
coastal  plain  in  which  transverse  consequent  and  longitudinal  sub- 
sequent valleys  are  formed  may  be  affected  by  partial  subsidence, 
in  which  case  erosive  activity  not  only  comes  to  a  standstill,  but 
deposition  will  actually  take  place  in  the  valleys,  if  subsidence  has 
been  sufficient  to  result  in  the  entrance  of  the  sea  into  the  valleys, 
and  the  consequent  drowning  of  the  same.  Examples  of  drowned 
consequent  valleys  are  seen  to-day  in  Chesapeake  and  Delaware 


DISSECTION    OF    THE    COASTAL   PLAIN          833 

bays  which  dissect  the  Atlantic  coastal  plain  of  North  America.  A 
drowned  subsequent  valley  or  inner  lowland  is  seen  in  Long  Island 
Sound,  the  northern  edge  of  Long  Island  forming  the  more  or  less 
ice-disturbed  and  moraine-covered  escarpment,  the  inface  of  a 
normal  cuesta,  now  largely  submerged.  Deposits  of  the  present 
geologic  epoch  are  being  formed  within  these  valleys,  which  were 
cut  in  the  partly  consolidated  Tertiary  and  Cretacic  clays  and  sands, 
the  stratification  of  which  is  almost  horizontal.  The  result  of  such 
deposition  will  be  that  horizontally  stratified  modern  deposits  come 
to  rest  upon  the  Cretacic  or  later  strata  of  similar  position  which 
form  the  bottoms  of  these  eroded  valleys,  and  that  laterally  they 
will  become  continuous  with  or  merge  into  the  horizontal  beds  of 
Cretacic  or  Tertiary  age,  of  the  valley  sides  and  of  the  rewashed 
material  of  which  these  modern  strata  will  in  part  at  least  be  com- 
posed. Since  these  old  drowned  valleys  have  in  places  a  width  of 
a  score  of  miles  or  more,  and  since  it  is  not  at  all  unlikely  that 
conditions  like  the  present  one  may  have  existed  at  different  stages 
in  the  formation  of  the  Atlantic  coastal  plain,  of  North  America — 
not  to  mention  earlier  coastal  plains  of  this  and  other  countries — 
the  significance  of  these  facts  becomes  apparent.  The  commingling 
of  the  older  and  newer  organic  remains  is  another  feature  charac- 
terizing such  deposits.  Thus,  in  Chesapeake  Bay,  modern  oyster 
shells  are  found  attached  to  oyster  shells  of  Miocenic  age. 

Effect  of  dissection  and  peneplanation  of  coastal  plain  strata  on 
outcrop.  Where  normal  deposition  with  continuous  subsidence  and 
progressive  overlapping  of  strata  occurs  the  undissected  coastal  plain 
will  show  on  elevation  the  highest  stratum  only,  which  then  rests 
directly  by  overlap  against  the  old  land.  The  formation  of  the 
inner  lowland  results  in  the  exposure  of  a  belt  of  lower  strata  next 
to  the  old  land,  while  the  edge  of  the  higher  stratum  is  farther  and 
farther  removed  from  the  old  land.  As  the  inner  lowland  is  wid- 
ened and  deepened,  lower  strata  appear  by  erosion  of  the  over- 
lapping ones,  and  the  map  of  a  strongly  dissected  coastal  plain 
region  will  show  several  belts  of  strata  next  to  the  old  land,  the 
lowest  exposed  one  being  nearest  it.  These  belts  of  strata  will  also 
appear  on  the  banks  of  the  consequent  streams,  but  will  progres- 
sively disappear  below  the  valley  bottoms  in  a  seaward  direction 
and  from  the  lowest  to  the  highest.  When  the  coastal  plain  has 
been  reduced  to  a  peneplain,  the  various  strata  composing  it  will 
outcrop  in  a  series  of  more  or  less  parallel  bands  from  the  lowest 
next  to  the  old  land  to  the  highest  of  the  series.  This  last  will  ap- 
pear as  a  belt  near  the  point  where  the  coastal  plain  passed  beneath 
the  sea-level  at  the  time  the  peneplanation  was  completed.  Thus  a 


834  PRINCIPLES    OF    STRATIGRAPHY 

glance  at  the  geologic  map  of  New  York  State  shows  a  series  of 
color  bands  representing  the  various  strata  of  an  ancient  (Palaeo- 
zoic) coastal  plain,  the  lowest  appearing  around  the  Adirondack  old 
land  and  along  the  border  of  the  crystallines  north  of  Lake  On- 
tario, while  each  later  one  is  further  and  further  .removed  south- 
ward, until  the  latest,  the  Carbonic  strata,  scarcely  extend  into  New 
York  State  at  all.  Now,  most  if  not  all  of  these  strata  once  ex- 
tended far  toward,  if  not  entirely  to,  the  Adirondacks,  and  to  the 
Laurentian  old  land  in  Canada.  Their  present  distant  outcrop  is 
in  large  measure  due  to  peneplanation  across  gently  inclined  strata. 
Subsequent  erosion  has,  of  course,  pushed  the  edges  of  many  of 
these  strata  further  south  than  where  they  were  left  at  the  end  of 
the  period  of  peneplanation,  but  the  amount  of  this  later  removal 
was  small  as  compared  with  the  greater  separation  of  outcrops 
effected  by  peneplanation.  It  was  formerly  thought  that  the  out- 
crop of  the  edges  of  strata  along  the  margin  of  the  old  crystalline 
land  marked  their  former  extent.  Since  the  strata  of  eastern  North 
America  crop  out  in  a  series  of  belts  margining  the  old-land,  each 
later  formation  falling  short  of  the  preceding  one,  it  was  believed 
that  North  America  rose  by  a  series  of  steps,  the  sea,  at  the  end  of 
each  period,  retreating  to  the  region  near  which  the  next  later  for- 
mation now  comes  to  an  end.  From  the  characters  of  the  forma- 
tions, however,  it  appears  that  they  accumulated  in  a  subsiding  sea, 
and  that  each  formation  in  turn  overlapped  the  preceding  ones,  with 
few  exceptions. 

The  present  appearance  of  the  outcrops  is  due  wholly  to  erosion, 
the  higher  formations  having  suffered  most.  Many  of  the  later 
Palaeozoic  strata  of  the  eastern  United  States  derived  their  clastic 
material  from  the  Appalachian  region  on  the  southeast,  and  their 
northwestward  limit  in  some  cases  was  far  beyond  the  border  lines 
of  the  present  Canadian  old  land,  a  great  portion  of  which  may  in 
fact  have  been  entirely  submerged  during  a  part  of  the  Palaeozoic. 
That  the  erosion  of  the  strata  continued  until  peneplain  conditions 
were  reached  is  shown,  not  only  by  the  fact  that  the  remnants  of 
this  old  surface  in  the  eastern  United  States  form  parts  of  a  some- 
what warped  plain  rising  southward,  but  also  and  more  especially 
by  the  fact  that  this  surface  is  not  formed  by  a  single  hard  stratum, 
but  by  various  hard  beds  which  have  been  beveled  across.  Thus  the 
Alleghany  plateau  of  western  New  York,  which  is  a  characteristic 
part  of  this  old  peneplain,  is  composed  of  the  beveled  edges  of  suc- 
cessively higher  southwestward  dipping  strata  as  shown  in  the 
following  diagram.  (Fig.  207.) 

This  beveling  of  the  strata  can  be  interpreted  only  as  the  result 


BEVELING   OF    STRATA 


835 


of  peneplanation,  in  other  words,  when  the  level  of  erosion  was 
reached,  erosion  could  go  no  further  because  this  surface  stood  so 
close  to  sea-level  that  the  streams  could  not  cut  lower.  Subsequent 
elevation  would  permit  of  the  cutting  of  lowlands  on  the  softer 
strata  (5,  9  and  12),  leaving  the  harder  ones  in  relief. 

That  this  beveling  of  the  strata  is  due  to  erosion  and  not  to  a 


•L.ONTARIO-  -pj 


U      JO  9  8         7  6  5    "      4  32 

FIG.  207.  Section  across  New  York  State,  from  Ontario  to  the  Pennsyl- 
vania line,  showing  the  peneplanation  of  the  strata  along  the 
dotted  line,  and  the  subsequent  carving  of  valleys  on  the  softer 
strata,  i,  Archaean ;  2,  Potsdam  or  Beekmantown ;  3  and  4,  Black 
River-Trenton ;  5,  Utica-Lorraine ;  6,  Queenston ;  7,  Medina- 
Clinton-Rochester ;  8,  Lockport-Guelph ;  g,  Salina ;  10,  Bertie- 
Cobleskill;  n,  Onondaga;  12,  Marcellus;  13,  Hamilton;  14, 
Genesee-Portage-Chemung.  2-6,  Ordovicic;  7-10,  Siluric;  11-14, 
Devonic. 

shoreward  thinning  is  shown  by  the  fact  that  the  material  of  the 
strata  does  not  change  toward  the  beveled  portion  as  it  would  if  that 
part  had  marked  a  progressively  retreating  shore  accumulation, 
while  the  fact  that  the  lowest  portion  of  the  beds  extends  farther 
than  the  higher  portions  shows  that  the  thinning  cannot  represent 
an  overlapping  transgressive  series.  The  following  diagrams  illus- 
trate the  thinning  of  the  strata  by  overlap  and  by  beveling.  (Figs. 
208,  A  B.) 


A  B 

FIG.  208.     Diagram*  illustrating  the  thinning  of  strata :  A,  by  overlap ;  B,  by 
beveling   through    erosion. 


Ancient  Coastal  Plains  Showing  Cuesta  Topography. 

Looking  over  the  geological  maps  of  the  world,  many  examples 
of  ancient  coastal  plain  strata,  in  which  a  cuesta  topography  has 
been  revived  after  peneplanation,  are  found.  The  Palaeozoic  strata 
of  New  York  and  Canada  furnish  excellent  examples,  though  part 
of  the  topography  is  drowned,  or  obliterated  by  subsequent  de- 
posits. (Figs.  209,  210.) 


836 


PRINCIPLES    OF    STRATIGRAPHY 


A  nearly  continuous  cuesta  in  face  may  be  traced  along  the  south 
shore  of  Lake  Ontario  from  Rochester  to  Niagara,  and  thence 
northwestward  through  Canada,  the  Indian  Peninsula  between 
Georgian  Bay  and  Lake  Huron,  and  across  the  Manitoulin  Islands. 
Turning  westward  on  these  islands,  it  passes  through  the  Northern 
Peninsula  of  Michigan,  and  then  turns  southward,  forming  the 
peninsula  between  Lake  Michigan  and  Green  Bay,  beyond  which  it 
continues  southward  through  eastern  Wisconsin. 


;v 


FIG.  209.  Map  showing  the  probable  drainage  and  topography  in  eastern 
North  America  during  Tertiary  time,  when  a  revived  cuesta- 
topography  was  produced. 

The  cuesta  is  cut  out  of  the  Lower  Siluric  formations  which 
here  consist  of  the  capping  hard  Niagaran  (Lockport)  limestones 
and  dolomites,  underlain  by  softer  shales  and  sandstones,  into  which 
the  inner  lowland  has  been  cut.  In  New  York  the  softer  strata 
are  thickest  while  the  overlying  hard  beds  thin  eastward.  Here  the 
inner  lowland  is  very  deep,  approaching  in  places  a  thousand  feet 
below  the  top  of  the  cuesta.  Most  of  it  is  submerged  by  the  waters 
of  Lake  Ontario.  Eastward  from  Rochester  the  cuesta  becomes 
less  defined,  owing  to  the  failure  of  the  hard  capping  stratum,  and 
it  finally  unites  with  the  next  higher  cuesta  to  the  south,  to  form 


ANCIENT    CUESTAS 


837 


the  Helderberg  escarpment.  Westward  the  limestone  thickens,  and 
hence  the  escarpment  becomes  bold,  but  the  inner  lowland  suffers. 
In  Western  Ontario  this  inner  lowland  is  largely  obliterated  by 
drift  deposits,  but  it  appears  again  in  the  basin  of  Georgian  Bay. 
The  basin  of  Green  Bay  likewise  occupies  a  part  of  the  inner  low- 
land in  its  western  extension,  south  of  which  the  deposits  of  drift 
somewhat  obscure  it.  There  is,  however,  a  chain  of  small  lakes 
(Winnebago,  etc.)  which  shows  its  continuation.  Lake  Winnipeg 


o. 


'V, 


FIG.  210.  A  later  stage,  showing  probable  river  adjustment  by  capture,  etc., 
as  deduced  from  the  present  topography.  The  partial  blocking 
of  the  valleys  by  glacial  drift,  the  glacial  over-deepening  of 
others,  and  the  subsidence  of  the  land  on  the  northeast,  produced 
the  present  topography  and  drainage. 

in  Canada  lies  in  a  similar  inner  lowland  faced  on  the  west  by  a 
cuesta  inface  of  the  Niagaran  formation.  In  a  few  places  the 
cuesta  is  broken  by  ancient  or  by  modern  stream  channels.  The 
most  pronounced  of  the  former  is  at  the  western  end  of  Lake 
Ontario  (Dundas  Valley)  and  in  the  channel  connecting  Georgian 
Bay  with  Lake  Huron,  and  continued  in  Saginaw  Bay  (Saginaw 
River  Valley).  (Grabau-i6 :  37-54.)  The  most  pronounced  of  the 
modern  stream  channels  are  those  of  the  Genesee  and  the  Niagara. 
North  and  west  of  this  cuesta  series,  i.  e.,  nearer  to  the  old  land, 


838  PRINCIPLES    OF    STRATIGRAPHY 

are  several  smaller  cuestas,  less  continuous,  but  still  in  places  quite 
pronounced.  These  are  carved  out  of  the  Ordovicic  limestones, 
where  they  rest  on  softer  shales  or  sandstones.  (Wilson-3i.) 
South  of  the  Niagara  cuesta  are  several  others  cut  into  the  De- 
vonic  strata.  The  most  pronounced  is  that  of  the  Onondaga  lime- 
stone crossing  the  Niagara  River  at  North  Buffalo  and  extending 
east  across  the  State  until  it  culminates  in  the  Helderberg  edge 
northwest  of  Albany.  This  extends  northwestward  from  Buffalo, 
and  crosses  Lake  Huron  as  a  submerged  ridge,  finally  reappearing 
in  Mackinac  Island,  beyond  which  it  merges  with  the  cuesta  formed 
by  the  Hamilton  strata,  which  continues  southward  along  the  east- 
ern border  of  Lake  Michigan. 

Throughout  western  New  York  and  Canada  this  cuesta  is  buried 
under  drift,  but  in  Lake  Huron,  though  submerged,  it  forms  a 
cliff  400  feet  high.  (Fig.  211.)  A  still  higher  but  generally  less 


FIG.  211.  Cross-section  of  Lake  Huron,  from  Point  au  Sable  (a)  across  nine- 
fathom  ledge  (b)  to  Cape  Hurd  (c),  showing  the  submerged 
cuesta  'and  inner  lowland. 


pronounced  cuesta  extends  eastward  across  central  and  southern 
New  York,  formed  by  the  sandy  Upper  Devonic  strata.  Eastward 
this,  too,  merges  into  the  Helderberg  escarpment. 

The  Palaeozoic  outcrops  of  northern  Europe  also  fall  into  line  as 
parts  of  a  series  of  discontinuous  cuestas.  Thus  the  drowned  region 
of  the  Baltic  shows  an  Ordovicic  cuesta  series,  partly  submerged  in 
the  islands  of  Oland,  Dago  and  the  coast  of  Esthonia,  the  infaces 
of  which  faced  the  old  land  of  Sweden  and  Finland.  The  drowned 
inner  lowland  includes  the  Kalmar  Sund.in  Sweden  and  the  Gulf  of 
Finland  in  Russia.  A  second  discontinuous  cuesta  formed  of  Silu- 
ric  rocks  runs  in  a  general  way  parallel  to  the  first  and  farther  to 
the  south  and  east.  This  comprises  the  islands  of  Gotland  and  Osel, 
and  continues  in  the  Baltic  provinces  of  Russia.  Central  Europe 
has  its  main  Mesozoic  cuestas  in  the  Swabian  Alp  which  extends 
across  southern  Germany  as  a  bold  escarpment  of  horizontal  Juras- 
sic limestones  from  Wiirttemberg  to  the  borders  of  the  Bohemian 
forest. 

England,  too,  has  its  Palaeozoic  cuesta  in  the  westward  facing 
Wenlock  Edge  of  Siluric  strata.  It  has  two  distinct  Mesozoic 
cuestas :-  one  in  the  range  of  oolite  cliffs  which  extends  from  Dorset 


MESOZOIC    CUESTAS  839 

to  the  Yorkshire  coast  and  forms  the  Cotswold  hills  of  middle 
England  with  the  Worcester  lowland  in  front  of  it,  and  the  other 
in  the  chalk  cliffs  which  extend  in  like  manner  from  the  Channel  to 
Flamborough  Head,  and  forms  the  Chiltern  hills  of  middle  Eng- 
land, the  Oxford  lowland  lying  to  the  west  of  them.  (Fig.  212.) 
All  of  these  topographic  features  are  revived,  being  probably  in 
the  second  if  not  later  cycle  of  erosion.  The  coastal  plain  of  Ala- 
bama, on  the  other  hand,  furnishes  an  example  of  a  cuesta  appar- 
ently in  the  first  cycle.  The  cuesta  itself  is  formed  by  the  Tertiary 
strata  of  the  coastal  plain,  the  inface  rising  rather  abruptly  200  feet 
above  the  lowland  and  being  locally  known  as  Chunnenugga  ridge. 
On  the  broad  upland  dissected  by  short  streams  running  down  the 


FIG.  212.  Stereogram  of  the  Mesozoic  coastal  plain  of  central  England :  A, 
old  land  of  Palaeozoics  (Wales)  ;  B,  Worcester  lowland  on  Trias- 
sic  sandstone;  C,  Cotswold  hills  or  Oolite  cuesta;  D,  Oxford 
lowland  on  Upper  Jurassic  and  Lower  Cretacic  clays,  etc.;  E, 
Chiltern  hills  or  -chalk  cuesta;  F,  Tertiary  coastal  plain.  (After 
Davis.) 

inface  (obsequent  streams)  lie  the  "hill  prairies,"  the  surface  being 
formed  by  a  resistant  limestone  bed.  This  slopes  south  to  the  coast 
and  supports  the  "coastal  prairies."  Extensive  pine  forests  also 
grow  on  this  surface.  The  inner  lowland,  which  lies  between  the 
inface  and  the  old  land  formed  by  the  rocks  of  the  Appalachians, 
is  so  level  that  rainfall  drains  slowly  and  roads  are  impassable  in 
wet  weather.  "It  is  called  the  'Black  Prairie'  from  the  dark  color 
of  its  rich  soil,  weathered  from  the  weak  underlying  limestone. 
This  belt  includes  the  best  cotton  district  of  the  state."  (Davis- 

5 : 135:) 

Minor  Erosion  Forms  of  Horizontal  Strata.  Among  these  is 
the  mesa  or  flat-topped  table  mountain,  the  surface  of  which  is 
formed  by  a  resistant  capping  stratum.  It  is  limited  on  all  sides 
by  erosion  cliffs,  and  it  may  constitute  one  of  the  last  remnants  of 
a  once  widespread  series  of  formations.  The  name  "mesa"  is  also 


840 


PRINCIPLES    OF    STRATIGRAPHY 


sometimes  applied  to  a  tableland  cut  out  of  a  peneplaned  region, 
where  the  strata  are  disturbed  or  where  the  material  is  crystalline 
rock.  Its  restriction  to  an  erosion  remnant  of  horizontal  strata  is 
desirable.  When  the  mesa  has  been  reduced  to  small  dimensions 
so  that  it  has  no  longer  an  extended  flat  top — the  name  butte  ap- 
plies, though  here  again  the  designation  is  not  always  uniform,  for 
the  name  is  applied  to  hills  of  varying  origin,  even  to  volcanic  cones. 
Restriction  here  would  serve  the  cause  of  accuracy  and  precision. 
A  tepee-butte  is  a  conical  erosion  hill,  so  named  from  its  resem- 
blance to  the  Indian  wigwam  or  tepee.  Tepee-buttes  abound  in  the 
region  east  of  the  Front  Range  in  Colorado,  where  they  are  formed 
by  the  resistance  to  erosion  of  a  core  of  organic  limestone  which  is 
surrounded  by  soft,  easily  eroded  shale.  These  have  been  described 
and  figured  in  Chapter  X  and  the  student  is  referred  to  the  paper 
by  Gilbert  and  Gulliver  there  cited. 


B.     EROSION  FEATURES  IN  DISTURBED  STRATA. 
2.     THE  MONOCLINE. 

When  the  old  land,  together  with  the  edge  of  the  coastal  plain 
lapping  onto  it,  suffers  an  uplifting  which  does  not  affect  the  coastal 
plain  strata  at  a  distance  from  the  old  land,  a  monoclinal  structure 


d 

FIG.  213.     Diagrams  illustrating  the  formation  of  a  simple  hog-back   (a,  b), 

and  of  complementary  hog-backs    (c,  d). 
• 

is  given  to  the  edge  of  these  coastal  plain  strata.  On  these  up- 
bending  ends  of  the  strata  erosion  will  proceed  in  much  the  same 
manner  as  in  the  normal  coastal  plain,  and  a  topography  com- 
parable to  the  cuesta  and  differing  from  it  only  in  the  greater  inclin- 


EROSION    OF    DISTURBED    STRATA  841 

ation  of  the  component  strata  will  be  produced.  The  resistant 
stratum  will  produce  a  ridge,  one  side  of  which  is  composed  of  the 
steeply  dipping  surface  of  the  resistant  stratum  and  comparable  to 
the  gentle  outward  slope  of  the  cuesta  surface,  while  the  other  is 
formed  of  the  eroded  edges  of  the  strata  composing  the  ridge,  and 
is  comparable  to  the  inface  of  the  cuesta.  (Fig.  213,  a  b.)-  Topo- 
graphic elements  of  this  type  are  common  on  the  flanks  of  the 
Rocky  Mountain  Front  Range  where  they  are  familiarly  known  as 
"hog-backs."  In  some  cases  these  hog-backs  may,  however,  be  parts 
of  normal  anticlines  of  which  the  crystalline  mountain  mass  was  the 
original  core.  The  outcropping  edges  of  the  component  strata  will 
not  appear  different  on  the  map  from  those  of  the  normal  cuesta, 
and  the  phenomenon  of  overlap  is  perhaps  as  frequently  preserved 
in  this  case  as  in  that  of  the  dissected  normal  coastal  plain. 


3.     EROSION  FEATURES  OF  THE  STRUCTURAL  DOME. 

Wherever  strata  are  locally  uplifted  into  the  form  of  a  broad, 
flat  dome,  as  in  the  case  of  the  Black  Hills,  a  radial  arrangement 
of  consequent  streams  will  come  into  existence,  and  a  series  of  radial 
consequent  valleys  will  be  incised  in  the  surface  of  the  dome.  The 
birth  of  numerous  insequent  streams  at  the  summit  of  the  dome 
will  cause  a  gradual  opening  up  of  a  series  of  summit  valleys.  If 
the  surface  stratum  is  a  resistant  one,  while  the  stratum  next  below 
is  readily  eroded,  a  compound  summit  valley,  drained  by  tributaries 
of  the  various  consequent  streams,  will  come  into  existence  on  the 
soft  stratum,  while  the  eroded  edge  of  the  hard  stratum  will  sur- 
round this  valley  as  a  series  of  ramparts  broken  at  intervals  by  the 
breaches  through  which  the  drainage  is  carried  out.  The  character 
of  the  enclosing  rampart  will  be  that  of  a  breached  circular  hog- 
back with  an  erosion  inface  and  a  steeply  inclined  outward  slope. 
Continued  erosion  by  the  tributary  (subsequent)  streams  will  widen 
the  circumference  of  the  rampart  by  pushing  it  down  slope,  and 
thus  increasing  the  size  of  the  summit  valley.  If  a  second  resistant 
layer  is  discovered  beneath  the  soft  layer  on  which  the  valley  was 
opened,  it  may  be  breached  in  a  manner  similar  to  the  first,  and  a 
second  inner  set  of  encircling  hog-back  ridges  may  come  into  exist- 
ence surrounding  an  inner  valley  opened  up  on  a  second  soft  layer. 
Several  sets  of  such  encircling  hog-backs  may  thus  be  produced, 
two  sets  always  being  separated  by  a  circular  valley  which  drains 
through  one  or  more  branches  in  the  outer  hog-back  ring.  If  the 
level  to  which  erosion  is  carried,  i.  e.,  base-level,  is  reached  while 


842 


PRINCIPLES    OF    STRATIGRAPHY 


the  center  is  still  composed  of  a  soft  stratum,  a  central  lowland  will 
remain  as  in  the  case  of  the  Weald  of  southeastern  England.  If, 
however,  erosion  goes  on  until  the  underlying  crystallines  are  ex- 
posed a  central  mountainous  area  will  remain  as  in  the  case  of  the 
Black  Hills.  (Fig.  214.) 

In  outcrop,  an  eroded  dome  will  show  the  strata  in  a  series  of 
concentric  rings,  the  oldest  at  the  center  and  the  youngest  outer- 


FIG.  214.  Stereogram  of  the  Black  Hills  dome,  showing  the  mountainous 
center  formed  by  the  resistant  crystallines,  and  the  rimming 
hog-backs  and  valleys.  (After  Davis.) 

most.  As  in  the  case  of  the  cuesta  and  the  monocline,  the  ultimate 
result  of  erosion  of  such  a  dome  is  the  obliteration  of  the  ridges, 
and  the  reduction  of  the  dome  as  a  whole  to  peneplain  condition. 
When  that  has  occurred  all  the  strata  involved  will  be  beveled  off 
toward  the  center  of  the  dome,  their  lower  edges  projecting  farthest 
up  onto  the  dome.  (Fig.  215,  A.)  A  structure  of  this  kind  is  not 
infrequently  mistaken  for  a  marginal  thinning  of  strata  on  the  shore 


A 


FIG.  215.     Diagrams  illustrating  the  thinning  of  strata  under  cover  toward  the 
center  of  a  dome:   A,  by  erosion;  B,  by  overlap. 

of  an  island.  In  this  case,  however,  the  strata  should  overlap  each 
other,  and  the  higher  portions  reach  farthest  onto  the  dome.  ( Fig. 
215,  B.)  The  thin  overlapping  edges,  moreover,  should  be  of  a  clas- 
tic character,  and  composed  in  part  of  material  derived  from  the 
shore  of  the  island,  while,  in  the  case  of  the  eroded  dome,  the  strata 
on  both  sides,  being  part  of  a  formerly  continuous  whole,  should  be 
of  the  same  character,  and  show  no  shore  features  on  the  thin 
edge.  Furthermore,  strata  deposited  in  this  area,  subsequently  to 


EROSION    OF    DISTURBED    STRATA  843 

the  erosion  of  the  dome  (Fig.  215,  A,  b  d  e)  would  progressively 
come  to  rest  upon  the  beveled  edges  of  older  and  older  strata,  in  the 
direction  of  the  center  of  the  dome,  the  relation  being  an  uncon- 
formable  one.  This  same  type  of  structure  might,  of  course,  be 
produced  by  a  gradually  retreating  sea  from  a  rising  island,  so  that 
each  succeeding  stratum  reaches  to  a  less  distance  than  the  pre- 
ceding. In  that  case,  however,  the  ends  of  the  successive  strata 
would  show  shore  characteristics,  and  fragments  of  the  lower  might 
be  enclosed  in  the  higher  formations. 

The  Cincinnati  and  Nashville  domes  are  typical  examples  of  low 
domes  with  very  gently  inclined  strata  formed  and  eroded  during 
Palaeozoic  time.  As  pointed  out  repeatedly  by  Dr.  Foerste  (15)  and 
others,  the  lower  Siluric  (Niagaran)  strata  found  on  the  flanks  of 
the  dome  conform  in  character  to  the  first  of  the  two  cases  cited, 
all  the  evidence  pointing  to  the  fact  that  the  Niagaran  strata  for- 
merly extended  across  the  domes,  which  therefore  formed  in  late 
Siluric  or  early  Devonic  time.  As  the  eroded  edges  of  the  strata 
are  disconformably  overlain  by  Mid-Devonic  limestones,  or  by 
Upper  Devonic  or  younger  black  shales,  it  is  evident  that  the  ero- 
sion of  the  dome  preceded  Mid-Devonic  time.  This  probably  oc- 
curred during  the  Helderberg  period,  while  the  greater  part  of 
North  America  was  above  sea-level. 

Subsequently  to  the  deposition  of  the  higher  Palaeozoic  over  this 
pre-Devonic  truncated  dome,  one  or  more  additional  domings  took 
place,  followed  by  erosion  which  again  exposed  the  lowest  central 
strata. 


4.     EROSION  FEATURES  ON  THE  ANTICLINE. 

The  anticline  differs  from  the  dome  chiefly  in  the  fact  that  the 
longitudinal  axis  is  many  times  longer  than  the  transverse.  Since 
the  anticline  must  come  to  an  end  in  either  direction  by  a  downward 
pitching  of  the  axis,  the  characteristics  of  the  simple  anticline  may 
be  considered  those  of  an  excessively  elongated  dome.  While  domes, 
however,  generally  occur  singly,  anticlines  occur  most  commonly  in 
series,  a  number  of  parallel  anticlines  being  separated  by  synclines. 
The  erosion  structure  of  such  anticlines  is  in  general  similar  in 
each  anticline  to  that  of  the  dome,  except  that  the  subsequent  val- 
leys and  the  hog-back  ridges  are  parallel,  instead  of  circumferential, 
and  the  transverse  consequent  gorges  in  the  ridges  are  parallel  in- 
stead of  radial.  The  most  important  difference  lies  in  the  duplica- 
tion of  the  structure  in  each  anticline  and  its  complication  by  the 


844 


PRINCIPLES    OF    STRATIGRAPHY 


intervening  synclines.     The  resultant  outcrops  have  been  discussed 
in  the  preceding  chapter. 

When  anticlines  are  partly  eroded  a  series  of  monoclines  or 
hog-backs  results,  similar  in  character  to  that  formed  by  the  uplifted 
upper  end  of  the  coastal  plain  as  above  described.  Monoclines 
formed  by  breached  anticlines  usually  occur  in  pairs  opposing  each 
other  as  in  the  Appalachians  of  to-day,  but  monoclines  without  a 
corresponding  opposite  occur  which  in  reality  represent  one  limb 
of  an  anticline  of  which  the  other  limb  has  been  entirely  removed. 
(Fig.  216.)  Thus  the  monocline  which  forms  the  Front  Range 
of  the  Appalachians  in  New  Jersey,  Pennsylvania  and  southward 


cofictfon across tfie QreotVodUy  dt^arnsliit.ry. 
Jo  illustrate  Chap  XXII  oftfincUtfeport,  1X31 


'tteyliniKlone . 
l(  Trias)  york. 


W&ry  pastlUy 
great  faults  should  le 
^ placed alony  lints  AB,CD. 


y/tu  AecTio*  AAaivJ  iturety  tht  great  depth  of  the 
Cort  Synclinal ,  but  not  Its  exact  thape  under 
ground.,  ft  indicates  the  e  lose  plications  alsoof-lhe 
Alate  and  limestone  belts ;  and  tke  vast  Jjenal  Zrosion 


FIG.   216.     Section  of  the  Appalachian  folds   near  Harrisburg,  to   show   the 
removal  of  the  eastern  part  of  the  folds  by  erosion. 

represents  merely  the  western  limb  of  an  anticline,  the  eastward 
continuation  of  which  has  been  entirely  removed  by  erosion.  This 
was  accomplished  by  peneplanation  which  cut  below  the  axes  of  the 
synclines  into  the  underlying  more  intensely  folded  rocks  in  which 
the  Appalachian  folds  are  not  recognizable.  The  same  is  in  part 
true  of  the  monoclines  facing  the  Front  Range  of  the  Rocky  Moun- 
tains. The  Triassic  and  Cretacic  strata  most  probably  once  ex- 
tended across  what  is  now  the  front  range  axis,  and  this  was  per- 
haps true  of  much  of  the  Palaeozoic  series  as  well.  From  the  fact 
that  the  axis  of  the  long  Front  Range  anticline  was  a  granite  one, 
erosion,  which  removed  the  formerly  continuous  sediments,  left  it 
in  relief,  so  that  it  holds  the  same  relation  to  the  flanking  mono- 
clines on  either  side  that  the  central  crystalline  mass  of  the  Black 
Hills  holds  to  its  encircling  hog-backs.  (Fig.  213,  c,  d,  p.  840.)  The 
completion  of  the  cycle  of  erosion  in  a  region  of  monoclinal  flexures 


EROSION    OF    ANTICLINES 


845 


results  in  the  formation  of  a  peneplain  across  which  rivers  wander 
with  little  or  no  regard  to  the  underlying  structure.  As  already 
outlined,  the  mapping  of  the  outcrops  of  the  strata  on  such  a  sur- 
face would  form  a  series  of  color  bands  parallel  for  a  long  dis- 
tance, but  uniting  when  the  pitch  of  the  anticline  carried  the  strata 
below  the  erosion  surface.  The  central  color  band  of  the  eroded 
anticline  would,  of  course,  represent  the  oldest  formation,  while  on 
either  side  of  this  would  be  bands  corresponding  on  opposite  sides 
and  representing  the  successively  younger  formations  from  the  cen- 
ter outward  (Fig.  190,  a,  b,  p.  806;  see  also  Figs.  217,  218.) 

Elevation  of  the  peneplain  and  renewal  of  the  erosive  processes 
will  result  in  the  revival  of  the  topography,  since  the  harder  layers 


.217.  Anticlinal  fold  with  pitch- 
ing axis,  truncated  across  the 
top.  The  harder  beds  form 
monoclinal  ridges;  the  valleys 
were  cut  on  soft  strata.  (After 
Willis.) 


FIG.  218.  Synclinal  fold  with  pitch- 
ing axis  eroded.  The  harder 
beds  form  monoclinal  ridges. 
(After  Willis.) 


will  again  be  carved  into  relief  by  the  concentration  of  the  erosive 
processes  on  the" softer  layers.  The  Appalachians  furnish  an  in- 
structive example  of  such  a  revived  topography — they  are  at  pres- 
ent in  the  second  if  not  in  a  later  cycle  of  erosion.*  This  fact  is 
well  brought  out  by  the  numerous  entrenched  transverse  streams 
which  cross  the  monoclines  more  or  less  at  right  angles.  These 
streams,  of  which  the  Susquehanna  is  a  good  example,  came  into 
existence  on  the  tilted  peneplain,  and  their  constant  downward  cut- 
ting made  possible  the  openings  of  the  longitudinal  valleys  on  the 
softer  strata,  by  the  tributary  streams. 

*  This  is  graphically  expressed  by  the  formula  nth  +  I  cycle  suggested  by 
Davis  for  such  cases,  where  it  is  known  that  the  region  is  not  in  the  first  cycle 
of  erosion,  but  where  it  is  impossible  to  say  how  many  cycles  have  been  completed. 
Thus  n  may  stand  for  one  or  for  more  than  one. 


846 


PRINCIPLES    OF    STRATIGRAPHY 


5.     THE  BASIN. 

The  basin  is  the  complement  of  the  dome,  representing  the  down- 
ward arching  of  the  strata.  As  in  the  dome,  the  basin  may  be 
gentle,  with  strata  so  slightly  inclined  as  to  seem  horizontal  or  it 
may  be  a  pronounced  one  with  highly  inclined  sides.  The  former 
is  represented  by  the  Paris  Basin  and  the  Michigan  Basin  and  is 
in  many  respects  the  most  significant  type  to  the  stratigrapher,  being 
often  difficult  to  detect.  The  Paris  Basin  represents  a  case  in  which 
the  successive  strata  have  been  breached  by  radial  consequent 
streams  running  from  the  surrounding  higher  old-land  to  the  lower 
center,  while  their  tributaries  carved  out  circumferential  valleys 
bounded  by  outward  facing  cliffs  of  the  "inface  type."  The  dis- 
sected basin  at  this  stage  differs  from  the  dissected  dome  in  having 
its  oldest  formations  on  the  outside,  the  circumferential  valleys 


FIG.    219.      Strata   of   a   basin,    trun-    FIG.    220.      The    same    series   after   a 
cated  and  covered  by  horizontal  second  folding  and  truncation, 

strata. 

being  cut  out  of  higher  and  higher  strata  toward  the  center,  while 
in  the  dome  the  youngest  formations  are  on  the  outside,  and  the 
successive  circumferential  valleys  are  cut  on  lower  and  lower  strata 
toward  the  center.  In  the  basin  the  infaces  or  escarpments  face 
outward;  in  the  dome  they  face  inward.  The  Paris  Basin  is  most 
probably  to  be  regarded  as  a  region  in  the  second  cycle  of  erosion, 
having  been  peneplained  once,  after  which  the  topography  has  been 
revived  by  a  resumption  of  stream  activity. 

The  Michigan  basin  forms  an  interesting  example  of  a  com- 
pound type.  At  the  beginning  of  Devonic  time,  the  basin  was 
formed,  after  which  erosion  beveled  off  the  margins,  leaving  the 
successive  formations  superimposed  after  the  manner  of  a  nest  of 
plates,  the  highest  being  the  smallest,  while  the  edges  of  the  suc- 
cessively lower  ones  project  beyond  the  higher.  Across  this  series 
were  deposited  the  Devonic  and  later  strata,  after  which  a  second 
downward  arching  took  place,  followed  by  beveling  of  the  edges  of 
this  later  formed  basin.  Thus  the  highest  formations  occupy  the 
center  of  the  area  and  are  surrounded  by  the  rims  of  successively 


THE    PENEPLAIN  847 

lower  formations.  (See  Figs.  219  and  220.)  The  dome  and  basin 
have  generally  a  definite  relation  to  each  other.  Thus  in  Europe 
the  Weald  dome  lies  north  of  and  immediately  adjacent  to  the 
Paris  Basin,  while  in  North  America  the  Michigan  Basin  is  sur- 
rounded by  domes.  As  already  outlined  in  the  preceding  chapter 
(see  map,  Fig.  192),  these  domes  and  basins  suffered  simultaneous 
deformations  at  at  least  two  distinct  periods,  but  some  of  the 
domes  and  perhaps  some  of  the  basins  may  have  suffered  repeated 
deformations  throughout  Palaeozoic  time. 


6.     THE  SYNCLINE. 

This  corresponds  to  a  much  elongated  basin,  and  the  charac- 
teristics it  exhibits  will  be  essentially  those  of  the  basin  except  that, 
instead  of  radiality  or  concentric  arrangement,  many  of  the  features 
will  be  characterized  by  parallelism  of  arrangement.  The  charac- 
teristics of  synclines  as  of  anticlines  are  best  exhibited  in  the  Appa- 
lachian region  of  North  America  and  the  Jura  Mountains  of 
Europe. 

7.     EROSION  FEATURES  IN  FAULTED  STRATA. 

These  have  already  been  discussed,  to  some  extent  in  Chapter 
XX.  Some  special  features  are  shown  in  Figs.  221  and  222. 


8.     THE  COMPLETION  OF  THE  CYCLE. 

THE  PENEPLAIN.  When  the  surface  of  a  country  is  worn  to  so 
low  a  relief  that  the  streams  have  practically  ceased  eroding  and 
are  throughout  in  a  graded  condition,  the  surface  of  the  region  may 
be  considered  as  in  the  peneplain  state.  This  is  by  no  means  a  per- 
fectly level  surface,  but  rather  one  of  a  rolling  or  undulating  topog- 
raphy, and  not  infrequently  erosion  remnants  or  monadnocks  rise 
considerably  above  the  general  level  of  the  peneplain.  Since  streams 
erode  their  beds  until  every  portion  is  graded,  the  stream  bed  repre- 
sents a  continuous  gentle  slope  to  sea-level.  As  long  as  the  rela- 
tive position  of  land  and  sea  remains  stable,  reduction  of  the  relief 
will  progress,  and  the  surface  of  the  land  will  approach  closer  and 
closer  to  the  level  of  the  sea.  If  that  could  be  reached,  the  region 
would  be  reduced  to  base-level.  It  is  obvious,  however,  that  as  the 
relief  is  reduced  more  and  more,  the  rate  of  reduction  rapidly  de- 


848 


PRINCIPLES    OF    STRATIGRAPHY 


creases,  so  that  the  process  of  base-leveling  goes  on  at  a  progres- 
sively diminishing  rate. 

While  the  harder  or  more  resistant  strata  of  any  region  are  the 
last  to  be  reduced  to  the  level  of  the  peneplain,  they  eventually  also 
succumb,  and  the  surface  of  the  peneplain  thus  shows  a  lack  of 
conformity  to  the  structure  of  the  country.  This  lack  of  conform- 
ity to  structure  is  one  of  the  most  characteristic  features  of  a  pene- 
plain, and  the  one  by  which  it  is  most  readily  recognized.  When 
the  peneplain  is  gradually  submerged  beneath  a  transgressing  sea, 
the  final  inequalities  may  be  smoothed  off  by  marine  planation.  In 
this  manner  erosion  surfaces  of  remarkably  level  character  may  be 
produced,  such  as  are  seen  on  the  Archaean  granites  of  the  Manitou 


FIG.  221.     Section   on   San   Juan    River,    Colorado,    showing  erosion   escarp- 
ments in  horizontal  and  tilted  strata. 
FIG.  222.    The  same  section  interpreted  by  the  assumption  of  a  fault. 

region  in  Colorado,  where  the  early  Palaeozoic  sandstones  rest  upon 
a  surface  almost  as  level  as  a  table  top.  (Crosby-i.)  (Fig.  52,  p. 
310.)  Where  transgression  of  the  sea  is  gradual  and  uniform  on  a 
peneplain  surface,  a  basal  conglomerate  or  sandstone  is  formed 
which  everywhere  rests  directly  upon  the  old  peneplaned  surface. 
The  age  of  this  sandstone  or  conglomerate  will,  however,  vary  as 
pointed  out  in  Chapter  XVIII,  being  younger  shoreward  and  older 
seaward.  Where  monadnocks  rise  above  the  level  of  the  submerged 
peneplain,  these  will  be  gradually  buried  under  the  accumulating 
coastal  plain  strata,  which  along  their  contact  with  the  monadnock 
will  be  of  a  more  or  less  coarsely  fragmental  character.  A  typical 
example  of  a  monadnock  buried  in  coastal  plain  strata,  and  now 
partly  resurrected  by  erosion,  is  found  in  the  Baraboo  ridges  of 
southern  Wisconsin.  An  example  of  a  monadnock  being  partly 
buried  by  marine  sediment  is  found  in  the  island  of  Monhegan,  off 


THE    PENEPLAIN 


849 


the  coast  of  Maine,  which  is  still  partly  above  the  level  of  the  sea, 
though  the  peneplain  from  which  it  rises  is  here  completely  sub- 
merged. 

In  an  old  region,  where  peneplanation  has  long  been  in  progress, 
the  surface  is  formed  by  a  layer  of  atmoclastic  material  of  greater 
or  less  depth:  With  this  are  mingled  peat  and  other  phytogenic 
material,  while  here  and  there  may  occur  a  deposit  of  wind-blown 
matter.  On  this  surface  the  rivers  will  assume  a  meandering  course 
which  has  no  regard  to  the  underlying  structure.  When  such 


Section  across  a  branching  fault. 


Fault  and  Monocline. 


Fault  with  thrown  beds  flexed  upward— a  dragged        Fault  with  thrown  beds  flexed  downward. 
fault. 

FIG.  223.     Erosion    scarps    formed   in   horizontal   and    in   flexed   strata,   com- 
pared with  erosion  and  fault  scarps  in  faulted  strata. 


material  is  exposed  to  the  activities  of  a  slowly  encroaching  sea,  it 
will  be  pretty  thoroughly  sorted  and  the  finer  material  carried  sea- 
ward to  settle  in  quieter  water.  But  if  transgression  is  rapid,  other 
sediments  may  be  deposited  over  the  ancient  soil,  which  will  remain 
relatively  undisturbed.  Such  ancient  buried  soils  are  sometimes  met 
with  in  the  geological  series  marking  former  periods  of  extended 
peneplanation. 

The  Relation  of  the  Peneplain  to  Sedimentation.  A  region  of 
low  relief  will  furnish  only  the  finest  material  for  its  rivers  to 
carry,  and  hence  the  sea  bordering-  a  peneplained  country  will 
receive  only  the  finest  lutaceous  sediment  which  is  washed  from 
the  lands  by  the  rains  and  swollen  streams.  Thus  lutaceous  sedi- 
ments, often  heavily  charged  with  decaying  organic  matter,  may 
accumulate  in  the  form  of  extensive  mud  flats  or  deltas.  The  pres- 


850  PRINCIPLES    OF    STRATIGRAPHY 

ent  Mississippi  and  Nile  deltas  are  examples,  being  composed  only 
of  the  finest  mud.  The  Black  Devonic  shale  of  Michigan  and  Ohio 
also  appears  to  represent  a  deposit  of  this  type,  as  already  outlined 
in  a  previous  chapter. 

When  the  continent  has  been  worn  so  low  that  little  or  no  sedi- 
ment is  carried  into  the  sea,  organic  deposits  may  accumulate  close 
to  the  shore.  Since  rivers,  even  in  low  countries,  are  probably 
never  without  their  modicum  of  silt,  it  follows  that  pure  organic 
accumulations  can  be  formed  near  shore  only  where  large  rivers  do 
not  discharge.  A  consideration  of  the  chalk  beds  of  England  and 
Ireland  shows  them  to  be  part  of  a  series  of  coastal  deposits  in  a 
slowly  westward  transgressing  sea.  This  is  partly  shown  by  the 
westward  overlapping  of  the  successive  members  on  an  eroded  pre- 
Cretacic  peneplain.  Thus  while  the  basal  conglomerates,  sands  and 
greensands  of  southeastern  England  are  of  Aptien  age  and  rest  dis- 
conformably  upon  the  Wealden,  the  basal  Cretacic  conglomerates, 
sandstones  and  greensands  of  northeast  Ireland  and  of  Mull  and 
Morvern  in  Scotland  are  of  Cenomanien  age.  Here  the  Aptien  and 
the  Gault  have  been  overlapped,  while  the  Cenomanien  of  the  north- 
west has  the  characteristics  held  by  the  Aptien  in  the  southeast. 
The  Cenomanien  in  the  southeast  is  a  glauconitic  chalk,  and  is  suc- 
ceeded by  the  pure  chalk  which  begins  with  the  Turonien.  In  the 
northwest  the  Turonien  is  still  a  glauconite  sand  to  be  succeeded  by 
lower  Senonien  glauconitic  chalk  and  only  toward  the  last  by  pure 
chalk.  (See  Fig.  146  in  Chapter  XVIII,  page  730.) 

It  is  thus  seen  that  the  great  mass  of  organic  material  which 
forms  the  chalk  was  deposited  in  comparatively  shallow  water  not 
very  remote  from  the  coast,  and  this  suggests  that  the  land  of  that 
time  must  have  been  in  a  state  of  peneplanation.  The  micro- 
organisms of  the  chalk  bear  out  this  interpretation,  for  shallow 
water  benthonic  forms  predominate.  The  possibility  of  eolian 
deposition  of  some  chalk  beds,  mentioned  in  an  earlier  chapter,  must 
not  be  overlooked. 

Dissection  of  the  Peneplain.  If  a  peneplain  is  elevated,  with  or 
without  tilting,  a  new  cycle  of  erosion  commences;  all  the  streams 
will  be  revived,  and  they  will  incise  their  valleys,  thus  dissecting 
the  peneplain.  At  first  the  stream  valleys  are  relatively  insignificant 
as  compared  with  the  broad,  gently  rolling  upland  of  the  elevated 
peneplain.  But  as  the  valleys  are  widened,  the  interstream  por- 
tions are  reduced  and  the  upland  dwindles  into  a  series  of  ridges 
and  peaks  which  eventually  become  lowered,  so  that  a  new  peneplain 
is  produced.  Thus  the  second  cycle  of  erosion  is  completed.  While 
the  upland  portion  of  the  elevated  peneplain  is  still  broad,  the  char- 


THE    PENEPLAIN  851 

acter  of  the  old  peneplain  surface  is  easily  seen.  As  the  valleys 
become  widened  and  the  interstream  portions  reduced,  the  old 
peneplain  level  is  less  and  less  readily  recognized,  the  uniform 
agreement  in  height  of  the  interstream  ridges  being  the  most  con- 
spicuous feature.  It  can,  however,  be  shown  that  uniform  height 
of  interstream  ridges  may  also  be  brought  about  in  a  country  where 
the  original  surface  was  very  diverse,  if  the  streams  are  uniformly 
spaced.  (Shaler-27.)  This  is  especially  true  if  the  streams  are  of 
approximately  equal  power,  and  the  rate  of  erosion  is  thus  more 
or  less  uniform. 

Age  of  the  Peneplain.  It  is  evident  that  the  peneplain  is  of 
later  age  than  that  of  any  of  the  strata  affected  by  the  erosion  in 
the  formation  of  the  peneplain.  In  the  case  of  folded  strata  which 
have  become  peneplaned  the  commencement  of  peneplanation  may 
be  regarded  as  simultaneous  with  the  folding,  and  since  in  a  strongly 
folded  region  even  the  latest  strata  deposited  may  be  involved  in 
the  folds  and  so  protected  from  complete  erosion,  we  may  not  be 
.  far  wrong  in  considering  that  folding  and  peneplanation  begin 
shortly  after  the  deposition  of  the  youngest  stratum  involved.  It 
must,  however,  be  borne  in  mind  that  folding  of  strata  without 
fracture  takes  place  at  some  distance  below  the  surface  (see  Chap- 
ters XIX  and  XX),  and  that  therefore  a  series  of  perfect  folds  in 
any  given  series  of  strata  suggests  that  these  strata  were  at  con- 
siderable depth  below  the  surface  at  the  time  of  the  formation 
of  the  folds.  Under  such  conditions,  when  perfectly  folded  strata 
are  found  near  the  surface  of  a  peneplain,  it  is  not  likely  that  the 
later  strata,  deposited  before  the  commencement  of  folding,  are 
included  within  the  folds.  Thus  within  some  of  the  strongly  folded 
strata  of  the  Hudson  River  group  in  Albany  County,  N.  Y.,  only 
middle  and  earlier  Ordovicic  strata  are  involved  so  far  as  known, 
though  there  is  every  reason  for  believing  that  the  folding  did  not 
take  place  until  late  Ordovicic,  if  not  early  Siluric  time. 

In  the  case  of  horizontal  strata  which  have  been  peneplained, 
the  latest  preserved  stratum  is  not  to  be  regarded  as  the  last  one 
deposited  before  elevation  and  erosion,  for  this  would  allow  no 
removal  of  strata  by  erosion  during  the  peneplanation.  In  general 
we  may  consider  that  the  amount  of  rock  removed  from  a  given 
region  during  a  stated  period  of  elevation  and  erosion  is  propor- 
tional to  the  distance  of  that  region  from  the  point  where  erosion 
was  replaced  by  deposition,  i.  e.,  from  the  seashore  or  piedmont 
plain  of  the  period.  Exceptions  to  this  must,  however,  be  recog- 
nized where  local  conditions  limited  or  accentuated  erosion,  as  in  the 
case  of  a  warped  surface  where  some  portions  of  a  given  formation 


852  PRINCIPLES    OF    STRATIGRAPHY 

were  raised  excessively  and  so  became  subject  to  pronounced  ero- 
sion, or  where  other  portions  were  proportionally  more  depressed 
and  so  escaped  great  erosion,  or  where  other  causes  were  active. 

The  end  of  the  period  of  peneplanation  is  commonly  marked  by 
the  age  of  the  strata  overlying  the  peneplain  surface.  Here,  how- 
ever, it  must  be  borne  in  mind  that  slow  subsidence  of  a  peneplain 
surface  produces  a  gradual  deposition  of  formations  which  suc- 
cessively overlap  each  other,  each  later  one  in  turn  coming  to  rest 
upon  the  old  peneplain  surface  beyond  the  edge  of  the  preceding 
one.  Thus,  the  pre-Cambric  peneplain  of  North  America  is  over- 
lain by  Lower  or  Middle  Cambric  strata  in  the  southern  United 
States,  by  Upper  Cambric  strata  in  the  Upper  Mississippi  Valley 
and  northeastern  New  York,  by  Lower  or  Middle  Ordovicic  in 
northwestern  New  York,  by  Middle,  and  later  Ordovicic,  in  por- 
tions of  Canada,  and  by  later  formations  in  other  parts.  In  each 
case  the  age  of  the  peneplain  terminates  with  the  age  of  the  over- 
lying bed,  while  the  part  still  above  water  continues  to  be  subject  to 
erosion.  Thus  these  higher  portions  continued  to  be  peneplained, 
though  at  an  exceedingly  slow  rate,  long  after  the  southern  end 
of  the  peneplain  was  buried  under  thousands  of  feet  of  strata. 

HIGH-LEVEL  PLAINS  OF  ARID  REGIONS.  In  arid  regions,  where 
the  rainfall  is  insufficient,  and  where  a  large  part  of  the  erosive 
work  is  done  by  wind,  high-level  plains  of  erosion  comparable  to 
peneplains,  but  having  no  definite  relation  to  sea-level,  may  come 
into  existence.  Under  the  influence  of  arid  erosive  forces,  the 
initial  relief  of  even  a  rugged  region  will  gradually  become  extinct, 
partly  by  erosion  and  partly  by  filling  of  the  desert  basins  with 
waste.  The  process  has  been  fully  described  by  Davis  (12)  and 
enlarged  upon  by  others.  A  few  quotations  from  Davis  will  serve 
to  point  the  essentials  of  the  process  and  its  results:  Under  the 
conditions  cited  "the  most  perfect  maturity  would  be  reached  when 
the  drainage  of  all  the  arid  region  becomes  integrated  with  respect 
to  a  single  aggraded  basin-base-level,  so  that  the  slopes  should 
lead  from  all  parts  of  the  surface  to  a  single  area  for  the  deposition 
of  the  waste.  The  lowest  basin  area  which  thus  comes  to  have  a 
monopoly  of  deposition  may  receive  so  heavy  a  body  of  waste  that 
some  of  its  ridges  may  be  nearly  or  quite  buried.  Strong  relief 
might  still  remain  in  certain  peripheral  districts,  but  large  plain 
areas  would  by  this  time  necessarily  have  been  developed.  In  so 
far  as  the  plains  are  rock-floored,  they  would  truncate  the  rocks 
without  regard  to  their  structure."  (12:  J#p.) 

"As  the  dissected  highlands  of  maturity  are  worn  down,  the 
rainfall  decreases,  and  the  running  streams  are  weakened  and  ex- 


PLAINS    OF   ARID    REGIONS  853 

tinguished ;  thus  .  .  .  the  winds  in  time  would  appear  to  gain  the 
upper  hand  as  agents  of  erosion  and  transportation.  If  such  were 
the  case,  it  would  seem  that  great  inequalities  of  level  might  be 
produced  by  the  excavation  of  wide  and  deep  hollows  in  areas  of 
weak  rocks.  As  long  as  the  exportation  of  wind-swept  sand  and 
of  wind-borne  dust  continued,  no  easily  denned  limit  would  be 
found  for  the  depth  of  the  hollows  that  might  thus  be  developed  in 
the  surface,  for  the  sweeping  and  lifting  action  of  the  wind  is  not 
controlled  by  any.  general  baselevel.  In  an  absolutely  rainless  re- 
gion there  appears  to  be  no  reason  for  doubting  that  these  abnormal 
inequalities  of  surface  might  eventually  produce  a  strong  relief  in 
a  still-standing  land  of  unchanging  climate ;  but  in  the  actual  deserts 
of  the  world  there  appears  to  be  no  absolutely  rainless  region ;  and 
even  small  and  occasional  rainfalls  will  suffice,  especially  when 
they  occur  suddenly  and  cause  floods,  as  is  habitual  in  deserts,  to 
introduce  an  altogether  different  regime  in  the  development  of  sur- 
face forms  from  the  rock  hills  and  hollows  which  would  prevail 
under  the  control  of  the  winds  alone.  The  prevailing  absence  of 
such  hill-and-hollow  forms,  and  the  general  presence  of  graded 
wadies  and  of  drainage  slopes  in  desert  regions,  confirm  this  state- 
ment." 

"As  soon  as  a  shallow  wind-blown  hollow  is  formed,  that  part 
of  the  integrated  drainage  system  which  leads  to  the  hollow  will 
supply  waste  to  it  whenever  rain  falls  there ;  the  finer  waste  will  be 
blown  away,  the  coarser  waste  will  accumulate,  and  thus  the  ten- 
dency of  the  winds  to  overdeepen  local  hollows  will  be  sponta- 
neously and  effectively  counteracted.  As  incipient  hollows  are 
formed  in  advancing  old  age,  and  the  maturely  integrated  drainage 
system  disintegrates  into  many  small  and  variable  systems,  each 
system  will  check  the  deepening  of  a  hollow  by  wind  action ;  hence 
no  deep  hollow  can  be  formed  anywhere,  so  long  as  occasional  rain 
falls."  (12-391-59,?.) 

With  the  continuance  of  the  processes  and  the  further  disin- 
tegration of  the  drainage,  the  surface  is  slowly  lowered,  leaving 
only  those  rock  masses  projecting  as  monadnocks  or  "Inselberge" 
which  most  effectually  resist  dry  weathering.  The  production  of 
the  Inselberg  landscape  chiefly  by  eolian  agencies  has  already  been 
considered  in  an  early  chapter. 

"At  last,  as  the  waste  is  more  completely  exported,  the  desert 
plain  may  be  reduced  to  a  lower  level  than  that  of  the  deepest 
initial  basin"  which  originally  was  a  temporary  recipient  of  the 
waste,  "and  then  a  rock-floor,  thinly  veneered  with  waste,  unre- 
lated to  normal  baselevel,  will  prevail  throughout — except  where 


854  PRINCIPLES    OF    STRATIGRAPHY 

monadnocks  still  survive."  (i2:jpj.)  This  condition  of  wide- 
spread desert-leveling  has  actually  been  reached  in  the  Kalahari 
region  of  South  Africa,  as  described  by  Passarge — and  these  ex- 
amples of  the  final  stage,  Davis  holds,  justify  the  assumption  that 
the  various  stages,  through  which  they  must  have  passed  to  reach 
this  last  stage,  and  the  characters  of  which  can  easily  be  deduced 
theoretically,  may  actually  find  representation  in  the  arid  regions 
of  the  world.  Furthermore,  fossil  examples  of  such  desert-leveled 
plains,  as  well  as  examples  of  stages  which  precede  the  final  stage, 
ought  to  be  looked  for  in  the  sections  of  the  earth's  crust,  and  we 
can  no  longer  assume  that  any  level  plain,  recent  or  fossil,  is  a 
normal  peneplain ;  the  possibility  that  it  may  be  a  high-level  desert 
plain  must  not  be  overlooked. 

Some  criteria  for  distinguishing  modern  peneplains  from  desert 
plains  are  given  by  Davis. 

"A  plain  of  erosion  lying  close  to  sea-level  in  a  region  of  normal 
climate,  and  therefore  traversed  by  rivers  that  reach  the  sea,  but 


FIG.  224.     Erosion-buttes  (Zeugenberge)  near  Guelb-el-Zerzour.    The  erosion 
is  mainly  eolian.      (After  Walther.) 

that  do  not  trench  the  plain,  might  conceivably  be  a  depressed  desert 
plain  standing  long  enough  in  a  changed  climate  to  have  become 
cloaked  with  local  soils;  but  it  is  extremely  unlikely  that  the  de- 
pression of  a  desert  plain  could  place  it  so  that  it  should  slope 
gently  to  the  seashore,  and  that  its  new-made  rivers  should  not 
dissect  it,  and  that  there  should  be  no  drifted  sands  and  loess 
sheets  on  adjoining  areas,  and  no  signs  of  submergence  on  neigh- 
boring coasts.  An  untrenched  plain  of  erosion  in  such  an  attitude 
would  be  properly  interpreted  as  the  result  of  normal  processes,  long 
and  successfully  acting  with  respect  to  normal  baselevel."  (12: 
•397-398.} 

"In  the  same  way  a  high-standing  plain  of  erosion  in  a  desert 
region  might  be  possibly  explained  as  an  evenly  uplifted  peneplain 
whose  climate  had  in  some  way  been  changed  from  humid  to  arid, 
whose  deep  weathered  soils  had  been  removed  and  replaced  by 
thin  sheets  of  stony,  sandy,  or  saline  waste,  and  whose  residual 
reliefs  had  been  modified  to  the  point  of  producing  shallow  basins. 
But  in  this  case  there  should  be  some  indications  of  recent  uplift 
around  the  margin  of  the  area,  either  in  the  form  of  uplifted  marine 


PLAINS    OF   ARID    REGIONS  855 

formations  whose  deposition  was  contemporaneous  with  the  ero- 
sion of  the  peneplain,  or  in  the  form  of  fault-escarpments  separat- 
ing the  uplifted  from  the  non-uplifted  areas.  Moreover,  it  is  ex- 
tremely unlikely  that  the  uplift  of  an  extensive  peneplain  could 
place  it  in  so  level  a  position  that  it  should  not  suffer  dissection 
even  by  desert  agencies;  hence  a  high-standing  desert  plain  is  best 
accounted  for  by  supposing  that  it  has  been  leveled  in  the  position 
that  it  now  occupies."  (12:  398.) 

"It  should  not,  however,  be  overlooked  that  there  is  some  danger 
of  misreading  the  history  of  a  depressed  desert  plain  which  has 
been  by  a  moderate  amount  of  normal  weathering  and  erosion 
transformed  into  a  normal  peneplain;  and  of  an  uplifted  peneplain 
which  has  been  by  a  moderate  amount  of  arid  weathering  and 
erosion  transformed  into  a  typical  desert  plain;  the  danger  of  error 
here  is  similar  to  that  Ly  which  a  peneplain,  wave-swept  and  scoured 
during  submergence',  might  be  mistaken  for  a  normal  plain  of 
marine  abrasion."  ( 12 :  300.) 

"If  an  old  rock-floored  desert  plain  be  gently  warped  or  tilted, 
marine  submergence  is  not  likely  to  follow  immediately,  but  the 
regular  continuation  of  general  degradation  will  be  interrupted. 
The  patches  and  veneers  of  waste  will  be  washed  from  the  higher 
to  the  lower  parts  of  the  warped  surface;  the  higher  parts,  having 
an  increased  slope,  might  be  somewhat  dissected,  and  would  cer- 
tainly be  exposed  to  more  active  degradation  than  before,  until 
they  were  worn  down  to  a  nearly  level  plain  again.  The  lower 
parts  would  receive  the  waste  from  the  higher  parts,  and  the  con- 
tinuance of  this  process  of  concentration  would  in  time  cause  the 
accumulation  of  extensive  and  heavy  deposits  in  the  lower  areas. 
Such  deposits  will  be,  as  a  rule,  barren  of  fossils ;  the  composition, 
texture  and  arrangement  of  their  materials  will  indicate  the  arid 
conditions  under  which  they  have  been  weathered,  transported,  and 
laid  down ;  their  structures  will  seldom  exhibit  the  regularity  of 
marine  strata,  and  they  may  reach  the  extreme  irregularity  of  sand- 
dune  deposits.  If  warping  continues,  the  desert  deposits  may  gain 
great  thickness;  their  original  floor  may  be  depressed  below  sea- 
level,  while  their  surface  is  still  hundreds  or  thousands  of  feet 
above  sea-level."  ( 12 :  400-401.) 

Examples  which  serve  to  illustrate  such  deposits  have  been 
described  from  South  Africa  (Passarge)  and  West  Australia,  where 
barren  sandstones  of  continental  origin  surround  the  monadnocks 
("Inselberge").  Ancient  examples  seem  to  occur  in  the  great 
deposits  of  barren  Uinta  sandstones  12,000  to  14,000  feet  thick  in 
some  localities  which  lie  at  the  base  of  the  Palaeozoic  series  in  the 


856 


PRINCIPLES    OF    STRATIGRAPHY 


region  of  the  present  Wasatch  Mountains.  The  basal  Palaeozoic 
sandstones  of  eastern  North  America,  from  a  few  feet  to  over  a 
thousand  feet  thick  ("Potsdam"  sandstone),  also  have  many  char- 
acters pointing  to  such  an  origin.  In  this  case,  of  course,  the  trans- 
gressing Paleozoic  sea  modified  the  deposits  to  a  certain  degree  and 
redeposited  a  part  of  them  as  fossiliferous  marine  sands  and  clays. 

"If  a  change  from  an  arid  toward  a  moister  climate  causes  a 
drainage  discharge  to  the  sea,  a  dissection  of  the  plain  will  ensue. 
The  valleys  thus  eroded  cannot  expectably  exhibit  any  great  de- 
gree of  adjustment  to  the  structures,  because  the  stream  courses  will 
result  from  the  irregular  patching  together  of  the  preexisting 
irregularly  disintegrated  drainage.  This  peculiar  characteristic, 
taken  together  with  the  absence  of  neighboring  uplifted  marine  de- 
posits, will  probably  suffice  in  most  cases  to  distinguish  desert  plains, 
dissected  by  a  change  to  a  moister  climate,  from  peneplains  dissected 
in  consequence  of  uplift;  but  there  still  might  be  confusion  with 
peneplains  dissected  by  superposed  streams."  (12:401.) 

Locally,  around  individual  mountains  in  an  arid  climate,  a  sur- 
face sloping  outward  in  all  directions  partly  due  to  erosion  and 
partly  to  deposition  is  produced  by  the  forces  operative  under  such 
conditions.  Such  a  plane,  though  never  very  perfect,  will  have  the 
appearance  of  a  broad-based  cone — the  center  of  which  is  the  un- 
dissected  mountain  remnant.  Dr.  Ogilvie  (21)  has  described  these 
as  forming  around  the  laccoliths  of  the  Ortiz  Mountains  in  New 
Mexico — and  has  named  them  "conoplains."  They  are  essentially 
elements  in  the  stages  of  desert  planation. 

C.     MINOR  EROSION  FEATURES. 

Many  of  these  have  already  been  noted  in  previous  chapters. 
We  may  recall  the  grooves  formed  by  eolian  corrasion  in  the  Libyan 
limestone  plateau  and  the  erosion  needles  capped  by  Operculina 
in  the  Libyan  desert  (p.  52)  ;  the  Yardangs  of  central  Asia  and 


FIG.  225.     Erosion  features   (Schichtenkopfe)   in  inclined  Cretacic  limestones. 
Chiefly  eolian.     Abu  Roasch.     (After  Walther.) 


MINOR    EROSION    FEATURES 


857 


the  erosion  monuments  of  Monument  Park,  Colorado  (p.  53)  ;  the 
facetted  pebbles  (p.  54)  ;  erosion  forms  produced  by  solution  (pp. 
174-176),  by  waves  (pp.  221-226),  by  rivers  (pp.  246-257),  and  by 
ice  (pp.  263-265).  A  striking  example  of  eolian  erosion  is  further 
shown  in  Fig.  225,  where  alternating  hard  and  soft  limestone  strata 


FIG.  226.     Solution  fissures  in  chalk,  forming  organ-pipe  structure.     The  hol- 
lows are  filled  with  sand  and  clay  from  above.     (After  Lyell.) 

inclined  at  a  considerable  angle  were  carved  into  fantastic  forms  by 
wind.  Another  example,  illustrating  the  effect  of  solution  on  lime- 
stone, is  given  in  Fig.  226,  which  shows  the  solution  fissures  in  chalk 
and  other  limestone  regions  where  cylindrical  depressions  often 
occur  in  great  numbers,  and  close  together,  forming  geological 
"organ  pipes"  (Geologische  Orgeln)  (Fig.  136,  p.  698).  Broad 
kettle-like  hollows  or  dolinas  are  also  produced  by  solutions  on 
joint-cracks.  These  may  be  up  to  i  km.  in  diameter  and  30  meters 
in  depth. 


BIBLIOGRAPHY    XXI. 


i. 


CROSBY,  WILLIAM  O,  1899.  Archaean  Cambrian  Contact  near  / 
Manitou,  Colorado.  Geological  Society  of  America  Bulletin,  Vol.  X,  * 
pp.  141-164. 

2.  DAVIS,  WILLIAM  MORRIS.     1896.     Plains  of  Marine  and  Subaerial  J 

Denudation.     Geological    Society  of   America    Bulletin,  Vol.  VII,  pp. 
378-398. 

3.  DAVIS,  W.  M.     1899.     The  Peneplain.     American  Geologist,  Vol.  XXIII,  V 

pp.  207-239. 

4.  DAVIS,  W.  M.      1899.      The  Geographic  Cycle.     Geographical  Journal  J 

(London),  Vol.  XIV,  pp.  481-584. 

5.  DAVIS,  W.  M.     1899.     Physical  Geography.     Ginn  &  Co. 

6.  DAVIS,  W.   M.     1899.     The  Drainage  of  Cuestas.     London  Geologists' 

Association  Proceedings,  Vol.  XVI,  pp.  75-93,  16  figures. 
DAVIS,  W.  M.     1900.     The  Physical  Geography  of  the  Lands.     Popular 
Science  Monthly,  Vol.  LVII,  pp.  157-170. 


7- 


858  PRINCIPLES    OF    STRATIGRAPHY 

8.  DAVIS.    W.    M.     1901.     Peneplains    of    Central    France    and    Brittany. 

Geological  Society  of  America  Bulletin,  Vol.  XII,  pp.  480-487. 

9.  DAVIS,  W.  M.     1901.     The  Geographical  Cycle.     Verhandlung  des  7ten 

Internationalen  Geographischen  Kongresses,  pt.  II,  pp.  221-231. 

10.  DAVIS,    W.    M.     1902.     Base-level    Grade   and    Peneplain.     Journal   of 

Geology,  Vol.  X,  pp.  77~IO9- 

11.  DAVIS,  W.  M.     1905.     Leveling  without  Base  Leveling.     Science,  N.  S., 

Vol.  XXI,  pp.  825-828. 

12.  DAVIS,  W.  M.     1905.     The  Geographic  Cycle  in  an  Arid  Climate.     Journal 

of  Geology,  Vol.  XIII,  No.  5,  pp.  381-407. 

(13.     DAVIS,  W.  M.     1905.     The  Bearing  of  Physiography  on  Suess'  Theories. 
American  Journal  of  Sciences,  Vol.  XIX,  pp.  265-273. 

14.  DAVIS,   W.    M.     1905.     The   Complication   o'   the   Geographical   Cycle. 

Compte  Rendu,  8th  International  Geographical  Congress,  pp.  150-163. 

15.  FOERSTE,  A.  E.     1902.     The  Cincinnati  Anticline  in  Southern  Kentucky. 

American  Geologist,  Vol.  XXX,  pp.  359-369. 

16.  GRABAU,  A.  W.     1901.     Geology  and  Palaeontology  of  Niagara  Falls 

and  Vicinity.     N.  Y.  State  Museum  Bulletin  No.  45. 

17.  GRABAU,  A.  W.     1908.     Pre-Glacial  drainage  in  Central  Western  New 

York.     Science,  N.  S.,  Vol.  XXVIII,  pp.  527-534- 

18.  JOHNSON,  DOUGLAS  W.     1903.     Geology  of  the  Cerillos  Hills.     (Lac- 

colith and  Dome  Mountain  Dissection.)     School  of  Mines  Quarterly, 
Vol.  XXIV,  pp.  173-246;  456-600. 

19.  JOHNSON,  D.  W.     1905.     Youth,  Maturity  and  Old  Age  of  Topographic 

Forms.     American  Geographical  Society  Bulletin,  XXXVII,  pp.  648-653. 

20.  KEYES,    C.   R.     1903.     Geological   Structure  of   New   Mexican   Bolson 

Plains.     American  Journal  of  Science,  Vol.  XV,  pp.  207-210. 

21.  OGILVIE,  IDA  H.     1905.     The  High  Altitude  Conoplain:     A  topographic 

form  illustrated  in  the  Ortiz  Mountains.     American  Geologist,  XXXVI, 
pp.  27-34. 

22.  PASSARGE,  SIEGFRIED.     1904.     Die  Kalahari.     Berlin. 

23.  PASSARGE,    S.     1904.     Rumpfflache    und    Inselberge.     Zeitschrift    der 

deutschen  geologischen  Gesellschaft,  Bd.  LVI,  pp.  193-209. 

24.  PASSARGE,   S.     1904.     Die   Inselbergelandschaft  im  tropischen  Africa. 

Naturwissenschaftliche  Wochenschrift.     N.  F.,  Bd.  Ill,  pp.  657-665. 
'25.     PENCK,  A.     1883.    Einfluss  des  Klimas  auf  die  Gestalt  der  Erdoberflache. 
Verhandlungen  des  3ten  deutschen  Geographentages,  pp.  78-92. 

26.  PENCK,  A.     1905.     Climatic  Features  in  the  Land  Surface.     American 

Journal  of  Science,  Vol.  XIX,  pp.  165-174. 

27.  SHALER,  N.  S.    1899.    Spacing  of  Rivers  with  Reference  to  the  Hypothesis 

of   Base-Leveling.     Geological  Society  of  America  Bulletin,  Vol.  X,  pp. 
263-276. 

28.  WALTHER,     JOHANNES.     1891.     Denudation    in    der    Wuste.     (See 

Bibliography  II.) 

29.  WALTHER,  JOHANNES.     1900.     Das  Gesetz  der  Wiistenbildung  (2nd 

ed.,  1912). 

30.  WILSON,  ALFRED  W.  G.     1903.     The  Laurentian  Peneplain.     Journal 

of  Geology,  Vol.  XI,  pp.  615-669. 

31.  WILSON,  A.  W.  G.     1904.     Trent  River  System  and  St.  Lawrence  Outlet. 

Geological  Society  of  America  Bulletin,  Vol.  XV,  pp.  211-242. 

32.  WILSON,    A.   W.    G.      1905.      Physiography   of   the   Archaean   Areas   of 

Canada.     International  Geographical  Congress,  8th  report,  pp.  116-135. 


D.   THE   PYROSPHERE. 
CHAPTER   XXII. 

GENERAL  SUMMARY  OF  PYROSPHERIC  ACTIVITIES. 

The  activities  of  the  pyrosphere  are  judged  by  their  surface 
manifestations,  and  by  the  observations  on  results  of  igneous  ac- 
tivities .in  the  past.  So  far  as  the  pyrosphere  itself  is  concerned 
direct  observation  is,  of  course,  out  of  the  question,  nevertheless 
much  may  be  learned  regarding  its  probable  character  by  experi- 
mentation and  the  study  of  igneous  activities  in  the  laboratory,  as 
well  as  in  the  field,  while  much  more  may  be  inferred  from  a  logical 
interpretation  of  past  igneous  work  in  portions  of  the  earth's  crust 
exposed  as  a  result  of  dislocations,  or  of  prolonged  erosion,  or  of 
both.  No  attempt  is  made  to  discuss  volcanic  activities  in  anything 
more  than  a  summary  manner,  though  the  subject  is  of  vast  geologi- 
cal importance.  The  science  of  pyrology  or  vulcanology  has  already 
developed  a  literature  which  only  a  specialist  may  hope  to  master. 
The  list  given  at  the  end  of  this  chapter  is  an  extremely  fragmentary 
one,  but  it  contains  a  sufficient  number  of  general  works  in  which 
the  subject  is  treated  from  a  comprehensive  viewpoint,  and  which 
will  open  for  the  student  the  gateways  to  the  special  fields  of  re- 
search in  which  ground  has  been  broken. 

VOLCANIC    ACTIVITIES. 

TYPES  OF  VOLCANIC  ACTIVITIES.  These  may  be  purely 
explosive  or  purely  extravasative  or,  what  is  more  frequent,  a 
combination  of  both  in  varying  proportions.  According  as  the  one 
or  the  other  prevails,  the  form  of  the  resulting  deposit  will  vary 
from  simply  conical  in  the  first  to  flat  and  plain-like  in  the  second 
case. 

SUBDIVISION  WITH  REFERENCE  TO  LOCATION.  Volcanic  mani- 
festations may  take  place  either  on  the  surface  of  the  lithosphere 
(effusive)  or  within  the  earth's  crust  (plutonic,  intrusive).  In 

859 


86o  PRINCIPLES    OF    STRATIGRAPHY 

the  latter  case  direct  observation  of  such  manifestations  is  im- 
possible, but  their  characters  may  be  inferred  from  the  results  of 
past  intrusive  and  plutonic  manifestations  as  indicated  by  the  char- 
acteristics of  intrusive  and  deep-seated  (plutonic)  igneous  masses. 
(See  ante,  Chapter  VII.) 

Extrusive  manifestations  may  further  be  divided  into  the  ter- 
restrial and  the  submarine,  the  latter  again  being  withdrawn  from 
direct  observation,  except  when  their  results  appear  above  the 
surface  of  the  sea,  after  prolonged  existence.  Indirect  observation 
on  the  results  of  submarine  eruptions  is  likewise  scanty,  mainly 
because,  in  the  case  of  older  volcanics,  it  is  at  present  difficult  to 
distinguish  with  certainty  between  submarine  and  subaerial  erup- 
tions, and  many  so-called  submarine  lava  flows  must  probably  be 
relegated  to  the  subaerial  type. 

In  discussing  the  types  of  eruptions,  the  primary  division  into 
explosive  and  extravasative  will  be  kept  in  mind,  and  under  each 
of  these  will  be  noted  the  subaerial  or  terrestrial  and  the  submarine 
types. 

Explosive  Eruptions. 

Terrestrial  Type.  Volcanoes  of  purely  explosive  type  are  prob- 
ably very  rare,  though  the  "maare"  craters  may  be  classed  here.  In 
the  typical  examples  of  the  Eifeler  Maare,  no  volcanic  cone  exists ; 
instead,  there  is  merely  a  more  or  less  circular  opening,  the  result 
of  the  explosion,  and  this  has  subsequently  been  filled  with  water. 
Lapilli,  bomblets,  and  even  large  bombs  often  abound  in  the  neigh- 
borhood of  the  maare  craters,  but  lava  flows  are  typically  absent. 
The  coarse  and  fine  lapilli  of  the  maare  region  in  the  Eifel  and 
Rhein  districts  form  stratified  deposits  which  have  all  the  appear- 
ance of  stratified  sands  of  clastic  origin.  As  outlined  in  Chapter 
VI,  the  lapilli  are  not  to  be  regarded  as  pyroclastic  in  the  true  sense 
of  the  word,  but  rather  as  granular  pyrogenics,  being  primarily  of 
endogenetic  origin,  and  classifiable  as  pyrogranulites  rather  than 
as  pyrarenytes.  True  pyroclastics  are,  of  course,  also  associated 
with  the  deposits  of  lapilli  and  bombs,  these  resulting  from 
the  clastation,  by  eruptive  explosion,  of  already  consolidated 
rock  masses,  either  of  igneous  or  of  "sedimentary"  origin.  The 
vicinity  of  the  Laacher  See,  the  largest  and  most  picturesque  of 
the  explosive  craters  of  Germany,  is  characterized  by  deposits  of 
volcanic  bombs  and  tuffs,  of  trachyte,  mingled  with  clastic  frag- 
ments of  granite  and  various  metamorphic  rocks,  brought  up  by 
the  explosion  from  great  depths  below  the  cover  of  Devonic  strata. 


EXPLOSIVE    ERUPTIONS  861 

Some  of  the  bombs  consist  of  a  remarkable  mixture  of  crystals, 
characteristically  developed  at  great  depth  within  the  earth's  crust, 
such  as  sanidine,  olivine,  hornblende,  garnet,  etc.  (Walther-4i : 
170-777.) 

A  modern  case  of  such  an  explosion  without  lava  extrusion 
occurred  in  Japan  in  1888,  the  explosion  being  a  sudden  and  violent 
one,  and  tearing  away  the  side  of  a  volcano  which  had  not  been 
active  for  at  least  a  thousand  years.  The  air  was  filled  with  ashes 
and  debris  as  in  a  typical  volcanic  eruption,  and  a  large  tract  of 
the  adjacent  region  was  devastated  and  many  lives  lost. 

Coon  Butte,  in  Arizona,  has  also  been  regarded  by  Gilbert 
(u:7#7)  as  a  possible  example  of  such  an  explosive  eruption — 
though  he  also  suggests  the  possibility  that  it  was  formed  by  the 
impact  of  a  meteorite.  Both  theories  have  had  their  advocates,  the 
former  origin  being  favored  by  Chamberlin  and  Salisbury  (4:596), 
while  the  latter  is  especially  defended  by  Fairchild  (8). 

The  cinder  cone.  While  the  explosion-craters  seen  in  the  Maare 
represent  probably  a  single  eruption,  or  one  which,  with  slight 
intervening  pauses,  lasted  only  for  a  comparatively  short  time,  the 
more  general  examples  of  explosive  volcanoes  last  sufficiently  long 
to  build  up  a  cinder  cone.  Such  eruptions  may  be  of  comparatively 
limited  duration,  and  may  occur  at  short  intervals,  as  in  the  volcano 
Stromboli  in  the  ^Eolian  Islands  north  of  Sicily  (Strombolian  type), 
where  the  interval  of  explosion  is  from  i  to  20  minutes,  as  shown 
by  the  "flash"  of  this  "Lighthouse  of  the  Mediterranean";  or  it 
may  be  of  a  more  violent  character  and  occur  at  great  intervals 
with  dormant  or  "strombolian"  periods  intervening.  Such  is  the 
case  in  Vulcano  of  the  same  group  of  islands,  and  in  other  violent 
volcanoes  (Vulcanian  type)  which  have  an  interval  of  decades 
(moderate  phase),  or  of  centuries  (grander  phase). 

Material  of  the  cinder  cone.  This  includes  the  bombs,  the 
lapilli,  and  the  volcanic  sand,  ash,  and  dust  which  fall  in  the  im- 
mediate vicinity  of  the  crater.  Not  all  the  ejected  material  falls 
here — much  being  carried  to  a  distance,  this  distance  increasing 
with  increasing  fineness  of  material.  Even  large  bombs  may  be 
hurled  beyond  the  actual  radius  of  the  cinder  cone,  one  such,  fully 
three  feet  in  diameter,  being  hurled  to  a  distance  of  a  mile  and  a 
half  during  the  eruption  of  Vulcano  in  1888  (Hobbs-i5  :77o).  A 
remarkable  example  of  the  propulsion  of  volcanic  ejecta  has  been 
described  by  Hovey  (17:560)  in  the  eruption  of  Mont  Pelee  in 
1902.  Frequent  explosions  of  dust  and  lava-laden  clouds  have 
brought  material  enough  from  the  crater  to  fill  the  gorge  of  the 
Riviere  Blanche.  "The  lower  portion  of  the  gorge  has  been  entirely 


862  PRINCIPLES    OF    STRATIGRAPHY 

obliterated  and  the  adjoining  plateau  elevated,  while  the  upper  and 
deeper  portion  near  the  center  has  been  almost  filled  by  ejecta. 
The  dust-flows  are  the  material  left  behind  by  the  dust-laden  clouds 
of  steam.  The  exploding  clouds  of  steam  were  so  overloaded  with 
dust  and  larger  fragments  of  comminuted  lava,  that'  they  flowed 
down  the  slope  of  the  mountain  and  the  gorge,  like  a  fluid  propelled 
at  a  high  velocity  by  the  horizontal  or  partly  downward  component 
of  the  force  of  the  explosion.  Many  large  fragments  of  solidified 
lava  were  carried  down  the  gorge  by  these  clouds.  Such  blocks 
10  to  15  feet  in  diameter  were  not  uncommon"  (17:560). 

Lapilli  vary  in  size  from  that  of  a  walnut  to  dust.  The  term 
is  somewhat  loosely  used,  and  should  be  restricted  to  pyrogenic 
material  in  a  state  of  division,  i.  e.,  pyrogranulytes  and  the  smaller 
pyrosphaerytes  (more  rarely  pyro-pulverytes)  which  by  their  ap- 
pearance show  that  they  were  unconsolidated  or  at  least  in  a  plastic 
state  on  eruption.  (See  ante,  Chapters  VI  and  XII.)  The  sand 
and  dust  are,  for  the  most  part,  true  pyroclastic  material  character- 
ized by  angularity  of  outline  and  density  of  material. 

The  forms  of  cinder  cones.  Cinder  cones  are  essentially  local 
accumulations  of  unconsolidated  materials,  and  so  their  form  is 
determined  by  the  general  laws  which  govern  the  accumulation  of 
such  material,  modified,  of  course,  by  the  special  influences  char- 
acteristic of  the  mode  of  accumulation.  The  form  will  also  vary 
in  accordance  with  the  prevailing  size  and  character  of  the  material, 
being  steeper  for  coarse  and  gentler  for  fine  material,  and  gentler 
also  for  rounded  material  (lapilli)  than  for  angular.  There  will 
be  further  variation  induced  by  the  abundance  or  scarcity  of  water 
vapor,  condensed  into  rain  in  the  vicinity  of  the  eruption,  the 
variation  being  analogous  to  that  found  in  the  slopes  of  alluvial 
cones  and  dry  "cones  of  dejection,"  or  between  that  of  alluvial 
cones  of  dry  and  pluvial  regions.  "Speaking  broadly,  the  diameter 
of  the  crater  is  a  measure  of  the  violence  of  the  explosion  within 
the  chimney.  A  single  series  of  short  explosive  eruptions  builds  a 
low  and  broad  cinder  cone.  A  long-continued  succession  of  moder- 
ately violent  explosions,  on  the  other  hand,  builds  a  high  cone  with 
crater  diameter  small  if  compared  with  the  mountain's  altitude,  and 
the  profile  afforded  is  a  remarkably  beautiful  sweeping  curve." 
(Hobbs-i5  :/^j.)  Owing  to  the  fact- that  material  near  the  summit 
lies  at  the  maximum  angle  of  repose,  while  that  lower  down  gener- 
ally has  a  lower  angle — the  product  of  change  wrought  by  time 
and  by  the  addition  of  material  fallen  from  the  sky  upon  the 
surface  of  the  original  slope — the  form  of  the  lateral  curve  of  the 
cinder-cone  will  be  a  faintly  concave  one,  whereas  that  of  a  lava 


THE    CINDER    CONE 


863 


cone  is  more  typically  convex.  This  is  shown  in  the  following 
sketch  of  a  cinder  cone  (Fig.  227)  and  appears  further  in  Fig.  232. 

Monte  Nuovo,  in  the  Bay  of  Baie,  near  Naples,  is  an  example  of 
a  cone  composed  almost  entirely  of  loose  cinders.  This  volcano 
had  its  birth  within  historic  time,  arising  on  the  borders  of  the 
ancient  Lake  Lucrinus  on  September  20,  1538,  and  attaining  a 
height  of  440  feet.  Other  volcanoes  largely  composed  of  cinders 
have  arisen  within  the  knowledge  of  man.  Among  them  are  Jorullo 
(Mexico),  1759;  Pochutla  (Mexico),  1870;  Camiguin  (Philippine 
Islands),  1871;  a  new  mountain  of  the  Ajusco  Mountain  group 
(Mexico),  1881 ;  and  the  new  mountain  of  Japan  formed  on  Sep- 
tember 9,  1910,  and  rising  to  a  height  of  690  feet. 

Both  Jorullo  and  the  new  Camiguin  volcano  started  from  fissures 
in  level  plains.  The  former  arose  in  the  night  of  September  28, 
1759,  35  miles  distant  from  any  then  existing  volcano,  and  its  sum- 


FIG.  227.  Campo  Bianco,  in  the 
Island  of  Lipari.  A  pumice-cone, 
breached  by  the  outflow  of  an 
obsidian  lava  stream. 


FIG.  228.  Experimental  illustration 
of  the  mode  of  formation  of  vol- 
canic cones  composed  of  frag- 
mental  materials.  (After  Judd.) 


mit  has  since  reached  an  elevation  of  4,265  feet  above  sea-level. 
The  Camiguin  volcano  had  a  growth  period  of  four  years  during 
which  it  reached  a  height  of  about  1,800  feet. 

Consolidation  of  cinder  cones.  Unless  extravasations  of  lava 
should  punctuate  the  eruptions  of  cinders,  the  cinder-cone  is  not 
likely  to  be  thoroughly  consolidated,  but  remains  rather  in  the  con- 
dition of  an  ash  or  sand  heap.  Diagenetic  processes  will,  of  course, 
go  on  throughout  the  mass  and  thus  consolidation  may  be  brought 
about,  aided  by  the  metamorphosing  effect  of  the  steam  and  hot 
vapors  accompanying  each  eruption,  and  penetrating  more  or  less 
through  the  mass  of  accumulated  material  (atmo-metamorphism). 

Submarine  Explosive  Eruptions,  Explosive  eruptions  are  prob- 
ably as  common  in  the  littoral  belts  of  the  sea  as  they  are  on  land, 
and,  indeed,  near  the  margins  of  the  lands  they,  in  common  with  the 
extravasative  eruptions,  may  be  more  frequent  than  elsewhere,  as 
discussed  beyond.  There  is  no  reason  for  doubting  that  explosive 
eruptions  also  occur  on  the  floor  of  the  deeper  sea — though  exam- 


864  PRINCIPLES    OF    STRATIGRAPHY 

pies  of  such  cinder-cones  rising  from  the  abyssal  sea-bottom  are 
unknown. 

The  Mediterranean  has  been  the  region  best  known  for  sub- 
marine volcanic  eruptions.  Of  these  a  number  have  been  of  the 
explosive  type,  though  more  generally  the  compound  (explosive 
and  extravasative)  type  prevailed.  The  most  noted  of  the  recorded 
submarine  eruptions  "occurred  in  the  year  1831,  when  a  new  vol- 
canic island  (Graham's  Island,  lie  Julia)  was  thrown  up,  with 
abundant  discharge  of  steam  and  showers  of  scoriae,  between 
Sicily  and  the  coast  of  Africa.  It  reached  an  extreme  height  of 
200  feet  or  more  above  sea-level  (800  feet  above  sea-bottom)  with 
a  circumference  of  3  miles,  but,  on  the  cessation  of  the  eruption, 
was  attacked  by  the  waves  and  soon  demolished,  leaving  only  a 
shoal  to  mark  its  site."  (Geikie-o,  1^50.)  "The  upper  part  of  this 
volcanic  cone,  above  the  sea  at  least,  seemed  to  have  been  solely 
composed  of  ashes,  cinders,  and  fragments  of  stone,  commonly 
small.  Among  these  fragments  of  limestone  and  dolomite,  with 
one  several  pounds  in  weight,  of  sandstone,  were  observed.  (De 
la  Beche-6:p5.)  These  fragments  were  broken  off  from  the  rocks 
through  which  the  eruption  passed  on  its  upward  way.  "During 
the  time  that  this  volcanic  mass  was  accumulating,  a  large  amount 
of  ashes  and  cinders  must  have  been  mingled  with  the  adjacent  sea 
before  it  reached  its  surface,  and  no  slight  amount  would  be  dis- 
tributed around,  when  ashes  and  cinders  could  be  vomited  into  the 
air.  Add  to  this  the  quantity  caught  up  in  mechanical  suspension 
by  the  breakers  and  there  would  be  no  small  amount  to  be  accumu- 
lated over  any  deposits  forming,  or  formed,  on  the  bottom  around 
this  locality  .  .  ."  (De  la  Beche-6  :p5,  pd).  These  deposits  in- 
cluded, of  course,  abundant  remains  of  organisms,  killed  by  the  ex- 
plosive eruption.  Another  example  of  a  volcano  formed  in  the  his- 
toric period  is  Sabrina  Island  in  the  Azores,  off  the  coast  of  St. 
Michaels.  Here  a  submarine  eruption  built  a  cone  of  loose  cinders 
to  a  height  of  about  300  feet,  and  a  circumference  of  about  a  mile. 
This,  too,  soon  disappeared  under  the  subsequent  attack  of  the 
waves. 

"The  formation  of  this  island  was  observed  and  recorded.  It 
was  first  discovered  rising  above  the  sea  on  the  thirteenth  of  June, 
1811,  and  on  the  seventeenth  was  observed  by  Captain  Tillard, 
.  .  .  from  the  nearest  cliff  of  St.  Michael's.  The  volcanic  bursts 
were  described  as  resembling  a  mixed  discharge  of  cannon  and 
musketry;  and  were  accompanied  by  a  great  abundance  of  light- 
ning." (De  la  Beche-6  :/PJ.)  A  sketch  made  at  that  time  is  here 
reproduced  (Fig.  229).  A  similar  occurrence  is  recorded  from 


SUBMARINE    ERUPTIONS 


865 


the  west  coast  of  Iceland,  where,  in  the  early  summer  of  1783, 
arose  an  island  of  volcanic  nature  about  thirty  miles  from  Cape 
Reykjanaes.  In  less  than  a  year,  however,  it  had  again  been  washed 
away  by  the  waves,  leaving  only  a  submerged  reef  or  shoal  from 
five  to  thirty  fathoms  below  sea-level. 

Numerous  submarine  eruptions  which  never  reach  the  surface 
no  doubt  occur  over  many  portions  of  the  ocean  floor.  In  these 
both  cinders  and  lava  enter,  sometimes  one  and  sometimes  the  other 


FIG.  229.  Sketch  of  the  submarine  volcanic  eruption  which,  in  June,  1811, 
formed  Sabrina  Island,  off  St.  Michaels  in  the  Azores.  (After 
De  la  Beche.) 

predominating.  On  the  floor  of  some  parts  of  the  deep  sea  volcanic 
ejectamenta  are  abundant,  and  these  are  in  part  at  least  due  to 
submarine  explosive  eruptions. 

Extravasative  Eruptions. 

Terrestrial  Type — Fissure  Eruption.  The  fundamental  charac- 
teristics of  this  type  are  best  developed  in  the  great  fissure  erup- 
tions which  have  resulted  in  the  formation  of  extensive  lava  fields, 
and  in  the  broad  flat  lava  domes  of  the  Hawaiian  group.  The 
fissures  from  which  the  great  lava  extravasations  take  place  are 
generally  ranged  parallel  with  and  near  to  the  coast  and  seem  to 
be  especially  prevalent  where  the  edge  of  the  land  drops  off  rapidly 


866  PRINCIPLES    OF    STRATIGRAPHY 

to  deep  sea.  The  most  stupendous  modern  examples  of  fissure 
eruptions  are  those  of  eastern  Iceland.  In  this  island  occur  a 
number  of  distinct  and  parallel  clefts  arranged  in  two  dominant 
series,  one  extending  northeast  and  southwest,  the  other  north  and 
south.  "Many  such  fissures  are  traceable  at  the  surface  as  deep 
and  nearly  straight  clefts  or  gjas,  usually  a  few  yards  in  width  but 
extending  for  many  miles.  The  Eldgja  has  a  length  of  more  than 
1 8  English  miles  and  a  depth  varying  from  400  to  600  feet." 
(Hobbs-i5:pp.) 

According  to  Thoroddsen,  the  lava  wells  out  quietly  from  the 
whole  length  of  some  of  these  fissures,  overflowing  on  both  sides 
without  the  formation  of  cones.  These  fissures,  therefore,  consti- 
tute connecting  dikes,  such  as  are  known  to  occur  under  the  older 
lava  flows  of  this  type.  At  three  of  the  wider  portions  of  the  great 
Eld  cleft  of  Iceland  the  lava  has  welled  out  quietly  without  the 
formation  of  cones,  flooding  an  area  of  270  square  miles.  Upon 
the  southern  narrower  prolongation  of  the  fissure,  however,  a 
row  of  low  slag  cones  appeared,  and  this  is  a  feature  characteristic 
of  other  fissures  in  Iceland,  as  well  as  the  great.  Skaptar  fissure 
reopened  in  1783,  emitting  great  volumes  of  lava.  Subsequently  the 
eruptive  processes  became  concentrated  at  the  wider  portions  of 
the  fissure  and  a  row  of  small  cones  was  left  over  the  line  of  the 
fissure.  Upon  this  fissure,  too,  stands  the  large  volcano  of  Laki. 
The  great  eruptions  and  the  larger  volcanoes  are  generally  found 
at  the  intersection  of  two  fissures,  as  in  the  case  of  the  great 
eruption  of  Askja  in  1875,  and  of  the  volcanoes  of  Java.  On  a 
small  scale,  the  formation  of  volcanoes  along  fissures  is  shown  in 
the  frozen  surface  of  the  lava  lake  in  the  caldron  of  Kilauea,  where 
miniature  volcanoes  form  whenever  the  crust  which  hardens  in  the 
lava-lake  becomes  fissured. 

The  connection  of  volcanic  activities  with  fissuring  of  the  earth's 
surface  is  further  shown  in  the  great  rift-valley  of  eastern  Africa, 
where  extensive  outpourings  of  lava  have  covered  portions  of  the 
valley  floor,  while  volcanoes  of  great  height  and  comparatively 
recent  origin  have  arisen  within  the  valley,  as  in  the  case  of  the 
Mfumbiro  Mountains,  already  referred  to,  which  block  the  rift- 
valley  north  of  Lake  Kivu  and  which  rise  to  great  altitudes,  the 
crater  rim  of  the  still  active  volcano  Kirungo-cha-Gongo  rising  to 
11,350  feet  above  the  sea-level,  while  Karisimbi  reaches  an  altitude 
approaching  14,000  feet.  (Fig.  21,  p.  125.)  The  valley  floor 
on  which  these  volcanoes  arose  was  considerably  less  than  4,000 
feet  above  sea-level ;  indeed,  this  same  valley  floor  in  the  region  of 
Lake  Tanganyika  to  the  south  actually  descends  below  sea-level. 


FISSURE    ERUPTIONS  867 

The  most  gigantic  outpouring  of  lavas  from  fissures  occurred  in 
late  Tertiary  or  early  Quaternary  time  in  western  North  America. 
There  lava  floods  formed  the  great  plains  of  the  Snake  River  region 
in  southern  Idaho,  and  the  vast  basaltic  plateau  of  Washington, 
Oregon,  and  northern  California.  This  lava  field  has  more  or  less 
interrupted  extensions  through  Nevada,  Arizona,  New  Mexico, 
and  the  western  half  of  Mexico  south  into  Central  America  and 
northward  through  British  Columbia  to  the  Alaskan  Peninsula  and 
the  Aleutian  Islands.  (See  the  Geological  Map  of  North  America.) 
The  main  lines  of  fissures  were  probably  parallel  to  the  Pacific  coast, 
but  of  this  nothing  is  visible,  except  the  general  trend  of  the  lava 
sheets  from  north  to  south.  The  area  covered  by  the  lava  outpour- 
ings aggregates  200,000  square  miles,  while  the  thickness  of  the 
sheet  averages  2,000  feet  and  reaches  in  some  places  3,700  feet. 
The  comparatively  recent  origin  and  the  location  of  the  lava  plateau 
have  precluded  much  destructive  work  by  the  surface  agents,  al- 
though the  Snake  River  has  cut  a  series  of  picturesque  gorges 
through  it.  The  cones  now  rising  from  this  surface  indicate 
localization  of  eruption  subsequent  to  the  outpouring  of  the  lava 
floods.  Prismatic  structure  is  well  developed  in  parts  of  these 
lava  sheets.  Intercalated  river  sediments  often  separate  successive 
flows. 

Remnants  of  early  Tertiary  basaltic  lavas  are  now  found  in 
numerous  places  in  northeast  Ireland,  western  Scotland,  the  lower 
Hebrides,  the  Faroe  islands,  and  faraway  Iceland.  These,  famous 
for  their  columnar  partings  (Giants'  Causeway,  Fingal's  Cave,  etc.), 
were  probably  part  of  a  once  continuous  lava  field,  now  dismem- 
bered by  the  agents  of  erosion,  not  the  least  of  which  is  the  sea. 
Numerous  dikes  of  similar  material  occur  in  regions  from  which 
this  lava  has  apparently  been  eroded,  and  these  dikes  probably 
mark  the  fissures  through  which  this  welling-up  of  the  lava  took 
place. 

These  dikes  are  extremely  abundant  in  the  northwest  of  Scot- 
land (Peach  and  Horn 6-28)  and  range  eastward  across  Scotland 
and  the  north  of  England  and  Ireland.  They  have  been  traced 
from  the  Orkney  Islands  southward  to  Yorkshire  and  across  Britain 
from  sea  to  sea  over  a  total  area  of  probably  not  less  than  100,000 
square  miles.  This  may  indicate  the  former  wide  extent  of  this 
basaltic  lava  field  which  then  rivaled  the  younger  one  of  western 
America.  When  erosion  has  been  carried  far  enough  in  the  great 
lava  plateau  of  western  North  America,  to  remove  a  considerable 
portion  of  the  lava  sheet,  there  will  no  doubt  appear  an  equally 


868  PRINCIPLES    OF    STRATIGRAPHY 

vast  number  of  dikes,  which  represent  the  filling  of  the  fissures 
through  which  the  lava  reached  the  surface. 

A  Cretacic  example  of  such  outpouring  of  basic  lava,  rivaling 
in  extent  that  of  the  northwestern  United  States,  is  seen  in  the  great 
bed  of  Deccan  trap  which  forms  the  surface  of  the  Deccan  Plateau 
in  India.  Here  the  depth  of  the  lava  is  from  4,000  to  6,000  feet. 
Where  the  basement  rocks  on  which  this  trap  sheet  rest  are  exposed 
by  erosion  along  the  margin  of  the  plateau  dikes  of  basalt  are  seen 
penetrating  them,  representing  in  part  the  fissures  through  which 


FIG.  230.     End  of  the  lava  flow  of  1881  near  Hilo,  Hawaiian  Islands.     The 
lava  surface  is  a  typical  pahoehoe  surface.     (After  Button.) 

the  lava  reached  the  surface.  No  cones  or  definite  vents  have  been 
found. 

What  appears  to  be  a  pre-Pakeozoic  example  of  such  eruptions 
is  seen  in  the  great  Keweenawan  lava  sheets  which  represent  a  pro- 
longed succession  of  outpourings  in  the  Lake  Superior  region, 
aggregatmg  an  enormous  amount  variously  estimated  as  reaching 
the  great  thickness  of  15,000  or  25,000  feet.  Here,  too,  there  is 
little  evidence  of  explosive  or  other  concentrated  volcanic  activity. 

The  lava  dome.  Where  eruptions  are  concentrated  about  a 
single  opening  a  mountain  of  lava  will  be  built  up  which  rises  in 
proportion  to  the  frequency  of  the  eruption  and  the  volume  of  lava 
poured  out.  Where  fragmental  material  is  absent,  as  in  the  Ha- 
waiian volcanoes,  the  slope  is  a  very  gentle  one,  though  the  actual 


LAVA    DOMES 


869 


height  is  great.  Though  now  rising  to  nearly  14,000  feet  above  sea- 
level  these  volcanoes  began  as  submarine  eruptions,  starting  on  the 
floor  of  the  deep  sea  and  having  a  total  height  of  20,000  or  30,000 
feet.  The  visible  portion  is  less  than  a  hundred  miles  in  diameter, 
but  the  actual  base  is  probably  much  more  than  twice  that.  The  two 
active  volcanoes  are  Mauna  Loa,  the  rim  of  which  is  13,675  feet 
above  sea-level ;  and  Kilauea,  which  is  less  than  4,000  feet  high  and 
appears  to  rest  on  the  flanks  of  the  larger  volcano.  The  craters, 
or  caldera,  have  each  a  circumference  exceeding  seven  miles,  being 
irregularly  elliptical  in  outline  with  the  sides  descending  in  a  series 
of  steps  to  the  central  pit,  which  is  formed  by  the  "frozen"  surface 
of  the  lava.  The  floor  of  the  pit  of  Kilauea  is  a  "movable  plat- 
form" of  frozen  lava  which  rises  and  falls  with  the  variation  in 


FIG.  231.     View  of  Kilauea  caldera  from  the  Volcano  House.     (After  But- 
ton.) 

the  pressure  of  the  lava  beneath.  The  difference  in  height  between 
1823  and  1884  was  estimated  by  Button  (7  112?)  to  be  nearly  400 
feet. 

"Beneath  the  floor  of  the  caldera,"  says  Button,  "we  may  con- 
jecture the  existence  of  a  lake  of  far  greater  proportions  than  those 
which  now  expose  a  fiery  surface  to  the  sky.  The  visible  lakes 
might  be  compared  to  the  air-holes  in  the  surface  of  a  frozen  pond." 
The  proof  for  this  is  found  in  the  fact  that  new  eruptions  are  not 
overflows  of  the  open  pools  of  lava,  but  break  out  anywhere  in 
the  floor  of  the  caldera.  (Fig.  231.) 

Acid  lava  domes.  Lavas  of  the  acid  type  are,  as  a  rule,  too 
viscous  to  form  mountains  of  gentle  slope,  occurring  more  often  as 
steep-sided  domes,  especially  if  the  lava  is  only  semi-fluid.  This 
is  well  shown  in  Figure  232,  where,  in  the  Auvergne  district  of 
France,  a  trachyte  cone  of  highly  viscid  lava  was  extruded  between 
cinder  cones.  The  domed  character  of  the  extravasated  pustular 


8;o 


PRINCIPLES    OF    STRATIGRAPHY 


cone  contrasts  strongly  with  the  concave  surfaces  of  the  cinder 
cones.  The  results  of  experiments  recorded  in  Figures  228  and 
233  show  the  fundamental  differences  between  fragmental  cones 
and  domes  of  pustular  lava. 

The  spine  of  Pelce.  What  is  regarded  by  many  as  a  most 
stupendous  example  of  the  extravasation  of  a  viscous  mass  of 
andesitic  lava — which  cooled  as  it  was  extravasated — is  found  in 
the  remarkable  spine  of  Mont  Pelee  which  formed  after  the  great 
eruption  of  1902.  According  to  Hovey  (16;  17;  18),  this  spine 
was  a  lava  mass  pushed  up  vertically  without  spreading,  the  mass 
cooling  either  in  the  upper  part  of  the  conduit  or  upon  its  appear- 
ance at  the  surface,  so  that  no  extended  flow  was  possible.  The 
spine  grew  at  an  average  of  forty-one  feet  per  day  during  a  period 


FIG.  232.  The  Grand  Puy  of  Sarconi, 
in  the  Auvergne,  composed  of 
trachyte,  rising  between  two 
breached  scoria-cones.  A  typical 
example  of  a  pustular  cone 
formed  of  highly  viscid* lava. 


FIG.  233.  Experimental  illustration 
of  the  mode  of  formation  of  vol- 
canic cones  composed  of  viscid 
lavas. 


of  eighteen  days  out  of  the  new  cone,  which  itself  had  attained  a 
height  of  1,600  feet  during  the  last  ten  days  of  May,  and  was  of 
the  same  character  as  the  spine.  As  the  spine  rose  1,100  feet  above 
this  new  cone  in  October  it  appears  that  the  total  elevation  of  this 
mass  above  the  top  of  the  cone  as  it  existed  prior  to  the  eruption 
of  May,  1902,  was  2,700  feet.  (See,  further,  Heilprin-i2;  Hill- 
I2a;  Jaggar-2o  and  Russell-34a.) 


Composite  Lava  and  Cinder  Cones. 

Volcanic  cones  built  by  a  combination  or  an  alternation  of  the 
explosive  and  extravasative  activities  are  by  far  the  most  common. 
They  generally  have  pronounced  slopes  and  are  more  resistant  than 
cones  built  wholly  of  cinders,  because  the  lava  binds  together  the 
loose  material  into  a  complex  mass.  This  is  sometimes  accomplished 
by  the  formation  of  radial  dikes,  as  in  the  case  of  ^Etna.  These 
represent  lateral  fissuring  of  the  cone  and  the  filling  of  these  fissures 


COMPOSITE    CONES 


871 


by  lava  (Figs.  234,  235).  The  lava  sometimes  extended  through 
these  fissures,  building  up  secondary  cones  or  monticules  on  the  flank 
of  the  main  cone,  as  in  the  case  just  cited.  Fissuring  of  the  cone  is 
of  common  occurrence  in  volcanoes,  the  lava  of  many  of  them  rarely 
or  never  overflowing  the  crater,  but  finding  an  outlet  at  a  lower 
level  through  the  side  of  the  volcano.  If  parasitic  cones  (monti- 
cules) are  built  up  over  such  a  fissure  these  may  remain  the  site  of 
eruption  for  a  long  period,  but  sooner  or  later  they  are  likely  to 
become  extinct,  and  then  they  may  be  buried  by  later  flows  and 
ejectamenta.  Cinder  cones,  which  are  relatively  weak  structures, 
will  be  breached  if  a  subsequent  lava  stream  is  poured  out,  and  this 


FIG.  235.  Basaltic  dikes  projecting 
from  stratified  scoria  or  tuff  in 
the  walls  of  the  Val  del  Bove, 


FIG.  234.  Diagram  illustrating  the 
formation  of  parasitic  cones 
(monticules)  along  lines  of  fis- 
sures formed  in  the  flanks  of  a 
great  volcano.  (After  Judd.) 


will  issue  from  their  sides.  (Fig.  227.)  Large  composite  cones 
may  be  breached  by  explosive  eruptions  and  the  shifting  of  the 
center  of  the  eruption.  A  new  cone  may  be  built  up  within  the 
breached  outer  rim  of  an  original  large  caldera,  as  in  the  case  of 
Vesuvius,  which  was  built  within  the  breached  rim  of  the  extinct 
Monte  Somma.  The  displacement  of  the  eruptive  point  may  be 
a  gradual  one,  when  a  series  of  adjoining  cones  will  result,  all  but 
the  youngest  being  breached  on  the  side  toward  the  direction  of 
migration  of  the  cones.  Examples  of  such  consecutively  breached 
cones  are  found  in  the  volcanic  region  of  central  France  (Mont 
Dore  Province),  and  elsewhere.  Many  variations  and  combinations 
occur,  and  the  student  is  referred  for  the  details  of  these  phenom- 
ena to  the  numerous  general  treatises,  some  of  which  are  listed  at 
the  end  of  the  chapter. 

Compound  volcanoes,  such  as  Vesuvius,  have  alternating  periods 
of  light  (or  Strombolian)  and  violent  (or  Vulcanian)  activity.  Dur- 


872  PRINCIPLES    OF    STRATIGRAPHY 

ing  the  former  cinder  cones  are  built  up  which  are  destroyed  again, 
in  part  or  entirely  during  the  violent  periods,  when  crater  formation 
is  the  marked  characteristic.  It  is  during  this  period  of  activity 
that  the  extravasative  eruptions  are  in  the  ascendency,  and  at  this 
time  also  fissuring  of  the  volcano  takes  place,  with  all  the  varied 
activities  which  accompany  such  a  state. 

Submarine  Cones.  Submarine  cones  of  pure  extravasation  are 
apparently  illustrated  by  the  Hawaiian  Islands,  though  the  early 
history  of  many  of  these  volcanoes  is  shrouded  in  obscurity.  Sub- 
marine cones  of  the  composite  type  are  well  known,  however. 
Probably  many  of  the  volcanoes  of  the  Mediterranean  began  as 
submarine  volcanoes  and  subsequently  reached  the  surface.  Vol- 
canoes of  this  type  are  also  known  from  the  Aleutian  island  group 
(Jaggar-2i),  while  volcanoes  apparently  rising  from  the  abyssal 
portions  of  the  sea  abound  in  the  western  Pacific.  A  singular  ex- 
ample of  a  volcanic  peak  projecting  from  mid-ocean  is  seen  in  the 
little  island  of  St.  Paul,  which  rises  from  the  Indian  Ocean  mid- 
way between  the  southern  end  of  Africa  and  the  west  of  Australia 
and  more  than  2,000  miles  distant  from  Madagascar,  the  nearest 
mass  of  dry  land.  This  little  island,  scarcely  2l/2  geographical 
miles  long  and  about  il/2  miles  broad,  is  the  mere  summit  of  a 
volcano.  The  crater  has  been  breached  by  the  waves  and  is  now 
occupied  by  the  sea,  the  break  in  the  rim  being  nearly  dry  at  low 
tide.  (Figs.  236,  237.) 

Mud  Volcanoes.  Of  an  origin  fundamentally  the  same  as  that 
for  lava  volcanoes  are  the  mud  volcanoes  found  in  various  regions 
of  the  world,  but  not  associated  with  igneous  eruptions.  They 
occur  in  Sicily,  the  Apennines,  Caucasus,  and  on  the  peninsulas  of 
Kertch  and  Taman  bordering  the  Black  Sea,  as  well  as  in  India. 
They  find  their  chief  activity  in  the  escape  of  various  gases,  which 
play  much  the  same  part  as  does  the  escaping  steam  in  igneous 
volcanoes.  Hydrocarbons,  carbon  dioxide,  nitrogen,  and  naphtha 
are  some  of  the  gases  emitted.  The  mud  volcanoes  of  Sicily  have 
been  explained  as  due  to  the  slow  combustion  of  sulphur  beneath 
the  surface.  Whatever  the  causes,  these  volcanoes  are  manifested 
on  the  surface  in  mounds  or  hillocks  of  mud.  They  generally 
occur  in  groups  and  range  in  elevation  up  to  several  hundred  feet, 
while  during  periods  of  explosion  they  throw  mud  and  stones  up 
into  the  air  to  much  greater  heights.  They  are  built  up  by  succes- 
sive outpourings  of  mud,  which  harden  and  form  a  foundation  for 
later  mud  flows.  "In  the  region  of  the  Lower  Indus,  where  they 
are  abundantly  distributed  over  an  area  of  1,000  square  miles,  some 
of  them  attain  a  height  of  400  feet,  with  craters  30. yards  across." 


COMPOSITE   CONES 


873 


( Geikie-9 1245. )    These  are  not  to  be  confused  with  the  mud  flows 
which  form  on  the  sides  of  volcanoes  from  the  saturation  of  dust 


FIG.  236.  View  of  the  Island  of  St.  Paul  in  the  southern  Indian  Ocean,  show- 
ing the  breach  in  the  rim  of  the  extinct  volcano  and  the  crater 
flooded  by  the  sea.  (From  a  sketch  by  Charles  Velain  in  Haug.) 

and  cinders  by  rain.  Such  flows  always  occur  in  regions  of  igneous 
extrusion  on  the  sides  of  igneous  volcanoes,  while  mud  volcanoes 
may  occur  in  any  region  where  gases  accumulate  beneath  the  sur- 


FIG.  237.     Map  of  the  Island  of  St.  Paul  in  the  southern  Indian  Ocean.     A 
breached  volcano.     (After  Charles  Velain  in  Haug.) 

face  in  large  enough  quantities  to  be  forced  out.  Neither  should 
these  mud  volcanoes  be  confused  with  mud  mounds,  cones,  or 
craterlets  which  form  along  earthquake  fissures  where  the  release 


874  PRINCIPLES    OF    STRATIGRAPHY 

of  pressure  sends  forth  a  stream  of  water  carrying  sand  and  mud 
with  it.     (See  farther  in  Chapter  XXIII,  on  Seismology.) 

Dissection  of  Volcanoes.  When  volcanoes  have  become 
extinct  the  ordinary  forces  of  erosion  set  in  and  progressive 
destruction  goes  on.  The  rapidity  with  which  this  takes  place 
varies,  of  course,  with  the  nature  of  the  material,  the  prevailing 
strength  of  the  erosive  forces,  and  with  other  factors.  Many  of 
the  Tertiary  volcanoes  of  the  Eifel  in  Germany  and  of  the  Auvergne 
district  in  France  are  still  almost  perfect,  while  others  of  earlier 
date  show  all  stages  of  dissection.  Of  interest  in  this  connection 
is  the  Kammerbuhl  near  Franzensbad  in  northern  Bohemia,  which 


FIG.  239.  Section  of  the  Kammer- 
buhl, showing  the  probable 
former  outline  of  the  volcano : 
a,  metamorphic  rock ;  b,  basaltic 
scoriae ;  c,  plug  or  neck  of  basalt ; 
FIG.  238.  The  Kammerbuhl,  an  old  d,  stream  of  basalt;  e,  alluvial 

volcanic  hill  in  Bohemia.  beds. 

Goethe  pronounced  an  extinct  volcano,  though  Werner  had  explained 
its  character  as  originating,  in  common  with  those  of  others  of 
similar  aspect,  through  the  combustion  of  a  bed  of  coal.  Goethe 
predicted  the  finding  of  a  core  of  volcanic  rock  in  the  center  of 
this  hill  were  a  tunnel  driven  into  it  horizontally.  The  excavating 
of  this  tunnel  in  1837  verified  this  prediction,  while  more  recent 
excavations  have  revealed  the  entire  structure,  showing  that  the 
small  lava  stream  on  the  side  of  the  hill  was  connected  with  the 
central  plug  or  neck  and  rested  on  basaltic  scoria.  The  above 
figures  show  the  appearance  of  this  hill  and  the  structure  ascer- 
tained by  these  excavations.  (Figs.  238,  239.) 

In  extensively  dissected  volcanoes  often  only  the  central  neck 
or  plug  remains,  as  in  the  case  of  the  volcanic  necks  of  the  Mount 
Taylor  Region  in  New  Mexico  (Johnson-22  '.303-324),  the  Leucite 
Hills  of  Wyoming  (Kemp-25),  and  many  others  of  this  type. 
Dikes  dissecting  the  tufa  beds  of  old  volcanoes  often  stand  out 
in  bold  relief  owing  to  the  steady  removal  of  the  easily  eroded  tufa 
enclosing  them.  Examples  of  such  are  known  from  many  locali- 
ties. The  geological  map  of  the  Spanish  Peaks  region  in  Colorado 
shows  excellently  the  numerous  radiating  dikes  which  center  in  the 
old  volcanic  necks  of  that  region. 


DESTRUCTION    OF   VOLCANOES  875 

Where  extinct  volcanoes  have  been  subject  to  the  attack  of 
the  waves  of  the  sea  sections  are  often  cut  which  reveal  their  struc- 
ture. This  is  the  case  in  the  island  of  St.  Paul,  already  noted,  and 
in  Vulcanello  on  the  shores  of  the  Island  of  Vulcano  in  the  Mediter- 
ranean. Some  of  the  outlying  islands  of  the  Sandwich  or  Hawaiian 
group  likewise  represent  partly  dissected  extinct  volcanic  cones 
whose  sides,  moreover,  are  deeply  gullied  into  a  series  of  parallel 
valleys  so  sharply  divided  one  from  the  other  as  to  effectively 
isolate  certain  of  the  organisms  inhabiting  them.  (See  Chapter 
XXIX.) 

Finally,  the  destruction  of  volcanoes  by  their  own  explosive  ac- 
tivity may  be  noted.  Examples  are  furnished  by  the  Vesuvian 
eruption  of  A.  D.  79,  which  shattered  the  cone  of  Monte  Somma; 
by  the  Japanese  volcano  Bandai-san,  of  which  a  considerable  portion 
was  blown  out  in  1888;  and  by  the  Javanese  volcano  Krakatoa, 
which  was  practically  blown  to  pieces  on  August  26  and  27,  1883, 
furnishing  the  most  stupendous  example  of  volcanic  activity  in 
modern  times.  "After  a  series  of  convulsions,  the  greater  portion 
of  the  island  was  blown  out  with  a  succession  of  terrific  detonations 
which  were  heard  more  than  150  miles  away.  A  mass  of  matter 
estimated  at  about  \V%  cubic  miles  in  bulk  was  hurled  into  the  air 
in  the  form  of  lapilli,  ashes,  and  the  finest  volcanic  dust.  .  .  . 
The  sea  in  the  neighborhood  was  thrown  into  waves,  one  of  which 
was  computed  to  have  risen  more  than  100  feet  above  tide-level, 
destroying  towns,  villages,  and  36,380  people."  (Geikie-p:^/^.) 
The  oscillations  of  the  wave  were  noted  at  Port  Elizabeth,  South 
Africa,  5,450  miles  away,  having  traveled  with  a  maximum  velocity 
of  467  statute  miles  per  hour.  The  air  waves  generated  traveled 
from  east  to  west  and  are  supposed  to  have  passed  three  and  a 
quarter  times  around  the  earth  (82,200  miles)  before  they  died 
away.  The  barometric  disturbances,  passing  round  the  globe  in 
opposite  directions  from  the  volcano,  proceeded  at  the  rate  of  almost 
700  miles  per  hour. 

Special  Erosion  Features.  An  interesting  type  of  erosion  has 
been  observed  on  some  steep-sided  volcanoes,  such  as  those  of  the 
islands  of  St.  Vincent  and  Martinique.  Vast  amounts  of  dust  were 
deposited  during  the  eruption  of  May,  1902,  and  these  formed  a 
bed  varying  from  a  few  inches  to  many  feet  in  thickness,  and 
extending  over  an  area  of  50  square  miles  on  each  island.  The 
heavy  rains  that  followed  the  eruption  turned  this  dust  into  a 
cement-like  mud  which  was  firm  enough  to  remain  in  place  and 
which,  during  the  eruptions  of  September  and  October  of  the  same 
year,  was  covered  by  a  new  layer  of  coarser  ejectamenta.  In  the 


876  PRINCIPLES    OF    STRATIGRAPHY 

valleys  the  permanent  and  periodical  rivers  were  loaded  with  the 
new  ash  to  such  an  extent  as  to  form  viscous  streams,  which,  how- 
ever, had  great  powers  of  erosion,  on  account  of  the  steep  slope  of 
the  declivities  down  which  they  flowed.  The  bottoms  and  sides  of 
the  gorges  were  deeply  grooved  by  the  sand  carried  down  in  this 
manner  by  the  flowing  water. 

''During  the  great  eruptions  the  ejected  material  was  drifted  into 
large  beds  in  the  gorges  extending  radially  down  the  Soufriere 
[on  St.  Vincent  Island].  The  massing  of  material  was  most  im- 
portant in  the  gorge  of  the  Wallibou  River  on  the  west,  and  in 
that  of  the  Rabaka  River  on  the  east,  side  of  the  island.  In  these 
gorges  the  bed  of  new  material  reached  a  thickness  of  from  60 
to  100  feet.  This  enormous  amount  of  material  was  almost  entirely 
washed  out  of  the  gorges  during  the  first  rainy  season  following 
the  eruptions  of  1902.  Not  less  than  150,000,000  cubic  feet  of 
ashes  have  been  washed  out  of  the  Wallibou  gorge  itself,  without 
taking  into  account  the  thousands  of  cubic  yards  of  fresh  ash  re- 
moved from  the  watershed  of  the  river  during  the,  same  period. 
All  this  material  was,  of  course,  transported  directly  to  the  ocean." 
(Hovey-i8:5<5o.) 


FORMATION   OF   THE   LAVA. 

Since  it  is  very  unlikely  that  at  any  point  within  the  earth's  crust 
the  temperature  is  sufficiently  high  to  melt  rocks  (see  Chapter  I) 
at  the  increased  fusing  point  caused  by  the  increase  in  pressure 
downward,  it  follows  that  some  other  factors  must  be  taken  into 
consideration  in  explaining  the  liquefaction  of  rock.  We  must, 
therefore,  seek  either  for  causes  producing  an  increase  of  tempera- 
ture, or  for  such  producing  a  decrease  of  pressure.  The  former 
may  be  found  in  the  energy  liberated  by  radio-active  substances, 
such  as  are  found  in  practically  all  the  rocks  of  the  earth's  crust,  as 
well  as  in  the  water  and  the  air.  Since,  says  Chamberlin  (3:679), 
"radio-activity  increases  as  we  go  from  air  to  water,  from  water 
to  sediment,  and  from  sediment  to  igneous  rock,  it  might  be  inferred 
.  .  .  that  radio-activity  would  be  found  to  reach  its  maximum 
concentration  in  the  heart  of  the  earth,  and  certainly  that  the  deeper 
parts  would  be  as  rich  as  the  superficial  ones."  This,  however, 
would  imply  a  more  rapid  increase  in  temperature  than  observation 
indicates.  Strutt  (quoted  by  Chamberlin)  has  computed  that,  if 
the  quantity  of  radio-active  substances  known  to  exist  in  surface 
rocks  is  also  found  throughout  the  rocks  of  the  upper  45  miles 


FORMATION    OF   LAVA  877 

of  the  earth's  crust,  the  rise  in  temperature  equal  to  that  observed 
in  deep  wells  and  mines  would  be  produced  by  this  cause  alone, 
irrespective  of  any  other  source  of  heat.  Whether  this  distribution 
is  equal,  or  whether  it  increases  or  decreases  downward,  can  not, 
at  present,  be  determined;  but  it  is  seen  that  if  we  start  with  an 
original  increase  in  temperature  downward  the  amount  added  to 
it  by  radio-activity  might  serve,  locally,  to  overcome  the  opposing 
effects  of  pressure  in  raising  the  fusing  point,  whereupon  reser- 
voirs of  molten  rock  would  be  formed  which  would  become  the 
source  of  volcanic  activity. 

If  excessive  temperature  increase  is  not  to  be  accepted  as  the 
cause  of  rock  fusion  at  a  depth,  we  must  turn  to  a  local  decrease 
of  pressure  to  permit  the  lowering  of  the  fusing  point  of  the  rocks. 
This  would  be  effected  by  the  formation,  locally,  of  rock  arches 
within  the  crust  capable  of  maintaining  the  weight  of  the  superin- 
cumbent portion  of  the  crust.  Such  arches,  or  domes,  by  relieving 
the  pressure,  would  permit  the  liquefaction  of  the  rock  mass  for 
some  distance  beneath  them,  provided  the  temperature  is  sufficiently 
high,  and  so  furnish  the  requisite  conditions  for  volcanic  activities. 

Arches  of  this  type  might  be  expected  to  form  along  the  margins 
of  the  continent  where  the  down-warping  of  the  continental  edges 
takes  place.  Now,  it  is  precisely  along  these  lines,  where  the  con- 
tinental margin  drops  off  steeply  to  the  deep  sea,  that  the  great 
volcanic  phenomena  of  the  past  have  been  located,  while  the  dis- 
tribution of  most  of  the  modern  volcanoes  of  the  earth  is  essentially 
in  harmony  with  this  idea.  Thus  by  far  the  largest  number  of 
still  active  or  but  recently  extinct  volcanoes  are  ranged  in  belts  or 
lines  parallel  to  the  margins  of  the  continents  or  within  the  oceanic 
areas.  The  most  important  belt  of  volcanic  activity  surrounds 
the  Pacific  Ocean,  the  deepest  and  perhaps  the  oldest  of  the  oceans 
of  the  earth,  and  the  one  which  has  experienced  the  least  change. 
This  belt  includes  the  volcanic  mountains  of  the  west  coasts  of 
South  and  Central  America,  of  Mexico,  and  of  the  western  United 
States  and  Canada  to  Alaska  and  the  Aleutian  Island  chain.  It  is 
continued  along  the  eastern  coast  of  Eurasia,  and  through  the 
Malaysian  islands  to  New  Zealand,  the  belt  being  finally  closed  by 
the  volcanoes  of  Victoria  Land,  King  Edward  Island,  and  West 
Antarctica.  It  is  significant  that  the  belt  for  the  most  part  is 
paralleled  by  an  inner  one  of  exceptional  depressions  the  great 
fore-deeps  of  the  marginal  Pacific.  That  these  are  produced  by 
downwarping  or  faulting  seems  certain,  and  this  would  imply  an 
arching  or  unwarping  of  the  adjoining  continental  margins. 


878  PRINCIPLES    OF    STRATIGRAPHY 


BIBLIOGRAPHY    XXII. 

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John  Murray,  London. 

2.  BONNEY,  T.  G.     1899.     Volcanoes,  Their  Structure  and  Significance. 

John  Murray,  London. 

3.  CHAMBERLIN,  THOMAS  C.     1911.     The  Bearing  of  Radioactivity  on 
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I  5.  DANA,  JAMES  D.  1890.  Characteristics  of  Volcanoes,  with  contribu- 
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6.     DE  LA  BECHE,   HENRY  T.     1851.     The  Geological  Observer,   Phil- 
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j  7.     DUTTON,   CLARENCE  E.     1884.     Hawaiian  Volcanoes.     Fourth  An- 
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XVIII,  pp.  493-504,  pis.,  54-56. 
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Macmillan  &  Co. 

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I2a.  HILL,  R.  T.  1905.  Pelee  and  the  Evolution  of  the  Windward  Archi- 
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243-288,  5  pis. 

13.  HITCHCOCK,  C.  H.     1909.     Hawaii  and  Its  Volcanoes.     Honolulu. 

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Journal  of  Geology,  Vol.  XIV,  pp.  636-655. 

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Region,  New  Mexico.     Bulletin  of  the  Geological  Society  of  America, 

Vol.  XVIII,  pp.  303-324,  pis.  25-30. 


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494  PP- 

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E.  THE    CENTROSPHERE   OR   BARYSPHERE. 


CHAPTER  XXIII. 

DIASTROPHISM,   OR  THE   MOVEMENTS  TAKING  PLACE  WITHIN 
THE   EARTH'S   CRUST  AND   THEIR   CAUSES., 

In  discussing  the  subject  of  diastrophism  under  the  heading 
of  the  Centrosphere,  it  is  intended  to  emphasize  the  fact  that 
the  great  mass  of  such  movements  is  directly  or  indirectly  induced 
by  gravity,  i.  e.,  the  terrestrial  phenomenon  of  weight  or  downward 
acceleration,*  which  has  for  its  two  components  the  gravitation  or 
attracting  force  between  bodies  and  the  centrifugal  force  due  to 
the  rotation  of  the  earth  on  its  axis. 

Other  forces  which  induce  earth  movements  have  their  origin 
in  the  interior  heat  of  the  earth ;  in  chemical  combination ;  in  molec- 
ular attraction  and  repulsion;  in  radio-activity;  in  electrical  and 
vital  energy;  in  the  centrifugal  energy  due  to  the  rotating  of  the 
earth  on  its  axis  and  its  revolution  around  the  sun ;  in  the  attraction 
of  the  moon  and  sun ;  and  in  the  radiant  energy  of  the  sun.  Im- 
pact with  heavenly  bodies  may  be  further  mentioned  as  a  source 
of  possible  energy.  But  'all  of  these,  except  perhaps  the  last, 
are  of  minor  significance  as  compared  with  gravity  as  the  great 
source  of  energy  influencing  earth  movements.  The  displacement 
of  the  earth's  center  of  gravity  through  any  cause,  and  the  conse- 
quent displacement  of  the  earth's  axis,  would  also  be  a  direct  cause 
of  the  setting  free  of  a  vast  amount  of  available  energy. 

CLASSIFICATION    OF    EARTH    MOVEMENTS. 

Earth  movements  may  be  classified  either  as  local  disturbances 
or  as  widespread  or  regional  ones.  The  movements  are  manifested 

*  The  amount  of  downward  acceleration  is  about  385.1  inches  (978  centi- 
meters) per  second  at  sea-level  at  the  equator,  and  387.1  inches  at  sea-level' at 
the  poles,  diminishing  slightly  on  mountain  tops.  The  centrifugal  force  at  the 

equator  is  — of  gravity. 

880 


CLASSIFICATION    OF    EARTHQUAKES  881 

as  seismic  disturbances,  of  which  earthquakes  and  sea-quakes  are 
the  recognized  effects,  while  the  products  of  the  disturbances  are 
tectonic  structures* 

Not  all  tectonic  structures  are  accompanied  in  their  formation 
by  seismic  disturbances,  for  some  deformations  may  go  on  so 
gradually,  and  at  such  a  uniform  rate,  that  no  surface  manifesta- 
tions are  felt.  In  this  class  fall  especially  the  large  or  epeirogenic 
earth  movements,  and  the  bradyseisms  noted  below. 


CLASSIFICATION  OF  SEISMIC  DISTURBANCES. 

Not  all  seismic  disturbances  are  due  to  earth  movements,  as 
the  term  is  here  used,  for  volcanic  activities,  especially  of  the  ex- 
plosive type,  may  generate  such  disturbances,  these  being  sometimes 
of  considerable  magnitude,  as  in  the  case  of  the  explosive  eruption 
of  Krakatoa  in  1883.  As  there  illustrated,  the  three  inorganic 
spheres — the  litho,  hydro,  and  atmosphere,  not  to  mention  the  bio- 
sphere— were  disturbed  by  this  explosion,  and  earthquakes,  sea- 
quakes, and  air-quakes  f  resulted.  The  air-waves  which  charac- 
terized the  last  passed  around  the  earth  several  times,  while  the 
sea  disturbances  or  tsunamis  J  generated  were  noticeable  more 
than  five  hundred  miles  away. 

Recognizing  the  different  modes  of  production  of  earthquakes, 
seismologists  have  divided  them  according  to  origin  into:  (Suess- 

38.) 

1.  Dislocation  or  fault  earthquakes. 

2.  Volcanic,  or  explosive  earthquakes. 

*  The  term  tectonic,  originally  applied  to  all  structures,  has  come  of  late  to  be 
more  especially  applied  to  structures  due  to  earth  movements,  or  deformation 
structures.  These  include  faults,  folds,  torsion  joints,  etc.,  but  not  stratification, 
unconformity,  overlap,  flow-structure,  or  any  other  original  structures,  nor  such 
secondary  structures  as  concretions,  enterolithic  deformation,  or  any  other 
structures  due  to  diagenetic  or  contactic  metamorphism. 

t  If  we  consider  that  the  term  seisma  refers  to  the  trembling  or  shaking  of  the 
geos,  or  earth  as  a  whole  (geoseism),  and  not  merely  to  the  tremblings  of  the  land, 
we  may  extend  the  meaning  of  the  term  seismology  so  as  to  cover  the  shaking  or 
trembling  of  any  portion  of  the  earth  as  the  result  of  such  disturbances.  We 
could  thus  distinguish:  lithoseisma,  or  earthquakes  proper  (land-quakes);  hydro- 
or  thalassoseisma  or  sea-quakes  and  atmoseisma,  or  air-quakes.  The  bioseisma  arc, 
of  course,  a  universal  accompaniment  of  all  these  disturbances. 

t  The  Japanese  term  for  the  "tidal  wave,"  or  "sea- wave"  of  sea-quakes. 
Suggested  for  general  adoption  by  Hobbs  (17). 


382  PRINCIPLES    OF    STRATIGRAPHY 

The  first  type  of  seismic  disturbance  may  be  spoken  of  as  bary- 
seismic* and  the  second  as  pyroseismic.  "f  these  terms  indicating 
the  relationship  of  the  disturbances  to  the  respective  spheres. 
Hoernes  (19)  has  designated  as  a  third  type  the  results  of  incaving 
of  the  roofs  of  fissures  (Einstursbeben)  which  characterize  the 
Karst  region  of  the  Dalmatian  coast.  This,  however,  is  to  be  classed 
as  a  special  phase  of  the  dislocation  (baryseismic)  type,  since  such 
cavings-in  of  cavern  roofs  are  merely  special  phases  of  faulting. 
In  the  same  way,  we  must  class  under  the  volcanic  or  explosive 
(pyroseismic)  type  the  tremors  resulting  from  explosions  of  g  m- 
powder  or  dynamite,  and  of  gases,  in  mines  and  elsewhere,  which 
may  not  be  sufficient  to  affect  the  seismograph,  but  are  certainly 
noticeable  as  sea-quakes  (submarine  explosions)  and  as  air-quakes. 
These,  as  well  as  the  disturbances  due  to  incaving,  may  be  dis- 
missed without  further  notice. 

The  Volcanic  or  Pyroseismic  Type  of  Earthquake.  This  is,  of 
course,  an  accompaniment  of  volcanic  activities  ;  but  such  dis- 
turbances are  not  necessarily  always  felt,  for,  even  if  they  occur, 
they  may  be  so  slight  as  to  escape  notice. 

The  Tectonic  or  Dislocation  (Baryseismic)  Earthquake.  This 
is  a  jar  occasioned  by  the  breaking  of  rock  under  strain.  "The 
strain  may  be  caused  by  the  rising  of  lava  in  a  volcano  or  by  the 
forces  that  make  mountain  ranges  and  continents."  The  rupture 
of  the  rock  mass  "may  be  a  mere  pulling  apart  of  the  rocks,  so  as 
to  make  a  crack,  but  examples  of  that  simple  type  are  compara- 
tively rare.  The  great  majority  of  ruptures  include  not  only  the 
making  of  a  crack  but  the  relative  movement  or  sliding  of  the  rock 
masses  on  the  two  sides  of  the  crack;  that  is  to  say,  instead  of 
a  mere  fracture,  there  is  a  geologic  fault."  (Gilbert-i3  \2.) 

The  walls  of  the  fault  plane  may  eventually  become  cemented 
together,  but  they  will  remain  as  a  plane  of  weakness  for  a  long 
time,  so  that  repeated  slipping  may  take  place,  making  the  region 
one  of  frequent  earthquakes.  This  has  been  the  case  in  the  repeated 
California  earthquakes,  of  which  the  San  Francisco  quake  of  1906 
is  the  most  recent.  The  fault-line  there  extends  for  several  hun- 
dred miles  northwest  and  southeast  and  nearly  parallel  to  the 
coast.  The  "Fossa  Magna"  crosses  Japan  from  north  to  south, 
while  the  southern  border  lands  of  Afghanistan  have  such  an 
habitual  earthquake-producing  fault-line  extending  for  120  miles. 

The  faulting  or  slipping  which  produces  the  earthquake  may 


*  From  the  Greek  fiapfa  =  heavy,  -f  a-eifffj-a  —  earthquake;   signifying  that 
weight  or  gravity  is  the  dominant  factor  in  their  production. 
t  From  the  Greek  irfy  =  fire,  -f-  <rd<rfw.  =  earthquake. 


BARYSEISMIC   DISTURBANCES  883 

be  deepseated  or  may  reach  the  surface.  The  depth  to  which  the 
dislocation  penetrates  may  be  very  great — it  may  pass  from  the 
zone  of  fracture  into  that  of  flowage;  but  the  origin  of  the  shock 
is  probably  never  deeper  than  30  geographical  miles,  and  usually 
does  not  exceed  5  to  15  miles.  (Hovey-2i  '.244.)  The  point  or 
locus  of  origination  of  the  earthquake  is  variously  called  the 
seismic  center,  centrum,  hypocenter,  origin,  or  focus.  This,  though 
conveniently  regarded  as  a  point,  is  really  a  space  of  three  dimen- 
sions which  in  different  cases  varies  much  in  size  and  shape  and 
may  be  of  great  magnitude.  The  part  of  the  earth's  surface  which 
is  vertically  above  the  center  is  the  epicenter  or  epicentral  or  epi- 
focal  tract. 

SURFACE  MANIFESTATIONS  OF  BARYSEISMIC  DISTURBANCES. 

The  surface  manifestations  of  an  earthquake-producing  fault 
or  other  tectonic  movement  may,  so  far  as  the  lithosphere  is  con- 
cerned, be  classed  as  rifting,  as  slipping,  and  as  disruption.  The 
first  is  mere  separation,  the  second  involves  displacement.  It  is  to 
the  latter  movement  that  the  term  faulting  is  commonly  applied. 


Rifting. 

As  a  result  of  rifting,  fissures  will  open  in  the  earth  (Fig.  240) 
and  these  may  remain  open  or  be  filled  by  injected  material.  So 
far  as  arrangement  is  concerned  these  fissures  may  be  in  parallel 
series,  as  in  the  case  of  the  fissures  formed  by  the  earthquake  of 
Sinj,  Austria,  in  1898,  in  which  slipping  also  occurred  along  each 
rift.  Or,  again,  these  fissures  may  radiate  from  a  center,  branch- 
ing repeatedly.  Such  fissures  were  formed  during  the  Calabrian 
earthquake  of  1783.  Finally,  fissures  formed  during  earthquakes 
may  be  irregularly  intersecting,  forming  a  network.  This  type  has 
been  observed  at  Aigon  in  the  Balkans  after  the  earthquake  of 
December  26,  1861 ;  in  Owens  Valley,  California,  after  the  earth- 
quake of  1872  (Whitney)  ;  and  in  Ecuador,  where  it  is  a  very 
characteristic  feature  of  the  Andes  region.  Whimper  (43)  says  of 
these:  "In  no  other  part  of  Ecuador  is  there  anything  equaling 
this  extraordinary  assemblage  of  fissures,  intersecting  one  another 
irregularly  and  forming  a  perfect  maze  of  impassable  clefts  .  .  . 
the  cracks  are  all  V-shaped  and,  though  seldom  of  great  breadth, 
are  often  very  profound,  .  .  .  Several,  at  least,  have  been 
formed  within  the  memory  of  man,  while  others  are  centuries  old." 


884 


PRINCIPLES    OF    STRATIGRAPHY 


These  intersecting  fissures  are  locally  known  as  earthquake  "que- 
bradas." 

Fissures  often  open  and  close  repeatedly,  even  during  the  same 


FIG.  240.     Small    earthquake   fissure   and   fault   in  the   Arizona   desert. 
(After  Branner.) 

disturbance ;  sometimes  in  closing,  the  walls  are  pressed  violently 
together,  while  shattering  of  the  adjoining  rock  masses  occurs,  with 
the  formation  of  autoclastic  material  or  fault-breccias.  This  gen- 


\\   '  )    IU        — . 


FIG.  241.  Section  of  one  of  the  sandstone  pipes  in  limestone  on  the  eastern 
coast  of  Anglesey  in  Wales.  (After  Greenly,  from  Hobbs.)  <*, 
cherty  limestone;  p,  sandstone  pipe;  7,  cherty  limestone. 

erally  falls  into  the  fissure,  more  or  less  filling  it,  or  it  marks  the* 
sides  of  the  fissure  for  some  distance  outward. 

Filling  of  the  Fissures.    Sandstone  Dikes.     Fissures  formed  by 
earthquakes  may  remain  open   for  a  longer  or  shorter  period  of 


SANDSTONE    DIKES;    CRATERLETS  885 

time,  becoming  gradually  filled  up  by  debris  which  falls  in  from 
above,  or  is  washed  into  them.  Such  is  the  case  in  several  vertical 
fault  fissures  at  Meriden,  Connecticut,  which  have  been  filled  by 
infiltration  of  trap  fragments  and  sandstone  from  above.  (Davis, 
in  Diller-8:^^.) 

Davis  says :  "These  fractures  traverse  a  sheet  of  lava  and 
are  chiefly  filled  with  angular  trap-fragments,  but  the  interstices  are 
occupied  with  sandstone,  not  in  fragments  as  if  it  had  fallen  in 
with  the  pieces  of  trap,  but  in  a  close-fitting  mass,  as  if  it  had 
settled  down  in  the  form  of  separate  particles  derived  from  the 
sandstone  originally  overlying  the  trap  sheet,  thus,  in  a  general  way, 
taking  a  structure  conformable  to  the  blocks  of  trap  that  it  sur- 
rounds, but  showing  also  a  tendency  to  a  transverse  or  horizontal 
stratification.  It  seems  probable  that  these  fissures  were  filled 
gradually  by  infiltration  from  above  .  .  ." 

In  some  cases,  however,  such  fissures  are  filled  at  the  time  of 
their  formation  by  sand  violently  injected  into  them  either  from 
below  or  above.  Cases  of  mud  and  sand  welling  up  from  volcanic 
fissures  have  been  frequently  observed,  and  seem  to  be  a  general 
accompaniment  of  such  fissures  near  the  surface.  In  some  cases, 
as  in  the  earthquake  of  Chemakha,  Turkestan  (Feb.  12,  1902),  "salty 
plastic  mud  exuded  from  the  open  faults  and  built  up  high  hillocks 
of  the  pasty  material,  which  were  surmounted  by  craters"  (Hobbs- 
18:134).  Subsequent  movement  along  the  plane  caused  a  dis- 
placement in  these  "mud  volcanoes"  to  the  extent  of  1.5  meters 
in  some  cases.  Sand  and  mud  injections  of  this  type  are  known 
from  older  geological  formations,  where  they  form  sandstone  dikes. 
Thus  Newsom  ($$'.233}  describes  a  sandstone  dike  2}/2  to  5  feet 
wide  from  California,  in  which  the  upward  bending  of  the  shales 
on  either  side  is  regarded  as  proving  its  injection  from  below. 
Others  from  the  same  general  region  are  also  described.  Violent 
injection  into  an  earthquake  fissure  of  loose  sand,  which  covered  the 
surface  of  the  rock,  seems  to  have  taken  place  in  the  case  of  the 
Lower  Devonic  sandstone  dike  (injected  into  Upper  Siluric  strata) 
at  Buffalo,  as  described  in  a  preceding  chapter.  For  a  general 
summary  of  sandstone  dikes  with  references  to  the  literature,  the 
student  is  referred  to  Newsom's  article  (33). 

Craterlets.  Analogous  to  the  injected  sandstone  dikes  are  the 
craterlets  formed  by  sand  and  mud  ejected  with  water  from  earth- 
quake fissures.  One  such  has  already  been  noted  in  connection 
with  the  Chemakha  earthquake.  Others  were  noted  in  the  Charles- 
ton earthquake  of  1886.  Some  of  these  which  were  aligned  along 
fissures  measured  20  feet  in  diameter,  while  the  water  and  sand 


886  PRINCIPLES    OF    STRATIGRAPHY 

ejected  from  them  shot  in  some  cases  20  feet  into  the  air.  Many  of 
the  craterlets,  especially  those  formed  during  the  Calabrian  earth- 
quake, are  merely  funnel-shaped  holes  in  the  ground,  and  so  re- 
semble the  volcanic  explosion  craters.  (Fig.  242.)  Such  craterlets 
formed  in  the  Mississippi  Valley  during  the  earthquake  of  1811. 
They  were  commonly  surrounded  by  a  ring  of  sand  and  carbonized 
wood,  sometimes  as  much  as  7  feet  in  height.  They  have  a  diam- 
eter ranging  from  20  to  100  feet,  and  some  were  sounded  to  a  depth 
of  20  feet  or  over. 

Much   sand   and   water   is   ejected    from   these    and   is    spread 
over  the  surrounding  country,  which  may  thus  be  blanketed  by  a 


FIG.  242.     Funnel-shaped  holes  formed  during  the  Calabrian  earthquake  of 
1783.     (C.  Vogt.) 

layer  of  sand  brought  from  below,  the  analogue  of  a  lava 
flow.  Sulphuretted  hydrogen  frequently  accompanies  these  erup- 
tions. 

Fossil  examples.  Ancient  craterlets  of  the  type  above  described 
have  been  noted  in  some  cases.  Thus,  on  the  coast  of  East  Angle- 
sey, in  Wales,  sandstone  pipes  have  been  observed,  penetrating  the 
Ordovicic  limestones,  and  having  a  general  funnel  form  comparable 
to  the  funnels  formed  by  the  Calabrian  earthquake.  They  are 
continuous  above  with  a  spreading-  blanket  of  sandstone,  which 
may  be  the  ejected  layer  of  sand.  The  entire  series  is  again  cov- 
ered by  the  Ordovicic  limestones  of  the  region.  A  section  of  this, 
copied  from  Hobbs,  is  shown  in  Fig.  241.  Care  must,  however,  be 
exercised  to  distinguish  these  fissures  from  the  solution  fissures 
subsequently  filled  by  sand  and  forming  the  organ-pipe  structure 
described  in  a  preceding  chapter. 


DISLOCATIONS  887 


Slipping. 

When  differential  movements  of  the  two  sides  of  a  fracture 
occur  a  fault  results.  This  movement  may  be  horizontal,  diagonal, 
or  vertical.  The  displacement  may  be  profound  or  very  slight.  It 
may  be  sudden  or  by  a  series  of  progressive  slips,  or  it  may  be 
the  resultant  of  a  series  of  slips  in  various  (even  opposite)  direc- 
tions, and  of  varying  amounts.  The  California  earthquake  of  1906 
and  the  Japanese  earthquake  of  1811  were  caused  by  slips  of  large 
amplitude  along  well-defined  seismotectonic  lines.  The  frequent 
New  England  quakes  are  due  to  a  relatively  large  number  of  slight 
adjustments  along  joint  planes.  These  minor  slippings  may  be 
so  slow  as  to  produce  no  perceptible  seismic  disturbances,  though 
they  may  find  a  surface  expression  in  minute  faults.  Here,  prob- 
ably, belong  the  numerous  minute  post-glacial  faults  of  New  Eng- 
land and  eastern  New  York.  (Woodworth-45.) 

The  local  rise  and  fall  of  the  land  in  response  to  adjustment 
to  stresses,  but  without  violent  shocks,  or  abrupt  ruptures,  may 
be  considered  as  forming  one  end  of  the  series  of  earthquake- 
producing  disturbances.  To  these  the  name  bradyseisms  has  been 
given,  and  they  are  well  illustrated  by  the  changes  of  level  re- 
corded in  the  ruins  of  the  Temple  of  Jupiter  Serapis  in  the  Bay 
of  Naples,  already  referred  to  in  an  earlier  chapter. 

On  the  surface  the  fault  is  expressed  by  the  dislocation  of 
structures,  such  as  fences,  roadways,  and  parts  of  buildings,  bridges, 
railroad  tracks,  or  of  natural  objects,  such  as  trees,  etc.,  while  if 
the  slipping  has  a  vertical  component,  a  fault  scarp  will  result. 
These  phenomena,  and  the  types  of  faults  and  their  effects,  have 
been  discussed  in  Chapter  XXI.  When  successive  shocks  from 
various  directions  are  experienced,  a  vortical  movement  of  objects 
may  result,  as  in  the  case  of  statues  turned  on  their  pedestals. 
The  various  effects  of  such  shocks  on  buildings  and  other  structures 
are  fully  illustrated  in  the  reports  on  the  recent  Californian  and 
other  earthquakes. 

Block  Movement.  The  faulting  may  be  manifested  as  a  block 
movement,  strips  of  land  dropping  or  rising  and  forming  rift 
valleys  (Graben)  or  fault  blocks.  On  a  large  scale,  these  form 
fault-block  mountains.  Such  faulting  occurred  in  connection  with 
the  Owens  Valley  earthquake  of  1872,  the  resulting  scarps  reaching 
in  some  cases  a  height  of  ten  feet  or  more.  At  Big  Pine,  Califor- 
nia, a  tract  of  land  200  to  300  feet  wide  sank,  some  portions  being 
depressed  20  feet  or  more,  leaving  vertical  walls  on  either  side. 


888  PRINCIPLES    OF    STRATIGRAPHY 

(Johnson-23.)  During  the  earthquake  of  Yakutat  Bay,  Alaska,  in 
1899,  great  sections  of  the  country  moved  as  individual  masses, 
some  blocks  being  elevated,  some  depressed,  the  extent  of  the  dif- 
ferential movement  reaching  30  to  47  feet.  Portions  of  the  sea- 
shore were  elevated ;  beaches  only  recently  abandoned  being  now  at 
a  considerable  height  above  the  sea,  while  many  of  the  depressed 
areas  became  submerged.  Similar  block  movements  occurred  dur- 
ing the  great  Icelandic  earthquake  of  1896. 

Disruptive  Effects  of  Earthquakes. 

The  more  pronounced  earthquake  shocks  often  have  a  very  de- 
structive effect  on  the  rocks  of  the  earth's  surface.  Land  slips  of 
great  extent  may  be  set  in  motion  by  them.  A  piece  of  land  one 
mile  long  fell  from  the  cliff  at  Scilla  during  the  Messina  earth- 
quake. 

Darwin  describes  the  overwhelming  forces  of  the  earthquake 
of  February  20,  1835,  in  Chile.  He  particularly  notes  the  effects 
on  the  islands  in  Concepcion  Harbor,  where  upward  of  a  hundred 
villages  were  destroyed  and  where  rocks  from  beneath  the  sea 
were  broken  off  and  cast  high  up  on  the  shore.  "One  of  these 
was  six  feet  long,  three  broad,  and  two  thick."  Darwin  describes 
the  destruction  on  Quinquina  Island  as  follows :  "The  ground  in 
many  parts  was  fissured  in  north  and  south  lines,  perhaps  caused 
by  the  yielding  of  the  parallel  and  steep  sides  of  this  narrow 
island.  Some  of  the  fissures  near  the  cliffs  were  a  yard  wide. 
Many  enormous  masses  had  already  fallen  on  the  beach,  and  the 
inhabitants  thought  that  when  the  rains  commenced  far  greater 
slips  would  happen.  The  effect  of  the  vibration  on  the  hard 
/  primary  slate,  which  composes  the  foundation  of  the  island,  was 
still  more  curious:  the  superficial  parts  of  some  narrow  ridges 
were  as  completely  shivered  as  if  they  had  been  blasted  by  gun- 
powder." This  effect,  which  was  rendered  conspicuous  by  the  fresh 
fractures  and  displaced  soil,  must  be  confined  to  near  the  surface, 
for  otherwise  there  would  not  exist  a  block  of  solid  rock  throughout 
Chile  ...  I  believe  this  convulsion  has  been  more  effectual 
in  lessening  the  size  of  the  island  of  Quinquina  than  the  ordinary 
wear-and-tear  of  the  sea  and  weather  during  the  course  of  a  whole 
century."  (Darwin-6,  Chap.  XIV.) 

Effects  of  Earthquakes  on  Topography. 

Many  minor  changes  in  topography  in  regions  of  frequent  seis- 
mic disturbances  may  have  their  origin  in  the  earth  tremors. 


SEA-QUAKES  889 

Changes  due  to  displacement  are  not  to  be  classed  in  this  category, 
as  they  are  due  to  the  same  cause  which  is  responsible  for  the 
earthquake,  namely,  the  faulting.  But  topographic  changes  caused 
by  the  shaking  of  the  earth  are  properly  classed  here.  Such  are 
the  formation  and  sudden  drainage  of  lakes ;  the  blocking  of  rivers 
by  land  slips;  the  shifting  of  river  channels  in  level  delta  regions, 
and  other  changes.  After  the  Indian  earthquake  of  1897  no  ^ess 
than  30  earthquake  lakes  were  produced.  The  earthquakes  of 
1811-12  caused  the  appearance  of  many  new  lakes  along  the  lower 
Mississippi,  owing,  probably,  to  the  local  settling  of  the  river  sedi- 
ment. One  of  these  is  Reelfoot  Lake,  in  Obion  county,  Tennessee, 
which  has  a  length  of  more  than  20  miles  and  a  width  of  seven 
miles;  the  water  in  places  covering  the  tops  of  submerged  cypress 
trees.  Near  Little*  Prairie  a  lake,  many  miles  in  length  but  only 
from  3  to  4  feet  in  depth,  came  into  existence.  Upon  its  disap- 
pearance it  left  behind  a  stratum  of  sand.  On  the  other  hand,  Lake 
Eulalie,  300  yards  long  and  100  yards  wide,  was  suddenly  drained 
through  parallel  fissures  which  opened  in  its  bottom.  Many  other 
examples  of  this  kind  might  be  cited. 

This  same  earthquake  was  responsible  for  a  local  and  temporary 
reversal  of  the  current  of  the  Mississippi.  Similar  phenomena 
have  been  observed  in  other  rivers. 


SUBMARINE  EARTHQUAKES  AND  SEA-QUAKES. 

As  might  be  expected,  seismic  disturbances  are  common  along 
the  borders  of  the  Pacific,  where,  as  before  noted,  we  have  the 
regions  of  down-warping,  and,  therefore,  the  region  of  stresses 
and  of  readjustments  to  these  stresses.  From  their  proximity  to  the 
sea  the  latter  is,  of  course,  strongly  affected  by  the  shocks,  and  sea- 
quake waves,  or  tsunamis,  are  the  result.  These,  on  account  of  their 
height  and  velocity,  are  exceedingly  destructive.  Perhaps  the  most 
memorable  one  is  that  which  destroyed  Lisbon  in  1775.  The  sea- 
quake originated  on  the  ocean  floor  fifty  or  more  miles  off  the 
coast  of  Lisbon,  and  the  vibrations  were  transmitted  along  the 
surface  of  the  water  in  a  series  of  monstrous  waves.  The  greatest 
of  these  was  sixty  feet  high,  and  was  followed  by  others  of  decreas- 
ing height.  Spending  their  strength  on  the  coast  of  Spain  the 
waves  passed  on  with  diminished  amplitude,  but  were  felt  even 
on  the  shores  of  the  West  Indies,  across  the  whole  expanse  of 
the  Atlantic. 


890  PRINCIPLES    OF    STRATIGRAPHY 

Even  greater  distances  have  been  traveled  by  tsunamis,  as,  for 
instance,  those  originating  in  an  earthquake  at  Concepcion,  Chile, 
which  "set  in  motion  a  wave  that  traversed  the  ocean  to  the  Society 
and  Navigator  Islands,  3,000  and  4,000  miles  distant,  and  to  the 
Hawaiian  Islands,  6,000  miles."  (Dana~5  :^/j.) 

The  velocity  of  these  mighty  waves  has  been  ascertained,  and 
is  seen  to  be  far  greater  than  that  of  ordinary  sea-waves,  though 
it  does  not  equal  that  of  earthquakes  proper.  "The  waves  of  the 
Japan  earthquake  crossed  the  Pacific  to  San  Francisco,  a  distance  of 
4,525  miles,  in  a  little  more  than  twelve  hours,  and,  therefore,  at  a 
rate  of  370  miles  per  hour,  or  over  six  miles  per  minute.  The 
waves  of  the  South  American  earthquake  of  1868  ran  to  the 
Hawaiian  Islands  at  a  rate  of  454  miles  per  hour."  (Le  Conte- 
26:137.) 

Seismic  disturbances  are  not  confined  to  the  shore,  however, 
but  also  occur  under  the  sea.  Both  pyroseismic  and  baryseismic 
disturbances  are  likely  td  affect  the  water  and  produce  pronounced 
disturbances.  That  faulting  occurs  on  the  bottom  of  the  deep  sea 
is  shown  by  soundings  and  studies  of  cable  routes.  The  frequent 
breaking  of  the  cables,  accompanied  by  thrusting  and  fraying,  fur- 
nishes visible  evidence  of  such  disturbances.  Precipices  from  3,000 
to  5,000  feet  in  height  have  been  detected  by  soundings  in  the 
Mediterranean,  a  difference  in  depth  of  2,000  feet  having  been 
noticed  between  the  bow  and  the  stern  of  the  cable  repair  ship. 
The  earthquake  of  October  26,  1873,  caused  the  cable  to  break  7 
miles  from  the  cable  office  at  Zante,  Greece,  by  the  formation  of  a 
submarine  fault  scarp  600  feet  in  height,  the  change  in  depth  being 
from  1,400  to  2,000  feet.  Similar  breaks,  with  the  formation  of 
submarine  fault  scarps  more  than  a  thousand  feet  in  height,  have 
been  reported  from  the  same  region.  Submarine  earthquakes 
ought  to  be  distinguished  from  sea-quakes  proper.  The  latter 
always  accompany  the  former  and  may  even  accompany  earth- 
quakes originating  in  the  land  near  the  sea.  On  the  other  hand, 
true  sea-quakes,  or  thalassoseisma,  may  be  formed  by  causes  which 
will  not  produce  earthquakes,  as,  for  example,  submarine  explosions. 
The  latter  represent  a  submarine  pyroseismic  disturbance  (whether 
of  a  submarine  volcano  or  a  submarine  mine),  and  this  is  the  only 
kind  of  directly  induced  sea-quake  or  thalassoseisma  possible.  Sec- 
ondarily induced  or  communicated  thalassoseisma  are,  however,  the 
most  frequent  type,  and  here  belong,  besides  the  effects  of  many 
volcanic  explosions  on  the  sea  coast  (e.  g.,  Krakatoa),  the  great 
series  of  baryseismic  disturbances  or  tectonic  faultings. 


DISPLACEMENT    OF    THE    POLES  891 


AIR-QUAKES. 

What  is  true  of  the  sea  is  in  an  even  greater  measure  true  of 
the  atmosphere.  This,  like  the  water,  is  too  mobile  to  permit  the 
setting  up  of  strains  within  its  mass,  and  so  baryseismic  disturb- 
ances cannot  originate  in  the  atmosphere  any  more  than  they  can 
in  the  hydrosphere.  Such  disturbances  may,  however,  be  com- 
municated from  the  baryseismic  disturbances  of  the  land.  Origin- 
ally induced  pyroseismic  disturbances  are,  however,  as  readily  pro- 
duced in  the  air  as  in  the  water,  and  they  are  more  readily  trans- 
mitted, owing  to  the  greater  mobility  of  the  atmosphere  over  that 
of  the  water. 

PERIODICITY  OF  EARTHQUAKES. 

Periods  of  strong  seismic  disturbances  (macroseisms)  are 
known  to  alternate  with  periods  of  relative  quiescence,  or  only 
minor  disturbances  (microseisms).  In  Japan  the  seismic  periods 
recur  about  once  in  thirteen  years,  though  observations  at  Kioto  in- 
dicate a  period  as  short  as  six  and  one- fourth  years.  Too  little 
is  yet  known  to  warrant  predictions  of  recurrences  of  earthquakes. 

MOVEMENTS  DUE  TO  DISPLACEMENT  OR  MIGRATION  OF  THE  POLES. 

The  theory  of  pole  migration,  or  the  shifting  of  the  earth's  axis 
of  rotation  with  reference  to  the  earth  itself,  together  with  the 
accompanying  changes  in  the  form  of  the  earth,  in  distribution 
of  land  and  sea  and  in  climatic  belts,  has  ever  proved  attractive 
to  speculative  geologists  who  sought  for  means  of  accounting  for 
the  ascertained  variations  in  the  surface  characters  of  the  earth  in 
the  past.  Thus,  evidence  is  accumulating  which  points  to  a  widely 
different  position  of  the  earth's  axis  during  Palaeozoic  time  from 
that  which  it  held  during  the  Mesozoic  and  subsequent  periods. 
This  evidence  is  furnished  in  part  by  the  occurrence  of  mild  cli- 
mate, and  even  of  tropical  vegetation,  in  regions  having  an  arctic 
climate  at  present,  and  in  part  by  the  presence  of  glacial  deposits 
where  tropical  conditions  prevail  to-day.  It  is  further  found  in 
the  occurrence  of  sediments  which  indicate  the  existence  during 
Palaeozoic  time  of  easterly  winds  where  now  the  westerlies  prevail. 
(See  ante,  Chapters  II  and  XIV,  also  Fig.  128,  page  636.) 

A  wealth  of  biological  evidence  has  been  accumulated  which 


892  PRINCIPLES    OF    STRATIGRAPHY 

also  seems  to  point  to  the  phenomenon  of  polar  migration.  (Sim- 
roth-37.)  The  signs  further  point  to  the  existence,  in  the  border 
regions  of  the  present  Atlantic,  of  large  continental  masses  which 
became  submerged  with  the  close  of  the  Palaeozoic.  Thus  Appa- 
lachia,  the  source  of  clastic  sediments  in  eastern  North  America 
during  the  whole  of  Palaeozoic  time,  disappeared  at  the  end  of  that 
period;  the  disappearance  being  coincident  with,  or  closely  related 
to,  the  formation  of  the  Appalachian  folds.  Similar  conditions  have 
been  ascertained  for  western  Europe.  As  demonstrated  in  an  ear- 
lier chapter,  the  clastic  sediments  of  North  America  indicate  that 
in  Palaeozoic  time  this  continent  came  under  the  influence  of  the 
trade  winds,  at  least  so  far  as  the  eastern  portion  is  concerned, 
while  in  Mesozoic  and  later  time  it  had  passed  into  the  region  of 
the  westerlies.  This  suggests  that  the  end  of  Palaeozoic  sedimenta- 
tion was  brought  about  by  a  profound  change  in  physical  geography 
which  affected  not  only  North  America,  but  also  the  earth  as  a 
whole.  A  comparatively  rapid  shifting  of  the  position  of  the  earth's 
axis  would  be  sufficient  explanation  of  the  profound  changes  which 
brought  about  the  all  but  universal  extinction  of  life,  so  that  only 
the  pelagic  and  deep-sea  types  of  the  oceans  (especially  of  the 
Pacific),  and  the  terrestrial  types  in  the  interior  of  the  continents, 
remained  unaffected.  These  probably  formed  a  source  from  which 
the  earth  was  repopulated  after  the  widespread  extermination 
of  life  on  the  margins  of  the  continents  and  in  shallow  water. 
That  migrations  of  the  poles  occurred  before  and  after  this  great 
cataclismic  shifting  is  indicated  by  the  nature  of  the  sediments, 
the  changes  in  climate  and  life  during  the  successive  periods,  and, 
especially,  by  the  occurrence  of  glacial  conditions  in  Pleistocenic 
times  in  regions  not  now  subject  to  such  conditions.  (See  ante, 
Chapters  II  and  VIIL)  The  map  (Fig.  245),  copied  from  Walther, 
shows  the  location  of  the  Pleistocenic  ice  sheets,  and  the  suggested 
position  of  the  pole,  to  account  for  its  occurrence.  All  such  wan- 
derings of  the  poles,  however,  if  they  occurred,  are  insignificant 
in  comparison  with  the  catastrophic  change  which  brought  to  an 
end  the  period  of  Palaeozoic  sedimentation  and  biologic  develop- 
ment. 

THE  PENDULATION  THEORY.  Though  frequently  suggested  as 
a  possible  cause  of  changes  in  the  geologic  development  of  the 
earth,  the  theory  of  polar  migration  seems  to  have  been  first  def- 
initely formulated  by  Paul  Reibisch  in  .1901.  Reibisch  developed 
the  theory  of  polar  pendulation,  or  swinging,  i.  e.,  a  back  and  forth 
migration  of  the  poles  along  certain  well-defined  paths.  Dr.  Hein- 
rich  Simroth,  of  the  University  of  Leipzig,  developed  this  theory 


THE    PENDULATION    THEORY 


893 


more  fully  in  his  book,  "Die  Pendtilations  Theorie,"  fortifying  it 
by  a  wealth  of  illustrations  furnished  by  the  distribution  of  animals 
and  plants  in  both  the  present  and  past  geologic  periods.  Simul- 
taneously with  Reibisch,  the  theory  of  polar  migrations  was  formu- 
lated by  Dr.  D.  Kreichgauer  (25),  who  approached  the  subject 
from  a  purely  geological  point  of  view.  He  endeavored  to  explain 
the  changes  of  climate  in  past  geological  periods  by  a  change  in 
the  position  of  the  earth's  equator  and  therefore  a  shifting  of  the 
north  pole,  which  he  thought  had  migrated  180°  since  Cambric 


FIG.  243.  Map  showing  the  hypothetical  wanderings  of  the  earth's  North 
Pole  during  the  successive  periods  of  its  history.  (After  Kreich- 
gauer.) 

time,  having  been  at  the  beginning  of  that  period  where  the  south 
pole  is  now.  Kreichgauer's  map,  showing  the  migration  of  the 
poles,  is  here  reproduced.  (Fig.  243.)  As  Simroth  points  out,  how- 
ever, Kreichgauer  did  not  consider  the  phenomenon  of  polar  pen- 
dulation. 

The  theory  of  polar  pendulation,  as  formulated  by  Reibisch 
(34)  and  developed  by  Simroth  (37),  postulates  the  existence  of 
two  "oscillation  poles"  (Schwingpole)  in  addition  to  the  two  ro- 
tation poles.  These  oscillation  poles  lie  in  the  region  of  modern 
Equador,  on  the  one  hand,  and  of  Sumatra,  on  the  other.  The 


894 


PRINCIPLES    OF    STRATIGRAPHY 


meridian  which  passes  through  the  rotation  and  oscillation  poles 
forms  the  culmination  circle  (Kulminatiomkreis) ,  and  it  divides 
the  earth  into  a  Pacific  and  an  Atlantic-Indian  hemisphere.  (Fig. 
244.)  Each  hemisphere  is  again  divided  by  the  equator  into  a  north- 
ern and  a  southern  quadrant.  The  meridian  of  10°  E.  longitude 
from  Greenwich,  which  bisects  each  hemisphere,  is  called  the 
oscillation  circle,  because  it  is  upon  it  that  the  poles  swing  back 
and  forth.  The  culmination  circle  is  so  called  because  each  point 
reaches  its  closest  approximation  to  the  poles  when  it  crosses  this 
circle. 


FIG.  244.  Map  of  the  earth,  divided  by  the  oscillation  circle  (near  the 
meridians  of  10°  E.  and  170°  W.  of  Greenwich)  into  two  hemi- 
spheres, according  to  the  theory  of  P.  Reibisch.  The  oscillation 
poles  form  the  centers  of  the  hemispheres.  The  vertical  meridian 
is  the  culmination  circle  (80°  on  the  left,  100°  on  the  right). 
The  concentric  rings  around  the  oscillation  axis  mark  the  paths 
along  which  the  points  cut  by  them  move  during  the  pendulation. 
(After  Simroth.) 

The  form  of  the  geoid,  i.  e.,  the  difference  in  length  of  the  axis 
of  rotation  and  the  equatorial  diameter,  amounting  to  more  than  40 
kilometers  (43  km.,  or  nearly  27  miles;  see  ante,  Chapter  I),  is  re- 
sponsible for  the  transgressions  and  regressions  of  the  sea;  and  the 
elevation  and  subsidence  of  the  land.  The  sea,  the  mobile  element, 
assumes  the  flattened  geoid  form  with  every  position  of  the  axis 
of  rotation,  but  the  land,  owing  to  its  greater  rigidity,  does  not  so 
readily  assume  this  form.  Hence,  as  every  point  approaches  the 
pole  during  the  pendulation,  the  waters  recede  from  it,  while  at 
the  same  time  they  rise  over  the  points  approaching  the  equator. 
The  differences  between  rise  and  fall  of  the  water  are  greatest  on 
the  oscillation  circle  and  decrease  progressively  to  the  oscillation 


THE    PENDULATION    THEORY  895 

poles,  where  they  are  zero.  A  point  on  the  oscillation  circle,  which 
lies  10,000  meters  below  sea-level  when  under  the  equator,  would, 
by  the  time  that  it  has  come  to  lie  at  the  pole  (after  a  rotation  of 
90°),  lie  10,000  meters  above  sea-level.  It  must  be  remembered 
that  every  point  on  the  globe  is  nearest  to  the  pole  as  it  crosses 
the  culmination  circle,  which,  together  with  the  ends  of  the  axis 
of  rotation,  may  be  regarded  as  having  a  fixed  position  in  space. 
At  the  moment  of  crossing,  therefore,  the  point  has  its  greatest 
elevation  above  sea-level,  while,  as  it  passes  away  from  the  culmina- 
tion circle,  the  sea-level  will  rise,  where  previously,  during  the  ap- 
proach, the  sea-level  fell.  This  seems  to  be  illustrated  by  Florida, 
which  at  present  lies  under  the  culmination  circle.  The  eastern 
half  has  a  rising  sea-level  and  would,  therefore,  be  passing  away 
from  it,  while  the  western  half  has  a  falling  sea-level,  i.  e.,  the  land  y 
emerges,  and  this  section  would,  therefore,  be  approaching  the 
culmination  circle.  All  this  would  indicate  that  the  earth  is  swing- 
ing in  such  a  way  that  the  north  pole  is  migrating  toward  Behring 
Sea,  which  thus  becomes  a  region  of  emergence,  and  away  from 
the  Greenland-Iceland  region,  where,  it  has  been  supposed,  the  pole 
had  its  location  in  Pleistocenic  time.  (Fig.  245.)  (See  ante,  Chap- 
ter II.) 

Owing  to  the  proximity  of  Florida  to  the  oscillation  poles 
(where  emergence  and  submergence  are  zero),  the  total  amount 
of  oscillation  of  the  sea  was  never  great,  and  hence  old  coral 
reefs  which  grew  near  the  surface  go  only  to  the  depth  of  50  ••/ 
feet.  In  Funafuti,  on  the  other  hand,  which  lies  not  far  from  the 
oscillation  circle  (under  which  the  greatest  variation  of  sea-level 
occurs),  the  reef  corals  grew  to  a  depth  of  more  than  600  feet. 
(See  ante,  Chapter  X.)  The  coral  islands  of  the  North  Pacific  lie 
in  the  quadrant  approaching  the  pole  and  the  culmination  circle, 
and  hence  they  show  at  the  present  time  a  retreating  sea-level;  as 
in  the  case  of  the  Hawaiian  Islands.  The  islands  of  the  South 
Pacific,  on  the  other  hand,  are  moving  toward  the  equator,  and 
hence,  in  this  case,  submergence  is  taking  place.  In  the  Indian 
Ocean,  again,  the  region  north  of  the  present  equator  is  one  of 
rising  sea-level  (submergence  of  reefs  and  islands),  while  that 
south  of  the  equator  is  one  of  falling  sea-level  (emerging  reefs). 
This  would  explain  why  the  Maldives,  north  of  the  equator,  are 
apparently  being  submerged,  while  the  Cocos  Islands  to  the  south 
are  rising  out  of  the  water. 

The  regions  around  the  oscillation  poles  were  always  tropical 
regions,  as  compared  with  the  regions  near  the  oscillation  circle. 
In  the  former,  therefore,  life  conditions  changed  little  and  slowly, 


896 


PRINCIPLES    OF    STRATIGRAPHY 


and  so  they  are  the  regions  where  ancient  types  persisted,  while  the 
region  near  the  oscillation  circle  (northern  North  America,  north- 
ern Eurasia,  western  Europe,  Africa,  and  Antarctica),  on  the  con- 
trary, showed  the  greatest  oscillation  in  climate  and  in  life  during 
the  successive  periods  of  the  earth's  history. 

When  we  next  consider  what  effects  the  shifting  of  the  poles 
would  have  on  the  form  of  the  lithosphere  we  realize  that,  while 
it  would  be  more  gradual  than  the  effect  on  the  hydrosphere,  it 


FIG.  245.  Map  of  the  Pleistocenic  Tee  Period,  showing  the  distribution  of  the 
ice  and  the  hypothetical  North  Pole.  (After  Walther.)  The 
black  dots  in  western  Europe  indicate  the  localities  where  re- 
mains of  early  man  have  been  found. 

must  still  result  in  a  series  of  important  changes,  if  the  hypothesis 
of  pendulation  is  correct.  The  influence  of  the  centrifugal  force 
on  the  equatorial  region  is  manifested  by  an  expansion  or  stretch- 
ing of  the  equatorial  zone,  and  this  will  result  in  the  formation  of 
depressions,  through  the  sinking  of  fault  blocks.  Depressions  in 
the  present  surface  of  the  lithosphere  are  most  marked  in  the 
quadrant  now  approaching  the  equator,  near  which  lie  all  the  large 
terrestrial  or  submarine  trenches  and  deeps.  Thus  the  great  sub- 
marine depressions  of  the  present  day,  the  Tonga  and  Kermadec 
deeps,  lie  in  the  South  Pacific  quadrant,  whereas  similar  depressions 


THE    PENDULATION    THEORY  897 

in  the  land,  such  as  the  Caspian  and  the  Dead  Sea,  etc.,  lie  in  the 
North  Atlantic  quadrant,  which  also  approaches  the  equator.  It 
should  be  noted,  however,  that  the  Marian  depression  with  the 
deepest  submarine  pit,  the  Nero  deep,  lies  mostly  north  of  the 
equator  and  therefore  in  the  opponent  quadrant.  However,  its 
proximity  to  the  equator  (less  than  20°  N.)  is  evident,  and  it  may 
be  regarded  as  still  retaining  the  characters  acquired  as  it  passed 
under  the  equator.  In  like  manner,  the  greater  part  of  the  African 
rift  valley  lies  in  the  south  Atlantic-Indian  quadrant,  though  again 
within  20  degrees  of  the  equator. 

Conversely,  regions  approaching  the  poles  are  regions  of 
shrinking  land,  and  hence  regions  where  mountain-making  through 
folding  is  marked. 

Ingenious  and  suggestive  as  this  theory  is,  and  much  as  it  seems 
to  throw  light  on  many  geological  as  well  as  biological  phenomena, 
it  is  still  too  new  and  too  little  tested  to  receive  more  than  re- 
spectful attention.  As  a  working  hypothesis  in  the  attempt  to  in- 
terpret the  history  of  the  earth,  it  is  likely  to  be  of  much  value. 
(See  the  application  of  this  theory  by  Yokoyama  to  the  interpreta- 
tion of  the  Pleistocenic  problem,  .given  in  Chapter  II.) 

In  this  connection  may  also  be  mentioned  the  recent  studies  by 
Eugenio  Jacobitti  (22),  who,  attacking  the  problem  as  a  study  in 
geology,  finds  the  wanderings  of  the  poles  to  be  of  a  more  irregular 
character,  through  the  various  geological  periods,  as  illustrated  in 
the  subjoined  figures  reproduced  from  his  paper.  (Figs.  246,  247.) 
He  also  reconstructs  a  series  of  charts  showing  the  position  of 
the  equator  in  the  successive  periods.  All  such  reconstructions  are, 
of  course,  premature,  and  must  be  taken  as  suggestions  rather  than 
as  demonstrations.  What  is  probably  the  most  complete  attempt  at 
restoration  of  the  earth's  surface  during  a  period  of  different  polar 
location  is  that  made  by  Koken  (233.)  for  the  Permic.  His  map 
not  only  locates  the  poles  but  also  the  lands  and  seas  of  the  period, 
as  well  as  the  ocean  currents,  etc.  See  ante,  page  536. 

It  may  again  be  remarked  here,  as  was  stated  in  Chapter  II,  that 
astronomers  have  generally  looked  with  disfavor  on  such  specula- 
tions, though  George  Darwin  concedes  the  possibility  of  the  pole 
having  wandered  some  10  or  15  degrees  from  its  original  position,  4 
provided  the  degree  of  rigidity  of  the  earth  is  not  so  great  as  to 
be  inconsistent  with  a  periodic  readjustment  to  a  new  form  of 
equilibrium.  Sir  William  Thompson  (Lord  Kelvin),  for  ^one, 
readily  entertained  the  idea  of  such  changes.  He  says:  "We 
may  not  merely  admit,  but  assert  as  highly  probable,  that  the  axis 
of  maximum  inertia  and  axis  of  rotation,  always  very  near  one  an- 


PRINCIPLES    OF    STRATIGRAPHY 


other,  may  have  been  in  ancient  time?  very  far  from  their  present 
geographical  position,  and  may  have  gradually  shifted  through  10, 


FIG.  246.  Map  of  the  hemispheres,  showing  the  hypothetical  migration  of 
the  North  Pole  during  the  successive  geologic  periods. 
(Jacobitti.) 

20,  30,  40,  or  more  degrees,  without  there  being  at  any  time  any 
perceptible  sudden  disturbance  of  either  land  or  water."   (42:11.) 


FIG.  247.     Map  of  the  hemispheres,  showing  the  hypothetical  migrations   of 
the  South  Pole  during  the  successive  geologic  periods.  (Jacobitti.) 

Various  theories  have  been  advanced  to  account  for  and  ex- 
plain such  wanderings  of  the  poles,  but  at  present  the  whole  sub- 
ject is  too  little  investigated  to  make  their  discussion  profitable. 
Geologists  must  first  gather  a  larger  body  of  facts,  which  will  tend 


ACTUAL    MIGRATIONS    OF   THE    POLES 


899 


either  to  prove  or  disprove  these  theories,  before  the  discussion  of 
causes  need  be  undertaken. 


Determined  Migrations  of  the  Poles. 

That  the  poles,  i.  e.,  the  points  of  intersection  between  the 
earth's  axis  of  rotation  and  the  surface  of  the  earth,  are  not 
actually  fixed,  but  wander  about  within  small  limits,  was  first 
recognized  toward  the  end  of  the  nineteenth  century.  From  thou- 
sands of  careful  observations  on  latitude  made  in  recent  years  .in 


+0*30 


+Oi/O       O'.OO     -O*/0      ~O*2O    -O~3Q 


-nfeo  +o~/o    0*00  -o'so  -  -c&o  -o'.So 


FIG.  24&  Map  showing  the  ascertained  migration  of  the  North  Pole  from 
1892  to  1894  (after  Milne)  ;  the  figures  indicate  the  number  of 
large  earthquakes  in  each  period. 

Europe  and  America  this  wandering  has  been  determined  to  lie 
within  a  circle  40  or  50  feet  in  diameter.  It  has  a  curiously  ir- 
regular, but  somewhat  spiral  path,  and  completes  its  erratic  circuit 
in  about  428  days.  The  path  described  by  the  North  Pole  between 
the  years  1892  and  1894  is  shown  in  the  above  map  by  Milne, 
in  which  each  year  is  divided  into  ten  parts.  (Fig.  248.)  The 
figures  show  the  number  of  earthquakes  which  occurred  in  each 
period,  the  largest  of  them,  as  John  Milne  has  pointed  out,  coin- 
ciding with  the  sharpest  curvature  in  the  path  of  the  pole.  As 
Milne  suggests,  both  the  abrupt  curvature  and  the  sharp  earthquake 


900  PRINCIPLES    OF    STRATIGRAPHY 

may  be  the  result  of  sudden  readjustments,  due  to  the  redistribution 
of  material  on  the  earth's  surface  by  currents  and  by  meteorological 
agents. 

Accompanying  the  changes  of  position  of  the  poles,  is,  of  course, 
a  change  in  the  position  of  the  equator,  the  plane  of  which  is  always 
at  right  angles  to  the  axis  of  rotation  of  the  earth.  A  further  re- 
sult of  such  changes  is  a  variability  of  terrestrial  latitudes  gen- 
erally. 

It  is  now  commonly  admitted  that  the  movement  of  large  bodies 
of  water,  or  of  air,  over  the 'surface  of  the  globe,  and,  more  es- 
pecially, an  accumulation  of  vast  masses  of  snow  and  ice  in  differ- 
ent regions,  may  all  be  causes  effecting  slight  displacements  of  the 
earth's  axis.  More  pronounced  effects  might  follow  from  wide- 
spread upheavals  or  depressions  of  the  surface  of  the  lithosphere. 

If  the  earth's  center  of  gravity  should  be  sensibly  displaced, 
momentous  rearrangements,  accompanied  by  pronounced  wander- 
ings of  the  pole,  would  result.  It  has  long  been  known  that  the 
center  of  gravity  does  not  coincide  with  the  center  of  figure  of 
the  earth,  but  lies  to  the  south  of  it.  This  is  due  to  the  greater 
aggregation  of  dense  material  in  the  southern  hemisphere,  but 
whether  this  is  a  result  of  original  distribution  of  matter,  or  is 
due  to  later  readjustments,  cannot  be  said.  Simroth  has  even 
suggested  that  the  in-falling  of  a  satellite,  or  second  moon,  into  the 
earth  in  the  African  region  may  have  been  a  possible  cause  of  the 
displacement  of  the  center  of  gravity,  and  that  the  pendulations  of 
the  earth's  axis  were  the  result  of  a  gradual  readjustment.  That 
meteoric  or  extra-telluric  bodies  reaching  the  earth  in  great  numbers 
may  sensibly  affect  the  center  of  gravity,  and  hence  the  position 
of  the  earth's  axis,  cannot  be  doubted. 


EARTH  MOVEMENTS  AND  GEOSYNCLINES. 

As  already  noted  in  Chapter  XX,  the  term  geosyncline  was  ap- 
plied by  Dana  (in  1873)  to  the  great  earth  troughs,  whether  simple 
or  compound,  which  are  formed  in  regions  of  excessive  deposition, 
the  Appalachian  region  being  taken  as  the  type  of  such  troughs. 
The  idea  of  great  downward  bowings  under  heavy  load  was  de- 
veloped much  earlier  by  James  Hall,  who  held  that  this  downward- 
bending  was  in  direct  response  to  the  load  added  by  the  sediment, 
and  thus,  in  effect,  constituted  an  isostatic  readjustment.  Dana, 
on  the  other  hand,  regarded  the  downward  bending  as  primary, 
and  of  the  nature  of  a  fold  due  to  compressive  strains,  and  the 


GEOSYNCLINES 


901 


filling  by  sediment  as  a  secondary  consequence.  Among  subsequent 
authors,  Haug  (14,  15)  has  greatly  extended  this  idea,  and  has  in- 
cluded under  this  title  all  great  submarine  depressions  parallel  to 
land  areas,  such  as  the  great  depressions  of  the  Pacific  coast.  (See 
Chapter  III  and  Figures  16  and  17,  pages  101  and  105.)  These  "fore 
deeps"  (Vortiefen)  are  undoubtedly  the  direct  result  of  deforma- 
tion under  strain,  but  they  are  not  areas  of  excessive  deposition. 
Indeed,  sedimentation  here  goes  on  with  extreme  slowness,  and  is 
confined  to  materials  normal  to  the  deep  sea.  Haug  has  identified 
among  many  of  the  deposits  bathyal  sediments  (see  Chapter  XV), 
•which  he  regards  as  accumulations  in  geosynclines,  and  he  holds 
that  the  great  thickness  of  these  deposits  indicates  a  progressive 
deformation  of  the  region  of  deposition.  He  finds  that  many 
bathyal  sediments  pass  laterally  into  neritic  or  shallow-water  de- 
posits, though  other  deposits  in  the  geosynclines  are  throughout  of 


FIG.  249.  Diagrammatic  section  of  a  geosyncline  according  to  Haug.  The 
numbers  i-io  indicate  the  successive  strata,  which  are  complete 
in  the  center  of  the  geosyncline  but  incomplete  on  its  margins, 
where  thinning  away  of  beds  and  overlap  of  others  is  characteris- 
tic. (After  Haug.) 

neritic  origin.  Haug  does  not,  apparently,  recognize  the  presence 
of  continental  sediments  in  the  geosynclines,  -though  he  finds  these 
on  the  margins.  This  type  of  sediment  is,  however,  eminently 
characteristic  of  the  Appalachian  region  throughout,  and  is  included 
in  the  main  mass  of  the  sediment  itself. 

The  bathyal  origin  of  many  of  the  sediments  in  the  geosyn- 
clines of  the  Alpine  region  and  elsewhere  is  by  no  means  wholly 
established,  and  it  may  be  questioned  whether,  on  the  whole,  sedi- 
ments of  that  class  are  abundant  or  widespread.  The  frequent 
marginal  disconformities  in  the  sediments  of  most  geosynclines 
lead  one  to  the  supposition  that,  after  all,  many  of  the  so-called 
bathyal  deposits  may  be  of  littoral  (neritic)  origin,  and  that,  fur- 
thermore, repeated  laying  bare  of  the  margins  of  the  geosyncline 
permitted  erosion  of  the  already  deposited  sediments. 

Haug  recognizes  the  shading  away  of  the  sediments  by  overlap 
and  by  thinning  toward  both  sides  of  the  geosyncline  (Fig.  249) 


902  PRINCIPLES    OF    STRATIGRAPHY 

and  he  explains  this  by  the  supposition  that  the  geosyncline  was 
located  between  two  continental  masses  and  not,  as  held  by  Ameri- 
can students,  on  the  borders  of  the  continent.  He  holds  that  the 
geosynclines  are  zones  of  weakness  and  mobility  between  two  rela- 
tively stable  masses. 

The  Himalayas  are  chosen  by  Haug  as  an  illustration  of  a  great 
geosyncline  (in  pre-mountain  time)  formed,  not  on  the  border  of 
a  sea,  but  between  two  continental  masses,  the  stable  Indian  land 
mass  on  the  south  and  a  similar  land  mass  on  the  north.  In  spite 
of  this  location,  he  holds  that  Palaeozoic  and  Mesozoic  sediments  in 
this  geosyncline  are  none  of  them  of  a  littoral  (neritic)  character. 
The  chains  of  central  Europe  are  in  like  manner  regarded  by  Haug 
as  occupying  the  sites  of  former  geosynclines.  If  the  expanded 
Mediterranean  basin  of  Mesozoic  time  is  to  be  considered  in  the 
light  of  a  geosyncline,  the  bathyal  nature  of  some  of  the  sediments 
therein,  or  at  any  rate  their  thalassogenic  character,  may  be  readily 
conceded.  It  may  be  questioned,  however,  if  the  use  of  the  term 
geosyncline  for  an  intracontinental  sea  with  abyssal  regions  (i.  e., 
a  mediterranean)  is  permissible.  Certainly  such  a  condition  did 
not  prevail  in  the  Palaeozoic  of  the  Appalachian  region.  Here  an 
accumulation  of  40,000  feet  of  sediment  was  accompanied  by  a 
downward  bowing  of  the  sea-floor  bordering  the  old  Appalachian 
continent.  But  this  was  probably  never  of  great  depth,  nor  was 
there,  as  a  rule,  a  land  mass  to  the  west  of  the  region  of  sedimenta- 
tion. Indeed,  as  has  already  been  pointed  out,  and,  as  has  elsewhere 
been  discussed  by  the  author  in  great  detail,  the  prevailing  sedi- 
ments were  of  shallow  water  and  terrestrial  type.  As  stated  in 
Chapter  XX,  it  seems  best  to  restrict  the  name  geosyncline  to  such 
regions  of  deposition,  and  use  the  name  fore-deep  for  regions 
known  to  have  descended  to  bathyal  or  abyssal  depths.  That  these 
fore-deeps  are  due  to  tectonic  movements  is  freely  conceded,  but 
the  geosyncline  of  the  Appalachian  type  is  most  probably  due  to 
isostatic  readjustments  incident  upon  the  loading  of  the  earth's 
surface  along  the  line  of  subsidence.  This  does  not  imply,  how- 
ever, that  the  subsequent  folding  of  these  strata  is  due  to  any 
other  cause  than  that  of  yielding  under  compressive  strain.  Such 
an  origin  alone  seems  to  be  possible,  in  view  of  the  many  features 
which  can  be  explained  only  as  originating  under  compressive 
stresses. 

GEOSYNCLINES  THE  SITES  OF  OROGENIC  DISTURBANCES.  As  long 
ago  pointed  out  by  Hall  and  Dana,  and  as  emphasized  by  Haug, 
the  geosynclines  are  the  sites  of  subsequent  foldings  of  the  strata, 
or,  conversely,  the  regions  of  folded  mountains  are  the  sites  of 


FOLDING    OF    THE    APPALACHIANS  903 

former  geosynclines.  Bailey  Willis  (44)  has  pointed  out  that 
the  gradual  downward  sinking  of  the  strata  in  the  geosyncline  gives 
them  an  individual  steepness  along  the  margin  of  the  depression, 
and  that  this  initial  dip  forms  the  beginning  of  the  deformation, 
and  determines  the  subsequent  folding  under  the  influence  of  lateral 
pressure.  The  folds  of  the  Appalachians  are  asymmetrical  anti- 
clines, with  the  steeply  inclined,  vertical,  or  even  overturned  limb 
on  the  northwest  or  away  from  the  present  ocean.  It  must,  how- 
ever, be  remembered  that  the  present  Atlantic  coast  is  near  the 
western  border  of  the  old  Appalachian  land,  and  that  hence  if  the 
folds  occurred  before  this  land  mass  disappeared  by  subsidence, 
the  thrusting,  which  was  from  the  east  or  southeast,  was  performed 
or  transmitted  by  this  ancient  land  mass.  In  this  westward  thrust- 
ing many  folds  were  not  only  overturned,  but  thrust-faults  of  con- 
siderable magnitude  were  developed.  Thus  the  crystalline  range 
of  the  Hudson  Highland  was  thrust  northwestward  over  the  Palaeo- 
zoic strata  (Berkey)  and  numerous  other  overthrusts  were  devel- 
oped in  the  Palaeozoic  and  older  strata  along  the  entire  Appalachian 
range. 

FORESHORTENING  OF  THE  CRUST.  During  the  folding  of  the 
Appalachians  there  was,  of  course,  a  considerable  amount  of  fore- 
shortening of  the  earth's  crust.  Lesley  long  ago  estimated  the 
movement  to  have  extended  over  a  distance  of  forty  miles,  while 
Claypole,  considering  the  major  folds,  arrived  at  the  approximate 
conclusion  that  a  section  of  the  earth's  surface  measuring  origin- 
ally one  hundred  and  fifty-three  miles  had  been  compressed  into 
sixty-five  miles.  (4.) 

Recently  R.  T.  Chamberlin  (2)  has  published  the  results  of 
some  careful  measurements  of  the  Appalachian  folds  in  the  district 
between  Harrisburg  and  Tyrone,  Pennsylvania,  and  these  have  fur- 
nished more  exact  data  for  the  estimation  of  the  amount  of  crustal 
foreshortening,  and  have  likewise  thrown  some  light  on  the  form 
and  thickness  of  the  crust  involved  in  the  folding.  He  concludes 
that,  so  far  as  his  measurements  warranted,  and  postulating  the 
correctness  of  the  assumed  basis  of  investigation,  the  region  west 
of  Harrisburg  showed  81  miles  of  strata  compressed  into  66  miles. 
The  uncertainties  of  this  result  lie  in  the  difficulty  of  eliminating 
the  amount  of  loss  due  to  thickening  and  thinning  of  strata  in 
various  parts  of  the  fold;  the  variation  in  closeness  of  folding;  or 
the  subsequent  relaxation  of  the  strata  under  the  influence  of 
gravity,  with  resultant  gliding  on  the  limb  of  the  fold.  These  un- 
certainties can  make  such  estimates  only  approximate. 

HEIGHT  OF  THE  FOLDS.     Assuming  that,  when  the  folding  of 


9o4  PRINCIPLES    OF    STRATIGRAPHY 

the  Appalachians  commenced,  the  strata  were  practically  horizon- 
tal and  the  upper  surface  of  the  youngest  beds  essentially  at  sea- 
level,  and  assuming,  furthermore,  that  the  higher  Carbonic  and 
Permic  beds  of  the  region  (above  the  Pottsville)  was  1,100 
feet  thick,  Chamberlin  concludes  that  3  miles  represents  the  average 
height  of  the  top  of  the  restored  Pottsville  conglomerate  over  the 
area  from  Tyrone  to  Harrisburg,  i:  e.,  the  vertical  deformation  was 
of  that  amount. 

There  are  here  several  assumptions  which  need  careful  consid- 
eration before  we  can  regard  this  as  anything  more  than  a  very 
general  estimate.  In  the  first  place,  if  we  regard  the  late  Palaeozoic 
sediments  as  terrestrial  in  type  rather  than  marine,  as  their  nature 
seems  to  indicate,  we  can  not  assume  an  initial  horizontality  with 
the  upper  strata  at  sea-level  throughout.  Even  on  the  basis  of  the 
gentle  gradient  of  the  present  delta-fan  of  the  Huang-ho  the  eleva- 
tion at  the  heads  of  the  delta  plains  would  be  some  500  feet  or 
more  above  sea-level,  and  from  the  coarseness  of  the  material  in 
the  deposits  it  is  likely  that  this  elevation  was  a  thousand  feet,  if 
not  more. 

In  the  second  place,  it  appears  that  the  estimate  of  the  original 
thickness  of  the  post-Pottsville  Palaeozoic  is  much  too  low.  A 
comparison  of  the  thickness  of  the  Pottsville  and  Kanawha  forma- 
tions between  the  eastern  and  western  portions  of  their  outcrops 
shows  the  thickness  of  these  two  formations  in  the  western  region 
to  be  only  one-fifth  or  one-sixth  that  of  the  part  preserved  in  the 
eastern  Appalachians.  Since  the  sediment  of  the  later  formations 
was  also  derived  from  the  Appalachian  old  land,  and  since  the 
nature  of  the  deposit  suggests  a  similar  origin  of  the  later  strata, 
it  does  not  seem  amiss  to  consider  that  a  similar  eastward  increase 
in  thickness  originally  obtained  in  the  case  of  these  higher  strata  as 
well.  This  would  make  the  Allegheny  alone  some  1,500  or  more 
feet  in  thickness  in  the  Appalachian  region,  while  the  remaining 
formations,  if  increased  at  the  same  rate,  would  aggregate  11,000 
or  12,060  feet,  making  a  total  above  the  Pottsville  in  round  num- 
bers of  about  13,000  feet  of  strata.  This  is  not  an  improbable 
thickness  when  we  consider  the  15,000  feet  of  late  Tertiary  delta 
deposits  of  the  Siwalik  formation  of  India  (see  ante,  Chapter 
XIV). 

CHARACTER  AND  THICKNESS  OF  THE  DEFORMED  MASS.  On  the 
assumed  elevation  of  about  3  miles  for  the  entire  area,  Chamberlin 
figures  out  the  thickness  of  the  part  of  the  crust  involved  in  the 
folding.  Since  different  sections  have  been  differently  affected, 
he  considers  each  independently  with  the  following  results : 


THICKNESS    OF    DEFORMED    SECTIONS 


905 


Section  Number 

i 

2 

3 

4 

5a 

5b 

Original  length  of  tract,  in 
miles  (a)  

17.8 

16.3 

13.56 

14.44 

9.6 

0   5 

Length  after  folding,  in 
miles  (6)  

14.0 

15.2 

12  .  I 

12.  IO 

7.  VI 

4   75 

Mean  elevation  through  fold- 
ing in  miles  (c) 

V4S 

2.  V] 

2.88 

2.71 

2.16 

c   ye 

Deduced  thickness  of  crustal 
block,  in  miles  (x)  

17.7 

32.7 

23-8 

14.00 

7.8 

5-7i 

be 
The  formula  for  ascertaining  (x)  is  x  =  -~-f 


The   following  diagram,   copied    from   Chamberlin,   shows   the 
location  of  the  sections,  the  extent  of  the   folding  and  the  cal- 


FlG.  250.  Plot  of  the  Tyrone-Harrisburg  folded  section,  representing  the 
thickness  of  the  deformed  shell  beneath  each  of  the  six  blocks  as 
developed  by  Chamberlin's  method  of  measurement.  The  lines 
A-B  and  B-C  are  drawn  through  the  middle  points  of  the 
bottom  lines  of  each  of  these  blocks,  except  section  2,  the  apex 
block.  The  triangle  G,  B,  F  is  drawn  equal  in  area  to  the  sum 
of  the  triangles  G,  H,  I  and  D,  E,  F.  The  whole  deformed  mass 
appears,  subject  to  the  necessary  limitations,  to  be  the  triangular 
block  A,  B,  C.  (After  R.  D.  Chamberlin.) 

culated  thickness  of  the  block  affected.  (Fig.  250.)  It  shows 
strikingly  the  fact  that,  where  the  crust  is  folded  intensely,  the 
thickness  of  the  crust  involved  is  least ;  where  folding  is  slight,  it  is 


906  PRINCIPLES    OF    STRATIGRAPHY 

greatest.  In  any  case,  folding  is  shown  to  be  a  superficial  phenome- 
non, a  conclusion  which  must  have  an  important  bearing  on  the 
mechanics  of  folding.  As  shown  by  the  section,  the  eastern  portion 
suffered  most,  the  western  portion  was  the  next  most  affected,  while 
the  intermediate  ones  suffered  the  least.  The  form  of  the  entire 
block  affected  is  that  of  a  triangular  prism,  the  lower  bounding 
planes  being  shear-zones.  This  is  the  form  which  such  a  block 
should  assume  theoretically,  two  sets  of  planes  of  greatest  tangen- 
tial stress  developing  at  right  angles  to  each  other,  and  approxi- 
mately at  an  angle  of  45  degrees  to  the  direction  of  greatest  pres- 
sure, though  varying  with  the  nature  of  the  material  and  other 
factors.  (Becker-i  150;  Hoskins-2O  '.865 ;  Leith-27  -.121.)  Experi- 
ments by  Daubree  have  shown  this  to  be  the  type  of  fracture  de- 
veloped in  compressed  blocks  where  a  triangular  prism  is  developed 
with  faces  approximately  at  45  degrees  to  the  direction  of  pressure. 
In  the  experiment  the  prism  was  lifted  without  folding,  the  other 
parts  being  thrust  under  it  on  both  sides  (Fig.  251).  The  exten- 
sive development  of  over  (or  under)  thrusts  along  the  western 
margin  of  the  folded  Appalachian  region  is  quite  in  harmony  with 
this  principle.  It  should,  however,  be  mentioned  here  that  there 
is  some  evidence  that  the  folds  of  the  Appalachians  were  not  purely 
asymmetrical  anticlines,  modified  by  overthrust,  but  that  the  Ap- 
palachians had  originally  a  fanfold  structure. 


CHANGES  DUE  TO  EXTRA-TELLURIC  INFLUENCES. 

The  impact  of  a  mass  of  meteoric  matter  upon  the  surface  of 
the  earth  would  form  an  effective  source  of  energy,  which  would 
set  into  motion  geological  agents  of  vast  magnitude.  If  the  mass  is 
sufficiently  large,  as  in  the  case  of  a  satellite,  a  great  displace- 
ment of  the  earth's  center  of  gravity  would  result,  with  the 
attendant  phenomena  already  outlined.  If  the  earth  were  bom- 
barded by  a  vast  number  of  meteoric  bodies,  if,  in  other  words, 
a  swarm  of  meteors  should  descend  upon  the  earth,  changes  affect- 
ing the  entire  earth  might  take  place.  Among  these  might  be  the  all 
but  universal  extermination  of  life,  as  well  as  the  modification 
of  the  lithosphere  and  hydrosphere,  and  perhaps  the  atmosphere 
as  well.  The  heat  of  impact  might  result  in  nearly  universal  nieta- 
morphism  of  the  rock  masses  of  the  earth,  with  the  accompanying 
destruction  of  the  record  of  life  in  these  rocks.  It  might  be 
asked  if  some  such  catastrophe  may  not  have  altered  the  surface 
of  the  earth  in  pre-Carhbric  time,  inaugurating  the  forces  which 


EXTRA-TERRESTRIAL   CAUSES  907 

produced  the  widespread  metamorphism  and  exterminating  most 
of  the  organisms  which  had  reached  a  high  state  of  development 
prior  to  the  opening  of  Palaeozoic  time.  Such  catastrophic  occur- 
rences are  within  the  range  of  possibility,  and,  indeed,  the  rising 
school  of  astro-geologists  regards  the  origin  of  the  earth  itself  as 
due  to  accretion  of  planetary  matter,  rather  than  to  the  development 
by  condensation  from  an  original  nebular  condition.  If  the  accre- 


FIG.  251.  Prism  of  wax,  deformed  under  pressure,  between  two  iron  plates 
(B,  B)  and  exerted  in  the  direction  shown  by  the  arrows.  Two 
main  sets  of  fissures  are  formed  nearly  at  right  angles  to  each 
other  (FF,  f)  leaving  a  triangular  prism  between  them.  RR, 
plexus  of  fine  fissures  at  right  angles  to  one  another.  Scale  1 175. 
(After  Daubree  from  Haug.) 

tion  theory  of  earth-building,  whether  from  planetesimals  or  from 
meteorites,  should  become  established,  the  recurrence  of  such  an 
event — the  repetition  of  the  celestial  bombardment  to  which  the 
earth  owed  its  origin — is  brought  within  the  range  of  probability, 
and  thus  the  stupendous  problem  of  the  origin  of  the  great  differ- 
ence everywhere  observed  between  the  Cambric  and  the  undoubted 
pre-Cambric  *  rocks  may  be  brought  a  step  nearer  solution. 

*  Some  of  the  undisturbed  clastic  rocks  now  referred  to  the  pre-Cambric 
have  not  yet  been  proven  to  be  such.  The  occurrence  of  disconformities  between 
Middle  Cambric  or  late  Lower  Cambric  and  underlying  unaltered  sediments  is 
not  conclusive  evidence  of  the  pre-Cambric  age  of  these  sediments,  especially  if 
they  are  of  continental  origin. 


908  PRINCIPLES    OF    STRATIGRAPHY 

BIBLIOGRAPHY  XXIII. 

(See  also  Bibliography  xx,  pp.  826-828.) 

i.     BECKER,  G.  F.     1893.     Finite  Homogeneous  Strain,  Flow  and  Rupture 
of  Rocks.  Bulletin  of  the  Geological  Society  of  America,  Vol.  IV,  pp.  13-90. 
v/  2.     CHAMBERLIN,  ROLLIN  T.     1910.     Appalachian  Folds  of  Central  Penn- 
sylvania.    Journal  of  Geology,  Vol.  XVIII,  No.  3,  pp.  228-251. 

3.  CHAMBERLIN,  THOMAS  C.,  and  SALISBURY,  ROLLIN  D.     1906. 

Geology,  Vol.  I. 

4.  CLAYPOLE,  E.  W.     1885.     Pennsylvania  Before  and  After  the  Elevation 

of  the  Appalachian  Mountains.  American  Naturalist,  Vol.  XIX,  pp. 
257-268. 

5.  DANA,  JAMES  D.     1895.     Manual  of  Geology,  4th  edition.     American 

Book  Co. 
,/6.     DARWIN,  CHARLES.     1841.     The  Voyage  of  the  Beagle. 

7.  DAVISON,  CHARLES.     1905.^    A  Study  of  Recent  Earthquakes.     Con- 

temporary Science  Series,  London. 

8.  DILLER,    J.    S.     1889.     Sandstone    Dikes.     Bulletin    of    the    Geological 

Society  of  America,  Vol.  I,  pp.  411-442,  pis.  6-8;  with  discussion  by 
Davis. 

9.  DUTTON,  CLARENCE  E.     1904.     Earthquakes  in  the  Light  of  the  New 

Seismology.     New  York  and  London. 

10.  FALB,  R.     1871.     Grundziige  einer  Theorie  der  Erdbeben  und  Vulcanen- 

ausbriicke.     Graz. 

11.  FALB,  R.     1874.     Gedanken  und  Studien  uber  den  Vulkanismus,  etc. 
,12.     GILBERT,  GROVE  KARL.     1893.     Continental  Problems.     Bulletin  of 

the  Geological  Society  of  America,  Vol.  IV,  pp.  179-190. 

13.  GILBERT,   G.  K.;   HUMPHREY,    RICHARD;    SEWELL,    JOHN    S., 

and  SOULfi,  FRANK.  The  San  Francisco  Earthquake  and  Fire  of 
April  1 8,  1906,  and  their  Effects  on  Structures  and  Structural  Material. 
United  States  Geological  Survey  Bulletin  324. 

14.  HAUG,  EMILE.    1900.    Les  geosynclinaux  et  les  aires  continentales.     Con- 

tribution a  1' etude  des  transgressions  et  des  regressions  marines.  Bulletin 
de  la  societe  geologique  de  France,  3rd  series,  Vol.  XXVIII,  pp.  617- 
71 1,  3  figs. 

15.  HAUG,  E.     1907.     Traite  de  Geologic.     T.  I. 

Vi6.     HAY,   ROBERT.     1892.     Sandstone   Dikes  in   Northwestern   Nebraska. 

Bulletin  of  the  Geological  Society  of  America,  Vol.  Ill,  pp.  50-55. 
VI 7.     HOBBS,  WILLIAM  H.     1907.     Origin  of  the  Ocean  Basins  in  the  Light  of 

the  New  Seismology.     Bulletin  of  the  Geological  Society  of  America, 

Vol.  XVIII,  pp.  233-250,  pi.  5. 

1 8.  HOBBS,  W.  H.     1907.     Earthquakes.     D.  Appleton  and  Company,  New 

York. 

19.  HOERNES,  RUDOLPH.     1893.    Erdbebenkunde.  Die  Erscheinungen  und 
»       Ursachen  der  Erdbeben,  die  Methoden  ihrer  Beobachtung.     Leipzig. 

20.  HOSKINS,   L.   M.     1896.     Flow  and  Fracture  of  Rocks  as  Related  to 

Structure.  Sixteenth  Annual  Report  of  the  United  States  Geological 
Survey,  1894-95,  Pt.  I,  pp.  845-872,  figs.  163-169. 

21.  HOVEY,  E.  O.     1909.     Earthquakes:    Their  Causes  and  Effects.     Pro- 

ceedings of  the  American  Philosophical  Society,  Vol.  XLVIII,  No.  192, 
pp.  235-258. 

22.  JACOBITTI,  EUGENIO.    Mobilita  dell  'Asse  Terrestre.  Studio  Geologico. 

Torino. 


BIBLIOGRAPHY    XXIII 


909 


23.  JOHNSON,  WILLARD  D.,  and  HOBBS,  W.  H.     1908.     The  Earthquake 

of   1872  in  Owens  Valley,   California.     Abstract:    Science,  N.   S.,  Vol  ^ 
XXVII,  p.  723- 

23a.  KOKEN,  E.     1907.     Indisches  Perm  und  die  permische  Eiszeit.     Neues 
Jahrbuch  fur  Mineralogie,  etc.,  Festband,  pp.  446—545,  Map. 

24.  KOTO,   B.     1893.     On  the  Cause  of  the  Great  Earthquake  in  Central 

Japan,   1891.     Journal  of  the  College  of  Science,  Imperial  University,'" 
Tokyo,  Vol.  V,  pp.  295-353,  pis.  XXVIII-XXXV. 

25.  KREICHGAUER,  D.     1902.     Die  Aequatorfrage  in  der  Geologic.     Steyl. 

26.  LE  CONTE,  JOSEPH.     1902.     Elements  of  Geology,  4th  edition.     D. 

Appleton. 

27.  LEITH,  C.  K.     1905.     Rock  Cleavage.     United  States  Geological  Survey 

Bulletin  239. 

28.  MARTIN,  LAWRENCE.     1910.     Alaskan  Earthquakes  of  1899.     Bulle- 

tin of  the  Geological  Society  of  America,  Vol.  XXI,  pp.  339-406,  pis.  29-30. 

29.  MALLET.     1862.     The  Great  Neapolitan  Earthquake  of  1857.     2  vols. 

30.  McGEE,  W.  J.     1893.     A  Fossil  Earthquake.     Bulletin  of  the  Geological  ^ 

Society  of  America,  Vol.  IV,  pp.  411-414. 

31.  MILNE,    J.     1898.     Earthquakes   and   Other    Earth    Movements.     4th 

edition. 

32.  MONTESSUS   DE   BALLORE,  F.  DE.     1906.     Les    Tremblements    de 

Terre.     Paris. 

33.  NEWSOM,  JOHN  F.     1903.     Clastic  Dikes.     Bulletin  of  the  Geological  ^ 

Society  of  America,  Vol.  XIV,  pp.  227-268,  pis.  21-31. 

34.  REIBISCH,    PAUL.     1901.      Ein   Gestaltungsprincip  der  Erde.      27ter 

Jahresbericht  des  Vereins  fiir  Erdkunde  zu  Dresden,  1901,  pp.  105-124; 
II,  ibid.,  1905,  pp.  39-53- 

35.  ROSSI,  M.  S.  DE.     1879  and  1882.     La  Meteorologia  Endogena.     2  vols. 

36.  RUDOLPH,  E.     1887-1898.     Ueber  submarine  Erdbeben  und  Eruptionen. 

Beitrage  zur  Geophysik.     Vol.  I,  1887,  pp.  133-365,  pis.  IV-VII;  Vol.  II, 
1895,  PP.  537-666;  Vol.  Ill,  1898,  pp.  273-336. 

36a.  SIEBERG,   AUGUST.     1904.     Handbuch  der   Erdbebenkunde.     Braun- 
schweig. 

37.  SIMROTH,  HEINRICH.     1907.     Die  Pendulations-theorie.     Leipzig. 

38.  SUESS,  EUARD.     1875.     Die  Entstehung  der  Alpen.     Vienna. 

39.  SUESS,    E.     1886.     Ueber    unterbrochene    Gebirgsfaltung.     Sitzungsbe- 

richte   der   koniglichen   Akademie   der  Wissenschaften   zu   Wien.     Bd. 
XCIV,  Abth.  i,  pp.  111-117. 

40.  SUESS,  E.     1898.    Ueber  die  Asymetrie  der  nordlichen  Halbkugel.    Ibid., 

Bd.  CVII,  Abth.  i,  pp.  89-102. 

41.  TAYLOR,  FRANK  BURSLEY.     1903.     The  Planetary  System.      Pub- 

lished by  the  author,  Fort  Wayne,  Indiana. 

42.  THOMPSON,  SIR  WILLIAM.     1876.     Report  of  the  British  Association. 

Report  of  Section  81. 

42a.  VAN  HISE,  C.  R.     1898.      Earth  Movements.     Wisconsin  Academy  of 
Arts,  Sciences  and  Letters,  Transactions,  Vol.  xi,  pp.  465-516. 

43.  WHIMPER,  EDWARD.     1892.     Travels  Among  the  Great  Andes  of  the 

Equator.     2nd  edition. 

44.  WILLIS,  BAILEY.     1893.     Mechanics  of  Appalachian  Structure.     Thir- 

teenth Annual  Report  of  the  United  States  Geological  Survey,  Pt.  II, 
pp.  211-281.     (See  also  reference  30,  on  page  828.) 

45.  WOODWORTH,  J.  B.      1907.      Postglacial  Faults  of  Eastern  New  York,  y 

New  York  State  Museum  Bulletin  107,  pp.  5-28,  5  pis. 


F.  THE  BIOSPHERE. 


CHAPTER  XXIV. 

SUBDIVISION  OF  THE  BIOSPHERE.     CLASSIFICATION  AND  GEN- 
ERAL  MORPHOLOGICAL   CHARACTERS   OF   ORGANISMS. 

The  organic  world  or  biosphere  falls  naturally  into  two  great 
subdivisions  or  kingdoms,  the  phytosphere,  or  plant  kingdom, 
and  the  zoosphere,  or  animal  kingdom,  though  organisms  occur  or 
have  occurred  which  are  not  readily  placed  in  either  division. 
The  detailed  study  of  organisms  has  developed  the  sciences  of 
phytology  (botany)  and  zoology,  with  its  many  subordinate  sciences. 
As  ordinarily  understood,  these  sciences  deal  with  the  plants  and 
animals  of  the  present,  or  Holocenic,  geological  epoch,  while  those 
of  the  many  epochs  of  the  earth's  history  anterior  to  the  present 
are  reserved  for  the  palaeontologist.  Such  a  division,  however,  is 
illogical,  for  the  life  of  the  earth  has  been  continuous  and  its  de- 
velopment has  been  progressive  from  the  earliest  time  to  the 
present  day.  The  scientific  palaeontologist  can  not  neglect  the  study 
of  the  existing  organisms,  nor  can  the  scientific  zoologist  and  botan- 
ist, or  student  of  the  present  living  world,  neglect  the  organisms  of 
the  past.  Palaeozoology  cannot  be  divorced  from  zoology,  nor 
palaeobotany  from  botany.  From  the  nature  of  the  organic  remains 
of  former  periods  it  follows,  however,  that  the  palaeontologist  lays 
most  stress  upon  the  hard  parts  of  organisms,  or  those  capable 
of  preservation,  in  former  as  well  as  the  present  geological  periods, 
while  the  botanist  and  zoologist  in  the  study  of  the  modern  floras 
and  faunas  tend  to  lay  more  stress  upon  the  soft  tissues  which 
perish  readily  and  so  are  not,  or  only  rarely,  preserved  in  the  case  of 
ancient  forms  of  life. 

There  are,  however,  good  reasons  for  believing  that  the  hard 
parts  of  organisms  form  in  some  respects  a  more  reliable  index 
to  their  relationship  than  do  the  soft  parts.  This  is  especially  the 
case  in  animals  which  build  external  hard  parts  which  increase  by 
serial  addition,  without  change  of  the  older  parts  deposited.  In 

910 


THE    ORGANIC    WORLD  911 

such  cases  we  are  certain  to  get  a  complete  record  of  the  individual 
development  of  the  animal  from  the  youngest  stages  in  which  such 
structures  are  formed  to  the  adult  or  even  old  age  stage.  Thus,  in 
the  case  of  the  molluscan  shell,  for  example,  we  have  a  complete 
record  of  the  individual  development  or  ontogeny,  all  the  changes 
being  indicated  in  the  successive  whorls  or  areas  of  the  shell,  from 
the  initial  shell-plate  to  the  adult.  Moreover,  such  shells  will 
preserve  the  detailed  features  assumed  necessarily  hy  the  mantle 
of  the  animal  in  conformity  with  development  and  increase  of  in- 
ternal organs,  features  which  are  evanescent  in  the  soft  parts  and 
can  in  many  cases  not  even  be  observed. 

What  has  just  been  stated  is  true  mainly  of  animals  whose 
hard  parts  are  external  structures,  retained  throughout  life  and 
increased  by  addition  in  one  region  only.  Such  additions  are  recog- 
nizable by  the  formation  of  growth  lines,  and  they  are  typically 
shown  in  the  shells  of  the  Mollusca,  as  already  noted.  Brachiopoda 
also  show  such  changes  in  external  form  but  there  are,  in  addition, 
changes  in  interior  structures,  for  the  study  of  the  development 
of  which  a  complete  series  of  individuals,  representing  all  the 
stages,  is  needed.  Corals  likewise  show  their  growth  lines,  and 
sections  made  across  the  older  part  in  most  cases  show  the  prog- 
ress of  development  of  the  individual.  Other  invertebrates  are  less 
satisfactory.  While  the  serial  development  of  parts  can.be  made 
out  in  the  plates  of  an  adult  echinoderm,  yet  the  fact  that  each 
plate  changes  with  the  progress  of  development  interposes  certain 
difficulties 'in  the  study  of  the  life  history,  and  for  its  complete 
determination  individuals  of  various  age  stages  are  needed.  This 
is  also  true  of  the  vertebrated  animals  where  the  internal  skeleton  or 
external  armor  changes  with  the  growth  and  development  of  the 
individual,  and  where,  therefore,  skeletons  of  the  young  as  well 
as  the  adult  are  needed  to  determine  the  entire  life  history. 


PLANTS  AND  ANIMALS  AS  INDICATORS  OF  THE  AGE  OF  THE  PERIOD 
IN   WHICH   THEY   OCCUR. 

Since  we  have  realized,  by  a  prolonged  study  of  modern  as 
well  as  ancient  organisms,  that  animals  and  plants  have  gradually 
increased  in  complexity  of  structure  and  diversity  of  form,  from 
the  earliest  times  to  the  present,  it  has  become  possible  to  use  the 
remains  of  organisms  embedded  in  the  strata  as  indices  of  the 
chronology  of  the  earth's  history,  and  by  extensive  collection  of 
facts  from  all  geological  levels,  and  over  wide  areas,  to  build  up  an 


9i2  PRINCIPLES    OF    STRATIGRAPHY 

organic  succession  which  parallels  the  stratigraphic  succession  in 
the  development  of  the  earth's  crust.  It  has  been  found  that  cer- 
tain groups  of  organisms  did  not  extend  beyond  a  certain  time 
period  in  the  earth's  history,  and  so  their  occurrence  in  the  strata 
indicates  the  upper  age  limit  of  these  strata.  Thus,  trilobites  are 
known  only  from  Palaeozoic  formations — hence  the  finding  of  one 
of  these  extinct  organisms  stamps  the  strata  in  which  it  occurs 
as  of  Palaeozoic  age.  More  restricted  occurrences  of  special  forms 
have  made  it  possible  to  recognize  the  geological  levels  with  greater 
precision,  thus  the  trilobite  Paradoxides  characterizes  only  the 
Middle  Cambric  rocks  of  the  earth's  crust  in  certain  regions,  while 
the  trilobite  Holmia  characterizes  the  lower  Cambric  strata  in  the 
same  regions.  Again,  the  Hydrozoan  Dictyonema  flabellifornie  is 
of  world-wide  distribution  in  the  basal  Ordovicic  strata.  Organisms 
used  in  this  manner  become  indices  of  geological  horizons  and,  since 
all  but  those  of  the  present  geological  period  occur  only  in  fossil 
form,  the  term  ''index  fossiF'  is  properly  applied  to  them.  This 
subject  will  be  considered  further  in  a  subsequent  chapter. 


CLASSIFICATION    OF    PLANTS    AND    ANIMALS. 

The  classification  of  plants  and  animals  is  a  process  of  assort- 
ment into  natural  groups,  or  groups  of  related  types,  and  the  ar- 
rangement of  these  groups  in  a  natural  order,  according  to  their 
genetic  relationship.  Groups  of  various  denominations  are  rec- 
ognized, the  smallest  of  those  in  general  use  being  the  spe- 
cies. Smaller  groups,  known  as  varieties  or  as  mutations,  are, 
however,  included  within  the  species.  Species  are  grouped  into 
genera,  each  genus  comprising  one  or  more  species.  The  generic 
and  specific  name  of  an  organism  are  always  used  together  in 
speaking  of  any  particular  species,  since  the  same  specific  name 
may  be  used  for  a  species  of  another  genus.  Thus,  the  fossil  brach- 
iopod  genus  Productus  includes  among  its  many  species  Productus 
muricatus.  Likewise  the  fossil  pelecypod  genus  Actinopteria  has 
among  its  species  Actinopteria  rnuricata,  while  another  brachiopod 
g-enus,  Strophalosia,  also  has  a  species  Strophalosia  muricata. 
These  three  species,  though  they  have  the  same  specific  name,  are 
not  at  all  related  to  each  other,  belonging  to  distinct  genera,  one 
of  which  belongs  to  a  different  division  or  phylum  of  the  animal 
kingdom  from  that  to  which  the  other  two  belong. 

Naming  of  genera  and  species.  (18.)  The  generic  name  is 
always  a  noun,  and  is  commonly  derived  from  the  Greek,  though 


PRINCIPLES    OF   TAXONOMY 


913 


generic  names  derived  from  the  Latin  are  not  uncommon.  Names 
compounded  from  the  two  languages  are  undesirable.  The  name 
should  always  express  some  prominent  character  of  the  genus,  as 
Orthoceras,  from  the  Greek  opOos  (orthos),  meaning  straight,  and 
Kfpas  (ceras),  meaning  horn,  the  essential  form  of  the  genus 
being  that  of  a  straight  horn.  Names  are,  however,  not  always 
chosen  with  such  direct  meaning,  while  not  infrequently  the  deriva- 
tion of  the  name  is  obscure  or  fanciful.  Proper  names  are  fre- 
quently chosen  for  generic  names,  as  Hyattella  for  a  genus  of 
brachiopods,  the  name  being  given  in  honor  of  the  great  American 
palaeontologist,  the  late  Alpheus  Hyatt.  In  the  formation  of  such 
names  the  original  name  is  reduced  to  the  genitive  case,  and  the 
termination  is  in  a  (a,  ia,  iia,  oia,  cca,  ella,  etc.).  When  the  original 
name  ends  in  y  this  letter  is  treated  as  a  consonant  and  the  termina- 
tion is  added.  Example :  from  Gray  we  may  derive  Grayia,  Gray- 
ella,  Graysia,  etc.  In  all  cases  the  form  of  the  word  must  be  the 
Latin  form,  the  Latin  equivalent  of  the  original  Greek  being  used. 
The  gender  of  the  generic  name  is  the  same  as  in  the  language 
from  which  it  is  derived.  If  the  generic  name  is  a  compound  of 
two  or  more  words,  the  terminal  word  determines  the  gender. 
Thus,  in  Orthoceras,  the  terminal  ceras  is  neuter  in  the  Greek,  and 
hence  all  names  ending  in  this  manner  are  neuter.  The  same  is 
true  of  the  words  nema  (thread),  stoma  (mouth},  and  desma 
(band),  often  employed  as  endings.  Special  uniform  endings  are 
often  employed  in  the  naming  of  genera  within  certain  classes,  such 
endings  having  reference  to  the  class.  Thus  pora  and  phyllum  are 
the  common  terminations  for  corals,  the  former  being  used  in  the 
poriferous  corals,  as  Aulopora,  Syringopora,  Tubipora,  etc.,  and 
the  latter  in  the  septate  corals,  especially  the  Tetraseptata ;  example : 
Cyatho phyllum,  Heterophyllum,  etc.  In  graptolites  the  termination 
graptus  is  common.  In  Cystoidea,  Blastoidea,  Crinoidea  and  Echi- 
noidea  the  common  terminations  of  the  generic  names  are  cystites, 
blastus,  crlnus,  and  echinus,  respectively,  though  these  are  by  no 
means  exclusively  employed.  Examples  are :  Pleurocystitcs,  Crypto- 
blastus,  Encrinus,  Eucalyptocrinus,  etc.,  and  Rhocchinus.  In 
Bryozoa  trypa  and  pora  are  frequent  endings ;  example :  Callotrypa, 
Bythopora.  In  Cephalopoda  ceras  is  the  prevailing  termination,  as 
in  Orthoceras,  Gephyroceras,  Phylloceras,  Lytoceras,  etc.,  though 
in  some  orders  of  ammonites  (e.  g.,  Discocampyli)  the  termination 
ites  is  the  prevailing  one ;  example :  Ceratites,  Stephanites,  etc. 
Among  Reptilia  saurus  is  a  common  termination ;  example :  Mosa- 
saurus,  Stegosaurus,  etc.,  and  names  of  fossil  birds  not  infrequently 


9i4  PRINCIPLES    OF    STRATIGRAPHY 

have  the  termination  pteryx  (wing);  example:  Archa>optcry.\-, 
Megalopteryx,  etc. 

The  generic  name  is  always  written  with  an  initial  capital. 
Specific  names,  on  the  other  hand,  have  the  value  of  adjectives  and 
should  always  be  written  with  a  small  initial  letter,  even  though 
they  are  derived  from  proper  names.  It  should  be  noted,  however, 
that  this  rule  is  not  universally  accepted. 

The  gender  of  the  specific  name,  as  expressed  in  its  termination, 
should  agree  with  that  of  the  generic  name.  Thus,  the  specific  name 
in  the  above  examples  is  miiricatus  in  Productus,  which  is  mascu- 
line, and  nmricata  in  the  other  two  genera,  which  are  feminine. 
In  general,  the  specific  name  is  derived  from  the  Latin,  while  all 
other  words  are  rendered  in  the  Latin  form.  Names  of  persons 
are  frequently  used  for  the  formation  of  specific  names,  an  appro- 
priate termination  being  added.  Geographical  names  likewise  are 
commonly  used  for  the  formation  of  specific  names.  The  more 
common  terminations  of  specific  names  thus  derived  are :  anus,  a,  inn 
(pertaining  to),  as  americanus,  linnccanus;  further,  ensis,  is,  e  (be- 
longing to  a  locality),  as  cincinnatiensis,  canadcnsis,  chicagoensis, 
kentuckiensis  (final  a  or  e  when  occurring  in  the  original  word  is 
dropped  and  terminal  y  changed  to  i)  ;  and,  finally,  i  as  halli, 
knighti,  etc.,  a  common  termination  for  names  derived  from  per- 
sons. Common  terminations  for  names  derived  from  other  words 
are :  atus,  a,  uwi,  as  costatus,  lobatus,  galeatus;  formis,  is,  e,  as 
tubiformis,  filiciformis,  etc. ;  inns,  a,  urn,  -  ex :  rugatinus;  oides 
(added  only  to  words  derived  from  the  Greek),  as  discoides,  etc., 
and  others. 

Priority  and  Synonymy  (13;  14;  15).  Since  there  is  such  a 
vast  number  of  specific  names  in  natural  history,  and  since  it  often 
happens  that  the  same  species  receives  distinct  names  by  different 
authors,  owing  to  ignorance  or  ignor'ance  of  each  other's  works,  it 
is  necessary  to  have  a  fixed  standard  by  which  the  name  which  is 
to  survive  is  invariably  chosen.  The  standard  is  priority — the  name 
used  in  the  first  description  of  the  species  being  adopted,  even  if  a 
later  proposed  name  is  more  suitable.  All  later  names  become 
synonyms.  In  certain  cases,  however,  exceptions  to  this  rule  are 
allowed.  Thus,  if  the  original  description  is  too  poor,  so  that 
the  true  characters  of  the  genus  and  species  cannot  be  ascertained, 
a  later  name,  proposed  with  a  better  description  or  illustration,  is 
often  accepted.  Where  a  name  has  long  been  in  general  use  the 
discovery  of  a  prior  name  ought  not  to  overthrow  the  established 
usage,  especially  if  the  older  name  has  itself  come  into  use  for 
another  species.  Thus  Spirifer  mucronatus  has  become  the  widely 


PRIORITY   AND    SYNONYMY 


915 


accepted  name  for  the  species  described  by  Conrad  as  Delthyris 
miicronata  in  1841.  One  of  the  numerous  varieties  of  this  species 
had,  however,  been  described  by  Atwater  in  1820  as  Terebratula 
pennata,  and  it  has  hence  been  argued  that  Spirifer  pennatus  and 
not  Spirifer  mucronatus  should  be  the  name  of  the  species.  Spirifer 
pennatus  has,  however,  come  into  use  for  another  species,  described 
under  that  name  by  Owen  in  1852.  The  adoption  of  Atwater's 
name  requires  not  only  the  discarding  of  a  well-known  and  appro- 
priate name,  but  also  requires  the  substitution  of  another  name 
for  Owen's  Spirifer  pennatus.  This  strict  adherence  to  the  rule  of 
priority  in  this  case  would  lead  to  so  much  confusion  that  it  is  much 
better  to  make  an  exception  and  retain  the  names  which  have  been 
so  extensively  used  in  the  literature. 

In  the  example  cited,  the  name  pennatus  has  been  given  to  two 
species  of  Spirifer  by  different  authors.  That  we  may  know  which 
species  is  meant,  it  is  necessary  to  write  the  name  of  the  author 
after  the  specific  name.  Thus,  in  the  case  cited,  the  names  should 
be  written :  Spirifer  pennatus  (Atwater)  and  Spirifer  pennatus 
Owen.  This  custom  of  adding  the  author's  name  is  a  general  one, 
and  should  always  be  observed  in  all  but  the  most  general  dis- 
cussions. When  the  author  of  the  species  has  placed  it  in  the 
wrong  genus,  or  if  the  species  is  subsequently  referred  to  a  new 
genus,  the  author's  name  after  the  species  is  placed  in  parentheses, 
and  frequently  the  name  of  the  person  who  first  placed  the  species 
in  the  correct  genus  is  added.  Thus,  in  the  examples  cited  above, 
Conrad  described  his  species  under  the  generic  name  Delthyris,  but 
it  belongs  to  the  genus  Spirifer ;  hence  the  name  is  written  Spirifer 
mucronatus  (Conrad).  Since  Billings  was  the  first  to  place  the 
species  in  the  genus  Spirifer,  his  name  may  be  added,  viz.,  Spirifer 
mucronatus  (Conrad)  Billings;  but  this  method  is  not  always 
adopted.  Sometimes  the  form  Spirifer  mucronatus  Conrad  sp.  is 
used. 

Synonymy. 

No  genus  can  have  two  species  of  the  same  name.  If  two 
authors  describe,  under  the  same  name,  two  different  species  of  the 
same  genus,  the  one  to  which  the  name  was  first  applied  retains  it, 
the  name  becoming  a  synonym  so  far  as  the  other  species  is  con- 
cerned; for  this  later-described  species  a  new  name  must  be  pro- 
posed. When  reference  to  the  first-described  species  is  made,  it  is 
often  desirable  to  note  the  fact  that  the  name  has  been  applied  to 
another  species  to  avoid  possible  confusion.  Thus  Dunker  in  1869 


916  PRINCIPLES    OF    STRATIGRAPHY 

described  and  named  Fusus  meyeri,  a  modern  species,  and  Aldrich 
in  1886  described  a  Tertiary  species  as  Fusus  meyeri.  Reference  to 
the  former  would  thus  be  made  as  follows :  Fusus  meyeri  Dunker 
1869  (non  Aldrich  1886).  Since  Aldrich  considered  his  species  a 
true  Fusus  he  was  forced  to  change  its  name  on  discovering  that 
the  name  had  been  preoccupied  for  that  genus.  So  in  1897  he  pro- 
posed the  name  Fusus  ottonis  for  this  species.  It  appeared,  how- 
ever, that  Aldrich's  species  is  not  a  true  Fusus,  but  belongs  to  a 
series  of  distinct  origin.  The  name  Falsifusus  (Grabau)  was, 
therefore,  proposed  for  it,  with  the  present  species  as  the  type, 
and,  since  this  genus  has  no  other  species  by  the  name  of  meyeri, 
it  became  proper  to  retore  that  specific  name  to  its  original  rank. 
Thus  we  now  have  the  synonymy  of  this  species  as  follows  (omit- 
ting references  to  authors  which  did  not  change  the  name)  : 

FALSIFUSUS  MEYERI — (Aldrich)   Grabau. 

1886  Fusus  meyeri  Aldrich * 

not  Fusus  meyeri  Dunker,  1869 

1897     Fusus  ottonis  Aldrich 

1904     Falsifusus  meyeri  Grabau 


In  this  case  the  specific  name  ottonis  not  only  becomes  a  syno- 
nym, but,  so  far  as  Fusus  is  concerned,  it  is  dead  and  cannot  be 
used  again,  even  for  a  new  species  of  Fusus.  Unless  this  rule  is 
observed  much  confusion  is  likely  to  arise.  Should  the  generic 
name  Falsifusus  be  found  invalid,  however,  the  type  species  Falsi- 
fusus meyeri  being  proved  a  true  Fusus  after  all,  the  specific  name 
ottonis  will  have  to  be  restored  to  its  original  rank,  the  species  in 
question  being  then  Fusus  ottonis.  The  general  rule  is  that  no  spe- 
cific name  which  has  become  a  synonym  in  a  genus  can  ever  be 
used  again  for  another  species  of  that  genus,  though  it  may  be 
used  for  species  of  other  genera.  If  an  old  comprehensive  species 
is  divided  into  a  number  of  species  the  original  name  is  retained 
for  that  subdivision  to  which  it  was  originally  applied,  or  to  which 
the  diagnosis  corresponds  most  closely.  For  the  other  subdivisions 
new  names  must  be  proposed.  If  two  authors  describe  the  same 
species  under  different  names,  the  name  given  in  the  earlier  de- 
scription is  retained,  the  other  one  becoming  a  synonym.  If  a  spe- 
cies is  transferred  from  one  genus  to  another,  in  which  there  is 
already  a  species  of  that  name,  that  one  of  the  two  species  to  which 
the  specific  name  in  question  was  first  applied  retains  it,  while  the 

*  The  dotted  lines  take  the  place  of  the  reference  to  the  literature  where 
this  name  was  used. 


NOMINA    NUDA  917 

other  species  takes  the  oldest  tenable  synonym  applied  to  it,  if  such 
exists,  otherwise  it  receives  a  new  name.* 

Manuscript  Names,  List  Names  (Nomina  Nuda).  Sometimes 
authors  propose  names  in  manuscript,  or  in  lists  with  the  intention 
of  giving  descriptions  later,  but  the  manuscripts  are  not  published 
or  the  descriptions  not  written.  Such  a  nomcn  nudum  has  no 
standing,  unless  a  subsequent  describer  chooses  to  adopt  it  and 
give  the  original  proposer  credit  for  the  name.  Thus  U.  P.  James 
in  1871  listed  Ambonychia  costata  in  his  catalogue  of  Lower  Silu- 
rian (Ordovicic)  Fossils  of  the  Cincinnati  group,  proposing  the 
name  without  description.  Meek  in  1873  described  the  fossils  for 
which  James  had  proposed  the  above  name,  which  Meek  adopted, 
and  credited  to  James.  In  this  case  the  description  was  based  on 
the  material  originally  named  by  James,  so  that  there  could  be  no 
question  regarding  the  applicability  of  the  name.  Even  so,  many 
subsequent  writers  have  credited  the  name  costata  to  Meek,  refus- 
ing to  recognize  James'  claim  to  priority.  In  general,  manuscript 
names  and  list  names  are  best  discarded. 

Generic  Names  as  Synonyms,  As  a  general  rule,  a  generic  name 
can  be  used  but  once  in  natural  history,  even  if  the  genus  to  be 
named  belongs  to  a  wholly  distinct  phylum  of  the  animal  or  plant 
kingdom.  Thus  in  1835  Swainson  proposed  the  generic  name 
Clavella  for  an  Eocenic  gastropod  shell,  but  this  name  had  been 
preoccupied  in  1815  by  Oken  for  a  crustacean^  The  name  Clavi- 
lithes  was  therefore  proposed  by  Swainson  in  1840  for  his  shell. 
Many  authors,  however,  consider  that  preoccupation  of  a  name 
disqualifies  it  for  subsequent  use  only  if  both  cases  are  within  the 
same  phylum,  and  in  the  case  cited  Clavella  is  retained  by  some 
for  the  gastropod  as  well  as  for  the  crustacean.  The  stricter  rule, 
however,  which  allows  one  name  to  be  used  once  only  is  the  better, 
since  it  avoids  all  ambiguity. f  When  species  described  under  differ- 
ent generic  names  are  found  to  belong  to  one  genus,  the  oldest  of 
the  generic  names  applied  to  them  is  retained,  the  others  becoming 
synonyms.  Such  synonyms  ought  not  to  be  used  again,  but  rele- 
gated to  the  limbo  of  invalid  terms.  If,  however,  the  supposed 
generic  identity  of  the  species  is  shown  to  be  untenable,  the  original 
name  or  names  must  be  restored  to  rank.  Thus  naturalists  have 
commonly  regarded  the  generic  name  Cyrtulus,  proposed  by  Hinds 

*For  further  extensive  discussion  of  this  question  see  recent  numbers  of 
Science. 

t  For  the  generic  names  used  in  zoology  up  to  1879,  see  Scudder  (25).  For 
those  used  subsequently  see  the  annual  lists  published  by  the  Zoological  Society 
of  London  in  the  Zoological  Record  (complete  index  every  ten  years,  1865-1906), 
continued  in  tehe  International  Catalogue  of  Scientific  Literature  since  1907. 


918  PRINCIPLES    OF    STRATIGRAPHY 

in  1843  for  a  modern  gastropod,  as  a  synonym  of  Clavilithes,  pro- 
posed by  Swainson  in  '1840  for  a  Tertiary  one,  and  relegated  the 
name  Cyrtulus  to  the  limbo  of  dead  terms.  As  the  types  of  these 
genera  are,  however,  widely  distinct,  the  name  Cyrtulus  must  be 
restored  to  its  original  significance. 

When  a  genus  includes  several  distinct  groups  of  species,  each 
of  which  is  subsequently  raised  to  the  rank  of  an  independent  genus, 
the  original  name  should  be  retained  for  the  group  considered 
most  typical  by  the  original  author,  or  corresponding  best  to  his 
diagnosis.  New  names  must  be  given  to  the  other  groups.  Thus 
the  name  Clavilithes  has  been  restricted  to  that  group  to  which 
the  generic  characters,  as  described  by  Swainson,  best  correspond 
(C.  parisiensis,  etc.),  while  another  group  included  by  Swainson 
under  the  same  generic  name  has  been  separated  under  the  term 
Rhopalithes  (R.  noa,  etc.). 

TYPES. 

A  type  in  natural  history  is  the  material  used  in  describing, 
defining,  and  illustrating  a  species  or  genus,  etc.  Two  kinds  of 
types  are  recognized — Primary  or  Proterotypes  and  Secondary  or 
Supplementary  types  or  Hypotypes  (Apotypes).  Typical  specimens 
(Icotypes)  not  used  in  the  literature,  but  serving  a  purpose  in 
identification,  are  further  recognized. 

Terms  Used  for*  Specific  Types.  The  following  terms  have 
been  proposed  and  have  come  into  more  or  less  general  use  (24) 
for  types  of  species: 

I.  Primary  types   (Proterotypes). 

a.  Holotypes. 

b.  Cotypes  (Syntypes). 

c.  Paratypes. 

d.  Lectotypes, 

II.  Supplementary  types  (Hypotypes  or  Apotypes). 

e.  Autotypes  (Heauto types). 

f.  Plesiotypes. 

g.  Neotypes. 

III.  Typical  specimens  (Icotypes). 
h.  Topotypes. 
i.  Metatypes. 
j.  Idiotypes. 
k.  Homoeotypes. 
1.  Chirotypes. 
IV.  Casts  of  Types  (Plastotypes). 


CLASSIFICATION    OF    TYPES  919 

I.  Among  the  primary  types  a  holotype  is  the  original  speci- 
men selected  as  the  type,  and  from  which  the  original  description 
(protolog),  or    the    original    illustration     (protograph),  is    made. 
A  cotype  (syntype)  is  a  specimen  of  the  original  series  when  there 
is  no  holotype,  the  describer  having'  used  a  number  of  specimens 
as  of  equal  value. 

A  paratype  is  a  specimen  of  the  original  series  when  there  is  a 
holotype.  When  the  original  describer  selected  one  specimen  out 
of  the  number  used  to  be  the  type  par  excellence,  i.  c.,  the  holotype, 
the  remainder  of  the  specimens  used  in  the  original  description  con- 
stitute the  paratypes. 

A  lectotype  is  a  specimen  chosen  from  the  cotypes  subsequently 
to  the  original  description  to  represent  the  holotype. 

II.  Among  the  supplementary  types : 

An  autotype  (heautotype}  is  a  specimen  not  belonging  to  the 
primary  or  proterotype  material  and  identified  with  an  already 
described  and  named  species  and  selected  by  the  nomenclator  him- 
self for  the  purpose  of  further  illustrating  his  species. 

A  plesiotype  is  a  similar  specimen  but  selected  by  some  one 
else  than  the  original  describer  of  the  species. 

A  neotype  is  a  specimen  identified  with  an  already  described 
and  named  species,  and  selected  to  represent  the  holotype  in  case 
the  original  material  (all  the  proterotypes )  is  lost  or  too  imperfect 
for  determination.  A  neotype  must  be  from  the  same  locality  and 
horizon  as  the  holotype  or  lectotype  which  it  represents. 

III.  Among  typical  specimens  or  Icotypes: 

A  topotype  is  a  specimen  (hot  used  in  the  literature)  from  the 
same  locality  and  horizon  as  the  holotype  or  lectotype. 

A  metatype  is  a  topotype  identified  by  the  nomenclator  himself. 

An  idiotype  is  a  specimen  (not  used  in  the  literature)  identified 
by  the  nomenclator  himself,  but  not  from  the  original  locality  or 
horizon  of  the  holotype  or  lectotype  with  which  it  is  identified,  i.  e., 
not  a  topotype. 

A  homotype  (homocotype)  is  a  specimen  (not  used  in  the  litera- 
ture) identified  by  a  specialist,  after  comparing  with  the  holotype 
or  lectotype. 

A  chirotype  is  a  specimen  upon  which  a  chironym  or  manuscript 
name  (a  name  never  published)  is  based. 

IV.  Casts  of  type  material   (plastotypes)  may  be  used  or  not 
in  descriptions  or  illustrations.     They  are  accordingly  holoplasto- 
type  or  any  other  protoplastotype.     Hypoplastotypes  and  icoplasto- 
types  also  may  be  made,  but  are  generally  of  comparatively  little 
value. 


920  PRINCIPLES    OF    STRATIGRAPHY 

GENERIC  TYPES.  Species  upon  which  genera  are  based  are 
genotypes*  Three  kinds  of  genotypes  may  be  recognized : 

Genoholotype — the  original  species  on  which  the  genus  is 
founded,  or  the  species  selected  by  the  author  from  those  originally 
described  as  the  type  of  the  genus. 

Genosyntype — one  of  a  series  of  species  upon  which  a  genus  is 
founded  when  there  is  no  genoholotype. 

Genolectotype — a  species  subsequently  selected  from  the  geno- 
syntypes  to  represent  the  genoholotype. 


Selection  of  the  Genotype  or  Type  Species  of  a  Genus. 

Many  genera  are  monotypic,  i.  e.,  had  only  one  species  when 
founded,  though  others  may  subsequently  have  been  referred  to 
them.  The  original  species  upon  which  the  genus  is  founded  in 
such  a  case  is  the  true  genotype  or  genoholotype.  When  a  genus 
is  founded  on  a  group  of  species  (heteiotypic)  the  originator  of 
the  genus  should  select  one  species  as  the  genoholotype.  This  has 
not  always  been  done,  especially  in  the  case  of  the  older  genera, 
the  genus  being  founded  on  a  group  of  species  or  genosyntypes  de- 
scribed at  the  same  time.  It  then  becomes  the  duty  of  the  first  re- 
viser of  the  genus  to  select  the  type  species  (genolectotype)  from 
the  original  species  (or  genosyntypes).  Two  principal  methods 
are  used  by  naturalists  in  such  cases — the  first  species  method  and 
the  elimination  method.  The  first  of  these  methods  appears  to  be 
the  simplest  one,  since  the  species  first  described  by  the  author  of 
the  genus  is  taken  as  the  type.  It  sometimes  happens,  however, 
that  the  first  species  is  not  the  most  typical  of  the  genus  as  defined 
by  the  author,  or  it  may  have  been  subsequently  separated  from  the 
other  species  and  perhaps  placed  in  a  genus  by  itself,  the  diagnosis 
of  which  differs  from  the  original  one,  or  is  more  circumscribed 
than  it.  In  such  a  case  it  is  the  practice  to  choose  the  genolectotype 
from  the  remaining  species  of  the  original  group.  Often  several 
sections  have  been  separated  from  the  original  group  and  placed  in 
distinct  genera.  By  this  process  of  elimination  the  genotype  thus 
becomes  restricted  to  the  remaining  species  (genosyntypes),  one  of 
which  must  be  selected.  This  selection  is  to  be  done  by  the  first 
reviser  of  the  old  genus  and  his  designation  of  the  genolectotype 
will  stand.  Occasionally  it  may  happen  that  all  the  original  species 
have  been  removed  to  new  genera,  in  which  case  the  last  one  so 

*  This  name  has  recently  been  employed  by  zoologists  and  botanists  in  a  very 
different  sense  (see  Osborn-i9), 


HIGHER    GROUPS    THAN    GENERA  921 

removed  is  to  be  taken  as  the  type  of  the  restricted  genus,  the  new 
name  applied  to  it  becoming  a  synonym. 

The  application  of  the  first  species  rule  to  the  determination 
of  the  type  of  the  genus  may  lead  to  a  great  many  unnecessary  and 
undesirable  changes,  but  where  possible  it  is  best  applied,  as  being 
the  most  readily  carried  out.  Where,  however,  this  would  lead  to 
confusion  in  the  nomenclature,  the  elimination  rule  is  best  followed. 
(For  illustration  and  discussion  see  Stone-26;  Allen-i2  and  sub- 
sequent articles  in  Science.) 

Union  of  Genera  into  Groups  of  Higher  Taxonomic  Value. 

Sub-families,  Families,  Super-families.  Genera  are  united  in- 
to families,  the  name  of  the  family  being  generally  derived  from  its 
principal  genus  or  the  one  longest  known.  The  termination  of 
families  in  zoology  is  generally  idee  (short  i),  as  Terebratulidce 
from  Terebratula.  Families  are  often  divided  into  sub-families, 
the  names  of  which  terminate  in  incc  (long  i),  as  Terebratulincc.  In 
Botany  the  family  generally  ends  in  acece,  as  Rosacecc,  but  there  are 
a  number  of  exceptions  to  this  rule.  Sub-families  in  botany  end 
in  ea  or  inece,  the  name  in  each  case  being  derived  from  the  prin- 
cipal genus.  Super-families — in  which  a  small  group  of  related 
families  are  united,  are  sometimes  made  use  of.  The  names  of 
these  end  in  acea,  the  name  being  derived  from  the  principal  family. 
Ex. :  Terebratulacea. 

Sub-orders,  Orders.  The  important  division  of  next  higher 
rank  is  the  order,  which  often  comprises  a  number  of  sub-orders. 
The  names  of  these  divisions  have  no  uniform  ending  in  zoology, 
though  the  terminal  letter  is  commonly  a,  the  termination  ata  being 
most  common.  Other  terminations  are :  ia,  oida  or  oidea,  acea,  era, 
etc.  In  botanical  nomenclature  the  orders  end  in  ales. 

Groups  of  Higher  Rank.  Above  the  orders  we  have  in  ascend- 
ing rank:  (super-orders},  (sub-classes)  classes,  (sub-types)  phyla 
(or  types),  sub-kingdom,  kingdom.  When  a  taxonomic  division 
of  higher  rank  takes  its  name  frojn  a  genus  the  name  of  which  is 
afterward  found  to  have  been  preoccupied,  and  so  has  to  be 
changed,  the  name  of  the  higher  division  must  also  be  changed. 

The  law  of  priority  is  not  strictly  applied  to  names  of  divisions 
of  higher  rank  than  genera,  since  newly  discovered  facts  often 
make  a  change  in  the  classification  necessary  when  the  substitution 
of  a  new  for  an  old  term  becomes  desirable.  A  uniform  termina- 
tion for  the  names  of  divisions  higher  than  families  is  much  to  be 
desired. 


922  PRINCIPLES    OF    STRATIGRAPHY 

Faunas  and  Floras.  An  association  of  all  the  animals  in  a  given 
locality  constitutes  the  fauna  of  that  locality,  while  a  similar  associa- 
tion of  the  plants  produces  the  flora.  In  the  study  of  past  geologic 
epochs  it  is  often  necessary  to  speak  of  the  totality  of  animal  or 
plant  life  in  any  given  formation.  This  constitutes  the  fauna  and 
flora,  respectively,  of  that  formation.  It  matters  not  whether  the 
formation  is  great  or  small — whichever  is  considered — all  the  animal 
remains  found  in  that  formation  together  make  up  the  fauna  of 
that  formation,  and  all  the  plant  remains  constitute  its  flora.  To 
designate  the  fauna  and  flora  of  a  time  period  we  may  conveniently 
employ  the  terms  chronofauna  and  chronoflora,  or  chronobios  for 
both.  Each  chronofauna  or  flora  comprises  numerous  geographic 
faunas  or  floras,  and  these  may  be  designated  the  loco  fauna  and 
locoftora,  or,  in  its  entirety,  the  locobios.  We  must,  of  course, 
realize  that  the  terms  fauna  and  flora  refer  to  the  assemblage  of 
animal  and  plant  life  as  a  whole,  in  the  time-period  of  the  forma- 
tion, and  at  the  locality  where  the  formation  now  occurs,  and  that 
therefore  the  fossil  remains  of  a  given  bed  do  not  adequately 
represent  the  fauna  or  flora  of  that  time,  since  many  types  have 
not  been  preserved.  Hence  the  term  fossil  faunas  is  useful  as  in- 
dicating that  only  a  certain  portion  of  the  original  fauna,  i.  e.,  that 
preserved  as  fossils,  is  spoken  of.  Thus  we  may  speak  of  the  fossil 
fauna  of  the  Hamilton  period  of  western  New  York,  by  which 
we  would  mean  that  portion  of  the  western  New  York  loco  fauna  of 
the  Hamilton  chronofauna  which  has  been  preserved. 

TABLE  I.    SUBDIVISIONS  OF  THE  PLANT  KINGDOM. 

Phanerogamous   plants. 
PHYLUM  V.     SPERMATOPHYTA  or  seed  plants. 

Class  2.     Angiosperma  (covered  seed-plants). 
Sub-class  2.     Dicotyledoneae  (seed-leaves  2). 
Sub-class  i.     Monocotyledonese  (seed-leaves  i). 
Class  i.     Gymnospermce  (naked-seeded  plants). 
Order  V.       Ginkgoales 
Order  IV.     Gnetales  (joint  firs). 
Order  III.    Coniferales. 
Family  2.     Pinaceae. 
Family  i.     Taxaceae. 

Order  II.      Cycadales  (cycads,  sago  palms). 
Order  I.        Cordai tales  (Cordaites). 

Cryptogamous  plants. 

PHYLUM  IV.     PTERIDOPHYTA  or  Fern  Plants  (Vascular  Cryptogams). 
Class  6.     Felicince. 

Order  IV.     Marattiales  (Ringless  Ferns). 
Order  III.    Feliciales  (True  Ferns). 


CLASSIFICATION    OF    PLANTS  923 

Order  II.      Cycadofiliciales. 

Order  I.        Hydropteridiales. 
Family  2.     Salviniacese. 
Family  I.     Marsiliaceae. 
Class  5.     Ophioglos since. 

Order  I.     Ophioglossales. 
Class  4.     Lycopodince. 

Order  IV.     Isoetalcs. 

Order  III.  Lepidodendrales. 
Family  2.  Sigillariaceae. 
Family  I.  Lepidodendraceas. 

Order  II.      Selaginellales. 

Order  I.        Lycopodiales  (Club-mosses). 
Class  3.     Psilotina. 

Order  I.        Psilotales. 
Class  2.     Sphenophyllincz. 

Order  II.      Cheirostrobales. 

Order  I.        Sphenophy Hales. 
Class  i.     EquisetincB 

Order  II.    Equisetales  (Horsetails)-. 

Order  I.      Calamariales  (Calamites). 

PHYLUM  III.     BRYOPHYTA  or  Moss-plants. 
Class  2.     Musci  (Mosses). 
Order  IV.     Bryales. 
Order  III.    Phascales. 
Order  II.      Andreacales. 
Order  I.        Sphagnales  (Peat-moss). 
Class  i.     Hepatic®  (Liverworts). 

PHYLUM  II.    THALLOPHYTA  or  Thallus  plants. 
C,   LICHENS. 

Class  2.     Basidiolichenes. 
Class  i.     Ascolichenes. 

Sub-class  2.     Discholichenes. 

Sub-class  i.     Pyrenolichenes. 
B.   FUNGI. 

Class  2.     Mycomycetes  (True  Fungi). 

Order  III.     Basidiales  (Mushrooms,  etc.). 

Order  II.       Ascomycetes  (Mildews). 

Order  I.         Ustilaginales.     (^cidiomycetes,  rusts). 
Class  i.     Phyco-mycetes  (Algo-fungi). 

Order  II.     Zygomycetes. 

Order  I.       Oomycetes. 
A.   ALG/E. 

Class  3.     Rhodophycea  (Red  algae). 
Class  2.     Pk&ophycecs  (Brown  algae). 

Order  IV.     Euphseophyceae. 

Order  III.     Cryptomonadaceas. 

Order  II.      Diatomaceae. 

Order  I.        Peridiniaceae. 


924  PRINCIPLES    OF    STRATIGRAPHY 

Class  i.     Chlorophyceoe.  (Green  algae). 
Order  III.    Characeae. 
Order  II.      Euchlorophyceae. 
Order  I.        Conjugataceae. 
PHYLUM  I.     PROTOPHYTA. 

Class  3.     Myxomycetes  (Slime-molds),    sometimes    regarded    as    Protozoa 

(Mycetozoa). 

Class  2.     Flagellata  (more  generally  regarded  as  Protozoa). 
Class  i.     Schizophyta. 

Order  II.     Cyanophyceae  (Blue-green  algae). 
Order  I.      Schizomycetes  (Bacteria). 


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THE   BIOSPHERE  933 


BRIEF    SUMMARY   OF   THE    MORPHOLOGICAL    CHAR- 
ACTERS   OF    THE    PHYLA    OF    PLANTS 
AND    ANIMALS. 

A.     PLANTS. 

PHYLUM  I — PROTOPHYTA.  This  division  is  not  often  employed, 
the  members  here  classed  under  it  being  referred  either  to  the  algse 
or  to  the  fungi.  It  is,  however,  a  convenient  division  for  those 
simple  plants  which  have  not  the  true  characters  of  either  of  the 
other  two  groups.  In  this  group  are  placed  organisms  which  com- 
bine characteristics  of  both  plants  and  animals.  Such  are  the 
Flagellata,  which  more  generally  are  placed  among  the  Protozoa, 
and  the  Myxomycetes,  which  are  also  regarded  by  some  zoologists 
as  Protozoa  under  the  name  Mycetozoa.  The  Flagellata  are  aquatic, 
and  so  named  from  the  fact  that  their  dominant  phase  is  a  "flagel- 
lula"  or  cell-body  provided  with  one,  few,  or,  rarely,  many,  long, 
actively  vibratile  processes.  They  are  attached  or  free  and  some  of 
them  (Volvocacece,  etc.)  develop  chlorophyll,  and  in  this,  and  in 
the  mode  of  multiplication,  they  have  the  characters  of  undoubted 
unicellular  plants.  Some  types  placed  here  (Coccolithophoridcc} 
(Fig.  104)  have  their  bodies  invested  in  a  spherical  test  strength- 
ehed  by  calcareous  elements  or  tangential  circular  plates  which  are 
variously  named  coccoliths,  discoliths,  cyatholiths,  or  rods  called 
rhabdoliths.  These  are  often  found  in  the  Foramini feral  ooze 
and  in  chalk. 

Flagellates  are  frequently  considered  as  forming  the  starting 
point  for  unicellular  plants  on  the  one  hand  and  Protozoa  on  the 
other.  That  they  have  given  rise  to  both  groups  is  held  by  good 
authorities.  The  largest  species  range  up  to  130^  in  length,  ex- 
clusive of  the  flagellum,  though  a  large  number  of  them  rarely 
exceed  2O/x  in  length. 

The  Myxomycetes  (Mycetozoa),  or  slime  molds,  are  sometimes 
classed  with  the  Fungi  and  also  with  the  Protozoa.  They  are  ter- 
restrial and  devoid  of  chlorophyll  and  reproduce  by  spores,  which 
are  scattered  by  the  air,  as  in  Fungi.  The  spore  hatches  out  as  a 
mass  of  naked  protoplasm,  which  assumes  a  free-swimming  flagel- 
late form,  multiplies  by  division,  and  then  passes  into  an  amoeboid 
stage.  By  fusion  of  many  amceboids  the  plasmodhun  is  formed, 
which  is  a  mass  of  undifferentiated  protoplasm  without  envelope  and 
endowed  with  the  power  of  active  locomotion.  It  penetrates  de- 
caying vegetable  matter  or  spreads  over  the  surface  of  living  fungi, 


934  PRINCIPLES    OF    STRATIGRAPHY 

and  may  reach  an  expanse  of  several  feet,  though  generally  small. 

The  Schizophyta  form  a  group  distinct  from  the  preceding  and 
unconnected  with  them  or  higher  types.  Bacteria  are  minute  uni- 
cellular plants,  devoid  of  chlorophyll,  and  multiplying  by  repeated 
division.  In  form  they  are  spherical,  oblong,  or  cylindrical,  often 
forming  filamentous  or  other  aggregates  of  cells.  The  absence 
of  an  ordinary  nucleus,  of  the  ordinary  sexual  method  of  repro- 
duction, and  the  manner  of  division,  unite  them  with  the  Cyano- 
phycece,  or  blue-green  algae.  Some  forms  (Sarcina)  show  relation- 
ship to,  or  analogies  with,  green  algae  (Palnicllacea),  while  others 
suggest  relationship  to  myxomycetes.  Again,  certain  features  sug- 
gest some  flagellates  and  many  forms  exhibit  a  power  of  indepen- 
dent movement  when  suspended  in  a  fluid.  The  group  is  no  doubt  a 
heterogeneous  one,  including  at  present  primitive  forms  of  many 
types  of  plants.  Their  size  is  commonly  i/w.*  in  diameter  and 
from  two  to  five  times  that  length,  though  smaller  and  larger  forms 
are  known.  They  occur  fossil  since  Devonic  and  probably  earlier 
time. 

The  Cyanophycece  are  unicellular  or  multicellular  and  contain, 
besides  chlorophyll,  a  blue-green  coloring  matter,  hence  their  name, 
though  the  actual  color  of  some  ranges  from  yellows  to  browns, 
reds,  purples,  or  violets  of  all  shades.  Generally  the  single  cells 
are  held  together  in  a  common  jelly.  Some  members  of  this  division 
secrete  lime  (Gloeocapsa,  Gloeothece)  and  serve  to  build  up  con- 
siderable deposits  (see  organic  oolites,  Chapter  XI).  Nearly  a 
thousand  species  of  Cyanophycese  are  known.  No  fossil  representa- 
tives are  known,  though  they  must  have  existed  in  earlier  ages. 

PHYLUM  II — THALLOPHYTA.  The  vegetative  portion  of  these 
plants  consists  of  one  or  many  cells  forming  a  thallus,  often 
branched.  There  is  no  differentiation  of  the  body  into  a  root, 
stem,  or  leaf,  while  the  internal  structure  is  comparatively  simple. 
Both  sexual  and  asexual  reproduction  take  place.  In  many  classi- 
fications the  Bacteria,  the  Cyanophycecc,  and  the  Myxomycetes  are 
also  classed  here,  and,  besides  them,  the  following  classes  are  made : 
i.  Peridinecu,  2.  Conjugate,  3.  Diatomacece  (Diatoms),  4.  Hetero- 
contecu,  5.  Chlorophycecc  (Green  algae),  6.  Characea?  (Stoneworts), 
7.  Rhodophycecc  (Red  algae),  8.  Eumycetes  (Fungi),  9.  Phycoin\- 
cetes  (Algal  fungi),  10.  Phccophycecc  (Brown  algae).  The  older  di- 
vision into  the  three  classes  of  a,  Alga,  bearing  Chlorophyll ;  b, 
Fungi,  without  Chlorophyll ;  and  c,  Lichens,  symbiotic  colonies  of 
algae  and  fungi,  is  the  most  familiar  and  will  be  used  here. 

*  One  micromillimeter  or  o.ooi  mm. 


PLANTS.    THALLOPHYTA  935 

a.     Alga. 

Algae,  or  seaweeds,  are  thallophytes  characterized  by  the  pres- 
ence of  Chlorophyll,  or  leaf-green,  though  the  color  is  by  no  means 
always  green.  They  are  largely  aquatic  in  habitat,  most  of  the  more 
striking  forms  occurring  in  the  sea.  According  to  the  prevailing 
color,  three  divisions  are  made — the  Green  Algae,  or  Chlorophycccc; 
the  Brown  Algae,  or  Phaophycece;  and  the  Red  Algae,  or  Rhodo- 
phycea.  The  Cyanophycece,  or  blue-green  algae,  are  also  frequently 
included  under  the  algae. 

The  Chlorophycecc  include  three  forms  in  which  the  chlorophyll 
is  not  accompanied  by  other  coloring  matter.  With  the  typical 
green  algae  (Euchlorophycece)  are  generally  included  the  divisions 
Conjugatacece  and  Characea,  which  have  a  separate  phyletic  stand- 
ing. The  common  green  sea-lettuce,  Ulva,  is  a  good  example  of  an 
expanded  form,  but  in  many  of  the  green  algae  (especially  the  Con- 
fervales),  the  thallus  consists  of  filaments,  branched  or  unbranched, 
attached  at  one  extremity  and  growing  almost  wholly  at  the  free 
end.  Some  forms  (Halimeda,  Acetabularia,  etc.)  are  encrusted 
with  lime  and  are  important  on  "coral"  reefs.  The  Pond-scums, 
or  Conjugates  (so  named  from  their  method  of  reproduction)  in- 
clude the  Desmids,  which  have  the  power  of  independent  move- 
ment. 

Quite  distinct  from  the  others  are  the  Characece,  the  most  highly 
differentiated  of  the  green  algae.  Of  these  the  common  stonewort, 
Chara,  growing  in  fresh  water  lakes,  is. the  typical  form.  This  is 
attached  to  the  bottom  of  pools  by  rhizoids  and  grows  upward  by 
means  of  an  apical  cell  forming  a  pointed  axis,  which  gives  off 
whorled  appendages  at  regular  intervals.  Long  branches  occur  in 
each  whorl,  and  these  give  off  secondary  whorls  of  jointed  ap- 
pendages. The  distance  between  the  nodes  from  which  the  ap- 
pendages arise  may  be  several  centimeters.  All  are  encrusted  with 
lime.  The  reproductive  organs  are  also  highly  differentiated. 
Antheridia  and  oogonia  are  formed  at  the  nodes  of  the  appendages. 
The  egg  cells,  or  oogonia,  when  ripe  are  surrounded  by  five  spirally 
twisted  cells,  and  crowned  by  a  circle  of  smaller  ones,  which  after- 
ward separate  to  allow  fertilization.  The  outer  cells  become  very 
hard  and  calcareous  and  are  extensively  preserved,  in  some  cases 
contributing  to  the  formation  of  limestones. 

Over  i, 600  species  of  true  green  algae  are  known.  The  Pond 
Scums,  or  Conjugate,  add  nearly  1,300  species  more,  while  the 
stoneworts,  or  Characeae,  are  represented  by  only  about  180  species, 
making  a  total  of  over  3,000  species. 


936  PRINCIPLES    OF    STRATIGRAPHY 

The  Phceophycece,  or  brown  algae,  are  distinguished  by  the  pos- 
session of  a  brown  coloring  matter  in  addition  to  the  chlorophyll. 
The  Peridiniacece  and  Diatomacea  are  included  here,  together  with 
the  Cryptomonadacea,  all  of  them  unicellular  plants  with  little  ex- 
cept color  in  common  with  the  true  brown  algae  (Eupluzophycece), 
which  are  multicellular.  Familiar  examples  of  the  last  class  are 
Fucus,  Laminaria,  and  Sargassum.  The  kelps  (Laminar  ia)  de- 
velop large  round  "stems"  which  branch  root-like  at  the  base  and 
have  an  oar-like  expansion  at  the  top.  The  rock-weeds  (Fucus)  de- 
velop air-bladders  which  serve  for  purposes  of  flotation.  They 
are  attached  to  the  rock  by  means  of  a  disc  or  root-like  expansion ; 
have  a  stem  of  rough  leathery  texture  which  forks  regularly;  and 
are  expanded  in  a  leaf-like  manner  with  thick  mid-ribs.  The  Gulf- 
weeds  (Sargassum)  have  distinct  stems,  leaves,  and  stalked  air- 
bladders,  and  strikingly  resemble  land  plants. 

The  diatoms  are  microscopic  unicellular  plants  of  a  yellow  or 
reddish-brown  color,  and  not  closely  related  to  the  other  algae  except 
perhaps  to  the  desmids.  The  cell  wall  is  impregnated  with  silica, 
so  that  its  shape  is  preserved  after  the  death  of  the  plant.  The 
"shell"  consists  of  two  parts,  one  overlapping  the  other  like  a  pill- 
box and  cover.  These  show  great  variety  of  form  and  have  the 
power  of  locomotion. 

Of  the  true  brown  algae  there  are  only  about  620  species.  The 
Peridiniacece  and  Cryptomonadacecc  comprise  only  about  220  spe- 
cies, but  the  diatoms,  recent  and  fossil,  include  about  5,000  species. 

The  Rhodophycece,  or  red  algae,  also  called  Floridecc,  are  "so 
named  from  the  presence  of  a  red  color  besides  the  chlorophyll. 
Species  growing  near  high-water  mark  are  generally  of  a  dark  hue 
and  may  be  mistaken  for  brown  algae.  The  Irish  moss,  Chondrus, 
is  a  good  example.  Those  growing  near  low-water,  or  in  the  shade 
of  other  algae,  are  bright  colored.  They  are  all  multicellular  and 
mostly  microscopic  in  size,  but  some  large  species  occur.  Lime- 
secreting  forms  are  common,  the  branching  Corallina,  the  encrust- 
ing Melobesia  and  Lithothamnion  abounding  both  in  recent  and 
fossil  state.  The  total  number  of  species  of  red  algae  is  about  1,400; 
this,  together  with  the  brown  algae,  840  species,  the  diatoms,  5,000 
species,  and  the  3,000  species  of  green  algae,  makes  a  total  of  over 
10,200  species  of  algae. 

Fucoids.  This  is  a  general  term  applied  to  impressions  on 
rocks,  suposed  to  represent  sea-weeds.  In  some  cases  land  plants 
and  even  traces  of  inorganic  structures  have  been  included  here. 
Ex. :  Fucoides  verticalis  of  the  Portage,  probably  a  land  plant ; 


THALLOPHYTA;    BRYOPHYTA  937 

Arthrophycus  harlani  of  the  Medina,  probably  a  trail;  Dendrophy- 
cus  triassicus  of  the  Newark  sandstone,  a  rill-mark  impression. 


b.     Fungi. 

Fungi  or  mushroom-plants  are  thallophytes  devoid  of  chloro- 
phyll, and  growing  often  in  the  dark.  They  arise  from  spores, 
and  the  thallus  is  either  unicellular  or  composed  of  tubes  or  cell- 
filaments  (hyphse),  which  may  be  branched,  and  have  an  apical 
growth,  or,  again,  they  are  composed  of  sheets  or  tissue-like  masses 
of  such  filaments,  forming  a  mycelium.  True  tissue  may  develop 
in  some  cases  by  cell-division  in  the  larger  forms.  Two  classes  are 
recognized :  Phycomycetes,  which  are  alga-like,  with  unicellular 
thallus  and  well-marked  sexual  organs,  and  Mlcomycetes,  or  higher 
fungi,  with  segmental  thallus  and  sexual  reproduction.  Some  of 
them  (Polyporus,  Dsedelia)  form  resistant,  more  or  less  woody, 
structures  growing  on  dead  trees. 

The  number  of  species  of  Fungi  is  probably  around  20,000, 
though  some  have  placed  it  as  high  as  50,000  or  even  150,000. 
Fossil  forms  extend  back  at  least  to  the  Carbonic,  where  they  occur 
as  hyphse  in  fossil  wood.  Good  specimens  are  also  found  in  amber 
of  Tertiary  age. 

c.     Lichens. 

The  lichens  are  terrestrial  thallophytes,  composed  of  algae  and 
fungi  living  together  symbiotically.  The  fungi  are  generally  Asco- 
mycetes,  the  higher  class  of  Basidomycetes  seldom  taking  part, 
while  the  algae  are  either  the  blue-green  algae,  Cyanophycea  or  the 
green  algae,  Chlorophycccc.  The  same  alga  can  combine  with  dif- 
ferent fungi  to  form  different  lichens.  The  fungal  portion  always 
forms  the  reproductive  organs,  though  the  algre  may  do  so  when 
separated  from  the  association,  and  growing  free.  Reproduction 
is  also  carried  on  by  fragmentation,  i.  c.,  the  breaking  off  of  parts 
capable  of  starting  new  plants.  There  are  some  thousands  of 
existing  species,  but  fossil  forms  have  not  been  recognized  except 
from  very  recent  formations.  It  is  not  unlikely,  however,  that 
lichenous  plants  formed  a  chief  element  of  the  ancient  land  vegeta- 
tion. 

PHYLUM  III— BRYOPHYTA.  The  Bryophyta  include  the  mosses 
and  liverworts,  both  terrestrial  plants.  In  the  former,  and  in  some 
of  the  latter  as  well,  the  plant  consists  of  a  stem  bearing  small 
leaves,  though  in  many  liverworts  this  distinction  is  not  present, 


938  PRINCIPLES    OF    STRATIGRAPHY 

but  a  thallus  is  formed  closely  applied  to  the  substratum.  The  at- 
tachment of  the  bryophytes  is  by  rhizoids,  true  roots  being  ab- 
sent. These  rhizoids  resemble  the  root-hairs  of  higher  plants. 
The  reproductive  organs  are  antheridia  and  archegonia,  serving 
for  sexual  reproduction.  The  former  are  stalked  and  develop  the 
spermatozoids,  while  the  archegonia  are  flask-shaped,  with  long 
neck,  the  egg-cell  lying  at  the  bottom.  From  the  fertilized  ovum  a 
capsule  arises,  generally  borne  on  a  stalk,  and  within  this  the 
spores  are  developed.  There  is  thus  an  alternation  of  generation 
— the  sexual  stage,  or  gametophyte,  developing  from  the  spore,  and 
the  asexual,  or  spore  stage  (sporogonium  or  sporophyte),  develop- 
ing from  the  fertilized  egg  of  the  gametophyte,  and,  in  turn,  pro- 
ducing the  spores.  The  spore-bearing  generation  is  throughout  life 
dependent  on  the  gametophyte,  whereas  in  pteridophytes  it  becomes 
an  independent  plant.  The  order  Sphagnales  contains  the  single 
genus,  Sphagnum,  with  numerous  species  known  as  bog-mosses. 
The  order  Andreaales  also  contains  a  single  genus,  Andreaea,  for 
the  most  part  an  Alpine  and  Arctic  plant,  growing  on  bare  rocks. 
The  order  Phascales  includes  a  few  small  species,  chiefly  of  the 
genus  Phascum.  The  order  Bryales,  on  the  other  hand,  contains  a 
very  large  number  of  genera  and  species. 

Fossil  mosses,  especially  of  the  genus  Hypnum,  have  been  ob- 
tained from  the  Miocenic  and  Quaternary  deposits  of  Europe  and 
the  Arctic  region,  and  also  from  western  America  (Green  River 
beds).  They  are  doubtfully  represented  in  Mesozoic  and  earlier 
deposits. 

PHYLUM  IV — PTERIDOPHYTA.  The  pteridophytes,  or  vascular 
cryptogams,  form  the  highest  division  of  the  flowerless  plants. 
Their  internal  vascular  structure  allies  them  with  the  higher  plants. 
In  them  alternation  of  generation  has  been  carried  farthest,  in 
that  the  first  stage  to  develop  from  the  germinating  spore  is  the 
gametophyte,  known  as  the  pro  thallus.  This  is  a  small,  flat,  green 
plant-organism  which  carries  on  its  under  side  the  archegonia  and 
antheridia,  together  with  the  rootlets  or  rhizoids.  This  sexual 
plant  is  independent  of  the  sporophyte  or  asexual  generation, 
while  the  latter  at  first  draws  nourishment  from  the  prothallus  but 
becomes  physiologically  independent  when  its  roots  develop.  This 
independence  of  the  two  generations  is  the  distinctive  feature  of 
the  pteridophytes,  whereas  in  bryophytes  the  sporophyte  is  through- 
out its  life  attached  to  the  gametophyte,  while  in  the  spermaphytes 
the  more  or  less  reduced  gametophyte  remains  enclosed  within  the 
tissues  of  the  sporophyte. 

The  Equisetales,  including  the  single  living  genus,  Equiset"m, 


PTERYDOPHYTA  939 

with  about  25  species,  and  the  extinct  Calamites,  represent  a  range 
in  height  from  a  few  inches  in  the  modern  forms  to  from  30  to  60 
meters  in  the  extinct  Calamites.  Equisetum  arises  from  a  subter- 
ranean rhizome,  which  may  be  a  meter  in  length,  and  is  jointed; 
the  aerial  shoot  consists  of  hollow  internodes,  with  whorls  of 
leaves  near  the  top  of  each,  the  leaves  cohering,  except  near  their 
tips.  In  section  the  aerial  stem  shows  a  hollow  central  cylinder, 
around  which  is  arranged  a  circle  of  fibrovascular  bundles,  triangu- 
lar in  section,  with  the  point  inward.  The  inner  end  is  occupied  by 
a  large  air  space,  and  outside  of  this  again  is  a  circle  of  long  air 
tubes  alternating  with  the  fibrovascular  bundles.  These  latter 
extend  into  the  leaves,  equaling  in  number  the  leaf  teeth. 

The  stem  of  the  extinct  Calamites  had  essentially  the  same 
structure,  but  with  secondary  growth  in  thickness.  In  all  large 
specimens  a  broad  zone  of  wood  is  added,  with  a  structure  compar- 
able in  the  true  Calamites  to  that  of  the  simplest  conifers.  The 
vascular  bundles  project  into  the  pith  as  in  Equisetum,  and  from 
their  more  resistant  character  they  will  remain  when  the  pith 
breaks  down.  A  rock-filling  of  the  hollow  cylinder  thus  made  will 
be  marked  by  longitudinal  grooves,  representing  the  projecting 
vascular  bundles.  In  Calamites  proper  these  grooves  alternate  at 
the  nodes,  while  in  Archseocalamites  they  are  continuous.  This 
shows  that  in  the  latter  the  leaves  were  superposed,  while  in  Cala- 
mites they  were  alternating.  In  modern  Equisetum  both  fertile 
and  sterile  branches  arise  from  the  rhizomes.  The  sterile  are  more 
slender  than  the  spore-bearing  ones,  and  bear  numerous  whorls  of 
branches,  which  form  a  bushy  plant,  from  which  the  name  "horse- 
tail" originated.  The  fertile  branches  bear  a  terminal  ustrobilus," 
or  cone  of  sporangiophores,  each  of  which  consists  of  a  hexagonal 
disk,  attached  by  a  stem  to  the  axis  and  supporting  on  its  under 
side  six  to  nine  large  spore-cases  or  sporangia.  The  outer  surfaces 
of  the  hexagonal  plates  form  the  solid  outer  surface  of  the  cone, 
the  sporangia  extending  inward  toward  the  axis.  They  are  not 
visible  until  the  cone  separates  into  its  component  parts.  Some 
Calamites  (Archaeocalamites)  agree  closely  with  this  mode  of 
organization,  but  in  others  the  structure  of  the  cones  was  more 
complicated,  this  being  brought  about  chiefly  by  the  insertion  of 
whorls  of  sterile  bracts  between  those  of  the  sporangiophores. 

The  Sphenophyllina,  known  only  from  the  Palaeozoic,  and  rep- 
resented by  the  genus  Sphenophyllum,  had  some  characters  of  the 
Equisetales.  The  slender,  little-branched,  and  probably  clinging 
stem  had  from  six  to  eighteen  wedge-shaped  or  linear  leaves  at 
the  swollen  nodes,  the  leaves  of  successive  whorls  not  alternating. 


940  PRINCIPLES    OF    STRATIGRAPHY 

The  structure  of  the  stem  is,  however,  more  like  that  of  lycopods, 
but  the  cone  again  suggests  affinities  with  the  Equisetales.  The 
sporangiophores,  however,  spring  from  the  bracts  instead  of  the 
axis.  The  class  combines  the  characters  of  ferns,  lycopods,  and 
Equisetales.  Their  nearest  living  relatives  are  probably  the  Psilo- 
tales  (Psilotum  and  Tmesipteris)  formerly  classed  with  the  Lyco- 
podiales. 

The  Lycopodina  are  represented  by  three  living  and  one  extinct 
orders.  The  Lycopodiales  are  represented  by  two  genera — Phyllo- 
glossum  with  one  species,  and  Lycopodium  with  nearly  a  hundred. 
Selaginella  with  between  300  and  400  species  and  Isoetes  with 
about  50,  mostly  aquatic,  species  are  each  the  sole  representatives 
of  their  respective  orders.  The  modern  genera  are  small  forms, 
but  the  extinct  orders  contained  some  of  the  largest  Palaeozoic 
trees,  reaching  100  feet  or  more  in  height.  A  general  external 
characteristic  of  these  plants  is  the  simple  form  of  the  leaves, 
which  are  generally  of  small  size,  while  the  sporangia  are  situated 
on  the  upper  surface  of  the  sporophylls.  In  structure  the  stem  is 
a  single  cylinder  (monostelic)  with  a  centripetal  development  of 
woody  tissue  (xylem).  The  earliest,  or  protoxylem,  is  at  the  periph- 
ery of  the  stele.  In  Selaginellales  the  stem  contains  one,  two, 
or  several  stele,  while  the  Lepidodendrales  are  monostelic,  as  in 
Lycopodium.  A  section  of  a  Lepidodendron  stem  shows  the  central 
pith,  often  destroyed,  surrounded  by  a  zone  of  primary  wood,  and 
outside  of  this,  in  most  cases,  a  zone  of  secondary  wood,  sharply 
defined  from  the  inner  zone  by  the  layer  of  protoxylem.  In  some 
of  the  smaller  species  the  wood  was  solid,  without  central  pith. 
The  cortex  or  bark  surrounds  this  and  is  bounded  externally  by  the 
persistent  leaf  scars.  In  Sigillaria  the  ring  of  primary  wood  is 
narrower.  The  leaf  scars  are  arranged  spirally  in  Lepidodendron, 
but  in  vertical  rows  in  Sigillaria.  Both  were  attached  to  large 
creeping  root-stocks  or  stigmaria,  which  were  provided  with 
numerous  cylindrical  "roots"  which  penetrated  the  soil  on  all 
sides. 

The  spores  of  lycopods  are  formed  in  sporangia  of  considerable 
size,  which  are  situated  on  the  upper  surface  and  near  the 
base  of  the  sporophylls.  These  are  arranged  in  definite  terminal 
cones,  or  they  may  resemble  the  foliage  leaves  and  occur  in  alter- 
nate zones  with  them.  In  Selaginella  the  sporophylls  are  arranged 
radially  in  the  cones,  these  terminating  the  branches.  A  single 
sporangium  is  borne  on  the  axis  just  above  the  insertion  of  each 
sporophyll.  Large  and  small  spores  (mega-  and  micro-spores) 
occur  in  this  genus,  but  in  Lycopodium  they  are  all  of  one  kind. 


PTERYDOPHYTA;  SPERMATOPHYTA     941 

In  the  Lepidodendrales  they  were  heterosporous,  at  least  in  some 
cases.  The  cones  of  Lepidodendron  and  allied  forms  (Lepidostro- 
bus)  vary  from  an  inch  to  a  foot  in  length,  according  to  species, 
and  are  borne  on  ordinary  or  on  special  branches.  The  sporophylls 
are  arranged  spirally  upon  the  axis  and  each  carries  a  single 
large  sporangium  on  its  upper  surface,  which  in  turn  carries  either 
an  enormous  number  of  minute  or  a  small  number  of  large  spores. 
The  upturned  and  overlapping  laminae  from  the  sporophyllae  form 
the  exterior  of  the  cone.  The  Lepidodendraceae  range  from  the 
Devonic  to  the  Permic,  while  the  Sigillariaceae  range  through  the 
upper  Palaeozoic  above  the  Devonic. 

The  Ferns  are  among  the  most  varied  of  existing  pteridophytes 
and  exhibit  a  wide  range  in  size,  from  the  little  epiphytic  Hymeno- 
phyllacea,  whose  fronds  are  hardly  a  centimeter  in  length,  to  gigan- 
tic tree-ferns,  80  feet  or  more  in  height.  The  leaves  or  fronds 
vary  from  simple  to  highly  compound,  each  pinna  or  pinnule  being 
characterized  by  a  mid-vein,  and  by  forking  lateral  veins.  The 
sporangia  are  borne  on  the  under  side  of  the  frond,  or  on  separate 
fronds.  In  the  Ophioglossales  a  separate  spike  is  produced.  In 
some  of  the  Palaeozoic  Cycadofilices  ( comprising  most  of  the  ferns 
of  that  period  *)  actual  seeds  instead  of  spores  were  produced,  the 
forms  also  being  intermediate  in  structure  of  the  stems,  etc.,  be- 
tween ferns  and  cycads.  The  water-ferns  or  Rhizocarps  (Hydro- 
pteridiales)  produce  both  mega-  and  micro-spores.  The  former 
produce  female,  the  latter  male,  prothallia.  The  common  pepper- 
wort,  Marsilea,  looking  like  a  small  four-leaved  clover,  is  a  good 
example. 

PHYLUM  V — SPERMATOPHYTA.  The  true  flowering  plants 
(Phanerogams),  or  seed-plants  (Spermatophyta),  comprise  the 
gymnosperms  and  the  angiosperms.  Conifers  are  the  most  abundant 
representatives  of  the  gymnosperms  in  the  northern  regions,  while 
the  palm-like  cycads  occur  in  tropical  districts.  They  are,  however, 
abundant  in  the  Jurassic  and  other  Mesozoic  deposits  of  America 
and  Europe.  The  late  Palaeozoic  Cordaitales  were  large  trees  with- 
wood  of  a  coniferous  type  (Daxoxylen  wood)  and  long  strap-shaped 
leaves. 

The  angiosperms,  including  all  the  true  flowering  plants,  are 
divided  into  the  Monocotyledons,  which  include  the  grasses,  palms, 
lilies,  etc.,  with  parallel-veined  leaves,  and  the  Dicotyledons  with 
net-veined  leaves.  The  latter  make  their  first  appearance  in  Co- 
manchic  time. 

*  Also  classed  as  a  separate  order  Pteridosperma  under  the  gymnosperms. 


942  PRINCIPLES    OF    STRATIGRAPHY 

ANIMALS. 

PHYLUM  I — PROTOZOA.  The  Protozoa  are  unicellular  animals 
either  naked  or  enclosed  in  a  cell  membrane.  In  addition,  many 
rhizopods  secrete  calcareous  or  siliceous  structures,  or,  by  cementa- 
tion, form  a  covering  of  foreign  substances.  One  or  more  nuclei 
are  generally  present,  and  reproduction  is  by  fission.  The  Rhizo- 
poda  include  the  Foraminifera,  which  secrete  shells  of  carbonate 
of  lime,  or  build  them  by  cementing  sand  grains,  etc.  The  shells 
have  one  or  more  chambers  (unilocular  or  multilocular).  If  many, 
they  increase  in  size  successively,  and  are  arranged  in  various  ways, 
including  nautilian  and  spiral  coiling.  In  many  forms  the  surface 
is  pierced  by  fine  pores — the  foramina — through  which  protoplasm 
is  extruded  in  fine  streamers  forming  the  pseudopodia.  In  size  the 
Foraminifera  shells  vary  from  minute  shells  to  those  an  inch  or 
more  in  diameter  (Nummulites).  They  range  from  the  Cambric  to 
the  present  with  several  thousand  species. 

.  The  Radiolaria  secrete  horny  or  siliceous  internal  structures, 
which  form  a  much  perforated  latticework,  ornamented  by  spines, 
bosses,  etc.  They  also  range  from  the  Cambric  to  the  present. 

PHYLUM  II — PORIFERA  (SPONGES).  The  sponges  are  aquatic 
multicellular  animals  in  which  the  body  is  penetrated  by  a  complex 
set  of  canals,  into  which  water  enters,  through  pores  in  the  outer 
wall.  From  the  canals  are  given  off,  at  intervals,  digestive  sacs,  and 
these  finally  converge  into  one  or  more  main  canals,  with  large  exter- 
nal excurrent  openings  or  oscula.  Modern  sponges  generally  secrete 
a  skeleton  of  horny  substance  (chitin)  and,  in  addition,  many  secrete 
siliceous  or  calcareous  rods  or  needles  (spicules)  which  are  often 
compound  in  form.  In  many  older  and  some  modern  forms,  these 
unite  into  solid  structures  so  that  the  form  of  the  sponge  is  pre- 
served. They  abound  in  all  marine  formations,  from  the  Cambric 
to  the  present.  The  number  of  extinct  and  living  species  is  very 
great. 

PHYLUM  III — CCELENTERATA.  The  coelenterates  have  a  body 
composed  of  two  cellular  layers,  the  ectoderm  and  endoderm,  the 
latter  enclosing  the  ccclomic  cavity  into  which  the  mouth  opens. 
An  intermediate  non-cellular  or  imperfectly  cellular  layer  is  often 
present  but  no  true  body  cavity  occurs.  The  animals  (polyps)  have 
a  simple  body  in  the  Hydrozoa — the  mouth  generally  at  the  end 
of  a  proboscis-like  elevation,  and  surrounded  by  tentacles.  Gen- 
erally they  are  compound,  many  polyps  being  united  by  hollow 
tubes.  Special  polyps  for  reproduction  (gonopolyps)  are  com- 
monly developed,  and  these  often  give  rise  to  medusae,  or  jelly-fish 


CCELENTERATA ;    MOLLUSCOIDEA  943 

— a  free-swimming  sexual  generation,  which,  however,  sometimes 
remains  attached  to  the  parent.  Many  Hydrozoa  secrete  a  horny 
or  chitinous  envelope,  which  ends  in  many  cases  in  cups  or  hydro- 
thecce.  In  the  fossil  graptolites  these  horny  structures  alone  are 
preserved,  as  compressed  carbonaceous  films.  In  other  cases 
(Hydrocorallines)  a  calcareous  structure  is  secreted,  which  may  be 
important  as  a  reef- former  (Millepora).  The  stromatoporoids  of 
the  Palaeozoic  are  believed  to  belong  to  this  group.  They  repre- 
sent enormous  accumulations  of  lime  taken  by  minute  organisms 
from  the  sea-water  and  built  into  their  structures.  These  are  often 
heads  of  great  size,  some  attaining  a  diameter  of  ten  feet. 

The  coral  or  anthozoan  polyp  is  more  complicated,  there  being, 
in  addition  to  the  parts  found  in  the  hydroid  polyp,  an  enteric  sac, 
or  stomodaum,  formed  by  invagination  of  the  mouth  area,  and  a 
series  of  fleshy  septa  or  mesenteries,  dividing  the  body  radially. 
Many  anthozoan  polyps  secrete  a  calcareous  structure  (coral) 
which  typically  is  characterized  by  a  series  of  radially  placed  calcar- 
eous plates  or  septa,  variously  united  by  transverse  structures  and 
surrounded  by  one  or  more  calcareous  walls.  In  Palaeozoic  time 
these  were  built  mostly  on  the  plan  of  four  and  grew  into  isolated 
horn-shaped  structures  on  the  broad  septate  end  of  which  the 
polyp  rested  (Tetraseptata) .  In  later  times  to  the  present  the  plan 
of  six  (Hexaseptata)  or  eight  (Octoseptata)  became  the  dominant 
one,  and  the  forms  became  compound,  so  that  in  some  modern 
coral  heads  thousands  of  individual  polyps  participate.  A  fourth 
group  in  which  the  septa  were  absent  or  represented  by  spines  only, 
while  the  walls  were  provided  with  pores  (Aseptata),  was  chiefly 
confined  to  the  Palaeozoic.  The  reproduction  of  the  Anthozoa  is 
carried  on  by  fission  and  by  ova. 

PHYLUM  IV — MOLLUSCOIDEA.  The  Molluscoidea  comprise  two 
classes  which  are  widely  different  in  their  external  adult  charac- 
ters but  closely  similar  in  their  early  life  history.  The  Bryozoa 
are  commonly  compound  aquatic  forms,  either  encrusting  other  ob- 
jects or  forming  solid  masses  not  unlike  in  form  to  some  early 
corals,  with  which  they  have  sometimes  been  united.  The  colony,  or 
zoarium,  consists  of  cells  (zo&cia)  generally  of  lime  and  loosely  or 
closely  aggregated,  in  the  latter  case  often  becoming  prismatic. 
They  are  hollow  or  divided  by  transverse  calcareous  partitions  or 
dissepiments  and  have  various  other  structures.  Smaller  tubes 
(mesopores)  are  present  in  some  cases.  Colonially  the  Bryozoa 
may  constitute  a  solid  mass  or  head,  a  flat  expansion,  a  network, 
in  which  large  open  spaces  are  left  between  series  of  zooecia  (as  in 
Fenestella,  etc.),  or  a  great  variety  of  other  forms.  In  Palaeozoic 


944  PRINCIPLES    OF    STRATIGRAPHY 

time,  when  the  number  of  specimens  was  considerably  over  a  thou- 
sand, they  often  acted  as  important  reef-formers.  Mesozoic  and 
Cenozoic  Bryozoa  (close  to  a  thousand  species)  also  contributed 
largely  to  calcareous  reefs.  (See  Chapter  X.)  The  animal  differs 
from  the  coral  polyp  by  the  possession  of  a  well-marked  body  cavity 
and  a  definite  alimentary  system. 

The  Brachiopoda  are  simple  animals  encased  in  a  shell  with 
dorsal  ventral  and  sometimes  accessory  valves.  In  general,  the 
ventral  valve  is  larger  and  some  provision  is  afforded  for  the 
emission  through  a  foramen  or  otherwise  of  the  fixing  organ,  or 
pedicle.  It  is,  hence,  called  pedicle  valve.  The  other  valve  carries 
supports  (crura  brachidia),  from  which  the  soft  internal  respira- 
tory organs,  the  brachia,  or  arms,  are  suspended ;  hence  the 
name  brachial  valve  is  applied.  The  accessory  pieces  are  either 
a  third  shell  plate  (pedicle  plate,  deltidial  plate}  secreted  by  the 
pedicle,  or  a  double  set  of  plates  (deltidial  plates}  meeting  in  the 
center  below  the  foramen.  These  accessory  plates  are  commonly 
very  small  and  situated  below  the  beak  of  the  pedicle  valve.  Open- 
ing and  closing  of  the  valves  is  effected  by  muscular  systems.  Sur- 
ficially  the  shells  are  either  smooth  or  variously  plicated,  and 
sometimes  spines  are  developed.  There  are  about  140  living  and 
over  6,000  fossil  species. 

PHYLUM  V — MOLLUSCA.  The  molluscs  are  soft-bodied  animals 
generally  enclosed  in  a  calcareous  shell.  The  headless  molluscs,  or 
Pelecypoda,  have  a  shell  of  two,  generally  symmetrical  valves  placed 
right  and  left  and  united  dorsally  by  a  hinge,  which  generally  in- 
cludes a  series  of  interlocking  hinge-teeth  and  sockets.  The  valves 
are  opened  either  by  an  external  ligamental  structure  variously  ar- 
ranged or  by  an  internal  compressible  resilium  which  often  has 
special  supports  or  resilifers  developed.  The  shell  is  closed  by  the 
adductor  muscles,  of  which  there  are  typically  an  anterior  and  a 
posterior  one  (dimyarian),  or  only  one,  situated  subcentrally 
(monomyarian) .  Externally  the  shell  is  smooth,  showing  only 
growth  lines,  or  it  may  be  ornamented  by  radiating  plications  or 
striations,  or  by  marked  concentric  ribs  parallel  to  the  growth-lines. 
A  horny  outer  covering,  or  periostracum,  is  generally  present.  The 
animal  is  provided  with  an  anterior  hatchet-shaped  foot,  and  with 
gills  which  hang  in  pairs  on  opposite  sides -of  the  abdomen,  and 
with  a  mantle,  the  attachment  of  which  to  the  shell  is  marked 
by  the  pallial  line,  and  the  outer  portion  of  which  secretes  the  shell. 
The  remainder  of  the  mantle  secretes  the  inner  shell  layer  (nacre- 
ous layer),  which  is  often  iridescent.  A  pair  of  siphons  (excurrent 
and  incurrent)  is  frequently  formed,  their  presence  being  generally 


MOLLUSCA  945 

indicated  by  a  pronounced  reentrant  in  the  pallial  line  below  the 
posterior  adductor  impression  (pallial  sinus). 

The  cephalophorous  mollusca  build  a  shell  of  only  one  part, 
though  extra  horny  or  shelly  pieces,  not  secreted  by  the  mantle,  may 
occur.  Such  are  the  opercula  of  certain  gastropods  and  the  aptychi 
of  ammonite  cephalopods.  In  the  gastropods  the  animal  is  pro- 
vided with  a  lingual  ribbon,  or  radula,  beset  with  teeth  and  having  a 
rasping  function.  In  the  cephalopods  horny  jaws  are  developed. 
In  Gastropoda  the  shell  is  normally  a  spiral  one,  though  in  some 
cases  the  coiling  is  in  a  single  plane,  as  is  typical  of  coiled  cephalo- 
pods. Both  right-  and  left-handed  coils  occur,  the  former  being 
more  common,  while  the  left-handed  coils  are  variations  in  some 
cases,  but  fixed  types  in  others.  The  apex  of  the  shell  is  formed 
by  the  protoconch,  generally  somewhat  differentiated  from  the 
conch.  The  latter  may  be  smooth  (except  for  growth  lines)  but 
is  more  generally  ornamented  by  plications  (spirals)  and  by  ribs 
which  extend  across  the  whorl  from  suture  to  suture.  The  ribs 
may  become  concentrated  into  spiral  rows  of  nodes,  or  spines  (hol- 
low emarginations  of  the  shell-lip)  may  result.  Temporary  resting 
stages  in  shell  growth  are  often  marked  by  varices  consisting  of 
abrupt  deflections  of  the  lip,  or  by  rows  of  spines  (Murex).  The 
mouth  of  the  shell  is  in  many  cases  drawn  out  into  an  anterior 
notch  or  a  long  canal.  The  inner  or  columellar  lip  of  specialized 
types  is  marked  by  oblique  plications.  Old  age  or  phylogerontic 
forms  often  have  the  last  whorl  loose-coiled  or  straight.  The  shell 
of  primitive  cephalopods  is  a  straight  cone  (Orthoceras)  divided 
regularly  by  transverse  septa,  which  are  pierced  by  the  siphuncle. 
All  the  resulting  chambers  are  empty,  representing  cut-off  space 
as  the  shell  became  too  small  for  the  growing  animal,  which  finally 
occupied  only  the  large  outer  or  living  chamber.  When  the  cham- 
bers are  all  filled  with  hardened  mud  and  the  shell  is  broken  away, 
the  edges  of  the  septa  are  seen,  forming  the  suture.  In  Nautiloidea 
this  suture  is  generally  simple,  but  in  Ammonoidea  it  is  often  much 
fluted  so  as  to  produce  a  complicated  pattern.  The  siphuncle  of 
nautiloids  is  generally  at  or  near  the  center,  while  that  of  the  am- 
monoids  is  external.  Curved  forms  (Cyrtoceras),  loose-coiled 
(Gyroceras),  and  close-coiled  (Nautilus  and  Ammonites)  shells  are 
progressively  developed.  Old  age  individuals,  or  phylogerontic 
groups,  generally  lose  the  power  of  coiling  in  the  last  whorl,  which 
may  be  loose-coiled  or  even  straight. 

Baculites,  one  of  the  last  survivors  of  the  ammonoids,  was 
straight  except  for  the  very  earliest  portion,  which  was  coiled. 
The  ammonoids  are  all  extinct,  ending  with  the  Cretacic.  Nautil- 


946  PRINCIPLES    OF    STRATIGRAPHY 

oids  are  represented  by  the  living  Nautilus.  These  two  groups 
are  classed  as  Tetrabranchiata.  The  Dibranchiata  are  represented 
by  the  living  Argonauta,  the  Octopus,  Squid,  Cuttlefish,  and 
Spirula.  The  last  is  an  internal  loose-coiled  shell  with  septa  and 
siphuncle.  A  straight-coiled  ancestor,  the  Jurassic  and  Cretacic 
Belemnites,  had  its  shell,  which  was  straight,  protected  by  a  heavy 
calcareous  outer  guard,  often  cigar-shaped,  and  when  perfect 
showing  the  hollow  at  one  end  occupied  by  the  shell.  A  modified 
portion  of  the  guard  alone  remains  in  the  cuttlefish,  the  so-called 
cuttlefish  bone,  which  is  embedded  in  the  fleshy  mantle  of  the 
animal. 

The  Pteropoda  have  thin  transparent  shells  of  various  shapes, 
but  rarely  coiled.  The  "foot"  of  the  animal  is  divided  into  two  wing- 
like  appendages  by  which  these  ''Butterflies  of  the  sea"  keep  them- 
selves afloat  on  the  water.  The  shell  of  the  Conulariida  and  Hyo- 
lithida  was  coarser  and  generally  rectangular  in  section  in  the 
former  and  variously  shaped  in  the  latter.  The  Scaphopoda  (Den- 
talium,  etc.)  have  conical,  often  curved,  shells,  open  at  both  ends, 
which  begin  as  a  saddle-shaped  structure  growing  into  a  ring  and 
increasing  in  length.  In  the  Polyplacophora  (Chiton,  etc.)  the  shell 
is  composed  of  several  pieces  arranged  serially. 

Pelecypoda  are  rare  in  the  Cambric  but  become  abundant  in 
the  succeeding  horizons.  There  are  about  10,000  fossil  species  and 
about  5,000  recent  ones.  The  Gastropoda  are  likewise  sparsely 
represented  in  the  Cambric.  They  appear  to  be  at  their  acme  of 
development  at  the  present  time,  there  being  some  15,000  living 
species,  as  compared  with  about  half  that  number  or  less  of  fossil 
ones.  Only  one  cephalopod  is  known  from  the  Cambric.  They 
abound  in  the  Ordovicic,  at  the  end  of  which  period  many  races 
died  out,  while  new  ones  arose.  The  Ammonoidea  begin  in  the 
Devonic,  reach  their  acme  in  the  Jurassic  and  die  out  in  the  Cretacic. 
The  Nautiloidea  and  Dibranchiata  (the  latter  appearing  first  in  the 
Trias)  have  modern  representatives. 

PHYLUM  VI — PLATYHELMINTHA,  AND  VII — VERMES.  The  pla- 
tyhelminths,  or  flat-worms,  are  soft-bodied,  worm-like  animals  with- 
out body  cavity  or  ccelom.  They  have  no  hard  parts,  and  nothing  is 
known  of  their  geological  history.  The  great  mass  of  animals 
classed  together  as  Vermes  is  in  reality  a  heterogeneous  assemblage, 
many  of  the  groups  having  no  direct  relationship  with  others  placed 
here.  Typical  worms  (chaetopods)  have  a  distinct  body  cavity  from 
which  the  enteric  and  digestive  tracts  are  separated.  The  body  is 
divided  into  many  similar  segments,  each  of  which,  except  the  oral 
one,  carries  on  each  side  two  bundles  of  bristles  or  setae,  a  dorsal 


VERMES;    ARTHROPODA  947 

and  a  ventral  one,  placed  typically  on  elevations  or  parapodia.  The 
head  segment  carries  appendages  varying  in  the  different  sub- 
classes. Aquatic  worms  possess  gills  for  breathing,  but  these  be- 
come more  or  less  modified  or  even  entirely  lost  in  the  mud-  and 
earth-worms.  The  alimentary  system  consists  of  an  anterior  mouth, 
an  intestinal  canal,  divisible  into  fore-gut,  mid-gut  and  hind-gut,  and 
ending  in  the  posterior  anus.  In  some  parasitic  forms,  this  system 
is  much  degenerated.  In  some  chaetopods  a  series  of  horny  cesoph- 
ageal  teeth  is  developed,  and  these  are  often  preserved  in  great  per- 
fection. The  conodonts  may  be  of  this  order. 

Many  worms  build  tubes  of  agglutinated  sand,  either  free,  or 
in  the  sand,  while  others  secrete  calcareous  tubes.  These  are  often 
well  preserved  and  show  the  presence  of  these  organisms  in  Cam- 
bric times.  Trails  left  by  errant  worms  on  mud  and  the  peculiar 
form  of  the  string  of  sand,  which  has  passed  through  the  annelid 
body,  all  serve  as  evidence  of  the  existence  of  the  worms  in  former 
periods. 

PHYLUM  VIII — ARTHROPODA.  The  arthropods,  or  jointed- 
legged  invertebrates,  comprise  a  number  of  distinct  assemblages  of 
organisms,  as  indicated  by  the  several  classes  included.  The  crus- 
taceans are  in  many  respects  the  most  characteristic,  but  even  they 
comprise  a  number  of  subclasses  of  very  diverse  characters.  The 
Myriopoda  and  Peripatus  are  worm-like.  The  former  occur  first 
in  the  Old  Red  Sandstone  (Devonic)  and  are  common  in  the  Car- 
bonic. The  oldest,  and  in  some  respects  the  most  generalized,  of 
the  Crustacea  are  the  Trilobites,  which  are  already  highly  developed 
and  very  numerous  in  the  Cambric.  They  do  not  extend  beyond 
the  Palaeozoic.  The  organism  is  covered  by  a  chitinous  exoskeleton 
in  which  a  head  or  cephalon,  a  thorax  and  an  abdomen  or  pygidimn 
are  distinguishable.  Each  division  consists  of  a  median  axis  and 
lateral  lobes  and  hence  shows  a  trilobate  division.  The  axis  of 
the  head  constitutes  the  glabella  and  the  lateral  portions  are  com- 
monly divided  into  fixed  and  free  cheeks,  the  latter  generally  carry- 
ing the  compound  eyes.  The  thorax  is  divided  into  a  number  of 
movable  rings,  but  the  pygidium  is  a  single  though  grooved  piece. 
The  mouth  is  ventral  and  the  head  is  provided  with  antennas. 
Jointed  thoracic  legs  were  also  present.  The  Entomostraca  are 
modified  crustaceans  with  a  shell-like  carapace.  They  are  repre- 
sented in  all  geological  horizons.  The  Ostracoda,  with  a  bivalve 
shell,  were  especially  abundant  in  the  Palaeozoic.  The  barnacles 
also  had  representatives  in  the  Palaeozoic  but  are  more  typical  in 
later  horizons.  The  animal  is  degenerate,  attached  either  directly 
or  by  a  fleshy  stalk.  In  the  former  case  a  circle  of  shell-plates  is 


948  PRINCIPLES    OF    STRATIGRAPHY 

developed,  forming  the  corona.  The  Phyllocarlda  were  of  great 
importance  in  the  Palaeozoic.  They  generally  had  head  and  thorax 
enclosed  in  a  carapace  consisting  mainly  of  two  valves,  with  acces- 
sory pieces.  The  ringed  abdomen  and  the  tailpiece  or  telson  (often 
triple)  projected  beyond  the  carapace. 

The  Decapoda  have  head  and  thorax  united  into  a  cephalo- 
thorax,  and  covered  by  a  single  carapace,  or  with  one  segment 
free.  Each  of  the  thirteen  cephalothoracic  segments  has  a  pair  of 
jointed  appendages,  some  of  which  are  modified  into  antennae  or 
mouth-parts.  The  abdomen  consists  of  seven  segments,  the  terminal 
one  being  a  telson.  In  the  Macrura  (lobsters,  crayfish,  etc.)  these 
segments  are  all  visible,  but  in  the  Brachiura  (crabs)  they  are  gen- 
erally turned  under  the  carapace.  Locomotor  appendages  (perelo- 
poda)  are  in  five  pairs,  and  with  few  exceptions  each  consists 
of  seven  joints.  Some  of  the  final  joints  are  claw-like,  others 
paddle-like,  and  others  again  merely  pointed  for  walking  pur- 
poses. Six  pairs  of  abdominal  legs  occur.  The  claws  are  often 
found  fossilized  separately.  Decapods  first  appear  in  the  Triassic. 
The  remaining  orders  show  various  modifications  of  the  decapod 
type.  They  are  mostly  rare  as  fossils. 

Among  the  Acerata  the  Merostomata  are  in  many  respects  of 
greatest  interest.  Some  Eurypterida  in  the  Devonic  reached  a  length 
of  six  feet,  but  were  smaller  in  other  horizons.  The  Limulava  are 
known  only  from  the  Middle  Cambric.  They  combined  trilobite 
with  eurypterid  characters.  The  eurypterids  had  a  short  cephalo- 
thorax,  a  ringed  abdomen  and  a  telson,  the  body,  as  in  Crustacea, 
being  covered  with  a  chitinous  exoskeleton,  which  was  repeatedly 
shed.  A  pair  of  compound  eyes  and  a  pair  of  median  simple  eyes 
or  ocelli  formed  the  chief  dorsal  features  of  the  carapace.  Ventrally 
this  bore  six  pairs  of  jointed  appendages,  the  first  preoral  and  che- 
late,  the  others  non-chelate,  the  last  usually  forming  a  large  paddle. 
The  first  six  segments  of  the  abdomen  bore  broad,  leaf-like  append- 
ages, referable  to  "gills."  The  posterior  segment  and  telson  were 
without  appendages.  The  number  of  known  species  is  over  150. 
The  Synxiphosura  (Cambric  to  Siluric,  few  species)  had  a  trilo- 
biti-form  abdomen,  which,  in  the  adult  Xiphosura,  of  which  Limu- 
lus,  the  horseshoe  crab,  is  the  only  living  example,  was  fused  into  a 
single  piece,  though  still  indicating  the  segments  and  trilobation. 
The  fossil  species  (few  in  number)  have  been  obtained  from  the 
Upper  Devonic,  the  Carbonic,  and  (genus  Limulus,  only)  from 
the  Mesozoic  and  Tertiary  of  Europe. 

The  scorpions  and  spiders  are  more  complex  Acerata  adapted 


INSECTA;    ECHINODERMATA  949 

to  a  terrestrial  life.  The  former  are  known  from  the  Siluric 
(Upper),  the  latter  from  the  Coal  Measures  on. 

Altogether  more  than  300  fossil  species  of  arachnids  and 
several  thousand  modern  species  are  known. 

Insects  are  known  from  the  Ordovicic  graptolite  slates  of 
Sweden  and  from  the  Siluric  of  France.  They  are  especially  well 
preserved  in  the  Carbonic  and  later  terrestrial  formations.  The 
Palaeozoic  forms  constitute  a  distinct  group  with  14  orders,  all  ex- 
tinct. Two  other  orders  were,  however,  also  represented  in  the  late 
Palaeozoic,  the  cockroaches  (Blattoidea)  being  especially  well  repre- 
sented on  account  of  the  hard  coriaceous  character  of  the  front 
wings  or  teginina.  The  number  of  known  Palaeozoic  insects  is  close 
to  1,000  species  while  the  Tertiary  and  Quaternary  have  furnished 
over  5,800  species.  There  are  over  384,000  living  species  (Hand- 
lirsch). 

PHYLUM  IX — ECHINODERMATA.  The  echinoderms  or  spiny- 
skined  animals  are  characterized  generally  by  an  apparently  radial 
form,  by  the  possession  of  calcareous  plates  or  sclerites  in  the  in- 
tegument, and  by  an  elaborate  internal  structure,  the  most  marked 
portion  of  which  is  the  highly  developed  water-vascular  system. 
The  oldest  known  forms  are  the  Cystoidea  (Cambric  to  Car- 
bonic) in  which  the  body  was  enclosed  in  a  calyx  of  irregular 
plates,  closely  united  by  sutures  and  generally  supported  on  a 
stem.  Arms  were  rudimentary  and  the  respiratory  and  water- 
vascular  system  were  not  pronounced.  The  Blastoidea  (Ordovicic 
to  Carbonic)  were  more  regular  in  the  arrangement  of  plates  and 
were  armless.  The  calyx  was,  however,  provided  with  five  petaloid 
ambulacral  areas  radiating  from  the  mouth.  The  Crinoidea  (Ordo- 
vicic to  Recent)  were  mostly  stemmed,  though  some  had  the  power 
of  separation  in  the  adult.  The  calyx  is  composed  of  regular  plates 
generally  arranged  in  five  series  and  terminated  by  branching  or 
simple  arms  often  of  great  length.  The  mouth  of  many  Palaeozoic 
forms  (Camerata)  was  under  a  vaulted  arch  or  tegmen,  and  the 
anus  was  often  placed  at  the  end  of  a  tube  or  proboscis.  The 
brittle-stars  and  starfish  have  the  body  cleft  into  five  or  more 
movable  rays,  which  are  supplied  with  branches  from  the  water- 
vascular  system  and  diverticula  from  the  other  body  organs.  The 
branch  begins  in  the  Ordovicic,  but  has  few  fossil  representatives. 
The  sea-urchins  or  Echini,  on  the  other  hand,  are  abundantly  repre- 
sented in  the  Mesozoic  and  later  strata.  Palaeozoic  forms  occur  as 
early  as  the  Ordovicic  (Bothriocidaris).  In  them  the  body  is  gen- 
erally covered  by  a  large  number  of  plates,  which,  however,  fall 
into  ten  zones,  five  anibulacral,  with  plates  pierced  for  the  tubed 


950  PRINCIPLES    OF    STRATIGRAPHY 

feet  or  ambulacra,  and  five  inter  ambulacral.  The  whole  forms  a 
more  or  less  solid  corona.  In  the  post- Palaeozoic  types  each  zone  is 
generally  composed  of  two  columns  of  plates,  so  that  there  are  in 
all  20  columns,  forming  5  ambulacral  and  5  interambulacral  zones. 
The  mouth  and  anus  are  generally  opposite  each  other  in  the 
Palccechinoidea,  and  in  the  Cidaroidea  and  Diadematoidea.  In  the 
others  the  anus  migrates  toward  the  mouth.  The  Clypeosteroidea 
and  Spatangoidea  show  an  elongation  of  form,  with  a  pronounced 
bilateral  symmetry.  In  most  of  the  Spatangoidea  the  mouth  passes 
forward,  so  as  to  lie  no  longer  in  the  median  axis.  In  the  IIolo- 
thuroidea  the  plates  of  the  integument  are  not  united,  the  body 
thus  being  soft  and  changeable  in  form  by  inflation.  The  separate 
plates  are  found  fossil  as  early  as  the  Carbonic. 

PHYLUM  X — PROTOCHORDA.  These  are  soft-bodied  animals, 
some  of  them,  as  the  Tunicates,  degenerate,  but  showing  affinities 
with  the  vertebrates,  in  the  possession  of  a  notochord,  branchial 
slits,  and  a  central  nervous  system.  The  Cephalochorda  (Am- 
phioxus)  are  fish-like  and  readily  mistaken  for  a  vertebrate,  while 
the  Enter opneusta  (Balanoglossus)  are  worm-like.  While  some  of 
these  have  been  considered  ancestral  to  vertebrates,  it  is  not  at  all 
impossible  that  the  suggestive  characters  are  independently  de- 
veloped. Vertebrates  arose  in  the  Palaeozoic,  and  no  modern  form 
is  likely  to  preserve  intact  all  the  primitive  characters  of  a  class. 

PHYLUM  XI — VERTEBRATA.  This,  the  most  highly  specialized 
phylum  of  the  animal  kingdom,  has  its  most  primitive  representa- 
tive in  the  Ostracoderma  of  the  early  Palaeozoic  (Cephalaspis, 
Pterichthys,  Bothriolepis,  etc.).  Known  definitely  from  the  De- 
vonic  and  Siluric,  there  are  fragments  indicating  their  existence 
in  the  Upper  Ordovicic  of  America.  They  retain  many  characters 
of  invertebrates  and  seem  to  unite  the  fish  with  the  eurypterids,  a 
group  of  Merostomes,  which  flourished  at  the  same  time.  (See 
Patten-2i ;  22.)  Their  most  striking  characteristic  was  a  well- 
developed  armor,  or  exoskeleton  of  bony  plates,  which  covered  the 
head  and  anterior  portion  of  the  body.  The  endoskeleton  was  not 
calcified  and  the  mouth  without  hard  parts.  Hence  all  we  know 
of  them  is  from  the  external  plates  and  scales.  The  Devonic 
Arthrodira  have  also  been  regarded  as  an  independent  class,  differ- 
ing from  fishes  in  that  their  jaw  elements  are  merely  dermal  ossifi- 
cations and  are  not  articulated  with  the  skull  (Dean).  The  head 
and  trunk  are  covered  by  symmetric  bony  plates,  the  head-shield 
is  movably  articulated  with  the  body-shield.  The  endoskeleton  is 
superficially  calcified,  and  paired  fins  are  rudimentary  or  absent. 
The  Devonic  Coccosteus,  Dinichthys  and  Titanichthys  are  examples. 


VERTEBRATA:    PISCES  951 


Pisces. 

The  Cyclostomata  (Agnatha)  represented  to-day  by  the  lam- 
preys, appear  to  have  had  some  representatives  in  the  remarkable 
Palaeospondylus  of  the  Old  Red  Sandstone.  The  Conodonts  have 
been  regarded  as  teeth  of  myxinoids.  The  elasmobranchs,  or 
sharks,  were  well  represented  in  the  Devonic  and  later  beds,  the 
first  three  orders  being  wholly  confined  to  the  Palaeozoic.  The 
endoskeleton  is  more  or  less  cartilaginous,  the  exoskeleton  and 
teeth  structurally  identical  (placoid  scales).  Generally  only 
teeth,  calcified  vertebrae  and  dermal  spines  are  preserved.  The 
true  sharks  and  rays  (Plagiostomi)  are  mostly  Mesozoic  and  later, 
but  examples  from  the  Carbonic  and  even  the  Mississipic  are 
known.  The  chimaeras,  however  (Holocephali),  had  representa- 
tives from  the  Devonic  on. 

The  ganoids  are  remarkable  in  that  their  trunk  and  tail  are 
usually  covered  with  scales,  consisting  of  a  thick  bony  inner  layer, 
and  an  outer  layer  of  enamel,  the  scales  being  in  some  groups  articu- 
lated by  a  peg-and-socket  arrangement,  and  in  others  overlapping. 
The  skull  is  covered  with  dermal  bones,  or  completely  ossified. 
The  vertebral  column  is  cartilaginous  or  shows  various  degrees  of 
ossification.  Most  of  the  Palaeozoic  ganoids  belong  to  the  order 
Crossopterygii  or  fringe-finned  ganoids.  Such  are  the  Devonic 
genera  Holoptychius  and  Osteolepis — and  numerous  Mississippi 
to  Permic  genera.  Other  crossopterygians  occur  in  the  Mesozoic, 
and  two  genera  (Polypterus  and  Calamoichthys)  are  still  living  in 
the  rivers  of  tropical  Africa.  The  cartilaginous  ganoids  (Chon- 
drostei)  range  from  the  Mesozoic  to  the  present  time,  a  number  of 
genera  being  still  extant,  such  as  the  sturgeons  and  paddle-fish. 

A  considerable  number  of  Palaeozoic  forms  also  belong  to  the 
Heterocerci,  an  order  ranging  from  the  Devonic  (Cheirolepis)  to 
the  Upper  Jurassic  (Coccolepis  of  the  Lithographic  beds).  Many 
Carbonic  and  Permic  species  (including  Palaeoniscus,  Platysomus, 
etc.,  the  common  forms  of  the  Kupferschiefer  of  Thuringia,  etc.), 
belong  to  this  order,  as  well  as  the  Triassic  Catopterus  of  North 
America.  The  Lepidostei  include  the  "bony  pikes"  (Lepidosteus) 
of  the  North  American  rivers,  and  many  Cenozoic  and  Mesozoic 
genera,  but  only  one  genus  (Acentrophorus)  has  Permic  representa- 
tives. Here  belong  the  widely  distributed  Triassic  Semionotus  and 
the  many  common  Jurassic  genera  (Dapedius,  Lepidotus,  Eugna- 
jthus,  Caturus,  etc.),  the  order  being  at  its  height  at  that  time. 
The  Amioidei  also  have  a  surviving  genus  (Amia)  in  the  rivers  of 


952  PRINCIPLES    OF    STRATIGRAPHY 

the  southern  United  States  and  Central  America,  while  other  mem- 
bers extend  as  far  back  as  the  Lias. 

The  Dipnoi,  or  Lung-Fishes,  range  from  the  Devonic  to  the 
present  time.  Their  skeleton  is  chiefly  cartilaginous,  but  the  upper 
and  lower  vertebral  arches,  the  ribs  and  fin-supports  exhibit  a  ten- 
dency toward  ossification.  They  have  paddle-shaped,  paired  fins 
and  a  highly  specialized  air-bladder  which  serves  as  a  lung.  Dental 
plates  are  common  in  the  Devonic  (Dipterus)  and  Carbonic  (Cte- 
nodus),  while  many  perfect  specimens  also  occur  in  these  deposits. 

These  fish  may  be  considered  as  approaching  Amphibians  in 
many  respects.  The  Teleosts,  or  bony  fishes,  appear  first  in  the 
Triassic  deposits,  and  increase  in  prominence  until  they  are  the 
leading  type  to-day. 

Amphibia. 

The  Amphibia  are  cold-blooded  terrestrial  vertebrates,  with 
partly  branchial  respiration,  in  early  stages,  while  in  some  forms 
gills  remain  functional  throughout  life.  The  limbs  are  never  fins 
and  are  rarely  absent.  The  Stegocephalia  (Carbonic  to  Upper 
Trias)  comprise  the  largest  known  Amphibians,  and  were  pro- 
tected by  a  dermal  armor  of  bony  scales  or  scutes.  The  teeth  were 
sharply  conical,  with  a  large  pulp-cavity,  and  the  walls  were  some- 
times highly  complicated  by  infolding  of  the  dentine  (Labyrintho- 
donts).  The  Gymnophiona  or  ccecilians  are  vermiform  amphibia, 
covered  with  scales  and  without  limbs.  They  are  restricted  to  the 
South  American  and  Indo- African  tropics.  The  Urodeles  are 
naked  bodied,  usually  with  two  pairs  of  short  limbs  and  persistent 
tail.  Gills  often  remain  throughout  life.  The  vertebrae  are  usually 
completely  ossified.  This  group  appears  first  in  the  Upper  Jurassic 
(Wealden),  and  has  living  representatives  in  the  newts  and  sala- 
manders. The  Anura  (frogs,  toads)  are  tailless  and  develop  by 
metamorphosis.  The  oldest  fossil  forms  are  from  the  Eocenic. 


Reptilia. 

Reptilia  are  cold-blooded,  naked,  scaly  or  armored  vertebrates 
of  terrestrial  or  aquatic  habit,  and  breathing  exclusively  by  lungs. 
There  is  no  metamorphosis  during  development.  The  Rhyncho- 
cephalia  date  from  the  Permic,  but  were  most  extensively  repre- 
sented in  the  Trias.  A  single  living  genus  (Hatteria  or  Spheno- 
don)  occurs  in  New  Zealand.  '  The  body  was  lizard-like,  long- 


VERTEBRATA;    REPTILIA  953 

tailed  and  sometimes  scaly.  The  Squamata  comprise  the  lizards 
and  snakes  and  two  extinct  groups  of  aquatic  reptiles  from  the 
Cretacic  (Mosasaurus,  etc.).  The  lizards  (Lacertilia)  have  1,925 
living  species  but  few  fossil  ones  are  known,  the  oldest  being  from 
the  late  Jurassic.  Of  the  snakes  (Ophid-ia)  nearly  1,800  recent 
species  but  only  about  35  fossil  ones  are  known,  chiefly  from  the 
Tertiary,  though  some  Cretacic  forms  are  probably  referable  to 
snakes.  The  Ichthyosauria  are  entirely  extinct  reptiles  which  in- 
habited the  Triassic,  Jurassic,  and  Cretacic  seas.  Their  body  was 
in  general  whale-  or  fish-like  and  the  jaws  were  furnished  with  nu- 
merous conical  teeth. 

The  Sauropterygia,  also  restricted  to  the  Mesozoic,  were  mostly 
marine,  lizard-like  reptiles,  with  long  necks  and  well-developed 
limbs,  with  five  normal  digits  (N othosauridce  Triassic)  or  paddle- 
shaped,  the  digits  elongated  by  supernumerary  phalanges  (Plesio- 
saurida,  Trias  to  Cretacic).  The  Theromorpha  were  primitive  land 
reptiles  with  many  mammalian  characters  and  often  of  grotesque 
forms  and  proportions  (Pareiasaurus,  Dicynodon,  etc.).  They 
lived  in  the  Permic  and  the  Triassic  of  North  America,  Europe, 
and  South  Africa. 

The  Chelonians  or  turtles  are  characterized  by  the  possession 
of  a  more  or  less  complete  bony  shell,  partly  composed  of  modified 
neural  spines  of  the  dorsal  vertebrae  and  partly  of  dermal  ossifica- 
tions more  or  less  intimately  united  with  the  former.  The  limbs, 
tail,  and  generally  the  neck  and  head  can  be  withdrawn  into  this 
shell.  In  general  a  dorsal  shield,  or  carapace,  and  a  ventral  one, 
or  plastron,  composes  this  shell  and  both  are,  as  a  rule,  superficially 
covered  by  a  horny  or  leathery  epidermal  layer  divided  by  grooves 
or  sutures  into  a  few  large  scutes  or  shields.  Their  arrangement 
is  independent  of  the  underlying  osseous  plates.  Turtles  first  ap- 
peared in  the  Upper  Triassic  (Keuper)  of  Europe. 

The  Crocodilia  are  lizard-like  reptiles  with  the  highest  internal 
organization  of  the  class.  Their  skeletal  structure  differs  widely 
from  that  of  lizards,  and  their  respiratory  organs  resemble  those 
of  birds.  The  entire  body  is  covered  with  horny  scales.  The  most 
primitive  groups  (Parasuchia),  resembling  the  Rhynchocephalia, 
occur  in  the  Trias  of  America  (Belodon  or  Phytosaurus,  and  Epis- 
coposaurus)  ;  of  Scotland  (Stagonolepis)  ;  and  the  Gondwana 
formation  of  India  (Parasuchus).  There  are  also  more  specialized 
Triassic  forms,  such  as  the  little  Aetosaurus  (of  which  24  complete 
individuals  occur  on  a  single  block  of  Stuben-sandstone  [Upper 
Keuper]  in  the  Stuttgart  Museum),  and  others  from  the  Trias  of 
Elgin,  Scotland. 


954  PRINCIPLES    OF    STRATIGRAPHY 

Typical  marine  Crocodiles  occur  in  the  Jurassic  and  Comanchic 
(Mesosuchia),  while  in  the  Cretacic-Tertiary  and  modern  times 
these  crocodiles  (Eusuchia)  again  lived  chiefly  in  fresh  water  and 
on  the  land.  They  include  both  long-snouted  (longirostral)  and 
broad-snouted  (brevirostral)  forms,  the  latter  comprising  the  alli- 
gators. 

The  Dinosauria  were  long-necked  and  long-tailed  reptiles  with 
limbs  adapted  for  support  of  the  body.  The  earliest  species  were 
Triassic,  the  latest  Cretacic.  A  bony  exoskeleton  was  developed  in 
some  forms,  consisting  of  isolated  bony  plates  or  spines,  or  of 
interlocking  scutes  forming  a  continuous  shield.  Most  dinosaurs, 
however,  were  naked  or  covered  by  scales.  The  skull  of  most  forms 
was  extremely  small  in  proportion  to  the  body,  while  the  legs  in 
many  cases  were  exceedingly  massive. 

The  Pterosauria,  or  winged  lizards,  ranged  from  the  Trias  to  the 
Cretacic,  and  their  whole  organization  was  adapted  to  an  aerial  ex- 
istence. They  ranged  from  the  size  of  a  sparrow  to  forms  which  had 
a  spread  of  wing  of  nearly  six  meters.  The  skull  was  bird-like  and 
generally  fitted  with  sharp,  conical  teeth,  mostly  long  and  sharply 
pointed  in  front  (Pteranodon,  Nyctodactylus,  Ramphorhynchus), 
but  sometimes  blunt  (Dimorphoden).  The  neck  and  tail  were  gen- 
erally long.  The  fifth  digit  of  the  hand  consisted  of  four  enor- 
mously elongated  phalanges,  which  were  turned  backward  to 
support  the  wing  membrane.  Three  families  are  known :  Rham- 
phorhynchidce  (Jurassic),  Pterodactylida  (Upper  Jurassic  and 
Cretacic),  and  Ornithocheirida  (Pteranodon,  etc.)  Cretacic. 


Aves. 

The  birds  form  a  homogeneous  and  circumscribed  class  derived 
from  the  reptiles  and  partaking  of  their  character  in  the  Jurassic 
and  Cretacic,  where  teeth  and  a  vertebrated  tail  still  existed.  The 
exoskeleton  consists  of  feathers,  horny  coverings  for  the  beak, 
claws,  etc.  The  endoskeleton  is  compact  but  light,  the  bones  being 
permeated  by  air-cavities  with  thin  but  dense-textured  walls,  rich  in 
calcium  phosphate.  The  vertebrae  have  peculiar  saddle-shaped  ar- 
ticulations which  allow  great  freedom  of  movement.  The  bones  of 
the  forearm  are  modified  into  wings.  The  oldest  bird,  Archseop- 
teryx  of  the  Jurassic,  had  its  jaws  provided  with  conical  teeth  like 
those  of  reptiles,  and  its  vertebral  column  had  about  20  caudal  verte- 
brae. The  Odontolcse  (with  Hesperornis)  and  Odontonncz  (with 
Ichthyornis)  also  had  toothed  jaws,  but  other  birds  were  free  from 


AVES;    MAMMALIA  955 

them.  The  Struthiones,  or  ostriches,  rheas,  cassowaries  and  emus 
are  all  large,  flightless  birds  with  small  wings,  a  keelless  sternum, 
and  well-developed  walking  legs.  They  also  include  the  extinct 
^Epyornis  and  the  equally  extinct  moas  (Dinornithida) ,  without  or 
with  extremely  rudimentary  wings  and  pectoral  arch  and  with 
massive  legs.  The  Struthiones  appear  first  in  the  Tertiary.  The 
New  Zealand  Apteryx,  a  small  flightless  bird,  represents  the  order 
Apteryges  and  the  living  tinamous  the  order  Crypturi.  Both  have 
only  fragmentary  fossil  representatives.  The  super-order  Euorni- 
thes,  with  13  orders,  includes  most  of  the  existing  birds.  A  few 
representatives  (cormorants,  etc.)  occur  in  the  Cretacic,  but  the 
great  majority  of  types  are  not  known  before  the  Eocenic  and 
many  not  until  later. 

Mammalia. 

The  mammals  are  warm-blooded  animals  with  the  body  typically 
covered  by  hair,  and  in  nearly  all  cases  they  bring  forth  their 
young  alive,  the  monotremes  alone  laying  eggs.  All,  however, 
suckle  their  young.  The  marsupials  (opossum,  kangaroo,  etc.) 
bear  their  young  in  an  immature  state,  and  these  are  then  placed  in  a 
pouch  or  marsupium.  The  placental  mammals  bear  perfect  young. 
The  Insectivora  go  back  to  the  Eocenic ;  they  comprise  the  moles, 
shrews,  hedgehogs,  etc.  The  Chiroptera,  or  bats,  also  go  back 
to  the  Eocenic.  The  Dermoptera  are  characterized  by  a  cutaneous 
expansion,  extending  from  the  wrists  to  the  ankles  and  forming  a 
parachute.  They  are  generally  called  flying  lemurs  and  are  un- 
known in  a  fossil  form.  The  Edentata,  chiefly  restricted  to  South 
America,  are  nearly  or  quite  toothless  and  include  the  living  ant- 
eaters  and  sloths,  the  armadillos,  with  jointed  armor,  and  the  ex- 
tinct Glyptodon  with  solid  armor.  Here  also  belong  the  giant 
sloths,  the  Megatherium,  the  Mylodon,  and  Grypotherium — all  of 
them  but  recently  extinct. 

The  Rodentia  comprise  the  gnawing  types  with  long,  sharp 
curved  incisors.  They  go  back  to  the  Eocenic.  The  Tillodontia 
are  extinct  forms  from  the  North  American  Eocenic.  They  are 
related  to  the  rodents.  The  Carnivora,  or  flesh-eaters,  comprise  a 
large  number  of  living  and  extinct  types,  such  as  the  Creodontia, 
of  the  Tertiary;  the  Fissipedia,  including  Canidcc  (dogs),  Ursidce 
(bears),  Viverrida,  Mustelidcc  (otters,  etc.),  Hyanidcc  (Hyaenas) 
and  Felidcc  (cats,  tigers,  lions,  panthers,  etc.)  ;  and  the  Pinnipedia, 
or  marine  carnivores,  such  as  seals,  sealions,  etc.  Many  of  these1 
have  representatives  in  the  Tertiary.  The  Cctacca,  ar  whales,  dol- 


956  PRINCIPLES    OF    STRATIGRAPHY 

phins,  etc.,  are  aquatic  (mostly  marine)  mammals,  and  occur  as  far 
back  as  the  Miocenic.  Squalodon  and  Zeuglodon  are  fossil  repre- 
sentatives. The  Sirenia  are  herbivorous  aquatic  mammals  repre- 
sented by  the  living  manatee  and  dugongs,  and  the  recently  extinct 
sea-cow  (Rhytina),  etc.  The  Ungulates,  or  hoofed  mammals,  com- 
prise: (i)  the  Eocenic  Amblypoda  (Coryphodon,  Tinoceras,  etc.), 
large,  heavy  creatures;  (2)  the  Proboscidea,  or  elephants  (Dino- 
therium,  Mastodon,  Stegodon,  Elephas,  etc.)  ;  (3)  the  Condilarthra 
(Phenacodus)  ;  (4)  the  Perissodactyla,  or  unevenly-toed  ungulates 
(Tapir,  Rhinoceros,  Titanothere,  and  the  horse  family)  ;  (5)  the 
Artiodactyla,  or  even-toed  ungulates,  divided  into  the  Bunodontia 
(pigs,  hippopotamus,  Anthracotherium,  etc.)  ;  and  Selenodontia, 
(Oreodon  [Tertiary],  camels,  deer,  etc.;  giraffes,  antelopes,  goats, 
sheep,  cattle,  etc.)  ;  (6)  Toxodontia — Tertiary  forms,  including 
Toxodon,  Typotherium,  etc. 

The  final  order  of  the  mammals  is  that  of  the  primates,  which 
includes  Quadrumana  (apes,  monkeys,  etc.),  and  the  Bimana,  or 
man. 

BIBLIOGRAPHY    XXIV. 

(Text-books  of  Palaeontology,  etc.) 

1.  BERNARD,    FfiLIX.     1895.     Elements   de   Paleontologie.     Bailliere   et 

Fils,  Paris. 

2.  GRABAU,  A.  W.,  and  SHIMER,  H.  W.     1909-1910.     North  American 

Index  Fossils.     2  vols.     A.  G.  Seiler  and  Company,  New  York. 

3.  GURICH,  GEORG.     1908-09.     Leitfossilien.     2  parts.     Gebruder  Born- 

traeger,  Berlin. 

4.  KOKEN,     ERNEST.     1896.     Die     Leitfossilien.     Hermann     Tauchnitz, 

Leipzig. 

5.  NICHOLSON,    ALLEYNE,  and    LYDEKKER,    RICHARD.     1889.     A 

Manual  of  Palaeontology.     2  vols.     W.  Blackwood  and  Sons,  Edinburgh 
and  London. 

6.  OSBORN,  HENRY  F.     1910.     The  Age  of  Mammals.     Macmillan  Com- 

pany, New  York. 

7.  STEINMANN,    GUSTAV.     1903.      Einfiihrung    in    die    Palaeontologie. 

Wilhelm  Engelmann,  Leipzig.     2nd  edition,  1907. 

8.  STROMER,  ERNST.     1909,1912.     Lehrbuch  der  Palaeozoologie.     2  parts. 

9.  ZITTEL,  KARL  A.  VON.   1881-85.  Handbuch  der  Pateontologie.     French 

translation,  Traite  de  Paleontologie,  by  Charles  Barrois,  Paris. 

10.  ZITTEL,  K.  A.  VON.     1895.     Grundziige  der  Palaeontologie.     2nd  Edi- 

tion, 1910-11.     2   vols.     Munich. 

11.  ZITTEL,  K.  A.,  VON.    1900.     Text-book  of  Palaeontology.    Translated  by 

Charles  R.  Eastman  with  collaboration  by  many  specialists.     2  vols. 
Macmillan  Company,  New  York. 

(Classification,  etc.) 

12.  ALLEN,  J.  A.     1906.     The  "Elimination"  and  "First  Species"  Methods  of 

Fixing  the  Types  of  Genera.     Science,  N.  S.,  Vol.  XXIV,  pp.  773-779. 


BIBLIOGRAPHY    XXIV  957 

13.  AMERICAN  ASSOCIATION    FOR  THE  ADVANCEMENT  OF  SCI- 

ENCE.    1877.     Report  of  the  Committee  on  Zoological  Nomenclature. 
Nashville  Meeting. 

14.  BRITISH  ASSOCIATION  FOR  THE  ADVANCEMENT  OF  SCIENCE. 

1842.     Report  of  the  Manchester  Meeting. 

15.  BRITISH  ASSOCIATION  FOR  THE  ADVANCEMENT  OF  SCIENCE. 

1865.     Report  of  the  Birmingham  Meeting. 

16.  BUCKMAN,  S.  S.     1909.     Yorkshire  Type  Ammonites,  Part  I. 

17.  ENCYCLOPAEDIA  BRITANNICA.     Eleventh  edition.     Articles  on  Zool- 

ogy and  various  Phyla,  Classes  and  Orders.     Also  Palaeontology  and 
Palaeobotany. 

1 8.  MILLER,  S.  A.    1889.    North  American  Geology  and  Palaeontology. 

19.  OSBORN,  HENRY  F.     1912.     First  Use  of  the  Word  "Genotype."     Sci- 

ence, N-.  S.,  Vol.  XXXV,  No.  896,  pp.  340-341. 

20.  PAL^EONTOLOGIA  UNIVERSALIS.     1904.     Edited  by  D.  P.  Oehlers. 

21.  PATTEN,  W.     1912.     The  Evolution  of  the  Vertebrates  and  Their  Kin. 

P.  Blakiston  &  Co.,  Philadelphia. 

22.  PATTEN,  W.     1913.     A  Problem  in  Evolution.     Popular  Science  Month- 

ly, Vol.  LXXXII,  pp.  417-435. 

23.  SCHUCHERT,   CHARLES.     On  Type   Specimens  in   Natural   History. 

Catalogue,  etc.,  of  Fossils,  Minerals,  etc.,  in  U.  S.  National  Museum, 
Pt.  I,  pp.  7-18,  with  bibliography  of  literature  on  type  terms. 

24.  SCHUCHERT,  CHARLES,  and  BUCKMANN,  S.  S.     1905.     The  Nom- 

enclature of  Types  in  Natural  History.     Science,  N.  S.,  Vol.  XXI,  pp. 
899-901. 

25.  SCUDDER,  SAMUEL.     1882.     Nomenclator  Zoologicus.     Bulletin  of  the 

United  States  National  Museum,  No.  19. 

26.  STONE,  WITMER.    1906.    The  Relative  Merits  of  the  "Elimination"  and 

' 'First  Species"  Method  in  Fixing  the  Types  of  Genera,  with  special  refer- 
ence to  Ornithology.     Science,  N.  S.,  Vol.  XXIV,  pp.  560-565. 


CHAPTER    XXV. 

BIOGENETIC   RELATIONS   OF   PLANTS   AND   ANIMALS.* 
THE  CONCEPTION  OF  SPECIES. 

A  species  is  commonly  held  to  comprise  a  group  of  individuals 
which  differ  from  one  another  only  in  a  minor  degree.  The  degree 
of  individual  difference  admissible  within  the  species  is  commonly 
a  matter  of  personal  opinion  and  probably  no  two  systematists  al- 
ways agree  as  to  the  precise  taxonomic  value  of  a  character  in  dif- 
ferent cases.  In  pre-modern  days  the  idea  of  permanence  and  im- 
mutability of  the  species,  or,  in  pre-Linnaean  days,  of  the  genus, 
dominated  the  minds  of  naturalists  generally,  though  there  were 
not  wanting,  at  nearly  all  times,  observers  to  whom  the  fixity  of 
specific  characters  appeared  as  a  dogma  unsupported  by  facts. 
That  variation  existed  within  the  specific  limits  was  admitted,  but 
the  believers  in  the  special  creation  and  immutability  of  species 
would  not  admit  that  this  variation  could  exceed  certain  limits, 
though  what  these  limits  were  was  a  matter  of  diverse  and,  more- 
over, of  constantly  changing  opinion.  No  matter  how  different 
the  end  members  of  a  perfectly  graded  series  of  individuals  were, 
if  that  gradation  was  established  all  those  members  were  placed 
within  the  limits  of  the  species.  Even  if  some  of  the  members  of 
the  series  were  originally  described  as  distinct  species  or  placed 
in  distinct  genera  the  discovery  of  intermediate  forms,  or  "con- 
necting links,"  caused  them  all  to  be  referred  to  one  species.  The 
differences  originally  deemed  amply  sufficient  for  specific  or  even 
generic  distinction  at  once  dwindled  in  taxonomic  value  to  the  rank 
of  varietal  characters  of  a  very  variable  species.  A  classic  case 
in  point  is  that  of  the  Tertiary  species  of  Paludina  (Vivipara)  from 
Slavonia.  (Neumayr  and  Paul-29).  (Fig.  252.)  In  the  lowest 
members  of  the  Paludina  beds  P.  neumayri  (Fig.  a),  a  smooth, 

*  The  principles  here  outlined  will  be  more  fully  discussed  in  "The  Principles 
of  Palaeontology"  by  Henry  F.  Osborn  and  Amadeus  W.  Grabau,  to  be  published 
shortly. 

958 


THE    CONCEPTION    OF    SPECIES 


959 


round-whorled  species,  is  the  characteristic  form,  while  the  highest 
beds  are  characterized  by  P.  hoernesi  (Fig.  &),  an  angular- whorled, 
strongly  bicarinate  type,  which  had  been  separated  under  the  dis- 
tinct generic  name  of  Tulotoma.  Certainly  these  end-forms  are 
widely  separated,  yet  from  the  intermediate  beds  individuals  con- 
stituting a  complete  gradational  series  from  one  to  the  other  have 
been  obtained.  This  discovery  led  many  to  reconsider  the  classifica- 
tion of  these  forms  and  to  group  them  all  as  varieties  under  one 
species. 

The  belief  in  the  mutability  of  species  was  gradually  accepted 


FIG.  252.  Series  of  Paludinas  (Vivipara)  from  the  Lower  Pliocenic  deposits 
of  Slavonia.  (After  Neumayr.)  a.  Paludina  neumayri,  k.  P. 
{Tulotoma}  hoernesi  from  the  highest  beds,  b-i,  intermediate 
forms,  showing  gradation,  from  the  intermediate  beds. 

by  naturalists  after  the  publication  of  "The  Origin  of  Species"  in 
1859.  To-day  there  is  scarcely  a  naturalist  of  prominence  who  does 
not  unhesitatingly  affirm  his  belief  in  the  mutability  of  species. 
Nevertheless,  we  may  ask,  with  Farlow:  "...  is  our  belief 
in  evolution  merely  dogmatic,  like  some  of  the  theological  doctrines 
which  we  believe  thoroughly  but  which  we  do  not  allow  to  inter- 
fere with  our  daily  life,  or,  ...  has  our  belief  modified  the 
manner  in  which  we  treat  what  we  call  species?"  (10)  When  we 
note  how  unwilling  systematists  are  to-day  to  recognize  more  than 
one  species  in  a  series  whose  end  forms  differ  widely,  when  a  suf- 
ficient number  of  members  are  known  to  bridge  over  all  the  more 
striking  gaps,  we  are  forcibly  impressed  with  the  fact  that,  uncon- 
sciously though  it  may  be,  the  majority  of  systematists  are  still 


960  PRINCIPLES    OF    STRATIGRAPHY 

influenced  by  the  old  inherited  ideas  of  the  fixity  of  specific  limits. 
Palaeontologists  are,  as  a  rule,  no  freer  from  the  shackles  of  in- 
herited ideas  than  are  the  workers  in  the  morphology  and  taxonomy 
of  living  plants  and  animals.  This  may  in  large  measure  be  ac- 
counted for  by  the  fact  that  the  very  recognition  of  such  a  thing 
as  a  species  carries  with  it  the  impression  of  an  entity,  and  the 
recognition  of  certain  characters  as  belonging  to  a  species,  in  a 
measure  carries  with  it  the  conception  .that,  if  those  characters  are 
modified  or  supplanted  by  others,  the  organism  in  question  no 
longer  belongs  to  that  species. 

That  the  Linnaean  species  is  a  fragment  or  group  of  fragments 
of  one  or  more  evolutional  series  separated  from  other  fragments, 
in  space  or  time,  by  the  extermination  of  the  connecting  links,  is 
pretty  generally  recognized  by  naturalists  of  a  philosophical  turn  of 
mind.  Among  such  the  belief  in  the  nonexistence  of  species  is, 
theoretically  at  least,  widely  held.  In  other  words,  naturalists  have 
come  to  the  conclusion  that  what  we  call  species  are  merely  "snap- 
shots at  the  procession  of  nature  as  it  passes  along  before  us,  and 
that  the  views  we  get  represent  but  a  temporary  phase,  and  in  a 
short  time  will  no  longer  be  a  faithful  picture  of  what  really  lies 
before  us."  "For  the  procession  is  moving  constantly  onward." 
(Farlow-io.) 

THE  MUTATION  OF  WAAGEN. 

Waagen  in  1868  (44)  recognized  two  kinds  of  variation  within 
the  species — geographic  and  chronologic.  To  the  former,  which 
comprises  the  variable  members  appearing  together  in  the  same 
rime  period,  though  they  may  be  geographically  separated,  he  re- 
stricted the  term  variation  or  variety,  while  for  those  occurring  in 
chronological  succession  he  proposed  the  term  "mutation,"  A  mu- 
tation may  then  be  defined  as  a  slightly  modified  form  of  the  species 
appearing  in  a  later  time-period,  and  in  this  sense  it  has  been 
commonly  used  by  palaeontologists.  As  an  example  of  a  number  of 
mutations  appearing  in  successively  higher  horizons,  the  Tertiary 
series  of  Paludinas  (Vivipara),  already  referred  to,  may  be  cited. 

Palaeontologists,  whose  business  it  is  to  study  large  series  of 
forms  from  each  successive  horizon,  have  since  recognized  that 
what  Waagen  called  varieties,  in  the  belief  that  they  had  no  very 
definite  relationship  to  each  other,  are  really  secondary  mutations 
or  sub-mutations  (Grabau-i7).  Thus  each  developing  series  has, 
on  reaching  a  higher  horizon,  become  modified  in  a  certain  definite 


MUTATION    OF    WAAGEN 


961 


way  and  within  this  horizon  the  derivatives  of  this   species  will 
become  modified  in  certain  definite  directions. 

As  an  illustration  may  be  chosen  the  Linnsean  species  of  brachi- 
opod  Spirifer  mucronatus  of  the  Middle  Devonic  of  eastern  North 
America  (Fig.  253).  This  is  represented  by  at  least  five  distinct 
mutations  in  successive  horizons,  or  in  distinct  basins.  Each  of 
these  five  mutations  differs  from  the  others  in  certain  more  or  less 
constant  characters,  which,  however,  are  the  result  of  definite 
modifications  of  the  preceding  more  primitive  types,  chiefly  by  the 
appearance  of  new  characters.*  Thus  these  mutations  are  readily 


FIG.  253.  Spirifer  mucronatus,  a.  primitive  mutation — b.-d.  mutation  thed- 
fordense.  b.  Long-winged  retarded  submutation,  shell  index 
1.7.  c.  The  most  accelerated  submutation  (shell  index  0.73).  d. 
The  same  drawn  with  curvature  eliminated  so  as  to  show  full 
length.  The  more  transverse  character  (higher  shell  index)  of 
the  younger  stages  is  shown  in  each. 

recognizable  and  separable  from  one  another  with  comparative 
ease.  Within  each  mutation,  however,  there  is  a  long  series  of  vari- 
ants, which  are  modified  by  a  progressive  change  in  the  relative 
proportion  of  width  and  height — a  modification  or  change  of  quan- 
titative rather  than  qualitative  character — a  type  of  change  to  which 
Osborn  has  applied  the  term  allometric,  while  the  resulting  char- 
acters are  allometrons.  The  change  in  proportion  in  each  of  these 
successive  mutations  is  from  broad-winged  to  short-winged  types, 
or  allometrons.  Expressed  in  shell  indices,  derived  by  dividing  the 
entire  width  along  the  hinge-line  by  the  height  measured  on  the 
curvature,  the  change  is  from  a  high  shell  index  to  a  lower  one. 
In  each  mutation  the  change  is  in  the  same  direction,  and  in  each 
a  dominant  type  can  be  designated  which,  as  a  sub-mutation,^  repre- 
sents, for  the  mutation  to  which  it  belongs,  that  index  to  which  the 
*  Termed,  by  Osborn,  Rectigradations.  (See  beyond.) 


962 


PRINCIPLES    OF    STRATIGRAPHY 


majority  of  individuals  of  that  fauna  approximate.  The  dominant 
sub-mutation  of  a  higher  mutation  will  be  found  to  have  a  smaller 
index  than  the  dominant  sub-mutation  of  a  lower  mutation.  In 
the  same  way,  the  most  primitive  sub-mutation  of  the  higher  muta- 
tion, i.  e.,  the  one  with  the  largest  shell  index,  has  a  smaller  index 
than  the  most  primitive  sub-mutation  of  the  lower  mutation.  In 
like  manner  the  most  specialized  sub-mutation  of  the  higher  (geo- 
logic) mutation  will  have  a  smaller  index  than  the  most  specialized 
sub-mutation  of  the  lower  mutation.  In  other  words,  not  only  has 
the  dominant  sub-mutation  of  the  higher  mutation  advanced  beyond 


75% 


5,0  To   - 


2.1    2J9 


1.1     1.0      0.85    0.73 


FIG.  254.     Curves  representing  the  range  in  shell  index  of  two  mutations  of 
Spirifer  mucronatus. 

that  of  the  lower  mutation  in  the  same  direction  of  modification  of 
proportions,  but  also  the  most  primitive  and  the  most  specialized 
sub-mutation  and  all  the  intermediate  sub-mutations  of  the  later 
mutations  are  ahead  of  the  earlier  one.  This  may  be  expressed  in 
the  accompanying  diagram  (Fig.  254),  where  the  height  of  the 
curve  represents  the  percentage  of  individuals  and  the  base  the 
decline  in  shell  index  from  3.0  to  0.5. 


MUTATION  THEORY  OF  DE  VRIES. 

In  1901  Professor  Hugo  De  Vries  published  his  epoch-making 
book  "Die  Mutations-theorie"  (6)  in  which  he  recognized  that  the 
Linnaean  "species"  was  in  reality  a  compound  of  innumerable 
groups  of  more  restricted  relationship.  These  minor  groups,  which 
have  generally  been  classed  together  as  a  "species,"  are  really  enti- 
ties composed  of  very  definite  associations  of  minute  characters, 
and  to  them  the  name  elementary  species  applies.  Of  these  ele- 
mentary species  there  may  be  very  many  in  a  Linnaean  species. 
These  elementary  species  De  Vries  thinks  arose  suddenly  by  a  new 
combination  of  the  elements  of  which  the  characters  of  organisms 
are  made  up.  These  elements  (Einheiten)  are  sharply  separated 


MUTATION;    ORTHOGENESIS  963 

from  one  another  and  the  resulting-  combinations  or  elementary 
species  are  likewise  distinct  and  definite  and  without  transitional 
connecting  forms.  They  are  constant  and  transmit  their  characters 
truly.  The  sudden  appearance  of  these  new  forms  is  a  process 
which  De  Vries  calls  "mutation,"  thus  using  Waagen's  term  for  a 
process  instead  of  a  result,  as  originally  proposed.  The  "elementary 
species"  as  defined  by  De  Vries  is,  in  a  measure,  identical  with  the 
mutation  of  Waagen,  in  that  the  variation  is  a  slight  and  definite 
one;  but  in  so  far  as  De  Vries  believes  in  the  stability  and  immuta- 
bility of  the  elementary  species,  they  do  not  correspond  to  the  muta- 
tion and  sub-mutation  (allometrons)  as  used  by  most  palaeontolo- 
gists to-day. 

ORTHOGENESIS  AND  THE  CONCEPT  OF  SPECIES. 

The  doctrine  of  definite  directed  variation,  or  Orthogenesis, 
which  finds  many  adherents,  especially  among  palaeontologists,  has 
led  to  a  very  logical  conception  of  the  method  by  which  species 
become  differentiated.  Though  independently  formulated  with 
more  or  less  precision  by  many  naturalists  this  doctrine  was  most 
consistently  and  vigorously  championed  by  the  late  Professor  Theo- 
dor  Eimer  of  Tubingen. .  Eimer's  illustrations  were  chiefly  drawn 
from  the  color  patterns  of  recent  animals,  especially  lizards  and 
butterflies  (9).  He  found  that  the  color  patterns  of  organisms  may 
be  reduced  to  four  types,  which  always  appear  in  the  individual 
development  in  a  definite  succession,  viz. :  ( i )  Longitudinal  stages, 
(2)  spots,  (3)  cross  stripes,  and  (4)  uniform  coloration.  Each 
succeeding  type  is  developed  out  of  the  preceding  one  and  replaces 
it  to  a  greater  or  less  extent.  When  in  a  large  number  of  indi- 
viduals all  developing  in  the  same  direction  (orthogenetically)  a 
complete  cessation  of  development  occurs  in  different  groups  at  indi- 
vidual stages,  the  individuals  thereafter  only  increasing  in  size,  but 
not  changing,  a  large  number  of  distinct  species  will  originate  which 
differ  from  one  another  to  the  extent  by  which  one  group  continued 
to  develop  beyond  the  other.  If  a  number  of  characters  develop, 
each  in  a  given  direction,  and  at  a  given  rate  in  a  large  group  of 
individuals,  all  starting  from  the  same  point,  cessation  of  develop- 
ment of  different  characters  at  different  times  will  soon  result  in 
the  formation  of  a  great  number  of  species  varying  in  one  or 
more  characters. 

We  may  assume,  by  way  of  illustration,  a  case  in  which  there 
are  three  structural  characters,  which  we  may  designate  characters 
(a),  (b),  and  (c),  in  a  given  group  of  individuals,  each  changing 


964  PRINCIPLES   OF    STRATIGRAPHY 

in  a  definite  order  and  at  a  uniform  rate.  A  certain  percentage 
of  these  individuals  may,  after  a  while,  cease  to  develop  character 
(a)  while  characters  (b)  and  (c)  continue  to  develop.  Later  in 
some  of  these,  character  (b)  may  cease  to  develop  further  and  (c) 
continue  alone,  while  in  others  (c)  ceases  to  develop  and  (b) 
continues.  In  another  portion  of  the  original  group  character  (b) 
may  cease  to  develop  first  and  (a)  and  (c)  continue,  after  which 
character  (a)  may  stop  in  some  and  (c)  in  others — the  other  char- 
acter continuing.  The  combinations  possible  by  this  method  will  be 
readily  recognized  and  the  number  of  different  types — mutations, 
varieties,  or  species,  according  to  the  rank  to  which  they  are  ad- 
mitted— will  be  readily  seen.  The  possibilities  of  differentiation 
will  be  further  recognized  when  it  is  considered  that  the  length 
of  time  during  which  each  character  develops  may  also  vary  greatly. 
Complete  cessation  of  development  of  characters  has  been  termed 
genepistasis  by  Eimer,  and  the  differential  cessation  heterepistasis. 

ACCELERATION  AND  RETARDATION  IN  DEVELOPMENT  (TACHYGENE- 
sis  AND  BRADYGENESIS). 

Another  principle  which  is  of  great  importance  in  this  connec- 
tion, and  which  was  first  clearly  recognized  by  Hyatt  and  by  Cope, 
is  acceleration  or  tachygenesis.*  Instead  of  a  uniform  rate  of  de- 
velopment some  organisms  may  .develop  more  rapidly  and  so  are 
able  to  reach  a  higher  stage  in  development.  Differential  accelera- 
tion may  obtain  between  the  different  characters.  Again,  retarda- 
tion (bradygenesis  *),  first  recognized  by  Cope,  may  progressively 
diminish  the  rate  of  development,  so  that  certain  individuals  in 
some  or  all  of  their  characters  may  fall  more  and  more  behind  the 
normal  rate  of  progress. 

Illustrations  of  Orthogenetic  Development.  Some  of  the  most 
satisfactory  series,  showing  development  in  definite  directions,  have 
been  brought  to  light  by  the  labors  of  palaeontologists.  Such  series 
are  especially  well  known  among  the  ammonoids,  a  class  of  cephalo- 
podous  Mollusca  which  began  its  existence  in  the  Devonic,  culmi- 
nated in  the  Jura,  and  had  its  last  representatives  in  late  Cretacic 
time. 

Some  of  the  earliest  studies  of  the  developmental  changes  of 
this  group  were  carried  on  by  Alcide  d'Orbigny  (8),  who  recognized 
a  distinct  succession  in  the  form  and  ornamentation  of  the  shell 

*  From  raxfo  =  fast  and  ppadfa  =  slow,  ytvceu  =  birth.  The  term  bradyge- 
nesis was  used  by  Grabau  in  1910  (16)  as  a  complement  of  the  term  tachygenesis. 


ACCELERATION    AND    RETARDATION  965 

from  rounded  and  smooth  in  youth;  through  ribbed,  and  tubercled, 
with  angular  and,  later,  keeled  whorls;  to  old  age,  which  was 
marked  by  a  complete  loss  of  all  ornamentation.  The  late  Pro- 
fessor Alpheus  Hyatt  was,  however,  the  first  to  recognize  the  sig- 
nificance of  these  changes  and  to  point  out  that  they  recapitulated 
the  adult  characteristics  of  successive  ancestors.  The  number  of 
recognizable  characters  of  which  the  development  may  be  studied 
is  exceptionally  large  in  the  Ammonite  shell.  Thus  there  is  the 
degree  of  coiling  or  involution,  which  varies  from  the  condition  in 
which  the  whorls  do  not  even  touch  each  other  through  whorls  in 
contact  and  whorls  impressed  on  each  other  to  complete  involution, 
in  which  the  last  whorl  covers  all  the  preceding  ones.  Then  there 
is  the  form  of  the  cross-section  of  the  shell  and  the  character  of 
the  outer  or  ventral  surface  of  the  shell,  which  varies  from  rounded 
through  angulated  to  various  degrees  of  channeled  and  keeled. 
Again  the  surface  ornamentation  varies  from  smooth  to  ribbed, 
noded,  or  even  spinous,  and,  finally,  and  in  many  respects  most 
significantly,  there  is  the  progressive  change  in  the  complexity  of 
the  septal  sutures,  from  simple  in  the  young  to  often  highly  complex 
in  the  adult.  In  addition  to  these,  the  form  and  position  of  the 
siphuncle  often  show  a  definite  variation,  which  may  be  of  consider- 
able importance.  To  give  a  concrete  example  of  the  changes  in 
the  individual  development  of  the  shell  and  the  correlation  of  the 
various  stages  with  the  adult  stages  of  ancestral  forms,  we  may 
select  a  closely  related  series  of  ammonites  of  the  family  Placenti- 
ceratida,  all  of  which  are  characteristic  of  the  Cretacic  formations 
of  North  America.  The  changes  here  are  chiefly  in  the  form  of  the 
cross-sections  and  the  characters  of  the  surface  ornamentations. 
The  most  advanced  form  of  the  series  is  Stantonoceras  pseudo- 
costatum  Johnson,  a  large,  robust  ammonite  with  a  broad,  rounded 
venter  and  rather  ill-defined,  coarse,  rib-like  elevations  on  the  lat- 
eral surfaces  of  the  whorls.  When  this  form  is  broken  down  it  is 
found  that  the  next  inner  whorl  has  a  flattened  ventral  band  bor- 
dered by  a  row  of  faint  elongated  nodes  on  either  side  and  a  large 
row  of  tubercles  on  the  ventro-lateral  angles.  At  this  stage  the 
species  has  the  characters  of  the  adult  Stantonoceras  guadalupce 
(Roemer),  which  may  be  regarded  as  an  immediate  ancestor.  A 
still  earlier  whorl  shows  a  very  narrow  flattened  venter,  with  a 
strong  row  of  elongated  nodes  on  either  side  of  the  flattening,  the 
surface  being  otherwise  smooth.  This  corresponds  to  more  primi- 
tive species,  Placenticeras  intermedium  Johnson,  and  P.  planum 
Hyatt,  one  or  the  other  of  which  was  probably  in  the  direct  line 
of  ancestry.  At  a  still  earlier  stage  in  these  shells  the  venter  is 


966 


PRINCIPLES    OF    STRATIGRAPHY 


hollowed  and  bordered  by  smooth  ridges,  while  the  surface  is 
smooth — features  characteristic  of  the  adults  of  certain  species  of 
the  genus  Protengonoceras  of  the  Lower  Cretacic.  In  all  these 
types  the  sutures  show  close  relationship  and  increasing  complexity 
with  the  progressive  changes  of  the  form  of  the  shell.  At  a  still 
earlier  stage  the  venter  is  flattened  without  channel,  the  section  of 
the  whorl  being  helmet^shaped,  while  the  earliest  marked  stage 
shows  a  rounded  venter.  The  sutures  of  this  early  stage  are  very 
simple,  corresponding  in  general  to  the  adult  suture  of  Devonic  or 
Carbonic  Goniatites,  which  the  form  of  the  shell  also  recalls.  As 


FIG.  255.  a.  Cross-section  of  'the  three  outer  whorls  of  Stantonoceras 
pseudocostatum  reduced.  (After  Johnson.)  b.  Cross-section  of 
the  inner  whorls  of  Stantonoceras  guadalupa,  enlarged.  (After 
Hyatt.) 

the  form  changes  the  complexity  of  the  sutures  increases  until  the 
complex  adult  suture  is  developed.  The  cross-sections  of  the  vari- 
ous stages  are  shown  in  Fig.  255.  The  early  "Goniatite"  stages  of 
Schloenbachia  aff.  chicoensis  Trask,  a  highly  developed  ammonite 
of  the  Lower  Cretacic  of  Oregon,  are,  according  to  J.  P.  Smith,  as 
follows  (43:5^1):  The  first  suture  (immediately  succeeding  the 
protoconch)  has  narrow  lateral  lobes  and  saddles  *  and  a  broad 
ventral  saddle.  The  second  suture  has  a  small  lobe  in  the  center 
of  the  broad  ventral  saddle,  which  is  thus  divided.  This  corre- 
sponds to  the  adult  suture  of  the  Devonic  genus  Anacestes,  a 
simple  form  of  "goniatite"  which  Hyatt  considers  the  immediate 
radicle  of  the  ammonoid  stock.  The  third  and  fourth  sutures  show 

*  Lobes  are  the  backward  loops  of  the  suture  and  saddles  the  forward  loops, 
i.  e.,  those  convex  toward  the  mouth  of  the  shell.  The  ventral  border  is  the 
outer  border  of  the  shell ;  the  space  between  the  inner  margins  of  the  whorl  is  the 
umbilicus,  in  which  can  be  seen  the  earlier  coils. 


ILLUSTRATIONS    OF    ORTHOGENESIS  967 

accentuation  of  the  lobes  and  saddles,  and  recapitulate  the  adult 
sutures  of  such  later  Devonic  types  as  Tornoceras  and  Prionoceras. 
The  fifth  suture  is  transitional  to  the  sixth,  which  is  characterized 
by  a  divided  ventral  lobe,  one  lateral  lobe  on  each  side,  and  another 
on  each  side  of  the  umbilical  border.  Here,  then,  the  lobe  which 
complicated  the  original  ventral  saddle  is  itself  divided  by  a  second 
low  ventral  saddle.  The  shell  at  -this  stage  has  a  low,  broad,  in- 
volute whorl,  and  in  this  and  the  character  of  the  suture  recalls  the 
adult  of  the  older  species  of  Glyphioceras.  The  typical  Glyphio- 
ceras  condition  is  represented  by  a  somewhat  later  suture,  and  still 
later,  with  the  appearance  of  a  second  lateral  lobe  next  to  the 
umbilicus,  the  shell  begins  to  resemble  the  late  Carbonic  goniatite 
Gastrioceras,  and  at  a  still  later  stage,  when  the  diameter  of  the 
shell  is  2.25  mm.,  a  third  lateral  lobe  appears  next  to  the  umbilicus 
which  subsequently  widens,  while  the  whorls  become  higher  and 
narrower.  In  this  stage  it  recalls  the  genus  Paralegoceras.  The 
next  stage  ushers  in  true  ammonitic  ornamentation  in  the  form  of  a 
ventral  keel  (2.7  mm.  diam.),  while  the  suture  still  remains  goni- 
atite-like.  But  when  the  shell  has  reached  a  diameter  of  3.2  mm.  the 
first  lateral  saddle  becomes  indented,  a  true  ammonoid  suture  thus 
coming  into  existence.  The  future  development  is  along  the  line 
of  increasing  complexity  of  suture. 

A  consideration  of  the  possible  mutations  which  may  come  into 
existence  by  the  operation  of  the  law  of  heterepistasis,  or  differ- 
ential arrestation  in  development,  and  by  the  operation  of  the  laws 
of  differential  acceleration  and  retardation  of  characteristics,  will 
convince  one  that  all  the  known  types  of  ammonites,  as  well  as 
many  yet  unknown  types,  may  be  accounted  for  in  this  manner. 
Not  only  all  .so-called  species,  but  every  individual  variation  will 
fall  into  its  proper  determinate  place  in  the  series  when  the  method 
of  analysis  of  individual  characters  has  become  sufficiently  de- 
tailed. 

Another  example,  taken  from  the  gastropods,  may  serve  to 
further  illustrate  the  principles  here  discussed  (Fig.  256).  The 
modern  Fulgur  caricum,  a  large  gastropod  occurring  on  the  Atlantic 
coast  between  Cape  Cod  and  the  Gulf  of  Mexico,  begins  its  embry- 
onic existence  with  a  smooth  shell  drawn  out  anteriorly  into  a  canal 
and  not  unlike  in  form  to  some  smooth  Fasciolarian  shells  (Fig. 
256,  b,  c).  At  a  very  early  age  the  shell  is  furnished  with  ribs  and 
then  an  angulation  appears  in  the  outer  whorl.  On  this  angulation 
the  ribs  are  soon  reduced  to  rounded  tubercles.  This  condition 
recalls  the  adult  characters  of  Lower  Miocenic  species  of  this  genus, 
which  never  pass  beyond  the  tubercled  stage.  This  stage  in  the 


968 


PRINCIPLES    OF    STRATIGRAPHY 


modern  species  is  succeeded  by  one  in  which  strong  spines  occur, 
caused  by  periodic  notchings  or  emarginations  of  the  shell  margin 
along  the  line  of  the  angulation.  The  tubercles  and  spines  pass  the 
one  into  the  other  by  what  appears  to  be  a  process  of  enlargement 
of  the  tubercles. 

When  we  come  to  consider  the  series  of  forms  which  lead  up 
from  the  tubercled  (Tertiary)  species  (F.  fusiformis,  F.  tuber cn- 
latum)  to  the  modern  form,  we  find  that  certain  intermediate 
characteristics  have  been  omitted.  As  shown  by  the  specimen  of 


FIG.  256.  Development  of  the  gastropod  shell  (Fulgur  and  Sycotypus).  a. 
Protoconch  of  _  Sycotypus  canaliculatus.  b,  c.  The  same  before 
hatching,  showing  smooth  shell;  animal  with  velum.  (The  early 
stages  of  Fulgur  caricum  are  identical  with  these.)  d.  Fulgur 
fusiformis.  e.  F.  rapum  (representing  F.  maximum),  f.  F. 
tritonis. 

F.  fusiformis  figured  (Fig.  256,  d),  the  last  part  of  the  last  whorl 
has  already  lost  the  tubercles  and  has  become  smooth  and  rounded 
in  outline.  This  is  prophetic  of  the  form  next  to  be  noted,  F.  maxi- 
mum (Fig.  256,  e).  In  this  shell  the  tubercled  stage  is  passed  through 
quickly — a  case  of  acceleration  in  development — and  the  smooth, 
rounded  whorl  stage  makes  up  the  greater  part  of  the  shell.  Thus 
the  normal  characters  of  F.  fusiformis  have  become  condensed  to 
a  few  whorls,  in  this  manner  making  room  for  the  smooth  whorl 
which  characterizes  the  shell.  It  is  in  certain  advanced  accelerated 
individuals  of  this  type  that  the  emarginate  spines  so  characteristic 


DEVELOPMENT  OF  A  GASTROPOD      969 

of  the  modern  F.  caricum  first  make  their  appearance.  In  a  more 
advanced  type,  F.  tritonis  (Fig.  256,  /),  the  characteristic  round 
"maximum"  type  of  whorl  has  become  restricted  to  a  few  earlier 
whorls,  the  adult  whorl  being  marked  by  the  spinous  "caricum"  type 
of  whorl.  Different  individuals  show  progressive  encroachment  of 
the  "caricum"  type  on  the  "maximum"  type,  until  the  latter  has 
been  completely  superseded,  the  spines  then  following  immediately 
upon  the  tubercles;  and,  in  still  more  advanced  forms,  becoming 
telescoped  with  them.  This  is  the  character  of  the  modern  type, 
where  the  tubercles  pass  imperceptibly  into  the  earliest  spines. 
It  is  thus  only  by  the  consideration  of  the  intermediate  Tertiary 


A  I— 

1      1                                2 

I 
1 

6 

n  1 

n  |_ 

1      1                2                 1                 3 

L)l 

r  \ 

I                                 1 

1   i     2     i      3      i      4 

L  1 

n  i 

1   i  2  i  3  i    4    i       5 

U  1 

Ei 

III                 1 
12345                    6 

1 

i 
P  i 

1                          1                           1                           1                           1 

1.23456               7 

r  i 
r  i 

II                           1                           1                            II 

1.2.3.4.5.                      7 

FIG.  257.     Diagram  illustrating  the  development  of  the  Fulgur  series. 

Stage  r  is  the  protoconch  which  persists  throughout. 

Stage  2  is  the  smooth  shell  stage  which  in  the  primitive  species  A  forms 
the  adult,  but  in  B  is  shortened. 

Stage  3  is  the  ribbed  stage,  which  is  wanting  in  A,  but  in  a  somewhat  more 
advanced  species  B  is  well  developed  in  the  adult. 

Stage  4  is  characterized  by  an  angular  whorl,  the  ribs  still  continuing.  It  is 
the  adult  character  of  species  C,  in  which  stages  2  and  3  are  condensed. 

Stage  5  is  the  tubercled  stage  characteristic  of  the  adult  of  F.  fusiformis. 

Stage  6  is  the  smooth  round-shelled  stage  found  in  the  old  age  of  species  D 
and  the  adult  of  E. 

Stage  7  (F.  maximum)  shows  the  caricum  spines  well  developed  in  species 
F  while  in  species  G  the  modern  F.  caricum,  Stage  6,  has  been  eliminated  and 
Stage  7  follows  directly  upon  the  tubercles  (Stage  5). 

types  that  the  true  history  of  the  development  of  the  Fulgurs  is 
learned,  the  individual  life  history  of  the  modern  F.  caricum  being 
an  abbreviated  and  incomplete  recapitulation  of  the  history  of  its 
race.  Here  acceleration  has  been  so  pronounced  as  actually  to 
eliminate  certain  stages  in  the  sequence  of  development.  The  pre- 


970  PRINCIPLES    OF    STRATIGRAPHY 

ceding  diagram   (Fig.  257)   will  summarize  this  method  and  also 
give  a  graphic  illustration  of  the  law  of  acceleration. 

Origin  and  Development  of  Characters  the  Important  Question: 
Rectigradations  and  Allometrons.  As  pointed  out  by  Osborn,  the 
origin  and  development  of  individual  characters  or  parts  is  the 
important  subject  for  investigation,  the  species  question  being  of 
minor  significance.  It  has  been  shown  in  the  preceding  sections 
that  characters  develop  more  or  less  independently  of  each  other, 
and  also  that  they  develop  in  recognizable  directions,  or  ortho- 
genetically.  Such  definitely  developing  characters  when  arising  as 
new  characters  are  termed  by  Osborn  rectigradations ;  whereas,  if 
they  are  due  to  a  change  in  proportion  of  such  characters,  they  are 
termed  by  him  Allometrons  (30:32). 


NOMENCLATURE  OF  STAGES  IN  DEVELOPMENT. 

Ontogenetic  Stages  and  Morphie  Stages.  In  the  preceding  ex- 
amples it  will  be  noted  that  the  stages  dealt  with  are  form  stages 
or  morphic  stages  only,  and  that  they  have  no  constant  relation  to 
the  actual  stages  in  successive  ontogenetic  development.  Thus, 
one  and  the  same  morphic  stage,  i.  e.,  stage  characterized  by  certain 
morphological  characters,  as,  for  example,  ribs,  tubercles,  or  spines, 
etc.,  may  be  characteristic  of  the  adult  of  one  individual,  and,  of  a 
more  youthful  stage,  of  another.  In  dealing  with  changes  in  form 
it  is  desirable  to  refer  each  morphic  stage  to  the  corresponding  adult 
stage  of  an  ancestor,  and  to  designate  it  by  the  name  of  that  ances- 
tor. Thus  the  tubercled  stage  of  Fulgur  tritonis  (Fig.  256,  /)  is  des- 
ignated the  F.  fusiformis  stage,  since  the  feature  in  question  charac- 
terizes the  adult  of  that  species.  In  like  manner,  the  smooth 
morphic  stage  of  F.  tritonis  is  designated  the  maximum  stage,  and 
the  spinose  stage  the  F.  caricum  stage,  from  the  species  in  which 
these  characters  belong  to  the  adult.  The  development  of  each  in- 
dividual (ontogeny)  comprises  a  series  of  stages  which  develops 
from  birth  to  old  age.  These  ontogenetic  stages,  or  onto-stages, 
are  similar  in  time-duration  for  related  organisms  and  are  further 
characterized,  in  a  general  way,  by  a  correspondence  in  the  pro- 
portional rate  of  growth  in  closely  related  types.  They  are,  how- 
ever, independent  of  the  morphic  characters,  for,  as  already  shown, 
a  certain  morphic  character  may  appear  in  one  individual  in  the 
adult  stage  and  in  another  more  accelerated  individual  in  a  more 
youthful  stage.  (Grabau-na.) 

Simple  Organisms.     Hyatt  and  others  have  given  us  a  set  of 


NOMENCLATURE    OF    STAGES    IN    ONTOGENY  971 

terms  which  are  applicable  to  the  ontogenetic  stages  of  development 
of  all  non-colonial  organisms,  and  hence  deserve  to  be  widely  and 
generally  used.  The  ontogenetic  cycle, 'or  cycle  of  individual  de- 
velopment (Hyatt-2o),  is  divided  into  the  Embryonic  and  the 
Ep-embryonic  periods,  and  each  is  further  subdivided  into  onto- 
stages  and  sub-stages,  as  follows : 


EMBRYONIC. 


EP-EMBRYONIC.  < 


Onto-stage. 
Prot-embryonic 
Mes-embryonic 
Met-embryonic 
Neo-embryonic 
Typ-embryonic 
Phyl-embryonic 

Nepionic 
Neanic 
Ephebic 
Gerontic 


Onto  Sub-stage. 

A  na-prot-embryonic 

Meta-prot-embryonic 

Para-prot-embryonic 

A  na-mes-embryonic 

Meta-mes-embryonic 

Para-mes-embryonic 

A  na-met- embryonic 

{  Mela-met- embryonic 
Para-met- embryonic 
A  na-neo-embryonic 
Meta-neo-embryonic 
Para-neo-embryonic 
A  na-typ-embryonic 
Meta-typ-embryonic 
Para-typ- embryonic 

[  Ana-phyl-embryonic 
M eta- phyl- embryonic 
Para-phyl-embryonic 

Ana-nepionic 

Meta-nepionic 

Para-nepionic 

Ana-neanic 

Meta-neanic 

Para-neanic 

A  na-ephebic 

Meta-ephebic 

Para-epnebic 

Ana-gerontic 

Meta-gerontic 

Para-gerontic 


The  sub-stages  ana,  meta,  and  para,  or  the  early,  intermediate, 
and  later  sub-stages,  are  useful  for  more  detailed  subdivision 
than  is  possible  with  the  stages  alone.  The  phyl-embryonic  is  the 
only  em?3ryonic  stage  with  which  the  palaeontologist  has  to  deal.  It 
is  the  first  stage  in  which  hard  parts  capable  of  preservation  are 
generally  formed.  The  phyl-embryonic  stages  of  the  following 
classes  of  invertebrates  have  been  definitely  recognized  and  named : 


972  PRINCIPLES.  OF    STRATIGRAPHY 

Simple  corals proto-corallum. 

Brachiopoda protegulum  (Beecher). 

Pelecypoda prodissoconch  (Jackson). 

Gastropoda protoconch  (protorteconch)  (Hyatt  and  Grabau). 

Scaphopoda periconch  (Hyatt). 

Cephalopoda protoconch  (Owen). 

Trilobites protaspis  (Beecher). 

Echinoidea protechinus  (Jackson). 

The  Nepionic  Stage  is  the  babyhood  stage  of  ep-embryonic  ex- 
istence. Its  exact  limitation  cannot  be  denned  in  general  terms, 
as  it  is  different  in  different  classes  of  organisms.  In  general,  it 
may  be  said  that,  for  ammonites,  it  covers  most,  if  not  all,  of  the 
morphic  stages  in  which  the  suture  is  of  the  goniatite  type.  In  the 
case  of  Schloenbachia,  cited  above,  the  morphic  stages,  up  to  the 
point  where  the  young  ammonite  resembles  in  its  sutures  the  genus 
Paralegoceras,  are  considered  by  Smith  to  belong  in  the  nepionic 
stage.  Here  the  neanic  stage  begins  shortly  before  the  suture  has 
lost  its  goniatite  character,  but  an  ammonite  character  has  made  its 
appearance  in  the  form  of  a  keel.  In  Fulgur  caricum  and  other 
advanced  species  of  this  group  of  gastropods  the  nepionic  stage 
may  be  regarded  as  completed  with  the  end  of  the  tubercled  condi- 
tion (F.  fusiformis,  morphic  stage). 

The  neanic  is  the  youthful  or  adolescent  stage,  which  comprises 
the  interval  during  which  the  organism  acquires  all  the  characteris- 
tics of  maturity.  When  this  condition  is  reached  the  organism 
enters  on  the  ephebic,  or  adult,  stage.  Long-lived  individuals  often 
show  old  age  or  senile  characteristics,  which  consist  especially  in  the 
loss  of  ornamentation  and  a  degenerate  change  in  the  manner  of 
growth.  This  is  the  gerontic  stage  in  the  ontogenic  cycle,  and  it  is 
followed  by  death. 

Gerontic  characteristics  may  appear  early  in  the  life  of  indi- 
viduals of  a  specialized  race.  Thus  the  loss  of  characters  and  the 
degenerate  change  in  growth  may  occur  while  the  individual  is  still 
in  the  adult  (ephebic)  stage  or  even  earlier.  Such  races  are  said 
to  be  phylogerontic  and  are  approaching  extinction.  Thus  the  late 
Cretacic  cephalopods,  which  lost  the  power  of  coiling  either  partly 
(Heteroceras,  etc.)  or  wholly  in  the  adult  (Baculites),  represent 
the  phylogerontic  terminals  of  the  degenerating  race  of  ammonoids. 

It  must,  however,  be  clearly  borne  in  mind  that  the  existence  of 
phylogerontic  lines  or  races  at  any  time  does  not  indicate  that  the 
phylum  or  class  as  a  whole  is  gerontic.  Even  within  the  same 
genus  there  may  be  found  species  showing  a  gerontic  tendency. 
The  phylogerontism  here  applies  only  to  the  particular  branch  in 
question,  while  the  rest  of  the  evolutional  tree  of  this  phylum  may 


CHARACTERS    OF    COLONIAL   FORMS  973 

be  perfectly  sound.  Many  early  Ordovicic  nautiloids  show  a  loss 
of  the  power  to  coil,  and  so  indicate  the  existence  of  degenerating 
or  phylogerontic  branches  at  a  time  when  the  class  of  cephalopods 
as  a  whole  had  not  yet  permanently  acquired  the  power  of  coiling. 
Gastropods  with  the  last  whorl  not  coiled  are  found  throughout 
the  geologic  series,  even  in  Lower  Cambric  time,  where  coiling  had 
but  just  begun.  Such  senile  branches  are,  of  course,  to  be  expected 
in  any  developing  series  where  wrong  or  too  hasty  experiments  may 
be  made  by  individual  genetic  lines.  (See  illustrations  in  North 
American  Index  Fossils.) 

Colonial  Forms.  These  require  a  specially  modified  nomencla- 
ture since  we  deal  not  with  individuals,  but  with  groups  of  indi- 
viduals. In  these  we  must  keep  separate  the  individual  life  history 
or  ontogeny  and  the  life  history  of  the  colony,  i.  e.,  colonial  on- 
togeny (astogeny  or  autogenesis).  The  first  form  considered  in  such 
cases  is  nepionic  so  far  as  the  colony  is  concerned.  To  express  this 
fact  Cumings  (5)  has  coined  the  terms  nepiastic,  neanastic,  ephe- 
bastic  and  gerontastic*  which  express  for  the  colony  what  the 
Hyattian  terms  express  for  the  individual.  The  first  completed 
individual  of  a  colony  may  be  dignified  by  a  distinctive  term,  though 
it  cannot  be  considered  homologous  with  the  phyl-embryonic  stage 
of  the  individual.  In  Hydrozoa  and  in  compound  corals  the  first 
completed  individual  is  the  prototheca  (the  sicula  of  graptolites,  the 
initial  pipe-like  corallite  of  the  Favositid  corals),  and  in  Bryozoa  it 
is  the  protoccium.  (Cumings-5.) 


INTRACOLONIAL  ACCELERATION  AND  RETARDATION. 

Colonial  organisms  may  suffer  differential  acceleration  or  re- 
tardation when  certain  groups  of  individuals  develop  either  more 
rapidly  or  more  slowly  than  others.  This  leads  to  the  formation, 
within  the  same  colony,  of  two  or  more  types  of  structure,  normally 
characteristic  of  distinct  species.  In  this  manner  we  can  ex- 
plain such  phenomena  as  the  occurrence  of  different  types  of  leaves 
upon  the  same  plant,  and  different  groups  of  individuals  in  the  same 
colony  of  animals  where  some  individuals  retain  ancestral  charac- 
ters, while  others  develop  further.  Among  plants  the  tulip  tree 
(Lyriodendron  tulipifera)  may  be  taken  as  an  illustration.  The 
two  and  four-lobed  types  of  leaf  are  characteristic  of  ancestral 
-Cretacic  species.  Modern  trees,  with  normally  6-lobed  leaves,  also 

*  From  &<rrv  (asty),  a  group  of  dwellings. 


974 


PRINCIPLES    OF    STRATIGRAPHY 


contain  adult  leaves  and  sometimes  entire  branches  in  which  the 
leaves  never  pass  beyond  the  four-lobed  or  even  two-lobed  type. 
By  retardation  the  ancestral  characters  are  retained  side  by  side 
with  the  normal  characters  of  the  modern  species.  Eight-,  10-,  12- 
and  sometimes  14-lobed  leaves  also  occur,  evidencing  local  intra 
colonial  acceleration. 

An  example  among  colonial  animals  will  further  make  this 
clear.  Favosites  canadensis  of  the  Ononclaga  limestone  is  charac- 
terized by  small  corallites  with  polygonal  openings,  while  among 
these  are  scattered  at  regular  intervals  larger  ones  with  nearly  cir- 
cular openings.  Favosites  placenta  of  the  middle  Hamilton  of 


FIG.  258.  Portions  of  the  surfaces  of  two  colonies  of  Favosites,  somewhat 
enlarged,  to  show  intracolonial  acceleration,  a.  F.  canadcusis, 
showing  the  regular  distribution  of  the  large  cylindrical  corallites 
among  the  smaller  prismatic  ones.  b.  F.  placenta,  showing  the 
F.  canad-ensis  condition  on  the  left,  and  the  large  prismatic 
corallites  on  the  right. 

Canada  when  young  (nepiastic)  has  the  characteristics  of  adult 
F.  canadensis,  but  when  colonially  adult  it  has  retained  the  F.  cana- 
densis  type  in  certain  portions  of  the  colony  only,  other  portions 
having  developed  a  uniform  series  of  large  corallites  with  polygonal 
apertures.  Here,  then,  certain  portions  of  the  colony  have  been 
retarded  in  their  development,  retaining  ancestral  characters,  while 
others  have  continued  to  develop.  In  the  upper  Hamilton  a  species 
of  the  F.  placenta  type  (F.  placentoides)  occurs  with  all  the  coral- 
lites uniform,  large  and  angular  in  aperture  (Fig.  258). 

Acceleration  in  certain  portions  and  retardation  in  others  when 
occurring  in  more  or  less  regular  manner  result  in  the  formation  of 
colonial  ornamentation,  such  as  is  so  characteristic  of  Bryozoa. 

Atavism  or  Reversion.  Not  infrequently  among  a  large  number 
of  individuals  of  a  species  characterizing  a  certain  horizon  a  few 
will  be  found  in  which  ancestral  characters  occur  in  the  adult,  thus 
recalling  species  of  a  lower  geologic  horizon.  This  atavism  or 


ATAVISM    OR   REVERSION  975 

reversion  of  the  species  to  ancestral  characters  may  often  be  seen 
to  be  nothing  more  than  an  arrestation  of  development  at  an  imma- 
ture morphic  stage,  when  the  characters  of  the  young  are  like  those 
of  the  adult  ancestor  of  earlier  geologic  horizons.  This  arrestation 
of  development  or  genepistasis  is  only  a  step  removed  from  pro- 
gressive retardation  in  development  of  which  it  forms  the  distal 
limit.  In  either  case,  whether  complete  or  partial  arrestation  (heter- 
epistasis)  occurs,  or  whether  development  is  retarded  altogether 
or  along  certain  lines,  the  resultant  form  will  seem  out  of  place 
in  the  horizon  characterized  by  the  more  advanced  species,  and  may 
sometimes  lead  to  mistaken  classification  of  the  strata  containing 
them. 

As  an  example  of  atavistic  individuals  occurring  in  a  horizon 
above  their  normal  may  be  cited  the  case  of  the  Devonic  brachiopod 
Spirifer  mucronatus  and  its  derivatives  already  mentioned.  This 
species,  so  far  as  known,  is  represented  by  the  elongated,  strongly 
mucronate  type  in  the  lower  Hamilton  beds  of  eastern  North 
America.  In  the  Upper  Hamilton  of  Ontario  occurs  the  mutation 
S.  thedfordense,  which  in  its  younger  stages  has  all  the  features  of 
the  typical  lower  Hamilton  form,  but  in  the  adult  it  is  proportionally 
much  less  extended,  without  mucronate  points,  without  the  charac- 
teristic plication  in  the  median  sinus  of  the  pedicle  and  groove  in 
the  median  fold  of  the  brachial  valve,  and  with  strongly  marked, 
regular  lines  of  growth.  With  this  species  occur  a  number  of 
individuals  which  have  been  retarded  in  their  development  and 
which,  hence,  recall  the  ancestral  type  in  some  of  their  characters — 
notably  the  strong  mucronate  lateral  extensions.  In  the  New  York 
province  of  the  Middle  Devonic  the  chief  developmental  changes 
acquired  by  S.  mucronatus  consist  in  the  relative  shortening  of  the 
mucronate  angles  as  the  shell  approaches  the  adult  stage,  until 
from  a  width  several  times  its  height  it  had  changed  to  a  form  in 
which  the  width  was  more  nearly  equal  to  the  height,  and  in  which 
the  mucronations  were  wholly  obliterated.  In  other  respects 
the  changes  were  very  slight.  With  this  mutation  occurs  not  infre- 
quently a  form  showing  arrestation  of  development  (genepistasis) 
at  an  early  stage,  and  hence  it  retains  into  the  adult  its  youthful 
mucronate  character,  which  recapitulates  the  ancestral  condition. 
These  arrested  individuals  thus  recall  in  practically  all  respects 
the  primitive  mucronate  type  from  which  they  are  derived. 

An  example  of  a  retarded  individual  from  the  Karnic  lime- 
stone of  the  California  Trias  is  cited  by  J.  P.  Smith.  This  was 
an  immature  specimen  of  the  ammonoid  genus  Trachyceras  which 
had  persisted  unusually  long  in  the  ancestral  Tirolites  stage,  thus 


976 


PRINCIPLES    OF    STRATIGRAPHY 


resembling  the  adult  of  that  genus  which  belonged  in  a  lower  hori- 
zon.    This  occurrence  threatened  to  cause  difficulty  in  correlation. 


PARALLELISM  AND  CONVERGENCE  IN  DEVELOPMENT. 

Homer  agenesis.  One  of  the  most  important  of  the  many  facts 
brought  to  light  by  the  researches  of  palaeontologists  is  that  many 
groups  of  organisms  develop  independently  in  similar  directions, 


FIG.  259.  Illustration  of  parallelism.  A  series  of  Eocenic  Fusoid  shells,  be- 
longing to  different  genera,  but  readily  mistaken  for  members  of 
the  same  genus  Fusus  under  which  they  were  originally  de- 
scribed, a.  Falsifusus  mey'eri;  b.  Fulgurofusus  rugatus.  c. 
Fusus  asper  X  i^.  d.  Early  whorls  of  same,  enlarged  X  10. 

and  that  hence  in  disconnected  series  species  with  similar  adult 
characteristics  may  develop.  These,  morphological  equivalents,  as 
Hyatt  has  termed  them  (or  Homoeomorphs  of  Buckman),  are  often 
so  much  alike  that  they  have  been  united  under  the  same  generic 
or  even  specific  name.  The  Eocenic  fusoid  shell  Falsifusus,  from 
the  Gulf  Coast  of  the  southern  United  States,  is  an  example  of 
this,  the  adult  form  having  all  the  characteristics  of  the  genus 
Fusus,  though,  as  shown  by  the  young  stages,  the  American  form 


PARALLELISM  AND  CONVERGENCE 


977 


is  probably  derived  from  a  Pleurotoma-like  ancestor,  and  not  a 
true  Fusus  at  all.*  (Fig.  252.) 

The  Eocenic  genus  Clavilithes  furnishes  a  number  of  striking 
examples  of  this  similar  development  or  homceogenesis,  as  Eimer 
has  termed  it.f  (Fig.  260.) 

The  typical  species  of  this  genus,  C.  parisiensis,  from  the  Cal- 
caire  Grossier  of  the  Paris  Basin,  finds  its  almost  exact  equivalent 
in  the  modern  Cyrtulus  serotinus,  Hinds,  of  the  Marquesas  region 
in  the  South  Pacific.  Clavilithes  became  extinct  in  the  Eocenic, 
while  Cyrtulus  is  a  derivative  from  the  modern  stock  of  Fusus. 
But  by  far  the  most  interesting  type  of  this  complex  series  is 


FIG.  260.  Clavilithoid  shells  showing  "convergence."  a,  b.  Cyrtulus  sero- 
tinus. A  modern  clavilithoid,  being  the  phylogerontic  terminal  of 
the  Fusus  series  (slightly  reduced),  c.  The  protoconch  and 
early  conch  stages  of  Clavilithes  parisiensis,  an  Old  World 
Eocenic  clavilithoid  (enlarged),  d.  Clavilithes  (f)  kennedy- 
anus,  a  New  World  Eocenic  clavilithoid  of  independent  origin 
(slightly  reduced). 

Clavilithes  scalar  is  (Lamarck),  from  the  Sables  Moyens  of  France. 
This  species  is  characterized  by  a  projecting  rim  or  flange  on 
the  shoulder  of  the  adult  whorl.  This  same  feature  is  reproduced 
in  Clavilithes  longcevus  (Solander)  of  the  Barton  Beds  of  England, 
which  is  of  wholly  independent  origin.  Again,  Clavilithes  f  cham- 
berlaini,  Johnson  and  Grabau,  from  the  Lower  Claibornian  of 
Texas,  shows  the  same  type  of  structure,  and  here,  too  it  is  inde- 
pendently derived.  Finally,  Rhopalithes  japeti  (Tournouer)  repre- 
sents this  same  feature  in  a  genus  entirely  distinct  from  Clavilithes 

*  The  distinction  is  not  accepted  by  all.     (Grabau-i4.) 

f  The  controversy  regarding  this  and  the  other  species  mentioned  here  is 
dealt  with  by  Grabau  (13:622  et  seq.)  in  the  Studies  of  Gastropoda  III. 


978  PRINCIPLES    OF    STRATIGRAPHY 

Examples  of  such  equivalents  could  be  multiplied  indefinitely.  In 
the  majority  of  cases,  where  classification  has  taken  account  only 
of  the  adult  characters,  such  homceogenetic  types  have  been  classed 
together  as  of  the  same  genus  or  species,  and  sometimes  even  as 
varieties  of  the  same  species. 

It  is  hardly  going  too  far  to  say  that  the  majority  of  classifica- 
tions of  invertebrates  now  in  vogue  may  be  likened  to  a  more  or 
less  warped  plane  passed  through  the  crown  of  a  tree;  all  the 
points  of  intersection  of  the  branches  and  the  plane  are  considered 
as  species,  while  all  the  neighboring  and  some  distant  ones  are 
grouped  together  in  a  genus,  or  family.  The  illogical  nature 
of  this  method,  which  is  the  natural  result  of  a  consideration  of 
adult  characters  only,  must  be  apparent. 

Morphologic  equivalents  have  been  recognized  most  frequently 
among  ammonoids.  Formerly  all  types  in  which  the  suture  was 
composed  of  simple  lobes  and  saddles  were  classed  as  Goniatites. 
All  those  in  which  the  lobes  were  crenulated  as  Ceratites,  and  all 
those  in  which  both  lobes  and  saddles  had  become  compound  were 
placed  in  the  genus  Ammonites.  It  is  now  known  that  many  and 
diverse  genetic  series  started  with  genera  of  the  goniatite  type, 
branched  out  in  diverse  genera  with  ceratite  sutures  and  that  from 
these  latter  were  derived  the  genera  in  which  the  suture  was  am- 
monitic.  Again,  similar  types  of  ornamentation  and  similar  de- 
grees of  coiling  or  involution  appeared  independently  in  distinct 
genetic  series,  thus  producing  species  which  often  closely  re- 
sembled each  other  in  the  adult  type,  but  which  had  a  wholly  dis- 
tinct ancestry. 

Among  vertebrates  many  cases  of  similar  independent  morpho- 
logical equivalents  have  been  discovered,  especially  in  the  class  of 
mammals,  and  in  that  of  reptiles.  It  sometimes  happens  that  it  is 
impossible  or  impracticable  to  separate  such  heterogenetic  homceo- 
morphs  into  their  respective  genera.  In  such  cases  a  generic  name 
is  retained  for  this  polyphyletic  group,  but  it  must  not  be  considered 
a  genus.  The  name  Circulus  (Bather)  has  come  into  use  for  such 
groups  of  homoeomorphs.  Platyceras  is  an  example  of  a  circulus 
among  gastropods ;  it  is  commonly  given  the  value  of  a  genus,  but 
its  species  are  phylogerontic  terminals  of  a  number  of  genetic 
series.  Many  of  the  generic  names  applied  to  graptolites,  such  as 
Tetragraptus,  Dichograptus,  etc.,  are  really  circuli,  for  they  repre- 
sent similar  stages  in  development  in  different  genetic  series.  Since 
they  occur  at  the  same  geologic  horizon  they  have  also  been  called 
''Geologic  genera"  (Ruedemann-39). 

A  distinction  has  commonly  been  maintained  between  cases  in 


PARALLELISM    AND    CONVERGENCE  979 

which  related  animals  or  plants  have  developed  in  a  similar  man- 
ner but  independently  and  those  in  which  unrelated  animals  or 
plants  have  developed  similar  characteristics  which  apparently 
bring  them  more  closely  together.  To  the  former  the  term  parallel- 
ism has  generally  been  restricted,  while  the  term  convergence  has 
been  applied  to  the  latter  case.  Of  course,  it  is  understood  that 
the  use  of  this  term  does  not  imply  that  the  organisms  in  question 
actually  converge  in  their  relationship,  as  seems  to  have  been  as- 
sumed by  some,  but  merely  that  the  convergence  is  only  a  morpho- 
logic one  and  may  lead  to  mistaken  ideas  of  relationship.  The 
similar  independent  development  of  the  projecting  flange  in  the 
species  of  Clavilithes,  cited  above,  may  be  considered  a  case  of 
pure  parallelism,  while  its  development  in  Rhopalithes  may  be  con- 
sidered a  case  of  convergence.  A  similar  case  of  convergence  is 
seen  in  the  American  Eocenic  Falsifusus  and  the  British  Eocenic 
Fusus,  already  cited,  both  of  which  have  adult  characteristics  which 
have  led  to  their  being  classed  in  the  same  genus.  That  they  are  of 
independent  ancestry,  however,  seems  to  be  established.* 

BIBLIOGRAPHY  XXV. 

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Palaeozoic  Species.      Memoirs  of  the  Boston  Society  of  Natural  History, 
Vol.  VII. 

24.  JACKSON,  R.  T.    1913.     Alpheus  Hyatt  and  His  Principles  of  Research. 

American  Naturalist,  Vol.  XLVII,  pp.  195-205. 

25.  JOHNSON,  DOUGLAS  W.     1904.     Geology  of  the  Cerrillos  Hills,  New 

Mexico.     School  of  Mines  Quarterly,  1903-04,  Part  II,  Palaeontology. 

26.  LOOMIS,  F.  B.     1910.     Ontogeny:    A  Study  of  the  Value  of  Young  Fea 

tures   in    Determining   Phylogeny.     Paleontologic   Record,    pp.    51-53. 
Reprinted  from  Popular  Science  Monthly. 

27.  LULL,  RICHARD  S.     1910.     Relation  of  Embryology  and  Vertebrate 

Palaeontology.     Ibid.,  pp.  47-50. 

28.  MORGAN,  THOMAS  HUNT.     1903.     Evolution  and  Adaptation.     Mac 

millan  Company,  New  York. 

29.  NEUMAYR,   MELCHIOR,  and    PAUL,   C.   M.     1875.     Congerien  und 

Paludinen-schichten    Slavoniens.     Abhandlungen    der   koniglich-kaiser- 
lichen  geologischen  Reichsanstalt.     Bd.  VII,  Heft  3. 

30.  OSBORN,  HENRY  F.     1907.     Evolution  as  It  Appears  to  the  Paleontolo- 

gist.    Seventh  International  Zoological  Congress  Proceedings.     Boston 


BIBLIOGRAPHY    XXV  981 

Meeting,  1907.     Advance  sheets,  1910.     Also  Science  N.  S.,  Vol.  XXVI, 
No.  674,  pp.  744-749,  Nov.,  1907. 

31.  OSBORN,    H.    F.     1908.     The   Four   Inseparable   Factors   of   Evolution. 

Science  N.  S.,  Vol.  XXVII,  No.  682.     Jan.,  1908,  pp.  148-150. 

32.  OSBORN,  H.  F.     1908.     Coincident  Evolution  through  Rectigradations. 

Ibid.,  Vol.  XXVII,  No.  697,  pp.  749-752. 

33.  OSBORN,  H.  F.     1910.     Paleontologic  Evidences  of  Adaptive  Radiation. 

The  Paleontologic  Record,  pp.  34-38.     Reprinted  from  Popular  Science 
Monthly. 

34.  OSBORN,  H.  F.     1911.     Biological  Conclusions  drawn  from  the  Study  of 

the  Titanotheres.     Science  N.  S.,  Vol.  XXXIII,  pp.  825-828. 

35.  OSBORN,  H.F.     1912.    The  Continuous  Origin  of  Certain  Unit  Characters 

as  Observed  by  a  Palaeontologist.     American  Naturalist,  Vol.  XLVI,  pp. 
185-206,  249-278. 

36.  OSBORN,  H.  F.     1912.     First  Use  of  Word  "Genotype."     Science  N.  S., 

Vol.  XXXV,  pp.  340-341. 

37.  OSBORN,  H.  F.     1912.     Tetraplasy,  the  Law  of  the  Four  Inseparable 

Factors  of  Evolution.     Journal  of  the  Academy  of  Natural  Sciences, 
Philadelphia.     Vol.  XV,  second  series,  pp.  273-309. 

37a.  OSBORN,   H.  F.     Assisted  by  Grabau,  A.  W.     1911.     Article  on  Palae- 
ontology.    Encyclopaedia  Britannica,  nth  Edition,  Vol.  xx,  pp.  579—591. 

38.  PENHALLOW,  D.  P.     1910.     The  Relation  of  Paleobotany  to  Phytogeny. 

The  Paleontologic  Record,  pp.  67-72.     Reprinted  from  Popular  Science 
Monthly. 

39.  RUEDEMANN,  RUDOLF.     1904.     Grapholites  of  New  York.     Memoir 

VI  of  the  New  York  State  Museum,  Part  I,  Vol.  I. 

40.  RUEDEMANN,  R.     1910.     Anatomy  and  Physiology  in  Invertebrate  Ex- 

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Vol.  XL,  pp.  95-121. 

42.  SHIMER,  H.  W.     1908.     Dwarf  Faunas.     Ibid.,  Vol.  XLII,  pp.  472-490. 

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Journal  of  Geology,  Vol.  V,  pp.  521  et  seq. 

44.  WAAGEN,    W.     1868.      Die    Formenreihe   des  Ammonites    subradiatus. 

Beneckes   Geognostisch-Palaeontologische   Beitrage,    Bd.    II,    pp.    179- 
256  (185-6). 


CHAPTER    XXVI. 

PHYSICAL  CHARACTERISTICS  OF   THE   INHABITABLE   EARTH.— 
BIONOMIC   CHARACTERS  OF  THE   ENVIRONMENT.* 

A  comprehensive  survey  of  the  inhabitable  world  shows  its 
divisibility  into  three  great  bionomic  realms,  each  of  which  has  its 
peculiar  characteristics  and  its  specially  adapted  forms  of  animal 
and  plant  life.  The  essential  character  of  each  is  determined  by  the 
nature  of  the  medium  in  which  the  organisms  live,  i.  e.,  whether  salt 
water,  fresh  water,  or  air.  We  have,  accordingly: 

1.  The  Marine,  or  Halo-biotic  realm. 

2.  The  Fresh  Water,  or  Limno-biotic  realm. 

3.  The   Terrestrial,    or   Atmo-biotic    (also   called    Geo-biotic) 

realm. 

While  each  of  these  is  distinct  from  the  others,  they  also  grade 
into  one  another  to  a  greater  or  less  extent  along  their  lines  of  in- 
tersection. Thus  the  marine  and  fresh-water  realms  intergrade 
in  the  estuaries  of  rivers,  where  the  water  is  brackish.  The  marine 
and  terrestrial  realms  intergrade  at  the  shore,  where  organisms 
are  periodically  exposed  between  tides  first  to  the  one  and  then 
to  the  other  medium.  Again,  the  terrestrial  and  fresh-water  flu- 
vial, lacustrine,  etc.,  realms  intergrade  along  the  margins  of  streams 
and  the  shores  of  lakes. 

Each  one  of  the  bionomic  realms  may  be  further  subdivided 
into  a  light,  or  photic  region,  and  a  dark,  or  aphotic  region.  Be- 
tween these  two  may  frequently  be  determined  a  dusk,  or  dysphotic 
region.  Schimper  (6)  has  defined  these  regions  in  the  marine 
realm  on  the  basis  of  plant  life  as  follows : 

The  photic  region  extends  over  such  depths  wherein  the  in- 
tensity of  sunlight  is  sufficient  for  the  normal  development  of 
macrophytes.  The  dysphotic  region  is  insufficiently  lighted  for  the 

*  This  and  the  succeeding  two  chapters  are  in  part  a  reprint,  with  additions 
and  emendations,  of  a  paper  published  by  the  author  in  1899  under  the  title 
Relation  of  Marine  Bionomy  to  Stratigraphy.  Bulletin  of  Buffalo  Society  Natural 
Sciences,  Vol.  VI,  pp.  319-365. 

982 


i 


CLASSIFICATION    OF    LIFE    DISTRICTS  983 

normal  development  of  macrophytes,  which  exist  there  but  scantily 
or  not  at  all,  while  certain  moderately  assimilating  microphytes, 
especially  diatoms,  still  exist.  The  aphotic  region  comprises  that 
part  of  the  sea  where  only  the  non-assimilating  vegetable  organisms 
can.  exist.  The  depth  at  which  these  regions  pass  into  one  another 
varies  with  the  locality  and  the  purity  of  the  water.  In  the  open 
sea  the  dark  region  begins  at  a  depth  of  about  200  fathoms.  In 
the  fresh  water  realm  the  aphotic  region  is  not  often  found,  though 
deep  lakes,  like  Lake  Superior  and  Lake  Geneva,  extend  to  depths 
not  penetrated  by  sunlight.  Such  cases  are,  however,  comparatively 
uncommon.  A  limno-aphotic  region  is  further  found  in  the  streams 
and  lakes  of  caves  where  the  sunlight  is  shut  out  by  the  roof 
of  the  cavern.  Caverns,  too  (natural  and  artificial),  constitute  the 
only  aphotic  region  of  the  terrestrial  realm,  and  they  are  often 
peopled  with  a  well-adapted  fauna  and  flora. 

The  final  division  into  life  districts  depends  on  the  absence  or 
presence  of  a  substratum,  and  this  division  can  be  equally  well 
carried  out  in  the  marine,  fresh  water,  and  terrestrial  realms.  The 
absence  of  a  substratum  compels  the  organism  to  float  or  swim  in 
the  medium,  and  for  this  purpose  special  organs  and  a  specially 
modified  body- form  commonly  exist.  The  substratum  may  be 
visited  for  food  or  other  purposes,  but  the  organism  is  perfectly 
at  home  in  the  medium. 

Each  realm  may,  then,  be  divided  into  the  following  life-districts, 
the  medium  being  salt  water,  fresh  water,  or  air,  according  as  the 
marine,  fluvio-lacustrine,  or  terrestrial  realms  are  considered : 

1.  Littoral  district:  Light;  substratum  present. 

2.  Pelagic  district:  Light;  substratum  absent. 

3.  Abyssal  district:  Dark;  substratum  present. 

4.  Abysso-pelagic  district:  Dark;  substratum  absent. 


I.     THE  LITTORAL  DISTRICTS. 

A.  Marine.  The  marine  littoral  district  extends  from  the 
shore  at  high-water  mark  to  the  edge  of  the  continental  shelf, 
where  it  quickly  merges  into  the  abyssal  district.  The  depth  to 
which  the  littoral  district  extends  is  approximately  200  meters, 
though  the  hundred-fathom  line  is  commonly  taken  as  the  seaward 
boundary  of  this  district.  Around  oceanic  islands  and  young  con- 
tinents the  littoral  district  is  very  narrow,  the  ocean  'floor  soon 
falling  off  to  deep  water.  The  origin  of  this  district  is  to  be 
sought  in  the  activities  of  various  geologic  agencies,  chief  among 


984  PRINCIPLES    OF    STRATIGRAPHY 

which  are  the  inland  cutting  of  waves  and  currents,  thus  extend- 
ing the  sea  landward ;  and  the  deposition  of  the  land-derived  detri- 
tus on  the  edge  of  the  continental  shelf,  thus  pushing  this  ed^e 
seaward  and  widening  the  submarine  platform.  Subsidence  of 
the  land  permits  the  advance  of  the  sea  over  the  low  country,  and 
broad  epicontinental  seas  are  formed,  which  fall  entirely  within 
the  littoral  life  district.  In  mediterraneans,  too,  the  littoral  belt  is 
generally  a  broad  one,  only  the  central  portion  descending  to  abyssal 
depth.  (See  further,  Chapter  III.) 

The  conditions  become  more  favorable  for  the  development  of 
littoral  life  as  the  continent  grows  older,  provided,  of  course,  that 
no  important  oscillatory  movements  occur.  As  time  progresses  the 
breadth  of  the  submerged  continental  shelf  increases,  both  by  land- 
ward cutting  and  by  seaward  building,  and  the  surface  of  the  land 
becomes  more  and  more  reduced,  thus  causing  a  decrease  in  the 
amount  of  detrital  material  which  can  be  carried  into  the  sea,  and 
a  concomitant  increase  in  the  purity  of  the  water.  When  peneplana- 
tion,  or  the  reduction  of  the  land  to  base-level,  has  been  accom- 
plished, the  amount  of  detritus  carried  into  the  sea  is  practically 
nil;  and  any  organisms,  like  corals,  adapted  only  to  pure  water, 
can  flourish  close  to  the  continental  shore,  and  deposits  of  a  purely 
organic  nature,  such  as  extensive  deposits  of  pteropod  or  foramini- 
feral  shells,  may  form  in  comparatively  shallow  water. 

The  epicontinental  sea  and  the  littoral  belt  of  the  mediterraneans 
are  especially  adapted  for  the  development  of  local  or  provincial 
faunas.  Such  provincializing  of  faunas  is  most  marked  if,  by  some 
oscillatory  movement  of  the  land  or  some  other  physical  change, 
the  basins  of  these  intracontinental  seas  become  separated  from  the 
littoral  district  of  the  ocean  sufficiently  to  prevent  intercommunica- 
tion between  the  organisms  of  the  two  provinces.  A  barrier  is  thus 
formed,  which  need  not  necessarily.be  a  land  barrier,  and  a  great 
diversity  of  faiinas  may  result.  A  rather  marked  diversity  of  fauna 
existed  in  early  Tertiary  time  between  the  Mississippi  embayment 
and  the  Atlantic  coast,  and  in  Palaeozoic  time  between  the  Bay  of 
New  York  and  the  central  interior  sea.  Recent  provincial  faunas 
are  frequently  met  with.  It  requires  only  a  comparatively  slight 
elevation  of  the  sea-floor,  or  a  moderate  deepening  of  the  abyssal 
oceanic  basins,  to  draw  off  the  water  from  the  shallower  regions 
and  lay  dry  large  portions  of  the  littoral  district.  Such  a  change 
would,  of  course,  result  in  an  almost  complete  extinction  of  the 
littoral  flora  and  fauna  thus  exposed  and  force  the  survivors  to  ac- 
commodate themselves  to  a  narrower  field.  Revival  of  stream  ac- 
tivities, consequent  upon  elevation  of  the  land,  would  result  in 


THE    LITTORAL   DISTRICT  985 

carrying  a  large  amount  of  debris  into  the  sea  and  thus  produce 
conditions  unfavorable  to  the  existence  of  many  organisms. 

Landward  the  littoral  district  interlocks  with  the  corre- 
sponding districts  of  the  terrestrial  and  fluvial  realms,  the  faunas 
and  floras  of  all  more  or  less  intermingling.  It  is  in  this  portion 
of  the  littoral  district  that  an  important  subdivision  must  be  con- 
sidered; namely,  the  shore.  The  shore,  as  already  noted  (ante, 
Chapter  XV),  is  that  part  of  the  littoral  district  which  lies  between 
the  highest  water  mark  (often  considered  as  including  even  the 
highest  point  of  the  wave  mark)  and  the  lowest  line  drawn  during 
the  lowest  ebb.  In  the  greater  part  of  this  division  of  the  littoral  dis- 
trict there  is  a  change  of  medium  twice  every  twenty-four  hours, 
and  a  change  of  the  consequent  physical  conditions  attendant  upon 
the  character  of  the  medium.  Organisms  living  in  this  portion  of 
the  littoral  zone  must  be  capable  of  withstanding  the  effects  of 
the  partial  or  complete  removal  of  their  normal  medium  for  a 
greater  or  less  time.  It  is  here  that  the  interlocking  of  the  terres- 
trial and  marine  floras  and  faunas  becomes  most  marked,  and  an 
intermingling  and  a  migration  from  one  district  into  the  other 
occur.  Migration  from  the  land  to  the  sea  is  exemplified  by  the 
whales,  seals,  and  other  aquatic  mammals,  which  have  become 
marine  in  so  far  as  their  mode  of  locomotion  is  concerned.  Owing 
however,  to  the  inability  of  air-breathing  animals  to  adapt  them- 
selves to  a  water-breathing  habit,  all  terrestrial  animals  passing 
into  the  sea  must  assume  a  pelagic  life,  where  they  can  retain  their 
normal  method  of  respiration. 

Among  other  animals  which  have  exchanged  their  normal  ter- 
restrial habit  for  a  prevailingly  marine  one  may  be  mentioned 
several  birds,  such  as  the  Penguins  and  the  Albatross;  certain 
snakes,  turtles,  and  crocodiles,  and  a  number  of  insects.  The  birds 
and  insects  here  considered  represent  a  passage  from  the  aerial  to 
the  marine  pelagic  district;  while  the  reptiles,  like  the  mammals, 
illustrate  a  passage  from  the  land  to  the  pelagic  district  of  the  sea. 

While  thus  the  land  fauna,  in  advancing  into  the  sea,  naturally 
takes  to  a  pelagic  life,  the  land  flora  can  adapt  itself  to  the  condi- 
tions of  the  littoral  district.  This  is  well  shown  by  the  eight  spe- 
cies of  phanerogams,  which  have  acquired  a  wholly  marine  habit, 
and  are  now  known  as  eel  grasses  or  sea  grasses.  In  the  case  of 
these  plants  the  adaptation  is  so  complete  that  they  can  no  longer 
live  out  of  their  adopted  habitat.  The  mangrove  plants,  on  the 
other  hand,  are  only  partially  accommodated  to  the  conditions  of 
the  marine  littoral  district,  for  it  is  necessary  that  their  crowns  of 
leaves  should  be  above  water. 


986  PRINCIPLES    OF    STRATIGRAPHY 

Marine  animals  and  plants,  likewise,  attempt  migrating  from  the 
sea  to  the  land.  In  their  adaptation  to  the  new  habitat  the  animals 
are  the  more  successful,  just  as  the  plants  are  the 'more  successful 
in  migrating  the  other  way.  Thus  two  genera  of  fish,  Periophthal- 
mus  and  Boleophthalmus,  are  able  to  pass  the  greater  part  of  their 
lives  out  of  water.  They  "skip  along  close  to  water-line  on  the 
seashore,  where  they  hunt  for  molluscs  (Onchidium)  and  insects." 
(Semper-7  :/#p.)  The  large  branchial  cavity  of  these  fishes  is  not 
completely  filled  by  the  gills,  but  serves  in  part  as  an  air  cavity  or 
primitive  lung.  In  a  number  of  fishes,  such  as  Anabas  scandens  of 
the  Philippines,  this  gill-cavity  is  further  modified  into  a  "laby- 
rinthine organ,"  or  much  prolonged  cavity,  the  mucous  membrane 
of  which  is  thrown  into  complicated  folds,  thus  greatly  increasing 
the  surface.  These  fish  can  exist  for  days  out  of  water  and  are 
able  to  make  long  overland  excursions.  Semper  holds  that  these 
fish  may  be  regarded  "as  Amphibians  with  quite  as  much  reason  as 
toads  and  frogs,  or  even  better,  since  they  are  capable  of  changing 
the  nature  of  their  respiration — of  air,  that  is,  or  of  water — at  will, 
and  suddenly  without  any  interruption."  Several  of  our  littoral 
gastropods,  e.  g.,  Littorina,  Ilyanassa,  etc.,  are  capable  of  existing 
out  of  water  for  a  considerable  time.  In  Brazil  Littorina  climbs 
the  trees  of  the  mangrove  high  above  water  and  oysters  and  other 
bivalves  are  attached  to  the  roots  of  these  trees  and  are  laid  bare 
at  low  tide.  Ampullaria  forms  a  connecting  link  between  sea 
and  land  snails,  for  it  not  only  breathes  by  means  of  a  gill  but  also 
has  a  pulmonary  sac  like  that  of  the  land  snails  into  which  air  is 
carried  by  means  of  a  long  breathing-siphon. 

The  possibility  that  related  species  of  marine  gastropod  Mollusca 
may  leave  the  sea  in  different  parts  of  the  world  and  give  rise  to 
terrestrial  forms,  which,  though  differing  from  their  marine  an- 
cestors, may  be  very  similar  to  each  other,  deserves  attention. 
In  this  way  some  of  the  puzzling  problems  of  distribution  of  ter- 
restrial gastropods  on  widely  distant  oceanic  islands  may  be  ac- 
counted for. 

Among  the  Crustacea  there  are  several  species  of  crabs  (e.  g., 
Birgus  latro,  etc.)  which  live  in  damp  woods  far  from  all  water 
and  whose  respiration  is  carried  on  chiefly  without  the  intermedia- 
tion of  their  normal  medium. 

The  advent  of  marine  vegetation  on  the  land  has  occurred  only 
up  to  the  limit  of  the  salt  spray  on  exposed  shores,  and  here  the 
number  of  species  is  small.  But  at,  or  just  below,  high-tide  limit 
a  number  of  algae  find  a  congenial  abode,  and  grow  there  in  luxuri- 
ant masses.  Chief  of  these  in  our  northern  latitudes  are  the  Fuci, 


THE    LITTORAL   DISTRICT  987 

with  Fucus  vesiculosus  and  Ascophyllum  nodosum  predominating. 
At  low-tide  these  hang  like  a  wet  fringe  over  the  exposed  rocks 
and  give  shelter  to  numerous  species  of  the  smaller  littoral  animals, 
as  well  as  other  algae. 

The  littoral  districts  of  the  marine  and  fluvial  realms  also  inter- 
lock along  the  shores  where  streams  mouth  into  the  sea  or  expand 
into  broad  estuaries.  Here  marine  animals  will  venture  up  into  the 
fresh  water  littoral  district,  while,  similarly,  fresh  water  animals 
pass  into  the  littoral  district  of  the  marine  realms.  The  common 
meeting-ground  of  the  two  approaching  floras  and  faunas  is  in 
the  estuarine  or  brackish  water  facies  of  the  littoral  districts. 

The  neritic  zone,  "Flachsee,"  or  thalassic  zone,  is  that  portion 
of  the  littoral  district  which  is  never  uncovered.  It  is  separated 
as  a  distinct  district  by  Walther,  Haug,  and  others,  who  restrict 
the  term  littoral  to  the  shore  zone.  It  is,  however,  so  intimately 
connected  with  the  shore  zone  in  all  its  physical  and  bionomic 
characteristics  that  a  separation  is  not  natural.  The  bottom  of 
the  neritic  zone  of  the  littoral  district  is  less  diversified  than  that 
of  the  shore  zone.  In  its  upper  portion  and  in  its  shoals  it  may 
partake  of  the  character  of  the  shore  zone,  but  in  its  deeper  por- 
tions the  character  of  the  bottom  is  usually  more  uniform,  being 
either  rocky  or,  what  is  more  common,  composed  of  fine  detrital 
material  mingled  with  organic  matter  in  various  stages  of  dissolu- 
tion. According  to  the  character  of  the  bottom,  plant  life  will  vary 
and  with  it,  to  a  greater  or  less  extent,  animal  life. 

Taken  as  a  whole,  the  littoral  district  is  the  most  important 
portion  of  the  sea,  both  from  a  bionomic  point  of  view  and  from  its 
bearing  on  palaeontology.  "The  littoral  region,"  says  Loven  (4:86), 
''comprises  the  favored  zones  of  the  sea,  where  light  and  shade,  a 
genial  temperature,  currents  changeable  in  power  and  direction, 
a  rich  vegetation  spread  over  extensive  areas,  abundance  of  food,  of 
prey  to  allure,  of  enemies  to  withstand  or  evade,  represent  an  in- 
finitude of  agents  competent  to  call  into  play  the  tendencies  to  vary 
which  are  embodied  in  each  species,  and  always  ready,  by  modify- 
ing its  parts,  to  respond  to  the  influences  of  external  conditions." 
This  district  may  perhaps  be  regarded  as  the  cradle  of  organic 
life,  from  which  were  peopled  the  abyssal  and  pelagic  districts,  on 
the  one  hand,  and  the  terrestrial  and  fluvial  realms  and  their  vari- 
ous districts,  on  the  other. 

B.  Fresh  Water.  The  littoral  district  of  the  fresh  water  realm 
is  almost  coextensive  in  area  with  that  of  the  streams  and  fresh 
water  lakes  and  ponds  of  the  world.  The  only  exception  to  this  is 
found  in  those  portions  of  very  deep  lakes  where  sunlight  does  not 


988  PRINCIPLES    OF    STRATIGRAPHY 

penetrate  to  the  bottom  and  in  the  subterranean  streams  and  lakes. 
The  fauna  of  the  limno-littoral  district  is  much  less  diverse  than 
that  of  the  corresponding  district  in  the  sea.  Whole  classes  of  ani- 
mals, like  those  of  the  Echinodermata,  the  Anthozoa,  the  Brachio- 
poda,  Cephalopoda,  Pteropoda,  Scaphopoda,  etc.,  are  normally  ab- 
sent from  fresh  water,  while  most  of  the  remaining  ones  are  poorly 
represented  by  genera  and  species,  though  often  prolific  in  indi- 
viduals. Plant  life,  on  the  contrary,  is  abundantly  represented,  not 
only  by  desmids,  diatoms,  and  fresh-water  algae,  but  also  by  the 
large  number  of  swamp  plants  which  grow  partly  submerged  and 
represent  the  transition  zone  between  the  terrestrial  and  limno- 
littoral  districts. 

C.  Terrestrial.  The  terrestrio-littoral  district  is  coextensive 
with  the  surface  of  the  land.  No  other  life  district  comprises  such 
a  range  of  physical  characteristics,  and  no  other  district  is  inhabi- 
ted by  such  a  variety  of  highly  specialized  types  of  animal  and 
plant  life.  Here  we  pass  from  the  cold  of  the  arctic  snow-fields 
to  the  burning  sands  of  the  tropics,  from  the  land  of  nearly  continu- 
ous rains  to  the  rainless  desert  regions,  parched  by  the  continued 
drought  of  years,  and  from  the  region  of  plentiful  food  supply  to 
the  stony,  arid  wastes,  where  the  nature  of  the  soil  is  hostile  to 
practically  all  forms  of  plant  life.  It  is  to  be  expected  that  under 
such  widely  varying  conditions  a  fauna  and  flora  should  develop 
which  in  its  variety  outruns  that  of  any  other  life  district,  and  which 
in  its  own  extremes  reflects  the  range  of  its  environment. 


II.     THE  PELAGIC  DISTRICTS. 

A.  Marine.  The  marine  pelagic,  or  halo-pelagic  district,  is 
the  common  meeting-ground  of  most  of  the  life  districts.  It 
touches  all  shores  and  communicates  with  the  corresponding  dis- 
tricts of  both  the  terrestrial  and  fluvial  realms.  It  has  direct  com- 
munication with  the  littoral  district,  many  inhabitants  of  which 
leave  the  bottom  at  times  to  lead  a  temporary  existence  in  the  pela- 
gic district;  while  many  pelagic  animals,  in  turn,  visit  the  bottom 
or  shores  for 'food.  Occasionally  inhabitants  of  the  pelagic  dis- 
trict enter  for  a  time  the  corresponding  district  of  the  terrestrial 
realms,  i.  e.}  the  aerial;  as,  for  example,  the  so-called  flying-fish; 
and,  in  turn,  as  already  noted,  many  aerial  animals  spend  a  part 
of  their  lives  in  the  marine  pelagic  district,  or  at  least  show  a  de- 
cided preference  for  a  pelagic  life.  The  passage  of  land  animals 
to  the  halo-pelagic  district  has  already  been  noted.  Similar  in- 


THE    PELAGIC    DISTRICTS  989 

termingling  of  fresh  water,  or  limno-pelagic,  and  salt  water  pelagic 
types  occurs  in  the  estuaries  and  stream  mouths,  and  it  is  notorious 
that  halo-pelagic  fish  will  enter  the  limno-pelagic  district  in  breed- 
ing time.  It  is  quite  probable,  as  Sir  William  Flower  suggests,  that 
the  Cetacea,  in  their  transition  from  a  terrestrial  to  a  marine  life, 
passed  through  a  stage  in  which  they  lived  in  fresh  water.  A  sim- 
ilar transition  for  the  sea-grasses  is  not  improbable,  though  they  can 
no  longer  live  in  fresh  water.  Intercommunication  between  the 
abysso-pelagic  and  pelagic  districts  also  occurs,  as  well  as  between 
the  abysso-pelagic  and  abyssal. 

B.  Fresh  Water.    The  pelagic  life  of  ponds,  lakes,  and  rivers 
is    much  less  varied  than  that  of  the  sea,  though,  as  will  be  seen 
later,  the  number  of  individuals  of  a  given  species  may  often  be  very 
great.     In  ponds  and  lakes  no  very  distinctive  characteristics  not 
found  in  shallow  seas  exist,  aside,  of  course,  from  the  distinctions 
due  to  the  difference  in  degree  and  kind  of  salinity.     In  rivers,  on 
the  other  hand,  we  must  consider  the  importance  of  currents,  which 
vary  greatly  in  strength,  but  are  essentially  constant  in  direction. 
It  is  this  constancy  which,  as  Chamberlin  has  pointed  out,  favors 
the  development  of  a  special  body  form,  the  resistance  of  which  to 
the  current  is  at  a  minimum.     Such  a  body  form  is  found  in  fish 
and  in  the  ancient  Eurypterida,  and  it  is  a  possibility  not  to  be 
lightly  set  aside  that  both  fish  and  eurypterids   originated  in  the 
rivers  of  the  Palaeozoic  and  earlier  lands.     Indeed,  this  is  all  but 
definitely  proven  for  the  Eurypterida  (O'Connell-5)  and  seems  to 
be  indicated  for  the  fish  as  well.     Significant  in  this  connection  is 
the  fact  that  the  early  remains  of  fish  as  of  eurypterids  are  not 
found  in  normal  marine  deposits,  but  in  those  which  are  at  least 
open  to  the  suspicion  that  they  are  formed  by  rivers  or  at  least  at 
the  mouths  -of  rivers,  while  the  best  preserved  remains,  and  the 
most  abundantly  represented  in  the  Palaeozoic,  are  found  in  river 
flood-plain  deposits  and  in  deltas.    This  subject  will  be  more  fully 
discussed  in  the  next  chapter  (Grabau-3). 

C.  Terrestrial.    The  pelagic  life  of  fresh  water  is,  as  we  have 
seen,  much  less  abundant  than  that  of  the  sea,  and,  again,  the  aerial 
life,  or  that  of  the  pelagic  district  of  the  land,  is  much  less  prom- 
inent than  that  of  the  streams  and  lakes.    This  gradation  is  in  direct 
correspondence  with  that  observed  in  the  gradation  in  the  density 
of  the  medium.     Moreover,  in  the  terrestrial  realm  the  pelagic  dis- 
trict is  only  temporarily  inhabited,  few,  if  any,  terrestrial  animals 
or  plants  spending  their  entire  existence  suspended  in  the  air.    The 
most  familiar  examples  of  animals  spending  a  part  of  their  lives 
at  least  in  the  atmo-pelagic  district  are :  insects  among  invertebrates, 


990  PRINCIPLES    OF    STRATIGRAPHY 

pterosaurs  among  reptiles,   the  birds,  and,  among  mammals,  the 
bats. 

III.     THE  ABYSSAL  LIFE  DISTRICT. 

A.  Marine.    The  marine  abyssal  districts  comprise  the  lightless 
depths,  or  generally  those  depths  exceeding  two  hundred  fathoms. 
(Chapter  III.)     As  assimilating  plant  life  is  absent  in  these  dis- 
tricts  the   food  supply  of   the  organisms   existing  in  them  must 
be  wholly  derived   from  the  districts   in   which   such   assimilating 
vegetation  exists.     A  large  proportion  of  the  food  of  the  abyssal 
animals  is  contained  in  the  organic  oozes  and  sediments  which  con- 
stantly settle  down  in  a  more  or  less  decomposed  state  from  the 
lighted  districts.    The  abysso-pelagic  district  is  frequently  invaded 
by  organisms  from  the  pelagic  district,  which  descend  into  the  dark 
regions  during  the  day. 

B.  Fresh  Water  and  C.  Terrestrial.     In  the  non-marine  realms 
the  lightless  districts  are  sparingly  represented.     Lakes  of  great 
depth,  whose  bottom  is  in  perpetual  darkness,  do  exist,  but  the  life 
of  these  dark  regions  is  mostly  unknown.     Cave  life,  on  the  other 
hand,  both  fluvio-lacustrine  and  terrestrial,  has  been  made  the  sub- 
ject of  much  study,  and  its  characteristics  are  known  to  harmonize 
with  the  peculiar  conditions  which  give  these  districts  their  especial 
stamp. 

BIBLIOGRAPHY  XXVI. 

1.  CHAMEERLIN,  THOMAS  C.     1900.     The  Habitat  of  the  Early  Verte- 

brates.    Journal  of  Geology,  Vol.  VIII,  pp.  400-412. 

2.  GRABAU,  A.  W.     1899.     The  Relation  of  Marine  Bionomy  to  Stratigraphy. 

Chapter  III  in  the  Geology  and  Palaeontology  of  Eighteen-mile  Creek. 
Bulletin  of  the  Buffalo  Society  of  Natural  Sciences,  Vol.  VI,  pp.  319-365. 

3.  GRABAU,  A.  W.     1913.     Ancient  Delta  Deposits  of  North  America.     Bul- 

letin of  the  Geological  Society  of  North  America,  Vol.  XXIV  pp.  498-526. 

4.  LOVEN,  SVEN.     1883.     On  Pourtalasia,  a  Genus  of  Echinoidea.     Stock- 

holm. 

5.  O'CONNELL,    MARJORIE.     1912.     The    Habitat   of   the    Eurypterida. 

Paper  presented  before  the   New  York  Academy  of  Sciences.      Also  in 
Grabau  (2),  pp.  499-515- 

6.  SCHIMPER,   A.   F.   W.     1898.      Pflanzengeographie   auf   physiologischer 

Grundlage.     Jena.     English  translation  by  W.  R.  Fisher.     Plant  Geog- 
raphy, Oxford,  1903. 

7.  SEMPER,  KARL.     1881.     Animal  Life  as  Affected  by  the  Natural  Condi- 

tions of  Existence.     Appleton  International  Scientific  Series,  Vol.  XXX. 


CHAPTER   XXVII. 
BIONOMIC   CLASSIFICATION  OF  PLANTS  AND  ANIMALS. 

A  bionomic  classification,  or  one  based  on  the  relationship  of 
the  organism  to  its  environment,  cannot  agree  with  one  based  en- 
tirely on  anatomic  characteristics.  It  is  a  more  primitive  classifica- 
tion, but  a  very  useful  one  from  many  points  of  view. 


SUBDIVISIONS. 

Primary  Divisions.  The  primary  divisions  of  the  organisms 
agree  with 'the  primary  divisions  of  the  life  districts,  i.  e.,  the 
marine,  fresh  water,  and  atmospheric  or  terrestrial.  We  have,  ac- 
cordingly, halo-bios,  limno-bios,  and  atmo-bios  (geo-bios),  each  of 
these  including  the  plants  and  animals  of  the  respective  realms. 

Secondary  Divisions.  The  next  division  is  based  on  the  rela- 
tion of  the  organism  to  the  substratum,  where  we  have  floating 
types  or  plankton,  swimming  types  or  nekton,  and  bottom  types 
or  benthos.  The  first  two  belong  to  the  pelagic  and  abysso-pelagic 
districts,  the  third  to  the  littoral  and  abyssal.  Their  further  sub- 
divisions and  relationships  are  as  follows : 

1.  Holoplankton:    organisms    spending    all    their 

lives  as  plankton  (ex.,  jelly  fish). 

2.  Meroplankton:    organisms    leading    a    plank- 

tonic  life  during  larval  stages  only  (ex., 
Crustacea,  echinoderms,  ccelenterates). 

3.  Pseudo plankton:      organisms      normally      at- 

tached but  floating  through  accident,  as 
the  Sargassum,  leaves  and  trunks  of  trees, 
or  parts  of  'dead  organisms,  such  as  shells  of 
molluscs,  etc. 

4.  Epiplankton:   organisms   living   upon    or   at- 

tached to  floating  objects  (ex.,  Crustacea 
and  hydroids  of  the  pseudoplanktonic  Sar- 
gassum ;  Lepas  attached  to  floating  logs,  etc. 

1.  Holonekton. 

2.  Meronekton. 

3.  Epinekton:  organisms  parasitically  or  other- 

wise attached  to  swimming  or  flying  ani- 
mals. 

991 


A.  Plankton  (floating  or- 
ganisms)  


B.  Nekton  (swimming  or 
flying  organisms) .... 


992  PRINCIPLES    OF    STRATIGRAPHY 

C.  Benthos  (bottom  or-  (  I.   Vagrant:  with  power  to  walk,  crawl,  or  1  Littoral 

ganisms) <  creep  over  the  bottom.  >      and 

[  2.  Sedentary:  Attached  to  the  bottom.          j  Abyssal. 

According  to  the  realm  in  which  the  organism  lives  we  have, 
therefore : 

I.  Marine  or  Halobios,  including 

A.  Haloplankton 

B.  Halonekton 

C.  Halobenthos 

II.  Freshwater  or  Limnobios,  including 

D.  Limnoplankton 

E.  Limnonekton 

F.  Limnobenthos 

III.  Terrestrial  or  Atmobios  (Geobios),  including 

G.  Atmoplankton 
H.   Atmonekton 
I.     Atmobenthos 

With  reference  to  depth,  we  may  further  subdivide  marine 
plankton,  etc.,  into  anoplankton  (from  av<o,  upward*)  or  that 
occurring  above  the  100  fathom-line;  this  may  be  divided  into 
anoholoplankton,  anomeroplankton,  anopseudoplankton  and  anoepi- 
plankton.  Below  100  fathoms  we  have  the  mesoplankton  (from 
/w,«ros,  middle),  and  again,  just  above  the  abyssal  depths  may 
occur  the  hypoplankton  (from  VTTO,  under),  anonekton,  mesonek- 
ton  and  hyponekton,  as  well  as  anobenthos  (littoral  district),  meso- 
benthos  (bathyal  district)  and  hypobenthos  (abyssal  district)  may 
also  be  recognized. 

Each  of  these  divisions  may  now  be  considered  in  detail. 


A.    Haloplankton. 

i.  Holoplankton.  The  term  plankton  was  introduced  by  Vic- 
tor Hensen  in  1887.  It  is  derived  from  the  Greek  TrXayK-ros,  which 
means  wandering  or  drifting  about  aimlessly.  The  true  plankton, 
or  holoplankton,  is  most  typically  developed  in  the  sea.  It  com- 
prises those  organisms  which  spend  their  lives  in  the  sea  drifting 
about  from  place  to  place,  without  power  to  direct  their  own 

*The  term  epiplankton  was  proposed  for  this  by  George  H.  Fowler  in  1911 
(Encyclopedia  Britannica,  nth  ed.,  vol.  xxi,  p.  721),  but  was  preoccupied  by 
Grabau  in  1909  as  above  defined  (3).  Hence  the  names-  anoplankton  and  ano- 
benthos are  here  proposed.  The  names  mesoplankton,  mesobenthos,  hypo- 
plankton  and  hypobenthos,  also  proposed  by  Fowler,  are,  however,  acceptable. 


HOLOPLANKTON ;  MEROPLANKTON      993 

course.  These  organisms  range  in  size  from  creatures  of  micro- 
scopic dimensions  to  medusae  50  cm.  in  diameter.  While  some  of 
the  larger  animals  of  this  group  have  power  to  propel  themselves 
through  the  water,  they  nevertheless  are  subject  to  the  force  of 
strong  waves  or  currents,  which  render  them  helpless.  Holoplank- 
tonic  organisms  are  wholly  pelagic,  and  are  characterized  by  a  more 
or  less  transparent  body  and  by  the  absence  of  opaque  skeletal  struc- 
tures, only  a  few  forms  retaining  delicate  calcareous  shells,  inherited 
from  their  benthonic  ancestors.  In  its  horizontal  distribution  the 
holoplankton  of  the  sea  is  dependent  chiefly  upon  the  marine  cur- 
rents, as  the  organisms  composing  it  are  practically  unable  to  carry 
on  independent  migrations,  though  many  of  them  can  dart  about 
in  quiet  water.  Hence  they  fall  an  easy  prey  to  actively  predaceous 
animals/  The  occurrence  of  holoplanktonic  animals  in  swarms  is 
also  accounted  for  by  their  lack  of  independent  locomotion,  for  the 
eggs,  liberated  by  the  floating  parent,  commonly  develop  without 
separating  far  from  the  parent,  with  which  they  are  carried  along 
by  the  currents  of  the  sea.  These  animals  have,  however,  the 
power  to  rise  and  descend  in  the  water,  and  during  the  day  many 
of  them  live  at  a  depth  of  from  fifty  to  one  hundred  and  fifty 
fathoms,  coming  to  the  surface  only  on  quiet  nights.  The  animals 
of  this  class  also  occur  in  the  abyssopelagic  district. 

2.  Meroplankton.  This  term  (from  /xepos,  a  part)  was  intro- 
duced by  Haeckel  in  1890  (4)  and  is  applicable  to  the  larvae  of  ben- 
thonic animals  which  lead,  during  the  larval  stages,  a  truly  plank- 
tonic  existence  and  which  occur  with  and  suffer  the  same  vicissi- 
tudes as  the  true  or  holoplankton.  The  upper  levels  of  the  ocean 
are  usually  crowded  with  such  meroplanktonic  organisms,  and  to 
them  is  due  the  horizontal  distribution  of  benthonic  species.  Float- 
ing about  in  the  sea  in  perfect  clouds  or  swarms  these  mero- 
planktonic organisms  pass  their  short  existence  a  sport  of  the  waves 
and  currents.  Sooner  or  later,  however,  they  sink  to  the  bottom, 
a  veritable  rain  of  seedling  organisms ;  and,  if  they  fall  on  a  fertile 
soil,  if  they  reach  the  proper  facies  of  the  substratum,  they  develop 
into  the  benthonic  adult ;  but,  if  they  fall  upon  an  unfavorable  bot- 
tom, or  if  the  food  supply  is  scarce,  they  perish.  Thus,  other  things 
being  favorable,  wherever  the  facies  of  sea-bottom  normal  to  a 
particular  species  of  benthonic  organism  exists,  the  bottom  may  be 
peopled  with  that  species  by  the  larvae  which  reach  it  from  the 
upper  waters,  where  they  were  carried  by  waves  and  currents 
during  their  meroplanktonic  wanderings.  As  Walther  says,  should 
unfavorable  circumstances  temporarily  destroy  a  whole  fauna,  its 
depopulated  home  would  at  once  be  surrounded  by  swarms  of 


994  PRINCIPLES    OF    STRATIGRAPHY 

delicate  larvae,  and,  as  soon  as  the  old  conditions  are  reestablished, 
this  fauna  will  again  appear  with  countless  individuals.  This  ex- 
plains the  sudden  reappearance  in  later  strata  of  the  fauna  of  an 
earlier  bed,  even  though  it  was  absent  from  the  intervening  strata. 
From  a  stratigraphic  point  of  view  the  meroplankton  is  of  vast 
importance,  for  to  it  is  due  the  wide  dispersal  of  the  benthonic 
organisms,  which  of  all  marine  life  forms  are  the  best  indices 
of  the  physical  conditions  of  the  sea  bottom.  It  is  during  the  larval 
period  that  benthonic  marine  invertebrates  spread  in  all  directions 
from  their  center  of  occupancy,  and  that  they  have  an  opportunity 
to  enter  and  occupy  distant  regions. 

3.  Pseudoplankton.     This  term  was  introduced  by  Schiitt   (8) 
for  such  organisms  which,  like  the  Sargassum,  are  normally  or  in 
early  life  benthonic,  but  continue  their  later  existence  as  plankton. 
Walther  has  extended  the  meaning  of  the  term  so  as  to  include 
those  organisms  which  are  carried  about  by  floating  objects,  to 
which  they  are  either  attached  as  sedentary  benthos  or  which  serve 
them  as  a   substratum  on   which  they  lead   a   vagrant  benthonic 
existence.     This  group,  however,  is  distinct,  and  is  separated  here 
under  the  name  of  epiplankton. 

Under  pseudoplankton  may,  however,  be  included  those  ben- 
thonic or  nektonic  organisms  which  become  planktonic  only  after 
death ;  i.  e.,  that  portion  of  the  plankton  which  consists  of  the  float- 
ing parts  of  dead  organisms,  such  as  the  leaves  and  trunks  of 
trees,  dead  insects  and  carcasses  of  vertebrates,  and,  above  all, 
the  shells  of  molluscs,  which,  on  the  death  of  the  animal,  are  dis- 
tributed more  or  less  widely,  according  to  the  nature  of  the  shell. 
Thus  the  shell  of  Spirula  is  widely  distributed  and  embedded  in 
contemporaneous  sediments  where  the  organism  never  lived,  and 
leaves  of  terrestrial  plants  are  found  in  sediments  far  from  land. 
Tree  trunks  from  tropical  America  are  carried  to  the  northeast 
coast  of  Iceland,  where  they  become  embedded  in  contemporaneous 
sediments. 

4.  Epiplankton.       This  term  (from  €7Tt,  upon)  was  proposed 
(Grabau-3)   for  those  organisms  which  live  upon  a  floating  sub- 
stratum, to  which  they  are  either  attached  or  upon  which  they  lead 
a  vagrant  existence.     The  substratum  may  be   holoplanktonic  or 
pseudoplanktonic,  the  latter  being  the  most  frequent.     Examples  of 
epiplankton  are  the  algae,  hydroids,  and  bryozoans  attached  to  the 
floating  Sargassum  and  other  algae;  and  the  Crustacea,  molluscs, 
and  other  animals  living  among  their  branches ;  and  the  organisms 
attached  to  floating  tree  trunks  and  other  pseudoplankton. 

A  large  number  of  algae,  especially  the  shallow- water  forms, 


EPIPLANKTON  995 

have  attached  to  them  sedentary  animals  as  well  as  other  species 
of  algae.  Among  the  animals,  hydroids  and  bryozoans  are  the  most 
common,  though  other  sedentary  animals,  such  as  Spirorbis,  are 
frequently  abundant.  Animals  belonging  to  the  vagrant  type  of 
the  benthos  are  by  no  means  rare.  The  large  fronds  of  the  Lami- 
naria  cast  up  on  our  northern  shores  during  every  storm  are  fre- 
quently veritable  menageries  of  invertebrate  life,  which,  under 
favorable  conditions,  may  float  about  for  days.  These  fronds,  for 
example,  are  commonly  covered  with  a  dense  growth  of  the  delicate 
littoral  hydroids  Obelia  and  Campanularia,  while  Bugula  and  other 
Bryozoa  and  Spirorbis  are  usually  common.  The  hollow  stem  is 
commonly  surrounded  by  an  extensive  growth  of  Membranipora, 
while  not  infrequently  tubularian  and  other  hydroids  find  this  a 
suitable  resting  place.  The  root-like  base  of  the  stem  often  em- 
braces the  shell  of  Modiola  or  Cyprina,  which  in  turn  is  over- 
grown with  coralline  algae.  Sponges  are  also  found  among  the 
"roots"  of  the  Laminaria,  and  Acmaea,  Chiton,  Crepidula,  Anomia, 
and  other  molluscs  are  attached  to  the  shell,  or  to  the  stone  which 
frequently  takes  its  place.  Finally,  worms  and  crustaceans  are  not 
rare  inhabitants  of  the  sheltering  space  between  the  branches  of 
the  "roots" ;  and  sea  anemones,  small  star-fish,  brittle-stars,  and 
sea  urchins  also  occur,  both  on  the  basal  portion  of  the  stem  and 
on  the  frond  itself.  Such  floating  menageries  may  be  carried  far 
out  to  sea  or,  what  is  perhaps  more  frequent,  may  be  driven  ashore. 
Not  infrequently  they  are  carried  far  up  into  the  estuaries  and, 
becoming  stranded,  are  buried  in  the  mud ;  or  else  they  are  cast  up 
on  mud  flats  behind  some  sheltering  bar  or  ledge. 

While  these  cases  illustrate  an  epiplanktonic  existence  due  to 
accident,  the  cirriped  Lepas  illustrates  a  habitually  epiplanktonic 
existence ;  this  barnacle  rarely  occurring  except  attached  to  floating 
objects.  Many  of  the  animals  found  on  the  Sargassum  seem  to 
be  characteristic  of  it  in  its  floating  condition,  not  occurring  on  it  in 
its  native  haunts.  (Ortmann-7.)  Walther  has  adduced  evidence 
which  goes  to  show  conclusively  that  many  of  the  larger  fossil 
Pentacrini,  and  perhaps  other  crinoids,  occurred  with  their  stems 
wound  around  floating  timbers,  and  he  explains  the  occurrence  of 
these  marine  animals  in  fresh  water  coal  strata  as  due  to  stranding 
in  estuaries  of  species  leading  an  epiplanktonic  existence. 

The  marine  or  haloplankton  forms  one  of  the  chief  sources  of 
food  for  many  marine  animals  and  is  everywhere  devoured  in 
vast  quantities.  Dead  organisms  which  sink  to  the  sea-floor  in  an 
incomplete  state  of  decomposition  form  the  chief  element  of  the 
organic  oozes  which  furnish  food  to  many  littoral  as  well  as  abyssal 


996  PRINCIPLES   OF    STRATIGRAPHY 

animals.  The  skeletal  portions  of  the  dead  plankton  often  accumu- 
late in  vast  quantities  on  the  bottom,  and,  in  the  greater  depths 
where  terrigenous  sediments  are  absent,  they  usually  form  diatoma- 
ceous,  radiolarian,  globigerina,  pteropod,  and  other  oozes.  The 
purity  of  such  oozes,  i.  e.,  their  freedom  from  clastic  sediment,  is 
usually  an  index  of  the  purity  of  the  water  in  which  they  were 
deposited,  but  from  this  we  cannot  always  decide  that  such  oozes, 
when  found  in  fossil  state,  indicate  deep  sea.  The  absence  of 
clastic  sediment  may  be  due  to  the  low  relief  of  the  land,  which 
may  have  been  worn  down  to  base-level,  thus  allowing  water  of 
moderate  depth  near  shore  to  be  free  from  detrital  material. 

B.     Halonekton. 

The  term  nekton,  derived  from  the  Greek  WJKTOS,  which  means 
swimming,  was  introduced  by  Haeckel  in  1890  (4),  for  those  ani- 
mals which  lead  an  actively  swimming  life.  The  group  is  typified  by 
the  class  of  fishes.  A  torpedo-like  form,  terminating  anteriorly 
in  a  head,  and  perfect  bilateral  symmetry  are  the  chief  character- 
istics of  these  animals.  A  strong  musculature  for  propulsion  is 
usually  situated  in  the  posterior  portion  of  the  body,  while  ap- 
pendages for  balancing  and  steering  are  also  usually  present.  The 
body  is  non-transparent  and  a  calcareous  supporting  skeleton  is 
ordinarily  developed.  Typical  nektonic  animals  of  the  modern  sea 
are:  the  squids,  the  fish,  and  the  degenerate  'mammals — whales, 
porpoises,  etc.  Besides  holonektonic  forms  there  are  in  the  sea 
epinektonic  ones,  i.  e.,  sessile  forms  more  or  less  pemanently  at- 
tached to  a  swimming  host!  The  whale  barnacle,  attached  to  the 
under  side  of  whales,  and  the  ship's  barnacles  are  examples  among 
invertebrates,  while  the  Pilot-fish  attached  by  suckers  to  sharks 
represent  this  type  among  vertebrates. 

C.     Halobenthos. 

The  term  benthos,  from  /?<n/0os,  the  depths  of  the  sea,  was  like- 
wise introduced  by  Haeckel  in  1890  (4).  It  covers  those  organisms 
which  inhabit  the  sea-bottom.  We  may  divide  the  benthos  into 
sedentary  and  vagrant  (vagile)  benthos,  the  former  attached  to 
the  bottom,  the  latter  moving  over  it.  Living  in  such  intimate  rela- 
tion with  the  sea-bottom,  halobenthonic  organisms  are  to  a  high 
degree  dependent  upon  its  facies,  and  their  remains  are  generally 
entombed  in  the  region  where  they  have  lived,  instead  of  being 


HALOBENTHOS  LIMNOPLANKTON      997 

deposited  anywhere  else,  as  in  the  case  with  planktonic  and  nektonic 
organisms.  The  sedentary  benthos  is,  to  a  large  degree,  dependent 
for  food  on  those  organisms  which  are  swept  within  its  reach 
by  the  currents,  while  the  vagrant  benthos  is  more  actively  en- 
gaged in  seeking  out  its  food.  Large  numbers  of  sedentary  ben- 
thonic  animals  have  assumed  a  radial  structure,  especially  well 
typified  in  corals  and  crinoids,  and  also  shown  in  the  corona  of 
the  barnacle;  while  others,  such  as  brachiopods,  have  a  bilateral 
symmetry  of  high  degree.  Some  of  the  lower  vagrant  benthonic 
animals,  e.  g.,  the  Echinoidea,  are  also  built  on  the  radial  plan,  but 
the  majority  of  the  free  benthonic  animals  are  bilaterally  symmetri- 
cal. Among  the  vagrant  benthos  the  struggle  for  existence  is  most 
intense,  and,  as  a  result,  the  variety  of  adaptations  and  the  wealth 
of  form  and  color  are  almost  unlimited.  Transitions  from  the 
vagrant  benthos  to  the  nekton  are  numerous,  and  it  sometimes 
becomes  difficult  to  decide  if  an  animal  belongs  to  the  vagrant 
benthonic  or  to  the  nektonic  type.  The  gradation  is  just  as  com- 
plete as  between  nekton  and  plankton.  In  general,  a  radial  form 
may  be  said  to  be  characteristic  of  the  sedentary  benthos,  while  a 
bilaterally  symmetrical  form  is  as  characteristic  of  the  vagrant 
benthos.  Examples  of  change  of  form  with  change  of  habit  occur 
in  many  classes.  Both  plants  and  animals,  themselves  belonging  to 
the  sedentary  benthos,  may  lead,  secondarily,  a  vagrant  life  by 
being  attached  to  vagrant  benthonic  forms.  These  may  be  regarded 
as  vagrant  epibenthos.  Among  plants,  algae  are  the  most  familiar 
examples,  while  among  animals  hydrozoa  (Hydractinia  on  shells 
inhabited  by  hermit  crabs),  actinians,  and  bryozoans  furnish  the 
most  characteristic  examples. 


D.     Limno  plankton. 

Fresh  water  plankton  is  met  with  in  all  fresh  water  lakes, 
ponds,  and  streams.  It  not  infrequently  occurs  in  surprising 
amounts.  Thus  studies  of  the  Illinois  River  and  its  tributaries 
have  shown  that  it  averages  2.7  parts  per  million  of  the  water  in 
the  stream,  and  that  the  total  average  moving  down  stream  past 
any  given  point  aggregates  75,000  tons  per  annum,  or  about  8.5  tons 
per  hour  (6).  The  holoplankton  here  is  largely  composed  of 
minute  plants,  while  the  meroplankton,  consisting  both  of  larval 
plants  and  animals,  constitutes  a  very  large  percentage  of  the 
mass.  Finally,  the  pseudoplankton  makes  up  a  not  inconsiderable 
portion  of  this  mass.  The  term  limnoplankton  has  been  restricted 


998  PRINCIPLES    OF    STRATIGRAPHY 

to  the  plankton  of  the  larger  fresh  water  seas  by  a  number  of 
writers,  notably  O.  Zacharias,  who  uses  the  term  hdco plankton  for 
the  plankton  of  shallow  ponds  and  potamo plankton  for  that  of 
rivers. 

E.     Limnonekton    (Heleonekton,   Potatnonekton). 

The  nekton  of  fresh  water,  like  that  of  the  sea,  is  typically 
represented  by  the  fish,  though  other  classes  of  animals,  such  as 
the  aquatic  mammal,  are  also  represented.  The  merostomes  of  the 
Palaeozoic  also  appear  to  belong  here.  An  interesting  example  of 
a  meronektonic  life  is  evidenced  by  the  tadpole,  while  an  epinektonic 
condition  exists  in  the  larval  fresh  water  mussel  (Unio)  which 
attaches  itself  to  the  gills  of  fishes. 


F.     Limnobenthos  (Heleobenthos,  Potamobenthos). 

Both  sedentary  and  vagrant  benthos  occur  in  fresh  water;  the 
former  is  chiefly  represented  by  plants,  but  a  number  of  inverte- 
brates also  belong  here.  Such  are  the  sedentary  infusoria,  rotifers, 
and  bryozoa,  and  the  fresh  water  sponges  and  hydrozoa,  though 
the  principal  members  of  the  latter  class  are  only  temporarily  at- 
tached and  may  move  about  at  will.  The  vagrant  benthos,  on  the 
other  hand,  is  well  represented  by  molluscs,  worms,  and  Crustacea, 
though  the  crawfish  also  leads  at  times  a  benthonic  life. 


G.      Atmoplankton.    H.  Atmonekton.    I.  Atmobenthos. 

Among  the  air-breathers  permanent  planktonic  and  nektonic 
types  are  unknown,  though  many  unicellular  plants,  especially  bac- 
teria, live  in  the  atmosphere  for  a  considerable  period  of  time,  and 
must  during  that  period  be  classed  as  atmoholoplankton.  The 
meroplankton,  however,  is  well  represented,  chiefly  by  the  spores  and 
seeds  of  plants,  which  are  wafted  about  by  the  winds,  and  so  be- 
come widely  dispersed.  Terrestrial  nekton  is  represented  by  in- 
sects, birds,  flying  reptiles,  and  bats.  None  of  these  lead  a  per- 
manently nektonic  life  in  the  air,  for  all  return,  more  or  less  fre- 
quently, to  the  substratum.  Nevertheless,  during  their  period  of 
flight,  which  often  is  very  long,  they  must  be  considered  as  nekton 
of  the  air.  The  benthos  of  the  earth's  surface  is  pretty  sharply 
divided  into  sedentary  benthos,  or  plants,  and  vagrant  benthos,  or 


ATMOPLANKTON— ATMOBENTHOS  999 

animals,  though  some  exceptions  occur  among1  the  lowest  plants, 
while  some  animals  lead  a  temporary  or  permanent  (parasitic)  at- 
tached existence. 

BIBLIOGRAPHY  XXVII. 
(See  also  Bibliographies  XXVI  and  XXVIII.) 

1.  CHUN,  CARL.     1890.     Die  pelagische  Thierwelt  in  Grossen  Tiefen.     Ver- 

handlungen  der  Gesellschaft  deutscher  Naturforscher  und  Aerzte.    Bremen. 

2.  GRABAU,  A.  W.     1899.     The  Relation  of  Marine  Bionomy  to  Stratigraphy. 

Chapter  III  in  Geology  and  Palaeontology  of  Eighteen-mile  Creek.  Bulle- 
tin of  the  Buffalo  Society  of  Natural  Sciences,  Vol.  VI,  pp.-  319-365. 

3.  GRABAU,  A.  W.     1909.     Some  New  or  Little  Known  Geological  Terms 

and  Their  Application  in  Stratigraphic  Writing.  Abstract:  Science,  N.  S., 
Vol.  XXIX,  p.  750. 

4.  H^ECKEL,     ERNST.       1890.      Planktonstudien.     Vergleichende    Unter- 

suchungen  iiber  die  Bedeutung  und  Zusammensetzung  der  pelagischen 
Fauna  und  Flora.  Jena. 

5.  HENSON,  VICTOR.     1887.     Ueber  die  Bestimmung  des  Planktons,  oder 

des  im  Meere  treibenden  Materials  an  Pflanzen  und  Thieren.  (V.  Bericht 
der  Commission  zur  Wissenschaftlichen  Untersuchungen  der  deutschen 
Meere.) 

6.  ILLINOIS  STATE  LABORATORY  OF  NATURAL  HISTORY.    Bulletin, 

Vol.  VI,  Art.  II. 

7.  ORTMANN,  ARNOLD.     1895.    Grundziige  der  marinen  Thier-geographie. 

Jena. 

8L  SCHUTT,  F.  1893.  Das  Pflanzenleben  der  Hochsee.  Plankton  Expedi- 
tion, Vol.  I.  Leipzig. 

9.  WALTHER,  JOHANNES.  1894.  Einleitung  in  die  Geologic  als  histor- 
ische  Wissenschaft.  I.  Bionomie  des  Meeres.  II.  Die  Lebensweise  der 
Meerestiere.  Jena.  Gustav  Fischer. 


CHAPTER   XXVIII. 
BIONOMIC   CHARACTERISTICS   OF   PLANTS  AND    ANIMALS. 

A  bionomic  consideration  of  the  different  classes  of  modern 
plants  and  animals  is  of  the  utmost  importance  to  the  stratigrapher, 
since  it  is  from  such  studies  that  he  is  enabled  to  interpret  the 
conditions  of  the  past,  in  so  far  as  they  are  indicated  by  organisms. 
The  present  chapter  will,  therefore,  deal  somewhat  at  length  with 
the  bionomic  characters  of  the  various  classes,  special  stress  being 
laid  on  those  types  which  are  capable  of  fossilization. 

BIONOMIC  CHARACTERS  OF  PLANTS  (Schimper-25). 

PROTOPHYTA. 

The  majority  of  these  primitive  plants  are  not  adapted  for 
preservation,  and  hence  are  unknown  in  the  fossil  state.  The  slime 
molds,  or  Myxomycetes,  occur  on  decaying  logs,  in  damp  wood,  on 
rotting  leaves,  etc.  The  Schizophytes  or  bacteria  are  every- 
where present.  They  are  abundant  in  the  plankton  of  the  shallower 
portions  of  the  sea,  but  rare  in  the  open  sea.  In  fresh  water,  in 
the  air,  and  in  the  soil,  as  well  as  in  all  decaying  substances,  they 
occur,  themselves  forming  the  principal  agents  of  decay.  Their 
work  in  the  formation  of  iron  ore  deposits  has  elsewhere  been  re- 
ferred to.  The  Cyanophycese  occur  in  the  sea,  in  fresh  water,  on 
moist  earth,  on  damp  rocks,  and  on  the  bark  of  trees.  They  enter 
the  intercellular  spaces  of  higher  plants,  and  may  enter  into  the 
structure  of  the  lichen  thallus.  Some  species  flourish  in  hot  springs 
with  a  temperature  as  high  as  85°  C.  Volvox  and  other  flagellates, 
most  of  which  are  generally  regarded  as  animals,  are  especially 
at  home  in  stagnant  water,  and  amidst  putrefying  organic  matter  in 
the  sea  or  in  fresh  water.  Many  flagellates  are  also  parasitic  and 
the  spores  of  some  may  survive  a  temperature  of  250°  to  300°  F. 
for  ten  minutes,  though  the  adults  are  killed  at  180°. 

1000 


BIONOMIC    CHARACTERS    OF    PLANTS          1001 


THALLOPHYTA. 

ALG.E.     The  lowest  of  the  green  algae  (Protococcaceae)  consti- 
tute,  with   the   diatoms,   the   Cyanophyceae,    and   the   bacteria   the 
chief   holoplanktonic   plants,   though   many   of   them   also   have   a 
benthonic  habit,  being  attached  chiefly  to  other  plants,  or  encrust- 
ing stones,  as  in  the  case  of  some  fresh  water  Cyanophyceae.    They 
are  mainly  inhabitants  of   fresh  water,  though  diatoms  are  also 
abundant  in  the  sea.     Protococcus  itself  is  terrestrial.    The  Charo- 
phycea,  often  classed  with  the  green,  algae,  secrete  lime.     This  is  • 
especially  true  of  Chara,  which  occurs  in  fresh  water  lakes  from 
two  meters  down,  and  which  is  probably  an  important  factor  in  the 
formation  of  fresh  water  limestones.     (See  ante,  page  471.)     The 
majority  of  the  green  algae  belong  to  the  benthos,  being  equally 
abundant   in  the  marine  and   fresh  water  realms.     The   red  algae 
are  benthonic  and  chiefly  marine,  though   some   species  occur  in 
fresh  water.     Lime- secreting  types  also  occur  in  this  class,  consti- 
tuting the  nullipores  or  coralline  seaweeds  which  inhabit  the  littoral 
district  of  the  sea,  chiefly  in  tropical  regions  but  to  some  extent 
also  in  temperate  climates.     They  occur  as  jointed  fronds  of  a  red 
color  (Corallina),  as  crusts  on  other  algae  (Melobesia),  or  as  ex- 
tensive  pink   incrustations   on    stones   or   shells    (Lithothamnion). 
They  are  especially  characteristic  of  depths  between  15  and  35  (or 
50)   fathoms,  where  they  constitute  the  "coralline  zone"  of  the  lit- 
toral district.    The  brown  algae  are  mainly  marine  benthonic  types, 
usually  attached  to  a  rocky  substratum.    The  common  brown  algae 
of  the  northern  coasts   (Fucus,  Ascophyllum)   have  already  been 
referred  to  as  clothing  the  rocky  ledges  and  forming  a  substratum 
for  Hydrozoa,  Bryozoa,  sponges,  etc.,  as  well  as  other  algae.  Though 
typically  attached,  some  forms,  like  the  Sargassum,  will  continue 
to  grow  and  multiply,  even  after  they  have  been  torn  from  their 
anchorage  and  carried   into  mid-ocean.     The   Sargassum  is  thus 
typically  pseudoplanktonic,  as  are  also  all  the  other  algae  attached 
to  it.    Many  of  the  brown  seaweeds  grow  to  great  size.    A  familiar 
example  is  the  common  kelp   (Laminaria)   of  the  Atlantic  coast, 
which  generally  grows  to  ten  or  more   feet  in  length,   while  the 
giant  kelp  of  the  Pacific  (Macrocystis)  is  said  sometimes  to  reach 
a  length  of  three  hundred  meters.     The  Laminarians  are  typical 
of  the  littoral  district  down  to  fifteen  fathoms,  this  interval  being 
known  as  the  zone  of  Laminarians.    The  large  species  all  grow  in 
the   deeper   portions   of   this   zone,   where   they   are  anchored  by 
their  "roots"  to  stones,  shells,  or  other  objects  of  support.     They 


ioo2  PRINCIPLES    OF    STRATIGRAPHY 

often  hold  on  to  objects  small  enough  to  be  carried  away  with 
the  seaweed  during  a  violent  storm ;  and  since  the  stipe  and  frond 
of  the  seaweed  are  commonly  covered  with  sedentary  benthonic  ani- 
mals, this  seaweed  forms  a  ready  agent  for  the  wider  dispersal  of 
such  organisms. 

In  general  the  larger  algae  are  attached  to  a  rocky  or  other 
hard  substratum  or  to  other  algae  (epiphytic).  On  muddy  or 
sandy  bottoms  algae  are  rare,  though  stranded  algae  may  be  buried 
in  numbers  in  mudflats.  The  large  algae  (macrophytes)  are  mostly 
restricted  to  the  photic  region,  where  they  are  distributed  in  the 
•  two  belts,  the  perpetually  submerged  (i.  e.,  below  low  tide)  and  the 
periodically  emerging  belt  (between  tides).  Marine  algae  are  found 
to  the  height  of  the  salt  spray  on  the  shore,  while  terrestrial  algae 
are  known  from  the  tropics,  where  they  live  as  epiphytes  on  leaves, 
especially  in  the  rainy  districts.  In  the  temperate  regions  they  are 
associated  symbiotically  with  fungi  to  form  lichens,  which  increase 
in  numbers  and  importance  as  the  climate  becomes  cooler.  They  and 
the  mosses  constitute  the  chief  epiphytes  and  epiliths  in  the  tem- 
perate and  cooler  climates.  Lichens  sometimes  form  structures 
which  under  favorable  conditions  may  be  preserved.  In  the  arctic 
regions  microscopic  red  and  brown  algae  (Sphaerella,  etc.)  often 
color  the  snow  and  ice  and,  together  with  many  other  microphytes, 
form  a  characteristic  element  of  the  vegetation  of  these  regions. 

Diatoms  are  important  rock-builders,  since  their  siliceous  skele- 
tons or  frustules  are  readily  preserved.  They  occur  both  in  fresh 
and  salt  water,  no  ditch,  pond,  or  pool  being  without  them,  and  they 
form  a  characteristic  member  of  the  marine  plankton.'  A  great 
many  types,  however,  are  benthonic,  forming  yellowish-brown 
films  on  the  mud  in  shallow  pools,  or  growing  attached  by  slender 
stalks  to  other  plants.  They  commonly  possess  the  power  of  mo- 
tion found  also  in  desmids  and  other  unicellular  plants.  Fossil 
diatoms  are  abundant  in  the  Tertiary  of  many  localities,  often  form- 
ing extensive  beds  of  nearly  pure  frustules,  generally  of  fresh 
water  origin.  Underlying  the  city  of  Richmond,  Virginia,  is  a 
bed  of  these  organisms  eighteen  feet  thick,  while  other  extensive 
deposits  occur  in  the  coastal  plain  of  Maryland  and  New  Jersey, 
as  well  as  in  many  other  parts  of  the  world.  In  Mesozoic  deposits 
they  are  less  abundant,  and  they  are  not  known  positively  from 
Palaeozoic  deposits,  probably  owing  to  alteration  of  the  frustule. 
Diatomaceous  deposits  are  often  erroneously  spoken  of  as  infusorial 
earth. 

FUNGI.  The  members  of  this  group  are  destitute  of  chlorophyll 
and,  consequently,  are  dependent  upon  organic  matter  for  food,  be- 


BIONOMIC    CHARACTERS    OF    PLANTS          1003 

ing  either  parasites  (growing  upon  living  organisms)  or  saprophy- 
tes (growing  upon  dead  organic  matter)  or  both  parasitic  and 
saprophytic.  Fungi  can  thus  grow  in  the  dark  regions  of  the 
earth,  sunlight  not  being  essential.  They  are  mostly  terrestrial 
(when  not  living  within  their  host),  though  some  marine  repre- 
sentatives are  known,  and  certain  of  the  molds  (phycomycetes) 
form  on  decaying  animals  in  fresh  water  or  sometimes  on  living 
fish  or  Crustacea.  The  large  terrestrial  fungi  are  most  characteristic 
of  the  temperate  zones,  the  tropical  species  being  mostly  small. 

LICHENS.  Lichens  are  terrestrial  plants  growing  chiefly  upon 
the  bark  of  trees,  rocks,  the  ground,  mosses,  and,  more  rarely,  upon 
perennial  leaves.  In  large  forests  they  hang  as  a  dense  growth 
from  the  trees  (Usnea),  but  in  other  cases  they  encrust  the  rough 
bark  of  the  trees.  They  may  also  occur  on  the  smooth  bark  of 
young  trees  or  shrubs,  and  sometimes  on  decayed  or  decaying 
wood.  All  of  these  are  classed  as  corticolous  lichens.  Saxicolous 
lichens  grow  on  rocks  and  stones,  which  they  disintegrate.  They 
comprise  the  calcicolous  forms,  growing  on  limestones,  or  other  cal- 
careous rocks,  on  the  mortar  of  walls,  ets.,  and  calcifugous  forms 
which  grow  on  rocks  of  non-calcareous  character.  Terrestrial 
lichens  grow  on  all  kinds  of  soil,  some  preferring  peaty,  some  cal- 
careous, some  sandy,  and  some  granitic  soil,  but  none  grow  on 
cultivated  soil. 

Muscle olous  lichens  grow  on  decaying  moss,  such  as  the  dead 
peat  mosses,  while  epiphyllous  species  grow  on  perennial  leaves, 
whose  vitality  they  do  not  affect.  The  distribution  of  lichens  is 
greater  than  that  of  any  other  class  of  plant,  occurring  from  the 
poles  to  the  equator,  practically  wherever  land  exists.  Lichens 
may  be  dried  so  thoroughly  that  they  can  easily  be  reduced  to 
powder,  yet  their  vitality  is  only  suspended,  and  moisture  will 
restore  them  to  renewed  activity.  Their  growth  is  extremely  slow, 
and  the  life  of  the  plant  seems  to  be  very  long,  in  some  cases  many 
hundreds  of  years. 

BRYOPHYTA  AND  PTERIDOPHYTA. 

These  are  wholly  absent  from  the  sea,  but  in  fresh  water  a 
few  bryophytes  are  known.  The  peat-moss  (Sphagnum)  grows 
abundantly  in  wet  woods  or  in  bogs.  The  growing  ends  increase 
while  the  old  portion  dies  off.  Among  the  pteridophytes  the  class 
of  Filicinse  has  an  aquatic  group  in  the  rhizocarps,  or  water  ferns 
(Hydropteridese),  which  grow  partly  submerged  or  floating.  The 
spores  of  these  plants  are  widely  distributed  by  flotation  and 


1004  PRINCIPLES    OF    STRATIGRAPHY 

may  become  enclosed  in  the  finer  lutaceous  sediments.  Spores 
referred  to  rhizocarps  (Protosalvinia)  are  found  in  abundance  in 
the  black  Devonic  shales  of  North  America,  and  it  lias  been  held 
that  the  black  color  and  petroliferous  character  of  these  shales 
are  wholly  due  to  the  spores  of  these  plants.  If  the  spores  are, 
indeed,  those  of  rhizocarps,  they  would  be  an  indication  of  the 
formation  of  the  black  shales  in  the  estuaries  of  rivers,  since 
these  plants  are  found  only  in  fresh  water. 

Ferns  are  most  abundant  in  the  tropics,  where  they  develop 
an  extraordinary  wealth  of  form,  and  vary  in  their  dimensions 
from  small  moss-like  plants  to  trees.  They  are  especially  character- 
istic of  humid  forests. 

Equisetina,  or  horse-tails,  are  represented  by  the  living  Equise- 
tum  and  by  the  extinct  Calamites,  which  latter  often  grew  into 
large  trees.  Equisetum  to-day  grows  in  low  moist  ground  and  in 
the  sand  and  gravel  of  railroad  embankments,  and  along  road  sides. 
Much  silica  is  present  in  the  epidermis  of  the  plants,  giving  to  it  a 
rough,  harsh  feel. 

Lycopodiacecc,  or  club-mosses.  These  are  to-day  represented 
by  small  prostrate  plants  found  mainly  in  the  deeper  woods.  In 
late  Palaeozoic  time,  however,  they  were  represented  by  forest  trees 
(Lepidodendron,  Sigillaria,  etc.)  A  few  aquatic  lycopods  exist 
(quill-worts,  Isoetae).  These  plants  grow  either  partly  or  com- 
pletely submerged,  and  in  general  resemble  the  smaller  club-mosses. 

Both  Equisetae  and  Lycopodiaceae  are  characteristic  of  the  tropic 
and  temperate  zones,  the  Lycopodiaceae  being  more  prominent  in 
the  tropics. 

SPERMATOPHYTA. 

By  far  the  greater  mass  of  spermatophytes  or  phanerogamous 
plants  are  terrestrial  in  habitat,  though  a  not  inconsiderable  number 
live  in  fresh  water.  Certain  members  of  the  pondweed  family 
(Potamogetonaceae)  and  the  frog's-bit  family  (Hydrocharitaceae), 
comprising  about  twenty-five  species  in  all,  have  become  wholly 
adapted  to  a  marine  benthonic  habit  and  are  known  as  sea-grasses. 
The  pondweed  family  is  represented  on  the  Atlantic  coast  by  the 
eel-grass  (Zostera  marina  L.)  and  the  ditch-grass  (Ruppia  nmri- 
tima  L.),  both  of  which  are  extremely  common,  and  both  of  which 
are  concerned  in  the  gradual  choking  of  the  marshes.  A  number 
of  species  are  partly  marine,  as  the  marsh-grass  (Spartina)  growing 
within  the  limit  of  tide-water.  The  mangrove,  as  already  noted, 
is  partly  adapted  to  a  marine  habitat,  all  of  it  but  the  leaves  being 
periodically  submerged. 


BIONOMIC    CHARACTERS    OF    PLANTS          1005 

All  degrees  of  freshwater  phanerogams  are  found,  from  those 
having  only  their  roots  in  the  water,  as  many  of  the  larger  swamp 
plants,  to  those  nearly  or  entirely  submerged.  Parasitic,  saprophytic, 
and  epiphytic  phanerogams  are  further  characteristic  types  adapted 
to  peculiar  habitats.  In  short,  the  variety  and  adaptability  of  the 
spermatophytes  are  as  multitudinous  as  the  variation  in  the  character 
of  the  terrestrial  realm. 

The  coniferous  gymnosperms  are  almost  wholly  confined  to 
temperate  climates,  especially  the  colder  belts,  but  cycads  are  most 
characteristically  tropical  plants.  Both  monocotyledons  and  dicoty- 
ledons are  more  commonly  represented  by  trees  in  the  tropical  than 
in  the  temperate  zone,  the  number  of  trees  diminishing-  toward  the 
colder  belts,  where  the  conifers  increase  in  number. 

Arboreal  vegetation  is  characteristically  unknown  in  regions 
where  the  sub-soil  is  permanently  frozen,  i.  e.,  where  the  mean  sum- 
mer temperature  is  below  10°  C.  Such  is  the  character  of  the  tree- 
less plains  of  northern  Canada,  the  coldest  part  of  the  North  Ameri- 
can continent,  where  the  mean  annual  temperature  is  below  — 8°  C. 
and  the  mean  summer  temperature  below  10°  C.  Here  sedges, 
grasses,  and  lichens  predominate,  while  trees  and  sphagnum-bogs 
are  conspicuously  absent. 

The  present  northern  extent  of  the  forest  regions  of  Canada 
is  limited  by  the  mean  summer  temperatures  of  io°-i5°  C.  Here 
the  poplar  (Populus  tremuloides  and  P.  balsatnifera) ,  the  birch 
(Betula  alba),  spruce  (Picea  alba  and  P.  nigra),  pine  (Pimts  bank- 
siana),  and  larch  (Lariv  americana)  occur,  while  beneath  them 
the  ground  is  often  an  extensive  sphagnum  swamp.  "Poplar,  birch, 
and  pine  extend  northward  as  far  as  the  heavy  forest  extends, 
while  larch  and  the  true  species  of  spruce  extend  northward  to 
the  northern  limit  of  trees,  becoming  small  and  dwarfed  before 
they  finally  disappear."  (Tyrrell-28:j#p-pi.) 

South  and  west  of  the  forested  area  are  the  grassy  plains,  which, 
because  of  their  dryness,  do  not  support  trees  or  sphagnum  bogs. 
As  these  plains  were  in  the  condition  of  the  frozen  tundra  after 
the  retreat  of  the  ice,  and  with  the  amelioration  of  the  climate 
became  dry,  no  trees  or  sphagnum  bogs  ever  developed  there. 


Ecology  and  Ecological  Adaptations  of  Sphermatophytes. 

Modern  spermatophytes,  as  a  whole,  are  divisible  into  a  number 
of  habitudinal  types,  among  which  the  following  are  the  most 
important : 


ioo6  PRINCIPLES    OF    STRATIGRAPHY 

1.  Hydrophytes   and   Hemihydrophytes.     Aquatic    plants    are 
marine,  or  brackish,  or  fresh  water.     The  marine  types  comprise 
the  grass-wracks  or  eel-grasses'  (Zoster a  marina,  and  Z.  nana).    A 
few  plants  are  confined  to  a  brackish-water  habitat  (Ruppia  niari- 
tima,  etc.),  while  others  are  adapted  to  both   fresh  and  brackish 
water.     The  aquatic  vegetation  of  ponds  and  lakes  may  be  divided 
into  types  with:   (a)   submerged  leaves,   (b)   submerged  and  float- 
ing leaves,    (c)    floating  leaves,    (d)    submerged  leaves  and  erect 
leaves  or  stems,   (e)   erect  leaves  or  stems,  and  lastly   (f)   marsh 
plants. 

2.  Xerophytes.     This  group   includes  the  plants  which   have 
devices  for  procuring  or  for  storing  water,  or  for  limiting  trans- 
piration, adaptations  related  to  dry  habitats.    They  have  frequently 
long  tap  roots  which,  in  some  cases,  reach  down  to  a  subterranean 
water  supply.    There  is  also  often  a  superficial  root  system.    Xero- 
phytes of  the  deserts  often  have  succulent  stems,  like  the  cacti  of 
southern    and    central    America.      In    other    deserts,    such    as    the 
Sahara,    succulents    are   not   prominent.      A    spiny   character   also 
characterizes  many  Xerophytes. 

3.  Bog  Xerophytes.     These  are  plants  living  in  the  peaty  soil 
of  fens  and  moors,  which,  though  physically  wet,  are  physiologically 
dry.     Such  plants  can  survive  a  partial  or  complete  drying  up  of 
the  bog. 

4.  Tropophytes.    These  are  plants  with  a  xerophytic  character 
during  the  unfavorable  season.    Thus  deciduous  trees  are  xerophytic 
during  the  leafless  period  of  winter  while  other  plants  survive  the 
unfavorable  period  by  means  of   their  bulbs,   rhizomes,   or   other 
special  structures. 

5.  Hygrophytes.     These  are  intermediate  between  Xerophytes 
and  hydrophytes  and  are  sometimes  called  Mesophytes.     Assimila- 
tion goes  on  throughout  the  whole  year,  except  during  periods  of 
frost  or  when  buried  by  snow. 

6.  Sciophytes.      These    are   plants   growing    in   the    shade    of 
forests.     They  may  be  hygrophytes   or  they  may   be  herbaceous 
tropophytes. 

7.  Halophytes.     These  are  plants  growing  in  saline  soils,  and 
they  are  characterized  by  xerophytic  adaptations.     Many  of  them 
are  succulent,  their  leaves  and,  to  some  extent,  their  stems  having 
much  water-storing  tissue. 

8.  Calcicole  and  Calcifuge  Plants.    Plants  invariably  inhabiting 
calcareous  soils  are  said  to  be  calcicoles,  while  calcifuge  species  are 
rarely  or   never   found   in   calcareous   soil.     They   are   sometimes 
termed  silicicoles. 


THE    BIOSPHERE  1007 

BIONOMIC  CHARACTERISTICS  OF  ANIMALS.* 
I.     PROTOZOA. 

FORAMINIFERA.  The  Foraminifera  are  typically  marine  organ- 
isms, though  a  considerable  number  of  species  has  become  adapted 
to  brackish  water,  living  in  estuaries  and  near  the  mouths  of 
streams,  while  many  species,  commonly  placed  in  this  class, 'live 
entirely  in  fresh  water.  Their  distribution  is  so  great  that  scarcely 
any  marine  sediments  are  wholly  free  from  the  shells  of  these  ani- 
mals. Most  Foraminifera  belong  to  the  vagrant  benthos,  though 
sedentary  benthonic  forms  also  occur.  Only  something  over  twenty 
living  planktonic  species  are  known,  these  belonging  chiefly  to  the 
genera  Globigerina,  Orbulina,  and  Pulvinulina  (Figs.  101-103),  the 
first  predominating.  The  small  number  of  species  is,  however, 
counterbalanced  by  the  enormous  number  of  individuals.  The  ben- 
thonic Foraminifera  are  confined  chiefly  to  the  littoral  district,  where 
the  character  of  the  bottom  and  the  temperature  of  the  water  exert 
important  influences  on  the  distribution  of  these  organisms.  A 
muddy  facies  of  the  sea-bottom  seems  to  be  conducive  to  the  ex- 
istence of  a  large  number  of  species,  but  the  rocky  bottoms  are  not 
without  their  types ;  while  algae  and  sea-grasses  commonly  form  the 
home  of  vast  numbers  of  these  organisms.  The  coarse,  sandy  and 
gravelly  bottoms  are  not  generally  inhabited  by  these  animals, 
though  their  dead  shells  are  not  uncommon  in  the  sands  along  our 
beaches ;  while  along  some  shores,  they  are  so  abundant  as  to  con- 
stitute the  greater  portion,  if  not  the  whole,  of  the  deposit.  Dana  (9) 
states  that  in  the  Great  Barrier-reef  region  of  Australia  the  shells 
of  Orbitolites  are  so  abundant  that  .  .  .  ''they  seemed  in  some 
places  to  make  up  the  whole  sand  of  the  beaches,  both  of  the 
coral  islets  and  of  the  neighboring  Australian  shore." 

The  vertical  range  of  the  benthonic  Foraminifera  is  very  great, 
species  sometimes  passing  through  a  range  of  several  thousand 
fathoms.  In  such  cases  there  is  often  a  change  in  the  size  or 
thickness  of  the  shell  with  the  change  in  depth.  Although  the 
planktonic  Foraminifera  comprise  so  few  species,  the  number  of 
their  individuals  is  enormous.  From  their  shells  the  Globigerina 
oozes  form  in  deep  water,  where  no  sediment  is  carried;  but  it  is 
evident  that,  in  a  region  where  the  land  is  reduced  to  near  base- 
level,  so  that  little  or  no  sediment  is  carried  into  the  sea,  pure 
accumulations  of  such  shells  will  occur  near  shore,  thus,  forming  a 

*  Only  those  represented  by  fossils  are  taken  into  account  here. 


ioo8  PRINCIPLES    OF    STRATIGRAPHY 

foraminiferal  ooze  in  shallow  water.  But  not  only  planktonic  shells 
but  the  benthonic  species  as  well  may  form  a  pure  accumulation 
of  foraminiferal  shells,  as  has  been  the  case  in  the  chalk,  in  which 
the  planktonic  species  are  practically  wanting.  ( Walther-29  :<?/5. ) 
Reproduction  of  the  Foraminifera  is  carried  on  by  fission,  budding, 
and  spore  formation.  In  the  first  two  cases,  the  resulting  part  and 
the  buds  have  the  characteristics  of  the  parent,  except  its  size,  and 
there  are  no  special  structures  which  serve  for  the  greater  distribu- 
tion of  the  species.  When  spores  are  formed,  these  may  be  pro- 
vided with  a  flagellum,  whereupon  the  organisms  pass  through  a 
mero-planktonic  stage. 

While  the  geographical  distribution  of  the  benthonic  species  is 
very  restricted,  and  influenced  by  the  facies  of  the  sea  bottom, 
the  geographical  distribution  of  the  pelagic  species  is  prevented 
from  being  world-wide  only  by  the  changes  in  the  temperature  of 
the  water  and  by  the  ocean  currents.  The  pelagic  species  are  ex- 
tremely abundant  in  tropical  regions,  and  their  shells  form  vast 
accumulations  on  the  sea-bottoms  over  which  they  live.  In  the 
great  depths  these  shells  are  absent,  for  they  may  be  completely  dis- 
solved while  they  sink  to  the  bottom,  or  shortly  after  reaching  it. 

RADIOLARIA.  The  Radiolaria  are  marine  planktonic  Protozoa. 
They  inhabit  principally,  the  open  sea,  where  they  occur  at  the 
surface  or  at  various  depths  below  it.  In  regions  of  terrigenous 
sedimentation,  or  where  an  influx  of  fresh  water  occurs,  these 
animals  are  seldom  met  with.  Hence  their  siliceous  shells  occur 
in  abundance  only  in  the  deposits  found  at  a  distance  from  shore, 
and  in  deep  water,  where  they  may  constitute  as  high  as  seventy 
per  cent,  of  the  mass.  The  greatest  abundance  of  radiolarian  skele- 
tons was  found  by  the  Challenger  expedition  at  a  depth  between 
2,000  and  4,475  fathoms — the  greatest  depth  sounded.  In  many 
places  in  the  Pacific  the  bottom  ooze  is  almost  entirely  composed 
of  radiolarian  shells  with  some  intermixture  of  sponge  spicules. 
The  celebrated  Barbados  earth,  a  Tertiary  deposit,  is  likewise  com- 
posed of  radiolarian  remains,  to  the  exclusion  of  almost  every  other 
organism. 

Fission,  budding,  and  spore  formation  constitute  the  methods 
of  reproduction  in  Radiolaria.  The  spores  may  be  provided  with 
flagella,  constituting  "swarm  spores,"  which,  like  their  progenitors,' 
lead  a  planktonic  existence. 

II.       PORIFERA. 

The  sponges  are  marine  or  fresh-water  animals,  of  a  sedentary 
benthonic  habit.  In  general  only  such  species  as  secrete  a  calcare- 


BIONOMIC    CHARACTERS    OF    PORIFERA       1009 

ous  or  siliceous  skeleton — either  continuous  or  consisting  of  separate 
spicules — are  capable  of  preservation  in  a  fossil  state.  The  vertical 
distribution  of  marine  species  ranges  from  the  shore  zone  down 
to  the  greater  depths  of  the  sea.  Not  infrequently  species  are  found 
which  regularly  undergo  an  exposure  of  several  hours  between 
tides,  though  most  littoral  species  occur  below  low-water  mark,  or  in 
tide  pools  from  which  the  water  is  never  drained.  Sponges  will 
grow  wherever  a  suitable  surface  for  attachment  is  found,  the  most 
usual  substratum  chosen  being  cliffs,  boulders,  shells,  or  the  stems 
and  "roots"  of  the  larger  algae.  In  deeper  and  quieter  water, 
the  sandy  and  gravelly  bottoms  are  inhabited  by  sponges,  and  in 
the  great  depths  they  occur  on  the  oozes  and  other  soft  deposits. 
A  pseudovagrant  (epi-vagrant)  benthonic  habit  is  assumed  by  a 
number  of  species,  which  attach  themselves  to  the  carapaces  of 
Crustacea.  Certain  sponges  bore  into  shells  and  other  calcareous 
substances,  forming  extensive  galleries  and  commonly  destroying 
the  shell.  Clione  sulphurea,  common  on  our  Atlantic  coast,  com- 
pletely riddles  shells,  and  then  forms  large  irregularly  rounded 
masses  of  a  sulphur  yellow  color,  often  entirely  enveloping  the 
shell. 

The  reproduction  of  the  sponges  is  either  asexual  or  sexual. 
In  the  former  case,  buds  are  formed,  which,  growing  larger,  with- 
out detaching  themselves,  put  out  buds  of  their  own,  thus  forming 
a  colonial  aggregation.  Sponges  torn  into  several  pieces  will  fre- 
quently form  as  many  new  individuals,  and  sponges  which  were 
placed  in  close  juxtaposition  by  Bowerbank  in  a  relatively  short 
time  united  into  one.  A  method  of  internal  gemmation  occurs,  in 
which  groups  of  cells,  or  gemmulse,  become  detached  and  after  a 
time  develop  into  complete,  sponges.  Sexual  reproduction,  from 
either  hermaphrodite  or  sexually  distinct  parents,  leads  to  a  free 
swimming  blastula.  This  develops  into  a  gastrula,  which  attaches 
itself  and  develops  into  the  adult.  Thus  a  mero-planktonic  stage 
occurs  in  sponges,  which  serves  as  a  means  of  extensive  distribu- 
tion. 

III.       CCELENTERATA. 

. »  . 

HYDROZOA.  The  Hydrozoa  are  typically  marine  Coelenterates, 
though  a  few  species  occur  in  fresh  water,  e.  g.,  Hydra  viridis  and 
H.  fusca,  Cordilophora  lacustris  and  the  fresh  water  medusa  of 
Lake  Tanganyika :  Limnocnida  tanganyika.  Some  Scyphomedusse 
(Aurelia,  Cyanea),  according  to  Moseley,  seem  to  prefer  to  float 
near  the  mouths  of  fresh  water  streams ;  while  in  New  South  Wales 


lOio  PRINCIPLES    OF    STRATIGRAPHY 

these  medusae  were  observed  floating  in  shoals  where  the  water 
was  pure  enough  to  be  drinkable.  The  majority  of  species  have  a 
sedentary  benthonic  stage,  the  hydriform  stage,  which  is  generally 
colonial,  the  compound  polyp  stock  being  attached  to  rocks,  algae, 
shells,  timbers,  or  other  objects  of  support,  by  means  of  a  thread- 
like branching  root-stock  or  hydrorhyza,  which  spreads  out  over 
the  object  of  support  and  from  which  the  individual  polyparia  arise, 
each  with  a  distinct  stem  or  hydrocaulus.  A  few  forms,  like  Hydrac- 
tinia  polyclina  and  some  Podocoryne,  are  pseudo-vagrant  benthos, 
being  attached  to  the  shells  of  gastropods  carried  about  by  hermit 
crabs.  Some  species,  like  Bougainvillia  fruticosa,  prefer  an  epi- 
planktonic  habit,  becoming  attached  to  floating  timbers,  a  similar 
habit  being  assumed  by  those  hydroids  which  live  attached  to  the 
floating  Sargassum.  An  epi-nektonic  manner  of  life  may  perhaps 
be  considered  the  habit  of  Hydrichthys,  which  lives  parasitically 
upon  a  fish.  Corymorpha  pendula,  though  not  attached,  lives  partly 
buried  in  the  mud  of  the  shallow  sea ;  while  Hydra  leads,  at  times 
at  least,  a  kind  of  vagrant  benthonic  life,  though  its  journeyings 
are  probably  never  very  great. 

Many,  if  not  most  Hydrozoa  have  a  distinct  medusiform  person 
which,  when  perfect,  is  perhaps  the  best  type  of  a  holo-planktonic 
organism.  In  a  few  Hydrozoa — Hydra  Sertularidae — the  medusi- 
form stage  is  wanting,  in  others  it  is  degenerate,  never  becoming 
free  (Clava)  ;  but  in  a  large  number  of  species  it  is  a  free  individual. 
Again,  in  the  Narco-  and  Trachymedusae,  as  well  as  in  some  others, 
only  the  medusa  occurs,  the  hydroid  being  suppressed.  Compound 
medusae  occur  as  well  as  compound  hydroids.  The  former  are 
the  Siphonophora  in  which,  by  budding  from  the  parent  medusa,  a 
compound  colony  is  formed  which  leads  a  holo-planktonic  existence. 
Lucernaria  is  an  example  of  a  medusa  attached  to  foreign  objects. 
The  medusae,  whether  free  or  attached,  produce  the  sexual  products 
which  give  rise  to  new  hydroid  colonies  or  directly  to  new  medusae. 
The  egg  develops  into  a  ciliated  planula  which  leads  a  mero-plank- 
tonic  existence  before  it  settles  down  to  become  a  benthonic 
hydroid,  or  before  it  develops  into  the  medusa.  A  number  of  hy- 
droids grow  attached  to  rocks  and  sea-weeds,  or  to  bridge  piles,  in 
such  a  position  as  to  become  regularly  exposed  for  several  hours 
each  day  during  ebb  tide.  Even  the  delicate  and  unprotected  Clava 
of  our  northern  shores  delights  to  live  under  such  conditions,  and 
is  rarely  found  in  deeper  water  or  in  tide  pools.  Most  hydroids, 
however,  can  not  withstand  such  exposure,  and  hence  they  are 
found  only  in  the  deeper  waters  or  the  deeper  tide  pools. 

The  majority  of  hydroids  are  inhabitants  of  the  littoral  district, 


BIONOMIC  CHARACTERS  OF  CCELENTERATA    ion 

and  they  usually  occur  in  the  more  moderate  depths.  The  tubularian 
hydroids  probably  never  extend  to  any  considerable  depths,  the 
deep-water  forms  belonging  chiefly  to  the  Plumularidae.  (Agassiz- 
i,  ii:j5-)  One  of  the  abyssal  Plumularians  was  obtained  by  the 
Blake  at  a  depth  of  1,240  fathoms,  which  exceeded  by  more  than 
300  fathoms  that  at  which  Plumularians  were  obtained  by  the  Chal- 
lenger. (Agassiz-i.) 

The  Palaeozoic  class  of  graptolites  or  Graptozoa  is  the  most  im- 
portant group  of  the  Coelenterata  from  a  stratigrapher's  point  of 
view,  for  it  constitutes  one  of  the  most  important  classes  of  index 
fossils  known. 

Lapworth  (Walther-29)  holds  that  the  majority  of  dendroid 
graptolites  (Dendroidea)  undoubtedly  grew  attached  to  sea- weeds, 
rocks,  or  other  supports,  in  the  manner  of  most  modern  hydroids, 
but  some  were  attached  to  floating  algae,  leading  an  epi-planktonic 
existence.  Cases  of  such  attachment  have  been  observed  among 
these  fossils. 

Lapworth  argues  that,  if  the  sicula  was  attached  by  means  of 
the  slender  basal  thread,  the  nema,  to  floating  objects  of  support, 
whether  disc  or  sea-weed,  the  second  and  succeeding  hydrothecae, 
growing  in  the  same  direction  as  the  sicula,  would  open  downward. 
This  suggests  that  the  earlier  graptolites  were  not  planktonic,  but 
grew  attached  to  sea-weeds  and  rocks  after  the  manner  of  modern 
hydroids.  This  view  is  taken  by  Hahn  (16)  with  reference  to 
Dictyonema.  In  later  genera  of  graptolites,  however,  which  may 
have  been  attached  to  floating  objects  (epi-plankton),  the  branches 
either  bent  backward,  so  as  to  cause  the  later  hydrothecae  to  open 
in  an  opposite  direction  from  the  sicula  and  early  hydrothecae;  or 
the  direction  of  growth  was  reversed,  the  second  and  succeeding 
hydrothecae  growing  backward  along  the  nema,  which  became  the 
supporting  rod  or  virgula. 

Some  of  the  graptolites  appear  to  have  led  a  holoplanktonic  ex- 
istence, the  nema  being  attached  to  a  central  organ  or  disc,  which 
probably  served  as  a  float.  This  was  long  ago  demonstrated  in  a 
number  of  species  by  Professor  Hall,  and  lately  has  been  shown  in 
great  detail  in  Diplograptus  by  Ruedemann.  This  observer  holds 
that  this  mode  of  attachment  was  characteristic  of  the  virgulate 
graptolites  (Axonophora)  as  a  whole,  while  the  Axonolipa  he 
thinks  were  attached  to  seaweeds.  (Ruedemann-25  15/5.)  Whether 
holo-planktonic  or  epi-planktonic,  either  method  of  life  accounts 
for  the  wide  distribution  of  the  graptolites.  The  fact  that  they  are 
almost  universally  found  in  carbonaceous  shales  suggests  that  float- 
ing algae  may  have  been  the  principal  carriers  of  these  organisms, 


ioi2  PRINCIPLES    OF    STRATIGRAPHY 

the  decaying  vegetable  matter  furnishing  the  carbon  for  coloring 
the  muds  in  which  the  organisms  were  buried.  On  the  other  hand, 
it  is  not  improbable  that  much  of  the  carbonaceous  material  was 
derived  from  the  graptolites  themselves.  The  general  slight  thick- 
ness of  these  beds,  and  the  fact  that  in  successive  beds  the  species 
change,  indicate  a  slow  accumulation  of  the  deposits  in  relatively 
quiet  water. 

According  to  Ruedemann's  observations  (23),  the  young  Diplo- 
graptus,  on  leaving  the  gonophore,  has  already  advanced  into  the 
sicula  stage,  so  that  a  free-swimming  planula  stage  appears  not  to 
exist.  It  is  probable  that  this  is  true  of  most,  if  not  all,  graptolites, 
and  that  hence  the  distribution  of  these  animals  is  such  as  will  be 
accounted  for  by  the  vicissitudes  which  they  met  with  as  a  floating 
colony. 

ANTHOZOA.  The  Anthozoa  are  typically  marine  sedentary  ben- 
thonic  animals,  inhabiting  the  warmer  waters  of  the  oceans.  A 
large  number  are  without  hard  supporting  parts,  and  consequently 
leave  no  remains,  while  others,  probably  the  majority  of  Anthozoa, 
secrete  a  calcareous  or  horny  corall'um,  which  is  capable  of  preserva- 
tion. Among  the  Actinaria,  or  fleshy  polyps,  a  certain  amount  of 
locomotion  of  a  creeping  or  gliding  nature  is  often  observable 
(Metridium,  etc.),  the  individuals  possessing  this  ability  thus  passing 
from  a  normal  sedentary  to  a  vagrant  benthonic  life.  A  few  forms 
are  also  met  with  among  the  plankton.  Occasionally  epi-planktonic 
individuals  are  met  with,  attached  to  floating  algae  or  timbers;  and 
epi-vagrant  benthonic  individuals  attached  to  moving  crustaceans 
are  not  unknown.  The  Madreporaria,  or  stone  corals,  are  normally 
sedentary  forms,  though  they  are  not  necessarily  attached,  but 
may  rest  upon  the  sands.  (Fungia,  some  Porites.) 

Though  the  normal  medium  of  the  Anthozoa  is  salt  water,  a 
few  are  known  in  brackish  and  even  in  tolerably  fresh  water.  Cili- 
cia  rubeola  is  reported  by  the  Challenger  (Vol.  XVI,  pt.  II;  36)  in 
the  river  Thames  in  New  Zealand;  and  Dana  (9:1^0)  states  that 

.  .  .  upon  the  reefs  enclosing  the  harbor  of  Rewa  (Viti 
Lebu),  where  a  large  river,  three  hundred  yards  wide,  empties, 
which  during  freshets  enables  vessels  at  anchor  two  and  a  half 
miles  off  its  mouth  to  dip  up  fresh  water  alongside,  there  is  a  single 
porous  species  of  Madrepora  (M.  cribripora),  growing  here  and 
there  in  patches  over  a  surface  of  dead  coral  rock  or  sand.  In  sim- 
ilar places  about  other  regions  species  of  Porites  are  most  common." 
Several  species  of  corals  grow  at  the  mouth  of  the  Rio  de  la 
Plata. 

Porites  limosa  flourishes  in  muddy  water,  and  Astrea  bower- 


BIONOMIC    CHARACTERS    OF   ANTHOZOA      1013 

banki  does  not  seem  to  mind  mud  or  sediment,  or  even  muddy 
brackish  water,  growing  on,  and  encrusting  the  stones  at  the  mouth 
of  the  Mangrove  Creek,  Australia,  these  stones  being  covered  with 
mud  and  slime,  and  being  washed  over  twice  in  the  twenty-four 
hours  by  muddy,  brackish  water.  (Tenison- Woods.)  A  common 
Red  Sea  coral,  Stylophora  pistillata,  is  recorded  by  Milne-Edwards 
and  Haime  from  the  intensely  salt  and  dense  waters  of  the  Dead 
Sea. 

The  simple  corals  (Caryophyllia,  etc.)  are  chiefly  found  on 
muddy  bottoms,  often  attached  to  a  shell  or  other  object  resting  on 
the  mud.  The  bathymetric  distribution  varies  from  shallow  water 
to  a  thousand  fathoms  or  more.  This  method  of  life  corresponds 
well  with  what  is  known  of  the  Palaeozoic  Tetraseptata,  which  com- 
monly lived  on  a  muddy  bottom,  with  their  bases  not  infrequently 
showing  signs  of  attachment  to  shells  or  other  foreign  objects.  The 
compound  corals  build  heads  or  stocks  often  of  great  size  and 
weight.  They  are  generally  attached  to  stones,  shells,  or  to  the 
rock  bottom  and,  through  rapid  increase  by  budding  or  division, 
masses  of  great  size  may  be  formed  over  a  small  object  of  support. 
Even  on  muddy  bottoms  a  small  object  of  support  may  serve  as 
the  nucleus  around  which  a  coral  mass  will  grow,  which,  as  it  in- 
creases in  size  and  weight,  will  sink  to  a  greater  or  less  depth  into 
the  mud  on  which  it  rests. 

The  typical  compound  or  reef  corals  are  very  restricted  in  their 
bathymetric  distribution.  They  do  not  normally  occur  below  fifty 
fathoms,  and  the  majority  live  in  less  than  twenty  fathoms  of 
water.  Very  many,  indeed,  live  so  close  to  the  surface  as  to  be 
exposed  at  the  lowest  tides.  A  minimum  annual  temperature  of 
twenty  degrees  centigrade  marks  the  regions  in  which  most  reef- 
building  corals  occur,  though  in  a  few  cases  colder  regions  are 
known  to  be  inhabited  by  true  reef-builders.  In  all  seas,  however, 
which  are  subject  to  freezing,  or  are  regularly  invaded  by  floating 
ice,  reef-building  corals  cannot  thrive,  and  hence  the  occurrence  of 
modern  or  ancient  coral  reefs  is  a  reliable  indication  of  a  minimum 
winter  temperature  above  freezing. 

The  reproduction  of  the  Anthozoa  is  both  asexual  and  sexual. 
The  asexual  method  is  carried  on  by  fission  and  budding,  the  new- 
formed  corallites  usually  remaining  united  with  their  parents,  thus 
producing  colonial  forms.  In  some  cases,  however,  the  buds  become 
free  and  begin  an  independent  life  (Eungia,  Balanophyllia,  etc.). 
New  colonies,  however,  are  mostly  begun  by  sexually  generated 
individuals.  From  the  fertilized  egg  develops  a  meroplanktonic 
ciliated  embryo,  in  appearance  not  unlike  the  planula  of  the  hydro- 


ioi4  PRINCIPLES    OF    STRATIGRAPHY 

zoa.     After  attachment  this  develops  into  the  polyp,   which  early 
begins  to  secrete  its  horny  or  calcareous  corallum. 


IV.      MOLLUSCOIDEA. 

BRYOZOA.  The  Bryozoa  or  Polyzoa  are  marine  or  fresh  water, 
chiefly  colonial,  benthonic  animals.  A  few  occur  parasitic  on  a  liv- 
ing substratum,  but  the  majority  of  species  are  epiphytically  attached 
to  algae,  to  hydroids,  etc.  (epizoon),  or  to  inorganic  objects  (epilith), 
either  basally  or  in  an  encrusting  manner.  The  majority  of  species 
are  marine;  and  their  bathymetric  distribution  ranges  from  the 
shore  zone,  where  they  are  exposed  at  low  tide,  to  the  abyssal 
depths,  a  species  of  Bifaxia  having  been  obtained  below  3,000 
fathoms.  The  majority  of  species,  however,  live  in  moderate 
depths.  While  the  Bryozoa  normally  lead  a  strictly  sedentary  ben- 
thonic life,  a  few  species  may  drift  about  with  the  sea-weed  to  which 
they  are  attached,  thus  assuming  an  epi-planktonic  habit.  Holo- 
planktonic  forms  are,  however,  unknown. 

Many  of  the  Palaeozoic  species  resembled  and  had  a  habitat 
similar  to  that  of  certain  corals,  often  forming  extensive  beds  or 
even  reefs  composed  of  few  species  but  of  an  enormous  number  of 
individuals. 

The  egg  of  the  bryozoan  develops  into  a  meroplanktonic  cili- 
ated larva,  which  later  on  settles  down,  becomes  attached,  and 
develops  into  a  full-grown  individual  which,  by  budding,  produces 
the  colony. 

BRACHIOPODA.  The  brachiopods  are  marine  benthonic  organ- 
isms, of  exceptional  stratigraphic  importance,  since  they  are  to  a 
high  degree  dependent  on  the  facies  of  the  sea  bottom.  Some 
species  of  Terebratula  and  Lingula  can  withstand  a  considerable 
exposure,  the  former  having  been  noted  out  of  water  for  hours 
together  at  low  tide.  Lingula  is  buried,  by  means  of  its  long 
fleshy  peduncle,  in  the  sand  near  shore ;  Crania  is  attached  to  rocks 
and  shells  by  one  of  its  valves;  but  the  majority  of  brachiopods  are 
attached  by  their  fleshy  pedicles  to  rocks,  shells,  corals,  or  to  one 
another.  They  seldom  live  on  muddy  or  sandy  bottoms,  but  are 
readily  embedded  in  these,  by  becoming  detached,  after  death, 
from  the  rocks  or  other  objects  to  which  they  adhered. 

The  bathymetric  distribution  of  the  Brachiopoda  ranges  from 
shallow  water  to  2,900  fathoms  (in  one  case)  ;  the  majority  of 
species  occurring,  however,  above  the  hundred-fathom  line,  while 
a  goodly  number  have  been,  obtained  in  depths  of  ten  fathoms  or 


BIONOMIC    CHARACTERS    OF    MOLLUSCA      1015 

less.  A  number  of  species  have  an  individual  range  of  several 
hundred  fathoms,  this  range  in  one  of  two  cases  being  nearly 
800  fathoms. 

The  mero-planktonic  larva  of  brachiopods  is  known  as  the 
cephalula,  and  consists  of  a  ciliated  umbrella-like  anterior  end,  car- 
rying four  eyes ;  a  middle  portion  carrying  the  mantle  lobes ;  and  a 
posterior  portion.  When  the  larva  becomes  attached  by  the  posterior 
end,  which  develops  into  the  pedicle  of  the  adult,  the  anterior  end 
becomes  enveloped  by  the  forward-turning  mantle  lobes  and  de- 
velops into  the  body  of  the  brachiopod. 


V.   MOLLUSCA. 

PELECYPODA.  The  pelecypods  are  marine  or  fresh-water  ben- 
thonic  molluscs,  which  lead  either  a  sedentary  or  a  vagrant  life. 
The  majority  of  species  live  in  the  sea,  but  of  these  some  can  adapt 
themselves  to  brackish  or  even  fresh  water.  Thus  species  of  Car- 
dium,  Solen,  Mya,  and  other  marine  pelecypods  have  been  obtained 
in  fresh,  or  nearly  fresh,  water ;  while  Unio,  on  the  other  hand,  has 
been  found  in  the  Brisbane  river  within  reach  of  the  flood  tide. 
In  the  neighborhood  of  Rio  Janeiro,  Solen,  and  Mytilus,  were 
found  living  with  fresh-water  Ampullaria  in  brackish  water  (Dar- 
win-io). 

A  number  of  pelecypods  inhabit  the  shore  zone,  but  the  majority 
of  these  live  buried  in  the  sands  and  muds,  and  so  are  protected 
from  desiccation  at  low  tide.  Mytilus  edulis,  however,  is  a  good 
example  of  a  shore  pelecypod,  for  it  habitually  grows  in  positions 
where  it  will  periodically  be  exposed  at  low  tide ;  while  Modiola 
plicatula  is  especially  common  in  salt  marshes,  where  it  is  covered 
only  for  a  short  period  at  high  water.  The  closely  related  Modiola 
modiola,  which  occurs  on  our  northern  shores,  is,  however,  seldom 
exposed,  growing  either  in  deep  water  or  in  tide  pools  which  are 
never  drained. 

Ostrea  arborea  is  another  striking  shore  mollusc,  growing  in 
vast  quantities  on  the  free  roots  of  the  mangrove,  and  withstanding 
a  periodic  exposure  under  a  tropical  sun.  Ostrea  borealis,  on  the 
other  hand,  is  at  home  only  in  water  of  several  fathoms'  depth. 
The  bathymetric  range  of  the  pelecypods  is  very  great,  and  even 
a  single  species  may  have  a  range  of  considerable  magnitude. 
Thus,  while  Mytilus  edulis  does  not  occur  below  fifty  fathoms, 
another  species,  M.  phaseolinus,  ranges  from  the  shore  to  a  depth 
of  3,000  fathoms.  In  the  greater  depths,  the  pelecypods  are  com- 


ioi6  PRINCIPLES    OF    STRATIGRAPHY 

monly  characterized  by  exceeding  delicacy  of  shell  and  sculpture, 
the  shell  being  often  quite  transparent.  Some  deep-water  species 
show  bright  colors,  but  the  majority  are  pale.  Altogether  there 
are  to  be  found  among  these  deep-water  species  "innumerable  illus- 
trations of  beauty,  adaptation,  or  unusual  characteristics  .  .  ." 
(Agassiz).  In  the  littoral  district,  on  the  other  hand,  the  thick- 
shelled  pelecypods  predominate,  and  this  is  especially  true  of  the 
shore  zone. 

Pelecypods,  like  brachiopods,  are  excellent  facies  indicators, 
for,  though  they  live  on  all  kinds  of  sea  bottom,  the  species,  or 
at  least  the  faunal  combinations,  are  dependent  on,  and  character- 
istic of,  the  particular  facies  on  which  they  live.  The  majority 
of  pelecypods  are  free  animals,  a  few,  such  as  the  oyster,  mussel, 
and  the  like,  being  attached  to  foreign  objects — either  by  direct 
cementation  or  by  a  byssus.  The  free  pelecypods  often  have  the 
power  of  locomotion,  Unio,  Mactra,  and  others  traveling  occasion- 
ally for  considerable  distances.  Generally,  however,  these  molluscs 
lie  buried  wholly  or  partially  in  the  sand,  and  never  change  their 
location  except  when  disturbed  by  storm  waves.  Some  few  pele- 
cypods (Pecten,  Lima)  have  the  power  of  swimming  short  dis- 
tances by  the  opening  and  closing,  in  rapid  succession,  of  their 
valves,  and  the  forcible  ejection  of  water.  Even  Solen,  though 
normally  a  burrowing  animal,  will  swim  for  some  distance  in  search 
of  the  proper  bottom,  and  it  may  often  be  seen  circling  around  in 
an  aquarium,  by  a  series  of  jerks,  due  to  the  periodic  ejection  of 
the  water  from  the  siphons.  A  number  of  pelecypods  bore  into 
wood  or  stone  (Teredo,  Lithodomus,  Saxicava,  etc.),  leading  a 
sedentary  life  within  the  habitation  thus  formed. 

The  bivalve  molluscs  have  many  enemies  which  prey  upon  them. 
Not  the  least  of  these  are  the  carnivorous  gastropods,  whose  depre- 
dations are  usually  marked  by  the  vast  number  of  shells  with 
round  holes  bored  into  them,  scattered  along  our  beaches.  Boring 
sponges  will  riddle  the  shells  of  littoral  species,  and  corallines, 
Bryozoa,  worms,  and  hydroids  will  attach  themselves  to  the  shells. 
There  is  abundant  evidence  in  the  riddled  and  punctured  shells 
that  even  the  Palaeozoic  molluscs  were  subject  to  similar  attacks 
of  boring  sponges  and  carnivorous  gastropods.  When  the  animals 
die,  their  valves  usually  fall  apart;  and  from  their  position,  and 
the  character  and  direction  of  the  waves  and  currents,  one  valve 
may  be  carried  shoreward,  the  other,  seaward.  This  explains  the 
frequent  predominance,  along  the  shore  and  in  certain  local  por- 
tions, of  fossiliferous  beds  of  one  valve,  the  other  being  entirely 
absent  or  at  least  very  rare. 


BIONOMIC    CHARACTERS    OF    MOLLUSCA      1017 

The  marine  pelecypod  normally  passes  through  a  mero-plank- 
tonic   larval  stage — the  trochophore — in  which  the  young  is   pro- 
vided with  a  velum,  furnished  with  vibratory  ciliae  (veliger  stage). 
At  certain  seasons  of  the  year  these  ciliated  embryos  swarm  in  th^ 
pelagic  district,  especially  in  the  neighborhood  of  the  shores,  where 
they  become  the  sport  of  the  currents,  which  distribute  them  far 
and  wide.    When  they  finally  settle  down  upon  the  sea  bottom,  on 
the  loss  of  the  velum,  they  develop  further  if  they  reach  the  proper 
substratum,  other  conditions  being   favorable.     Vast  numbers   of 
the  larvae  are  destroyed  before  they  reach  the  bottom,  serving  as 
food  for  all  kinds  of  animals,  or  succumbing  to  unfavorable  condi- 
tions ;  and  vast  numbers  of  others  die  from  falling  on  an  unfav- 
orable  bottom.      That   most   species   nevertheless    develop   to   the 
fullest  extent  is  due  to  the  enormous  fecundity  of  most  pelecypods. 
As  an  extreme  example  may  perhaps  be  mentioned  our  common 
northern   oyster,    Ostrea   virginiana,    which,    according   to    Brooks 
(2:xxviii),  produces  nine  millions  of  eggs.     In  fresh-water  pelecy- 
pods the  mero-planktonic  veliger  larva  exists  in  one  species  only 
(Dreissensia  polymorpha),  which  is  believed  to  have  migrated  from 
salt  to  fresh  water  in  recent  geologic  times.     (Lang- 19.)     In  the 
other  freshwater  pelecypods  the  development  proceeds  in  a  different 
manner,  special  adaptations  to  special  modes  of  life  being  met  with. 
In  some  cases  (Pisidium,  Cyclas)  the  eggs  develop  in  special  brood- 
capsules  in  the  gills  of  the  mother,  which  they  leave  with  shell 
fully  formed,  as  young  bivalves.     In  these  genera  the  velum  re- 
mains  rudimentary,  the  animal   passing  through  the  trochophore 
stage  within  the  gills  of  the  mother.     In  the  Unionidae  the  embryo 
passes  through  its  several  stages  in  the  gill  of  the  mother,  leaving 
it  with  a  bivalve  shell,  which  is,  however,  furnished  with  a  trian- 
gular process  on  the  ventral  border  of  each  valve,  by  means  of 
which  the  embryo  attaches  itself  to  the  fins   (Anodonta)   or  gills 
(Unio)  of  fishes.     In  this  manner  the  animal  leads  an  epinektonic 
existence,  becoming  enclosed  by  the  rapid  growth  of  the  epithelium 
of  the  part  where  the  embryo  is  attached,  and  leading  then  a  truly 
endo-parasitic  life.     After  several  weeks  the  embryo  has  become 
transformed   into   a   young   mussel,   which,   breaking   through   the 
enclosing  tissue  of  its  nest,  falls  to  the  bottom  of  the  water,  there 
to  develop  into  the  adult. 

SCAPHOPODA  AND  AMPHINEURA.  The  first  of  these  classes  is 
represented  by  the  Dentalidae;  the  second  by  the  Chitonidae,  which 
alone  are  important  palaeontologically.  Both  are  marine,  being  of 
a  sedentary  benthonic  habit,  though  not  permanently  attached. 
Dentalium  lies  buried  in  the  mud  and  sands  usually  at  great  depths, 


ioi8  PRINCIPLES    OF    STRATIGRAPHY 

while  Chiton  and  its  allies  cling  to  stones,  shells,  etc.,  and  are 
rare  in  deep  water,  where  only  their  more  archaic  representatives 
occur.  A  few  species  of  Dentalium  occur  in  moderately  shallow 
water,  but  most  of  them  live  below  the  hundred  fathom  line,  some 
reaching  a  depth  of  2,000  fathoms  or  more.  Chiton  seldom  ex- 
tends below  500  fathoms.  In  both  groups  a  mero-planktonic  larva 
occurs. 

GASTROPODA.  The  gastropods  are  typical  benthonic  animals, 
inhabiting  the  sea,  fresh  water,  and  the  land.  They  almost  invari- 
ably belong  to  the  vagrant  benthos,  though  the  degree  of  locomotion 
varies  greatly  among  the  different  species.  Among  the  exceptions 
to  the  general  vagrant  habit  are  Vermetus  and  some  other  genera, 
which  lead  a  truly  sedentary  benthonic  life,  being  attached  to  rocks 
or  shells.  Some  genera,  like  Capulus,  adhere  continually  to  shells 
and  the  tests  of  echinoderms  and  Crustacea ;  while  the  limpets, 
though  adhering  powerfully  to  rocks  and  shells  by  the  muscular 
foot,  are,  nevertheless,  in  the  habit  of  crawling  about  in  search  of 
food.  Swimming  and  floating  gastropods  are  also  known,  the 
latter  (Janthina,  Glaucus,  etc.)  belonging  to  the  true  plankton. 

The  number  of  species  living  on  land  and  in  fresh  water  is 
relatively  small,  though  the  individuals  often  occur  in  great  num- 
bers. The  sea  is  the  home  of  most  gastropods,  though  some  marine 
forms  can  live  in  fresh  water,  while  conversely  fresh-water  forms 
have  been  found  in  water  temporarily  salt.  Thus  Limnsea  was 
found  by  Darwin  (10)  in  Brazil,  in  a  fresh-water  lake  to  which 
the  sea  had  access  at  least  once  a  year. 

Among  the  normally  fresh-water  gastropods  several  occur  which 
have  become  adapted  to  a  marine  life.  Thus  Planorbis  glaber  was 
found  at  a  depth  of  1,415  fathoms  at  Cape  Teneriffe,  and  two 
species  of  Nerita  have  been  found  in  the  sea.  Limnaea  and  Neri- 
tina  live  in  the  Baltic,  where  the  water  contains  from  10  to  15  per- 
mille  of  salt. 

The  variety  of  form  and  coloration  is  exceedingly  great  among 
the  gastropods,  a  fact  which  can  easily  be  correlated  with  their  high 
degree  of  cephalization  and  actively  vagrant  life.  They  occupy  all 
parts  of  the  sea,  being  much  less  dependent  on  the  facies  of  the 
sea  bottom  than  the  pelecypods  are.  The  division  into  carnivorous 
and  herbivorous  forms  is  also  much  more  strongly  emphasized  than 
in  the  pelecypods,  which  live  largely  upon  the  plankton. 

The  shore  zone  is  occupied  by  a  number  of  species,  which  can 
withstand  periodic  exposure.  Many  of  them  require  this  exposure 
and  will  invariably  crawl  to  the  surface  if  kept  in  confinement, 
even  if  the  water  is  kept  cool  and  well  aerated.  Other  species, 


BIONOMIC    CHARACTERS    OF    MOLLUSCA      1019 

again,  live  in  shallow  water,  even  if  stagnant,  and  will  not  stand 
a  long  exposure. 

Various  species  of  Neritina  (N.  dubia,  N.  ziczac,  etc.)  live 
habitually  high  up  on  the  trees  of  the  mangrove  swamps,  deposit- 
ing their  eggs,  however,  on  the  surface  of  the  water.  Others  occur 
on  the  dry  land,  far  from  any  water.  (Semper-26.) 

Nassa  obsoleta  covers  the  gentle  muddy  beaches  at  low  tide, 
where  dead  organisms  remain  for  it  to  feed  upon,  and  it  also 
abounds  on  every  exposed  mud  flat  on  our  northern  coast.  Littorina 
rudis  and  L.  palliata  are  commonly  found  on  the  New  England 
shore  clinging  to  rocks  or  to  the  stems  of  the  marsh-grass  (Spar- 
tina),  high  up,  where  they  are  exposed  to  the  air  for  half  the  day. 
The  lack  of  a  siphon  forces  these  animals  to  live  above  the  mud 
(12:168).  On  the  marshes  of  Cold  Spring  Harbor,  these  species 
of  Littorina  occur  in  places  where  they  are  "submerged  for  only 
a  short  time  at  high  tide,  and  then  under  water  that  is  nearly  fresh." 
(Davenport-i2:/dp.)  In  the  Mississippi  sound  Davenport  found 
nearly  all  of  the  individuals  of  Littorina  irrorata  "living  on  the 
stems  of  the  short  marsh-grass  twenty  to  thirty  centimeters  above 
the  water  level  and  exposed  to  the  sunlight."  Littorina  rudis  lives 
prevailingly  where  it  is  much  exposed.  On  the  English  Channel  it 
has  been  found  two  meters  above  the  other  marine  animals,  where 
it  is  moistened  only  by  the  highest  tides  (Fisher-i3  :i&?)  ;  and  on 
the  New  England  coast  it  is  sometimes  found  in  similar  positions. 
Species  of  Littorina  are  reported  as  passing  the  winter  out  of  water, 
with  their  gill  chambers  full  of  air.  (Simroth-27:^.) 

The  majority  of  gastropods  are  shallow-water  forms,  though  a 
number  of  them  range  to  depths  of  between  1,000  and  2,000 
fathoms.  The  deep-sea  gastropods  are  characterized  by  faint  col- 
ors, though  often  this  is  counterbalanced  by  the  brilliancy  and 
beauty  of  the  iridescence,  and  even  the  non-iridescent  abyssal  spe- 
cies give  out  "a  sort  of  sheen  which  is  wanting  in  their  shallow- 
water  allies."  (Agassiz-i,  ii:<5j.)  The  coarse  ornamentation  by 
knobs,  spines,  etc.,  so  common  in  shallow-water  species,  does  not 
occur  in  the  deep-sea  forms,  where  the  ornamentation  is  more 
delicate,  and  often  of  exquisite  richness  and  beauty.  Gastropods 
feeding  on  vegetable  matter  are  wanting  in  the  deep  sea,  where  no 
vegetable  matter  occurs,  except  what  is  brought  down  as  sediment. 
The  food  of  deep-sea  molluscs  is  largely  confined  to  soft-tissued 
animals,  since  thick  shells  and  other  hard  armors  are  generally  ab- 
sent in  these  depths.  Agassiz  states  that  the  Pleurotomidae  out- 
number any  other  group  of  molluscs  in  the  abyssal  fauna.  These 
gastropods  are  characterized  by  a  notch  in  the  outer  lip  near  the 


1020  PRINCIPLES    OF    STRATIGRAPHY 

suture,  which  serves  for  the  discharge  of  the  refuse,  thus  pre- 
venting fouling  of  the  water  used  for  respiration.  Some  of  these 
molluscs  are  provided  with  hollow  barbed  teeth  and  poison  fangs, 
which  they  use  to  kill  their  prey.  This  apparatus  "is  even  more 
fully  and  generally  developed  in  the  related  group  of  the  Conidae, 
few  of  which  reach  any  great  depth."  ( Agassiz-i,  ii  :66.) 

A  few  gastropods  are  viviparous  (Paludina  vivipara,  Littorina 
rudis),  producing  their  young  in  advanced  state  of  development. 

In  nearly  all  the  marine  gastropods  a  veliger  larva  occurs,  the 
velum  being  generally  large,  wing-like,  and  fringed  with  cilia.  This 
velum  may  be  retained  until  the  shell  is  long  past  the  protoconch 
stage.  While  in  most  marine  gastropods  the  veliger  larva  leads,  a 
mero-planktonic  existence,  some  marine  forms  (Fulgur,  Sycoty- 
pus),  and  the^  oviparous,  land,  and  fresh-water  gastropods  pass 
through  their  veliger  stage  within  the  egg  capsule,  losing  the  velum 
and  other  larval  organs  before  passing  from  the  capsule,  which  they 
leave  as  young  gastropods  with  well-developed  shells. 

In  the  case  of  the  marine  forms  cited,  the  velum,  though  of 
no  use  to  the  animal  as  a  locomotor  organ,  is  very  large,  and  is 
lost  only  just  before  the  embryo  leaves  the  egg  capsule.  In  terres- 
trial and  fresh-water  forms,  on  the  other  hand,  the  velum  is  re- 
duced to  a  single  ring  of  cilia  or  to  two  lateral  ciliated  streaks. 
(Lang-ip,  ii:^5/),  while  in  some  terrestrial  species  it  is  wanting 
entirely.  It  is  obvious  that  the  distribution  of  species  thus  de- 
prived of  a  temporary  'pelagic  life  must  be  more  restricted,  other 
things  being  equal,  than  that  of  species  having  a  free  veliger  stage 
of  greater  or  less  duration. 

Land  snails  generally  require  a  considerable  amount  of  moisture 
in  the  atmosphere  in  order  to  be  able  to  live  an  active  life.  Hence 
they  are  found  most  abundantly  near  streams  and  in  damp  woods 
and  ravines,  where  they  live  on  the  ground  or  on  the  vegetation. 
Nevertheless  they  can  withstand  a  considerable  amount  of  desicca- 
tion by  burying  themselves  in  the  soil  or  closely  clinging  to  rocks 
or  trees.  Even  the  deserts  have  their  species,  which  obtain  their 
required  moisture  chiefly  from  the  dew,  and  from  the  succulent 
plants  on  which  they  feed.  Hence  the  presence  of  snail  shells  in 
loess  deposits  is  not  necessarily  indicative  of  deposition  by  water. 
Some  remarkable  cases  are  recorded  by  Woodward  (31  '.14),  of  the 
suspension  of  vitality  in  snails  and  their  subsequent  revivification. 
Thus  a  specimen  of  a  desert  snail  which  had  been  affixed  to  a  card 
in  the  British  Museum  for  a  period  of  four  years  (1846-1850), 
again  came  to  life  upon  being  immersed  in  tepid  water. 

PTEROPODA.     The   pteropods    are   marine   planktonic    molluscs 


BIONOMIC    CHARACTERS    OF    MOLLUSCA       1021 

which  live  in  vast  numbers  in  the  pelagic  district,  usually  some 
distance  from  shore.  While  able  to  swim  about  in  the  water,  they 
are,  nevertheless,  at  the  mercy  of  the  waves  and  currents.  Their 
food  consists  of  pelagic  organisms,  and  not  uncommonly  one  species 
of  pteropod  will  prey  upon  another.  They  shun  the  light,  descend- 
ing during  the  day  to  the  regions  of  perpetual  twilight  or  even 
darkness,  some  descending  as  far  as  700  fathoms.  Nearly  all  the 
shelled  pteropods  of  the  present  time  are  confined  to  warmer 
waters,  and  are  especially  abundant  in  the  warm  ocean  currents. 
Their  shells  often  accumulate  in  vast  numbers  on  the  ocean  bottom. 
A  veliger  larva,  similar  to  that  of  the  gastropods,  occurs. 

CEPHALOPODA.  The  cephalopods  are  marine  nektonic  or  ben- 
thonic  molluscs  inhabiting  water  of  moderate  depths.  Swimming  is 
accomplished  by  the  forcible  ejection  of  water  from  the  hyponome, 
and  probably  also  by  the  use  of  the  arms.  Among  the  dibranchiata 
the  majority  of  Sepioidea  (Squids,  Calamaries)  are  active  swim- 
mers, usually  inhabiting  the  open  sea,  but  appearing  periodically  on 
the  coasts  in  great  shoals.  They  live  mostly  on  small  fish.  The 
Octopoda  are  less  adapted  to  active  swimming,  'lying  usually  in 
wait  for  their  prey  on  the  sea-bottom  or  in  crevices  and  hollows. 
The  Argonauta  is,  however,  a  partial  exception  to  this,  for,  though 
it  crawls  about  on  the  sea-bottom  like  other  octopods,  it  is  often 
met  with  swimming  at  or  near  the  surface,  by  the  ejection  of  the 
water  from  its  hyponome.  Argonauta  is,  therefore,  like  other 
cephalopods,  at  times  a  vagrant  benthos,  at  others  a  nekton,  in- 
clining perhaps  more  to  the  latter,  as  do  the  decapods ;  while 
other  octopods  are  commonly  benthonic.  Among  the  less  active 
decapods,  Sepia  may  be  mentioned  as  more  normally  a  vagrant 
benthonic  form,  crawling  about  on  the  sea-bottom,  though  able 
to  swim  as  well.  A  sedentary  benthonic  cephalopod  is  also  known. 
This  is  Spirula,  which  attaches  itself  to  rocks  like  an  actinia 
(Agassiz,  Walther),  or  lies  partly  buried  in  the  mud,  with  its 
beautiful  coiled  and  chambered  shell  wholly  concealed  by  the 
fleshy  parts.  A  perfect  specimen  was  dredged  off  Grenada  in  the 
Caribbean  by  the  Blake,  from  a  depth  of  950  fathoms.  (Agassiz-i, 
ii:<5/.) 

Spirula  would  seem  to  be  a  widely  distributed  form,  judging 
from  the  occurrence  of  its  shell  in  almost  all  parts  of  the  tropical 
and  temperate  seas.  The  animal  is  very  rare,  however;  only  one 
specimen  with  soft  tissues  preserved  having  been  obtained  by  the 
Challenger  expedition.  This  was  taken  close  to  the  island  of 
Banda  in  360  fathoms  (Challenger  Narrative).  Altogether  perhaps 
only  half  a  dozen  animals  with  the  soft  parts  preserved  have  been 


1022  PRINCIPLES    OF    STRATIGRAPHY 

obtained.  The  wide  distribution  of  the  shell  of  Spirula  is  due  to 
the  fact  that  after  the  death  of  the  animal  the  shell  ascends  to  the 
surface,  owing  to  the  air-filled  chambers,  and  then  becomes  a  part 
of  the  plankton.  It  is  carried  hither  and  thither  by  the  currents 
and  waves,  and  finally  may  reach  the  sea-bottom  in  regions  remote 
from  its  original  home,  and  be  buried  in  sediments  of  every  descrip- 
tion, and  under  conditions  in  which  the  animal  never  existed. 
Thus  the  shell  of  Spirula  becomes  an  excellent  index  fossil,  being 
widely  distributed  and  buried  in  all  kinds  of  sediment. 

To  a  more  restricted  degree  this  method  of  pseudo-planktonic 
distribution  of  the  shell,  after  the  death  of  the  animal,  occurs  also 
in  Nautilus,  the  only  modern  representative  of  the  tetrabranchiate 
cephalopods.  The  animal  belongs  to  the  benthos,  living  in  shallow 
water  in  the  tropics.  Occasionally  it  swims  near  the  surface,  but 
before  long  it  returns  to  the  bottom,  where  it  crawls  about  with  its 
shell  uppermost,  feeding  on  Crustacea  and  other  animals.  On  the 
death  of  the  animal  the  shell  may  float  for  a  considerable  time  on 
the  surface,  buoyed  up  by  the  air  in  the  chambers,  and  thus  it  may 
be  carried  for  a  greater  or  less  distance  before  it  settles  to  the 
bottom,  where  it  will  be  buried  in  all  kinds  of  sediment  (Walther). 
The  verity  of  such  statements  has,  however,  been  questioned  by 
Ortmann  and  others,  who  believe  that  the  Nautilus  shell  is  seldom 
carried  far  from  the  region  inhabited  by  the  living  animal. 

What  is  true  of  the  shells  of  Nautilus  and  Spirula  is  true  of 
the  shell  of  Sepia,  and  was  undoubtedly  true  of  the  shells  of  Am- 
monites as  well.  (Walther-29:5op;  30:^56*  et  seq.)  In  fact,  we 
may  even  believe  that  the  shells  of  the  Ammonites  were  better 
floaters  than  either  those  of  Spirula  .or  Nautilus,  for  these  two 
genera  are  retrosiphonate,  the  siphonal  funnels  passing  backward 
and  thus  giving  more  ready  access  to  the  water;  while  the  shells  of 
the  Ammonites  were  prosiphonate,  their  siphonal  funnels  bending 
forward  like  the  neck  of  a  bottle,  and  thus  making  the  entrance 
of  water  more  difficult.  This  conception  of  the  planktonic  wan- 
derings of  the  shells  of  cephalopods  after  the  death  of  the  animal 
furnishes  a  satisfactory  explanation  of  many  anomalies  observed 
in  the  occurrence  of  these  animals  in  the  geologic  series.  It  ac- 
counts, especially,  for  the  sudden  appearance  and  disappearance  of 
the  same  species  in  widely  separated  localities,  irrespective  of  the 
character  of  the  rock,  and  of  its  normal  faunal  contents.  This 
widespread  distribution  of  these  shells  makes  them  excellent  index- 
fossils,  so  that  even  small  formations  may  readily  be  correlated  by 
their  species  of  Ammonites,  even  though  widely  separated. 

It  does  not  follow,  of  course,  that  ammonoid  shells  must  always 


BIONOMIC    CHARACTERS    OF    VERMES         1023 

be  regarded  as  strangers  which  have  drifted  to  their  present  posi- 
tion ;  in  fact,  it  is  often  easy  to  see  that  such  has  not  been  the  case 
in  any  particular  locality,  from  an  examination  of  the  shells  them- 
selves, as  well  as  from  the  extraneous  evidence.  Thus,  according 
to  Clarke  (5:155,  et  seq.),  the  ammonoids  of  the  Naples  beds  of 
western  New  York  "...  bear  sufficient  demonstration  in 
themselves  that  they  have  lived  and  died  in  these  sediments." 
Many  of  the  most  delicate  shells  retain  their  apertures  unbroken, 
and  their  suface  ornamentation  uninjured,  a  fact  which  is  not  con- 
sistent with  transportation  by  waves  and  currents.  The  presence 
of  the  young  in  all  stages  of  development  further  argues  for  an 
indigenous  occurrence.  "On  the  other  hand,"  says  Clarke,  "there 
are  excellent  reasons  for  regarding  the  prenuncial  Intumescens 
fauna,  that  of  the  Styliola  [Styliolina]  limestone,  as  due  to  trans- 
portation from  some  adjoining  province  not  yet  known  to  us." 
The  Goniatites  of  this  fauna  are  associated  with  the  millions  of 
holo-planktonic  Styliolina,  with  floated  logs,  and  probably  other 
pelagic  organisms,  and  the  sediment  in  which  they  were  embedded 
was  such  as  probably  was  not  conducive  to  the  well-being  of  such 
animals,  so  that  their  occurrence  is  best  explained  by  the  hypothesis 
of  flotation. 

Of  the  embryology  of  Nautilus,  and  hence  of  the  whole  group  of 
Tetrabranchiata,  nothing  is  known.  The  Dibranchiata  develop  di- 
rectly within  the  egg  capsule,  no  veliger  stage  occurring. 


VI.     PLATYLELMINTHA.       VII.     VERMES. 

These  worms  are  marine,  fresh-water,  or  terrestrial  animals. 
They  belong  chiefly  to  the  benthos,  though  some  marine  forms  lead  a 
partially  nektonic  existence,  while  others  are  typically  planktonic. 
Several  oligochsetous  annelids  have  become  adapted  to  a  marine 
life,  though  the  group  is  normally  fresh-water  or  terrestrial.  Among 
the  benthonic  species  all  grades  of  a  sedentary  life  are  observable, 
from  the  tube-building  orders,  which  live  permanently  in  attached 
tubes,  to  those  which  only  temporarily  occupy  a  given  area.  Tubi- 
colous  worms,  which,  like  Spirorbis,  attach  their  tubes  chiefly  to 
algse,  may  often  lead  an  epi-planktonic  existence  when  the  algae  are 
torn  from  their  anchorage  and  washed  away  by  currents. 

A  muddy  bottom  seems  to  be  the  favorite  haunt  of  the  littoral 
species,  except  such  forms  as  build  attached  tubes  (e.  g.,  Serpulidae, 
etc.),  which  occupy  stony  and  shelly  bottoms.  These  latter  often 
build  extensive  reefs  of  interwoven  calcareous  tubes. 


1024  PRINCIPLES    OF    STRATIGRAPHY 

Besides  calcareous  tubes,  many  worms  build  tubes  of  aggluti- 
nated sand  grains  or  shell  particles,  and  worms  living  in  the  shells 
of  dead  molluscs  are  frequently  met  with.  These  agglutinated  sand 
tubes  are  often  very  resistant,  sometimes,  with  the  castings,  covering 
the  mud  flats  and  beaches  in  great  numbers,  and  not  infrequently 
being  heaped  together  in  windrows.  The  dredge  brings  large 
numbers  of  these  tubes,  together  with  numerous  castings,  from  the 
deeper  water.  The  bathymetric  distribution  of  the  worms  is  varied. 
The  majority  are  undoubtedly  littoral  species,  but  deep-sea  forms 
are  also  common.  Beyond  the  hundred-fathom  line  the  tubicolar 
annelids  are  the  most  characteristic,  specimens  having  been  ob- 
tained from  a  depth  of  4,000  fathoms  off  Teneriffe  (Challenger). 
Other  worms  also  occur.  Even  species  of  the  same  genus  have  a 
widely  varying  distribution  in  depth.  Thus  the  tubicoloid  genus 
Spirorbis  has  its  littoral  species  growing  within  the  shore  zone ; 
while  another  species,  S.  nautiloides,  has  been  dredged  at  a  depth 
of  700  fathoms.  Similarly,  the  Sipunculid  Phascolosoma  is  repre- 
sented along  our  northern  shores  by  a  species  living  in  mud  and 
sand  above  low  tide,  while  the  Blake  brought  up  a  species  in  a-  Den- 
talium  shell  from  a  depth  of  1,568  fathoms.  (Agassiz-i,  ii:5J.) 
The  Myzostomidse  are  parasitic  on  living  Comatula,  and  also  have 
been  found  on  the  column  segments  of  Jurassic  crinoids  (Graff). 

Among  the  annelids,  the  family  Eunicidse  is  of  particular  in- 
terest, in  that  its  several  members  are  characteristic  of  different 
bathymetric  zones,  thus  furnishing,  in  a  measure,  an  index  to  the 
bathymetric  position  of  the  fauna  which  they  characterize.  This 
family  is  well  represented  in  the  lithographic  shales  of  Bavaria. 
(Ehlers.) 

Among  the  worms  regeneration  of  lost  parts  and  generation  of 
new  individuals  from  fragments  of  old  ones  are  not  uncommon. 
Thus,  in  one  of  our  common  halo-pelagic  worms,  Autolytus,  swim- 
ming buds  carrying  the  sexual  products  are  periodically  constricted 
off,  each  regenerating  a  new  head,  with  highly  developed  eyes  at 
the  anterior  end.  The  oligochaete  Lumbriculus  in  autumn  falls 
into  pieces,  all  of  which  are  able  to  regenerate  into  complete  ani- 
mals. (Lang-iQ;  ii^d/.) 

A  mero-planktonic  ciliated  larva,  the  trochophore,  is  character- 
istic of  worms,  this  being  the  product  of  a  sexual  mode  of  repro- 
duction. These  larvae  are  often  obtained  in  vast  numbers  in  the 
tow-net,  together  with  other  mero-planktonic  and  many  holo-plank- 
tonic  forms. 

The  oesophageal  teeth  of  annelids  are  abundantly  represented 
in  many  bituminous  shales,  from  the  Palaeozoic  on.  Some  of  these 


BIONOMIC    CHARACTERS    OF    CRUSTACEA      1025 

objects,  known  as  conodonts,  were  formerly  regarded  as  the  teeth 
of  mixinoid  fishes  or  as  radulae  of  gastropods. 


VIII.     ARTHROPODA. 
Crustacea. 

Trilobita.  The  trilobites  are  extinct  Palaeozoic  Crustacea  of  an 
undoubted  marine  habitat,  probably  able  to  swim  as  well  as  crawl, 
and  so  belonging  at  one  time  to  the  nekton,  at  another  to  the  vagrant 
benthos.  Whether  or  not  a  mero-planktonic  larva  existed  is  not 
known,  but  it  might  be  assumed  from  the  wide  distribution  of  some 
species.  Since  trilobites  cast  off  their  exoskeletons,  as  does  Limulus, 
some  of  these  may  have  floated  a  considerable  distance,  coming  to 
lodge  where  trilobites  never  lived.  It  is  certain  that  from  the 
number  of  fossil  trilobites  we  cannot  judge  the  number  of  individ- 
uals existing  at  a  given  place,  since  a  number  of  specimens  may  rep- 
resent the  cast-off  exoskeletons  of  one  individual.  Trilobites,  like 
many  modern  Crustacea,  probably  turned  on  their  backs  while  sink- 
ing to  the  sea-floor,  this  accounting  for  the  frequent  overturned 
position  in  which  their  remains  are  found. 

Phyllopoda;  Copepoda.  These  belong  largely  to  the  plankton, 
the  phyllopods  occurring  mostly  in  fresh  water,  the  copepods  having 
fresh  water  (Cyclops)  and  marine  representatives.  The  copepods 
further  comprise  commensal  forms,  which  live  in  the  branchial 
cavity  of  Ascidians  (Notodelphus)  or  on  the  carp  (Argulus)  ;  and 
a  large  number  of  parasitic  types.  Some  of  them,  however,  are 
only  occasionally  or  temporarily  parasitic.  Some  phyllopods  have 
a  bivalve  shell  (Estheria,  etc.),  which  is  frequently  preserved  in 
the  finer  fresh  water  sediments  of  continental  formations.  A  plank- 
tonic  nauplius  larva  occurs.  The  eggs  of  some  phyllopods  have 
the  power  to  withstand  desiccation  for  years.  In  fact,  the  eggs 
of  Apus  do  not  develop  unless  they  have  been  subjected  to  desicca- 
tion for  some  time  (Semper).  This  accounts  for  the  periodic 
reappearance  of  these  organisms  in  the  temporary  water  bodies 
of  desert  regions.  The  occurrence  of  such  types  (Estheria)  in 
otherwise  unfossiliferous  deposits  thus  indicates  that  these  deposits 
may  be  of  desert  origin. 

Ostracoda.  The  ostracods  are  marine  or  fresh-water,  planktonic 
or  vagrant  benthonic  Crustacea  whose  imperfectly  segmented  body 
is  enclosed  in  a  bivalve  shell.  The  majority  of  the  marine  forms 
are  holo-planktonic,  living  in  shallow7  water  or  in  moderate  depths, 


1026  PRINCIPLES    OF    STRATIGRAPHY 

though  a  few  species  were  found  by  the  Challenger  at  depths  ex- 
ceeding 2,000  fathoms.  Some  species  are  cosmopolitan  and  the 
order  is  represented  in  nearly  all  waters,  their  shells  occurring  in 
nearly  all  the  bottom  deposits.  The  animals  are  also  abundant  on 
alga?,  over  which  they  crawl  slowly.  The  fresh-water  Cypris 
swims  about,  subject,  however,  to  the  influences  by  which  other 
members  of  the  plankton  are  affected ;  or  it  crawls  about  on  the 
vegetation.  Cypris  is  also  represented  in  brackish  and  salt  water. 
Its  eggs  have  the  power  to  withstand  desiccation  for  a  long  time, 
and  hence  the  species  can  continue  in  water  bodies  which  become 
periodically  dried  up,  as  in  desert  regions.  The  larva  of  the  ostra- 
cods  is  a  pelagic  nauplius. 

Cirripedia.  The  cirripeds,  or  barnacles,  are  marine  sedentary 
benthonic  Crustacea  which  have  degenerated  much  from  the  true 
type  of  crustacean,  owing,  no  doubt,  to  their  attached  mode  of  life. 
The  body  is  covered  with  calcareous  plates  variously  arranged, 
which  fall  apart  after  the  death  of  the  animal;  after  which,  from 
single  pieces,  it  is  quite  impossible  to  determine  the  species,  owing 
to  the  great  variation  of  the  skeletal  parts.  (Darwin.)  Balanus 
and  its  congeners  are  sessile,  being  attached  to  the  rocks  and  other 
solid  supports  along  the  shore,  seldom  venturing  into  water  of 
great  depth.  Some  species  are  periodically  exposed  for  many 
hours  at  low  tide,  some,  in  fact,  never  being  covered  more  than  one 
or  two  hours  at  flood  tide,  so  high  up  on  the  shore  do  they  attach 
themselves.  Balanus  has  been  found  at  a  depth  of  500  fathoms, 
but  it  usually  lives  in  lesser  depths.  Balanus  improvises  occurs  also 
in  brackish  water,  and  some  species  of  this  barnacle  have  been  re- 
ported from  fresh  water  (Tscherniansky).  Coronula  diadema 
leads  an  epi-nektonic  life,  attaching  itself  to  the  body  of  whales. 
Verruca  incerta,  a  common  West  Indian  type,  occurs  in  the  Glo- 
bigerina  ooze.  Lepas  and  its  congeners  are  pedunculate,  attach- 
ing themselves  by  a  fleshy  peduncle,  which  represents  the  elongated 
head  end.  The  majority  of  the  Lepadidae  are  pelagic,  leading  an 
epi-planktonic  existence,  attached  to  floating  logs,  pumice,  or  other 
objects.  Three  species  of  Lepas  were  found  by  the  Challenger 
attached  to  the  Sargassum.  Some  members  of  this  family  descend 
into  deep  water,  Scalpelluni  regiuni  having  been  dredged  by  the 
Challenger  from  nearly  3,000  fathoms.  These  abyssal  cirripeds  are 
usually  attached  to  nodules,  dead  or  living  shells,  corals,  large 
Crustacea,  to  spines  of  sea  urchins  and  other  objects.  (Agassiz- 
i,  11:50.)  The  cirripeds,  upon  hatching  from  the  egg,  pass  through 
several  larval  stages,  the  first  of  which  is  the  nauplius  stage.  In 
this  the  body  is  unsegmented,  with  median  frontal  eyes,  dorsal 


BIONOMIC    CHARACTERS    OF    CRUSTACEA      1027 

shield,  frontal  sensory  organs  and  three  pairs  of  limbs.  After 
a  series  of  moults  the  Cypris  stage  is  reached,  in  which  the  larva 
is  enclosed  in  a  bivalve  shell,  like  that  of  the  Ostracoda.  During 
these  stages  the  larva  belongs  to  the  mero-plankton.  When  it 
settles  down  and  becomes  attached  it  passes  through  a  pupa  stage, 
during  which' the  transformation  of  the  larva  into  the  cirriped 
takes  place. 

PJiyllocarida.  These  are  mostly  extinct  forms,  represented  in 
all  the  divisions  of  the  Palaeozoic.  Several  living  genera  (Nebalia, 
etc.)  are  regarded  as  belonging  %ere,  and  these  are  marine.  They 
are  swimmers,  and  their  development  is  direct,  without  metamor- 
phosis. Some  of  the  Palaeozoic  forms  referred  to  this  class  were 
undoubtedly  marine  (Stenotheca,  Ribeiria),  but  the  majority  seem 
to  have  been  fresh  water  forms  living  in  the  rivers  of  the  Palaeozoic 
lands.  This  is  inferred  from  their  peculiar  occurrence  in  sediments 
which  could  only  have  been  formed  at  the  mouths  of  streams  and 
in  playa-like  basins.  At  any  rate,  they  did  not  seem  to  be  normal 
inhabitants  of  the  open  sea,  but,  if  marine  at  all,  lived  near  the 
mouths  of  great  streams. 

Schlzopoda,  Stomatopoda,  Sympoda.  These  are  marine  Crus- 
tacea, capable  of  swimming  about  by  the  use  of  their  abdominal 
legs  and  caudal  fin.  Larval  stages  are  often  wanting. 

Decapoda.  The  decapods  belong  chiefly  to  the  benthos,  inhab- 
iting either  fresh  or  salt  water,  rarely  the  land.  Pelagic  species  also 
occur,  some  of  which  are  good  swimmers;  while  a  few  belong  to 
the  plankton  and  others  to  the  epi-plankton,  living  on  the  Sargas- 
sum.  They  commonly  feed  on  living  or  dead  animal  matter.  The 
bathymetric  distribution  varies  greatly,  though  the  majority  of 
species  are  confined  to  comparatively  shallow  water,  generally  not 
exceeding  fifty  fathoms.  A  considerable  number,  nevertheless,  are 
abyssal.  The  range  of  individual  species  is  often  great;  Alpheus 
avarus,  for  example,  is  said  to  range  on  the  Australian  coast  from 
less  than  ten  to  about  2,500  fathoms  (Challenger},  though  this  is 
questioned  by  Ortmann  (21:75).  Among  the  hermit  crabs  occur 
some  forms  which  have  left  their  native  element  and  have  taken 
to  the  land.  The  Challenger  found  some  of  them  in  the  mountains 
of  the  Antilles,  up  to  300  meters.  They  sometimes  inhabit  the 
shells  of  land  snails  and  have  been  seen  climbing  trees.  Among 
the  true  crabs,  or  Brachyura,  shallow-water  species  predominate, 
comparatively  few  occurring  below  400  fathoms.  A  number  of 
species  live  in  fresh  water  or  on  land.  The  majority  of  decapods 
leave  the  egg  in  the  zoe'a  stage,  in  which  the  abdominal  region  is 
perfectly  segmented,  though  still  without  appendages,  except  per- 


1028  PRINCIPLES    OF    STRATIGRAPHY 

haps  the  rudiments  of  the  sixth  pair.  The  compound  eyes  are 
stalked.  Other  larval  stages  follow  until  the  adult  is  reached. 
These  larvae  often  occur  in  vast  quantities  in  the  plankton. 

Arthrostraca.  This  super-order  includes  mostly  marine  forms, 
though  the  order  Isopoda  comprises  marine,  fresh  water,  and  ter- 
restrial types.  The  latter  occur  in  damp  woods,  under  moss,  stones, 
or  logs,  and  are  also  abundant  in  the  crevices  of  rocky  cliffs.  The 
marine  Isopods  are  common  in  shallow  water,  on  algae,  or  swim- 
ming about  in  tide  pools.  Chiridotea  cocca  lives  on  sandy  shores, 
moving  about  just  below  the  surface  of  the  sand,  and  leaving  a 
meshwork  of  curious  trails  in  its  wake.  Some  of  the  lower  sand 
flats  are  often  found  covered  with  these  markings.  The  animal 
is  usually  found  at  the  end  of  the  trail,  its  whereabouts  being  in- 
dicated by  a  little  lump  of  sand.  Limnoria  lignorum  eats  its  way 
into  driftwood  or  bridge  piles,  often  completely  riddling  and  de- 
stroying the  wood.  Caprella  clings  to  hydroids  and  slender  sea- 
weeds. Though  chiefly  found  in  the  littoral  district,  some  abyssal 
species  are  known,  several  having  been  obtained  at  a  depth  of  over 
3,600  meters.  Sometimes  different  species  of  the  same  genus  range 
from  shallow  water  to  great  depths.  Blind  species  are  common 
in  the  Mammoth  and  other  caverns.  A  number  of  types  are 
parasitic  on  fishes.  The  Amphipods  are  chiefly  marine,  though 
fresh  and  brackish  water  species  also  occur  in  marine  genera 
(Gammarus).  Cyamus  is  parasitic  on  the  skin  of  whales.  Several 
species  live  on  the  beach  just  above  the  reach  of  the  ordinary  tide, 
where  they  hide  under  the  dead  seaweed  or  burrow  in  the  sand 
(Orchestia).  They  generally  move  about  by  leaps  and  hence  are 
commonly  known  as  beach  fleas.  Talorchestia  lives  in  a  similar 
manner  just  a  little  below  high- water  mark  and  the  beach  at  low 
tide  is  often  completely  riddled  by  its  burrows.  A  number  of 
Orchestidae  can  live  wholly  out  of  the  water  in  damp  woods  or  in 
the  dry  stream  beds. 

Acerata. 

Merostomata.  The  Xiphosurans  are  represented  by  the  single 
living  genus  Limulus,  which  is  a  marine  vagrant  benthonic  animal, 
though  often  swimming  on  its  back  when  young.  The  usual  habitat 
of  this  animal  is  in  shallow  water,  where  it  is  often  partly  buried  in 
the  mud  or  sand.  Portions  of  the  coast  are  often  strewn  with  the 
cast-off  exoskeletons  of  Limulus,  which  usually  lie  on  their  backs, 
a  position  which  these  structures  will  naturally  take  on  sinking  to 
the  bottom. 


BIONOMIC  CHARACTERS  OF  MEROSTOMES     1029 

The  young  Limulus  on  hatching  is  a  trilobitiform,  free-swim- 
ming, commonly  meroplanktonic  organism  without  caudal  spine 
(J.  S.  Kingsley). 

Modern  Limulus  is  restricted  to  the  eastern  shores  of  America 
and  Asia.  A  Tertiary  species  (L.  decheni}  is  known  from  the 
Oligocenic  brown  coal  of  Teuchern,  near  Merseburg,  in  Saxony, 
an  occurrence  scarcely  suggestive  of  marine  habitat.  A  marine 
species  (L.  walchi)  is  abundant  in  the  lithographic  slates  of  Ba- 
varia, associated  with  land  forms,  however.  A  small  species  occurs- 
in  the  Bunter  Sandstein  of  the  Vosges,  a  formation  chiefly  of  ter- 
restrial (river)  origin,  and  suggesting  that  Limulus  in  the  Trias 
was  still  a  river  animal.  This  was  most  probably  true  also  of 
Protolimulus,  which  occurs  in  the  Chemung  delta  deposits  of 
Pennsylvania.  The  Carbonic  Xiphosurans,  Prestwichia,  and  Beli- 
nurus  were  undoubtedly  fresh-water  (river)  organisms,  occurring 
in  the  non-marine  coal  deposits.  Cyclus,  on  the  other  hand,  is 
found  in  the  interbedded  limestone  of  the  Coal  Measures,  as  well 
as  in  the  Coal  Measures  themselves.  The  habitat  may  have  been 
marine,  but  not  necessarily  so,  since  these  carapaces  could  easily 
have  been  washed  from  the  land. 

Altogether  it  seems  as  if  the  early  Xiphosurans  were  river-living 
animals,  venturing  perhaps  occasionally  into  the  sea  (euryhaline) 
and  assuming  their  marine  habitat  in  the  Mesozoic  and  modern 
times. 

The  Synxiphosurans  may  have  been  partly  marine  and  partly 
fresh  water,  The  Upper  Cambric  Aglaspis  suggests  their  derivation 
from  the  trilobites.  This  occurs  in  the  St.  Croix  sandstone  of 
Wisconsin,  a  terrestrial  deposit  reworked  by  the  sea.  The  Siluric 
genera  Neolimulus,  Bunodes,  Hemiaspis,  and  Bunodella  occur  in 
deposits  which  are  partly  marine  and  partly  of  delta  type.  It  is 
not  improbable  that  most  of  them  were  derived  from  the  land- 
waters  and  buried  in  the  sea  margin  deltaic  deposits.  The  possi- 
bility of  a  marine  character  for  some  can,  however,  not  be  denied. 
Pseudoniscus,  on  the  contrary,  in  America  occurs  in  the  Pittsford 
black  shale  deposits,  which  are  most  suggestive  of  influx  of  fresh 
water,  and  hence  a  non-marine  habitat  is  indicated.  The  European 
species  are  from  Oesel  and  their  real  habitat  is  doubtful.  (O'Con- 
nell-2o.) 

The  Eurypterida  have  generally  been  considered  marine,  but 
the  elaborate  study  of  the  habitat  of  these  organisms  made  by  Miss 
O'Connell  (20)  points  unmistakably  to  a  non-marine  habitat  of 
these  merostomes  since  pre-Cambric  time.  The  majority  of  forms 
occur  in  rocks  not  explainable  as  normal  marine  sediments,  but  as 


1030  PRINCIPLES    OF    STRATIGRAPHY 

delta  or  as  playa-lake  deposits  without  direct  connection  with  the 
sea.  Individuals  are  occasionally  found  in  marine  deposits  which 
cannot  be  interpreted  as  deltas,  but  in  such  cases  the  remains  are 
of  single  individuals  or  are  fragments.  Since  all  known  specimens 
of  this  kind  represent  merely  the  exoskeleton  (Clarke  and  Ruede- 
mann— 6),  it  is  easy  to  see  that  they  may  have  reached  their  resting 
place  as  pseudoplankton.  A  characteristic  mode  of  occurrence 
of  these  organisms*  is  in  the  black  muds  intercalated  in  torrential 
conglomerates  and  sandstones.  The  geographic  distribution,  too, 
is  of  such  a  character  as  to  indicate  a  river  rather  than  a  marine 
habitat.  For  further  discussion  of  this  problem  see  page  1043  anc^ 
the  references  there  cited. 

The  Limulava  are  known  only  from  the  Cambric,  where  they 
are  found  in  a  remarkable  state  of  preservation  in  black  bituminous 
shales  (sapropellutytes),  together  with  trilobites,  worms  and  other 
animals  suggesting  a  marine  habitat. 

Arachnida;  Pantapoda.  The  spiders  and  scorpions  are  typically 
terrestrial  animals,  breathing  by  means  of  trachea.  The  Panta- 
poda (Pycnogonida),  or  sea-spiders,  however,  constitute  a  class 
of  marine  organisms,  resembling  in  many  characters  the  Arach- 
nida, of  which  class  they  are  often  considered  relatives.  There  is 
also  a  true  spider,  Argyroneta  aquatica,  which  leads  an  aquatic 
life  in  fresh  water.  Scorpions  first  appear  in  the  Siluric,  where 
they  are  associated  with  eurypterids,  from  which  they  may  have 
been  derived.  Spiders  are  known  from  the  Coal  Measures,  but 
insects  date  from  the  Ordovicic  graptolite  slates  of  Sweden  (Pro- 
tocimex). 

Myriopoda  and  Insecta. 

These  are  also  terrestrial  tracheates,  but  with  marine  representa- 
tives. 

Larvae  of  insects  also  live  in  the  sea,  and  a  number  of  adult 
insects  are  marine  in  habit,  though  continuing  to  breathe  air.  Many 
insects  and  spiders  have  been  met  with  in  the  open  sea,  far  from 
land,  swimming  in  great  numbers  on  the  surface,  while  others  have 
been  found  creeping  between  rocks  under  water  by  the  shore.  The 
bug  Halobates  comprises  some  fourteen  species  living  on  the  sur- 
face of  the  sea,  running  about  like  the  fresh-water  bug  Hydro- 
metra,  often  hundreds  of  miles  from  land.  In  the  Upper  Siluric 
of  France  a  primitive  cockroach,  Pal&oblattina,  has  been  obtained. 
Myriopods  have  been  found  in  the  Devonic,  but  more  abundantly  in 
the  Carbonic.  The  Palaeozoic  myriopods,  like  the  Palaeozoic  insects. 


BIONOMIC  CHARACTERS  OF  ECHINODERMS   1031 

were  distinct  from  the  Mesozoic  and  recent  forms.     The  modern 
Chilopoda  date  from  the  Tertiary ;  the  Diplopoda  from  the  Cretacic. 


ECHINODERMATA. 

CYSTOIDEA  AND  BLASTOIDEA.  These  classes  are  entirely  extinct, 
being  confined  to  the  Palaeozoic.  They  were  undoubtedly  marine 
organisms  like  all  the  echinoderms. 

CRINOIDEA.  The  crinoids  are  without  exception  marine  organ- 
isms, though  Ante  don  rosacea  has  been  taken  in  water  containing 
only  25  permille  of  salts,  or  nearly  a  third  less  than  in  normal  sea- 
water.  The  majority  of  crinoids  belong  to  the  sedentary  benthos, 
being  anchored  or  attached  to  the  sea-bottom  either  by  a  stem  or 
by  the  base  of  the  calyx.  Antedon  must  be  classed  with  the  vagrant 
benthos  for,  although  it  ordinarily  rests  on  the  sea-bottom  or  other 
stationary  objects  of  support,  it  is  able  to  walk  about  on  the  bottom 
by  means  of  its  arms ;  and  also  to  swim  with  graceful  movements 
through  the  water.  Planktonic  crinoids  appear  to  have  existed  in 
the  Mesozoic  seas  (Saccocoma,  Uintacrinus),  and,  as  already  noted, 
Walther  has  furnished  evidence  which  indicates  that  some  of  the 
stemmed  Pentacrini  of  the  Lias  led  an  epiplanktonic  life,  grow- 
ing attached  to  floating  timbers  with  which  they  were  carried  about, 
calyx  downward. 

Kirk  (18)  has  recently  brought  forward  evidence  to  show  that 
many  Palaeozoic  as  well  as  later  crinoids  separated  from  their  stems 
late  in  life  and  assumed  secondarily  a  planktonic  existence,  the 
crowns  floating  away,  while  the  dead  stems  remained  behind  to 
separate  into  their  component  ossicles  .and  form  a  bed  of  crinoidal 
limestone. 

The  bathymetrical  distribution  of  the  modern  crinoids  ranges 
from  shallow  water  to  2,000  fathoms,  rarely  more.  One  species  of 
Antedon  (A.  abyssicola,  Carp.)  has  been  obtained  at  a  depth  of 
2,900  fathoms,  but  most  of  the  species  of  this  genus  live  in  shal- 
low water,  A.  lovcni,  occurring  in  three  to  four  fathoms.  This 
genus  is  perhaps  the  most  cosmopolitan  of  the  modern  crinoids,  its 
geographic  range  being  between  eighty  degrees  northern  and  fifty- 
two  degrees  southern  latitude.  The  following  modern  stalked  cri- 
noids have  been  obtained  in  less  than  ninety  fathoms  of  water 
( Walther-2(j  1298-300)  : 

Eudiocrinus  indivisus  Semp.,  30  fathoms   (54  meters). 
Metacrmus  rotundus  Carp.,  70  fathoms  (128  meters). 


1032  PRINCIPLES    OF    STRATIGRAPHY 

Pentacrinus  asterius  L.,   80   fathoms    (range   80-320    fathoms 

equals  146-584  meters). 
P.  decorus  Wy.  Th.,  84  fathoms  (range  84-667  fathoms  equals 

153  to  1,219  meters). 
P.  miilleri  Oerst,  84  fathoms  (range  84-531  fathoms  equals  153 

to  970  meters). 
Promachocrinus  kerguelensis  Carp.,  28  fathoms   (range  28-120 

fathoms  equals  51-218  meters). 

Rhizocrinus  lofotensis  Sars,  80  fathoms  (range  80-1,900?  fath- 
oms equals  146-3,474  meters). 

R.  rawsoni  Pourt.,  73  fathoms  (range  73-1,280  fathoms  equals 

133-2,340  meters). 

The  egg  of  Antedon  develops  into  an  egg-shaped  mero-plank- 
tonic  larva,  which  has  a  tuft  of  long  flagella  on  the  anterior  end 
and  five  ciliated  rings  surrounding  it ;  no  mouth  or  anus  is  present. 
This  embryo  swims  about  for  a  period  of  time,  varying  from  a  few 
hours  to  several  days,  and,  on  settling  down  to  a  benthonic  life, 
attaches  itself  at  a  point  on  the  ventral  side  between  the  first  and 
second  ciliated  rings.  The  whole  anterior  part,  as  far  as  the  third 
ciliated  ring,  becomes  the  stalk,  the  posterior  part  developing  into 
the  calyx.  In  Antedon  the  stem  is  retained  only  during  the  early 
stages  of  development,  the  adult  animal  being  free. 

ASTEROIDEA  ;  OpHiuROiDEA.  These  belong  to  the  marine  vagrant 
benthos,  living  mainly  in  shallow  water  or  in  moderate  depths, 
though  some  species  descend  to  depths  of  2,000  fathoms  or  over. 
Some  littoral  starfish  can  undergo  an  exposure  for  several  hours 
in  regions  laid  bare  by  the  tide.  A  muddy  or  sandy  bottom  seems 
to  be  the  most  characteristic  facies  for  these  animals,  and  from 
such  bottoms  hundreds  are  often  brought  up  in  a  single  haul  of 
the  dredge.  Their  relative  scarcity  in  beds  in  which  they  are  known 
to  occur  is  probably  due  to  the  fact  that,  after  the  death  of  the  ani- 
mal, the  skeleton  quickly  falls  apart  into  its  component  plates,  which 
become  separately  embedded  in  the  sediments.  In  the  majority  of 
the  Asterozoa  meroplanktonic,  bilaterally  symmetric,  ciliated  larvae 
occur,  which  in  the  Asteroidea  are  known  as  bipinnaria  and  brach- 
iolaria,  and  in  the  Ophiuroidea  as  pluteus.  These  are  often  found 
in  great  numbers  in  the  pelagic  fauna. 

ECHINOIDEA.  The  Echinoids,  or  Sea  Urchins,  are  without  ex- 
ception marine  vagrant  benthonic  animals,  living  usually  in  large 
numbers  in  moderate  depths.  A  few  species  descend  to  depths 
between  2,000  and  3,000  fathoms,  but  the  majority  prefer  the 
shallow  portions  of  the  littoral  districts.  On  the  coast  of  Maine 


BIONOMIC    CHARACTERS    OF    VERTEBRATES  1033 

thousands  of  Strongylocentrotus  drobachiensis  are  exposed  at  very 
low  tides,  lying  among  stones  and  covered  with  fragments  of  shells 
and  small  pebbles.  The  Echinoidea  delight  in  a  sandy  bottom,  from 
which  they  are  brought  up  in  vast  numbers  at  each  haul  of  the 
dredge.  Some  species  prefer  fine  mud,  in  which  they  are  often 
buried  to  some  extent.  When  living  on  rocks  they  commonly  ex- 
cavate holes  for  themselves,  and  even  the  solid  granite  has  been 
known  to  be  thus  attacked  by  the  animal.  If  corners  and  crannies 
are  available,  these  are  often  occupied  by  the  animal  in  preference 
to  the  drilled  hole. 

The  larva  of  echinoids  is  known  as  a  pluteus,  and  is  a  mero- 
planktonic,  bilaterally  symmetrical,  usually  more  or  less  ciliated 
organism,  with  a  number  of  processes  or  arms.  It  is  often  carried 
by  marine  currents  to  great  distances,  remaining  in  some  cases 
afloat  for  several  weeks  before  settling  down. 

HOLOTHUROIDEA.  The  holothurians,  like  the  echinoids,  are  ma- 
rine benthonic  organisms,  but  their  habit  of  life  is  often  more 
sedentary  than  vagrant,  the  animals  being  buried  in  the  sand  and 
mud,  though  never  attached.  Their  bathymetric  range  is  from  the 
shore  zone,  where  they  may  be  dug  out  of  the  sand  at  low  tide,  to 
the  depths  of  the  abyssal  district.  Sandy  or  muddy  bottom  is  usu- 
ally preferred  by  these  animals,  though  many  live  among  coarse 
blocks,  and  vast  numbers  occur  among  the  coral  masses  of  every 
coral  reef.  The  ciliated  larva,  or  auricularia,  of  the  holothurians  is 
a  mero-planktonic  organism  with  definite  mouth  and  anal  opening. 

From  the  fact  that  only  isolated  plates  occur  in  the  skin  of 
the  holothurians,  they  do  not  constitute  any  important  part  of 
marine  deposits. 


X.     PROTOCHORDATA. 

These  animals  are  all  marine  and  unknown  in  the  fossil  state. 
XL     VERTEBRATA. 

OSTRACODERMA.  These  extinct  fish-like  animals  appear  to  have 
led  primarily  a  fluviatile  and  lacustrine  existence,  if  we  may  judge 
by  the  strata  in  which  they  occur.  The  earliest  remains  are  frag- 
ments from  an  Upper  Ordovicic  sandstone  (Harding  sandstone)  of 
Colorado,  which  was  probably  deposited  as  a  terrestrial  sediment 
and  subsequently  in  part  reworked  by  the  advancing  sea.  The  late 
Siluric  transition  beds  of  Great  Britain  and  eastern  North  America, 


1034  PRINCIPLES    OF    STRATIGRAPHY 

and  the  beds  of  the  Old  Red  Sandstone  type  of  the  same  countries, 
show  the  best  preserved  representatives,  these  beds  being  strictly 
non-marine  deposits.  Some  of  the  best  preserved  specimens  of 
Bothryolepis  are  from  the  fresh  water  (river,  flood-plain  and  delta) 
deposits,  which  constitute  the  Gaspe  sandstone  of  eastern  Canada. 

The  Upper  Siluric  bone-bed  (Ludlow)  of  England  also  fur- 
nishes these  remains,  and  this  deposit  may  have  been  formed  in 
an  estuary,  or  an  enclosed  basin  near  the  sea.  A  few  fragmentary 
remains  have  been  obtained  from  marine  Siluric  and  Devonic  strata, 
but  these,  like  the  similar  occurrences  of  eurypterids,  are  not  satis- 
factory evidence  of  the  marine  character  of  these  fishes.  In  Penn- 
sylvania, remains  occur  in  sandstone  beds,  most  probably  of  river 
origin,  belonging  in  the  Upper  Siluric  (Monroan)  horizon. 

PISCES.  The  earliest  true  fish  appear  in  the  Siluric,  but  are 
more  typical  of  the  Devonic.  Here  the  Arthrodires  were  espe- 
cially abundant,  many  of  them  still  inhabiting  the  rivers  of  the 
continent.  They  began  to  migrate  into  the  sea,  however,  judging 
from  the  more  numerous  remains  found  in  open  sea  deposits,  such 
as  the  Onondaga  limestone.  The  abundant  fish  fauna  of  the  Upper 
Devonic  shales  of  Ohio  is  associated  with  tree  trunks,  spores  of 
land  plants,  etc.,  in  sediments  suggesting  a  river  delta  rather  than 
open  sea.  These  Upper  Devonic  fish  did,  however,  live  in  the  seas 
of  that  time  as  well,  for  their  remains  are  also  found  in  undoubted 
marine  strata.  The  Cyclostomi  (or  Lampreys)  seem  to  be  first 
represented  by'  the  remarkable  Palaeospondylus  of  the  Old  Red 
Sandstone  of  Caithness,  Scotland.  The  Elasmobranchs,  or  sharks, 
also  lived  in  the  rivers  of  Old  Red  Sandstone  time,  and  their  re- 
mains are  found  in  the  semi-terrestrial  deposits  of  the  Upper  Siluric 
in  Europe  and  America.  These  fish,  however,  entered  the  sea  in 
Devonic,  if  not  in  Siluric,  time,  and  thereafter  became  chiefly  ma- 
rine organisms,  continuing  so  down  to  the  present  time. 

The  living  ganoids  either  inhabit  fresh  water  rivers  exclusively, 
or,  as  in  the  case  of  the  sturgeons,  enter  the  rivers  from  the  sea. 
In  Palaeozoic  and  Mesozoic  time  they  were  marine  and  fluviatile. 
The  living  Dipnoi  inhabit  the  tropical  swamps  of  South  America 
(Lepidosiren)  and  of  Africa  (Protopterus)  and  also  the  rivers  of 
Queensland  (Ceratodus).  Ceratodus  also  occurs  in  the  Bunter 
Sandstein  of  Wiirttemberg,  the  Keuper  of  Austria,  the  Stonesfield 
slates  of  England,  and  the  fresh  water  Jurassic  of  Colorado.  It 
also  occurs  in  the  Kota-Maleri  beds  of  India  and  in  the  Karoo 
formation  of  South  Africa.  All  of  these  formations  represent  river 
deposits.  With  few  exceptions  the  other  Dipnoans  (Ctenodipterini) 
also  occur  in  fresh  water  (chiefly  river)  deposits,  such  as  the  Old 


BIONOMIC    CHARACTERS    OF    AMPHIBIA       1035 

Red  Sandstone,  the  Devonic  sandstones  of  Canada,  the  Coal  Mea- 
sures and  the  continental  Permic  deposits.  The  living  Protopterus 
of  Africa  regularly  spends  the  dry  season  of  several  months  in  its 
crust  of  dried  mud,  leading  a  latent  existence  or  summer  sleep  until 
the  rains  again  soften  the  crust  and  release  the  fish. 

The  various  species  of  mud-fish  are  examples  of  fishes  leading 
an  amphibious  life,  for  these  have  been  transported  in  their  "nest" 
of  dried  mud  halfway  round  the  world  without  suffering.  Dean 
believes  that  the  vitality  of  these  fish  becomes  exhausted  by  being 
kept  in  water  all  the  time,  which  deprives  them  of  their  periodic 
summer  rest.  Many  fresh-water  fish  regularly  swallow  air  and 
will  die  if  prevented  from  doing  so,  even  more  quickly  than  frogs 
which  have  been  similarly  placed,  although  the  latter  are  provided 
with  true  lungs. 

A  few  other  types  of  fish  are  able  to  live  in  the  air  for  a  certain 
length  of  time,  as,  for  example,  the  tropical  fish  (Periophthalmus 
and  Boleophthalmus),  referred  to  in  the  preceding  chapter,  which 
spend  a  good  part  of  their  existence  on  the  beach,  and  Anabas 
scandens  of  the  Philippines  is  able  to  exist  for  days  out  of  water. 

Many  fresh-water  fish  periodically  visit  the  sea,  while  marine 
fishes  as  frequently  ascend  fresh-water  streams. 

AMPHIBIA.  The  amphibians  are  cold-blooded,  aquatic  or  ter- 
restrial vertebrates,  usually  without  dermal  covering,  which,  how- 
ever, is  present  in  some  forms  as  a  corneous  or  osseous  structure. 
These  animals  breathe  by  gills  and  by  lungs,  the  former  remain- 
ing functional  throughout  life  in  some  species.  True  limbs  are 
generally  present  in  the  Amphibia,  and  are  used  for  swimming  or 
walking. 

The  Carbonic  and  Triassic  Stegocephalia  were  mostly  ar- 
mored, especially  on  the  ventral  side.  They  lived  on  land  or 
possibly  in  fresh  water.  The  larger  forms  were  predatory  and 
probably  fed  on  other  amphibians,  fishes,  and  Crustacea.  The 
Coecilians  (Gymnophiona)  are  worm-like,  legless  amphibians  con- 
fined to  the  tropics.  They  are  unknown  in  the  fossil  state.  The 
Urodeles  are  naked-bodied  types  with  generally  two  pairs  of  limbs 
and  persistent  tail.  They  inhabit  fresh  water  (newts),  where  the 
gills  remain  permanent;  or  ^amp,  shady  places  on  the  land  (sala- 
manders), where  they  lose  their  gills.  They  subsist  on  worms, 
gastropods,  small  aquatic  animals,  and  fish  spawn.  Permanent 
larval  forms  (Axoldtl)  of  the  land  form,  Amblystoma,  inhabit 
the  lakes  and  ponds  of  Mexico  and  other  countries.  These  have 
the  form  of  large  tadpoles  about  to  be  transformed,  with  legs  and 
external  gills.  They  reproduce  in  this  state,  some  of  them  never 


1036  PRINCIPLES    OF    STRATIGRAPHY 

reaching  the  Amblystoma  stage.  The  Urodeles  began  in  the  Cre- 
tacic  and  continue  to  the  present. 

The  Anura  (frogs  and  toads)  pass  through  a  tadpole  stage, 
during  which  they  breathe  by  means  of  gills  and  lead  an  aquatic 
life.  On  transformation  they  lose  the  gills  and  the  tail  and  become 
air-breathers,  though  frogs  can  remain  under  water  for  a  very 
long  period  of  time,  absorbing  oxygen  through  the  skin.  The 
Anura  are  wholly  post-Mesozoic  in  age.  No  marine  amphibians 
are  known. 

REPTILIA.  The  Rhynchocephalia  comprised  terrestrial  and  aqua- 
tic forms,  often  of  great  size.  The  Squamata  include  two  Cretacic 
groups  of  marine  reptiles,  some  of  which,  like  the  mosasaurs,  were 
of  large  size.  The  lizards  (Lacertilia)  and  snakes  (Ophidia)  are 
chiefly  terrestrial  reptiles,  though  some  of  the  latter  (Hydrophidce) 
live  in  the  water.  Some  Pleistocenic  species  attained  a  length  of 
10  meters,  but  modern  forms  are  all  small.  The  lizards  are 
mostly  provided  with  legs,  while  the  snakes  are  legless.  At  the 
present  time,  lizards  are  chiefly  restricted  to  the  warmer  regions 
of  the  earth's  surface.  Comparatively  few  forms  pass  beyond  the 
fortieth  parallel,  while  above  the  sixtieth  parallel  lizards  are  prac- 
tically absent ;  though  Lacerta  vivipara,  a  species  ranging  over 
nearly  the  whole  of  Europe,  extends  northward  to  the  seventieth 
parallel  in  Norway,  and,  together  with  the  blind-worm  (Angius 
fragilis)  occurs  in  Lapland  but  is  absent  from  the  New  World.  Both 
groups  probably  appeared  in  the  Cretacic.  The  fish-lizards  (Ich- 
thyosauria  and  Sauropterygia)  were  wholly  nektonic  in  habit,  liv- 
ing in  the  sea,  but  breathing  by  means  of  lungs.  They  were,  there- 
fore, neither  true  holo-nekton  nor  atmo-nekton,  but  a  transitional 
type  between  the  two,  as  are  other  vertebrates  which  lead  a  per- 
manently nektonic  life  (e.  g.,  whales,  etc.).  Some  species  inhabited 
fresh  or  brackish  water. 

The  Theromorphs  were  habitually  walking  animals.  It  is  be- 
lieved by  many  that  the  mammals  have  arisen  from  these  reptiles. 

The  Chelonia  or  turtles  are  terrestrial  or  aquatic  in  habit,  but, 
like  all  other  reptiles,  are  air-breathers.  A  few  types  are  exclusively 
marine,  but  the  larger  number  live  in  fresh-water  lakes  or  rivers. 
It  has  been  supposed  that  the  ancestral  species  were  aquatic,  living 
in  swamps  and  shallow  water,  like  modern  crocodiles ;  and  that 
from  these  descended  the  fluviatile  types,  from  which  in  turn  were 
derived  the  early  marine  types,  on  the  one  hand,  and  the  terrestrial, 
on  the  other. 

The  modern  crocodiles  are  aquatic  reptiles  living  in  fresh  water, 
swamps  and  streams.  The  oldest  Triassic  crocodiles  (Parasuchia 


BIONOMIC    CHARACTERS    OF   REPTILIA        1037 

and  Pseudosuchia)  are  all  found  in  terrestrial — partly  fluviatile  and 
partly  eolian — deposits,  such  as  the  Newark  beds  of  eastern  North 
America,  the  Stuben  Sandstein  of  Germany,  the  Elgin  sandstone 
of  Scotland,  and  the  Gondwana  beds  of  India.  They  appear  to  have 
been  land  and  river  forms.  The  Mesosuchia  in  Jurassic  and  Co- 
manchic  time  had  taken  to  a  marine  life,  but  in  the  Cretacic  and 
later  periods,  the  crocodiles  were  chiefly  fluviatile  or  terrestrial. 
In  the  Pliocenic  alligators  and  crocodiles  became  extinct  in  Eu- 
rope, but  in  America  they  continued  in  the  tropical  and  sub-tropical 
districts.  The  crocodiles  inhabit,  further,  nearly  all  the  larger 
streams  and  many  lakes  of  Africa,  India,  and  the  north  coast  of 
Australia  (Heilprin).  The  Dinosaurs  are  wholly  confined  to  the 
Mesozoic,  where  they  were  represented  by  a  wealth  of  types.  They 
comprise  three  groups:  1st,  carnivorous  land  forms  (Theropoda) , 
varying  in  size  from  that  of  a  cat  (Compsognathus)  to  that  of  an 
elephant  (Megalosaurus,  Trias  to  Cretacic),  and  mostly  very  gro- 
tesque in  appearance.  They  walked  upon  their  hind  limbs,  the 
shorter  fore  limbs  being  lifted  from  the  ground  and  the  body  being 
further  balanced  and  supported  by  a  huge  tail.  Some  leaping  or 
kangaroo-like  forms  likewise  occurred  (Trias  to  Cretacic).  2d. 
Massive  herbivorous  quadrupedal  forms  without  dermal  armor 
(Sauropoda,  Middle  and  Upper  Jurassic  and  Lower  and  Upper 
Cretacic),  and  comprising  some  of  the  most  prodigious  land  animals 
known;  Brontosaurus  having  a  length  upward  of  18  meters,  and 
Diplodocus  upward  of  20  meters.  3d.  (Predentata) .  Large  herbiv- 
orous unarmored  bipedal  (Iguanodonts),  and  armored  quadru- 
pedal forms  with  small  skulls  (Stegosauridfu) ,  or  with  large  horned 
skulls  (Ceratopsidcc) .  The  carnivorous  dinosaurs  were  frequenters 
of  the  estuaries  and  deltas  of  rivers,  and  roamed  about  the  low, 
flat,  and  muddy  flood  plains  of  rivers,  as  shown  by  the  countless 
footprints  preserved  in  the  rocks  of  the  Newark  system,  the  Bunter 
Sandstein,  and  other  non-marine  deposits  of  early  Mesozoic  age. 
The  Pterosauria  or  Ornithosaurs  (Jurassic  and  Cretacic)  were  a 
remarkable  group  of  bird-like  lizards,  with  hollow  bones  and  fore 
limbs  adapted  for  flight,  after  the  manner  of  bats ;  some  forms  be- 
ing strong  and  others  weak  flyers. 

AVES.  Birds  are  essentially  aerial  nekton.  A  number  of  living 
and  extinct  forms  (Drom&ognathce,  with  the  Struthiones,  the  New 
Zealand  Apteryx  and  the  South  American  Tinamous),  are  either 
nearly  wingless  or  have  wholly  or  to  a  considerable  extent  lost 
the  power  of  flight,  even  though  possessing  small  wings.  To  com- 
pensate for  this  loss  the  legs  are  generally  powerfully  developed, 
especially  in  the  Struthious  birds  (ostriches,  rheas,  cassowaries, 


1038  PRINCIPLES    OF    STRATIGRAPHY 

emus,  and  the  extinct  ^Epyornys  and  the  Moas).  The  majority  of 
birds  have  the  power  of  flight  to  a  greater  or  less  extent,  some  forms 
being  able  to  remain  in  the  air  for  a  long  time  (gulls,  petrels), 
though  flightless  forms  exist  in  several  orders  of  the  Euornithes. 
Some  are  especially  adapted  to  a  natatory  existence  (penguins, 
ducks,  etc.),  while  others  spend  much  of  their  life  wading  in  streams 
and  ponds  (herons,  storks,  ibises,  cranes,  snipes,  etc.). 

MAMMALIA.  This,  the  highest  class  of  vertebrates,  is  primarily 
adapted  to  a  terrestrial  life,  though  volatorial  or  atmonektonic 
types  (Chiroptera,  or  bats)  and  natatorial  or  halo-  and  limnonek- 
tonic  (hydronektonic)  types  (Cetacca,  or  whales,  and  Sircnia,  or 
sea-cows)  are  also  known.  Among  the  terrestrial  mammals,  climb- 
ing or  arboreal  types,  running  and  walking  or  cursorial  types,  leap- 
ing or  saltatorial  types,  and  burrowing  or  fossorial  types  are  dis- 
tinguishable. 


BIBLIOGRAPHY   XXVIII. 

1.  AGASSIZ,  ALEXANDER.     1888.     Three  Cruises  of  the  Blake.     2  vols. 

Bulletin  of  the  Museum  of  Comparative  Zoology,  Vols.  XIV,  XV. 

2.  BROOKS,  W.  K.     1881.     Developpement  de  1'huitre  Americaine.    Archives 

de  Zoologie  Experimentale  et  Generate,  T.  IX.      Notes  et  Revue,  pp. 
xxviii— xxix. 

3.  CHAMBERLIN,  THOMAS  C.     1898.     A  Systematic  Source  of  Evolution 

of  Provincial  Faunas.     Journal  of  Geology,  Vol.  VI,  pp.  597  et  seq. 

4.  CHUN,  CARL.     1888.     Die  pelagische  Thierwelt  in  grosseren  Meerestief  en 

und  ihre  Beziehungen  zu  der  Oberflachen  Fauna.     Bibliothoca  Zoologica, 
Heft. i. 

5.  CLARKE,  JOHN  M.     The  Naples  Fauna,  Pt.  I.     Fifteenth  Annual  Report 

of  the  New  York  State  Geologist.     .    \ 

6.  CLARKE,  J.  M.,  and  RUEDEMANN,  RUDOLF.     1912.     The  Eurypte- 

rida.    Monograph  of  the  New  York  State  Museum,  No.  XIV,  and  plates.. 

7.  CONN,   H.   W.     1885.     Marine   Larvae  and  Their  Relation   to  Adults. 

Studies  of  the  Biological  Laboratory  of  Johns  Hopkins  University,    Vol. 
Ill,  pp.  165-192,  pis.  VIII,  IX. 

8.  DALL,  WILLIAM  H.     1890.     Deep  Sea  Molluscs  and  the  Conditions 

Under  Which  They   Live.     Presidential  Address.     Biological   Society, 
Washington.     Proceedings,  Vol.  V,  pp.  1-27. 

9.  DANA,  JAMES  D.     1872.     Corals  and  Coral  Islands. 

10.  DARWIN,  CHARLES.     1841.     Voyage  of  the  Beagle. 

11.  DAVIDSON,    TH.     1886.     A    Monograph  of   the   Recent   Brachiopoda. 

Transactions  of  the  Linnaean  Society  of  London.    Zoology,  IV. 

12.  DAVENPORT,  C.  B.     1903.     Animal  Ecology  of  the  Cold  Spring  Sand 

Spit.     University  of  Chicago,  Decennial  Publication,  X. 

13.  FISCHER,  PAUL.     1887.     Manuel  de  Conchyliologie.     Paris. 

14.  FUCHS,    TH.     1882.     Ueber    die    pelagische    Flora    und    Fauna.     Ver- 

handlungen   der   koniglich-kaiserlichen    geologischen    Reichsanstalt   in 
Wien,  pp.  49-55. 


BIBLIOGRAPHY    XXVIII  1039 

15  H^ECKEL,  ERNST.  1893.  Planktonic  Studies.  Translated  from  the 
German  by  George  W.  Field.  Report  of  United  States  Fish  Commission, 
1889-1891,  pp.  565-641. 

16.  HAHN,    F.   FELIX.     1912.     Dictyonema   Fauna  of   Navy  Island,    New 

Brunswick.  New  York  Academy  of  Science,  Annals,  Vol.  XXII,  pp. 
135-160,  pis.  xx-xxii. 

17.  HENSEN,  VICTOR.     1890.     Einige  Ergebnisse  der  Plankton  Expedition 

der  Humboldt  Stiftung.  Sitzungsbcrichte  der  Berliner  Akademie  der 
Wissenschaften,  von  13  ten.  Marz,  1890,  pp.  243-253. 

18.  KIRK,  EDWIN.     1911.     Some  Eleutherozoic  Pelmatozoa.     United  States 

National  Museum  Proceedings,  Vol.  XLI,  pp.  1-137.  Contributions 
from  the  Geological  Department  of  Columbia  University,  Vol.  XXI, 
No.  6. 

19.  LANG,  ARNOLD.     1891-1896.     Text  Book  of  Comparative  Anatomy. 

Translated  by  H.  M.  and  M.  Bernard,  Vols.  I,  II.    London,  Macmillan. 

20.  O'CONNELL,    MARJORIE.     1912.     The   Habitat   of   the   Eurypterida. 

Paper  presented  before  the  New  Academy  of  Sciences,  November  meeting. 

21.  ORTMANN,    ARNOLD    E.     1896.     Grundziige   der    Marinen   Tiergeo- 

graphie.     Jena,  Gustav  Fischer. 

22.  ORTMANN,  ARNOLD  E.     1896.     An  Examination  of  the  Arguments 

Given  by  Neumayr  for  the  Existence  of  Climatic  Zones  in  Jurassic 
Times.  American  Journal  of  Science,  4th  series,  Vol.  I,  p.  257. 

23.  RUEDEMANN,   RUDOLF.     1895.     Development  and  Mode  of  Growth 

of  Diplograptus.  McCoy.  Fourteenth  Annual  Report  New  York  State 
Geologist,  pp.  219-249,  pis.  1-5. 

24.  RUEDEMANN,  R.     1904.     Graptolites  of  New  York,  Part  I.     New  York 

State  Museum  Memoirs,  Vol.  VII. 

25.  SCHIMPER,  A.  F.  W.     1898.      Pflanzengeographie  auf  Physiologischer 

Grundlage.  Jena,  G.  Fischer.  English  Translation  (Plant  Geogra- 
phy) by  W.  R.  Fischer,  Oxford,  1903. 

26.  SEMPER,  KARL.     1881.     Animal  Life  as  Affected  by  the  Natural  Con- 

ditions of  Existence.     International  Scientific  Series,  Vol.  XXX. 

27.  SIMROTH,  HEINRICH.     1891.     Die  Entstehung  der  Landtiere.     (See 

also  Die  Pendulations-theorie,  1907.) 

28.  TYRRELL,  J.  B.      1910.     Changes  of  Climate  in  Northwestern  Canada 

Since  the  Glacial  Period.     In  Veranderung  des  Klimas,  etc.     Stockholm, 

PP-  389-39 1- 

29.  WALTHER,  JOHANNES.     1897.     Ueber  die  Lebensweise  fossiler  Meeres- 

thiere.  Zeitschrift  der  deutschen  geologischen  Gesellschaft.  Band 
XLIV,  Heft  II,  pp.  209-273. 

30.  WALTHER,  J.     1894.     Einleitung  in  die  Geologie  als  historische  Wissen- 

schaft.     I.  Bionomie  des  Meeres.     II.  Die  Lebensweise  der  Meeresthiere. 

31.  WOODWARD,  S.  P.     1880.     Manual  of  the  Mollusca. 


CHAPTER    XXIX. 


CHOROLOGY,  OR  THE  PRINCIPLES  OF  THE  GEOGRAPHICAL  DIS 
TRIBUTION   OF  ANIMALS  AND   PLANTS. 

Having  briefly  considered  the  life  districts  of  the  habitable 
earth,  and  the  bionomic  characters  of  plants  and  animals,  we  may 
now  enquire  into  the  laws  which  govern  the  geographical  distribu- 
tion of  organisms.  It  is  clear  that,  whatever  the  present  distribution 
of  plant  and  animal  life,  it  has  not  always  been  so.  Even  the  most 
cosmopolitan  species  had  its  circumscribed  center  of  origin,  for 
it  is  extremely  unlikely  that  the  same  species  originated  in  more 
than  one  locality.*  From  this  locality,  its  center  of  dispersion,  it 
spread  to  occupy  whatever  territory  was  available.  Occupancy  of 
new  territory,  however,  is  possible  only  if  this  territory  corresponds 
in  facies  to  that  from  which  the  species  is  derived,  in  the  degree 
in  which  the  species  is  dependent  upon  the  facies.  Hence  the  exo- 
dists  from  their  land  of  birth  are  not  always  able  to  find  a  suitable 
place  of  settlement,  and,  though  their  numbers  may  be  vast,  a 
large  proportion  is  sure  to  perish. 

The  factor  of  greatest  importance  in  determining  whether  or 
not  an  area  is  to  be  permanently  occupied  by  the  members  of  a 
newly  arrived  species  is  the  organic  factor,  or  the  question  of  food 
supply  and  protection  from  enemies.  If  the  food  supply  is  insuf- 
ficient, or  if  contending  species  hold  the  ground,  the  new  arrivals 
may  be  prevented  from  occupying  the  territory,  even  though  the 
facies  is  otherwise  adapted  to  their  needs. 

*  Strictly  speaking,  of  course,  a  species  is  monophyletic  and  can  arise  only 
in  one  locality.  But  types  so  similar  that  they  may  easily  be  mistaken  for  the 
same  species  may  arise  in  different  localities.  Thus,  what  appears  to  be  the  same 
species  of  Fusus  (F.  closter)  occurs  in  the  West  Indies  and  in  the  Red  Sea,  but 
they  are  most  probably  of  independent  origin.  Organisms  of  such  similar 
characteristics  that  they  are  commonly  mistaken  for  members  of  the  same  genus 
are  frequently  met  with  in  widely  separated  localities,  where  they  have  arisen 
independently.  The  independent  origin  of  horses  in  America  and  in  the  Old 
World  was  advocated  by  Cope  but  rejected  by  others.  Some  widely  separated 
pulmonate  gastropods,  placed  in  the  same  genus,  may  have  arisen  independently 
from  marine  ancestors. 

1040 


GEOGRAPHICAL    DISTRIBUTION  1041 


DISPERSAL  AND  MIGRATION. 

It  will  help  us  to  realize  the  dependence  of  organisms  on  their 
environment  if  we  distinguish  two  modes  of  distribution,  the  in- 
voluntary and  the  voluntary.  The  former  may  be  called  dispersal; 
the  latter,  migration./ 

Dispersal  is  the  distribution  of  animals  and  plants  by  causes  not 
primarily  involving  the  activities  of  these  organisms,  as  the  carrying 
of  the  seeds  of  plants  by  the  wind,  the  carrying  of  marine  or  fresh 
water  planktonic  or  meroplanktonic  organisms  by  currents  and  the 
like.  Migration,  on  the  contrary,  is  accomplished  by  active  move- 
ments in  search  of  food,  or  to  escape  from  enemies,  and  is  confined 
chiefly  to  animals,  though  stolonal  propagation  of  plants  may  also  be 
classed  as  a  species  of  migration.  Migrants  are  composed  of  the) 
nekton  and  the  vagrant  benthos,  while  dispersants  comprise  the  holo-/ 
plankton,  the  epiplankton,  and  the  meroplankton.  Sedentary 
benthonic  organisms  cannot  migrate,  but  they  may  be  carried  by 
a  floating  sub-stratum,  and  their  mero-planktonic  young  may  be 
dispersed  and  thus  settle  in  other  districts.  Migrating  organisms 
require  a  continuity  of  the  conditions  of  existence  in  space,  such 
as  continuous  shores  for  the  marine  vagrant  littoral  benthos,  or  a 
more  or  less  uniform  medium  for  pelagic  migrants.  The  involun- 
tary dispersal  of  organisms,  on  the  other  hand,  may  often  go  on  in 
spite  of  barriers  which  migrants  could  not  surmount.  Thus,  as 
already  pointed  out,  the  meroplanktonic  young  of  the  vagrant 
benthos  may  have  a  much  wider  distribution  than  could  ever  be 
brought  about  by  the  migration  of  the  adults,  who  are  often  re- 
stricted by  barriers  not  present  in  the  pelagic  district.  Fresh-water 
molluscs,  for  example,  are  dispersed  widely  in  streams,  lakes,  and 
ponds  which  are  discontinuous,  and  to  which  the  adults  could  not 
migrate.  Again,  plants  may,  by  the  dispersal  of  their  seeds,  sur- 
mount streams  or  other  barriers,  which  root  or  stolonal  migration 
could  never  bring  about.  The  wide  dispersal  of  cocoanut  palms, 
by  flotation  of  the  nut,  is  a  good  example. 

Littorina  littorea  may  be  instanced  as  a  type  which  has  mi- 
grated down  the  Atlantic  coast  within  the  space  of  a  few  years. 
Originally  introduced  from  England,  it  characterized  Halifax  har- 
bor in  1852  and  slowly  made  its  way  southward  and  northward. 
In  1855  it  was  noted  at  Bathurst,  Bay  of  Chaleur;  in  1868  on  the 
coast  of  Maine,  appearing  at  Portland  in  1870.  At  Salem,  Massa- 
chusetts, it  was  first  noted  in  1872,  and  at  Barnstable,  Cape  Cod, 
in  1875.  It  was  rare  at  Woods  Hole  in  1875,  common  in  1876,  and 


1042  PRINCIPLES    OF    STRATI!  IRAI'HY 

appeared  at  New  Haven,  Connecticut,  in  1880  (Morse-jj).  In  1898 
Littorina  rudis  and  L.  palliata  were  still  the  predominant  types  on 
the  Long  Island  coast,  but  by  1901  L.  littorea  had  gained  a  marked 
predominance  (Balch-3),  and  it  is  still  rapidly  advancing.  (Daven- 
port-n  :i68.)  Since  the  opening  of  the  Suez  Canal  in  1869  many 
Mollusca  of  the  Mediterranean  have  migrated  into  the  Red  Sea. 

BARRIERS  TO  MIGRATION  AND  DISPERSAL.  Under  barriers  to 
migration  and  dispersal  we  may  place  topographical  barriers  first, 
such  as  northward  and  southward  stretching  continents  for  marine 
organisms,  desert  tracts  for  fresh  water  organisms,  and  great  bodies 
,  of  water  for  terrestrial  organisms.  But  topographical  barriers  are 
not  the  only  ones,  nor  in  many  cases  the  most  important.  Differ- 
ences in  temperature,  character,  and  direction  of  winds  and  ocean 
currents,  improper  facies  of  the  substratum,  and  insufficient  food 
supply,  as  well  as  hostile  species,  constitute  some  of  the  chief  bar- 
riers to  distribution.  If  by  some  means  or  other  a  barrier  is  sur- 
mounted, and  a  new  colony  is  established,,  the  new  colony  may 
become  more  or  less  isolated,  the  barrier  proving  too  effective  for 
all  but  a  few  individuals.  "Migration,"  says  Ortmann  (38:186),. 
"is  often  slow  or  only  possible  under  peculiar  circumstances,  often 
it  is  accidental,  and  only  a  few  individuals  can  transgress  the 
original  limits  on  rare  occasions;  then  even  migration  acts  as  a 
means  of  separation.  The  few  individuals  occupying  a  new  local- 
ity are  afterward  practically  separated  from  the  original  stock 
remaining  in  their  native  country,  and  thus  they  may  develop  sep- 
arately into  a  different  species,  even  in  the  case  that  immigration 
from  the  original  stock  is  not  altogether  impossible,  since  any  rare 
individuals  of  the  latter  reaching  the  new  colony  from  time  to  time 
are  soon  absorbed  by  the  new  form  and  their  characters  disappear 
by  the  continuous  crossing  with  the  modified  individuals  and  by  the 
transforming  power  of  the  external  conditions." 
*  Where  barriers  are  numerous,  the  number  of  species  of  a  given 
group  of  animals  or  plants  is,  as  a  rule,  much  greater  than  where 
barriers  are  few.  Thus  in  the  eastern  United  States,  where  impor- 
tant barriers  are  wanting,  only  one  true  species  of  chipmunk  occurs ; 
while  in  California,  where  barriers  are  numerous,  a  dozen  or  more 
species  and  sub-species  are  found  (Jordan— 25).  On  the  other  hand, 
the  fauna  and  flora  of  a  region  with  few  barriers  are  likely  to  show 
a  greater  variety  of  organisms  of  types  which  do  not  interbreed 
than  is  found  in  a  region  with  many  barriers,  since  immigration 
of  many  different  types  is  possible  into  an  open  region,  but  pre- 
vented by  the  barriers  of  a  closed  region.  Where  separation  by 
barriers  has  brought  about  the  formation  of  distinct  species,  nearly 


BARRIERS    TO    MIGRATION  1043 

related  species  are  normally  found  in  adjoining  districts,  and  not 
generally  in  the  same  or  in  widely  separated  districts.  It  is  uni- 
versally true  that  in  such  cases  the  species  of  a  genetic  series 
within  the  same  chronofauna,  or  fauna  of  the  same  geological  time 
division,  differ  more  widely  the  further  they  are  removed  in  space, 
and  are  closely  related  in  immediately  adjoining  loco  faunas.  This 
is  beautifully  illustrated  by  the  mutations  of  the  Hawaiian  Acha- 
tinellidae,  a  group  of  brilliantly  colored  tree  snails,  different  species 
of  which  inhabit  the  different  rugged  valleys  incised  in  the  margins 
of  the  extinct  volcanic  craters  of  these  islands.  The  most  nearly 
related  mutations  of  these  snails  live  in  adjoining  valleys,  where, 
nevertheless,  they  are  almost  wholly  isolated  from  the  inhabitants 
of  the  neighboring  valleys.  Here  the  amount  of  divergence  in 
characters  between  the  occupants  of  two  valleys  can,  as  Gulick 
says,  be  roughly  estimated  by  measuring  the  number  of  miles  be- 
tween the  valleys.  Recently  Gulick  has  formulated  this  in  the  fol- 
lowing law :  "Forms  that  are  most  nearly  related,  and  are,  there- 
fore, the  least  subject  to  sexual  and  impregnational  isolation,  are 
distributed  in  such  a  manner  that  their  divergence  is  directly  pro- 
portional to  their  distance  from  each  other,  which  is  also  the  mea- 
sure of  the  time  and  degree  of  their  geographical  isolation ;  while 
those  most  manifestly  held  apart  by  sexual  instincts  and  impregna- 
tional incompatibilities  do  not  follow  this  law."  (Gulick-i 9:^7.) 
The  trout  of  the  modern  (Holocenic)  chronofauna  furnishes  a 
good  illustration  of  this  law.  Thus  Salmo  clarki,  the  cut-throat 
trout  of  the  Columbia  and  Missouri  rivers— which  interlace  at  their 
headwaters — has  its  nearest  relatives  in  the  basin  of  Utah  (S.  vir- 
ginalis)  and  in  the  Platte  (  S.  stomias).  "Next  to  the  latter  is 
Salmo  spilurus  of  the  Rio  Grande,  and  then  Salmo  pleuriticus  of 
the  Colorado.  The  latter  in  turn  may  be  the  parent  of  the  Twin 
Lakes  trout,  Sahno  mdcdonaldi.  Always  the  form  next  away  from 
the  parent  is  onward  in  space  across  the  barrier."  ( Jordan-25 : 
547.)  The  distribution  of  the  fossil  eurypterids  of  the  American 
Siluric  in  such  a  manner  as  to  parallel  the  distribution  of  the  trout 
above  mentioned  has  been  cited  as  a  proof  of  the  river  habitat  of 
these  organisms.  (Grabau-i8.)  It  should  be  emphasized,  how- 
ever, that  isolation  cannot  always  be  determined  to  be  a  factor  in 
the  production  of  species,  and,  indeed,  if  variation  is  orthogenetic, 
the  development  of  new  mutations  in  a  progressive  series  can  very 
well  go  on  within  one  area.  Thus  many  of  the  pronounced  muta- 
tions of  Planorbis  in  the  Steinheim  strata  occurred  within  the  same 
Tertiary  locofauna.  In  the  Eocenic  locofauna  of  the  Paris  basin 
a  large  number  of  successive  mutations  in  each  of  a  number  of 


1044  PRINCIPLES    OF    STRATIGRAPHY 

genetic  series  of  molluscs  occurred  side  by  side,  and  the  same  is 
also  true  to  some  extent  of  the  corresponding  molluscan  fauna  of 
the  Gulf  States  of  America. 

FAUNAL  GROUPS.  The  fauna  of  any  area  may  be  considered 
as  belonging  to  one  or  more  of  the  following  groups :  endemic  spe- 
cies, immigrants  and  erratics,  and  relicts.  Endemic  species  are 
those  which  originated  in  the  locality  in  which  they  are  found. 
Immigrants  have  invaded  the  region,  and  erratics  have  been  car- 
ried there  accidentally,  and  both  have  established  themselves  in  the 
new  region.  Relicts  are  remnants,  in  favored  places,  of  a  once 
widely  distributed  fauna,  which,  by  the  breaking  up  of  the  area 
which  they  occupied,  became  resolved  into  a  number  of  local  rem- 
nants, which  remain  separated. 

FACTORS  GOVERNING  DISPERSAL  AND  MIGRATION.  In  all  cases 
when  considering  the  laws  which  govern  the  distribution  of  or- 
ganisms it  is  necessary  to  consider  two  phases  of  the  subject : 
first,  the  chemical,  physical,  and  organic  characters  of  the  localities ; 
and,  second,  the  nature  and  habits  of  the  organisms — their  bionomic 
characteristics.  If  the  two  are  harmonious  in  a  given  case,  it 
is  evident  that  the  locality  considered  can  be  inhabited  by  the  or- 
ganism in  question.  Under  chemical  characters  we  must  consider 
the  composition  of  the  medium  and  its  variation ;  and  under  physi- 
cal characters  we  comprise  climate  and  topography  of  the  sub- 
stratum ;  while  under  organic  characteristics  we  include  the  presence 
of  suitable  food  in  sufficient  quantity,  and  absence  or  paucity  of 
competing  organisms. 

Inorganic  Factors.    The  Medium. 

Composition  of  Medium.  Under  this  heading  we  include  the 
salinity  of  the  sea ;  the  inclusion  of  air  and  other  gases  in  the 
water,  and  of  water  and  carbon  dioxide  in  the  air.  The  salinity  of 
the  sea  is  its  most  characteristic  bionomic  feature.  On  the  whole, 
salinity  is  a  pretty  constant  factor,  varying  but  slightly  in  surface  ex- 
tent or  in  depth  in  the  open  sea.  Along  the  continental  margins, 
however,  in  the  bays  and  marginal  seas,  a  great  variation  is  observa- 
ble. The  question  of  variation  has  already  been  discussed  at  length 
(Chapter  IV),  but  a  few  salient  points  may  here  be  repeated. 
Thus  in  the  Red  Sea,  where  the  supply  of  water  is  scanty,  and  the 
evaporation  great,  the  salt  constituent  is  4.3  per  cent,  or  43  permille ; 
while  in  the  Baltic,  where  the  supply  of  fresh  water  is  abundant  and 
evaporation  is  small,  the  surface-salinity  is  very  low,  averaging  7 
permille.  The  decrease  in  salinity  eastward  is  very  striking;  thus  it 


FACTORS    GOVERNING   DISTRIBUTION         1045 

is  34  permille  in  the  Skagerak,  22  permille  in  the  Kattegat,  6  per- 
mille  at  Riga  and  3  permille  at  the  northern  end  of  the  Gulf  of 
Bothnia  (Uleaborg).  The  vertical  range  is  also  greater  than  in  the 
open  sea,  the  salinity  in  the  ''Great  Belt"  of  the  Baltic  increasing 
downward  from  10  permille  on  the  surface  to  30  permille  at  the  bot- 
tom (66  meters). 

Stenohalinity  and  euryhalinity.  Many  animals  cannot  live  in 
water  with  less  than  30  or  35  permille  of  salts;  i.  e.,  that  of  the 
normal  open  sea.  These  stenohalic  *  types  will  die  when  the  sal- 
inity is  lowered  or  raised.  Euryhalic  f  types,  on  the  other  hand,  can 
suffer  a  considerable  freshening  of  the  water,  and  will  live  as  long 
as  any  salt  remains.  Brackish-water  organisms  are  adapted  to  a 
small  amount  of  salt  and  will  suffer  if  the  amount  is  increased.  The 
brackish  state  of  water  has  never  been  definitely  delimited,  but  prob- 
ably a  salinity  of  2  or  3  permille  (.2  to  .3  per  cent.)  would  be  the  up- 
per limit.  Of  other  mineral  matter  besides  the  normal  salts  iron  in 
the  form  of  ferrous  carbonate  (FeCO3)  may  sometimes  be  present 
in  considerable  quantity,  especially  in  more  or  less  land-locked 
portions.  Such  excess  of  iron  or  of  other  minerals  in  solution 
appears  to  have  a  distinct  effect  on  the  growth  of  the  fauna  living 
in  the  water,  resulting  in  its  dwarfing,  as  has  been  repeatedly  found 
by  experiments.  As  an  example  may  be  mentioned  the  fauna  of 
the  Clinton  iron  ore  layer  of  Rochester,  which  consists  of  individuals 
having  "an  average  of  about  one-third  the  diameter  of  the  same 
species  in  the  beds  just  above  and  below"  (Loomis-28 :  #95).  The 
fauna  of  the  Tully  pyrite  layer  of  western  New  York,  consisting  of 
upward  of  forty-five  species,  is  composed  of  individuals  "on  an 
average  only  one-fifteenth  the  size  of  the  same  species  in  the  normal 
and  preceding  Hamilton  fauna."  (Loomis-28  :p^o.)  In  this  case 
the  dwarfing  was  undoubtedly  in  part  effected  by  the  H2S  liberated 
by  sulpho-bacteria  from  decaying  organic  matter.  The  reaction  of 
this  upon  the  iron  carbonate  produced  the  pyrite  which  enclosed 
the  fauna.  (FeCO3+2H2S+O=FeS2+CO,+2H,O.) 

Quantity  of  Air.  The  quantity  of  air  in  the  water,  both  salt 
and  fresh,  depends  upon  the  depth  and  the  amount  of  agitation. 
Deeper  strata  of  water  have  necessarily  less  air  than  those  nearer 
the  surface,  while  agitated  water  will  include  more  air  than  still 
water.  It  is  upon  the  oxygen  of  this  included  air  that  all  animals 
are  dependent,  and  when  it  is  present  in  insufficient  quantity  the 
animals  generally  perish,  though  some  will  come  to  the  surface  for 
more  air.  In  partially  enclosed  bodies  of  water  where  the  density 

*  From  <rTQi/6s  =  narrow  and  AXs  =  the  sea,  (salt)* 
f  From  ftpts  =  broad. 


io46  PRINCIPLES    OF    STRATIGRAPHY 

of  the  bottom  layers  is  greater  than  that  of  the  surface,  vertical 
currents  are  slight,  and  hence  the  lower  strata  are  poor  in  oxygen 
and  unable  to  support  animal  life.  Thus  in  the  Black  Sea  animal 
life  is  practically  absent  below  a  depth  of  125  fathoms,  though 
dead  planktonic  organisms  sink  to  the  bottom,  where  they  are 
decomposed  by  anaerobic  bacteria.  The  great  depths  of  the  Black 
Sea  are  covered  by  a  layer  of  black  mud,  from  which  H2S  is 
abundantly  separated  and  which  is  rich  in  pelagic  diatoms  and  frag- 
ments of  very  young  pelecypods  from  the  meroplankton.  The 
presence  of  abundant  H2S  in  these  depths  is  characteristic.  It  is 
separated  by  the  sulphobacteria  from  the  dead  organic  matter  and 
the  sulphates  of  the  sea  water.  Accompanying  it  is  the  formation 
of  iron  sulphide  and  the  separation  of  carbonates,  especially  CaCO3. 
Pure  atmospheric  air  contains  almost  21  per  cent,  of  oxygen  and 
about  79  per  cent,  of  nitrogen  (see  ante,  Chapter  II).  There  is 
always,  however,  some  carbon-dioxide  and  water  vapor  present, 
the  quantity  varying  with  the  temperature  and  the  movements  of 
the  air,  besides  being  very  variable  in  different  localities. 

Carbon-dioxide,  while  necessary  to  plant  life,  is  injurious  to 
the  higher  types  of  animals,  if  the  proportion  is  above  I  to  2,000 
of  volume.  A  somewhat  larger  quantity,  however,  has  no  serious 
effect  on  some  lower  forms  of  terrestrial  animals,  and  in  some 
cases  it  may  even  be  beneficial  to  them.  The  moisture  in  the 
air  is  necessary  to  the  existence  of  most  terrestrial  organisms,  many, 
indeed,  being  unable  to  exist  in  a  region  where  the  percentage  of 
water  vapor  in  *  the  air  is  low.  Nevertheless,  some  animals  are 
found  in  extremely  dry  regions,  and  these  are  not  infrequently  types 
which  belong  normally  to  moist  climates.  Land  snails,  for  ex- 
ample, generally  require  much  moisture,  and  large  numbers  of 
such  animals  perish  during  the  dry  summers,  or  survive  only  by 
burying  themselves  in  the  earth  or  in  crevices  of  rocks,  and  closing 
the  mouth  of  the  shell  with  a  membranous  operculum.  In  deserts 
these  snails  can  obtain  moisture  only  during  the  night  or  early 
morning  from  the  heavy  dews  which  result  through  excessive  radia- 
tion, and  it  is  only  during  these  times  that  they  lead  an  active  life. 

In  the  saturated  atmosphere  of  the  tropical  forests  are  found 
many  types  of  animals  which  are  normally  aquatic.  Thus  a  type 
of  leach,  allied  to  the  medicinal  leach  of  the  fresh  water  ponds, 
lives  on  trees  in  the  moist  forests  of  India  and  the  Indian  islands ; 
and  a  number  of  species  of  land  planarians  are  known,  mostly  from 
the  tropics.  Many  amphipod  Crustacea  of  the  family  Orchestidae, 
or  beach  fleas,  live  exclusively  on  land,  though  they  have  the  gills 
of  the  true  water  species.  These  require  a  very  moist  atmosphere. 


CLIMATE    AND    TEMPERATURE  1047 

Numerous  other  types  of  normally  aquatic  animals  can  live  on  land 
in  a  moist  atmosphere.  Some  of  these  animals  which  have  become 
adapted  to  a  terrestrial  life  can  be  drowned  by  being  kept  under 
water;  and  this  is  true  even  of  a  number  of  fish,  which  habitually 
come  to  the  surface  to  swallow  air. 

Volume  of  Water,  The  volume  of  water  has  in  many  cases  a 
direct  effect  upon  the  size  of  the  animals  living  in  it,  the  controlling 
factor  being  the  amount  of  water  allotted  to  each  individual.  Thus 
in  experiments  on  the  common  fresh  water  snail,  Limncca  stagnalis, 
Semper  found  that  if  a  large  number  of  individuals  developed  in  a 
given  quantity  of  water,  the  size  of  their  shell  will  be  smaller  than 
that  of  a  smaller  number  occupying  the  same  amount  of  water. 
Again,  a  number  of  individuals  developing  in  a  limited  amount  of 
water  will  have  smaller  shells  than  the  same  number  of  individuals 
developing  in  a  larger  amount  of  water.  This  would  be  noticeable 
in  a  gradually  filling  lake  basin,  where  the  shells  in  the  lower  strata 
would  be  larger  than  those  of  the  upper  strata.  Here  the  diminish- 
ing food  supply,  which  may  be  supposed  to  characterize  a  shoaling 
lake,  would  be  another  factor  contributing  to  the  same  result.  In 
Semper 's  experiment  it  was  found  "that  the  favorable  effect  of 
an  increase  of  volume  of  water  is  highest  between  100  and  500 
cubic  centimeters  for  each  individual,  and  that  it  then  gradually 
decreases,  till,  at  5,000  cubic  centimeters,  it  would  seem  to  cease 
entirely;  i.  e.,  an  increase  of  volume  above  this  maximum  has,  as 
it  appears,  no  further  effect  whatever  upon  the  rapidity  of  growth." 
Fouling  of  a  limited  quantity  of  water  by  the  excretions  of  the 
animals  also  causes  dwarfing.  The  number  of  eggs  produced  under 
unfavorable  conditions  is  also  smaller. 


Climate. 

Climate  and  Temperature.  The  climate  of  the  sea  is  much  more 
uniform  than  that  of  the  land.  It  is  true  that,  in  the  very  shallow 
parts  of  the  sea,  the  water  is  often  heated  to  such  a  degree  as  to 
make  these  regions  uninhabitable  for  most  animals.  Ordinarily, 
however,  the  continual  change  of  water,  due  to  tidal  and  other 
currents,  is  sufficient  to  keep  the  temperature  at  a  moderately  low, 
and  more  or  less  uniform,  degree.  The  daily  range  of  temperature 
in  the  sea  is  of  less  importance  to  organisms  than  the  total  amount 
of  heat  received ;  for  daily  changes  affect  chiefly  the  upper  strata 
of  the  water,  which  are  directly  influenced  by  the  heat  of  the  sun. 
At  a  moderate  depth  below  the  surface,  the  stratum  of  mean 


1048  PRINCIPLES    OF    STRATIGRAPHY 

temperature  is  reached ;  this,  where  not  affected  by  oceanic  currents, 
varying  mainly  with  the  change  in  latitude.  It  is  to  this  region 
of  unvarying  temperature  that  many  of  our  littoral  vagrant  benthos 
descend  on  the  approach  of  winter;  so  that,  as  every  collector 
knows,  many  tide  pools  and  sandy  bottoms  of  moderate  depth  be- 
come deserted  during  the  colder  months.  Many  marine  organisms 
are  eurythermal,  i.  e.,  able  to  bear  a  considerable  range  of  tempera- 
ture. Others,  again,  are  stenothermal,  a  comparatively  slight  devia- 
tion from  the  normal  temperature  of  their  medium  being  fatal  to 
them.  The  larvae  or  eggs  of  stenothermal  animals  are  often  able 
to  resist  very  great  changes  of  temperature  which  would  destroy 
the  adult  animal.  Thus  the  winter  eggs  of  some  of  the  lower  Crus- 
tacea, the  germs  of  Bryozoa  and  of  fresh  water  sponges,  resist  any 
degree  of  cold,  while  the  full-grown  individuals  perish  in  the  au- 
tumn. Many  insects  cannot  survive  the  winter,  though  the  eggs 
and  the  embryo  within  the  eggs  commonly  withstand  the  severest 
cold.  On  the  other  hand,  the  young  may  be  more  susceptible  to 
changes  in  temperature  than  the  adult.  Brooks  found  that,  in  the 
case  of  the  oyster,  the  difference  of  2°  or  3°  F.  in  the  temperature 
of  the  water  was  sufficient  to  kill  the  whole  larval  brood.  Thus, 
as  Dall  says,  "By  inhibiting  natural  increase  ...  a  species 
may  be  as  sharply  limited  in  its  permanent  range  as  if  material 
barriers  interposed."  (Dall-9  :?/#.) 

Cold-blooded  animals  can  usually  withstand  a  lowering  of  tem- 
perature better  than  warm-blooded  animals.  Thus  frogs  and  toads 
can  be  frozen  into  the  ice  and  survive,  and  so  can  certain  fishes 
(e.  g.}  Salmon,  etc.). 

In  all  cases  a  rapid  change  of  temperature  is  more  fatal  to  or- 
ganisms than  is  a  gradual  one;  for  many  normally  stenothermal 
types  can  by  degrees  adapt  themselves  to  a  higher  or  lower  tem- 
perature. When  once  acclimatized  it  is  the  change  from  the  normal 
temperature  of  the  new  habitat  which  affects  the  organism.  Thus 
members  of  a  species  acclimatized  to  more  tropical  regions  will  be 
affected  by  a  fall  of  temperature  to  a  point  where  members  of  the 
same  species  in  more  northern  regions  are  wholly  unaffected. 

Currents.  One  of  the  marked  features  of  the  media  characteriz- 
ing the  three  organic  realms  is  the  frequent  presence  of  currents 
within  them.  These  may  be  temporary  or  fixed,  and,  according  to 
this  characteristic  and  their  strength,  they  become  powerful  factors 
in  the  influence  which  they  exert  upon  the  distribution  of  organisms 
in  the  realms  in  question.  In  the  air,  currents  are  most  numerous 
and  also  more  variable,  though  certain  air  currents,  as  the  "trade 
winds/'  have  a  great  constancy  within  certain  limits.  Irregular 


CURRENTS    AND    DISTRIBUTION  1049 

and  variable  air  currents  often  greatly  influence  the  migration  of 
aerial  organisms,  even  the  strongest  flyers  being  carried  away  by 
them.  But  the  greatest  influence  exerted  by  air  currents  on  organ- 
isms is  in  the  dispersal  of  seeds  of  plants,  which  thus  may  become 
widely  scattered.  Air  currents  are  the  chief  cause  of  the  persistent 
ocean  currents,  which  are  of  such  importance  in  the  distribution  of 
life.  In  fresh  water  lakes  temporary  currents  may  be  set  up  by  the 
winds,  but  these  are  of  minor  significance.  The  important  currents 
in  fresh  waters  are  those  due  to  gravity,  as  exemplified  in  every 
stream  and  river.  That  river  currents  are  of  great  importance 
in  the  distribution  of  fluvial  life,  as  well  as  in  the  transportation  of 
terrestrial  animal  and  plant  life,  is  a  matter  of  common  knowledge. 

By  far  the  most  important  currents  affecting  the  life  districts 
of  the  earth  are  the  ocean  currents,  for  they  not  only  aid  in  the  dis- 
tribution of  organisms,  but  they  are  also  instrumental  in  imparting 
to  sea  and  land  characters  which  they  would  not  otherwise  possess. 

The  characteristics  of  the  ocean  currents  of  the  present  geologic 
period  (Holocenic)  may  be  taken  as  an  illustration,  especially  since 
it  is  highly  probable  that  similar  conditions  prevailed  throughout 
most  of  Tertiary  time.  The  depth  of  the  moving  bodies  of  water 
constituting  the  oceanic  currents  is  from  50  to  100  fathoms ;  and 
the  direction  of  motion  corresponds  to  that  of  the  prevailing  winds. 
As  already  discussed  at  length  in  Chapter  V,  each  of  the  great 
oceans  has  its  own  eddy-like  current,  moving  slowly  around  it  and 
leaving  the  central  portion  in  a  relative  state  of  quiescence.  In 
the  northern  hemisphere  the  currents  move  in  the  direction  of  the 
hands  of  a  clock,  i.  e.,  clockwise ;  in  the  southern  hemisphere,  coun- 
ter-clockwise. As  a  result,  the  motion  of  the  waters  is  westward 
at  the  equator,  both  north  and  south  of  it,  and  eastward  in  the 
polar  ends  of  the  north  and  south  oceans,  respectively.  Hence 
dispersals  of  organisms  dependent  on  ocean  currents  would  be 
from  east  to  west  in  the  equatorial  regions,  as  from  the  west  coast 
of  Central  America  to  the  east  coast  of  Asia,  and  from  the  west 
coast  of  South  America  to  Polynesia  and  Australia.  It  is  true 
that  the  equatorial  counter-current  sets  eastward  between  the 
north  and  south  equatorial  currents,  but  this  is  a  relatively  weak 
current.  The  comparatively  warm  drift  across  the  north  Pacific 
(Kuroshiwo  drift)  is  an  aid  to  eastward  migration  and  dispersal 
across  the  north  Pacific,  and  this  would  probably  be  much  more 
effective  if  the  cold  water  from  the  Arctic  were  shut  off  by  the 
closure  of  Behring  strait.  Such  conditions  existed  during  part  of 
Tertiary  time,  and  thus  may  have  greatly  aided  migration  of  ma- 
rine organisms  in  this  direction.  The  cold  west-wind  drift  or 


1050  PRINCIPLES    OF    STRATIGRAPHY 

Antarctic  stream  of  the  South  Pacific,  together  with  the  cold  Peru- 
vian current  of  the  west  coast  of  South  America,  acts  as  a  barrier 
to  migration  of  warm  water  animals  and  plants  from  Australia  to 
South  America,  and  probably  did  so  throughout  Tertiary  time. 

In  the  Atlantic  the  peculiar  conformation  of  Africa  and  South 
America  results  in  the  splitting  of  the  South  Equatorial  current  into 
the  Brazilian  current,  flowing  southward  along  the  east  coast  of  South 
America,  while  the  main  current  crosses  the  equator  into  the  Carib- 
bean Sea  and  the  Gulf  of  Mexico.  Here  again  the  cold  west-wind 
drift  and  the  cold  Benguela  current  on  the  west  coast  of  South 
Africa  prevent  dispersion  between  the  southern  portions  of  these 
continents  of  all  warm  water  types.  The  presence,  however,  in 
the  modern  fauna  of  gastropods  on  the  east  coast  of  South  America, 
which  appear  to  be  derived  from  species  inhabiting  Indo-Pacitic 
waters,  suggests  that  migration  of  tropical  animals  up  the  west 
coast  of  Africa  is  possible  under  certain  conditions,  in  spite  of  the 
cold  Benguela  current.  In  the  North  Atlantic,  the  Gulf  Stream, 
with  its  northeastward  drift,  favors  dispersal  of  species  from  the 
east  American  to  the  west  European  coast ;  while  the  return  Canary 
and  North  Equatorial  currents  may  well  be  effective  in  carrying 
planktonic  organisms  from  the  northeast  African  coast  and  the 
Mediterranean  to  the  West  Indian  waters  of  tropical  America. 

A  factor  which  must  be  taken  into  consideration  is  the  varying 
rapidity  of  flow  of  the  currents.  Thus  the  Gulf  Stream,  as  it  issues 
from  the  Florida  straits,  has  an  average  velocity  of  80  or  90  miles 
a  day,*  while  the  drifts,  like  that  crossing  the  middle  North  Atlantic, 
may  have  a  velocity  of  only  from  ten  to  fifteen  miles  per  day.  If 
the  meroplanktonic  stage  of  a  normally  benthonic  animal  is  passed 
through  very  quickly  it  is  evident  that  before  the  creature  can  be 
carried  very  far  it  will  end  its  pelagic  existence  and  sink  to  the 
bottom.  In  the  case  of  such  larvae  carried  by  the  transoceanic 
currents,  the  depths  to  which  they  will  settle  after  having  been 
carried  for  a  few  days  is  likely  to  be  such  as  to  prove  destructive 
to  the  organism.  Thus  organisms  taken  up  by  the  Gulf  Stream  as 
it  leaves  the  Florida  coast  would,  even  if  the  stream  retained  its 
maximum  velocity,  have  to  travel  considerably  over  a  month  be- 
fore they  could  reach  the  European  coast,  while  with  the  actually 
diminishing  velocity  of  the  drift  in  the  North  Atlantic  the  time 
required  will  be  many  months.  Before  that  time  most  meroplank- 
tonic organisms  will  have  completed  their  metamorphosis  and  have 
perished  on  an  uncongenial  bottom.  Holoplanktonic  types,  how- 
ever, and  even  nektonic  animals  are  widely  dispersed  by  these  cur- 

*  It  varies  from  1.5  to  2.5  meters  per  second. 


CURRENTS;    TOPOGRAPHY  1051 

rents.  Thus  even  Middle  and  South  Atlantic  fish  are  carried  by 
the  Gulf  Stream  to  the  Norwegian  coast,  though  these  do  not  gen- 
erally propagate  themselves  in  these  northern  waters. 

One  mode  of  dispersal  that  must  not  be  overlooked  is  that  ef- 
fected by  the  epiplanktpn.  The  transportation  of  the  Crustacea, 
Hydrozoa  and  other  organisms,  with  the  Sargassum,  from  the 
Bahamas  to  the  middle  North  Atlantic,  is  an  example.  Trunks  of 
trees  from  the  forests  of  the  Mississippi  and  the  Orinoco  are  car- 
ried northward  by  the  Gulf  Stream,  past  the  coast  of  Norway,  as 
far  as  Spitzbergen,  whence  they  are  again  carried  southward  and 
cast  ashore  on  the  northeast  coast  of  Iceland.  Sea-weeds,  molluscs 
and  other  organisms  are  frequently  found  attached  to  these  trees, 
having  made  the  long  journey  on  their  floating  substratum.  Seeds 
of  land  plants  commpnly  accompany  these  woods. 

The  warm  ocean  currents  also  have  an  important  influence  on 
the  relative  abundance  of  the  benthonic  life  in  the  regions  traversed 
by  them.  Being  rich  in  plankton,  and  thus  supplying  an  abundance 
of  food  to  the  animal  life  inhabiting  the  sea-bottom  below  it,  it  is 
not  surprising  to  find  that  here  the  bottom  life  is  developed  in  the 
greatest  luxuriance,  and  that  vast  accumulations  of  organic  lime- 
stones occur  in  the  littoral  regions  thus  affected.  This  is  true,  how- 
ever, only  of  those  portions  of  the  littoral  district  which  lie  at  a 
sufficient  depth  below  the  surface  to  escape  the  motion  of  the 
streaming  water,  which  might  otherwise  prevent  the  attachment 
of  the  benthos  as  it  settles  down.  Thus,  off  Charleston,  South 
Carolina,  in  depths  from  100  to  350  fathoms,  the  sea-floor  is 
but  sparsely  settled  beneath  the  Gulf  Stream. 

Topography.  Next  to  the  climate  of  the  sea  the  topography 
of  the  sea-bottom,  and  that-of  the  adjacent  land,  are  the  most  pow- 
erful factors  in  determining  the  distribution  of  marine  organisms. 
The  facies  of  the  ocean  floor,  or  the  material  of  which  it  is  com- 
posed, is  perhaps  the  most  significant  part  of  sea-bottom  topog- 
raphy, though  submarine  ridges  and  barriers  are  of  great  im- 
portance, especially  when  such  barriers  cut  off  marginal  bodies  of 
water,  the  inhabitants  of  which  may  be  prevented  from  interming- 
ling. The  separation  thus  produced  may  lead  to  the  development 
of  local  faunas  and  floras.  The  importance  of  the  greater  inequali- 
ties of  the  sea-bottom  and  the  submarine  continental  shelves  and 
deep  oceanic  basins  that  result  from  them,  as  well  as  the  conforma- 
tion of  the  coast-line,  with  its  varying  facies,  has  already  been  con- 
sidered. (See  Chapter  III.) 

Of  all  topographical  features  which  influence  the  distribution  of 
marine  organisms,  northward  and  southward  stretching  bodies  of 


1052  PRINCIPLES'  OF    STRATIGRAPHY 

land,  like  the  continents  of  North  and  South  America,  are  perhaps 
the  most  important.  For  since  they  form  a  continuous  barrier 
across  the  warmer  portions  of  the  ocean,  extending  into  the  cold 
regions,  the  migration  of  the  warmer-water  species  from  one  side 
to  the  other  is  prevented.  Thus  the  marine  faunas  on  the  opposite 
sides  of  North  or  South  America  differ  widely. 

By  the  application  of  this  principle  to  the  Cambric  faunas  of 
North  America  and  Europe,  it  has  become  apparent  that  a  more 
-or  less  continuous  land  mass,  sufficient  to  prevent  intermingling 
of  faunas,  separated  the  Atlantic  and  Pacific  oceans  in  Cambric 
time.  This  land  barrier  must  have  extended  from  New  England 
northeastward,  joining  this  land-mass  to  the  Scottish  highlands, 
and  southward,  forming  the  Appalachian  old-land,  which  was 
joined  with  the  continent  of  South  America.  On  opposite  sides  of 
this  land-mass  different  faunas  flourished;  in  the  lower  Cambric 
the  Olenellus  fauna  on  the  west  and  the  Holmia  fauna  in  the  At- 
lantic; in  Middle  Cambric  time  the  Olenoides  and  Paradoxides 
faunas  flourished  in  these  respective  basins  (see  the  maps  in 
Grabau-i7).  (See  also  Figs.  264a-c.) 

The  only  topographic  element  of  importance  in  lakes  and  other 
bodies  of  standing  fresh  water  is  the  enclosing  land  mass,  which 
prevents  direct  migration  from  one  lake  into  another.  In  rivers 
the  presence  of  rapids  and  falls  may  become  a  barrier  to  all  but  the 
most  agile  of  swimmers.  Here,  however,  the  barrier  is  most  ef- 
fective against  upstream  migration.  The  banks  likewise  constitute 
barriers. 

Terrestrial  animals  and  plants  are  often  prevented  from  migrat- 
ing or  becoming  dispersed  by  the  existence  of  topographic  barriers 
in  the  form  of  mountains  of  great  height  and  consequent  range  in 
climate;  by  large  bodies  of  water,  deep  river  gorges  and  impass- 
able streams ;  and  by  extensive  desert  tracts ;  the  last  being  produced 
by  a  combination  of  the  topographic  and  climatic  factors.  For  ani- 
mals of  a  more  limited  range  of  habitat,  minor  topographical  bar- 
riers become  restrictive,  as  shown  by  the  distribution  of  the  Hawai- 
ian tree  snails  (Achatinellidce) ,  already  referred  to,  for  which  the 
exposed  ridges  separating  adjoining  ravines  form  almost  impass- 
able barriers. 

The  Organic  Factors. 

The  organic  conditions  of  the  three  realms  likewise  exert  an 
important  influence  on  the  distribution  of  animal  and  plant  life. 


THE    ORGANIC    FACTOR  1053 

By  organic  conditions  is  meant  the  nature  and  abundance  of  food 
supply  and  the  relative  importance  of  competing  organisms.  Since 
plants  primarily  furnish  the  food  supply  of  animals,  those  regions 
rich  in  plant  life  are,  in  general,  well  adapted  for  the  existence  of 
animal  life.  Yet  even  in  regions  where  plant  life  is  wholly  absent, 
as  in  the  deep  sea,  an  abundant  fauna  exists,  the  food  supply  of 
which,  however,  is  derived  from  the  illuminated  regions  where 
plants  grow. 

Closely  related  to  the  food  supply  is  the  struggle  for  a  living 
among  species  and  individuals.  It  is  a  well-known  fact  that  most 
of  the  lower  animals  have  such  an  enormous  offspring  that,  sup- 
posing none  were  destroyed,  in  a  short  time  all  the  space  in  a  given 
region  would  be  occupied  by  the  progeny  of  a  single  pair;  and  the 
number  would  be  such  as  to  exceed  enormously  that  permitted  by 
the  food  supply.  Migration  to  new  regions  is  therefore  a  necessity, 
and  emigrants  are  continually  sent  out  in  all  directions  from  the 
mother  country.  If  no  other  occupants  were  in  the  region,  an 
intraspecific  struggle  for  existence  would  be  witnessed  in  every 
locality  settled  by  these  migrants — members  of  the  same  species 
fighting  among  themselves  for  a  living.  Such  a  struggle  would, 
of  course,  result  in  the  destruction  of  vast  numbers  and  in  the 
emigration  of  others.  But,  when  the  newly  opened  area  is  entered 
simultaneously  by  several  species,  or  if  the  area  is  already  occu- 
pied by  other  species,  an  interspecific  struggle  occurs,  the  outcome 
of  which  depends  on  the  relative  ability  of  the  contending  species 
to  hold  their  own.  The  resident  species  may  be  driven  out  by  the 
newcomer,  or  it  may  hold  its  own  and  prevent  the  intruder  from 
settling;  or,  again,  what  is  perhaps  more  common,  the  two  species 
may  accommodate  themselves  side  by  side  and  jointly  occupy  the 
disputed  area. 

An  example  of  a  struggle  between  resident  and  invading  spe- 
cies is  found  in  the  faunas  of  the  Portage  beds  of  New  York  State. 
The  resident  fauna  was  the  Ithaca  fauna,  derived  by  modification 
from  the  preceding  Hamilton  fauna.  The  invading  fauna  came 
from  Eurasia,  invading  the  New  York  area  from  the  northwest. 
The  interspecific,  or  interfaunal,  struggle  continued  throughout 
Portage  time,  the  invading  species  gradually  acquiring  the  mastery. 


BlOGEOGRAPHICAL   PROVINCES. 

At  each  period  of  the  earth's  history,  zoogeographic  and  phyto- 
geographic  provinces  existed  which  were  more  or  less  distinctly  sep- 


1054  PRINCIPLES    OK    STRATIGRAPHY 

arable  from  one  another  and  which  varied  from  period  to  period. 
Even  within  the  same  period  the  geographic  provinces  are  not 
constant  for  all  animals  or  plants,  because  some  groups  of  animals 
and  plants  are  not  affected  by  barriers  which  are  restrictive  to 
others.  Nevertheless  a  general  division  of  the  earth's  surface  into 
biotic  provinces  is  possible,  up  to  a  certain  extent ;  at  least  within 
the  marine  and  terrestrial  realms.  Within  these  two  realms  the 
distribution  of  organisms  is  the  resultant  of  migration  and  dis- 
persal, not  only  of  the  organisms  themselves,  but  also  of  their 
ancestors  in  preceding  geologic  periods.  Thus  the  problem  of 
geographic  distribution  of  a  given  group  of  organisms  resolves  itself 
into  a  study  of  the  migrations  and  dispersions  of  the  ancestral  types 
of  these  organisms  from  the  point  of  their  origin  in  past  time. 
From  the  point  of  origin  or  center  of  distribution  a  process  of 
adaptive  radiation  has  carried  the  organism  outward  and  onward  in 
space  and  time.  Barriers  arising  across  the  path  of  distribution  break 
the  continuity  of  the  range ;  and  from  these  separated  remnants,  or 
relicts,  arise  new  diversified  types,  along  a  number  of  distinct  lines 
radiating  from  the  central  stock,  the  resultants  being  in  general 
well  adapted  each  to  a  particular  phase  of  the  environment.  In 
other  distinct  provinces  similar  lines  of  evolution  may  give  rise 
to  parallel  series  of  modifications ;  so  that,  in  provinces  widely  sep- 
arated, similar  lines  may  arise  independently,  the  closeness  of  the 
resemblance  seemingly  indicating  a  close  geographic  connection 
between  the  provinces.  The  species  of  the  gastropod  genus  Clavi- 
lithes  are  an  excellent  example  of  this  phenomenon.  This  genus 
is  represented  by  a  number  of  very  marked  species  in  the  Eocenic 
strata  of  the  Paris  Basin.  A  parallel  series  occurs  in  the  London- 
Hampshire  Eocenic  basin,  but  there  are  scarcely  any  identical  spe- 
cies. Another  parallel  series  occurs  in  the  Gulf  Eocenic  of  the 
United  States,  a  province  entirely  distinct  from,  and  without  com- 
munication with,  the  European  provinces,  which  .themselves  were 
closely  circumscribed.  Nevertheless,  the  American  series  has  the 
same  specific  types  as  the  Paris  series,  corresponding  species  of 
the  two  generic  stocks  being  scarcely  distinguishable,  so  far  as  the 
specific  characters  are  concerned ;  though  it  is  an  easy  matter  to 
separate  them  generically — that  is,  to  place  each  species  in  its 
proper  genetic  series.  If,  as  seems  highly  probable,  these  two 
groups  of  Clavilithids  had  a  common  ancestor,  in  early  Eocenic, 
Palaeocenic,  or  late  Cretacic  time,  they  became  entirely  separated 
in  mid-Eocenic  time,  and  the  parallel  specific  types  arose  indepen- 
dently. 


BIOGEOGRAPHICAL    PROVINCES  1055 

Marine  Provinces. 

The  following1  are  the  marine  zoogeographical  regions  of  the 
present  geologic  epoch,  as  given  by  Ortmann  (38:  66)  : 

I.  Littoral  life-district 

1.  Arctic  region 

2.  Indo-Pacific  region 

3.  West  American  region 

4.  East  American  region 

5.  West  African  region 

6.  Antarctic  region 

II.  Pelagic  life-district 

1.  Arctic  region 

2.  Indo-Pacific  region 

3.  Atlantic  region 

4.  Antarctic  region 
III,    Abyssal  life-district 

No  regions  distinguishable. 

Marine  geographical  provinces  have  been  distinguished  for  sev- 
eral classes  of  organisms  by  different  authors.  Among  these  the 
following  may  be  mentioned  : 

I.  Corals.     Dana   recognized  three  principal  regions:   (i)   Red 
Sea  and  Indian  Ocean;  (2)  the  whole  of  the  Pacific  Islands  and  the 
adjacent  coasts  of  Australia;  (3)  the  West  Indies.    The  last  region 
is  the  most  isolated  and  it  contains  the  largest  proportion  of  peculiar 
forms. 

II.  Higher  Crustacea.    Prof.  J.  D.  Dana  also  proposed  to  divide 
the  oceans  into  the  three  main  areas,  based  on  the  distribution  of 
the  Crustacea.     These  are:   (i)   the  Occidental;    (2)   the  Africo- 
European,   comprising   the   western    shores   of   the   Atlantic,   both 
African  and  European;  and   (3)   the  Oriental,  which  includes  the 
vast  area  from  the  east  coast  of  Africa  to  the  Central  Pacific.    Each 
region  is  subdivided  into  local  and  climatic  provinces. 

III.  Barnacles.    Darwin,  considering  the  distribution  of  the  spe- 
cies of  barnacles,  divided  the  oceans  into  the  following  regions : 
(i)   The  North  Atlantic,  comprising  North  America  and  Europe 
down  to  N.  lat.  30°;  (2)  the  West  American,  from  Behring  Strait 
to  Tierra  del  Fuego ;  (3)  the  Malayan,  from  India  to  New  Guinea; 
(4)  the  Australian,  comprising  Australia  and  New  Zealand.     The 
third  and  fourth  regions  are  the  richest  in  species. 

IV.  Mollusca.     S.  P.  Woodward  (61)  divided  the  oceans  into 
three  main  divisions  or  regions:     (i)  The  Atlantic;  (2)  the  Indo- 
Pacific,   corresponding   to   Dana's   Oriental   region    for  Crustacea ; 
and  (3)  the  West  American.    The  following  is  the  modified  system 
of  Woodward  (Lydekker-29:/o/<5)  : 


1056 


PRINCIPLES    OF    STRATIGRAPHY 


Molluscan  Regions. 


A.  Atlantic  and  Circumpolar  regions, 


B.  Indo-Pacific  regions 


C.  Australian  regions. 


D.  American  regions. 


1.  Arctic  sub-region 

2.  Boreal  " 

3.  Celtic    " 

4.  Lusitanian     sub-region 

5.  West  African  "        " 

6.  South  African" 

1.  Indo-Pacific  sub-region. 

2.  Japanese  sub-region 

1.  Australian  sub-region 

2.  Neozealandian  sub-region 

1.  Aleutian    sub-region 

2.  Calif ornian 

3.  Panamic 

4.  Peruvian 
5..  Magellanic 

6.  Argentinian 

7.  Caribbean 

8.  Trans- Atlantic ' 


V.  Fishes.    Gunther  (20)  recognized  the  following  marine  zoo- 
logical regions  based  on  the  distribution  of  shore-haunting  fishes : 

i.  Arctic  ocean.  2.  Northern  temperate  zone  divided  into:  (a)  the  temperate 
North  Atlantic  and  (b)  the  temperate  North  Pacific  with  further  subdivisions 
of  each.  3.  Equatorial  zone,  divided  into:  (a)  Tropical  Atlantic,  (b)  Tropical 
Indo-Pacific,  and  (c)  Pacific  coast  of  tropical  America  with  further  subdivisions. 
4.  Southern  temperate  zone  with  several  subdivisions,  and  5.  Antarctic  ocean. 

VI.  Marine    Mammals.      The     following    marine    geographic 
regions  based  on  the  distribution  of  seals,  sea-cows,  and  cetaceans 
have  been  recognized  by  Sclater   (43)  : 

1.  Arctatlantica  (seals  of  the  sub -family  Phocinae). 

2.  Mesatlantica  (monk  seal  and  manatis). 

3.  Philopelagica    (Indian   ocean,    etc.),    characterized   by   the  presence  of 
dugongs  and  absence  of  seals. 

4.  Arctirenia  (North  Pacific)  with  Phoca,  and  sea-bears  and  sea-lions,  for- 
merly the  northern  sea-cows  (Rhytina)  now  also  the  gray  whale  (Rhachianectes).v 

5.  Mesirenia  (Mid-Pacific)  without  sea-cows,  but  with  the  elephant-seal 
(Macrorhinus). 

6.  Notopelagica  (Southern  ocean)  with  four  peculiar  genera  of  seals,  numerous 
sea-bears  and  sea-lions,  and  two  peculiar  whales,  the  pigmy  whale  and  Arnoux's 
beaked  whale. 


BIOGEOGRAPHICAL    PROVINCES  1057 


Former  Marine  Geographic  Provinces. 

The  most  elaborate  attempt  to  divide  the  world  into  marine 
zoogeographical  provinces  for  one  of  the  past  geological  periods  of 
the  earth's  history  is  that  of  the  late  Victor  Uhlig  of  Vienna,  in 
his  "Die  marinen  Reiche  des  Jura  und  der  Untern  Kreide"  (52). 
He  recognizes  at  least  four  large  faunal  districts,  based  mainly  on 
the  distribution  of  fossil  cephalopods,  namely : 

1.  The  boreal. 

2.  The  Mediterranean — Caucasian. 

3.  The  Himamalayian. 

4.  The  Japan  Province. 

5.  The  South  Andine  realm. 

The  boreal  realm  of  the  Jurassic  time  originally  defined  by 
Neumayr  was  circumpolar  in  the  arctic  region  with  extensions  into 
the  heart  and  the  northern  region  of  Russia  to  the  east  of  the  Urals 
and  westward  to  Greenland,  including  the  Urals  and  Scandinavia 
as  probable  islands.  A  narrow  southward  extension  included  the 
region  of  the  Lena  River  and  the  lower  Amur.  The  Pacific  ex- 
tension of  this  realm  comprises  Alaska  and  the  western  coast  of 
America  (California,  Nevada,  etc.)  to  the  head  of  the  Gulf  of  Cali- 
fornia and  with  an  epicontinental  lobe  extending  into  Montana, 
Wyoming,  Idaho  and  eastward  to  the  Black  Hills  (Logan  Sea). 
This  region  has  been  separately  named  the  North  Andine  Province. 
On  the  whole,  the  boreal  was  a  shallow  sea,  with  a  peculiar  and 
uniform  fauna.  Coral  reefs  were  conspicuously  absent. 

The  Mediterranean-Caucasian  realm  comprised  the  expanded 
Mediterranean  area,  which  extended  eastward  to  the  borders  of 
India  and  northward  to  the  Caucasus  Mountains.  It  included  the 
Jurassic  formations  of  the  Alps.  Between  it  and  the  Boreal  realm 
of  Russia  lay  the  mid-European  province  of  Neumayr,  which,  by 
Haug,  Uhlig,  and  others,  is  regarded  as  a  neritic  border  zone  of 
the  deeper  Mediterranean  sea.  The  characteristic  genera  of  am- 
monites of  the  Mediterranean  realm  (Phylloceras,  Lytoceras)  are 
regarded  by  Haug  as  stenothermic  and  able  to  live  only  in  the 
deeper  waters  where  temperature  changes  are  slight;  while  the 
other  genera  were  eurythermic  and  so  had  a  wider  distribution. 

The  Himamalayian  realm  comprised  northern  India  and  the 
Himalayan  region,  and  extended  thence  to  the  Malay  archipelago. 
In  it  are  recognizable  an  argillo-arenaceous  and  a  calcareous  facies, 
a  part  of  the  latter  being  often  considered  as  abyssal.  Two  related 


1058  PRINCIPLES    OF    STRATIGRAPHY 

provinces  are  recognized:  (a)  the  Ethiopian,  comprising  the  east 
coast  of  Africa  and  part  of  Madagascar;  and  (b)  the  Maorian, 
in  Oceanica.  The  Japan  Province  is  a  small  one  limited  to  the 
Japanese  archipelago  and  Korea.  It  is  characterized  by  a  comming- 
ling of  boreal  and  Malayian  features,  though  less  markedly  related 
to  the  latter.  The  South  Andine  realm  comprised  Central  America 
and  the  whole  west  coast  and  the  southern  end  of  South  America, 
and  appears  to  be  likewise  represented  in  the  southern  coast  of 
Africa. 

Considering  these  realms  as  a  whole  it  appears  that  the  faunas 
of  the  last  four  are  more  closely  related  to  each  other  than  they  are 
to  the  boreal.  Haug  has  united  the  Mediterranean-Caucasian,  the 
Himamalayian,  and  the  North  Andine  realms  into  a  single  broad 
equatorial  faunal  arid  climatic  belt  which  is  sharply  contrasted  with 
the  Holarctic-Boreal  belt.  Such  a  broad  zonal  division  is  favored 
by  Uhlig. 

On  the  whole,  it  appears,  as  Koken  (27:550)  pointed  out,  that 
the  distribution  of  marine  faunas  is  less  dependent  on  climatic 
differences  than  on  the  distribution  and  development  of  coast  lines. 

Present  and  Former  Biogeographic  Provinces  of  the  Land. 

The  terrestrial  provinces  of  the  present  time  are  generally  com- 
prised within  three  great  divisions  or  sub-realms,  as  first  proposed 
by  Blanford,  and  under  these  are  included  a  number  of  distinct 
regions.  As  commonly  accepted,  these  are : 

I.  Arctogaea,  or  northern  sub-realm,  with 

1.  Arctic,  or  circumpolar  region. 

2.  Ethiopian,  or  African  region  (south  of  the  Sahara). 

3.  Indo-Malayan,    or    Oriental    region    (including    southern 

Asia  and  the  Malayan  islands). 

4.  Malagasian,  or   Madagascar   region. 

5.  Nearctic,  or  North  American  region. 

6.  Palaearctic,  or  Eurasiatic  region. 

II.  Notogaea,  with  four  regions : 

1.  Austro-Malayan. 

2.  Australian. 

3.  Polynesian. 

4.  Hawaiian. 

III.  Neogaea,  comprising  South  America,  with  one  region: 

i.  Neotropical. 


BIOGEOGRAPHICAL    PROVINCES  1059 

To  these  may  be  added  the  Antarctic  continent,  or  Antarctogaa,  the 
former  existence  of  which,  connecting  most  of  the  other  regions, 
seems  to  be  demonstrated  by  a  number  of  independent  lines  of  evi- 
dence, as  developed  in  the  study  of  the  distribution  of  a  great 
variety  of  types  of  organisms. 


Fresh  Water  Bio  tic  Provinces. 

Simpson  (47)  has  proposed  the  following  regions  as  subdivisions 
of  the  fresh  water  realm,  based  on  the  distribution  of  the  fresh 
water  mussels  or  Unios  in  the  present  chronofauna. 

1.  Palsearctic.  5.  Neotropic. 

2.  Ethiopic.  6.  Central  American. 

3.  Oriental.  7.  Mississippian. 

4.  Australian.  8.  Atlantic. 

The  Pal(carctic  region  comprises  Europe,  North  Asia,  and 
western  North  America;  the  Oriental  includes  the  Malaysian  Is- 
lands to  New  Guinea.  Simpson  holds  that  the  mussels  originated  in 
North  America  in  the  Triassic,  whence  they  migrated  or  dispersed 
into  South  America,  from  which  region  they  passed  by  an  old 
Antarctic  land  bridge  to  New  Zealand  and  Australia,  thence  to 
southern  East  Asia,  whence  they  entered  the  remaining  part 
of  Asia,  Europe  and  Africa.  In  early  Tertiary  time  they  migrated 
across  northeast  Asia  to  northwest  America. 

It  should  be  noted  in  this  connection  that  the  active  migration 
of  the  adult  is  a  comparatively  slow  process,  and  is,  of  course,  con- 
fined to  streams.  The  young  are  attached  to  the  gills  of  fishes  and 
so  are  much  more  rapidly  distributed.  Here,  too,  of  course,  con- 
tinuous water  bodies  are  required.  But  there  are  other  methods 
of  dispersal  by  means  of  which  these  shells  can  transgress  land 
barriers  often  of  considerable  extent.  Notable  among  these  are 
the  dispersal  of  the  eggs  and  young  shells  by  water  birds,  to  whose 
feet  they  become  attached,  and  by  large  water  beetles  and  other 
insects.  Thus,  while  large  bodies  of  sea  water  cannot  be  traversed 
in  this  way,  narrow  straits  could  easily  be  covered. 

Perhaps  a  better  index  to  the  former  land  connections  is  found 
in  the  distribution  of  the  fresh  water  crayfish.  Their  migrations 
were  traced  to  a  certain  extent  by  Huxley  (24),  later  by  Faxon, 
and  most  recently  by  Ortmann  (39). 

The  distribution  of  the  family  Potamobiidce  Huxl.,  compris- 
ing two  genera,  Cambarus  and  Potamobius,  may  be  briefly  con- 


io6o  PRINCIPLES    OF    STRATIGRAPHY 

sidered.  The  first  of  these  genera  includes  67  species,  and  is 
found  only  in  the  eastern  parts  of  North  America,  Mexico,  and 
Cuba.  The  genus  is  divisible  into  five  groups,  the  smallest  of 
which  contains  three  species  and  the  largest  twenty-six.  The  first 
group  of  sixteen  species  is  restricted  chiefly  to  the  southern  parts 
of  the  United  States  and  Mexico.  The  most  primitive  species  belong 
chiefly  to  the  southwest ;  and  in  fact  this  is  also  true  of  the  primitive 
species  of  the  second  and  fifth  groups.  This  fact  points  to  an  origin 
of  the  genus  in  the  southwest,  its  starting  point  being  apparently  in 
Mexico.  The  second  genetic  group,  with  eight  species,  shows  a 
striking  discontinuity  of  distribution,  isolated  representatives  being 
found  in  Mexico,  the  Gulf  States,  the  southern  Atlantic  States, 
and  Cuba;  all  of  them  separated  from  the  members  of  the  group 
found  in  the  southwestern  and  central  States.  This  indicates  that, 
after  the  migration  of  the  species  of  this  group  from  Mexico  into 
the  United  States,  unfavorable  physical  conditions  at  intermediate 
points  broke  up  the  former  continuous  range.  The  third  group, 
with  thirteen  species,  has  a  continuous  distribution  in  the  Alle- 
ghany  mountains  and  in  the  east ;  a  single  species  reaching  north  to 
the  Gulf  of  St.  Lawrence  region.  It  also  extends  northward  in 
the  Mississippi  region,  but  is  less  prominent,  and  is  represented  at 
only  one  station  in  the  southwest,  and  there  by  a  single  species. 
The  fourth  group,  with  twenty-six  species,  is  also  scarce  in  the 
south  and  southwest,  but  is  abundant  in  the  Upper  Mississippi- 
Missouri-Ohio  basin.  Eastward  it  extends  up  the  Ohio  into  Penn- 
sylvania, Virginia,  Maryland,  New  Jersey,  and  New  York,  its 
northeastern  limit  being  near  Montreal.  In  the  central  region  it 
extends  northward  to  Lake  Winnipeg  and  the  Saskatchewan  River, 
the  most  northerly  locality  known  for  this  genus.  Westward  it 
extends  to  Wyoming.  The  fifth  group  consists  of  three  species,  one 
occurring  near  New  Orleans,  the  other  two  in  Mexico.  On  the 
whole,  the  most  primitive  species  are  in  the  Mexican  region,  the 
probable  birthplace  of  the  genus,  as  has  already  been  suggested. 
Here  also  has  remained  a  rather  primitive  side  branch,  group  5- 
The  other  groups  advanced  northward  and  northeastward,  the 
most  specialized  becoming  discontinuous  on  account  of  adaptation 
to  a  changed  environment. 

Cambarus  appears  to  be  derived  directly  from  a  less  specialized 
fresh  water  crayfish,  Potamobius,  which  has  a  strikingly  discon- 
tinuous distribution,  one  group  of  seven  species  occupying  a  con- 
tinuous area  in  Europe  and  western  Asia,  and  another  in  western 
North  America.  A  third  group,  separated  as  the  subgenus  Cam- 
baroides,  occurs  in  northeastern  Asia ;  this  group,  according  to 


BIOGEOGRAPHICAL   PROVINCES  1061 

Ortmann,  forming  a  morphologic  equivalent  (homceomorph)  of 
Cambarus,  though  not  closely  related  to  it.  Ortmann  believes  that 
the  three  groups  originated  from  a  common  ancestor  whose  home 
was  in  eastern  Asia.  A  branch  was  sent  out  westward,  which  finally 
reached  Europe ;  while  another  branch  migrated  eastward,  reaching 
western  America  by  means  of  a  land  area  connecting  Asia  and 
America.  Of  these  migrants  a  single  species  has  remained  behind 
in  Unalaska.  When  finally,  by  geographical  changes,  the  European 
and  American  branches  became  separated  from  the  Asiatic  one, 
each  developed  independently,  the  result  being  three  distinct  groups, 
as  above  stated.  From  members  of  the  American  group,  which  had 
reached  Mexico,  the  genus  Cambarus  developed,  in  a  remote  period, 
becoming  differentiated  into  five  groups,  through  processes  of  geo- 
graphical isolation. 

From  the  distribution  of  these  and  other  -fresh  water  decapods 
Ortmann  concludes  that  the  following  land  connections  must  have 
existed  in  the  near  past. 

1.  Northeast  Asia  with  Northwest  America  across  the  Behring 

Sea. 

2.  East  Asia  with  Australia. 

3.  South  Asia  with  Madagascar  and  Africa. 

4.  New  Zealand  with  Australia. 

5.  Australia  with  South  America. 

6.  West  Indies  with  Central  and  South  America. 

7.  South  America  with  Africa. 

Ortmann  holds  that  the  above  connections  were  necessary;  for, 
while  a  few  species  of  fresh  water  crayfish  or  crabs  have  been 
found  in  brackish  or  even  salt  water,  this  occurrence  is  very  excep- 
tional, the  animals  being  preeminently  dwellers  in  fresh  water,  so 
that  a  migration  across  oceans  or  parts  of  oceans  is  practically  pre- 
cluded. Furthermore,  since  these  animals  cannot  live  out  of 
water  for  any  great  length  of  time,  deserts  or  waterless  tracts  form 
absolute  barriers  for  them.  The  eggs  of  these  creatures  are  carried 
under  the  abdomen  of  the  female,  and  the  young  hatch  in  a  state 
similar  to  the  parents.  While  water  fowl  or  other  agents  may  oc- 
casionally effect  a  passive  transport,  such  cases  are  rare  and  have 
never  been  observed.  "The  whole  character  of  the  distribution  of 
the  different  species  is  against  the  assumption  of  exceptional  means 
of  dispersal."  (Ortmann-39.)  The  connection  of  Asia  and  north- 
west America  by  way  of  Behring  Sea  is  also  indicated  by  the  dis- 
tribution of  mammals  and  other  land  animals.  The  connection  con- 
tinued probably  through  the  whole  of  Tertiary  time.  The  connec- 


1062  PRINCIPLES    OF    STRATIGRAPHY 

tion  between  eastern  Asia  and  Australia  is  also  indicated  by  the 
distribution  of  the  snails  (Helix).  This  bridge  appears  to  have 
existed  before  the  Upper  Cretacic.  The  connection  between  Africa 
and  India  demanded  by  the  distribution  of  the  fresh  water  decapods 
seems  to  have  been  in  mid-Cretacic  time  or  earlier.  Other  facts 
show  that  this  union  continued  through  Eocenic  time.  The  con- 
nection between  New  Zealand  and  Australia  is  believed  to  have 
been  by  way  of  New  Caledonia  and  New  Guinea,  and  belongs  to 
pre-Eocenic  time;  while  that  between  Australia,  New  Zealand  and 
South  America,  generally  assumed  by  students  of  zoogeography,  is 
believed  by  Ortmann  to  have  been  across  the  Pole,  and  to  have  con- 
tinued to  the  end  of  Mesozoic  time.  There  are  indications  that 
the  West  Indies,  Central  America,,  and  the  northern  margin  of 
South  America  formed  the  "Antillean  continent"  during  Jurassic 
and  Cretacic  time,  a  remnant  of  and  successor  to  Appalachia ;  after 
this  was  broken  up,  the  northern  remnant,  consisting  of  the  Greater 
Antilles  and  parts  of  present  Central  America,  probably  remained 
a  unit  up  to  the  Eocenic,  after  which  it  was  dismembered,  to  be 
once  more  established  in  Pleistocenic  time,  and  finally  destroyed 
in  the  present.  Finally,  the  connection  between  South  America  and 
Africa  is  believed  to  have  existed  in  Jurassic  and  early  Cretacic 
time,  but  was  severed  in  subsequent  periods. 

Terrestrial  animals,  especially  mammals,  are  even  better  indices 
of  former  land  connections  than  the  fresh  water  animals  cited, 
inasmuch  as  even  moderate  dividing  straits  form  absolute  barriers 
to  the  majority  of  types.  For  an  extensive  account  of  this  subject 
the  student  is  referred  to  Lydekker's  "Geographical  Distribution 
of  Mammals." 

RELICTS. 

RELICT  FAUNAS  AND  LAKES.  The  occurrence  of  halo-limnic 
organisms  or  animals  or  plants  normally  of  marine  type  in  conti- 
nental seas  or  lakes  has  been  a  matter  of  great  scientific  interest 
ever  since  Loven,  in  1860,  announced  the  presence  of  Crustacea 
closely  related  to  marine  types  in  the  great  fresh  water  lakes  of 
Sweden,  and  showed  by  the  geological  structure  of  the  region  that 
these  organisms  entered  the  lakes  at  a  time  when  they  were  con- 
nected with  the  sea.  They,  therefore,  constituted  the  relics  of  a 
former  marine  fauna,  which  had  mostly  become  extinct  by  the  grad- 
ual freshening  of  the  waters  of  the  lakes  after  the  connection  with 
the  sea  was  broken.  Similar  left-over  marine  faunas  or  relicts 
were  discovered  in  many  other  continental  seas,  both  fresh  and 


RELICT    FAUNAS    AND    LAKES  1063 

salt;  some  of  these  occurrences,  like  that  of  the  sea-dog,  or  harbor 
seal,  Phoca,  in  the  Caspian  and  other  seas,  had  been  known  pre- 
viously, and  used  by  Pallas  and  V.  Humboldt  to  demonstrate  the 
former  connection  of  these  lakes  with  the  oceans.  Oscar  Peschel 
(41)  in  1875  applied  the  name  relict  seas  (Reliktenseen)  to  these 
bodies  of  water,  which  he  regarded  as  derived  from  the  sea  by 
the  growth  of  enclosing  land.  He  and  most  authors  since  his 
time  regarded  all  continental  seas  containing  marine  organisms  as 
relicts,  even  though  some  of  these  seas  are  far  inland.  Credner 
(8),  however,  strongly  opposed  this  view,  evidently  believing,  with 
Penck,  that  a  distinction  should  be  made  between  a  relict  fauna 
and  a  relict  sea.  The  former  may  enter  the  lake  by  a  process  of 
migration,  as  is  believed  to  be  the  case  in  many  instances  where 
the  seals  (Phoca)  are  found  in  fresh  water  lakes  the  geologic 
surroundings  of  which  show  that  they  never  were  a  part  of  the 
ocean;  or  where  a  marine  fauna  has  entered  a  lake  basin  of  inde- 
pendent origin  through  a  temporary  connection  with  the  sea.  Such 
is  the  case  with  the  Great  Lakes  of  North  America,  some  of  which 
are  known  to  have  been  temporarily  invaded  by  the  sea  by  way  of 
the  Hudson-Champlain  depression  during  early  Pleistocenic  time, 
but  the  origin  of  which  was  wholly  independent  of  the  sea  (16). 
Thus  Lake  Ontario  was  a  fresh  water  lake  before  it  became  tempo- 
rarily connected  with  the  sea.  Credner  classes  as  true  relict  seas 
all  those  which  at  one  time  were  a  part  of  and  connected  with  the 
oceans.  He  makes  the  following  divisions  : 

I.  Relict  seas  due  to  damming  and  isolation  of  parts  of  the  sea, 
through  a  growth  to  above  the  sea-level  of  enclosing  rock 
masses. 

II.  Relict  seas  due  to  isolation  of  basin-like  depressions  in  the 
sea-floor,   owing   to   a   negative   change    in   the   sea-level. 
Emersion  lakes. 
III.  Relict  seas  due  to  shrinking  of  former  mediterraneans. 

The  first  division  includes  (a)  coastal  lakes  due  to  damming 
of  bays  and  inlets,  by  growth  of  deltas  (Lake  Akiz),  or  by  the 
enclosure  of  bodies  of  water  between  the  growing  delta  and  the 
open  coast  (Lake  Pontchartrain  and  others  in  the  Mississippi 
delta)  ;  (b)  coastal  lakes  or  lagoons  (barachois)  due  to  the  growth 
of  sand-bars  (Kurische  Haff)  and  barrier  reefs;  (c)  atoll  seas  or 
coral  island  lagoons,  and  others. 

Under  the  second  division  are  comprised  the  marginal  lakes 
of  the  fjord  type,  as  on  the  coast  of  Norway,  Scotland  (Loch 
Lomond),  Iceland  (Lagarfljotj,  and  others.  Credner  classes  Lake 


1064  PRINCIPLES    OF    STRATIGRAPHY 

Champlain  in  this  group,  but  this  basin  can  hardly  be  said  to  have 
been  a  part  of  the  sea  in  the  sense  that  the  marginal  fjord  lakes 
are.  It  is  an  ancient  erosion  basin  of  truly  continental  origin,  as  is 
the  case  with  most  of  the  Great  Lakes.  The  Champlain  valley  was 
temporarily  invaded  by  the  sea,  as  was  Lake  Ontario,  both  being 
primarily  continental  basins  due  to  erosion  and  damming.  For  this 
group  a  separate  division — that  of  relict  seas  due  to  invasion — 
might  be  erected.  In  this  category  may  belong  Lake  Venern  and 
Lake  Vettern  of  Sweden,  both  of  which  are  old  erosion  basins 
and  may  have  been  lakes  before  the  marine  invasion.  This  group 
of  relict  seas  is  more  nearly  related  to  the  true  lakes  which  contain 
a  relict  fauna. 

Among  other  lakes  containing  a  pronounced  relict  fauna,  Lake 
Baikal  of  central  Asia  and  Lake  Tanganyika  of  central  Africa 
are  perhaps  the  best  known.  The  relict  nature  of  the  former  basin 
has  been  much  questioned  (Credner-8,  ii:^5),  but  the  relict  nature 
of  a  part  of  the  fauna  is  commonly  conceded  (Hoernes-22).  Be- 
sides the  seal  Phoca  baikalensis,  B.  Dyb.,  and  a  number  of  fish, 
among  them  Salmo  migratorius  Pallas,  planarians,  and  sponges  are 
represented  by  types  more  closely  related  to  marine  than  to  fresh 
water  forms.  One  of  the  sponges  especially  (Lubomirskia  baika- 
lensis, W.  Dyb.)  is  a  truly  marine  type,  occurring  in  Behring  Sea. 
The  molluscan  fauna  of  Lake  Baikal  is  especially  peculiar.  Of  the 
twenty-five  described  species  of  gastropods  only  three  are  found 
elsewhere,  but  none  outside  of  Siberia  (Dybowski,  W.-I3).  There 
is  a  marked  resemblance,  however,  between  this  fauna  and  that  of 
the  Tertiary  fresh  water  lakes  of  eastern  Europe,  which  most 
probably  were  the.  source  whence  the  Baikal  fauna  migrated. 

The  relict  fauna  of  Lake  Tanganyika  is  a  most  interesting  and 
remarkable  one  (Moore— 32).  It  includes  the  fresh  water  medusa 
Limnocnida  tanganyica,  the  first  and  almost  the  only  jelly-fish  found 
outside  of  the  sea ;  and  a  number  of  molluscs  which  can  be  traced 
back  to  ancestors  .probably  in  the  Jurassic  seas  of  that  region. 
Some  of  these  would  unhesitatingly  be  classed  as  marine  types  if 
found  in  a  fossil  condition,  which  is  particularly  true  of  the  Fulgur- 
like  genus  Holacantha,  of  which  four  species  inhabit  this  lake ;  and 
of  the  trochoid  genus  Limnotrochus,  also  represented  by  four  spe- 
cies (Bourguignat-4).  This  association,  with  Planorbis,  Physa, 
Vivipara,  and  other  normal  fresh  water  forms,  would,  if  found 
embedded  in  the  strata,  lead  to  some  interesting  speculations  re- 
garding the  conditions  of  deposition. 

The  relict  fauna  of  the  Scandinavian  and  Finnish  lakes,  of 
which  there  are  no  less  than  thirty-one,  comprises  seven  Crustacea, 


MARINE    RELICTS;    BIPOLAR    FAUNAS          1065 

three  fish,  and  one  seal  (Phoca  annellata  Nilss).  The  Crustacea 
are  especially  interesting.  Mysis  oculata  Fabr.  var.  relicta  is  the 
most  widely  distributed  type.  It  is  a  variety  of  a  true  marine 
form  which  occurs  in  the  northern  seas  on  the  coast  of  Labrador 
and  Greenland.  The  same  variety  occurs  in  lakes  Superior,  Michi- 
gan, and  Ontario,  in  the  Gulf  of  Bothnia,  and  in  the  Caspian  Sea. 
The  other  marine  Crustacea  of  the  Scandinavian-Finnish  seas  are 
three  amphipods ;  one  isopod,  one  phyllopod,  and  one  lophyropod. 

Relict  seas  derived  from  the  shrinking  of  former  mediterraneans 
are  found  in  the  Caspian  and  Aral  seas,  which  are  still  shrinking. 
These  seas  are  fragments  of  a  once  extensive  southeast  European- 
Asiatic  mediterranean  of  later  Tertiary  time  (Sarmatien).  The 
relict  fauna  of  the  Caspian  includes,  besides  the  seal  (Phoca  cas- 
pica),  sixteen  species  of  molluscs,  including  Cardium,  Adacna, 
Venus,  etc. ;  two  Crustacea,  four  sponges,  and  a  number  of  fish. 
These  seas  are  further  characterized  by  having  salty  or  brackish, 
instead  of  fresh,  water. 

MARINE  RELICTS — BIPOLAR  FAUNAS.  "Bipolarity  .in  the  strict 
sense,"  says  Ortmann,  "i.  e.,  the  presence  of  an  identical  species  at 
the  North  and  South  Poles,  while  it  is  absent  in  the  intermediate 
regions,  is  extremely  rare,  and  there  are  hardly  any  well-established 
cases.  Bipolarity  in  a  wider  sense — presence  of  closely  allied  spe- 
cies at  the  poles,  while  in  the  intermediate  regions  allied  forms 
are  absent — is  a  well-established  fact."  The  known  cases  are  chiefly 
of  pelagic  animals.  Ortmann  thinks  that,  in  some  cases,  as  medu- 
sae, pteropods,  and  tunicates,  the  ancestors  lived  in  the  tropical 
seas  of  Tertiary  time,  and  their  descendants  migrated  both  north 
and  south,  the  tropical  forms  subsequently  becoming  extinct.  The 
difference  between  the  north  and  south  polar  types  in  other  cases 
is  explained  by  Ortmann  as  due  to  different  sources  of  the  migrants, 
the  Arctic  faunas  being  derived  from  the  old  Mesozoic  Mediter- 
ranean waters,  and  the  Antarctic  from  Pacific  waters.  Other  ex- 
amples of  marine  relicts,  or  the  occurrence  of  faunas  in  basins  of 
the  sea,  while  they  have  become  extinct  in  the  neighboring  region, 
is  shown  by  the  fauna  of  Quahog  Bay  near  Portland,  Maine ;  and 
in  the  southern  parts  of  the  Gulf  of  St.  Lawrence,  as  about  Prince 
Edward's  Island,  and  the  opposite  coast  of  Nova  Scotia,  where  the 
water  is  shallow  and  much  warmer  than  on  most  parts  of  the 
Maine  coast.  Here  Venus  mercenaria  is  found'  in  some  abundance, 
associated  with  oysters  and  other  southern  species  which  are  absent 
from  the  New  England  coast.  They  constitute  "a  genuine  southern 
colony,  surrounded  on  all  sides,  both  north  and  south,  by  the 
boreal  fauna."  (Verrill  and  Smith-54  :j<5o.) 


io66  PRINCIPLES    OF    STRATIGRAPHY 

TERRESTRIAL  RELICTS.  These  are  faunas  and  floras  which  have 
migrated  into  certain  regions  during  a  period  of  different  climatic 
conditions,  and  then  became  stranded  in  certain  spots  where  the 
environment  remained  uniform,  while  the  surrounding  area 
changed.  The  Arctic  plants  and  butterflies  of  Mount  Washington 
in  New  Hampshire  are  examples.  These  occupied  the  region  dur- 
ing the  general  refrigeration  of  the  climate  in  the  last  glacial  pe- 
riod, and  on  the  retreat  of  the  ice  were  left  stranded  on  the  higher 
points  where  these  conditions  were  more  nearly  normal  for  them. 
According  to  Professor  Asa  Gray,  37  northern  species  of  plants 
still  remain  and  thrive  on  the  summits  of  the  White  Mountains  of 
New  Hampshire,  and  part  of  them  also  on  the  Adirondack  and 
Green  Mountains.  A  number  of  these  species  were  found  on 
a  Greenland  nunatak  by  the  Jensen  expedition  of  1878. 

DWARF  FAUNAS  AND  MICRO-FAUNAS. 

These  are  faunas  in  which  all  the  individuals  are  of  much 
smaller  size  than  their  norm,  and  which  therefore  clearly  lived 
under  conditions  preventing  the  organisms  from  reaching-  their 
full  size.  That  such  conditions  are  primarily  environmental  is 
indicated  by  the  fact  that  all  the  organisms  are  affected,  whereas, 
if  individuals  only  were  dwarfed,  or  only  members  of  one  species, 
this  might  be  considered  as  more  likely  an  individual  response. 
Micro'-faunas  are  associations  of  small  species  determined  by  the 
peculiarity  of  physical  conditions  and  not  due  to  dwarfing  of 
normally  large  species.  While  dwarfed  forms  of  known  larger  spe- 
cies are  readily  enough  recognized,  it  is  not  always  easy  to  say 
whether  a  given  fauna — not  known  elsewhere — is  dwarfed  or  is  a 
micro-fauna  due  to  selection. 

Shimer  (45)  has  listed  the  chief  agencies  of  dwarfing  noted 
in  recent  and  fossil  marine  invertebrate  faunas,  as  follows: 

1.  A  change  in  the  normal  chemical  content  of  the  sea  water. 

(a)  Due  to  freshening  of  the  sea  water. 

(b)  Due  to  a  concentration  of  the  salt,  iron,  etc. 

(c)  Due  to  an  increase  in  H2S  and  other  gases. 

2.  Presence  of  sand  and  other  mechanical  impurities   in  the 

water. 

3.  A  floating  habitat. 

4.  Variation  in  temperature. 

5.  Extremes   in   depth   of   water   and   variation   in   amount   of 

water  per  individual. 


DWARF    FAUNAS    AND    MICROFAUNAS         1067 

As  an  illustration  of  the  dwarfing  due  to  the  freshening  of  sea 
water  Shimer  cites  the  organisms  of  the  Black  and  Caspian  Seas, 
which  are  freshened  by  the  influx  of  stream  water  (see  tables  of 
salinity,  pp.  146,  154).  As  shown  by  Forbes  (14),  the  species  of 
molluscs  in  the  Black  Sea  are  all  smaller  than  those  same  species 
in  the  British  seas.  Cardium  edule,  the  common  cockle  of  the 
British  coast,  is  dwarfed  when  it  lives  in  the  brackish  water  of 
the  estuaries.  The  shell  is  not  only  reduced  in  size,  but  becomes 
thin  and  has  its  external  character  less  strongly  marked.  The 
cockles  of  the  Caspian  Sea  are  small,  thin,  and  smooth,  with  lateral 
or  central  teeth  or  both  suppressed.  The  cockle  of  the  Green- 
land estuaries  is  likewise  thin,  smooth  and  almost  edentulous,  the 
rudiments  of  hinge-teeth  occurring  in  the  young  but  disappearing 
in  the  adult.  This  species  is  abundant  in  the  Pliocenic  Crag  de- 
posits of  Suffolk  and  Norfolk,  especially  in  the  fluvio-marine  por- 
tion. Among  other  species  dwarfed  by  brackish  water  are  M ya 
arenaria  and  Littorina  littorea. 

Shimer  described  a  diminutive  Pleistocenic?  fauna  from  the 
estuarine  clays  of  the  Hudson  bottom  opposite  Storm  King,  40 
feet  below  the  bed  of  the  river.  This  fauna  consisted  mainly  of 
large  numbers  of  Mulinia  lateralis  (Say)  and  a  lower  development 
of  Trivia  trivittata  Say.  These  species  live  at  present  off  the  New 
England  and  New  Jersey  coasts  in  normal  marine  or  but  slightly 
freshened  water,  where  their  size  is  almost  twice  that  of  the  Hud- 
son estuary  specimens. 

Dwarfing  due  to  concentration  of  salt,  i.  e.,  increase  in  salinity, 
is  shown  to  some  extent  in  the  Mediterranean,  which,  with  a  salinity 
of  39  permille,  has  many  of  its  species  smaller  than  their  repre- 
sentatives in  the  open  water  of  the  British  and  Spanish  coasts. 
The  dwarfed  faunas  of  the  European  Permic  have  in  part  been 
ascribed  to  such  concentration  of  the  water.  The  possibility  of 
dwarfing  of  faunas  through  an  excess  of  iron  salts  has  been  shown 
by  experiments  upon  fishes  and  tadpoles,  which  in  eight  months 
were  retarded  in  growth  from  3  to  5  mm.  Fossil  examples  are 
found  in  the  Pyrite  layer,  which  in  the  Genesee  Valley  and  west-1 
ward  in  New  York  replaces  the  Tully  limestone  of  the  Upper 
Devonic.  In  this  the  fauna  of  45  species  was  found  by  Loomis 
(28)  to  be  on  the  average  only  one-fifteenth  the  size  of  the  normal 
form.  The  dwarfing  was  apparently  due  to  presence  of  much  iron 
in  solution,  in  the  form  of  ferrous  carbonate,  and  this  was  precipi- 
tated as  pyrite  by  sulphuretted  hydrogen  derived  from  the  decay- 
ing organic  matter  (FeOCO2+HaS=FeS+CO2+H2O).  The 


io68  PRINCIPLES    OF    STRATIGRAPHY 

Clinton  iron  ore  also  contains  a  somewhat  dwarfed  fauna  which 
may  have  been  due  to  the  presence  of  much  iron  in  the  sea  water. 

Dwarfing  effects  due  to  an  abundance  of  H.,S  in  the  water  are 
shown  in  the  Black  Sea,  where,  owing  to  the  slight  vertical  cur- 
rents, much  stagnation  occurs,  and  much  H2S  is  separated  out 
(see  ante,  Chapter  IV).  Here  life  below  a  certain  depth  is  prac- 
tically absent,  while  the  bottom  deposits  are  strewn  with  young 
shells  from  the  plankton.  The  dwarf  faunas  of  the  Palaeozoic 
Black  shales  have  been  considered  as  produced  by  conditions  such 
as  now  exist  in  the  Black  Sea,  but  the  depth  during  the  formation 
of  most  of  them  was  probably  slight,  thbugh  stagnation  was  no 
doubt  marked. 

The  presence  of  mud  or  other  mechanical  impurities  likewise 
exerts  a  dwarfing  effect  on  many  organisms.  This  is  illustrated 
by  the  fauna  of  the  eastern  part  of  the  Mediterranean,  where  a 
large  quantity  of  fine  mud  brought  in  by  the  Nile  is  held  in  suspen- 
sion. (De  Lapparent-i2:/j^.)  Shimer  thinks  that  the  dwarfed 
faunas  of  the  late  Siluric  rocks  of  eastern  New  York  (Rosendale, 
Cobleskill,  Rondout,  Manlius)  are  due  to  the  presence  of  an  abun- 
dance of  lime-mud,  of  the  same  kind  of  which  the  strata  are  com- 
posed. This  is  a  general  characteristic  of  Palaeozoic  calcilutytes. 

Dwarfing  of  organisms  due  to  a  floating  habitat  is  seen  in  the 
case  of  a  California  coast  Pecten  (P.  latiauritus),  which  when 
growing  near  the  coast  is  large  and  more  strongly  sculptured  than 
when  fastened  to  floating  kelp  far  from  the  coast  (var.  fucicolus). 
The  molluscs,  living  on  and  among  the  sea-weed  which  crowds  the 
eastern  shallower  part  of  the  harbor  of  Messina,  are  throughout  of 
smaller  forms,  but  are  present  in  enormous  number  of  individuals. 
(Fuchs-i5:<?cxf)  Walther  (56)  remarks  upon  this  that  the  physi- 
cal conditions  of  a  special  type  of  plant  life  here  cause  indirectly 
the  origin  of  the  micro-fauna.  The  micro-fauna  here  is  not  so 
much  a  dwarf  fauna  as  one  due  to  selection  of  small  species  by  the 
peculiar  characteristics  of  the  habitat. 

The  influence  of  variation  in  temperature  on  the  size  of  the 
individuals  is  illustrated  by  the  experiment  of  Semper  (44)  on 
Linmcca  stagnalis,  in  which  he  found  that  growth  began  at  a 
temperature  of  12°  C,  but  that  a  lower  temperature  retarded  or 
completely  arrested  growth,  though  not  affecting  the  life  of  the 
animal.  "If,"  says  Semper  "a  Limnaea  came  to  be  placed  in  a 
pool  or  stream  where  for  only  two  months  of  the  year  the  tempera- 
ture is  higher  than  the  minimum  (12°  C.),  growth  will  be  checked 
throughout  the  greater  part  of  the  year,  and  a  diminutive  race 
result,  since  sexual  maturity  cannot  be  reached  with  a  lower  tern- 


CAUSES    OF    DWARFING  1069 

perature."  Excessive  temperature  also  causes  dwarfing,  for  polar 
species  entering  waters  the  temperature  of  which  is  higher  than 
their  optimum  will  remain  smaller  than  normal.  Thus  northern 
species  of  Pecten  never  reach  the  same  size  in  warmer  southern 
waters.  The  same  rule  holds  for  mammals  and  birds.  The  dwarfing 
of  the  faunas  of  the  Black  and  Caspian  seas  may  be  in  part  caused 
by  the  extremes  of  temperature  in  these  waters. 

Variation  in  the  amount  of  water  supplied  likewise  affects 
the  size  of  aquatic  animals.  Thus  Semper  found,  in  experiment- 
ing with  Limncca  stagnalis,  that  "the  smaller  the  volume  of  water 
which  fell  to  the  share  of  each  animal  the  shorter  the  shell  re- 
mained." (Semper-/j4:/d7.)  With  the  same  number  of  whorls, 
the  average  length  of  shell  for  a  given  number  of  animals  in  100  c.c. 
of  water  was  J4  inch,  while  the  same  number  of  animals  in  2,000 
c.c.  of  water  had  an  average  shell  length  of  ^4  inch. 

Deep-water  individuals  are  also,  as  a  rule,  smaller  than  the 
shallow-water  forms,  various  factors,  such  as  difference  in  tempera- 
ture, density  and  salinity  of  water,  of  food  supply,  etc.,  being  op- 
erative here. 

The  dwarf  faunas  of  the  Windsor  limestone  ( Mississippi  of 
Nova  Scotia)  and  of  the  Magnesian  limestone  or  Zechstein  of 
Europe,  is  probably  due  to  several  causes,  notably  the  decrease 
in  volume  of  water  and  the  accompanying  increase  in  salinity  of 
the  water,  these  deposits  being  intercalated  between  continental 
sediments.  Similar  dwarfed  faunas  are  obtained  from  the  Cretacic 
of  New  Mexico  and  southern  Colorado.  (Stanton-49;  Shimer  and 
Blodgett-46:6>.) 

BIBLIOGRAPHY   XXIX. 

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17.  GRABAU,  A.  W.     1910.     Ueber  die  Einteilung  des  Nordamerikanischen 

Silurs.  Compte  Rendu  du  XIme  Congres  Ge"ologique  International, 
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18.  GRABAU,  A.  W.     1913.     Ancient  Delta  Deposits.     Bulletin  of  the  Geo- 

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23.  HOLLICK,   ARTHUR.     1893.     Plant  Distribution  as  a  Factor  in  the 

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Museum.  Bulletin  69,  pp.  892-920. 

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CHAPTER    XXX. 

FOSSILS,    THEIR    CHARACTER    AND    MODE    OF    PRESERVATION. 
DEFINITION  AND  LIMITATION  OF  THE  TERM  FOSSIL. 

Fossils  are  the  remains  of  animals  and  plants,  or  the  direct  evi- 
dence of  their  former  existence,  which  have  been  preserved  in 
the  rocks  of  the  earth's  crust.  By  direct  evidence  is  meant  the  im- 
pressions left  by  animals  in  transition,  the  structures  built  by  them, 
etc.  Beds  of  iron  one  and  deposits  of  apatite  or  of  crystalline 
limestone  must  be  considered  indirect  and  not  always  reliable  evi- 
dence of  the  former  existence  of  organisms,  since,  in  these  cases, 
organisms  were  only  the  agents  active  in  their  formation.  Under 
remains  preserved  in  the  earth's  crust  must  be  included  those 
formed  in  the  northern  ice  fields,  for  we  have  seen  that  these  ice 
masses  are  to  be  regarded  as  a  portion  of  the  rocky  crust  of  the 
earth,  though  in  most  respects  the  least  permanent  one. 

It  has  been  a  common  custom  to  limit  the  term  fossil  to  those 
remains  which  were  buried  prior  to  the  present  geologic  period. 
This  will  be  seen  from  the  common  text-book  definitions  of  this 
term.  A  few  of  them  may  be  quoted.  Fossils:  "All  remains  or 
traces  of  plants  and  animals  which  have  lived  before  the  beginning 
of  the  present  geological  period,  and  have  become  preserved  in 
the  rocks."  (Zittel,  Eastman's  translation.)  "Remains  of  animals 
and  plants  which  have  existed  on  the  earth  in  epochs  anterior  to 
the  present,  and  which  are  buried  in  the  crust  of  the  earth,  are 
called  fossils."  (Bernard's  Elements,  adapted  from  the  English 
translation.)  "All  the  natural  objects  which  come  to  be  studied 
by  the  palaeontologists  are  termed  'fossils'  .  .  .  Remains  of 
organisms  .  .  .  found  ...  in  those  portions  of  the  earth's 
crust  which  we  can  show  by  other  evidence  to  have  been  formed 
prior  to  the  establishment  of  the  existing  terrestrial  order  .  .  ." 
(Nicholson  and  Lydekker,  Manual  of  Palsentology.)  "Of  those 
animals  and  plants  which  have  inhabited  the  earth  in  former  times, 
certain  parts,  decomposable  with  difficulty,  or  not  at  all,  have  been 

1073 


1074  PRINCIPLES    OF    STRATIGRAPHY 

preserved  in  the  strata  of  the  earth,  and  these  we  call  fossils,  or 
petref  actions."  (Steinmann,  Einfiihrung  in  die  Palaontologie, 
translated.)  This  definition  in  terms  of  past  geologic  time  is  an 
arbitrary  one,  and  is  not  based  on  any  distinction  in  character 
between  the  remains  which  were  buried  before  and  those  which 
were  buried  during  the  present  geologic  epoch.  Thus  the  marine 
shells  in  the  post-glacial  elevated  clays  of  northern  New  England 
and  Canada  (Leda,  Saxicava,  etc.)  differ  in  no  wise  from  those 
of  the  same  species  buried  in  the  modern  deposits  off  the  present 
coast.  "In  the  former  case  the  strata  have  been  elevated  several 
hundred  feet ;  while  in  the  latter  case  they  still  retain  their  original 
position,  or,  at  least,  have  experienced  no  appreciable  disturbance. 
In  like  manner  many  of  the  Miocenic  and  Pliocenic  shells  are  not 
only  of  the  same  species  as  those  recently  buried  on  neighboring 
shores,  but  the  changes  which  they  have  undergone  since  burial  are 
frequently  not  greater  than  those  experienced  by  shells  buried  in 
modern  accumulations.  The  difference  in  the  alteration  is  merely 
one  of  degree,  and  with  proper  discrimination  specimens  can  be 
selected  which  show  all  grades  of  change,  from  the  unaltered  state 
of  shells  in  modern  mud-flats  to  the  crystalline  condition  of  an 
ancient  limestone  fossil,  in  which  the  original  structure  has  been 
completely  lost."  (Grabau-i3  :o/,  p#.)  It  is  thus  seen  that  it  is 
far  more  logical  to  extend  the  term  "fossil"  so  as  to  include  all 
remains  of  animals  and  plants  preserved  from  the  time  of  the 
earliest  fossiliferous  strata  to  the  present.  This  is  the  position 
taken  by  Lyell,  who  defines  a  fossil  as :  "Any  body  or  the  traces 
of  the  existence  of  any  body,  whether  animal  or  vegetable,  which 
has  been  buried  in  the  earth  by  natural  causes."  In  this  definition 
made  by  the  geologist  the  time  element  is  entirely  omitted  and  in 
this  respect  it  contrasts  markedly  with  the  definitions  quoted  above 
from  palaeontologists.  Of  the  latter,  however,  D'Orbigny  forms 
an  exception,  for  he  considers  the  term  "fossil"  to  comprise  "all 
bodies  or  vestiges  of  bodies  of  organisms  buried  naturally  in  the 
rocks  of  the  earth  and  found  to-day,  except  when  actually  in  the 
living  state."  (Cours  £lementaire  de  Paleontologie,  Vol.  I,  p.  13.) 
Geikie,  too,  neglects  the  time  element  in  his  definition  of  a  fossil. 
He  says :  "The  idea  of  antiquity  or  relative  date  is  not  necessarily 
involved  in  this  conception  of  the  term.  Thus,  the  bones  of  a  sheep 
buried  under  gravel  and  silt  by  a  modern  flood  and  the  obscure 
crystalline  traces  of  a  coral  in  ancient  masses  of  limestone  are 
equally  fossils."  (Text-book  of  Geology,  3d  ed.,  p.  645.)  This 
general  definition  of  a  fossil  is  the  one  insisted  upon  by  Grabau 
and  Shimer  in  "North  American  Index  Fossils"  (Volume  I,  page  i.) 


PRESERVATION    OF    FOSSILS  1075 


FOSSILIZATION. 

"Geologic  time  is  continuous,  and  the  development  of  life  is 
progressive.  No  break  divides  the  present  from  the  past,  and  the 
geologic  phenomena  of  the  present  epoch  are  controlled  by  the  same 
laws  which  governed  those  of  past  time.  Fossilization  is  a  mere 
accident  by  which  some  animals  and  plants  are  preserved,  and  it 
resolves  itself  into  a  process  of  inhumation,  neither  the  nature 
of  the  organism  nor  the  time  or  mode  of  burial  being  of  primary 
significance.  These  are  of  first  importance  in  determining  the 
degree  of  preservation  which  the  fossil  is  to  experience,  and,  conse- 
quently, the  nature  of  the  record  which  is  to  remain ;  but  they  do 
not  affect  the  process  of  fossilization,  which  is  merely  the  burial 
of  the  dead  organism.  Thus  the  idea  of  change  is  not  necessarily 
involved  in  the  concept  of  a  fossil,  although  it  is  true  that  few 
organisms  long  remain  buried  without  undergoing  some  chemical 
change.  Examples  of  the  preservation  of  organisms  in  an  almost 
unchanged  condition  are  nevertheless  known,  the  most  conspicuous 
being  the  mammoths  frozen  into  the  mud  and  ice  of  Siberia,  and 
retaining  hair,  skin,  and  flesh  intact ;  and  the  insects  and  other  ani- 
mals included  in  the  amber  of  the  Baltic,  where  they  have  remained 
unchanged  since  early  Tertiary  time.  Ordinarily,  however,  the 
flesh  of  the  buried  animal  soon  decays,  and,  consequently,  no  rec- 
ord of  the  soft  parts  is  retained.  In  plants  the  decay  is  less  rapid, 
and  the  buried  vegetable  remains  may  be  indefinitely  preserved  in 
the  form  of  carbonaceous  films. 

'The  hard  parts  of  animals  are  best  preserved  as  fossils.  Such 
are  the  shells  and  other  external  skeletal  structures  secreted  by  a 
variety  of  animals,  as  crustaceans,  molluscs,  echinoderms,  corals, 
and  so  forth ;  and  the  bones,  teeth,  and  other  hard  structures  of 
the  vertebrates.  Besides  the  actual  remains  of  animals  and  plants, 
any  evidence  of  their  existence,  which  is  preserved,  is  commonly 
included  under  the  name  of  fossil.  Thus  impressions  made  by 
living  animals  and  plants  in  the  unconsolidated  rock  material,  and 
structures  built  by  animals  from  inorganic  material,  are  fossils  if 
properly  buried.  Examples  of  the  first  are  the  footprints  of  verte- 
brates ;  the  tracks  and  trails  of  jelly-fish,  worms,  molluscs,  or 
Crustacea;  the  burrows  of  worms,  borings  of  animals  in  stones  or 
shells,  and  the  impression  made  by  sea-weeds  in  motion.  Among 
the  second  class  are  worm  tubes  built  of  sand  grains ;  foraminiferal 
shells,  built  of  foreign  particles ;  flint  implements  and  other  utensils 
of  primitive  man ;  and  the  relics  of  the  Swiss  Lake  dwellers  .  .  . 


1076  PRINCIPLES    OF    STRATIGRAPHY 

(Grabau-i3:p#,  pp.)  Here  belong,  further,  ancient  buried  cities, 
like  Pompeii;  the  Roman  coins,  weapons,  etc.,  buried  in  the  peat 
bogs  of  Flanders  and  the  north  of  France ;  and,  in  fact,  all  artificial 
productions  of  early  man  or  other  animals  which  have  been  pre- 
served. Finally,  coprolites,  or  the  characteristic  excrementa  of 
animals,  have  frequently  been  preserved,  and  these  constitute  a 
class  by  themselves.  Thus  four  distinct  types  or  classes  of  fossils 
may  be  recognized,  viz.:  (Grabau  and  Shimer-14  :j.) 

1.  Actual  remains  and  their  impressions. 

2.  Tracks,  trails,  and  burrows  of  organisms. 

3.  Artificial  structures. 

4.  Coprolites. 

These  may  now  be  discussed  more  fully. 


TYPES  OF  FOSSILS. 
I.     Actual  Remains. 

Preservation  of  Soft  Tissues.  As  has  already  been  noted,  a 
number  of  cases  are  known  where  the  fleshy  portions  of  animals 
have  been  preserved.  The  mammoth  (Elephas  primigenius) ,  and 
the  rhinoceroses  frozen  into  the  mud  and  ice  of  Siberia  are  classi- 
cal examples.  Insects,  spiders,  and  myriopods  have  been  preserved 
in  great  perfection  in  the  Oligocenic  amber  of  the  Baltic  provinces. 
This  fossil  resin  was  produced  by  a  species  of  pine  (Finns  succiui- 
fer)  and  its  quantity  was  so  great  that  the  deposits,  though  they 
have  been  worked  since  very  ancient  times,  have  not  yet  been 
exhausted. 

Remains  of  man  and  other  animals  have  been  found  perfectly 
preserved  in  peat-bogs  where  they  had  been  entombed  for  hun- 
dreds of  years.  Mummification,  or  the  preservation  of  the  flesh 
in  dried  condition,  must  also  be  noted  in  this  connection,  for  in 
this  manner  many  remains  of  the  human  period  have  been  pre- 
served. Natural  mummies  have  been  found  in  saline  soil  at  Arica 
in  Chili  (South  America),  and  they  have  also  been  found  occa- 
sionally in  dry  caverns  and  in  crypts,  notably  in  Bordeaux,  France. 
In  the  desert  region  west  of  the  Peruvian  Cordillera  in  South 
America  climatic  and  other  conditions  have  proved  particularly 
favorable  to  the  natural  preservation  of  human  remains.  "The 
tombs  and  graves  [of  the  Incas]  are  usually  found  on  elevated 
places  outside  of  the  valleys  where  the  extreme  dryness  of  the  air 


PRESERVATION    OF    SOFT   TISSUE  1077 

combines  with  the  nitrous  character  of  the  sand,  into  which  mois- 
ture has  seldom  found  its  way,  to  desiccate  and  preserve  the  bodies 
of  the  dead,  thus  mummifying  them  naturally.  The  same  factors 
have  caused  the  clothing  and  objects  placed  with  the  dead  to  be 
preserved  for  many  centuries."  (Mead-i^  :#.)  Bodies  of  animals 
have  been  similarly  mummified,  particularly  those  of  household 
pets,  such  as  dogs  and  parrots ;  and  foods,  such  as  corn  and  beans, 
have  been  perfectly  preserved.  In  the  Atacama  desert  in  Chile,  in 
the  Chuquicamata  copper  mining  district,  was  found  the  body  of  a 
miner  who  had  been  caught,  while  at  work,  by  a  cave-in  of  the  roof 
of  a  mine  in  a  side  hill.  "The  stone  and  earth  surrounding  the 
mummy  were  impregnated  with  anhydrous  sulphate  of  copper 
(brochantite),  and  sulphate  of  copper  (blue  vitriol).  This  mineral 
prevented  the  organic  matter  from  decomposition."  "The  skin 
has  not  collapsed  on  the  bones,  as  in  the  mummies  found  usually 
in  the  region,  but  the  body  and  limbs  preserve  nearly  their  natural 
form  and  proportions,  except  for  the  crushing  .  .  ."  which 
took  place  on  the  caving-in  of  the  mine.  The  age  of  the  mummy 
is  unknown,  but  it  is  probably  several  hundred  years  old,  as  indi- 
cated by  the  primitive  character  of  the  implements  embedded  with 
the  body. 

Preservation  of  animal  tissue  by  impregnation  with  mineral 
matter  also  occurs.  As  an  example  may  be  mentioned  the  well- 
preserved  body  of  a  negro  woman  which  had  been  buried  for  fifty- 
seven  years  and  was  found  near  Tuskegee,  Macon  county,  Alabama, 
in  1894.  The  body  lay  in  a  sandy  soil  where  the  water  from  a  near- 
by spring  kept  it  continually  wet.  In  this  water,  silica,  lime,  and 
magnesia  were  held  in  solution,  and  silica,  lime,  and  oxide  of  iron 
in  suspension.  About  50  per  cent,  of  the  substance  of  the  body 
had  been  replaced  by  mineral  matter.  Lead  was  also  found  present 
in  the  body  and  might  have  been  active  in  its  preservation.  (Sted- 
man-23.)  All  told,  however,  the  complete  preservation  of  the  ani- 
mal body  is  of  rare  occurrence,  and  probably  never  dates  back 
very  far  in  geologic  history.  A  remarkable  exception  to  this  rule 
is  found  in  the  muscle  fibers  of  Devonic  and  later  fish,  and  in 
Mesozoic  reptiles,  which  have  been  so  perfectly  preserved  by  a 
process  of  replacement  that  their  structure  can  readily  be  de- 
termined under  the  microscope.  These  will  be  noted  again  in 
the  discussion  of  modes  of  preservation. 

Impressions  of  the  soft  parts  in  rocks,  or  even  a  carbonaceous 
film  representing  them,  are  found  under  favorable  conditions.  The 
most  familiar  examples  of  this  kind  are  ferns  and  other  plant  re- 
mains, but  those  of  animals  are  not  unknown.  In  the  fine  litho- 


1078  PRINCIPLES    OF    STRATIGRAPHY 

graphic  lutytes  of  the  Solnhofen  district  in  Bavaria  have  been 
found  the  impressions  of  medusae  and  of  naked  cephalopods  with 
the  inkbag  still  containing  the  sepfa  in  a  solidified  state,  while  the 
beautiful  impressions  of  insect  wings  and  the  membranous  wings 
of  pterosauria  are  among  the  most  noted  preservations  obtained 
from  this  rock. 

Even  more  perfect  examples  of  the  preservation  of  soft  parts 
have  recently  been  obtained  by  Walcott  from  the  Stephen  shale 
(Cambric)  of  western  Canada  (26).  Here  worms,  holothurians, 
and  other  soft-bodied  animals  occur  in  a  wonderful  state  of  preser- 
vation, so  that,  in  many  cases,  even  the  internal  anatomy  can  be 
ascertained.  The  appendages  of  trilobites  and  other  organisms  are 
also  well  preserved.  The  rock  in  which  these  fossils  occur  is  an 
exceedingly  fine-grained  sapropellutyte.  Other  remarkable  pres- 
ervations of  soft  tissues  in  rock  of  this  type  are  known  from  the 
Lias  of  Wurttemberg,  where,  at  Holzmaden,  the  impression  of  the 
skin  of  the  Ichthyosaurians  has  been  obtained. 

Preservation  of  Hard  Structures  and  of  Petrified  Remains. 
The  hard  parts  of  animals  are  best  adapted  for  preservation.  This 
is  particularly  the  case  where  these  parts  are  either  calcareous 
or  siliceous.  Such  are  the  shells  of  Protozoa;  the  spicules  of 
sponges ;  the  coral  of  the  coral-polyps ;  the  test  of  the  echinoderm ; 
the  shell  of  brachiopod  or  mollusc;  the  calcareous  structure  of 
Bryozoa ;  the  exoskeleton  of  Crustacea ;  and  the  bones  and  teeth 
of  fishes,  amphibians,  reptiles,  birds,  and  mammals.  But  hard 
parts  of  a  purely  organic  origin  are  also  commonly  preserved. 
These  are  the  structures  composed  of  chitin  and  conchiolin.  Chit  in, 
or  entomolin,  as  it  is  also  called,  is  the  substance  of  which  the  elytra 
and  integuments  of  beetles  and  other  insects  are  composed,  and 
which,  commonly  with  an  admixture  of  calcium  carbonate  or 
phosphate,  forms  the  carpace  and  other  exoskeletal  parts  of  Crusta- 
cea, etc.  Its  composition  is  probably  expressed  by  the  formula 
C15H26N2O10.  Chitinous  structures  of  other  animals  are  the  peri- 
sarc  of  Hydrozoa  and  the  similar  network  of  horny  fibers  in  the 
Ceratospongise.  Conchiolin  is  the  organic  matter  of  shells  which, 
on  solution  of  the  lime  by  acids,  remains  as  a  soft  mass.  The 
young  shells,  particularly  the  protoconch,  consist  wholly  of  this 
material.  It  is  generally  strengthened  by  subsequent  deposition  of 
calcium  carbonate,  but  in  some  cases,  as  in  the  nautiloids,  it  seems 
to  remain  in  the  original  chitinous  condition,  and  is  occasionally 
preserved. 

These  structures,  whether  of  chitin  or  conchiolin,  are  preserved 
either  as  impressions,  or,  more  generally,  as  carbonaceous  films. 


PRESERVATION    OF    HARD    STRUCTURES       1079 

Sometimes  various  minerals,  as  pyrite,  or  chlorite,  or  even  talc, 
replace  them.  The  same  thing  may  be  said  of  the  cellulose  com- 
posing the  tissues  of  plants,  where  decomposition  is  a  slower  process 
than  in  the  fleshy  tissues  of  animals.  The  cell  structure  of  plants 
may  thus  be  conserved  for  a  long  period,  and  this  is  especially  the 
case  where  there  is  a  nearly  complete  exclusion  of  air,  as  in  fine 
sediments  or  in  peat  bogs. 

The  first  requisite  in  fossilization  is  the  burial  or  inhumation 
of  the  remains.  Even  the  hard  parts  of  animals  will  be  destroyed 
if  exposed  too  long  to  the  atmosphere.  Thus  the  bones  of  the 
American  bison,  which,  during  the  process  of  extinction  that  this 
animal  was  undergoing  on  the  western  plains,  were  abundantly 
scattered  about,  are  fast  disappearing  by  decay,  so  that  shortly 
no  traces  of  them  will  remain  except  where  they  have  been  buried. * 
This  fact  must  be  borne  in  mind  in  considering  the  remains  of 
earlier  mammals.  Those  found  can  constitute  but  a  small  portion 
of  the  skeletons  once  scattered  about  but  which  disintegrated  before 
the  slow  process  of  burial  by  continental  waste  or  by  dust  saved 
them.  The  soft  tissues  of  animals  and  the  tissues  of  plants  decay, 
of  course,  rapidly,  and  even  inhumation,  except  in  the  cases  noted 
above,  will  not  check  the  process  of  decay.  Immersion  in  water 
likewise  results  in  the  decay  of  organic  matter,  for  bacteria  here 
become  an  active  agent  in  the  dissolution  of  tissues.  Hard  struc- 
tures, such  as  shells  or  bones,  will  also  suffer  destruction  by  solu- 
tion, especially  if  the  waters  are  rich  in  carbon  dioxide.  Thus,  as 
already  noted  in  an  earlier  chapter,  the  shells  of  many  Protozoa 
are  dissolved  after  the  death  of  the  animal  before  they  settle  down 
to  the  abyssal  portions  of  the  sea,  and  hence  deposits  of  these  shells 
are  generally  absent  from  the  greater  deeps,  though  abundant  in 
regions  of  lesser  depth.  Solution  may  continue  even  after  burial 
if  the  beds  are  raised  above  the  sea-level,  and  if  they  are  per- 
meable. 

The  buried  hard  parts  of  animals  generally  undergo  a  process 
of  petrifaction,  which  most  commonly  is  either  calcification  or 
silicifi cation,  or  sometimes  the  first  followed  by  the  second,  i.  e., 
a  replacement  of  the  lime  by  silica,  or,  more  rarely,  the  reverse. 
Pyritization,  or  the  replacement  of  the  remains  by  iron  pyrites 
(or,  more  frequently,  by  marcasite)  and  replacement  by  iron  oxide, 
sphalerite,  barite,  vivianite,  glauconite,  or  other  minerals,  also 
occurs.  The  process  of  replacement  differs  in  different  groups 
of  organisms. 

*A  certain  percentage  of  these  bones,  however,  has  been  picked  up  and 
burned  for  commercial  and  other  purposes. 


io8o  PRINCIPLES   OF    STRATIGRAPHY 


Petrifaction  of  non-mineral  substances. 

(a)  Replacement  of  soft  animal  tissue.     As  stated  above,  the 
muscle  tissues  of  a  number  of  groups  of  vertebrates  have  been 
known  to  be  preserved  in  a  most  remarkable  manner.    In  the  upper 
Devonic  shales    (Cleveland   shales)    of   Ohio  the  muscular  tissue 
of  cladodont  sharks  has  been  mineralized  in  such  a  perfect  manner 
that  in  places  "they  suggest  in  color,  distinctness,  and  texture  the 
mummified  tissue  of  recent  fish."     (Dean-io:^/,/.)     Similarly,  well- 
preserved  muscular  tissue  has  been   found  in  fishes  of  the  litho- 
graphic stone   (Reis-2o,  pi.   II),  and  in  other  deposits  both  finer 
and  coarser.     The  muscular  mass  thus  preserved  is  pure  mineral, 
composed  of  about  So%-\-  of  calcium  phosphate.    Reis  holds  that  the 
muscular  tissue  was  in  a  semi-decomposed  condition,  that  minerali- 
zation took  place  quickly,  and  that  the  remains  must  have  been  so 
effectively  enclosed  that   decomposition  was  checked.     The  phos- 
phate, he  thinks,  is  derived  from  the  body  of  the  animal  and  precipi- 
tated on  contact  of  the  decomposing  material  with  the  calcium  car- 
bonate of  the  surrounding   sediment.     Dean,   on   the  other  hand, 
favors  the  view  that  the  phosphate  was  deposited  from  solution 
within  the  undecomposed  tissue  of  the  shark,  which  thus  became 
mineralized  before  it  had  time  to  decompose.     The  partial  replace- 
ment of  human  bodies  mentioned  above  is  analogous  to  the  more 
ancient  case  here  cited. 

(b)  Petrification  of  plants.    ( Roth-22  -.605. )     Aside  from  the 
unicellular  diatoms,  in  which  the  cell  walls  of  the  living  plant  are 
impregnated  with  amorphous  silica,  and  the  unicellular  to  multi- 
cellular  lime-secreting  algae,  the  tissues  of  plants  may  in  general 
be  regarded  as  free  from  mineral  matter.     But  plants  immersed  in 
mineral  waters,  or  buried  where  such  waters  have  free  access,  are 
saturated   and   completely   impregnated   with   the   mineral   matter. 
Colloidal  silica  is  most  favorable  for  the  preservation  of  the  delicate 
cell  structures,  while  calcite  or  other  minerals  of  high  crystallizing 
power  will  cause  deformation  if  not  disruption  and  complete  de- 
struction of  the  cell  walls. 

A  mass  of  wood  completely  penetrated  by  and  saturated  with 
silica  still  shows  its  original  form  and  structure,  even  to  the  orna- 
mentation of  the  cell  walls,  which,  in  a  properly  prepared  slide,  will 
not  appear  very  different  from  the  fresh  or  dried  tissues.  Even 
in  appearance  the  impregnated  wood  resembles  the  unaltered  wood, 
being-  fibrous  and  splintery,  and  the  change  is  often  noticeable  only 
from  the  difference  in  weight  and  hardness.  The  silica  of  wood 


PETRIFACTION    OF    PLANTS  1081 

thus  saturated  may  be  dissolved  in  concentrated  hydrofluoric  acid, 
when  the  woody  tissue  will  be  left  behind  unattacked.  This  shows, 
according  to  Goppert,  a  cellular  structure  which  in  most  cases 
is  sufficient  for  the  generic  determination  of  the  wood. 

Replacement  of  the  cell  walls  themselves  generally  follows 
impregnation,  and  thus  the  wood  becomes  wholly  changed  to  silica. 
Under  these  circumstances  the  finer  structure  is  often  destroyed 
and  the  mass  becomes  uniform  and  breaks  with  a  conchoidal  frac- 
ture. Illustrations  of  this  are  found  in  the  brilliantly  colored, 
agatized  woods  of  Arizona,  fragments  of  which  are  hardly  dis- 
tinguishable from  agates  of  wholly  inorganic  origin. 

Opalized  woods  are  not  uncommon.  Here,  as  in  the  case  of 
woods  replaced  by  quartz,  the  structure  of  the  wood  is  generally 
retained,  and  in  some  cases  the  interior  has  been  found  to  be  but 
slightly  impregnated  with  the  opal,  or  even  to  be  unaltered  wood, 
thus  showing  the  progress  of  opalization  from  without  inward. 
(Blum-4:/p7.) 

Calcified  woods  are  not  uncommon,  occurring  in  all  formations, 
from  the  Devonic  up.  They  have  been  found  in  limestones,  sand- 
stones, shales,  basaltic  conglomerates,  volcanic  ashes  and  tuffs,  and 
other  deposits.  Daubree  found  at  Bourbonne-les-Bains,  in  the  de- 
partment of  Haute-Marne,  France,  piles  of  red  beechwood,  in 
places  so  completely  impregnated  with  transparent  calcium  car- 
bonate that  on  solution  in  hydrochloric  acid  only  3.1  per  cent,  of 
insoluble  matter,  showing  plant  structure,  remained.  The  piles 
supported  an  ancient  Roman  canal,  and  when  found  were  buried 
about  8  meters  below  the  surface. 

Aragonite  is  also  known  to  have  replaced  wood.  Even  gypsum 
has  been  found  replacing  wood  in  some  Tertiary  beds,  and  phosphate, 
as  well  as  fluorite  of  lime,  is  likewise  known  in  this  connection. 
Barite  also  has  replaced  wood  in  some  limestones  of  the  Lias,  and 
a  talc-like,  complex  silicate,  probably  pyrophyllite,  has  been  found 
replacing  fronds  of  Neuropteris  and  Pecopteris  and  the  leaves  of 
Annularia  in  Carbonic  rocks  in  the  Piedmont  district.  Chlorite  has 
been  found  occurring  in  a  similar  manner.  So  delicate  is  the  replace- 
ment that  the  venation  is  easily  recognizable,  although  no  part  of  the 
original  organic  matter  remains.  Wood  largely  replaced  by  sulphur 
and  devoid  of  structure  has  been  found  in  Cesena,  Italy,  and 
plant  remains  replaced  by  sulphur  have  also  been  obtained  from 
the  Tertiary  beds  of  Aragon.  (Blum-7  ://o.) 

In  the  Carbonic  and  later  coal-bearing  horizons  wood  replaced 
by  siderite,  often  with  considerable  iron  oxide,  or  wholly  by  limonite 
or  hematite,  is  not  uncommon  in  various  parts  of  the  earth;  while 


io82  PRINCIPLES    OF    STRATIGRAPHY 

sphalerite,  galenite,  and  marcasite  are  also  known.  Galenite  has 
been  reported  as  replacing  the  fronds  of  ferns  in  some  Coal  Meas- 
ures of  Saxony.  Malachite,  azurite,  and  chalcocite  are  found  in 
carboniferous  marls,  probably  of  Jurassic  age,  in  the  district  of  An- 
gola, West  Africa,  in  the  Urals,  and  in  other  regions.  Even  mod- 
ern cedar  wood  has  been  found  coated  with  and,  in  some  cases, 
largely  replaced  by  malachite,  as  reported  by  Dr.  A.  F.  Rogers 
from  Brigham,  Utah  (21).  From  a  tuff  bed  enclosed  between 
basaltic  flows  below  the  Limburg  (Germany)  wood  of  Primus 
nadus  (?)  replaced  by  a  kaolin-like  substance  has  been  obtained  in 
abundance.  This  still  retains  the  structure  and  occasionally  car- 
bonaceous remnants  of  the  wood  occur. 

Where  the  actual  plant  remains  have  been  removed  by  decay  an 
impression  or  mold  often  remains,  in  which  a  cast  of  the  plant  may 
be  formed  by  infiltrating  foreign  material.  Such  casts  are  common 
in  the  Carbonic  sandstones  of  the  Joggins  region  of  Nova  Scotia, 
in  western  Scotland  and  elsewhere.  Trunks  of  Calamites,  Sigillaria 
and  Lepidodendra,  together  with  their  rootstalks,  Stigmaria,  are 
abundant  in  these  strata  as  sandstone  casts,  resulting  from  the  filling 
of  the  cavities  left  by  the  decaying  wood. 

Decaying  wood  or  other  delicate  parts  of  plants  may  leave  a 
record  behind  in  the  rocks  in  the  form  of  a  film  of  colored  mineral 
matter,  precipitated  by  the  decaying  organic  matter,  or  by  the  re- 
moval of  the  coloring  matter  of  that  portion  of  the  rock  covered 
by  the  decaying  plant.  This  process  of  self-inscription  upon  the 
rock  by  the  plant  has  been  termed  autophytography  (White-28), 
the  first  mode  producing  a  positive  picture,  and  the  second  a  nega- 
tive one. 

Petrifaction  of  mineral  structures. 

(a)  Protozoa.     The  shell  of  the  Foraminifera  is  typically  com- 
posed of  carbonate  of  lime,  either  in  the  form  of  calcite  (vitreous 
species)    or   of    aragonite    (porcellaneous   species).     The    skeletal 
structures  of  Radiolaria  are  mainly  of  silica,  though  horny  types    (of 
acanthin)  also  occur.    Both  types  of  Protozoa  are  well  adapted  for 
preservation  and  extensive  deposits  of  them  are  known,  such  as  the 
Radiolarian  beds  of  Barbados  (Miocenic)  and  the  chalk  of  west- 
ern Europe  (Cretacic). 

(b)  Sponges  and  hydrozoans.     These  organisms  are  generally 
capable  of  preservation  on  account  of  the  chitinous  material  which 
composes  the  network  of  many  sponges  and  forms  the  perisarc  of 
the  Hydrozoa.    They  are  most  commonly  preserved  as  carbonaceous 


PETRIFACTION    OF    INVERTEBRATES  1083 

films,  but  cases  of  pyritization  among  the  graptolites  are  not  un- 
common. Such  pyritized  specimens  stand  out  in  relief  and  afford 
good  material  for  sectioning.  (Wiman-27.)  Pyrophyllite  also 
has  been  found  replacing  these  organisms,  which  thus  became  out- 
lined in  white  on  the  dark  shales  in  which  they  occurred.  (Blum-5  : 


In  a  considerable  number  of  sponges  siliceous  or  calcareous 
spicules  occur,  frequently  uniting  into  a  solid  network,  and  then 
preserving  the  form  of  the  sponge.  The  siliceous  spicules  of 
sponges  are  sometimes  replaced  by  calcite  in  the  process  of  fossili- 
zation. 

(c)  Silicification  of  corals.     Most  corals  are  composed  of  cal- 
cium carbonate  in  the   form  of  aragonite,  with  the   exception  of 
the  Alcyonaria,  which  are  calcite.     Often  a  small  percentage  of 
magnesium  carbonate  is  present.     The  structure  of  the  corals  is 
frequently  very  porous,  but   it  is  most  probable  that  these  pores 
are  first  filled  by  calcium  carbonate,  and  that  silicification  is  a  proc- 
ess of  replacement  pure  and  simple.     While  silicified  corals  pre- 
serve the   form  well,  the  finer  structure   is  commonly   destroyed. 
The  ringed  structure,  known  as  Beekite  rings  and  more  fully  de- 
scribed  under   the   section   on   molluscan   shells,   occurs   rarely   in 
corals;  the  rings  seldom  occur  so  abundantly  or  of  such  size  as  in 
molluscs  or  brachiopods.     Corals  are  occasionally  replaced  by  other 
minerals,  sphalerite  having  been  most  frequently  observed. 

(d)  The  brachiopod  shell.    In  a  number  of  inarticulate  brachio- 
pods the  shell  consists  chiefly  of  chitin,  and  here  the  preservation  is 
similar  to  that  of  other  chitinous  structures.     In  Lingula,  alter- 
nating layers  of  chitinous  and  calcareous  matter  make  up  the  shell, 
but  in  the  majority  of  species  the  shell  is  wholly  composed  of  cal- 
cium carbonate.     This   is   present   in   the   form   of   calcite.     The 
greater  portion  of  the  shell  is  composed  of  a  layer  of  fibers  or 
prisms  of  calcic  carbonate  which  constitutes  the  inner  layer  of  the 
shell.     Outside  of  this  is  a  thin  lamellar  layer  of  calcic  carbonate, 
covered  in  turn  by  the  periostracum.  or  outer  corneous  film.     In 
a  large  number  of  species  the  shell  is  traversed  by  vertical  canals 
or  tubules   which   expand  upward   and   terminate   in   the   lamellar 
layer,  not  piercing  the  periostracum. 

Calcification  and  silicification  occur  in  the  brachiopods  as  in 
the  mollusc  shells,  the  tubules,  when  present,  forming  additional 
spaces  for  the  infiltration  of  lime  or  silica.  Details  will  be  men- 
tioned in  the  description  of  molluscs.  Nearly  all  the  minerals  men- 
tioned under  molluscs  have  been  found  replacing  brachiopod  shells  ; 
i.  e.,  pyrite,  galenite,  sphalerite,  the  various  iron  oxides,  barite,  etc. 


1084  PRINCIPLES    OF    STRATIGRAPHY 

(e)  Shells  of  molluscs.  These  are  composed  of  calcareous  salts, 
either  carbonate  of  lime  or.  mixed  carbonate  and  phosphate  of 
lime,  penetrated  and  bound  together  by  an  organic  network  of  con- 
chiolin.  In  the  Pelecypoda  the  shell  consists  of  three  layers :  ( i ) 
the  outer  or  periostracum,  a  horny  integument  without  lime;  (2) 
the  middle  prismatic  or  porcelaneous  layer,  consisting  of  slender 
prisms  perpendicular  to  the  surface  and  closely  crowded;  and  (3) 
the  inner  or  nacreous  layer,  which  has  a  finely  lamellate  structure 
parallel  to  the  shell  surface.  Many  pelecypod  shells  consist  en- 
tirely of  aragonite.  In  Ostrea  and  Pecten  the  whole  shell  is  cal- 
cite,  while  in  some  others  (Pinna,  Mytilus,  Spondylus,  etc.)  the 
nacreous  layer  is  aragonite,  while  the  prismatic  layer  is  calcite. 
In  the  gastropod  and  cephalopod  shell  the  inner  or  nacreous  layer  is 
often  wanting,  while  the  periostracum  is  generally  present.  The 
structure  of  the  middle  layer  differs  much  from  that  of  the  pele- 
cypods.  The  shells  are  mostly  aragonite,  except  those  of  a  few 
gastropods  (Scalaria  and  some  species  of  Fusus)  and  a  few 
cephalopods  (e.  g.,  the  guard  of  Belemnites),  which  are  of  calcite. 

The  first  process  of  alteration  in  the  shells  is  the  removal  by 
decay  of  the  horny  periostracum  covering  the  shell  and  of  the 
conchiolin  which  penetrates  the  calcareous  mass.  As  a  result  the 
shell  is  rendered  porous,  which  can  be  proved  by  applying  it  to  the 
tongue,  when  it  will  be  found  to  be  adhesive.  This  porous  condition 
may  be  observed  in  many  Miocenic  and  later  shells.  The  aspect 
of  a  shell  which  has  thus  undergone  the  first  change  is  more  or  less 
chalky,  instead  of  firm  and  often  shiny,  as  in  the  fresh  shell.  Fre- 
quently shells  composed  of  aragonite  are  entirely  destroyed,  while 
in  those  in  which  both  calcite  and  aragonite  occur  the  latter  is  dis- 
solved away  while  the  calcite  remains  unimpaired.  Water  carrying 
salts  in  solution  will  enter  the  pores  and  there  deposit  its  mineral 
matter,  until  the  pores  are  filled.  If  the  matter  in  solution  is  car- 
bonate of  lime,  this  process  of  infiltration  will  result  in  the  complete 
calcification  of  the  shell,  whereby  the  finest  structural  details  will 
be  fully  preserved.  Those  portions  of  the  shell  which  originally 
were  aragonite  may  be  changed  to  calcite.  In  some  cases,  however, 
the  whole  shell  is  converted  into  crystalline  calcite,  and  then  the 
finer  structure  is  destroyed.  At  other  times  granular  limestone  re- 
places the  shells.  If,  however,  the  infiltrating  substance  is  silica, 
the  process  of  fossilization  does  not  stop  with  the  filling  of  the 
pores,  but  from  the  greater  insolubility  of  the  silica  it  becomes  the 
dominating  substance  and  gradually  replaces  the  more  soluble  lime. 
This  process  is  frequently  most  active  around  certain  centers,  and 
is  then  indicated  by  the  formation  of  concentric  rings  of  silica 


PETRIFACTION    OF    MOLLUSC    SHELL          1085 

(Kieselringchen),  which  have  been  named  beekite  rings,  after  Dr. 
Bee'k,  sometime  Dean  of  Bristol,  who  first  called  attention  to  them. 
These  rings  often  form  a  regular  ornamentation  of  the  surface  of 
shells  and  have  been  mistaken  for  original  features.  According  to 
T.  M.  McKenny  Hughes  (15:^5  ct  scq.},  these  rings  form  in  a 
layer  */$  to  j4-inch  thick,  just  beneath  the  outside  film  of  lime. 
Blum  (4:190)  records  cases  where  the  calcium  carbonate  of  the 
shell  is  still  largely  retained,  while  at  many  places  single  tubercles 
of  silica  project,  surrounded  each  by  one  or  two  rings,  but  seldom 
more.  This  was  especially  noted  in  brachiopods.  In  some  cases 
the  shell  was  changed  to  chert  with  only  scattered  rings.  A  shell  of 
Or  this  rectangular  is  from  the  Carbonic  limestone  was  wholly  silici- 
fied,  the  silica  appearing  in  the  form  of  small  spheres  which  are 
arranged  in  place  of  the  former  radial  striations  of  the  shell.  A 
shell  of  Gryphsea  contained  several  layers  of  silica  in.  the  form  of 
beekite  rings.  A  Plicatula  armata  had  its  inner  surface  preserved 
in  compact  yellowish-brown  chert;  while  its  outer  surface,  with 
all  its  original  roughnesses,  was  composed  of  beekite  rings.  Pecten 
vagans  showed  the  reverse,  with  a  layer  of  stalactitic  quartz  be- 
tween the  two  layers.  Area  had  both  outer  and  inner  surfaces  made 
up  of  beekite  rings,  while  between  these  layers  appeared  a  porous 
mass  of  chert.  A  specimen  of  Exogyra  reniforniis  from  the  Oxford 
Oolite  was  replaced  by  beekite  rings,  while  Trigonia  costata,  to 
which  it  adhered,  was  replaced  by  chert  only.  Belemnite  guards 
had  their  surfaces  covered  with  beekite  rings,  while  the  interior 
was  still  fibrous  calcite.  Others  had  been  changed  entirely  to 
beekite.  The  rings  here  had  become  concentric  cylinders,  the  axes 
of  which  coincided  with  the  original  calcite  fibers.  In  other  cases 
the  guard  was  composed  of  a  number  of  concentric  layers  or  fun- 
nels, each  of  which  was  composed  of  beekite  rings. 

So  far  as  present  observation  goes,  there  seems  to  be  no  in- 
herent character  within  the  organism  or  the  formation  within  which 
it  is  embedded  which  determines  whether  silicification  is  to  be  ac- 
companied by  the  formation  of  beekite  rings  or  not.  Both  cases 
have  been  found  within  the  same  formation  at  the  same  locality  and 
within  the  same  genus. 

Silicified  shells  are  among  the  most  acceptable  fossils,  for  they 
will  readily  weather  out  in  relief  or  even  become  entirely  free,  or 
they  may  also  be  easily  separated  from  the  enclosing  matrix  by 
the  use  of  weak  acid. 

A  great  variety  of  minerals  besides  silica  replaces  the  calcium 
salts  of  mollusc  shells.  The  chambers  of  ammonites  often  con- 
tain ankerite  (Quenstedt),  others  again  are  chiefly  filled  by  stron- 


io86  PRINCIPLES    OF    STRATIGRAPHY 

tianite  (Sandberger).  In  the  Zechstein  of  Altenburg  shells  of 
Schizodus  have  been  found  replaced  by  malachite,  which  fills  the 
space  between  external  and  internal  mold.  Gypsum  has  also  oc- 
casionally served  as  replacing  substance  of  pelecypods  and  gastro- 
pods. Barite  is  not  an  uncommon  replacing  agent  of  molluscan  as 
well  as  brachiopod  shells  and  other  hard  structures.  In  the  Lias 
of  Whitby,  England,  the  ammonites  are  commonly  replaced  by 
barite,  colored  brownish  by  bituminous  matter.  Celestite  or  angle- 
site  more  rarely  takes  the  place  of  barite.  Vivianite  not  uncom- 
monly replaces  the  guards  of  Belemnites  in  the  New  Jersey  Creta- 
cic,  as  well  as  shells  of  other  molluscs.  Even  wulfenite  has  been  re- 
corded as  replacing  the  shell  of  an  Isocardia.  Iron  pyrite  or  marca- 
site  is  a  common  replacing  agent  of  mollusc  shells,  especially  those  of 
ammonites.  This  substance  often  becomes  altered  to  limonite,  and 
not  infrequently  disintegrates  altogether,  where  not  protected  from 
the  air;  and  thus  beautiful  fossils  are  destroyed.  Blum  records  the 
case  of  an  Avicula  in  which  the  outer  surface  was  pyrites  and 
the  inner  calcite.  Sphalerite,  and,  rarely,  smithsonite,  galenite,  and 
other  metallic  salts,  replace  the  shells  of  pelecypods  and  gastropods 
and,  more  rarely,  of  cephalopods.  In  the  Cote-d'Or,  a  Liassic 
pelecypod  has  been  found  completely  replaced  by  specular  hema- 
tite, while  ordinary  red  hematite  is  not  infrequently  found  replacing 
mollusc  shells.  Chlorite  has  been  found  replacing  shells  in  several 
cases.  In  the  Tertiary  beds  of  Aragon,  Spain,  Planorbis  has  been 
found  replaced  by  native  sulphur  (Blum-?:///,  if 6)  ;  and  Tertiary 
Helix  from  near  Madrid  has  been  reported  replaced  by  meerschaum 
or  sepiolite. 

(f)  Crustaceans,  Merostomes,  Insects,  etc.     As  has  been  noted 
above,  the  exoskeleton  of  Crustacea  is  composed  of  chitin  impreg- 
nated with  calcium  carbonate  and  phosphate.    Sometimes  the  chitin 
carbonizes  and  a  black  mass  of  carbon  mixed  with  lime  remains, 
which  is  susceptible  of  a  high  polish.    Again,  the  organic  matter  may 
be  entirely  removed  and  replaced  by  calcium  carbonate  or  other  min- 
erals.     Thus    trilobite    tests    are    sometimes    changed    entirely    to 
crystalline  calcite.    Pyrite  not  infrequently  replaces  the  tests  of  tri- 
lobites,  as  in  the  famous  specimens  of  Triarthrus  becki  from  near 
Rome,  New  York,  discovered  by  Valient,  in  which  Matthew  and 
Beecher  have  found  the  antennae  and  legs  beautifully  preserved,  the 
whole  test  having  become  pyritized.     The  exoskeletons  of  mero- 
stomes  correspond  closely  to  those  of  Crustaceans.    The  insect  body 
is  rarely  preserved,  except  the  wings  and  the  elytra  of  beetles,  owing 
to  the  absence  of  mineral  matter. 

(g)  Echinoderms.   This  class  of  animals  is  characterized  by  the 


PETRIFACTION    OF    ECHINODERMS  1087 

possession  of  calcareous  dermal  plates  wholly  composed  of  calcite, 
which  in  many  groups  form  a  solid  test  or  enclosure  for  the  main 
mass  of  viscera  within.  The  plates  are  not  firmly  united  with  each 
other,  but  they  have  the  power  to  grow  and  change  form  during 
the  life  of  the  individual.  A  characteristic  feature  of  all  the  skele- 
tal parts  is  their  extreme  porosity.  This  is  true  of  the  test  and 
the  spines  of  the  sea-urchin  as  well  as  of  the  calyx,  arms,  and 
stem  of  the.crinoids.  The  porosity  shows  in  section,  and  it  is  also 
indicated  by  the  fact  that  the  specific  gravity  of  a  recent  Cidaris 
spine,  with  its  pores  unfilled  by  water,  is  only  1.46,  while  the  com- 
pletely calcified  spine  has  a  specific  gravity  of  2.7.  The  hollow 
spaces  constitute  about  43  per  cent,  of  the  spine.  (Haidinger, 
Blum-4:/di.)  During  the  life  of  the  animal  the  pores  in  the  cal- 
careous tissue  are  occupied  by  organic  matter  (chitin),  which  is 
removed  by  decay  after  death.  Furthermore  (Haidinger),  each 
skeletal  element  of  the  echinoderm  test  is  composed  of  an  individual 
crystal,  the  crystalline  axis  of  which  is  coincident  with  the  organic 
axis;  and  the  new  lime  which  fills  the  pores  crystallizes  in  con- 
tinuity with  the  calcite  of  the  original  structures.  As  a  result,  per- 
fect cleavage  is  obtained  in  the  skeletal  parts,  each  plate  or  spine 
having  virtually  become  a  perfectly  cleaving  calcite  fragment.  The 
axis  of  the  crystal  coincides  with  the  organic  axis  of  the  part. 
(Hessel,  Blum.)  In  crinoid  stems  the  cleavage  often  shows  a  rota- 
tion of  axis  in  the  successive  joints,  so  that  corresponding  cleavage 
planes  make  an  angle  with  each  other.  (Blum-4:/<5i.)  Accord- 
ing to  investigations  carried  on  by  Dr.  A.  F.  Rogers  (21)  the 
twisting  is  sometimes  such  as  to  place  the  crystals  composing  the 
successive  joints  into  a  twinning  position.  At  other  times  it  is  ir- 
regular, and  again  in  some  species  there  is  no  twisting  at  all. 

Silicification  of  echinoderms  occurs  more  rarely.  When  it  does 
occur,  beekite  rings,  while  present,  are  often  less  pronounced  and 
abundant  than  in  molluscs  or  brachiopods.  (Blum-4:/p^.) 

Pyrites  occasionally  replaces  echinoderm  structures.  Thus  pyr- 
itized  crinoid  stems  are  not  uncommon  in  some  formations.  Pyri- 
tized  spines  of  Cidaris  have  been  recorded  from  the  Oolite  of  Helgo- 
land. (Blum-4:^o^.) 

Entire  specimens  of  Liassic  Pentacrinites  are  found  in  the  sa- 
propellutytes  of  Holzmaden,  Wiirttemberg,  replaced  by  iron  di- 
sulphide. 

Cerussite  (lead  carbonate)  has  been  found  as  a  frequent  re- 
placing agent  of  crinoid  remains  in  the  lead-bearing  formations  of 
the  department  of  Kielce,  southwestern  Russia.  These  replaced 
remains  commonly  have  the  aspect  of  crystals  of  this  mineral,  with 


io88  PRINCIPLES    OF    STRATIGRAPHY 

which  they  occur  loose  in  the  gange  of  the  ore-beds.  (Blum- 
4:209.) 

(h)  Vertebrates.  The  bones  of  vertebrates  contain  much  cal- 
cium phosphate  with  the  calcium  carbonate,  the  whole  being  bound 
together  by  the  organic  ossein,  or  bone-cartilage.  According  to 
Berzelius,  the  bones  of  mammals  consist  of:  bone  cartilage  32.17 
per  cent. ;  ducts  1.13  per  cent. ;  basic  phosphate  of  lime  with  a  trace 
of  fluoride  of  calcium,  54.04  per  cent. :  carbonate  of  lime,  11.30  per 
cent.;  phosphate  of  magnesia,  1.16  per  cent.;  and  carbonate  of 
sodium  with  a  trace  of  the  chloride,  1.20  per  cent.  The  organic 
substance  is  replaced  by  the  mineralizer,  which  is  commonly  calcium 
carbonate.  Sometimes  complete  crystallization  takes  place.  Among 
the  bones  found  in  the  gypsum  beds  of  the  Paris  basin  and  other 
regions  many  had  been  more  or  less  impregnated  with  gypsum. 

Pyritized  skeletons  of  Ichthyosaurs,  Plesiosaurs  and  other  rep- 
tiles, as  well  as  higher  types,  are  common.  Where  marcasite  is  the 
replacing  agent  decomposition  readily  sets  in  and,  if  the  matrix 
is  a  clay  slate  (argillutyte),  alum  efflorescence  marks  the  progress 
of  this  decay. 

Chalcopyrite  is  common  as  a  coating  of  fish  remains  in  Thur- 
ingia  and  Hessia,  though  seldom  wholly  replacing  them.  Bornite 
occasionally  performs  the  same  office.  Native  copper  sometimes 
results  from  the  alteration  of  these  coatings.  Cinnabar  sometimes 
occurs  in  the  same  manner  as  the  copper  ores,  seldom  completely 
replacing  the  fish  remains. 

The  teeth  of  mammals  are  rich  in  phosphate  of  lime,  60  per 
cent,  or  more  of  this  salt  being  present.  To  the  large  proportion 
of  this  substance  the  durability  of  the  teeth  is  attributable,  they 
being  among  the  most  frequently  preserved  parts  of  mammals.  The 
enamel  of  the  teeth  contains  a  somewhat  larger  percentage  of  phos- 
phate of  lime  than  the  dentine,  a  difference  which  is  expressed  in 
the  diverse  degrees  of  preservation  of  these  parts.  (D'Orbigny- 

n:57.) 

Eggs  of  vertebrates  have  not  infrequently  been  found  well 
preserved.  Examples  are:  the  eggs  of  the  Moas  of  New  Zealand, 
Chelonian  eggs  from  the  Tertiary  of  Auvergne,  France,  in  which 
the  shell  was  filled  with  mud  which  subsequently  hardened ;  the 
Miocenic  egg  from  South  Dakota  described  by  Farrington  (12), 
which  was  completely  silicified,  and  the  fossil  egg  of  Quaternary 
age  from  Arizona,  described  by  Morgan  and  Tallmon  (18),  in 
which  the  shell  is  perfectly  preserved,  showing  the  same  structure 
found  in  modern  hen's  eggs,  the  shell  agreeing  in  composition 
with  that  of  the  egg  of  the  wild  goose.  The  interior  with  the 


SPECIAL    MODES    OF    PRESERVATION          1089 

exception  of  a  small  space  near  the  periphery  was  rilled  solidly 
with  a  beautiful  crystalline  mass  of  the  mineral  colemanite.  "In 
several  places  next  the  shell  a  semi-fluid  layer  of  bitumen  occurs, 
which  probably  represents  the  original  organic  matter  within  the 
shell." 

Excessive  silicification. 

In  some  cases,  notably  in  the  Carbonic  strata  of  the  Mississippi 
Valley  region,  it  has  happened  that  silica  has  been  deposited  to 
excess  in  crinoids,  shells  or  corals,  with  the  result  that  the  original 
form  has  been  wholly  destroyed,  the  fossil  at  the  same  time  swell- 
ing out  enormously.  This  excessive  deposition  goes  on  more  par- 
ticularly along  lines  of  fracture,  or,  as  in  the  crinoid  calices, 
between  the  component  plates.  These  become  more  and  more 
separated  as  the  deposition  of  silica  goes  on,  and  they  also  become 
sunken  below  the  level  of  the  network  of  silica.  Eventually  they 
are  probably  buried  in  the  accumulation  of  silica  which  closes  over 
them.  Thus  from  a  small  fossil  in  which  all  the  plates  are  discerni- 
ble, a  large  mass  of  structureless  silica  is  formed,  which  seldom 
gives  a  clue  to  its  origin.  (Bassler-i.) 

Molds  and  Casts.  Whenever  organisms  are  buried  in  material  of 
sufficient  plasticity  to  adapt  itself  to  the  contours  of  the  buried 
bodies,  molds  of  the  exteriors  of  these  bodies  will  be  made.  Such 
molds  may  be  temporary  or  they  may  be  persistent  ones.  Lutace- 
ous  material  generally  furnishes  the  most  perfect  molds.  Even  soft 
tissues,  when  encased  in  a  matrix  which  solidifies  rapidly  enough, 
may  leave  a  mold  behind  after  decay.  Thus  the  bodies  of  human 
beings  buried  in  the  volcanic  mud  which  overwhelmed  Herculaneum 
and  Pompeii  left  behind  a  perfect  mold  of  their  exterior.  Again, 
the  calcareous  tufa,  forming  constantly  in  many  portions  of  the 
earth,  encloses  leaves,  mosses,  or  even  fish  and  other  animals  and 
covers  them  with  a  crust  of  lime.  On  the  subsequent  decay  of 
the  enclosed  body  a  perfect  mold  of  its  exterior  is  commonly  pre- 
served from  which  an  artificial  cast  could  be  made.  Viscous  lava 
also  may  flow  around  and  enclose  a  foreign  body,  which,  if  it  is 
able  to  withstand  the  heat  of  the  molten  mass,  may  leave  a  distinct 
mold  or  impression.  Impressions  of  medusae  are  known  from  the 
Cambric  of  the  southeastern  United  States  (Walcott-25).  When 
two  valves  of  a  bivalve  mollusc  become  buried  in  juxtaposition,  the 
space  between  them  is  filled  with  mud  and  thus  an  internal  mold 
is  produced.  The  same  occurs  in  gastropods,  in  cephalopods  and 
in  other  shelled  animals,  and  may  also  be  found  in  trilobites  and 


1090  PRINCIPLES    OF    STRATIGRAPHY 

other  Crustacea.  This  mold  of  the  interior  is  commonly  spoken 
of  as  a  "cast,"  which  is  wholly  erroneous,  since  the  cast  reproduces 
the  original  in  a  new  substance,  whereas  the  mold  is  a  reverse 
copy.  Between  the  external  and  internal  mold  a  cast  may  be  formed 
by  infiltration  of  mineral  matter  or  by  artificial  means.  Not  un- 
commonly the  removal  of  the  shell  by  solution  is  followed  by  a 
closing  of  the  cavity  between  the  external  and  internal  mold,  owing 
to  the  pressure  to  which  the  enclosing  rocks  are  constantly  subjected. 
In  such  cases,  the  more  strongly  marked  surface  features  will  be 
impressed  upon  the  smoother  surface,  or,  in  general,  the  features 
of  the  exterior  will  be  impressed  on  the  mold  of  the  interior,  which 
thus  shows  the  normal  external  features,  though  weakened,  to- 
gether with  a  reversed  impression  of  the  interior.  This,  as  shown 
by  J.  B.  Woodworth,  is  illustrated  by  many  Palaeozoic  mussels, 
which  are  represented  by  internal  molds  (Steinkerne).  These  show 
the  lines  of  growth  and  other  features  of  the  exterior  of  the  shell, 
and,  on  the  same  specimen,  may  be  seen  the  mold  of  the  scars  mark- 
ing the  former  attachment  of  the  mussel. 

In  the  Tampa  beds  of  Florida  natural  casts  of  corals  occur. 
The  original  corals  have  been  removed  by  solution,  but  have  left 
behind  hollow  molds  in  which  afterward  geodes  of  chalcedony  were 
formed,  the  exterior  of  which  accurately  reproduces  in  silica 
the  form  of  the  corals.  On  the  whole,  while  natural  molds — both 
external  and  internal — are  common,  and  characteristic  of  nearly 
all  porous  rocks,  natural  casts  are  correspondingly  rare.  It  should, 
however,  be  noted  that  pseudomorphs  are  closely  akin  to  casts  as 
here  defined,  since  in  them  the  replacement  is  pari  passu  with  the 
removal  of  the  original  substance  of  the  shell  or  other  hard  struc- 
ture, while  in  normal  casts  complete  removal  of  the  original  sub- 
stance precedes  deposition  of  the  new  material. 


2.     Tracks,  Trails  and  Burrows  of  Animals. 

Tracks.  These  are  made  by  vertebrates  walking  or  hopping 
along  the  soft  sand  or  mud,  which  will  register  their  footprints. 
If  the  mud  is  very  soft  the  footprint  will  be  closed  again  by  the 
flowage  of  the  mud,  but,  if  it  is  viscous,  or  so  nearly  dry  as  to 
remain  permanent,  the  footprints  may  readily  be  preserved.  Nu- 
merous reptilian  footprints  are  known  from  the  Newark  sandstones 
of  the  Connecticut  Valley  and  the  related  district  of  New  Jersey. 
Lull  (16)  believes  that  these  may  have  been  partially  hardened  by 
the  heat  of  an  underlying  lava  sheet,  which  was  only  recently 


TRACKS,    TRAILS    AND    BURROWS  1091 

covered  by  sediments  and  had  not  yet  cooled  completely.  This  is 
not  necessary,  however,  since,  as  shown  in  an  earlier  chapter,  foot- 
prints may  be  preserved  for  a  long  period  by  mere  drying  of  the 
mud.  Even  the  delicate  impressions  of  the  web  membranes  of 
the  foot  were  frequently  preserved,  which  seems  to  indicate  that 
the  arenaceous  mud  must  have  been  fairly  hard  and  resistant 
before  the  next  layer  of  sand  was  spread  over  it.  This  later  layer 
on  its  under  side  furnishes  accurate  impressions  in  relief  of  the 
footprint,  which,  though  rudely  reproducing  the  form  of  the  foot 
which  made  the  impression,  reproduces  the  impression  in  reverse. 
Since  the  original  fossil  is  the  impression  (of  which  there  may  be 
many  made  by  one  individual)  and  not  the  animal's  foot,  the  relief 
impression  of  it  must  be  considered  a  mold  and  not  a  cast. 

Trails.  These  are  made  by  animals  crawling  over  the  mud  and 
dragging  their  bodies  along.  Jelly-fish  floating  in  shallow  water 
may  have  their  tentacles  dragging  along  over  the  bottom,  thus 
leaving  distinct  impressions.  Plants  are  not  infrequently  dragged 
along  over  the  shallow  sea-bottom,  with  the  result  that  a  certain 
type  of  trail  is  made  on  the  mud  which  may  be  indistinguishable 
from  similar  trails  made  by  floating  animals.  Even  attached  plants, 
like  the  beach  grass  on  the  sand-dunes,  may  have  a  very  charac- 
teristic semi-circular  trail  when  swung  about  by  the  wind.  Sea- 
weeds partly  buried  on  an  uncovered  mud  flat  may  be  moved  by 
the  wind  and  so  'produce  similar  markings.  These  may,  in  some 
instances,  be  preserved,  as  appears  to  have  been  the  case  in  the 
structures  described  as  Spirophyton  from  the  Palaeozoic  rocks  of 
North  America  and  elsewhere. 

Burrows.  While  tracks  and  trails  are  made  by  animals  in 
transit,  burrows  are  the  temporary  or  permanent  abodes  of  animals. 
At  the  end  of  many  trails  of  molluscs  or  Crustacea  a  mound  is 
found  which  marks  the  place  where  the  creature  has  temporarily 
buried  itself  in  the  sand.  This  type  of  burrow  is  not  generally 
well  preserved,  though  under  favorable  conditions  it  may  be  found. 
At  the  end  of  a  peculiar  trail  on  the  Potsdam  sandstone  of  New 
York,  known  as  Climactichnites,  Woodworth  (29)  has  discovered 
an  oval  impression  which  he  considers  to  have  been  made  by 
the  animal  in  resting.  This  may  possibly  represent  the  collapsed 
burrow. 

The  remarkable  structures  known  as  Daemonelix  which  occur 
in  the  Miocenic  deposits  of  the  Nebraska  region  and  which  were 
first  described  as  sponges  and  have  often  been  considered  as  plants, 
are  probably  the  burrows  of  some  species  of  burrowing  mammal. 
The  strata  in  which  they  occur  are  of  the  continental  type  of  de- 


1092  PRINCIPLES    OF    STRATIGRAPHY 

posit  and  the  skeletons  of  rodents  have  been  found  in  the  expansion 
at  the  base  of  the  erect  spiral.  The  material  which  has  filled  the 
burrow  has  solidified  and  now  forms  a  solid  core  or  mold  of  the 
original  burrow.  It  should,  however,  be  said  that  sections  of  the 
core  disclose  what  appears  to  be  a  cellular  structure,  which  has  led 
to  the  supposition  that  the  Dsemonelix  is  not  a  burrow  but  a  plant, 
which  grew  around  the  skeleton  and  has  been  preserved  in  the  atti- 
tude of  growth. 

The  borings  of  sponges  in  shells  (Clione)  and  the  excavations 
made  by  molluscs  and  echinoderms  in  wood  and  stone  represent 


FIG.  261.     Two  views  of  a  typical  example  of  Dccmonclix  circumaxilis,  from 
the  Miocenic  beds  of  Nebraska.     (After  Barbour.) 

permanent  lodgments  of  the  organisms,  and  are  more  nearly  of 
the  grade  of  artificial  structures  than  is  the  case  with  the  burrows 
before  mentioned,  which  are  more  transient,  and  more  nearly  re- 
lated to  trails  made  in  transit.  For  illustration  of  the  burrows  of 
echinoids  of  limestone  in  Brazil,  see  Branner  (8). 

Burrows  like  the  Devil's  Corkscrew,  above  described,  if,  indeed, 
they  are  burrows,  and  like  the  borings  of  aquatic  animals,  are  pre- 
served by  reason  of  the  character  of  the  material  in  which  they 
were  excavated.  Worm-tubes,  on  the  other  hand,  so  characteristic 
of  the  sandy  and  muddy  beaches,  are  maintained  by  a  lining  or 
cement  of  mucus,  secreted  by  the  animal.  These,  therefore, 
carry  us  a  step  further  into  the  class  of  undoubtedly  "artificial 
structures." 


ARTIFICIAL    STRUCTURES;    COPROLITES       1093 


3.     Artificial  Structures. 

Beginning  with  the  worm-tubes  already  mentioned,  or  even  with 
the  excavations  made  by  some  animals,  we  have  this  type  of  fossil 
increasing  in  importance  as  we  rise  in  the  scale  of  organic  being. 
Even  as  far  down  as  the  group  of  rhizopods  we  find  many  types 
building  shells  by  cementing  foreign  particles  with  the  aid  of  a 
secretion.  This  type  of  habitation  is  analogous  to  the  worm-tube 
already  mentioned.  Though  represented  in  most  classes  of  animals, 
it  is  not  until  we  reach  man  that  these  artificial  structures  assume 
any  great  importance. 

Thus  the  implements  of  stone,  shell,  bone  or  metal,  the  pottery 
and  the  copper,  bronze  and  iron  vessels;  the  beads  and  other  orna- 
ments ;  the  coins  and  the  habitations  of  man  from  the  rude  exca.va- 
tion  in  the  rock  to  the  buried  cities  of  historic  time,  with  all  their  ac- 
cessories, belong  to  this  type  of  fossils.  This  group,  therefore,  falls 
largely  in  the  province  of  Anthropology,  or  the  science  which  is 
concerned  with  man  in  all  his  relations,  including  his  palaeontology. 


4.     Coprolites. 

The  excrements  of  certain  animals  have  a  definite  and  recogniz- 
able form,  and  so  become  valuable  indices  to  the  former  presence 
of  such  animals.  Most  important  among  these  are  the  coprolites 
of  fishes  and  reptiles,  the  latter  constituting  important  fossils  in 
the  Mesozoic  rocks.  Very  much  concerning  the  food  of  the  ani- 
mal can  often  be  learned  from  the  remains  found  within  the  copro- 
lite.  The  excrements  or  "castings"  of  worms  also  belong  here. 
They  generally  consist  of  cord-like  masses  of  molded  sand  which 
have  passed  through  the  intestine  of  the  worm  and  from  which 
the  nutrient  organic  matter  has  been  abstracted.  They  cover  some 
modern  beaches  in  great  quantities,  and  are  not  infrequently  pre- 
served. Certain  echinoderms,  particularly  holothurians,  have  rec- 
ognizable excrements.  Rothplotz  has  found  an  abundance  of 
calcareous  rods  in  the  bottom  deposits  of  Great  Salt  Lake,  which 
he  regards  as  excrements  of  Artemia,  an  abundantly  represented 
crustacean  in  this  body  of  water.  They  closely  resemble  known 
excrements  of  Artemia,  but  are  calcareous,  since  the  species  of  the 
Salt  Lake  are  supposed  to  feed  on  calcareous  algae. 


1094  PRINCIPLES    OF    STRATIGRAPHY 


MECHANICAL  DEFORMATION  OF  FOSSILS. 

Wherever  rocks  containing  fossils  have  been  under  pressure, 
or  have,  through  other  means,  suffered  mechanical  disturbances, 
the  fossils  commonly  show  a  more  or  less  pronounced  deformation. 
Two  types  of  deformation  may  be  considered:  (i)  that  due  to 
the  normal  desiccation  and  consequent  shrinking  of  the  rocks  in 
otherwise  undisturbed  regions,  and  (2)  that  due  to  erogenic  dis- 
turbances. The  first  type  is  especially  marked  in  shales,  and  is  due 
to  the  vertical  pressure  exerted  by  the  overlying  rock  and  the  verti- 
cal shrinking  of  the  shales  upon  the  loss  of  water.  Shells  of 
brachiopods  and  pelecypods  are  commonly  flattened  out,  while  gas- 
tropods, cephalopods  and  trilobites  are  most  frequently  distorted  by 
this  vertical  pressure.  The  amount  of  compression  can  sometimes  be 
estimated  by  noting  the  sagging  of  the  strata  on  either  side  of  a  con- 
cretion enclosed  by  them.  Again,  it  may  be  estimated  from  a  com- 
parison of  the  compressed  shell  with  uncompressed  examples  from 
the  same  formation,  but  preserved  in  limestone  bands  or  lenses.  The 
latter  have  suffered  little  or  no  vertical  compression  on  account  of 
the  fact  that  the  component  grains  of  the  rock  were  already  as  firmly 
packed  when  the  rock  solidified  as  they  were  ever  likely  to  be. 

The  second  group  begins  with  the  deformations  due  to  horizon- 
tal slipping  within  a  stratum,  owing  to  the  pressure  of  a  superin- 
cumbent mass.  Under  such  circumstances  slickensides  are  fre- 
quently produced  within  a  given  formation,  and  fossils  may  readily 
be  affected  by  such  movements.  Lateral  compression  of  the  strata, 
either  slight  or  sufficient  to  produce  foldings,  will  distort  the  fossils 
embedded  in  them  arid  not  infrequently  alter  their  form  so  that 
they  are  no  longer  recognizable.  A  brachiopod,  for  example,  by 
compression  may  assume  the  outline  of  a  pelecypod,  and  may  readily 
be  mistaken  for  one.  When,  through  strong  compression,  cleavage 
is  induced  in  a  given  stratum,  the  fossils  of  that  bed  may  become 
largely  or  entirely  destroyed.  The  same  is  true  if  metamorphism 
affects  the  strata,  though  occasionally,  as  in  the  Palaeozoic  of  Scan- 
dinavia, fossils  are  found  in  schists  and  other  metamorphic  rocks. 


INDEX  FOSSILS. 

Fossils  which  serve  to  indicate  definite  geological  horizons  are 
called  Index  Fossils  (German,  Leitfossilien).  The  best  index 
fossils  for  marine  formations  are  furnished  by  invertebrates,  though 


INDEX    FOSSILS  1095 

marine  vertebrates,  when  well  preserved,  are  also  good  horizon 
markers.  The  very  detailed  knowledge  of  vertebrate  anatomy 
required,  however,  to  determine  the  genera  and  species  makes  verte- 
brate remains  available  only  to  the  trained  specialist.  Plants  fur- 
nish good  and  reliable  index  fossils  for  terrestrial  or  delta  forma- 
tions, although  their  distribution  is  much  more  subject  to  limita- 
tions, owing  to  climatic  influence.  The  same  may  be  said  to  be 
true  of  land  vertebrates.  The  subject  is  further  discussed  under 
correlation,  in  .Chapter  XXXIL 


BIBLIOGRAPHY    XXX. 

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2.  BASSLER,  R.  S.     1910.     Adequacy  of  the  Paleontologic  Record.     The 

Paleontologic  Record,  pp.  6-9,  reprinted  from  Popular  Science  Monthly. 

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4.  BLUM,  J.  REINHARD.      1843.      Die  Pseudomorphosen  der  Mineralogie, 

and  First  Appendix  (Erster  Nachtrag)  1847.     Stuttgart. 

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Brazil.     Bulletin  of  the  Geological  Society  of  America,  Vol.  XVI,  pp. 

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Fossils,  Invertebrates.     Vol.  I. 

15.  HUGHES,    T.  McKENNY.     1889.     On   the   Manner   of   Occurrence   of 

Beekite  and  Its  Bearing  upon  the  Origin  of  Siliceous  beds  of  Palaeozoic 
Age.     Mineralogical  Magazine,  Vol.  Ill,  No.  40,  pp.  265-271. 

16.  LULL,    RICHARD    S.     1904.     Fossil    Footprints   of   the   Jura-Trias   of 

North  America.     Memoirs  of  the  Boston  Society  of  Natural  History, 
Vol.  V,  97  pp.,  i  pi. 

17.  MEAD,  CHARLES  W.     1907.     Peruvian  Mummies.     American  Museum 

of  Natural  History.     Guide  Leaflet  No.  24. 


1096  PRINCIPLES    OF    STRATIGRAPHY 

18.  MORGAN,  WILLIAM   C.,   and   TALLMON,    MARION   C.     1904.     A 

Fossil  Egg  from  Arizona.     California  University,  Department  of  Geology, 
Bulletin,  Vol.  Ill,  pp.  403-410,  2  pis. 

19.  NICHOLSON,    H.   ALLEYNE,  and   LYDEKKER,    RICHARD.     1889. 

Manual  of  Palaeontology.     2  vols.     Third  edition. 

20.  REIS,  OTTO  M.     Die  Coelacanthinen,  mit  besonderer  Beriicksichtigung 

der  im  weissen  Jura,  Bayerns  Vorkommenden  Arten.   Palaeontographica 
XXXV,  pp.  1-96,  pis.  I-V. 

21.  ROGERS,  AUSTIN  F.     Private  Communication. 

22.  ROTH,  I.     1879.     Allgemeine  und  chemische  Geologic,  Vol.  I.     Especially 

literature  on  fossilization  of  plants. 

23.  STEDMANN,  J.  M.,  and  ANDERSON,  J.  T.     1895.     Observations  on  a 

so-called  petrified  man,  with  a  report  on  chemical  analysis  by  J.  T. 
Anderson.     American  Naturalist,  Vol.  XXIX,  pp.  326-335. 

24.  STEINMANN,    GUSTAV.     1903.      Einfuhrung    in    die    Palaeontologie. 

Wilhelm  Engelmann,  Leipzig. 

25.  WALCOTT,  CHARLES  D.     1898.     Fossil  Medusae.     Monograph  of  the 

United  States  Geological  Survey.     XXX. 

26.  WALCOTT,  C.  D.     1911.    Cambrian  Geology  and  Palaeontology.     Smith- 

sonian Institution  Collections,  Vol.  57. 

27.  WIMAN,  C.     1895.     Ueber  die  Graptolithen.     Geol.  Inst.  Upsala,  Bull., 

Vol.  II,  No.  2. 

28.  WHITE,  C.  H.     1905.     Autophytography :  a  Process  of  Plant  Fossilization. 

American  Journal  of  Science,  4th  series,  Vol.  XIX,  pp.  231-236. 

29.  WOOD  WORTH,  JAY  B.     1903.     On  the  Sedentary  Impression  of  the 

Animal  whose   trail  is  known  as   Climactichnites.     New   York   State 
Museum  Bulletin  69,  pp.  959-966,  2  pis,,  3  figs. 


G.   PRINCIPLES  OF  CLASSIFICATION  AND  COR- 
RELATION OF  GEOLOGICAL  FORMATIONS. 

CHAPTER    XXXI. 

NOMENCLATURE  AND   CLASSIFICATION   OF   GEOLOGIC 
FORMATIONS. 

DEVELOPMENT    OF    CLASSIFICATIONS. 

The  history  of  the  earth  is  written  in  the  strata  of  the  earth's 
crust.  Like  all  histories,  it  is  a  continuous  succession  of  events,  but 
the  record  of  these  events  is  never  complete  and  seldom  even  un- 
broken in  any  given  region.  It  is  of  the  first  importance  to  the 
chroriographer  of  earth  history  that  he  should  find  a  continuous 
record,  in  order  that  he  may  have  a  measure  by  which  to  judge 
the  partial  records  of  -any  given  region  and  to  discover  the  breaks 
and  imperfections  in  the  local  records  thus  presented.  (Grabau-5.) 
The  question  then  arises :  under  what  conditions  may  we  expect  to 
obtain  a  continuous  record  and  how  are  we  to  guard  against  the 
introduction  of  errors? 

We  have,  in  the  first  place,  to  deal  with  the  time  element  in  the 
history  of  the  earth.  In  human  history  the  time  element  is  a  mea- 
surable factor,  its  duration  being  recorded  in  years  and  centuries. 
No  such  precise  measurements  are  possible  in  earth  history,  al- 
though several  attempts  have  been  made  to  reduce  geologic  time  to 
units  of  human  chronology.  (For  methods  and  results,  see  beyond.) 
But  while  we  cannot  now,  and  probably  may  never,  hope  to  divide 
geologic  time  into  centuries  and  millenniums,  we  can  divide  it  into 
periods,  each  of  which  has  its  own  special  significance  in  the  his- 
tory of  the  earth.  The  basis  for  such  subdivision  was  long  ago 
found  in  the  succession  of  organic  types  from  relatively  simple  to 
highly  complex  forms.  As  long  as  the  doctrine  of  special  creation 
of  organic  types  was  held,  and  with  it  the  belief  in  successive  acts 
of  creation,  and  more  or  less  complete  extinction  of  the  faunas  and 

1097 


1098  PRINCIPLES    OF    STRATIGRAPHY 

floras  preceding,  it  was  a  comparatively  simple  matter  to  divide 
the  earth's  history  into  periods  or  eras  characterized  by  these  suc- 
cessive changes  in  the  ancient  inhabitants  of  the  earth.  That  there 
was  much  apparent  justification  for  this  belief  in  the  characters  of 
the  faunas  and  floras  found  in  the  strata  of  the  earth  cannot  be 
questioned.  Thus,  trilobites  are  even  to-day  unknown  from  strata 
later  than  Palaeozoic,  nor  until  recently  have  strata  containing  am- 
monites been  recognized  as  older  than  the  Mesozoic.  That  sudden 
disappearances  of  whole  organic  assemblages,  and  the  equally  sud- 
den appearance  of  others  of  a  different  type  occur  repeatedly  are 
matters  of  common  observation ;  but  it  was  not  always  recognized 
that  such  sudden  changes  are  seldom  universal  in  extent,  though 
generally  traceable  over  wide  areas.  While  abrupt  changes  in  or- 
ganic content  of  the  strata  have  come  to  be  generally  regarded  as 
marking  the  lines  between  the  greater  divisions  in  the  earth's  history, 
they  are  correlated  with,  and,  in  fact,  dependent  on,  widespread 
physical  breaks  in  the  continuity  of  the  strata  which  compose  the 
earth's  crust.  Such  physical  breaks  were,  indeed,  taken  as  the  planes 
of  division  by  the  pioneers  in  stratigraphy,  who  considered  strati- 
graphic  succession  rather  than  geologic  chronology.  Thus,  about 
the  middle  of  the  i8th  Century  Lehman,  a  German  miner  (u) 
proposed  a  threefold  division  of  the  rocks  of  the  earth's  crust  into 
(i)  "Primitive"  (Primitiv)  or  "Urgebirge,"  including  all  the  igne- 
ous and  metamorphic  rocks  in  which  there  was  no  sign  of  life  and 
which  showed  no  evidence  of  having  been  derived  from  the  ruins  of 
preexisting  rocks,  and,  therefore,  of  chemical  origin,  antedating  the 
creation  of  life;  (2)  Secondary,  comprising  the  fossili-ferous  strata, 
and  largely  composed  of  mechanical  deposits,  produced  after  the 
planet  had  become  the  habitation  of  animals  and  plants;  and  (3) 
Alluvial  deposits,  due  to  local  floods,  and  the  deluge  of  Noah. 
Fiichsel,  a  contemporary  of  Lehmann,  recognized  that  certain  groups 
of  strata  belonged  together  and  constituted  a  geologic  formation. 
He  held  that  each  formation  represented  an  epoch  in  the  history  of 
the  earth,  and  thus  he  brought  into  consideration  the  time  element 
in  the  earth's  history.  Half  a  century  later  Werner  introduced  his 
"transition  formations"  between  the  primitive  and  secondary  rocks, 
comprising  a  series  of  strata,  first  found  in  northern  Germany,  which 
were  intermediate  in  mineral  character  between  the  crystallines  and 
sedimentaries  and  partook  in  some  degree  of  the  characters  of  both. 
This  Uebergangsgebirge,  or  transition  formation,  consisted  princi- 
pally of  clay  slates,  argillaceous  sandstones  or  graywackes  and  cal- 
careous beds,  which,  in  the  region  studied  by  Werner,  were  highly 
inclined  and  unconformably  overlain  by  the  horizontal  Secondary 


DEVELOPMENT    OF   CLASSIFICATION  1099 

strata.  The  latter,  including  formations  up  to  the  top  of  the  chalk, 
were  called  by  Werner  the  Plotsgebirge  formation,  on  account  of 
their  horizontally,  and  because  they  were  the  stratified  rocks  par  ex- 
cellence. The  term  Plots  signifies  "a  level  floor,"  and  had  been 
generally  used  since  the  time  of  Agricola  for  stratified  rocks.  With 
the  Flotz  were  included  the  trap  rocks  of  the  Secondary  strata,  as 
subordinate  members,  these  being  held  by  Werner  and  his  followers 
to  be  the  result  of  aqueous  precipitation.  All  deposits  above  the 
chalk  were  referred  by  Werner  to  alluvial  deposits  under  the  desig- 
nation Angeschwemmtgebirge.  Werner's  followers  later  on 
distinguished  a  series  of  strata  between  the  chalk  and  the  alluvium, 
and  applied  to  this  the  term  Newer  Plots  (Neues  Flotsgebirge). 
These  are  the  rocks  subsequently  named  "Tertiary"  by  Cuvier  and 
Brongniart.  In  the  Wernerian  terminology,  the  characters  of  the 
strata  themselves  rather  than  their  time  relations  were  considered, 
and  Fuchsel's  term  "formation"  was  applied  by  Werner  and  his 
followers  to  groups  of  strata  of  similar  lithic  composition.  Thus 
he  spoke  of  limestone  formation,  sandstone  formation,  slate  forma- 
tion, etc.  The  term  "transition"  strata  soon  began  to  take  on  chron- 
"ologic  meaning,  and  it  was  widely  applied  to  rocks  older  than  those 
designated  as  Secondary.  It  was  still  retained  even  after  it  was 
shown  that  these  strata  are  not  always  transitional  in  mineral  char- 
acter and  that  strata  belonging  to  the  Secondary  or  even  later  series 
had  sometimes  the  mineralogical  character  of  the  original  Transition 
rocks. 

At  the  time  of  Lyell,  the  strata  of  the  earth's  crust  were  gen- 
erally divided  into  Primary,  Transition,  Secondary,  Tertiary  and 
post-Tertiary.  It  had  become  recognized  that  crystalline  and 
metamorphic  rocks  were  not  all  of  one  age,  but  that  some  were  even 
newer  than  the  Secondary  formation.  As  a  chronologic  term,  Pri- 
mary had  come  to  be  applied  by  some  to  the  fossiliferous  rocks  older 
than  the  Secondary,  while  it  had  become  a  matter  of  some  question 
whether  any  of  the  crystalline  rocks  really  antedated  the  oldest 
fossiliferous  deposits.  Lyell,  to  avoid  confusion,  used  the  term 
Primary  Fbssiliferous  formation  "because  the  word  primary  has 
hitherto  been  most  generally  connected  with  the  idea  of  a  nonfos- 
siliferous  rock."  About  this  time  the  terms  "Paleozoic"  *  "Meso- 
zoic^  f  and  "Cccnozoic'  f  were  introduced  to  replace  the  terms 
Primary  Fossiliferous  (the  former  Transition),  Secondary  and 

*  Proposed  by  Sedgwick,  1838.  From  ira\cu6s,  palaios,  ancient,  and  fwij, 
zoe,  life. 

f  Proposed  by  Philips,  1841,  from  /«?<H>S,  mesos,  middle;  icaivfa,  new,  recent. 
The  latter  was  also  written  Kainozoic. 


i ioo  PRINCIPLES    OF    STRATIGRAPHY 

Tertiary,  but  they  met  at  first  with  little  favor.  Palaeozoic  was  the 
first  to  be  adopted,  while  Secondary  and  Tertiary  were  still  re- 
tained. Later  Mesozoic  gradually  replaced  Secondary,  but  Tertiary 
has  still  retained  its  hold  in  geologic  literature  to  the  present  day. 
To  it  the  Quaternary  *  has  been  added,  which  comprises  the  forma- 
tions designated  by  Lyell  as  Post-Pliocene,  together  with  his  Later 
Pliocene  or  Pleistocene.  These  have  frequently  been  included  with 
the  Tertiary  under  the  term  Caenozoic  (=Kainozoic),  but  they  have 
also  been  separated  under  the  term  Psychozoic,  introduced  by  Le 
Conte,  but  limited  by  him  to  the  most  recent  formations,  which  in- 
include  abundant  remains  of  man. 

It  is  thus  seen  that  the  classification  at  first  proposed  as  a  rock 
classification  became  a  chronologic  one,  as  geologists  began  to 
perceive  that  all  kinds  of  rock  may  be  formed  during  each  period 
of  the  earth's  history.  When  the  fossils  of  each  of  these  four  divi- 
sions became  better  known,  it  was  found  that  each  was  character- 
ized by  its  peculiar  assemblage  of  organisms.  It  was  further 
found  that  in  most  regions  the  strata  of  each  of  these  larger  sub- 
divisions were  separated  from  those  above  or  below  by  a  marked 
unconformity,  so  that  records  of  disturbances  of  widespread  occur- 
rence were  looked  upon  as  generally  marking  the  dividing  lines 
between  the  greater  subdivisions  of  the  earth's  history.  The  use 
of  unconformities  in  defining  limits  of  geologic  formations  was  also 
extended  to  the  further  subdivision  of  the  larger  units,  and,  in 
fact,  such  breaks  have  frequently  been  advocated  as  the  best  avail- 
able criterion.  But  geologists  have  pretty  generally  recognized 
the  fact  that  a  classification  based  on  unconformities  is  an  incom- 
plete one,  and  that  a  complete  record  of  geologic  time  can  be  ex- 
pected only  in  a  series  resulting  from  continuous  deposition.  Such 
a  series  is,  however,  nowhere  obtainable,  since  in  no  known  region 
of  the  earth  has  there  been  continuous  and  uniform  deposition. 
Stratigraphers  are  thus  compelled  to  construct  their  typical  section 
from  fragments  of  overlapping  sections  from  all  parts  of  the  world. 
Each  fragment  thus  used  in  the  building  up  of  the  typical  scale 
must  be  complete  in  itself,  and  its  relationship  to  the  next  adjoining 
fragments  of  the  scale  must  be  determined. 


Selection  of  the  Type  Section. 

What,  then,  are  the  criteria  which  must  guide  us  in  the  selection 
of  our  typical  section?    First  and  foremost,  the  section  must  show 

*  Proposed  by  Morlot  in  1854. 


CHARACTERISTICS    OF    TYPE    SECTIONS  noi 

continuous  deposition.  No  sharp  break  either  lithic  or,  faunal  should 
occur  between  the  members,  but  all  should  be  transitional.  The 
character  and  origin  of  the  strata  composing  the  section  must  be 
carefully  considered,  since  all  rocks  are  not  of  equal  value  as  in- 
dices of  continuous  deposition. 

Hydroclastic  rocks  are  by  far  the  most  reliable  indices  of  depo- 
sition, since  none  other  are  formed  under  so  uniform  an  environ- 
ment. Marine  sediments,  further,  are  more  reliable  than  those  of 
fresh  water  lakes,  since  the  latter  are  only  temporary  features  of 
the  earth's  surface  and  are  preceded  and  succeeded  by  conditions 
which  will  of  necessity  destroy  the  continuity  of  formation  of  strata. 
Thus  marine  formations  alone  will  serve  for  the  erection  of  a 
standard  scale,  all  formations  of  a  continental  type,  whether  of 
fresh  water  or  of  atmo-,  anemo-,  or  pyroclastic  origin,  must  be  ruled 
out  of  the  standard  scale.  Hence  the  Old  Red  Sandstone  of  Brit- 
ain, the  non-marine  Carbonic  formations,  the  Newark,  Potomac, 
Dakota  and  Laramie  formations  of  North  America,  are  all  to  be 
discarded  in  the  making  of  a  true  geologic  formation  scale.  Even 
among  marine  strata,  there  are  some  which  must  be  ruled  out,  as 
not  furnishing  a  reliable  account  of  the  progress  of  rock  deposi- 
tion. Thus  sandstones  and  conglomerates,  either  as  basal  members 
or  intercalated  between  a  series  of  clay  or  lime  rocks,  are  almost 
sure  to  introduce  an  element  of  uncertainty,  if  not  error,  into  the 
section,  even  if  the  gradation  above  and  below  is  a  perfect  one. 
As  has  been  pointed  out  in  an  earlier  chapter,  shore-derived  silice- 
ous elastics  of  coarse  grain,  when  not  forming  a  basal  sandstone  or 
conglomerate,  can  become  widespread  only  by  an  oscillatory  move- 
ment of  the  land,  which  results  in  a  temporary  retreat  and  re- 
advance  of  the  sea.  Such  a  change  involves  almost  certainly  a  time 
interval  unrecorded  in  the  section,  but  represented  rather  by  an 
unrecognizable  break  within  the  terrigenous  member  itself.  An 
example  of  such  a  formation  is  found  in  the  St.  Peter  Sandstone 
of  central  United  States,  a  formation  which  in  itself  represents  a 
disconformity,  constantly  increasing  in  magnitude  toward  the  north, 
where  it  includes  an  unrecorded  interval  elsewhere  represented  by 
from  2,000-3,000  feet  of  limestones.  Shore  deposits  of  all  kinds 
should  be  ruled  out  in  the  establishment  of  a  typical  section,  for 
they  represent  local  conditions  and,  therefore,  cannot  furnish  re- 
liable evidence  of  the  general  progress  of  development. 

Deposits  formed  in  an  enclosed  basin,  whether  marine  or  con- 
tinental, are  likewise  unsatisfactory  for  purposes  of  establishing 
a  general  scale.  Such  deposits  at  present  included  in  the  standard 
scale  of  North  American  strata  are :  the  Medina  and  Salina  forma- 


1 102  PRINCIPLES    OF    STRATIGRAPHY 

tions  of  New  York,  which  were  formed  under  local  and  in  part 
continental  conditions,  and  cannot,  therefore,  represent  a  standard 
by  which  the  more  widespread  marine  conditions  existing  elsewhere 
can  be  measured.  Wherever  possible,  such  local  formations  should 
be  taken  out  of  the  standard  scale  of  strata  and  replaced  by  forma- 
tions of  purely  marine  origin.  These  may,  of  course,  not  exist 
within  the  limits  of  the  territory  for  which  the  scale  is  made,  in 
which  case  the  old  terms,  perforce,  have  to  be  retained. 

The  best  example  of  a  truly  representative  classification  of  the 
divisions  of  a  larger  formation,  which  has  yet  been  devised,  is  that 
of  the  Triassic  system.  In  no  one  region  of  the  world  is  there  a 
complete  representation  of  marine  Triassic  strata;  in  fact,  the  best 
known  divisions  of  this  system  are  to  a  large  extent  non-marine. 
But,  by  a  careful  study  of  all  the  widely  dissociated  marine  mem- 
bers and  their  relation  to  each  other,  a  standard  classification,  more 
nearly  perfect  than  that  of  most  other  similar  formations,  has  been 
devised.  By  its  use  the  various  dissociated  marine  members  of 
each  region,  as  well  as  the  non-marine  members,  may  be  measured 
and  the  time  relation  of  each  to  the  others  and  to  all  may  be 
ascertained. 

Time  Scale  and  Formation  Scale. 

While  the  time  scale  is  thus  of  primary  importance  as  a  stand- 
ard of  comparison,  a  formation  scale  is  also  needed.  A  formation 
is  a  stratigraphic  unit,  composed  in  general  of  similar  or  closely 
related  strata  and  characterized  by  a  particular  assemblage  of  organ- 
isms (fauna  or  flora).  Sometimes  a  formation  may  consist  of  a 
single  stratum — more  frequently  it  comprises  many  strata.  The 
rules  recently  promulgated  by  the  United  States  Geological  Survey 
for  the  government  geologists  in  the  preparation  of  the  geologic 
folios  of  the  United  States  (18:^5)  make  the  formation  the  carto- 
graphic unit,  and  define  it  among  sedimentary  rocks  as  follows : 
"Each  formation  shall  contain  between  its  upper  and  lower  limits 
either  rocks  of  uniform  character  or  rocks  more  or  less  uniformly 
varied  in  character,  as,  for  example,  a  rapid  alternation  of  shale 
and  limestone."  It  is  further  suggested  that,  "As  uniform  con- 
ditions of  deposition  were  local  as  well  as  temporary,  it  is  to  be 
assumed  that  each  formation  is  limited  in  horizontal  extent.  The 
formation  should  be  recognized  and  should  be  called  by  the  same 
name  as  far  as  it  can  be  traced  and  identified  by  means  of  its  lith- 
ologic  character,  its  stratigraphic  association,  and  its  contained 
fossils." 


TIME    AND    FORMATION    SCALE 


1103 


Subdivisions  of  Time  and  Formation  Scales. 

The  primary  divisions  of  the  geologic  time  scale  are,  as  we  have 
seen,  based  on  the  changes  in  life,  with  the  result  that  fossils  alone 
determine  whether  a  formation  belongs  to  one  or  the  other  of 
these  great  divisions.  The  primary  divisions  now  generally  recog- 
nized are  as  follows : 


C\\A 

Corresponding 

Present  name. 

Definition. 

vJlQ 

Equivalent. 

formation  as 
generally  used. 

Psychozoic 

Mind-life 

Quaternary* 

Quaternary 

Cenozoic 

Recent-life 

Tertiary 

Tertiary 

Mesozoic 

Mediaeval-life 

Secondary 

Mesozoic 

Palaeozoic 

Ancient-life 

Transition  or  Pri- 

Palaeozoic 

mary  Fossilifer- 

ous 

. 

Eozoic  (or  Proterozoic) 

Dawn  of  life  (or  ^ 

(  Algonkianf 

First  life)          \ 

Primary 

\ 

Azoic 

Without  Life  J 

v.  Archaean  J 

Corresponding  to  each  time  division  we  have  a  formational  divi- 
sion, which  represents  the  rock  material  accumulated  during  the 
continuance  of  that  time.  As  will  be  seen  from  the  above  table, 
the  formation  scale  now  generally  in  use  is  made  up  partly  of  the 
old  names  in  vogue  during  Lyell's  time,  partly  of  the  newer  names, 
and  in  part  of  distinct  names  applied  to  the  rocks  of  these  divisions 
by  American  geologists  and  adopted  by  workers  in  other  countries 
as  well. 

A  number  of  terms  have  been  proposed  by  which  the  subdivi- 
sions of  the  time  and  formation  scale  are  to  be  known,  but  at 
present  there  is  no  unanimity  in  the  usage  of  these  terms.  The 
following  are  the  most  important  of  the  proposals  made,  the  num- 
bering being  in  the  order  of  magnitude  of  the  categories : 

*  In  many  text-books  the  Quaternary  is  included  with  the  Tertiary  under 
Cenozoic,  which  is  not  the  historic  sense  of  the  term.  Post-Tertiary  time  is 
essentially  characterized  by  the  presence  of  man  and  may  be  separated  as 
Psychozoic. 

f  Walcott,  1889.     From  a  tribe  of  North  American  Indians. 

t  Proposed  by  Dana. 


1 104  PRINCIPLES    OF    STRATIGRAPHY 

1.  International   Geological   Congress.     At    the   first   meeting 
of  the  Congress  in  Paris  in  1878  a  commission  was  appointed  to 
frame  a  plan  of  procedure  for  the  unification  of  geologic  classifi- 
cation  and   naming.     The   recommendations   of   this   Commission, 
adopted  at  the  Bologna  Congress  in   1881,  as   far  as  they  affect 
the   point   in    question,    are   as    follows.      (i)    Era — Group;    (2)  • 
Period — System;     (3)     Epoch — Series;     (4)     Age — Stage;     '(5) 

.     .     .     — Assize.      No    time    equivalent    for    (5)     (Assize)    was 
designated. 

During  succeeding  Congresses  proposed  modifications  of  this 
scheme  were  discussed  until  in  1900  the  8th  Congress,  convened 
in  Paris,  accepted  the  following  scheme: 

Chronologic.  Stratigraphic. 

i.  Era  (Eres).  i.  (No  stratigraphic  term). 

2.  Period  (Pe"riode).  2.  System  (Systeme). 

3.  Epoch  (fipoque).  3.  Series  (Series).* 

4.  Age  (Age).  4.  Stage  (Etage).f 

5.  Phase  (Phase).  5.  Zone  (Zone). 

Periods,  and  the  corresponding  systems,  have  a  worldwide  value, 
and  are  characterized  by  the  development  of  the  organisms  during 
the  period,  and  their  entombment  in  the  strata  of  the  system.  Pe- 
lagic faunas,  where  available,  are  especially  characteristic,  owing 
to  their  wide  distribution  and  independence  of  local  environments. 
The  termination  of  the  names  of  periods  and  systems  adopted  is  ic, 
ique  (French)  ;  isch  (German)  ;  ico  (Spanish,  Italian,  Portuguese, 
Roumanian)  ;  Ex.  Cambric  (Cambrique,  Kambrisch,  Cambrico)  ; 
Devonic  (Devonique,  Devonisch,  Devonico)  ;  also  Carbonic  (Car- 
bonique,  Karbonisch,  Carbonico)  ;  Cretacic  (Cretacique,  Kretacisch, 
Kreide  Formation),  etc. 

Periods  are  generally  divisible  into  three  epochs  each,  which  are 
designated  by  the  prefixes  Palceo-,  Meso-,  and  Neo-.  For  Palcco- 
the  term  Eo  may  be  used,  wherever  the  name  is  long  and  the  name 
itself  further  abbreviated.  (Williams-ig.)  Thus,  while  Palaeocam- 
bric,  Mesocambric  and  Neocambric  are  used,  Eodevon,  Mesodevon 
and  Neodevon,  or,  Eocret,  Mesocret  and  Neocret,  may  be  used  for 
these  longer  terms.  Locally,  series  are  commonly  given  names  de- 
rived from  typical  localities,  these  ending  in  ian  (ien,  Fr.,  etc.),  as 
the  following  example  will  show : 

*  German,  Abtheilung.         f  German,  Stufe;  Italian,  piano;  Spanish,  piso. 


STRATIGRAPHIC   AND    TIME    SCALES  1105 

Epoch  Local  name  of  series. 

Eastern  United  States.       Western  Europe. 

Neodevonic .  .  . .  /  Chautauquan          1  f  Famennien 

{  Senecan  /  \  Frasnien 


Mesodevonic 


f  Erian  }  f  Givetien 


\  Ulsterian  J  1  Eifelien 


/  Oriskanian  1  f  Coblentzien 

Eodevomc 1  Helderbergian  Taunusien 

(  Gedmien 

The  values  of  these  local  series  are  not  always  uniform  nor 
equivalent.  In  practice  it  is  often  more  convenient  to  speak  of 
Lower,  Middle  and  Upper  Siluric,  Devonic,  etc.,  series  (German: 
Unterdevon,  Mitteldevon,  Oberdevon,  etc. ;  French  Devonien  in- 
fcrieur,  Devonien  moyen,  Devonien  superieur,  etc.).  These  terms 
are  commonly  employed  in  a  general  discussion  of  the  strata  of  a 
series. 

Ages  and  their  corresponding  stages  receive  local  names. 
Stages  are  relatively  restricted  in  areal  distribution  and  dif- 
ferent countries  have  different  stages  corresponding  to  the  same 
age. 

Stages  end  in  ian  (ien,  Fr. ;  ian,  Germ.* ;  iano,  Spanish,  Italian, 
Portuguese,  Roumanian).  Thus  we  have  Bartonian,  Bartonien,  etc. ; 
Portlandian,  Portlandien,  etc.,  stages. 

The  stratigraphic  division  of  the  fifth  order,  the  zone,  is  often 
needed,  and  this  division  is  named  wherever  possible  after  a  par- 
ticular species  of  organism  which  characterizes  it.  Thus  we  have 
in  the  Lias  of  England  the  following  17  zones  characterized  by 
particular  species  of  ammonites.  (Geikie-4:ujj.) 

Ii  7  zone  of  Lytoceras  jurense 
1 6  zone  of  Dactylioceras  commune 
15  zone  of  Harpoceras  serpentinus,  etc. 
14  zone  of  Dactylioceras  annulatum 

A/r-jji    T-  T-  f  1 1  zone  of  Paltopleuroceras  spinatum 

Middle  Lias  or  Liassian  «    °  ,  A       7\ ,  ..  , 

|  12  zone  of  Amaltheus  margantatus 

*  The  German  terms  are  often  contracted,  instead  of  Astian  Stufe,  Astistufe 
is  used. 


iio6  PRINCIPLES    OF    STRATIGRAPHY 


1 1  zone  of  Liparoceras  henleyi,  etc. 

10  zone  of  Phylloceres  ibex 
9  zone  of  ^Egoceras  jamesoni 
8  zone  of  Deroceras  armatum 
7  zone  of  Caloceras  raricostatum 


Lower  Lias  or  Sinemurian^ 


6  zone  of  Oxynoticeras  oxynotum 
5  zone  of  Arietites  obtusus,  etc. 
4  zone  of  Arietites  turneri,  etc. 
3  zone  of  Arietites  bucklandi 
2  zone  of  Schlotheimia  angulata 
I  zone  of  Psiloceras  planorbe 

In  the  Trias,  too,  a  number  of  distinct  zones  marked  by  species 
of  ammonites  or  other  fossils  are  recognized. 

II.  Dana's  System.     In  the  last  edition  of  his  Manual  (3:40*5), 
Professor  James  D.  Dana  gives  the  following  classification: 

Chronologic.  Stratigraphic. 

I.  Aeon  (Ex.:  Palaeozoic).*  I.  Series  (Ex:  Palaeozoic). 
2.  Era  (Ex.:  Siluric).  2.  System  (Ex.:  Siluric). 

3.  Period  (Ex.:  Palaeo-Siluric).  3.  Group  (Ex.:  Niagaran). 

4.  Epoch  (Ex.:  Clinton).  4.  Stage  (Ex.:  Clinton). 

III.  United  States  Geological  Survey.    The  United  States  Geo- 
logical Survey  in  its  ruling  of  1903  makes  the  period  the  unit  of  the 
time  scale  and  correlates  with  it  the  system  of  the  formation  scale, 
thus  following  the  usage  of  the  International  Congress.     The  sys- 
tems recognized  are :    "Quaternary,  Tertiary,  Cretaceous,  Jurassic, 
Triassic,  Carboniferous,  Devonian,  Silurian,  Ordovician,  Cambrian, 
Algonkian,  and  Archaean."    No  complete  scheme  is  formulated,  only 
the  following  terms  being  used: 

Chronologic.  Stratigraphic. 


I I 

2.  Period.  2.  System. 

3 3.  Series. 

4 4.  Group. 

As  far  as  this  scheme  was  developed  it  is  thus  seen  to  correspond 
to  the  one  promulgated  by  the  International  Congress,  with  the 
exception  that  group  is  used  for  the  division  of  the  fourth  order 

*  Examples  added  by  the  author. 


STRATIGRAPHIC    TERMINOLOGY  1107 

instead  of  stage.     The  terminations  of  the  names  of  the  systems 
are  not  altered  to   correspond   to  that  adopted   by  the   Congress. 


Unification  of  Terminology. 

In  the  development  of  the  classification  of  the  geologic  forma- 
tions, the  systems  were  gradually  introduced  either  by  intercalation 
of  a  previously  unknown  system  between  two  well-established  ones, 
as  the  Devonian  between  the  Silurian  and  Carboniferous;  or  by 
the  separation  of  the  new  system  from  an  older  one  with  which  it 
was  formerly  included,  as  Ordovician  from  Silurian.  No  uniform 
method  of  derivation  of  these  names  was  followed,  though  the 
majority  of  names  had  a  geographic  origin.  Neither  was  uni- 
formity of  termination  considered,  though  among  the  later-formed 
names  ian  was  generally  selected.  This  heterogeneous  terminology 
has  become  so  firmly  embodied  in  the  framework  of  stratigraphic 
classification  that  it  probably  will  be  a  long  time  before  we  can 
hope  to  replace  it  by  a  more  homogeneous  one.  Such  terms  as 
Carboniferous  are  wholly  out  of  harmony  with  the  majority  of 
other  terms  and  ought  to  be  discarded.  But  the  adoption  of  a 
uniform  termination  of  these  names,  as  suggested  by  the  Congress, 
and  as  is  widely  practiced,  particularly  in  Europe,  will  do  away 
with  the  most  objectionable  part  of  this  terminology  and  bring  it 
into  harmony  with  the  remaining  portion  of  the  scheme.  In  the 
table  on  p.  1108  the  systems  used  in  this  work  are  given  with  the 
termination  used  by  the  International  Congress,  and  with  it  the 
old  heterogeneous  termination.  The  author  and  derivation  of  each 
term  is  given.  (See  also  table  on  page  22.) 

A  tendency  toward  splitting  up  some  of  the  larger  systems  and 
uniting  others  has  been  shown  by  many  stratigraphers.  The 
Palseocenic  has  been  introduced  in  the  Cenozoic  and  united  with  the 
Eocenic  and  Oligocenic  as  Pabeogenic;  Miocenic  and  Pliocenic  have 
been  united  as  Neogenic;  and  Pleistocenic  and  Holocenic  as  Ceno- 
genic.  The  Liassic  has  also  been  separated  as  a  distinct  system  by 
some  European  stratigraphers.  Recently  this  method  of  subdi- 
vision has  been  carried  to  great  extremes  in  the  works  of  Schuchert 
and  Ulrich,  to  which  the  student  is  referred  (14;  17).  The  sub- 
divisons  advocated  by  Ulrich  are  more  extreme  than  the  facts  seem 
to  warrant,  and  they  have  not  generally  been  adopted. 

Local  Stages  arid  Substages.  Generally,  detailed  study  of  a 
given  region  will  show  the  occurrence  of  numerous  local  forma- 


iio8 


PRINCIPLES    OF    STRATIGRAPHY 


ERAS. 

SYSTEMS 
Chiefly  accord- 
ing to  recom- 
mendation of 
International 
Congress. 

SYSTEMS 
Old  usage. 

FOUNDER. 

ORIGIN  OR  DERIVATION 

OF   NAME. 

Psychozoic  or  j 
Quaternary     "i 

Holocenic 
Pleistocenic 

Recent 
Pleistocene 

Portuguese    Com- 
mitted. C.  (1885) 
Lyell  (1839) 

Wholly  recent.* 
Most  recent.* 

f 

Pliocenic 

Pliocene 

Lyell  (1833) 

More  recent.* 

Cenozoic 

Miocenic 

Miocene 

Lyell  (1833) 

Less  or  intermediate  re- 

or 

cent.* 

Tertiary 

Oligocenic 
Eocenic 

Dligocene 
Eocene 

Bey  rich  (1854) 
Lyell  (1833) 

Few  recent.* 
Dawn  of  recent.* 

Cretacic 

Cretaceous 

Omalius  d'H  alloy 

Greta  chalk  (chalk  bear- 

(1822) 

ing) 

Comanchic 
Jurassic 

3omanchean 
Jurassic 

R.  T.  Hill  (1893) 
Alexander    von 
Humboldt  (i?95) 

Comanche  Indians 
Jura  Mountains 

Triassic 

Triassic 

F.     von      Alberti, 

Original   three-fold   divi- 

(1834) 

sion 

Permic 

Permian 

Murchison  (1841) 

Government    of      Perm  , 

Russia 

Carbonic 

Carboniferous 
(Pennsylvanian) 

Conybear  (1822) 
H.      S.     Williams 

Coal-bearing 
Pennsylvania 

(1891) 

Mississippic 

Sub-Carbonifer- 

D.D.Owen (1852) 

Below    the    coal-bearing 

ous  (Mississip- 

strata 

Palaeozoic  or 
Primary 
Fossiliferous 

Devonic 
Siluric 

pian) 
Devonian 

Silurian  (Upper 

A.  Winchell  (1870) 
Sedgwickand  Mur- 
chison (1839) 
Murchison  (1835) 

Mississippi  valley 
Devonshire,  England 

Ancient   tribe   of   Silures 

Silurian) 

inhabitingSouth  Wales, 

etc. 

Ordovicic 

Ordovician 

Lapworth  (1879) 

Ancient  tribe  of  western 

(Lower  Silurian) 

Murchison  (1835) 

England 

(Up'r  Cambr'n) 

Sedgwick  (1835) 

Cambric 

Cambrian 

Sedgwick  (1835) 

Old  Roman  Province  of 

Cambria,  N.  Wales 

Thus  names  were  derived,  in  part,  from  the  age  of  the  formation,  in  part,  from  their  lithic 
character  and  contents,  in  part  from  typical  localities,  and  in  part  from  former  inhabitants  of 
typical  localities. 

tions  of  the  value  of  stages  or  substages,  as  in  the  following  case: 

Hiatus  and  disconformity 

{Lucas  dolomite 
Amherstburg  limestone 
Anderdon  limestone 
Flat  Rock  dolomite 


Upper  Siluric  or  Monroan.^ 
(Neosiluric) 


Hiatus  and  disconformity 


Sylvania  sandstone 


Hiatus  and  disconformity 


f  Raisin  River  series 
Bass  Island    I  Put-in-Bay  series 
Series        1  Tymochtee  shale 

I  Greenfield  dolomite 


Hiatus — disconformity 
*  Referring  to  the  percentage  of  modern  organisms  present. 


STRATIGRAPHIC  NOMENCLATURE 


1109 


Where  fully  developed  most  formations  include  several  zones. 
Thus,  in  Maryland  and  West  Virginia,  the  Oriskany  formation, 
which  belongs  to  the  Oriskany  stage  of  the  Lower  Devonic  series 
of  eastern  North  America,  contains  at  least  two  zones,  the  upper,  or 
Hipparionyx  proximus,  zone,  258  feet  thick,  and  the  lower,  90 
feet  thick  with  Anoplotheca  flabellites  and  other  fossils.  In  some 
cases,  however,  what  has  been  considered  a  single  formation  may 
represent  an  aggregation  of  apparently  uniform  lithic  character, 
of  such  great  stratigraphic  range  as  not  only  to  transgress  the  limit 
of  a  series,  but  even  that  of  a  system.  An  example  of  this  is  found 
in  the  Arbuckle  and  Wichita  sections  of  Indian  Territory  and  Okla- 
homa, where  the  following  pre-Mississippic  formations  were  for- 
merly recognized :  (Ulrich-i6.) 


[Upper* 


Devonic    Middle 
I  Lower 

(  Upper 

Siluric     j  Middle 
I  Lower  { 

f  Upper  { 

Ordovicicj  Middle 
I  Lower 


Woodford  chert  (Woodford  formation)  probably  Post- 

Devonic 
Absent 


Hunton  limestone  (Himton  formation) 


Sylvan  shale  (Sylvan  formation) 

Viola  limestone  (Viola  formation) 
Simpson  formation 


{Upper      1  Arbuckle  limestone  (Arbuckle  formation) 
Middle)  *  Reagan  sandstone 
Lower         Absent 

It  has  since  been  found  that  the  Hunton  formation  is  not  a 
unit,  but  represents  fragments  of  several  distinct  formations  sep- 
arated by  large  breaks  and  unrepresented  time  intervals  (13). 


PRINCIPLES  GOVERNING  THE  NAMING  OF  FORMATIONS. 

A  formation  may. retain  its  name  only  so  far  as  its  essential 
unity  is  retained,  though  change  in  lithic  character  does  not  neces- 
sarily require  a  change  of  name.  Thus,  when  a  shaly  formation 
in  one  locality  can  be  traced  into,  and  can  be  shown  to  be  the  ex- 
act depositional  equivalent  of,  a  limestone  formation  in  another 

*The  classification  is  by  tjie  author,  and  is  made  in  harmony  with  the 
present  classification  of  the  formations  supposed  to  be  included  in  the  divisions 
given. 


I IIO 


PRINCIPLES    OF    STRATIGRAPHY 


locality,  both  should  be  called  by  the  same  name.  Such  exact 
equivalency,  however,  seldom  obtains.  The  following  figures 
copied  from  Willis'  paper  (20)  show  the  case  mentioned  and 
the  far  more  common  cases  in  which  such  depositional  equiva- 
lency is  not  complete.  In  Diagram  II  the  m  (shale)  formation 
grades  into  the  n  (limestone)  formation,  but  with  a  prolonged  over- 
lap. In  this  case  neither  formation  is  the  exact  equivalent  of  the 
other,  and  both  may  occur  together.  Hence,  each  should  receive 
a  different  name.  An  example  of  this  kind  is  furnished  by  the 


•   Lmesttitc  or  formation.  '—^ — » 

m  ttiau  «r  nmalun. 


FIG.  262.     Diagrams    showing    horizontal    variation    in    sediments.       (After 
Willis.) 

Catskill  and  Chemung  formations,  which  grade  into  each  other  by 
overlap,  the  Catskill  alone  being  present  in  eastern  New  York  and 
the  Chemung  alone  in  western  New  York,  while  between  these 
points  parts  of  both  are  present.  In  the  diagram  cited,  the  near 
shore  overlapping  the  offshore  deposits,  the  overlap  is  regressional 
and  a  replacing  one  and  due  to  shoaling  of  the  water.  In  the  Cat- 
skill-Chemung  case,  a  continental  formation  overlaps  a  marine  one. 
Diagram  III  represents  three  formations  on  the  right  equivalent 
to  the  shale  formation  (m)  on  the  left.  This  shale  formation  (m) 
is  represented  on  the  right  by  its  middle  portion,  while  the  lower  is 
replaced  by  a  sandstone  formation  and  the  upper  by  a  limestone 
formation.  Each  of  the  two  new  formations  receives  a  distinct 
name,  as  p  sandstone  formation  and  s  limestone  formation.  If  the 
name  "m  shale"  is  retained  for  the  middle  member,  a  new  name 
(#)  for  the  entire  group  p  m  s  must  be  given,  the  x  group  being 
then  equivalent  to  the  m  shale  of  the  left  hand  locality,  but  in- 
cluding the  m  shale  at  the  right  hand  locality.  A  better  method, 
however,  is  to  give  the  shale  on  the  right  hand  a  new  name  (k) 
and  call  the  group  p  k  s  the  m  group,  this  being  equivalent  to  the 


STRATIGRAPHIC  NOMENCLATURE      mi 

m  shale.  While  a  difference  of  opinion  exists  as  to  whether  or  not 
the  name  m  should  be  applied  in  the  above  case  to  the  middle  mem- 
ber, it  is  generally  agreed  that,  when  the  shale  formation  m 
breaks  up  into  a  number  of  units,  as  in  diagram  IV,  none  of  which 
can  absolutely  be  identified  with  the  original  mass  m,  each  of  the 
smaller  members  should  receive  a  distinct  name,  while  collectively 
they  may  be  called  the  m  group,  being  the  exact  equivalent  of  the 
m.  shale.  If  lenses  of  sandstone  or  conglomerate  of  importance 
are  present  in  a  formation  these  should  receive  distinct  names,  as 
n  and  p  lenses  in  m  shale.  (Diagram  VI.)  If  only  one  lens  is 
present,  however,  this  may  be  known  by  the  same  name  as  the 
enclosing  formation,  though  it  may  be  better  to  give  even  a  single 
lens  a  distinct  name.  Thus,  in  the  Cattaraugus  formation  of  south- 
western New  York  and  adjacent  areas  in  Pennsylvania,  three  con- 
glomerate lentils  occur,  the  Wolf  Creek,  near  the  base,  the  Sala- 
manca higher  up,  and  the  Kilbuck  still  higher  up.  In  some  locali- 
ties only  one  of  the  upper  two  lentils  is  present:  in  others  both  are 
absent.  The  desirability  of  distinct  names,  even  where  only  one  of 
these  lentils  occurs,  is  apparent. 

Where  the  main  mass  is  of  uniform  character,  but  contains 
thin  beds  of  another  character,  the  whole  may  be  classed  as  one 
formation  (m),  while  the  minor  strata  are  spoken  of  as  distinct 
members.  (Diagram  VII.)  Thus  the  Waldon  sandstone  forma- 
tion of  the  southern  Appalachians  contains  the  Sewanee  coal  mem- 
ber besides  shale  and  other  coal  members  and  conglomerate  lenses. 

Names  of  sedimentary  formations  are  derived  from  localities 
where  the  formation  is  best  developed  or  where  it  was  first  studied. 
"The  most  desirable  names  are  binomial,  the  first  part  being  geo- 
graphic and  the  other  lithologic  (e.  g.,  Dakota  sandstone,  Trenton 
limestone,  etc.)  The  geographic  term  should  be  the  name  of  a 
river,  town,  or  other  natural  or  artificial  feature  at  or  near  which 
the  formation  is  typically  developed.  Names  consisting  of  two 
words  should  be  avoided.  Names  taken  from  natural  features  are 
generally  preferable,  because  less  changeable  than  those  of  towns  or 
political  divisions.  When  the  formation  consists  of  beds  differing 
in  character,  so  that  no  single  lithologic  term  is  applicable,  the 
word  "formation"  should  be  substituted  for  the  lithologic  term 
(e.  g.,  Rockwood  formation)"  (18:^.) 

SELECTION  OF  NAMES  FOR  SYSTEMS,  SERIES  AND  STAGES 
(GROUPS).  These  divisions,  as  already  noted,  are  of  much  wider 
distribution  than  formations.  The  names  of  systems  are  mostly 
uniform  throughout  the  world,  as  Devonic,  Triassic,  Cretacic,  etc. 
American  terms  have  in  some  cases  been  proposed  where  the  origi- 


1 1 12  PRINCIPLES    OF    STRATIGRAPHY 

nal  European  names  seemed  less  desirable.  Thus,  Taconic  has 
been  used  for  Cambric,  Champlainic  for  Ordovicic,  Ontario  for 
Siluric,  Guadaloupic  for  Permic.  Where  names  proposed  origin- 
ally for  series  became  those  of  systems,  on  the  raising  of  the 
original  series  to  the  rank  of  a  system,  they  naturally  differed  in 
different  countries.  Thus  the  original  Subcarboniferous  is  known 
as  the  Mississippic  in  America  and  is  now  regarded  as  a  separate 
system,  while  in  eastern  Europe  it  is  the  Donjetic  and  in  western 
Europe  the  Dinantic.  The  old  Lower  Cretacic  or  Infra-Cretacee  *  is 
the  Neocomic  of  Europe,  in  its  broader  sense,  and  the  Comanchic 
of  America.  The  names  of  series  generally  differ  in  different  coun- 
tries, and  those  of  stages  in  the  different  sections  of  the  same  coun- 
try. The  name  in  either  division  is  derived  from  a  typical  locality 
and  the  appropriate  ending  (ian,  ien)  is  affixed.  When  the  name 
itself  is  not  adaptable  in  its  original  form,  the  practice  generally  has 
been  to  substitute  the  Latin  form  (Turonien  from  Touraine,  Cam- 
panien  from  Champagne  and  Carentonien  from  the  Charent). 
Sometimes  the  name  is  derived  from  the  original  name  of  the 
locality,  as  Cambrian  from  Cambria,  the  old  Roman  name  for 
North  Wales,  and  Cenomanien  from  Coenomanum,  the  old  Latin 
name  of  the  town  of  Mans  in  the  Department  of  Sarthe  and  Roth- 
omagien  from  Rothomagus,  the  Roman  name  of  Rouen. 


MAPPING. 

The  question  is  often  asked :  Should  geologic  maps  express 
primarily  formations  or  geologic  horizons  ?  In  other  words,  should 
the  mapping  be  based  on  lithic  formations  or  on  time  units?  The 
decision  generally  has  been  in  favor  of  the  mapping  of  lithic  units 
or  formations.  Generally  the  units  have  been  small  enough  to 
allow  a  grouping  into  systems,  and  these  have  then  been  referred 
to  their  proper  time  period.  This  method  is  apparently  the  most 
satisfactory,  since  all  mappable  features,  such  as  the  outcrops 
themselves,  as  well  as  the  topography  of  the  region,  are  the  direct 
consequence  of  the  lithic  formations,  and  have  no  regard  whatever 
to  time  relations.  The  present  outcrops  show  only  the  present  ex- 
tent of  the  formations,  and  give  no  clue  to  the  former  extent  of  the 
strata  deposited  during  a  given  time  interval,  except  in  so  far  as 
the  lithic  character  of  the  formation  indicates  this. 

Mapping  on  Formational  Basis.  The  United  States  Geological 
Survey  has  adopted  the  formation  as  its  cartographic  unit,  mapping 

*  In  recent  classifications  this  term  is  discarded.    See  Haug  Traite",  p.  1170. 


GEOLOGICAL   MAPPING  1113 

being  hence  conducted  on  a  lithic  basis.  "As  uniform  conditions 
of  deposition  were  local  as  well  as  temporary  it  is  to  be  assumed 
that  each  formation  is  limited  in  horizontal  extent.  The  forma- 
tion should  be  recognized  and  should  be  called  by  the  same  name 
as  far  as  it  can  be  traced  and  identified  by  means  of  its  lithologic 
character,  its  stratigraphic  association  and  its  contained  fossils." 
(18:75.)  I*1  mapping  it  is  often  impossible  to  draw  a  sharp  line 
when  two  contiguous  formations  grade  into  each  other.  In  such 
cases  the  boundary  has  to  be  more  or  less  arbitrarily  established. 
An  example  of  this  is  the  Siluro-Devonic  boundary  of  the  Helder- 
bergs.  Here  in  some  places  the  Manlius  or  uppermost  Siluric 
member  is  found  to  grade  up  into  the  Coeymans  or  lower  Devonic 
member  both  lithically  and  faunally.* 

Mapping  on  Faunal  Basis.  When  two  formations  of  the  same 
lithic  character  are  separable  by  their  faunal  content  only  it  is 
often  found  practicable  to  map  them  separately  on  a  purely  faunal 
basis.  In  such  a  case  it  is  frequently  necessary  to  represent  the 
transition  portion  by  a  commingling  of  colors  of  the  two  series. 
Sometimes  the  faunal  change  is  a  horizontal  one,  where  two  distinct 
faunas  occupied  different  portions  of  the  province  at  the  same  time, 
there  being  no  change  in  lithic  character.  An  example  of  this  is 
seen  in  the  two  Portage  faunas  of  New  York,  the  Ithaca  and  the 
Naples,  which  existed  side  by  side  throughout  Portage  time.  This 
is  expressed  on  the  map  by  two  colors,  or  two  shades  of  the  same 
color,  which  horizontally  pass  into  each  other  or  overlap  along  the 
line  of  interlocking  of  the  faunas.  (Clarke-2.) 

Mapping  of  Discontinuous  Formations.  It  is  a  matter  of  com- 
mon experience  that  formations  change  in  passing  away  from  the 
shore  line,  certain  more  terrigenous  ones  (as  sandstones,  etc.) 
coming  to  an  end  and  others  of  more  truly  marine  origin  (such  as 
limestones)  appearing.  As  a  result,  detailed  maps  of  adjoining 
areas,  not  parallel  to  the  old  shore  line,  may  exhibit  considerable 
diversity  of  formations,  and  it  may  even  happen  that  quadrangles 
not  so  far  removed  from  each  other  may  exhibit  scarcely  any  for- 
mations of  the  same  name.  Thus  the  Columbia  quadrangle  of 
Central  Tennessee  (Hayes  and  Ulrich-9)  and  the  McMinnville 
quadrangle  of  eastern  Tennessee  (Hayes-8)  have  no  formations 
in  common,  though  they  are  separated  by  an  interval  f  of  only 

*  This  is  not  always  the  case,  however,  and  this  close  relationship  has  been 
.denied  by  Ulrich.  But  there  can  be  no  question  of  this  gradation  in  the  Schoharie 
region  of  New  York  (see  Grabau-6). 

f  The  Chattanooga  formation  which  appears  on  both  maps  is  not  of  the 
same  age,  being  younger  in  the  more  eastern  quadrangle. 


IH4 


PRINCIPLES    OF    STRATIGRAPHY 


two  quadrangles.  This  distinctness  is  partly  due  to  the  fact  that 
formations  represented  in  one  are  wanting  in  the  other,  owing  to 
discontinuity  of  sequence  (represented  by  either  unconformities  or 
disconformities).  It  would,  however,  be  just  as  true  if  the  forma- 
tions were  complete  in  both.  The  greater  number  of  subdivisions 
found  in  the  more  western  nearer  shore  phase  of  the  lower 


is 


(Ordovicic)  system,  while  the  Siluric  and  Mississippi  systems  have 
their  nearer  shore  phase  in  the  eastern  sections.    The  following  dia- 


FIG.  263.  A.  Section  showing  variation  of  strata  from  shore  seaward.  B. 
The  same  section  after  folding  and  erosion.  C,  D.  Maps  of 
the  same  region,  representing  the  two  end  quadrangles  which 
have  scarcely  any  formations  in  common. 

grams  (Fig.  263)  illustrate  the  change  in  formations  away  from 
shore,  and  the  resultant  differences  in  the  cartographic  units  of  two 
quadrangles  separated  by  an  interval  of  one  quadrangle  only.  In 
the  eastern  portion  of  the  section  only  sands  were  deposited,  con- 
stituting but  one  formation.  Owing  to  repeated  oscillation  during 
the  deposition  of  these  sands,  a  series  of  intercalations  of  the  more 
off-shore  clays  and  the  still  more  distant  limestones  occurred. 
Two  anticlinal  folds  were  formed  which  subsequently  suffered 
erosion  and  exposed  the  succession  of  beds.  The  strike  of  the  eroded 
strata  is  northeasterly,  though  the  section  is  due  east  and  west  at 


CHARACTER  AND  KINDS  OF  GEOLOGIC  MAPS    1115 

right  angles  to  the  original  shoreline.  The  two  quadrangles  mapped 
have  only  formations  b,  c,  and  d  (called  b1,  cl,  d1)  in  common. 
Formation  b1  of  the  western  quadrangle  is,  however,  more  nearly 
equivalent  to  the  upper  part  of  c,  as  it  appears  in  the  eastern  quad- 
rangle. The  bed  c1  of  the  western  quadrangle  is  only  a  part — the 
lower — of  bed  c  as  it  appears  in  the  eastern  quadrangle,  while  d1 
and  d  are  almost  exact  equivalents.  In  the  eastern  quadrangle  occur 
the  formations  a  and  e,  which  are  not  found  in  the  western 
one,  while  the  latter  shows  formations  /,  g,  h,  i,  m  and  y,  not  found 
in  the  eastern  quadrangle.  In  the  eastern  quadrangle,  furthermore, 
the  formations  differ  on  opposite  sides  of  the  valley,  b  being  tHin 
on  fhe  eastern  and  thick  on  the  western  side,  while  c  and  d  of  the 
western  side  are  represented  by  e  on  the  eastern  side. 


Types  of  Geological  Maps. 

Formation  and  System  Maps.  Two  kinds  of  geological  maps 
are  in  vogue  in  most  countries.  These  are  the  formation  map  and 
the  system  map.  The  first  takes  account  of  the  geological  forma- 
tions, and  is  illustrated  by  the  folio  sheets  of  the  Geological  Atlas 
of  the  United  States,  already  referred  to.  In  these  each  formation 
is  given  a  distinct  color,  or  pattern,  all  the  formations  of  a  system 
generally  being  grouped  together  under  a  similar  tint,  such  as  pink, 
brown,  etc.  For  the  production  of  such  maps,  large  scale  base- 
maps  are  needed,  those  used  by  the  United  States  Geological  Sur- 
vey being  mostly  on  the  scale  of  I  to  62,500,  or  approximately  i 
inch  to  a  mile.  As  the  scale  of  the  map  is  increased,  smaller  units 
can  be  mapped,  and  structural  details  not  representable  on  the 
smaller  scale  map  may  be  introduced.  The  system  map  aims  to 
represent  in  distinctive  colors  only  the  geologic  systems,  each  of 
which  receives  a  distinct  color  pattern.  The  new  geological  map 
of  North  America,  issued  by  the  United  States  Geological  Survey, 
may  be  taken  as  an  example  of  this  type.  Here  eighteen  distinct 
color  shades  are  used  to  represent  the  systems  from  the  Cambric 
to  the  Quaternary,  though  for  convenience  the  boundary  in  a  few 
cases  is  not  drawn  precisely  at  the  dividing  line  between  the 
systems. 

The  International  Geological  Map  of  Europe  is  also  a  system 
map,  though  the  attempt  has  there  been  made  to  differentiate  by 
distinctive  shades  the  lower,  middle  and  upper  portions  of  some  of 
the  systems  (e.  g.,  Triassic,  Jurassic,  etc.). 

Intermediate  Maps.    Maps  intermediate  between  the  system  and 


in6  PRINCIPLES    OF    STRATIGRAPHY 

formation  map  are  also  known.  The  best  examples  are  the  com- 
plete maps  of  New  York  State,  on  the  scale  of  5  miles  to  I  inch, 
while  the  map  issued  with  the  summary  final  report  of  the  Second 
Geological  Survey  of  Pennsylvania  may  serve  as  another  example. 
These  maps  represent  series  rather  than  formations,  though  in 
many  cases  the  series  consist  practically  of  one  formation  only,  such 
as  the  Onondaga  limestone.  In  other  cases  the  unit  mapped  in- 
cludes what,  on  a  map  of  larger  scale,  would  be  represented  as 
several  distinct  formations.  Such,  for  example,  is  the  Clinton  series 
which  on  the  New  York  State  map  is  shown  by  one  color  only, 
while  on  the  map  of  the  Rochester  quadrangle  it  is  shown  as  five 
distinct  formations.  The  Portage  group,  represented  as  a  single 
unit  on  the  State  map,  is  divided  into  eleven  formations  on  the 
Canandaigua-Naples  map  (1/62,500),  exclusive  of  the  Genesee 
shale  and  the  Tully  limestone. 

Notation  of  Formations  on  Map.  In  addition  to  the  color  and 
pattern  used  in  the  representation  of  the  formations  or  larger 
units,  a  conventional  sign,  which  may  be  a  letter,  or  combination 
of  letters,  or  a  number  is  used.  This  insures  greater  ease  in  identi- 
fying the  formation  on  the  map.  The  United  States  Survey, 
in  its  folios,  has  adopted  a  group  of  letters  as  the  symbol,  the 
first  letter  representing  the  horizon,  the  other  the  name  of  the 
formation.  Thus,  on  the  Hancock  quadrangle,  where  the 
Siluric  is  represented  by  five  formations  some  of  the  symbols 
are:  Sc,  Clinton  shale;  Smk,  McKenzie  formation;  Stw,  Tonolo- 
way  limestone.  The  S  in  each  case  signifies  Siluric  (Silurian). 
In  the  Geological  Map  of  North  America,  above  referred  to, 
numbers  are  used  to  further  differentiate^  the  systems  from  one 
another. 

Legend.  In  order  that  the  proper  superposition  of  the  forma- 
tion may  be  ascertained,  a  legend  is  added  consisting  of  small 
rectangles  colored  to  correspond  to  the  color  pattern  which  it  repre- 
sents on  the  map,  and  furnished,  moreover,  with  the  corresponding 
symbol  and  the  name  of  the  formation.  These  rectangles  are  ar- 
ranged in  the  order  of  superposition  or  sequence.  As  a  rule,  the 
oldest  formation  is  put  at  the  bottom  and  the  youngest  on  top. 
The  New  York  State  Survey  has,  however,  adopted  in  some  of  its 
larger  maps  the  reverse  arrangement,  the  oldest  being  on  the  top. 
This  is  done,  apparently,  to  bring  the  color  pattern  of  the  legend 
into  harmony  with  that  of  the  map ;  in  which  the  successive  older 
formations  crop  out  in  belts  of  decreasing  age  from  the  north 
southward. 


GEOLOGICAL   SECTIONS  1117 


Continuous  and  Discontinuous  Mapping. 

Since  rock  outcrops  are,  as  a  rule,  scattered  over  a  consider- 
able area  with  intervening  portions  in  which  the  rock  is  covered 
by  glacial  or  other  loose  soil  deposits,  two  modes  of  mapping  on 
the  same  scale  have  come  into  usage.  The  first  is  the  mapping  of 
outcrops  only,  forming  what  may  be  called  outcrop  maps.  The 
intervening  covered  spaces  may  be  left  blank  or  may  be  colored 
for  the  superficial  deposits.  The  result  will  be  a  map  very  difficult 
to  read  and  to  follow,  while  the  structure  of  the  region  is  not 
readily  ascertainable  from  such  a  map.  The  practice  of  printing 
the  pattern,  representing  the  superficial  unconsolidated  deposit, 
over  the  color  pattern  of  the  formation  is  adopted  in  some  quarters, 
as  in  the  case  of  the  International  Geological  Map  of  Europe. 
American  maps,  as  a  rule,  represent  rock  formations  only,  with- 
out the  overtint  for  superficial  unconsolidated  deposits.  These  de- 
posits are  either  entirely  omitted  or  represented  on  a  separate  map. 
It  is,  of  course,  understood  that  in  such  cases  the  map  does  not 
represent  an  accurate  picture  of  the  surface  features  of  the  litho- 
sphere,  but  is  hypothetical  so  far  as  the  covered  portions  are  con- 
cerned. In  a  region  of  simple  structure  no  appreciable  errors  are 
likely  to  arise  from  such  a  mapping,  but  in  a  complicated  region  this 
may  readily  be  the  case. 

SECTIONS. 

Types  of  Sections.  Geological  sections  are  of  three  kinds :  ( I ) 
the  natural  cross-section,  (2)  the  columnar  section,  and  (3)  the 
ideal  section.  The  natural  cross-section  represents  structure  (in 
so  far  as  it  is  ascertainable)  and  surface  features,  and  is  the  one  most 
generally  employed  in  connection  with  geological  representation. 
It  gives  the  third  dimension  of  the  land  form,  the  other  two  being 
furnished  by  the  map.  Cross-sections  should,  whenever  the  scale 
permits  it,  be  drawn  to  the  natural  scale,  i.  e.,  vertical  and  horizontal 
scales  should  be  alike.  In  some  instances  this  is  not  possible,  owing 
to  the  smallness  of  the  scale  and  the  large  number  of  structural 
features  to  be  represented.  In  such  cases  an  exaggeration  of  the 
vertical  over  the  horizontal  scale, is  necessary,  but  this  should  not 
be  over  five  times,  or,  in  rare  cases,  ten  times,  the  horizontal.  It 
must  be  borne  in  mind  that  vertical  exaggeration  of  the  scale  always 
involves  an  increase  in  the  steepness  of  dip  of  the  strata  and  a  cor- 
responding distortion  of  other  characters. 


ni8  PRINCIPLES    OF    STRATIGRAPHY 

Columnar  sections  are  designed  to  show  the  superposition  and 
relative  thickness  of  the  strata  of  the  region  which  they-  represent, 
provided  they  are  drawn  to  scale.  They  serve  their  main  purpose 
in  giving  a  quick  and  comprehensive  view  of  the  stratigraphy  of  a 
region  and  in  making  comparison  with  other  regions  possible.  If  a 
uniform  set  of  scales,  each  a  multiple  of  the  others,  could  be  adopted, 
ready  comparisons  of  published  sections  for  different  regions  would 
be  possible,  and  would  greatly  facilitate  the  work  of  correlation. 

Ideal  sections  are  attempts  to  restore  the  conditions  as  they  were 
before  deformation  or  erosion  has  taken  place.  The  term  is  also 
sometimes  used  for  generalized  cross-sections,  but  this  is  better 
avoided.  In  so  far  as  structure  is  eliminated,  the  columnar  section 
is  an  ideal  section,  but  sections  to  which  the  term  is  best  applicable 
should  show  a  wider  relationship  than  is  possible  in  a  columnar 
section.  Fig.  152,  page  739  and  Figs.  157  and  158,  page  743,  are 
examples  of  ideal  cross-sections. 


THE  LENGTH  OF  GEOLOGICAL  TIME. 

Various  estimates  of  the  actual  length  of  geologic  time  have  been 
attempted,  the  basis  of  most  of  such  estimates  being  the  rate  of 
deposition,  ascertainable  in  modern  river  systems,  or  the  rate  of 
erosion  of  river  canyons,  such  as  the  Niagara,  the  Yellowstone, 
Colorado,  etc.,  and  the  rate  of  retreat  of  the  Falls  of  St.  Anthony. 
(See  Williams- 1 9.)  If  it  can  be  ascertained  that  the  beginnings 
of  erosion  have  a  definite  relation  to  some  other  event  which  itself  is 
of  definite  value  in  geochronology,  a  basis  for  a  rational  estimate  of 
the  actual  time  duration  is  furnished.  Such  a  relationship  seems  to 
have  existed  between  the  beginnings  of  the  Falls  of  Niagara  and  of 
St.  Anthony,  and  the  end  of  the  Pleistocenic  glacial  period.  So 
many  questionable  factors,  however,  enter  into  the  problem,  that 
it  is  scarcely  worth  while,  with  our  present  incomplete  knowledge, 
to  attempt  much  more  than  the  most  general  estimate.  Thus 
Cambric,  Ordovicic  and  Siluric  time  has  been  estimated  at  10,000,- 
ooo  years ;  Devonic  time  at  2,000,000  years ;  Mississippic  to  Permic 
time  at  5,000,000  years,  making  a  total  of  17,000,000  years  for  the 
Palaeozoic.  Mesozoic  time  has  been  estimated  at  7,000,000  years, 
Caenozoic  at  3,000,000  years  and  Psychozoic  at  50,000,  marking  a 
total  of  27,050,000  years  since  the  beginning  of  Cambric  time.  This 
estimate  is  conservative,  others  having  made  a  much  larger  one.  Thus 
Dana's  estimate  of  the  age  the  earth  was  at  least  48,000,000  years. 
Geikie's  estimate  ranges  from  100,000,000  to  680,000,000  years, 


LENGTH    OF    GEOLOGIC    TIME  1119 

while  McGee  has  suggested  a  possible  age  of  7,000,000,000  years 
for  our  earth.  Since  we  have  not  as  yet  ascertained  the  actual 
thickness  of  the  stratified  rocks  of  the  earth,  and  since  we  know  so 
little  about  the  rate  of  erosion,  we  must  conclude  that  all  such  esti- 
mates are  premature  and  almost  valueless,  and  that  even  the  esti- 
mates of  the  proportional  length  of  duration  of  the  various  divi- 
sions are  extremely  hypothetical.  Geological  time  was  long,  very 
long,  as  measured  in  terms  of  human  chronology — long  enough  to 
permit  the  development  of  the  multifarious  forms  of  life  upon  the 
earth.  Only  a  part  of  this  time  is  recorded  in  the  known  rocks  of 
the  earth's  crust — for  there  are  probably  many  lost  intervals,  the 
duration  of  which  we  cannot  even  estimate. 


BIBLIOGRAPHY  XXXI. 

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2.  CLARKE,  J.  M.     1903.     The  Naples  Fauna  in  Western  New  York.     New 

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American  Book  Company,  New  York. 

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American  Journal  ot  Science,  4th  series,  Vol.  XXXII,  pp.  256-268. 

14.  SCHUCHERT,  CHARLES.     1910.     Paleogeography  of  North  America. 

Geological  Society  of  America  Bulletin,  Vol.  XX,  pp.  427-606,  56  pis. 


1 120  PRINCIPLES    OF    STRATIGRAPHY 

15.  SINCLAIR,  W.  J.     1910.     Interdependence  of  Stratigraphy  and  Paleon- 

tology. The  Paleontologic  Record,  pp.  9-11.  Reprinted  from  Popular 
Science  Monthly. 

1 6.  ULRICH,  EDWARD  O.     1904.     In  Tail's  Preliminary  Report  on  the 

Geology  of  the  Arbuckle  and  Wichita  Mountains  in  Indian  Territory  and 
Oklahoma.  United  States  Geological  Survey,  Professional  Paper  No.  31, 
pp.  11-81. 

17.  ULRICH,  E.  O.     1911.     Revision  of  the  Paleozoic  System.     Bulletin  of 

the  Geological  Society  of  America,  Vol.  XXII,  pp.  281-680,  pis.  25-29. 

1 8.  UNITED    STATES    GEOLOGICAL    SURVEY.     1903.      Nomenclature 

and  Classification  for  the  Geologic  Atlas  of  the  United  States.  24th 
Annual  Report. 

19.  WILLIAMS,  HENRY  S.     1895.     Geological  Biology.      An    Introduction 

to  the  Geological  History  of  Organisms.    New  York.    Henry  Holt  &  Co. 
I9a.  WILLIAMS,  HENRY  S.     1893.      The  Elements  of  the  Geological  Time 
Scale.     Journal  of  Geology,  Vol.  I,  pp.  283-295. 

20.  WILLIS,    BAILEY.     1901.     Individuals   of   Stratigraphic   Classification. 

Journal  of  Geology,  Vol.  IX,  pp.  557-569- 


CHAPTER    XXXII. 

CORRELATION:    ITS  CRITERIA  AND   PRINCIPLES— 
PAL^OGEOGRAPHY. 

CORRELATION. 

"The  fundamental  data  of  geologic  history  are:  (i)  local  se- 
quences of  formations;  and  (2)  the  chronologic  equivalences  of 
formations  in  different  provinces.  Through  correlation  all  forma- 
tions are  referred  to  a  general  time  scale,  of  which  the  units  are 
periods.  The  formations  made  during  a  period  are  collectively  des- 
ignated a  system!'  (Rule  14,  Nomenclature  and  Classification  for 
the  Geologic  Atlas  of  the  United  States.) 


History  of  Development  of  Methods  of  Correlation. 

Correlation  of  strata,  or  the  establishment  of  an  orderly  relation- 
ship between  the  formations  of  separate  regions,  has  been  one  of 
the  chief  aims  of  stratigraphers  ever  since  the  days  of  Werner  and 
William  Smith.  Werner's  correlations  were  based  on  the  lithic 
character  of  the  strata,  but  William  Smith  in  England  and  Cuvier 
and  Brogniart  in  France  made  their  identifications  of  strata  by 
means  of  the  organic  remains  included  in  them.  Each  of  these 
workers  based  his  investigation  upon  the  ascertained  succession 
of  strata  in  the  region  selected  by  him  as  typical,  and  thus  the 
three  fundamental  criteria  of  correlative  geology :  lithic  similarity, 
likeness  of  fossil  content  and  superposition  of  strata,  were  made 
use  of  by  the  pioneers  in  stratigraphy. 

The  efforts  of  these  founders  of  stratigraphy  were  directed 
chiefly  toward  establishing  the  identity  or  correspondence  of  strata 
between  different  localities ;  and,  when  it  was  recognized  that  strata 
were  formed  at  different  periods  in  the  earth's  history,  the  effort 
was  further  directed  toward  establishing  the  time-equivalency  or 
synchroneity  of  strata.  Before  fossils  were  extensively  studied, 

II2I 


1 122  PRINCIPLES    OF    STRATIGRAPHY 

similarity  of  superposition  and  lithic  identity  were  taken  as  the 
guides  to  synchroneity,  a  proceeding  which  naturally  led  to  many 
erroneous  correlations.  Thus  McClure  and  Eaton  in  their  early 
studies  of  the  rocks  of  the  United  States  were  entirely  guided  by 
superposition  and  lithic  and  structural  character  of  the  rocks,  their 
classification  being  modeled  upon  that  of  Werner.  Both  McClure 
and  Eaton  identified  the  undisturbed  Palaeozoic  formations  of  east- 
ern United  States  with  the  Secondary  or  Mesozoic  formations  of 
England,  being  thus  influenced  in  their  correlation  by  another  cri- 
terion, namely,  the  relative  position  of  the  strata.  Lithic  similarity 
caused  Eaton  to  identify  the  Rochester  shale  of  New  York  (Lower 
Siluric)  with  the  Lias  of  England  (Lower  Jurassic).  Lithic  sim- 
ilarity and  similarity  of  superposition  led  many  of  the  early  geolo- 
gists to  identify  the  Potsdam  sandstone  and  the  quartzose  sand 
rock  of  Vermont  as  of  the  same  age,  though  one  is  Upper  and 
the  other  Lower  Cambric.  In  the  same  manner  lithic  similarity 
led  some  of  the  earlier  geologists  to  identify  the  Upper  Cambric 
or  early  Ordovicic,  Lake  Superior  sandstone  with  the  Triassic  sand- 
stone of  New  Jersey  and  the  Connecticut  Valley,  while  the  ribbon 
limestones  of  Pennsylvania  and  New  Jersey,  of  Cambric  and  Lower 
Ordovicic  age,  and  the  Waterlimes  of  the  Hudson  River  region — of 
Upper  Siluric  age — were  not  so  long  ago  thought  to  be  stratigraphic 
equivalents,  on  account  of  their  great  similarity  in  lithic  characters. 
Superposition,  sometimes  erroneously  inferred,  similarity  of  lithic 
character,  and  superficial  comparison  of  fossils  led  Bigsby  in  1824 
to  identify  the  Rideau  sandstone  of  Kingston,  Ontario  (Lower 
Ordovicic),  with  the  Medina  of  the  Niagara  and  Genesee  gorges 
(Lower  Siluric),  and  both  with  the  Old  Red  Sandstone  of  Eng- 
land, on  account  of  lithic  resemblance  of  the  two  formations,  and 
the  apparent  similarity  of  fossils  in  the  limestones  overlying  them. 
In  his  later  investigations  Eaton,  like  Bigsby,  made  use  of  fossils 
in  correlation,  but  the  comparisons  made  by  both  were  of  the 
crudest,  being  chiefly  by  classes  of  organisms.  Thus  the  Ordovicic 
conglomerates  opposite  Quebec  were  correlated  by  Bigsby  with  the 
"Carboniferous  limestone"  of  England,  because  both  contain  re- 
mains of  trilobites,  "encrinites,"  "corallites"  and  other  fossils.  An- 
other of  the  early  correlations  of  formations  by  lithic  characters  was 
made  in  1821  by  Dr.  Edwin  James.  He  considered  that  the  sand- 
stone of  Sault  Ste.  Marie  (Cambric  or  early  Ordovicic)  the  Trias- 
sic sandstone  of  the  eastern  foothills  of  the  Rocky  Mountains,  the 
Catskill,  Medina  and  Potsdam  sandstones  of  New  York  and  the 
Newark  sandstone  of  New  Jersey  were  of  the  same  relative  geologic 


HISTORY    OF    CORRELATIVE    GEOLOGY        1123 

age  and  occupied  a  place  similar  to  that  assigned  to  the  "Old  Red 
Sandstone"  by  Werner.  Geologists,  however,  were  not  long  in  find- 
ing out  that  beds  of  the  same  lithic  character  are  not  all  of  the 
same  age,  but  it  has  taken  them  much  longer  to  realize  that  beds  of 
the  same  age  are  not  always  of  the  same  or  even  similar  lithic  char- 
acter. 

With  the  detailed  study  of  the  New  York  strata  by  the  five 
geologists  and  palaeontologists  on  the  survey  (Mather,  Emmons, 
Vanuxem,  Conrad  and  Hall),  correlation  by  fossils  became  recog- 
nized as  the  most  reliable  known  method.  At  first  American  species 
were  directly  identified  with  European  types,  and  such  identification 
was  in  many  cases  not  far  wrong.  Extensive  collections  of  fossils, 
however,  soon  showed  that  the  rocks  of  this  country  contained  an 
assemblage  of  organisms  largely  peculiar  to  themselves  and  specifi- 
cally, if  not  generically,  distinct  from  that  of  Europe.  Correlation  by 
similarity  of  faunas  was  then  substituted  for  correlation  by  species 
and  so  the  general  correspondence  of  the  strata  in  the  two  continents 
was  established.  The  need  of  an  American  standard  of  comparison 
was  soon  felt,  and  such  a  need  was  supplied  by  the  development 
of  the  "New  York  series"  of  geological  formations.  The  succes- 
sion of  New  York  strata  and  the  organic  remains  characterizing 
them  was  so  thoroughly  worked  out  that  "it  is  and  has  been  for 
decades  a  standard  of  reference  for  all  students  of  the  older  rocks 
throughout  the  world."  (Clarke-n.)  Professor  James  Hall  was 
one  of  the  first  in  America  to  recognize  the  importance  of  naming 
formations  from  localities  in  which  they  were  best  exposed.  In 
his  report  to  the  New  York  State  legislature  in  1839  he  urges  that 
neither  lithic  character  nor  characteristic  fossils  is  a  satisfactory 
source  from  which  to  derive  the  name  of  the  formation,  for  the 
first  may  change  while  the  second  is  not  always  ascertainable  and 
may  even  be  absent.  He  holds  that  it  "becomes  a  desideratum  to 
distinguish  rocks  by  names  which  cannot  be  traduced,  and  which, 
when  the  attendant  circumstances  are  fully  understood,  will  never 
prove  fallacious."  Such  names  can  be  derived  only  from  localities. 
It  is  most  fortunate  that  this  principle  was  recognized  before  the 
New  York  series  of  formations  was  fully  promulgated  in  the  final 
reports  of  the  survey.  As  a  result,  the  majority  of  formations  were 
named  from  typical  localities,  only  a  relatively  small  number  re- 
taining the  lithic  or  palaeontologic  names  given  them  by  the  earlier 
investigators.  More  recently  these,  too,  have  been  replaced  by 
names  derived  from  typical  localities,  of  which  the  following  is  a 
partial  list: 


1 124  PRINCIPLES    OF    STRATIGRAPHY 

Calcif erous i replaced  by  Beekmantown. 

Birdseye replaced  by  Lowville. 

Waterlime  (of  Buffalo) replaced  by  Bertie. 

Coralline replaced  by  Cobleskill. 

Waterlimes  (of  the  Hudson) replaced  by  Rondout  &  Rosendale 

Tentaculite  limestone replaced  by  Manlius. 

Lower  Pentamerus replaced  by  Coeymans. 

Delthyris  shaly replaced  by  New  Scotland. 

Upper  Pentamerus replaced  by  Becraf t. 

Upper  Shaly replaced  by  Port  Eweh. 

Cauda-Galli replaced  by  Esopus. 

Corniferous replaced  by  Onondaga 

As  the  Palaeozoic  formations  of  other  districts  of  North  America 
were  studied,  it  was  found  that  the  correspondence  between  them 
and  the  New  York  formations  was  not  as  close  as  could  have  been 
hoped.  Not  only  did  the  lithic  character  of  the  strata  change 
when  traced  away  from  the  type  locality,  but  the  superposition  did 
not,  in  many  cases,  correspond,  some  formations  being  absent  alto- 
gether while  others  were  found  to  be  united  in  a  single  unit,  often 
of  slight  thickness.  Even  the  fossils,  which  had  gradually  come  to 
be  looked  upon  as  the  surest  indicators  of  position  in  the  geologic 
scale,  appeared  in  horizons  not  known  to  contain  them  in  New  York. 
Thus  the  chain-coral  Halysites  was  universally  thought  to  be  char- 
acteristic of  the  Lower  Siluric  (Niagaran)  age,  until  it  was  dis- 
covered that  this  coral  also  occurred  in  the  Ordovicic,  in  some  of 
the  localities  west  of  New  York,  and  in  the  Anticosti  region,  while 
in  eastern  New  York  it  was  found  in  an  Upper  Siluric  horizon,  the 
Cobleskill,  which  is  stratigraphically  many  hundred  feet  above  the 
Niagaran  beds.  In  like  manner  Tropidoleptus  carinatus  and  some 
of  its  associates,  believed  formerly  to  be  restricted  to  the  Hamilton 
(Mid-Devonic)  formation,  were  found  in  south  central  New  York 
to  occur  in  the  Ithaca  (Portage)  beds  and,  again,  in  the  Chemung 
(Upper  Devonic). 

Recurrent  faunas  have  also  been  described  from  the  Mississipic. 
Weller  (53)  found  Devonic  elements  in  the  Kinderhook  fauna,  and 
Williams  and  others  have  described  such  recurrence  of  Devonic 
elements  in  the  Spergen  and  other  Mississippi  beds  of  central 
North  America.  Ulrich  (49  -.296)  has  noted  the  occurrence  of  the 
trilobite  Triarthrus  becki  in  the  Fulton  shale,  and  in  the  Southgate 
beds  156  feet  above  it. 

Chronological  Equivalency,  Contemporaneous  and  Homotaxial 
Formations.  Chronological  equivalency  as  one  of  the  fundamental 
data  of  geologic  history  has  repeatedly  been  assailed  by  eminent 
scientists.  Huxley,  indeed,  went  so  far  as  to  question  the  possi- 


CONTEMPORANEOUS    AND    HOMOTAXIAL        1125 

bility  of  determining  in  any  case  the  existence  of  contemporaneous 
strata,  and  he  coined  the  term  homotaxis,  signifying  similarity  of 
order,  to  express  the  correspondence  in  succession  rather  than  exact 
time  equivalence.  Geikie  also  held  that  "strict  contemporaneity 
cannot  be  asserted  of  any  strata  merely  on  the  ground  of  similarity 
or  identity  of  fossils"  (14:608),  and  H.  S.  Williams,  among 
American  authors,  has  most  strenuously  insisted  on  the  impossibility 
of  recognizing  strict  contemporaneity  among  strata  of  widely  sepa- 
rated regions.  Williams  would  refer  formations  not  to  a  general 
time  scale,  but  to  a  stratigraphic  scale,  of  which  not  "periods"  but 
systems  are  units.  He  advocates  the  revision  of  Rule  14  of  the 
U.  S.  Geological  Survey  quoted  at  the  beginning  of  this  chapter 
so  as  to  read  (56:73$)  : 

"The  -fundamental  data  of  geologic  history  are:  (i)  the  local 
sequence  of  formations  and  (2)  the  similarity  of  the  fossil  faunas 
of  the  formation  of  different  provinces.  Through  correlation  all 
formations  are  referred  to  a  standard  stratigraphic  scale,  of  which 
the  units  are  systems." 

Contrary  to  the  views  of  Huxley  and  other  writers,  some  of 
whom  like  Edward  Forbes  went  so  far  as  to  assert  that  similarity 
of  organic  content  of  distant  formations  is  prima  facie  evidence,  not 
of  their  similarity,  but  of  their  difference  of  age,  most  modern 
stratigraphers  have  come  to  believe  in  the  possibility  of  essential 
chronological  equivalency  of  formations  characterized  by  the  same 
faunas,  recognizing  at  the  same  time  the  fact  that  such  equivalency 
is  not  necessarily  indicated  by  the  similarity  of  faunas,  and  that  a 
given  fauna  may  appear  earlier  and  continue  longer  in  some  sections 
than  in  others.  The  rapidity  of  migration  shown  by  modern  faunas 
indicates  that,  if  the  path  is  open  and  no  barriers  exist,  widespread 
migration  or  dispersal  may  occur  within  such  short  time  limits  as 
to  be  considered  almost  homochronic. 

Contemporaneity  of  Faunas.  That  several  distinct  faunas  may 
exist  side  by  side  in  not  too  widely  separated  districts  is  a  well 
known  fact.  The  difference  of  faunas  north  and  south  of  Cape 
Cod  on  the  Atlantic  Coast  may  be  mentioned  as  a  modern  ex- 
ample; also  the  difference  between  the  Red  Sea  fauna  and  that  of 
the  Mediterranean,  and,  finally,  the  distinct  faunas  on  opposite  sides 
of  the  Isthmus  of  Panama.  In  all  of  these  cases  a  partial  or  com- 
plete land  barrier  separated  the  faunas.  In  the  case  of  Cape  Cod, 
this  barrier  is  incomplete  and,  although  aided  by  cold  currents  from 
the  north,  it  has  not  entirely  prevented  the  migration  around  it  of 
the  faunas.  The  other  two  barriers  were  complete,  and  separated 
faunas  of  different  provinces,  but  the  transsection  in  1869  °f  tne 


1 126  PRINCIPLES    OF    STRATIGRAPHY 

Suez  barrier  by  the  canal  has  permitted  a  certain  commingling  of 
faunas,  a  phenomenon  predictable  for  the  faunas  on  opposite  sides 
of  the  Isthmus  of  Panama  on  the  completion  of  the  canal. 

Contemporaneous  faunas  existed  in  North  America  at  various 
times  in  its  geologic  history.  The  most  noted  case  is  that  of  the 
Upper  Devonic.  An  indigenous  fauna,  the  Ithaca  fauna,  derived 
largely  by  development  from  the  earlier  Hamilton  fauna,  occupied 
the  eastern  area  in  New  York  and  Pennsylvania,  while  an  immigrant 
fauna,  the  Naples  fauna,  occupied  the  region  to  the  west  of  this. 
At  first  the  two  faunas  were  separated  by  a  land  barrier,  but  this 
was  subsequently  submerged.  Nevertheless,  the  two  faunas  con- 
tinued in  their  essential  integrity  through  Portage  time,  though  the 
area  of  occupancy  of  each  varied  from  time  to  time,  but  within 
comparatively  narrow  limits. 

Prenuncial  Faunas,  Colonies.  Prenuncial  faunas  are  the  ad- 
vance invaders  of  a  new  territory  of  members  of  a  foreign  host, 
which  subsequently  occupies  the  territory.  Such  have  been  noted 
in  some  cases,  especially  in  that  of  the  Styliolina  limestone  of  the 
Upper  Devonic  of  New  York,  which  marks  the  first  invasion  of 
the  Naples  fauna  into  this  Upper  Devonic  province. 

The  term  "Colonies"  was  employed  by  Barrande  to  designate 
the  appearance  of  a  fauna  normal  to  a  later  geological  horizon, 
during  a  period  when  an  earlier  fauna  still  flourished.  Though  the 
examples  cited  by  Barrande  have  proved  to  be  mostly  inadequate 
to  establish  his  theory,  the  fact  remains  that  faunas  in  their  en- 
semble suggestive  of  a  much  later  period  may  appear  in  deposits 
otherwise  marked  by  the  normal  fauna  of  that  period.  Thus,  during 
the  Upper  Siluric  (Upper  Monroan)  time,  a  fauna  in  large  measure 
suggestive  of  Middle  Devonic  time  flourished  in  Michigan,  Ohio, 
and  Ontario  (Anderdon  fauna).  In  this  fauna  something  over 
twenty  species  have  exact  specific,  or  closely  similar,  representatives 
in  the  Onondaga  or  Schoharie  formation.  This  similarity  is  largely 
found  in  the  coral,  brachiopod,  pelecypod,  and  trilobite  elements  of 
the  fauna,  while  the  cephalopods  and  gastropods  are  of  typical 
Siluric  species.  The  whole  fauna  is  succeeded  by  a  normal  Siluric 
fauna,  and  is  separated  by  an  extensive  hiatus  from  the  overlying 
limestones  of  Middle  Devonic  age.  The  explanation  of  this  com- 
mingling of  faunas  is  found  in  the  fact  that  two  faunas,  with  dis- 
tinctive characters,  existed  simultaneously,  one  of  which  furnished 
the  faunal  elements  with  Devonic  affinities,  but  did  not  make  much 
headway  against  the  resident  normal  Siluric  fauna.  Continuing  to 
modify  in  its  own  center  of  distribution,  the  more  specialized  fauna 
finally  evolved  into  the  normal  Middle  Devonic  fauna  of  that  region, 


STANDARD    SECTIONS  1127 

some  parts  of  which  spread  widely  over  the  earth,  and,  with  ele- 
ments derived  from  other  sources,  constituted  the  local  Middle  De- 
vonic  faunas  of  eastern  North  America.  (Grabau  and  Sherzer-2oa.) 

Standard  or  Type  Sections.  In  general  the  first  section  studied 
is  taken  as  the  type  section  for  the  country.  Often  it  is  not  the 
most  complete  nor  the  most  perfect  section,  as  in  the  case  of  the 
Devonic  section  of  southern  England  (Devonshire),  which  is  less 
perfect  than  that  of  the  Rhine  region;  or  the  Cretacic  section  of 
Colorado  and  Montana,  which  is  less  complete  than  that  of  Texas 
and  Mexico.  In  such  cases  it  not  infrequently  happens  that,  by  a 
process  of  natural  selection,  the  poorer  section  is  gradually  re- 
placed by  the  better,  as  in  the  case  of  the  Rhenish  Devonic,  which 
is  now  more  frequently  used  for  comparison,  or  the  Cambric  of 
Scandinavia,  which  is  more  satisfactory  than  that  of  Wales.  In 
America  the  type  section  for  the  Palaeozoic  formations  is  found  in 
the  State  of  New  York.  This  not  only  was  the  first  section  thor- 
oughly studied  in  this  country,  but,  what  is  more  significant,  it 
turned  out  to  be  in  many  respects  the  most  complete  and  most  rep- 
resentative of  all  American  Palaeozoic  sections.  So  truly  repre- 
sentative is  this  section  that,  "  .  .  .  while  other  classifications 
proposed  for  these  rocks,  contemporaneously  or  subsequently,  have 
fallen  to  the  ground,  it  has  withstood  all  the  attacks  of  time." 
(Clarke-n.) 

Not  a  little  did  the  detailed  palaeontologic  work  carried  on  by 
the  State  Survey  of  New  York  contribute  to  this  prominence  of  the 
New  York  Section.  No  other  American  region  has  had  the  organic 
remains  of  its  formations  so  fully  investigated  and  descriptions  and 
illustrations  of  them  published  in  such  a  complete  manner.  This 
thoroughness,  for  which  in  a  large  measure  James  Hall  was  re- 
sponsible, has  forever  made  the  New  York  column  the  foundation 
on  which  all  other  work  on  Palaeozoic  Stratigraphy  of  America 
must  be  based. 

In  spite  of  this  fact,  however,  the  relationships  between  the 
various  local  sections  of  the  State  of  New  York  have  not  yet  been 
fully  ascertained,  and  each  year  facts  are  discovered  which  de- 
mand a  modification,  in  details,  of  these  standard  sections. 

Nor  is  the  New  York  column  as  a  whole  complete  and  without 
flaws.  Undoubted  Middle  Cambric  appears  to  be  but  slightly  de- 
veloped in  the  state,  while  the  Lower  and  Upper  Cambric  also  are 
not  fully  represented,  so  far  as  the  sections  have  been  studied. 
Hence  the  American  type  sections  for  these  formations  are  ob- 
tained from  other  regions :  that  for  the  Lower  Cambric  from  north- 
western Vermont  and  that  for  the  Middle  Cambric  in  the  Acadian 


1 128  PRINCIPLES    OF    STRATIGRAPHY 

provinces  of  Canada.  In  the  latter  region  is  likewise  found  a  more 
complete  representation  of  the  Upper  Cambric  formations  than 
has  yet  been  ascertained  to  exist  in  the  State  of  New  York. 
It  is  on  this  account  that  the  East  Canadian  names  Bretonian, 
Acadian  and  Etcheminian  (cf.  Georgian)  have  been  used  for  the 
Upper,  Middle  and  Lower  Cambric,  respectively.  (Grabau-i/.) 

Again,  a  hiatus  exists  in  New  York  between  the  Ordovicic  and 
Siluric,  the  upper  part  of  the  Ordovicic  not  being  represented,  at 
least  not  by  fossiliferous  formations.  The  lower  Siluric,  too,  is 
less  satisfactorily  represented  in  New  York  than  elsewhere,  for, 
as  currently  understood,  it  begins  with  a  sandstone  formation,  the 
Medina,  which  is  a  shore  formation,  where  not  of  non-marine  origin. 
For  the  Upper  Ordovicic  and  Lower  Siluric,  then,  the  New  York 
column  has  to  be  piecejl  out  by  formations  developed  elsewhere, 
the  standard  selected  being  the  Cincinnati  group  of  the  south-cen- 
tral states  for  the  one,  and  the  lower  Mississippi  region  for  the 
other.*  Even  within  the  lower  Ordovicic  there  is  an  incomplete 
representation  of  the  top  of  the  Beekmantown  and  of  the  Chazy  for- 
mation, this  incompleteness  being  measurable  by  thousands  of  feet  of 
limestone  in  the  Mohawk  Valley,  but  by  very  much  less  in  the  Lake 
Champlain  region.  The  Salina  of  New  York,  of  Mid-Siluric  age, 
also  forms  an  unsatisfactory  member  of  the  standard  series,  as  al- 
ready pointed  out,  since  it  represents  abnormal  conditions  of  sedi- 
mentation. Aside  from  these,  however,  the  New  York  column 
represents  an  eminently  satisfactory  standard  of  the  Palaeozoic 
formation  below  the  Mississippic. 

The  standard  American  series  for  the  Mississippic  is  that  of  the 
Mississippi  Valley,  though  that  is  not  itself  a  complete  section. 
The  standard  marine  sections  for  the  Carbonic  and  Permic  have  not 
yet  been  fully  worked  out  for  this  country.  The  former  is  found 
in  Kansas,  Missouri  and  Arkansas ;  the  latter  in  Texas.  No  Ameri- 
can Triassic  or  Jurassic  standards  are  recognized,  the  fragmentary 
development  of  these  formations  being  referred  to  foreign  stand- 
ards. The  Comanchic  and  Cretacic,  on  the  other  hand,  are  well 
represented  by  formations  in  Mexico,  Texas  and  the  Great  Plains 
region,  which  localities  have  furnished  the  standard  section's.  The 
Comanchic  is  well  represented  in  the  southern  areas,  but  the  sections 
of  the  typical  Cretacic  in  the  standard  region  (Colorado  and  Mon- 
tana) are  incomplete  at  the  bottom  and  at  the  top,  where  they 
include  non-marine  formations,  «.  e.,  the  Dakota  sandstone,  and  the 

*  The  Anticosti  section  promises  to  be  one  of  the  most  perfect  North  American 
Lower  Siluric  (Niagaran)  sections,  but  it  is  not  as  yet  certain  in  how  far  this 
section  belonged  to  a  distinct  geographic  province.  (See  Schuchert~39:5J2.) 


METHODS    OF    CORRELATION  1129 

Laramie  formation.  The  standards  of  the  North  American  marine 
Eocenic  and  Oligocenic  are  found  in  the  Gulf  States,  while  those 
of  the  Miocenic  and  Pliocenic  are  found  on  "the  Atlantic  coast  of 
Maryland  and  Virginia,  the  Carolinas  and  Florida.  All  these  locali- 
ties together,  however,  furnish  only  a  partial  standard  of  the 
American  marine  Tertiary. 

A  Double  Standard.  In  some  cases  it  has  been  found  most 
practicable  to  have  a  double  standard  of  formations:  one  marine, 
the  other  non-marine.  This  has  been  most  fully  worked  out  for  the 
American  Tertiary,  where  the  continental  deposits  of  the  Great 
Plains  region  serve  as  a  standard  of  comparison  for  similar  de- 
posits of  other  American  regions,  while  the  Gulf  and  Atlantic 
Coast  deposits  serve  as  our  standard  of  marine  formations.  In 
western  Europe  the  Carbonic  is  represented  by  the  non-marine 
Westphalian  and  Stephanian,  while  the  corresponding  marine  forma- 
tions of  eastern  Europe  are  the  Moscovian  and  Uralian.  In 
America  the  Pocono-Mauch  Chunk  formations  are  the  non-marine 
equivalents  of  the  Mississippic,  and  the  Pennsylvanic  (Pottsville- 
Monongahela)  is  the  non-marine  standard  of  the  Carbonic,  the 
marine  standard  being  still  undetermined,  though  in  part  represented 
in  the  Kansas  section.  The  Laramie,  Belly  River,  Bear  River,  and 
Dakota  formations  form  a  nearly  complete  non-marine  standard  for 
the  American  Cretacic,  and  the  Kootanie  for  the  Comanchic. 


Methods  of  Correlation. 

The  means  by  which  formations  of  different  localities  are  cor- 
related may  be  summarized  as  follows : 

1.  Superposition. 

2.  Stratigraphic  continuity. 

3.  Lithic  characters. 

4.  Organic  conteiits. 

5.  Unconformities  or  disconformities. 

6.  Regional  metamorphism. 

7.  Diastrophism. 

i.     Superposition. 

The  basis  of  all  stratigraphic  work  is  the  ascertainment  of  the 
order  of  superposition  of  the  strata.  No  correlation  of  the  strata 
in  any  two  localities  is  possible  until  the  exact  superposition  in 


1 130  PRINCIPLES    OF    STRATIGRAPHY 

each  has  been  ascertained.  The  general  law  of  superposition  is : 
that,  of  any  two  strata  of  sedimentary  rocks,  the  one  zvhich  was 
originally  the  lower  is  also  the  older.  This  does  not,  of  course, 
apply  to  intruded  igneous  rock,  for  a  much  later  sheet  of  intrusive 
material  may  find  its  way  between  strata  very  much  older  and 
so  be  followed  by  strata  older  than  itself.  In  exceptional  cases, 
too,  sedimentary  rocks  may  not  follow  this  rule,  as  in  the  case  of 
deposits  in  caverns  cut  out  of  older  rocks.  Here  strata  may 
actually  form  beneath  the  surface  of  the  lithosphere  and  hence 
below  an  older  stratum. 

Of  course,  in  regions  of  faulting  and  strong  folding,  the  order 
of  the  strata  may  be  reversed,  so  that  it  becomes  necessary,  first 
of  all,  to  demonstrate  the  original  position  of  the  formations. 

In  the  ascertainment  of  the  superposition  of  strata  of  a  given 
region  great  care  must  be  taken  to  note  the  existence  of  strati- 
graphic  breaks.  Disconformities  of  strata  are  often  difficult  to 
recognize,  but  unless  ascertained  are  sure  to  introduce  an  element  of 
error  into  the  geologic  columns  of  the  region.  Abrupt  changes 
in  sedimentation  are  a  useful  guide  in  the  location  of  such  discon- 
formities  and,  in  fact,  where  such  sudden  changes  occur  it  may 
be  taken  as  an  indication  of  the  possibility  of  the  existence  of  such 
a  hiatus,  though  this  alone  is  not  sufficient  proof  of  its  existence. 
A  good  example  of  a  great  hiatus  indicated  only  by  an  abrupt 
change  in  the  character  of  the  rock  is  found  in  the  case  of  the  con- 
tact of  the  Black  Chattanooga  shale  with  the  gray  Rockwood  clays 
in  eastern  Tennessee.  Here  there  seems  to  be,  at  times,  no  other 
indication,  than  this  sudden  change  in  character,  of  the  absence, 
between  these  two  formations,  of  more  than  the  entire  Devonic 
system  of  strata.  Indication  of  erosion  surfaces,  and  the  inclusion 
of  the  fragments  of  the  lower  in  the  upper  beds,  commonly  charac- 
terize the  disconformity,  but  give  no  clue  as  to  the  magnitude  of 
the  hiatus.  The  change  from  one  lithic  unit  to  another  may  be 
abrupt,  without  necessarily  indicating  a  disconformity.  In  such 
cases,  generally,  there  is  some  alternation  of  beds  of  the  two  series 
before  the  complete  disappearance  of  the  lower  series..  Thus  the 
Black  Shale  at  the  top  becomes  intercalated  with  thin  bands  of 
the  overlying  formation,  and  itself  occurs  at  intervals  in  the  form  of 
thin  layers  for  some  time  after  the  extensive  development  of  the 
overlying  series. 

Correlation  by  superposition,  however,  is  a  method  fraught 
with  grave  dangers.  Thus  a  succession  of  formations  from  sand- 
stones to  shales  and  limestones  in  one  part  of  a  province  is  not 
necessarily  the  same  as  a  similar  series  in  another  part  of  the  same 


METHODS    OF    CORRELATION  1131 

province,  and  most  probably  not  the  same  as  a  similar  series  in 
another  geologic  province.  Indeed,  from  a  consideration  of  the 
phenomena  accompanying  marine  progressive  overlap,  it  becomes 
apparent  that  even  within  the  same  province  the  two  series  are  dif- 
ferent, unless  they  are  situated  along  a  line  parallel  to  the  old 
shore  of  the  time  when  the  strata  accumulated. 


2.     Stratigraphic  continuity. 

When  a  formation  can  be  traced,  with  but  slight  interruptions, 
over  a  wide  area,  the  general  assumption  is,  that  it  is  synchro- 
nous in  all  its  outcrops.  This  is  true  enough  where  the  tracing 
of  the  formation  is  parallel  to  the  old  shore  line,  or  source  of  sup- 
ply, but  not  always  true  when  at  an  angle  with  that  line.  This  is 
especially  the  case  when  the  formation  in  question  is  of  terrigenous 
origin,  formed  either  as  a  marine  or  as  a  fluviatile  deposit.  A 
basal  sandstone  or  conglomerate,  formed  in  a  transgressing  sea, 
rises  in  the  scale  shoreward ;  in  a  regressing  sea  it  rises  seaward 
(see  Chapter  XVIII).  The  Mahoning  sandstone  of  the  Lower  Con- 
emaugh  of  northwestern  Pennsylvania  had  been  traced  almost  con- 
tinuously around  the  bituminous  coal  field  and  united  with  the 
Charleston  sandstone  of  the  Kanawha  district  of  West  Virginia. 
It  has  since  been  shown,  however,  that  these  sandstones  are  part 
of  a  series  rising  and  overlapping  northwestward,  and  that,  where- 
as the  Charleston  end  of  the  series  lies  in  the  Lower  Allegheny,  the 
Mahoning  sandstone  proper  forms  the  westernmost  part  of  the 
series,  lying  at  the  base  of  the  Conemaugh.  (Campbell.) 

Limestones  are,  however,  much  more  continuous,  and,  if  traced 
for  moderate  distances,  are  apt  to  hold  their  own  pretty  well. 
This  is  especially  the  case  with  limestone  beds  of  slight  thickness 
interbedded  with  shales.  Thus  the  Encrinal  limestone  has  been 
recognized  in  all  its  outcrops,  from  Thedford,  Ontario,  to  the 
Genesee  Valley,  a  distance  of  over  200  miles,  holding  its  own 
throughout  in  lithic  character  as  well  as  fossil  content,  though 
there  are  other  strata  which  have  been  mistaken  for  it  farther 
east.  It  forms  a  prominent  plane  of  'correlation  of  the  strata,  for 
it  seems  pretty  certain  that  this  limestone  in  all  of  its  occurrences 
represents  simultaneous,  or  nearly  simultaneous,  accumulation  as 
the  result  of  widespread  uniformity  of  conditions.  (Shimer  and 
Grabau-43.) 

The  Agoniatite  limestone  of  the  New  York  Marcellus  has  been 
traced  from  Buffalo  to  Schoharie,  and  southward  to  Maryland. 


n32  PRINCIPLES    OF    STRATIGRAPHY 

This  limestone,  intercalated  between  black  shales,  indicates  a  pe- 
riod of  widespread  uniform  conditions,  followed  by  a  resumption 
of  the  Black  Mud  sedimentation.  It  therefore  serves  as  an  excel- 
lent horizon  marker,  by  which  the  rocks  above  and  below  can  be 
correlated.  Still  another  example  is  the  Cobleskill  of  New  York, 
which  has  been  traced  across  the  State,  chiefly  by  its  fauna,  and 
serves  as  a  datum-plane  for  the  strata  above  and  below  it. 


3.    Lit  hie  characters. 

Correlation  by  lithic  characters  is  possible  only  in  very  limited 
areas,  and  where  it  can  be  used  in  connection  with  stratigraphic 
continuity  and  order  of  superposition.  Under  certain  conditions, 
however,  the  lithic  character  becomes  an  important  guide  in  cor- 
relation. An  example  is  the  St.  Peter  sandstone,  a  pure  silicarenyte, 
which  has  been  widely  recognized  by  its  lithic  character,  and  its 
enclosure  within  pure  limestone  or  dolomytes.  The  uniformity  of 
grain  and  composition  over  thousands  of  square  miles  of  area 
is  its  most  remarkable  feature.  As  already  outlined,  however 
(Chapter  XVIII),  the  St.  Peter,  though  occupying  a  definite  posi- 
tion in  the  scale,  encloses  within  itself  a  hiatus,  which  constantly 
widens  northward,  so  that  the  top  of  the  sandstone  is  higher  in 
the  scale  and  the  bottom  is  lower  in  the  northern  region,  as  com- 
pared with  its  more  southern  occurrence.  Moreover,  there  are 
formations,  such  as  the  Sylvania  sandstone  of  Ohio  (Upper  Sil- 
uric),  which  are  lithically  identical  with  the  St.  Peter,  and  might 
be  mistaken  for  it,  if  lithic  character  alone  were  considered. 

An  intercalated  shore-derived  formation  between  offshore 
formations  can  generally  be  recognized  in  its  various  outcrops  by 
its  lithic  character.  Such  a  formation  represents  an  oscillation  of 
the  land  during  sedimentation,  either  a  shoaling  or  a  total  retreat 
of  the  sea,  followed  by  a  re-advance  or  a  deepening.  Lithic  charac- 
ter then,  when  taken  in  conjunction  with  superposition,  may  be 
a  valuable  guide  in  correlation.  Intercalated  off-shore  beds  among 
terrigenous  formations  may  likewise  serve  a  good  purpose  in  cor- 
relation. Thus  the  Ames  or  Crinoidal  limestone,  a  marine  bed,  has 
been  widely  recognized  as  an  intercalated  bed  in  the  non-marine 
Conemaugh  formation  of  the  bituminous  coal  field.  In  this  case 
the  correlation  is  confirmed  by  the  contained  fauna. 

Another  way  in  which  lithic  character  serves  a  useful  purpose 
in  correlation  is  by  the  occurrence  of  what  may  be  called  sympa- 
thetic changes  in  sedimentation.  Thus  two  regions,  one  more  dis- 


METHODS    OF    CORRELATION  1133 

tant  from  the  shore  than  the  other,  may  experience  a  sympathetic 
change  in  sedimentation,  when  simultaneously  affected  by  an  oscilla- 
tory movement.  Thus,  when  in  the  near-shore  region  muds  change 
upward  into  sands,  and  still  higher  into  muds  again,  the  corre- 
sponding change  in  the  more  distant  region  may  be  from  lime- 
stones to  terrigenous  muds  and  higher  still  to  limestones  again. 
Such  sympathetic  changes  seem  to  have  taken  place  between  the 
New  York  and  Michigan  Hamilton  deposits. 


4.     Organic  contents. 

Correlation  by  organic  contents,  or  Pakeontologic  correlation, 
has  been  found  to  be  the  most  reliable  method,  far  surpassing  in 
importance  any  other  single  method.  Nevertheless,  there  are  many 
pitfalls  which  must  be  guarded  against,  and  the  sources  of  error 
must  be  recognized  and  taken  into  account. 

(a)  Index1  fossils.  Index  fossils  have  already  been  defined 
as  species  characteristic  of  definite  geologic  horizons,  and  typically 
occurring  only  in  beds  of  that  horizon  (page  1094).  Index  fossils 
in  order  to  be  efficacious  must  be  of  limited  vertical  but  wide  hori- 
zontal distribution.  Thus  the  brachiopod  Hypothyris  cuboides 
characterizes  a  certain  zone  in  the  Upper  Devonic  of  America, 
Europe  and  Asia,  while  the  Goniatite  Manticoceras  intumescens 
likewise  characterizes  late  Devonic  rocks  throughout  much  of  the 
northern  hemisphere.  Similarly,  Spirifer  disjunctus  has  a  limited 
vertical  range,  combined  with  a  wide  horizontal  one,  being  char- 
acteristic of  the  Upper  Devonic  of  many  countries.  Locally,  the 
type  may  transgress  the  normal  vertical  range,  as  in  the  case  of 
the  last-mentioned  species,  which  passes  up  into  Lower  Mississippic 
beds  in  eastern  North  America,  or,  as  in  the  case  of  Tropidoleptus 
carinatus,  a  widespread  index  fossil  of  the  Mid-Devonic,  but  which 
locally  passes  into  the  Upper  Devonic.  The  best  index  fossils  are 
those  which  are  capable  of  wide  distribution,  and  remains  of  which1 
will  occur  in  regions  where  the  organisms  may  never  have  lived, 
and  in  sediments  which  may  differ  widely  from  those  forming  the 
normal  facies  of  sea  bottom  for  the  type  in  question.  As  pointed 
out  in  an  earlier  chapter,  epiplanktonic  and  pseudoplanktonic  forms 
are  most  likely  to  produce  such  index  fossils.  The  shell  of  Spirula, 
a  dibranchiate  cephalopod  of  the  modern  fauna,  illustrates  the  wide 
distribution  possible  by  flotation,  though  the  animal  has  been  found 
to  occur  only  in  a  few  localities  in  deep  water.  Epiplanktonic  Hy- 
drozoa  and  Bryozoa  likewise  suffer  a  wide  distribution  through 
the  flotation  of  their  host. 


1 134  PRINCIPLES    OF    STRATIGRAPHY 

Among  the  pseudoplankton  the  shells  of  Ammonites  should 
be  especially  noted  as  being  included,  at  least  to  some  extent,  in  sedi- 
ments of  varied  character  over  wide  areas. *  The  genera  and  spe- 
cies of  ammonites  as  a  rule  were  short-lived  cephalopods,  different 
species  characterizing  different  zones.  Besides  having  their  shells 
widely  distributed  after  death,  by  flotation,  living  ammonites  also 
seem  to  have  spread  rapidly  and  widely,  probably  during  a  mero- 
planktonic  stage. 

Holoplanktonic  organisms  may  also  suffer  a  wide  distribution 
and,  if  they  contain  parts  capable  of  preservation,  these  may  be 
entombed  in  sediments  of  widely  different  character.  Such  cases 
are  seen  in  the  pteropod  oozes  of  various  geologic  horizons. 

The  wide  distribution  of  the  Ordovicic  graptolites  was  probably 
due  to  epiplanktonic  as  well  as  holoplanktonic  dispersion.  Grapto- 
lite  species  were  short-lived,  hence  successive  zones  are  characterized 
by  distinct  types  over  a  wide  area.  Plants  whose  seeds  are  widely 
distributed  by  winds  or  other  agents  produce  good  index  fossils 
for  continental  deposits.  Here,  however,  the  climatic  factor  exer- 
cises a  limiting  influence,  since  plants  will  only  grow  where  climatic 
conditions  are  favorable. 

(b)  Grade  of  index  fossil.  The  grade  of  the  index  fossil  com- 
monly has  a  very  direct  relation  to  the  magnitude  of  the  strati- 
graphic  divisions  to  be  correlated.  Thus,  while  the  class  of  trilo- 
bites  as  a  whole  may  serve  for  the  recognition  of  Palaeozoic  rocks 
the  world  over — none  having  as  yet  been  found  outside  of  the 
Palaeozoic — smaller  subdivisions  must  be  used  for  the  correlation 
of  more  restricted  stratigraphic  divisions.  Thus  the  family  Cono- 
coryphidce  among  the  trilobites  is  characteristic  of  the  Cambric, 
and  any  member  of  that  family  will  serve  to  determine  the  Cambric 
age  of  the  strata  in  which  it  occurs.  The  family  Olenidce  is  princi- 
pally restricted  to  the  CJambric,  though  some  members  occur  in 
the  Ordovicic.  The  most 'characteristic  types,  nevertheless,  serve  to 
correlate  the  Cambric  formations  in  all  their  occurrences-.  While  any 
of  the  more  characteristic  genera  of  this  family  (Olenidae)  will 
thus  serve  in  correlating  Cambric  formations  as  a  whole,  certain 
genera  of  this  family  serve  as  indices  of  the  three  principal  sub- 

*  The  pseudoplanktonic  dispersal  of  the  shells  of  Ammonites  is  strongly 
advocated  by  Walther,  but  questioned  by  Ortmann  (34),  Tornquist  (46),  J.  P. 
Smith  and  others.  Tornquist  has  urged  against  such  interpretation  the  observa- 
tion that  in  the  Jurassic  and  Cretacic  the  Ammonites  are  distributed  according 
to  climatic  zones.  Examples  of  dispersal  by  flotation  are,  however,  known,  for 
as  shown  by  Clarke  (Naples  fauna)  the  Goniatite  fauna  of  the  Styliolina  or  Ge- 
nundewah  limestone  of  western  New  York  ("prenuncial  intumescens  fauna") 
must  be  regarded  as  derived  in  this  manner.  (See  also  Chapter  XXIX.) 


METHODS    OF    CORRELATION  1135 

divisions.  Thus  Olenellus  and  Holmia  characterize  the  Lower  Cam- 
bric, Paradoxides  the  Middle  Cambric,  and  Olenus  and  Dikelloceph- 
alus  the  Upper  Cambric.*  Again,  the  Middle  Cambric  may  be 
subdivided  into  a  number  of  zones,  each  characterized  by  a  species 
of  Paradoxides.  These  species  are  either  identical  or  representative 
in  the  corresponding  zones  of  the  East  American  and  West  Euro- 
pean Middle  Cambric. 

The  dendroid  graptolite  Dictyonema  may  serve  as  an  example 
of  a  genus  of  more  extended  range,  some  of  whose  species  are, 
nevertheless,  good  index  fossils.  The  genus  itself  begins  in  the 
transition  beds  from  the  Upper  Cambric  to  the  Lower  Ordovicic, 
where  D.  ftabelliforme  is  a  characteristic  index  fossil  and  is 
of  almost  worldwide  distribution.  Other  species  characterize  the 
Siluric  and  still  others  the  Devonic. 

(c)  Correlation  by  equivalent  stages  in  development.  Among 
organisms  characterized  by  community  of  descent  corresponding 
stages  in  development  are  sometimes  reached  in  different  lines  of 
evolution  at  about  the  same  time  period.  Such  homceomorphic 
representatives  (morphological  equivalents,  see  Chapter  XXV) 
may  thus  serve  as  indices  of  a  given  horizon  even  where  inter- 
communication has  not  occurred.  Thus  Goniatites  the  world  over 
characterize  the  upper  Palaeozoic,  but  Goniatites  are  derived  along 
different  lines  of  descent.f  The  simpler  types  along  the  various 
lines  of  descent  characterize  the  Devonic,  while  those  with  more 
complicated  sutures.4  greater  involution,  or  marked  ornamentation 
are  mostly  characteristic  of  the  Mississippic  and  Carbonic.  The 
Ceratite  type,  in  which  the  lobes  of  the  sutures  are  further  modi- 
fied by  secondary  indentations,  while  the  saddles  are  entire,  are 
typically  developed  along  the  various  lines  of  evolution,  in  the 
Trias.  Finally,  the  Ammonite  type,  in  which  both  lobes  and  saddles 
are  modified  by  additional  indentations,  appears  chiefly  in  the  Juras- 
sic, in  the  various  evolutional  lines,  and  continues  into  the  Cretacic. 
Owing  to  these  facts  the  orginal  idea  prevailed  that  Goniatites  con- 
stituted one  genus,  characteristic  of  the  formations  from  the  Devonic 
to  the  Carbonic;  Ceratites  formed  another  genus  characteristic  of 
the  Trias ;  while  Ammonites  was  regarded  as  a  genus  characterizing 
the  time  from  the  Jurassic  to  the  Cretacic  inclusive. 

It  is  now  known,  however,  that  many  exceptions  to  this  general 
rule  exist.  Genetic  series,  in  which  acceleration  of  development 
prevailed,  reached  the  Ceratite  or  even  the  Ammonite  stage  in  pre- 
Triassic  time.  Thus  the  genus  Prodomltes  from  the  Lower  Missis- 

*  For  illustrations  see  Grabau  and  Shimer,  North  American  Index  Fossils 
Vol.  II.  f  See  Chapter  XXV,  p.  978.  }  See  Chapter  XXIV,  p.  945- 


u36  PRINCIPLES    OF   STRATIGRAPHY 

sippic  (Chouteauan)  has  advanced  into  the  Ceratite  stage,  while 
Waagenoceras  of  the  Permic  has  already  true  Ammonite  (phylli- 
form)  sutures.  Sometimes,  by  retardation,  a  type  remains  in  a 
more  primitive  evolutional  stage,  one  which  normally  characterizes  a 
lower  horizon.  The  case  of  the  Triassic  ammonite  Trachyceras, 
cited  by  J.  P.  Smith  (45),  from  the  Karnic  limestone  of  California, 
and  referred  to  in  Chapter  XXV,  belongs  here.  This  had  persisted 
in  the  more  primitive  Tirolites  stage  and  so  suggested  correlation 
of  the  beds  with  those  of  a  lower  horizon.  The  "Pseudoceratites" 
of  the  Cretacic  (Hyatt-23)  form  another  instructive  example.  In 
these  types  (Protengonoceras,  Engonoceras,*  etc.)  arrestation  in 
development  affects  the  later  stages  (the  earlier  stages  being  ac- 
celerated with  reference  to  the  corresponding  stages  of  their  Juras- 
sic ancestors),  so  that  the  adult  sutures  remain  in  the  ceratite  or 
even  goniatite  stage.  This  is  a  case  of  heterepistasis,  the  cessation 
in  development  affecting  only  the  sutures.  What  appears  to  be  a 
good  example  of  corresponding  stages  in  development  in  distinct 
provinces  at  about  the  same  time  period,  thus  serving  for  inter- 
regional correlation,  is  seen  in  the  case  of  Clavilithes  of  the  Parisian 
Eocenic,  and  the  corresponding  morphologic  equivalents  of  the 
Eocenic  of  the  Gulf  States  of  North  America.  The  American 
series  of  species  parallels  the  Parisian  to  such  an  extent  that  they 
have  been  regarded  as  varieties  of  the  Parisian  species.  There  is 
every  reason  for  believing,  however,  that  they  represent  an  in- 
dependent development.  (Grabau-i5.) 

The  graptolites  present  other  examples  of  corresponding  stages 
in  development  reached  in  distinct  genetic  series  at  approximately 
the  same  time.  Thus,  Dichograptus,  Tetragraptus,  Didymograptus, 
etc.,  represent  stages  in  development  rather  than  monophyletic 
genera,  but,  since  these  stages  appear  simultaneously  in  the  various 
lines  of  descent,  they  may  be  used  as  geologic  genera,  eminently 
adapted  for  correlative  purposes.  (Ruedemann-38.) 

(d)  Correlation  by  faunas  and  floras.  Representative  species. 
When  the  index  species  themselves  are  not  represented,  correlation 
by  means  of  the  sum  total  of  associated  organisms  must  be  made. 
Thus  Paradoxides  is  absent  from  the  Middle  Cambric  of  the  Ap- 
palachian and  Pacific  provinces  of  North  America,  nor  are  any 
of  the  associated  species  of  the  other  genera  present  in  these  faunas. 
Representative  species,  however,  occur  and  the  sum  total  of  the 
Middle  Cambric  faunas  of  the  various  provinces  has  similarity 
of  expression,  which  is  almost  as  good  as  absolute  identity.  The 
lower  Middle  Cambric  of  the  Atlantic  Coast  and  of  western  Europe 

*  For  illustrations  see  North  American  Index  Fossils,  Vol.  II. 


METHODS    OF    CORRELATION  1137 

has  different  species  of  Paradoxides  in  the  different  provinces,  but 
these  species  are  representative,  so  that  they  serve  to  correlate  even 
the  zones.  The  zones  with  their  representative  or  identical  spe- 
cies are  as  follows : 

Eastern  North  America.  Western  Europe. 

Paradoxides  forchhammeri  P.  forchhammeri 

P.  davidis  P.  davidis 

P.  abenacus  P.  tessini 

P.  eteminicus  P.  rugulosus 

P.  lamella tus  P.  celandicus 

Even  between  provinces  as  close  as  New  Brunswick  and  east- 
ern Massachusetts  the  species  are  representative  rather  than  iden- 
tical. Thus  Paradoxides  harlani,  the  large  Middle  Cambric  trilo- 
bite  of  eastern  Massachusetts,  is  representative  of  P.  eteminicus  of 
New  Brunswick,  while  Acrothele  gamagii  of  the  Massachusetts 
Middle  Cambric  is  the  representative  of  A.  matthewi  of  New  Bruns- 
wick. The  Meekoceras  beds  of  the  Lower  Trias  of  the  Himalayas, 
Siberia,  California,  Idaho  and  Utah  are  readily  correlated,  though 
no  species  common  to  these  regions  are  known.  The  genera,  how- 
ever, which  characterize  them  are  sufficiently  short-lived  and  the 
species  of  the  different  provinces  are  closely  representative. 
(Smith-45.) 


5.     Correlation  bv  unconformities  and  dis conformities. 

Correlation  by  unconformities  has  in  the  past  been  extensively 
employed,  and  some  stratigraphers  have  advocated  the  use  of  un- 
conformities as  a  primary  basis  for  correlation.  A  little  reflec- 
tion, however,  will  show  that  such  a  method,  when  used  indis- 
criminately, is  sure  to  lead  to  confusion  and  false  correlation,  for 
it  is  a  well-ascertained  fact  that  folding  of  formations  was  not 
simultaneous  in  different  parts  of  a  region,  nor  in  different  regions, 
but  may  be  earlier  in  some  and  later  in  others.  Thus,  while  there 
was  a  rather  widespread  period  of  folding  in  later  Palaeozoic  time, 
both  in  Europe  and  North  America,  this  folding  began  in  the  De- 
vonic  in  some  sections,  and  not  until  the  Permic  in  others.  More- 
over, the  formation  next  succeeding  the  unconformity  is  by  no 
means  always  the  same  one,  and  grave  mistakes  have  been  made 
by  assuming  this  to  be  the  case.  Thus  in  some  cases  the  Triassic 
beds  rest  directly  upon  the  folded  Palaeozoics,  while  in  other  cases 
beds  of  much  later  age,  even  Cretacic  or  Tertiary,  succeed  them. 


1 138  PRINCIPLES    OF    STRATIGRAPHY 

In  the  same  way  the  beds  resting  upon  the  truncated  Ordovicic 
folds  in  New  York  and  Pennsylvania  vary  considerably  in  age. 
The  conglomerates  succeeding  the  unconformity  were  originally  all 
classed  as  basal  Siluric.  In  reality  some  are  of  Lower  and  some 
are  of  Middle  Siluric  age,  while  in  still  other  cases  beds  of  upper 
Siluric  or  even  younger  age  rest  directly  upon  the  truncated  roots 
of  the  old  folds. 

Nevertheless,  with  due  circumspection  it  is  possible  to  use 
great  and  widespread  unconformities  for  broad  correlation  of 
formations.  Since  there  were  two  periods  of  widespread,  if  not  uni- 
versal, disturbance  of  the  earth's  crust,  besides  many  minor  ones, 
these  at  least  have  a  considerable  value  in  correlation.  One  of 
these  occurred  before  the.  beginning  of  Palaeozoic  time,  and  the 
other  came  to  an  end  before  the  beginning  of  Mesozoic  time.  Thus 
everywhere,  the  world  over,  the  Archaean  rocks  are  separated  from 
the  Palaeozoic  formations  by  great  unconformities.  This  does  not 
apparently  hold  for  all  pre-Cambric  rocks,  however,  since  some  of 
the  formations  commonly  referred  to  the  Algonkian  are  separated 
from  the  Cambric  only  by  a  disconformity.  It  may,  however,  be 
true,  as  already  pointed  out,  that  the  unaltered  or  but  slightly 
altered  rocks,  like  the  Belt  terrane,  the  Uinta  sandstone,  and  others, 
are  not  necessarily  pre-Palaeozoic.  They  are  known  to  be  pre- 
Cambric,  or  better,  in  most  cases  only  pre-Middle  Cambric,  and, 
since  they  are  largely, 'if  not  entirely,  of  non-marine  origin,  they 
may,  in  part  at  least,  represent  the  continental  equivalents  of  the 
marine  Lower  Cambric  beds.  The  unconformity  between  the  Palae- 
ozoic and  Mesozoic,  though  widespread,  is  nevertheless  much  more 
restricted  than  the  earlier  one  mentioned.  Moreover,  it  is  of  suffi- 
cient constancy  to  make  possible  this  broad  correlation,  though,  as 
before  remarked,  there  is  no  guarantee  that  the  beds  next  succeed- 
ing are  everywhere  of  the  same  age. 

-  Disconformities  are,  to  a  certain  extent,  better  criteria  for  cor- 
relation, especially  the  larger  and  more  extensive  ones,  which  can 
be  interpreted  as  due  to  eustatic  movements  of  the  sea.  Withdraw- 
als or  transgressions  of  the  sea,  due  to  change  in  sea-level,  will 
affect  all  continents  more  or  less  in  the  same  manner,  and  thus 
serve  as  a  primary  basis  for  subdivision.  The  danger  with  this 
method  lies  in  the  difficulty  of  distinguishing  between  the  local  and 
the  widespread  character  of  the  disconformity  and  the  tendency 
which  it  induces  to  multiply  the  number  of  breaks  in  the  geologic 
column  by  assuming  that  the  minor  breaks  of  one  locality  are 
necessarily  reproduced  elsewhere. 

That  there  are  widespread  breaks   in   the  geological  column, 


METHODS    OF   CORRELATION  1139 

which  are  undoubtedly  due  to  eustatic  movements  of  the  sea,  be- 
comes more  and  more  apparent.  The  widespread  mid-Jurassic 
transgression  of  the  sea  over  Europe  is  well  known  and  the  discon- 
formity  (and  occasional  unconformity)  produced  by  this  trans- 
gression has  been  used  for  widespread  correlation.  The  great 
Mid-Ordovicic  hiatus  first  observed  in  North  America/  (Grabau- 
16;  18),  and  the  similarly  widespread  hiatus  in  the  tipper  Ordo- 
vicic  (Weller-52),  are  now  known  to  be  marked  in  North  Europe 
as  well  (Bassler-5).  In  like  manner  the  Mid-Siluric  hiatus  and 
disconformity  so  widespread  in  North  America  appear  also  to  be 
present  in  the  Baltic  region  of  Russia  and  Sweden  and  in  the 
Bohemian  Palaeozoic  district.  The  probabilities  are  that  in  Mid- 
Siluric  time  the  sea  left  a  large  part  of  the  present  land  area  dry. 
Similar  widespread  disconformities  are  recognized  in  the  Mesozoic. 


6.     Correlation  by  regional  metamorphism. 

Regional  metamorphism  has  already  been  defined  as  an  altera- 
tion or  metamorphism,  which  affects  extensive  regions  and  which  is 
primarily  due  to  tectonic  disturbances.  Such  metamorphism  may, 
of  course,  occur  at  any  time  in  the  history  of  the  earth,  but  when- 
ever it  does  occur  it  will  affect  all  the  formations  of  the  region  in 
which  it  takes  place,  though,  obviously,  some  formations  may  be 
more  strongly  affected  than  others.  This  being  the  case,  it  follows 
that,  wherever  unaltered  rocks  overlie  the  metamorphosed  ones, 
the  age  of  the  former  cannot  date  back  of  the  period  of  meta- 
morphism, and  that,  hence,  the  lower  limit  of  their  age  is  fixed 
by  this  period  of  metamorphism.  Evidently  there  is  no  guarantee 
here,  however,  that  the  strata  of  the  overlying  series  are  all  of 
the  same  age,  though  within  moderate  limits  this  is  probably  true. 
One^general  rule  may,  perhaps,  be  formulated,  and  within  certain 
limits  applied,  namely,  that,  of  two  formations  in  contact,  the  more 
strongly  metamorphosed  one  is  the  older.  Here,  however,  the  same 
caution  is  necessary  that  is  required  in  applying  the  rule  of  greater 
deformation  to  two  deformed  formations  in  contact.  Some  forma- 
tions are  more  subject  to  metamorphism  than  others,  just  as  some 
formations  are  more  subject  to  deformation. 

The  method  of  correlation  by  metamorphism  is,  perhaps,  the 
most  applicable  to  the  determination  of  the  boundary  line  between 
the  pre-Palaeozoic  and  later  formations,  though  even  here  it  seems 
not  always  to  be  reliable.  This  would  appear  from  the  fact  that 
extensive  sedimentary  formations,  such  as  the  Belt  series  of  Mon- 


1 140  PRINCIPLES    OF    STRATIGRAPHY 

tana,  and  its  continuation  into  Canada,  with  a  thickness  of  over 
12,000  feet,  and  similar  formations  in  Utah  (Uinta  quartzite) 
and  in  the  Grand  Canyon  district  (Unkar  and  Chuar  series*) 
have  suffered  no  appreciable  metamorphism,  though  from  their 
relationship  to  the  overlying  Cambric  formations  they  are  believed 
to  be  of  pre-Cambric  age.  The  Torridon  sandstone  of  Scotland  is 
another  example  of  a  formation  underlying  the  Olenellus-bearing 
sandstones  (Lower  Cambric),  the  two  being  separated  by  a  slight 
unconformity,  while  the  American  formations  are  generally  sep- 
arated from  the  Cambric  only  by  a  disconformity,  or  at  least  by  an 
unconformity  in  which  the  deformation  of  the  lower  beds  has 
been  so  slight  as  to  appear  non-existent.  If  these  formations  are 
really  pre-Cambric,  and  not  basal  Cambric,  they  may  well  represent 
an  earlier  system,  which,  however,  still  belongs  in  the  Palaeozoic; 
or  they  may  represent  a  pre-Palaeozoic,  but  still  post-Algonkic  sys- 
tem, one,  the  formation  of  which  succeeded  the  apparently  world- 
wide metamorphism  which  has  affected  the  Algonkic  and  earlier 
formations. 

Finally,  it  must  be  noted  that  extensive  metamorphism  has  af- 
fected rocks  of  Palaeozoic  and  even  of  much  later  age.  The  schists 
and  marbles  of  the  New  York  City  area  are  believed  by  many  to 
be  the  altered  Cambro-Ordovicics,  which,  north  of  the  Highlands, 
appear  unmetamorphosed.  Berkey,  however,  holds  that  they  be- 
long to  the  pre-Cambric  (6),  a  view  strongly  advocated  by  Crosby. 
A  similar  difference  of  opinion  exists  with  reference  to  the  meta- 
morphic  rocks  of  New  Jersey,  especially  those  in  the  region  about 
Franklin  Furnace. 

On  the  whole,  it  will  be  seen  that  correlation  by  metamorphism, 
while  serviceable  and  often  very  reliable  within  certain  limits,  is, 
nevertheless,  a  method  likely  to  mislead.  We  need  but  recall  that 
the  early  stratigraphers  classed  all  metamorphic  rocks  as  Pri- 
mary, and  that  this  included  the  metamorphosed  Palaeozoic  forma- 
tions of  western  Europe,  as  well  as  the  metamorphosed  Mesozoic 
and  later  formations  of  the  Alps.  Or  we  may  compare  the  older 
and  newer  maps  of  New  England  and  of  the  Appalachians,  where 
we  shall  find  that  many  of  the  formations  formerly  classed  as  pre- 
Cambric  are  now  placed  into  the  Palaeozoic.  The  international 
map  of  Europe  also  shows  many  areas  of  pre-Cambric  rock,  where 
more  recent  study  has  led  the  observers  to  place  the  metamorphic 
formations  high  in  the  geological  column. 

*  In  the  Chuar  group  fossils  of  Palaeozoic  character  have  been  found, 
which  suggests  that  these  formations  form  a  pre-Cambric  Palaeozoic  system  if 
they  are  not  actually  a  part  of  the  Lower  Cambric, 


METHODS    OF    CORRELATION  1141 


7.     Correlation  by  diastrophism. 

The  recognition  of  the  widespread  character  of  hiatuses  or  gaps 
in  the  sedimentary  series,  noted  in  preceding  sections,  suggests 
that  the  causes  of  these  breaks  are  of  more  or  less  universal  extent. 
These  causes  are  diastrophic,  or  deformative  of  the  earth's  crust, 
for  every  hiatus  signifies  a  retreat  of  the  sea,  followed  by  a  read- 
vance,  indicating,  thus,  a  relative  rise  of  the  land-mass,  which  re- 
sults in  the  emergence  of  large  tracts,  followed  by  a  relative  de- 
pression, resulting  in  submergence.  If  these  movements  affect  in- 
dividual land  blocks  only,  the  regression  and  transgression  are 
chiefly  confined  to  this  block,  while,  at  the  same  time,  as  has  been 
shown  in  Chapter  I,  a  reverse  change  in  relative  level  of  sea  and 
land  may  be  noted  on  the  stationary  blocks,  this  being  brought  about 
by  the  readjustment  of  the  entire  sea-level,  necessitated  by  the 
partial  displacement  of  it  in  one  region.  Thus,  if  one  land  block 
rises  independently  of  the  others,  its  shores  will  suffer  a  negative 
or  retreatal  movement,  and  its  margins  will  emerge.  As  a  result 
of  this,  however,  there  will  be  a  partial  elevation  of  the  sea-level 
as  a  whole,  due  to  the  displaced  water,  and  this  will  affect  all 
blocks,  including  the  emerging  one.  In  the  latter  it  will  tend 
merely  to  reduce  somewhat  the  total  amount  of  sea-retreat  which 
the  elevation  of  the  block  would  bring  about,  but  in  the  stationary 
blocks  there  would  be  a  universal  advance  of  the  sea  over  their 
margins.  Thus  retreatal  movements  in  one  continent  would  be 
correlated  with  transgressive  movements  in  the  other,  and,  since 
emergence  is  followed  by  erosion,  and  submergence  by  deposition, 
base-leveling  of  one  continent  would  go  on,  with  deposition  beyond 
its  margins,  at  the  same  time  that  deposition  over  the  submerged 
margins  of  the  other  continents  and  a  reduction  in  the  erosive  ac- 
tivities over  the  unsubmerged  portions  of  those  continents  would 
occur. 

If  the  movement  affects  the  suboceanic  crustal  block,  however, 
a  universal  sinking  or  rising  of  the  sea-level  will  result,  in  con- 
formity with  the  lowering  or  elevation  of  this  block.  This  will  be 
manifested  in  a  universal  retreat  and  readvance  of  the  sea  along  all 
continental  margins,  with  the  production  of  a  widespread  hiatus 
in  the  succession  of  formations.  If  the  interval  between  the  two 
movements  is  a  large  one,  with  comparative  stability  of  the  land,  the 
base-leveling  processes  will  tend  to  wear  the  country  down  to  a 
nearly  uniform  level,  while  the  resultant  marginal  deposits  will  terfd 
further  to  raise  the  sea-level,  and  thus  set  the  gravitative  movement 


1 142  PRINCIPLES    OF    STRATIGRAPHY 

going.  The  shrinking  of  the  land  from  invading  lower  temperatures 
will  likewise  tend  to  reduce  the  level  of  the  land,  and  so  permit 
the  sea  to  transgress  across  it  anew. 

If  erosion  is  not  uniform  in  amount,  owing  to  variable  hardness 
of  formations,  or  to  other  causes,  the  resulting  hiatus  will  vary 
in  magnitude  from  point  to  point.  For,  though  the  time  interval 
between  the  retreat  and  readvance  of  the  sea  in  two  localities  might 
be  the  same,  it  is  obvious  that  the  missing  formations  will  be  more 
extensive  than  can  be  accounted  for  by  non-deposition,  since,  dur- 
ing the  interval  of  exposure,  erosion  removes  a  part  of  the  earlier 
deposited  sediments.  The  amount  thus  removed  in  different  sections 
may  vary  greatly,  and,  hence,  the  gap  in  the  series  will  vary  from 
place  to  place. 

Chamberlin  (9:504)  has  considered  four  stages,  which  must  be 
taken  cognizance  of  in  correlation  by  general  diastrophic  move- 
ments: (i)  "the  stages  of  climacteric  base-leveling  and  sea  trans- 
gression; (2)  the  stages  of  retreat,  which  are  the  first  stages  of 
diastrophic  movement  after  the  quiescent  period;  (3)  the  stages 
of  climacteric  diastrophism  and  of  greatest  sea-retreat;  and,  (4) 
the  stages  of  early  quiescence,  progressive  degradation,  and  sea- 
advance/' 

(i)  The  stage  where  base-leveling  and  sea  transgression  have 
successively  reached  their  climax  is  especially  characterized  by 
diminution  in  land,  a  reduction  in  the  amount  of  solution,  oxidation 
and  carbonation  of.  rocks,  and,  hence,  in  the  abstraction  of  carbon 
dioxide  from  the  "atmosphere,  coupled  with  the  greatest  extension 
of  lime  deposition  and  hence  the  setting  free  of  carbon  dioxide. 
Thus  there  will  be  a  tendency  toward  the  amelioration  of  the  cli- 
matic conditions,  and  this  will  aid  the  great  expansional  evolution 
of  marine  life  favored  by  the  broad  expansion  of  the  littoral  belt 
and  the-  formation  of  numerous  epicontinental  seas.  New  marine 
faunas  and  floras,  often  of  a  provincial  type,  will  come  into  exis- 
tence, which  are  likely  to  arise  through  parallel  evolution  from 
closely  related  ancestors  in  the  various  provinces.  Thus  a  wide- 
spread basis  for  faunal  correlation  will  be  inaugurated,  such  faunas 
comprising  not  identical,  but  rather  closely  representative,  species. 
Pathways  for  extensive  migration  along  the  littoral  belts  of  the 
oceans  also  result,  and  these  tend  to  produce  widespread  uniformity 
of  the  littoral  fauna  of  the  oceans.  Such  periods  of  extensive  trans- 
gression of  the  sea  and  corresponding  expansional  evolution  are 
seen  in  the  late  Cambric  and  early  Ordovicic,  in  the  Middle,  and 
early  Upper  Ordovicic,  in  the  early  Siluric,  Middle  Devonic,  early 


METHODS    OF    CORRELATION  1143 

Mississippic  and  in  the  Middle  and  early  Upper  Jurassic  (Callovian 
to  Oxfordian),  as  well  as  in  the  early  part  of  the  Cretacic. 

(2)  The    stages    of    initial    diastrophism    and    sea-retreat    are 
marked  by  the  increase  in  deposition  of  the  material  resulting  from 
the  deep  decomposition   of  the  rock,  during  the  period  of  base- 
leveling;  the  increasing  deposition  of  terrigenous  elastics,  and  the 
consequent  change  in  the  character  of  the  fauna,  a  turbid  water 
fauna  taking  the  place  of  the  one   previously  flourishing  in  the 
purer  waters.    The  littoral  belt  is  narrowed,  the  epicontinental  seas 
disappear,  and  the  evolution  of  shallow-water  life  and  the  migration 
of  organisms  are  restricted. 

(3)  When  the  climax  of  the  regression  is  reached  the  restric- 
tion in  the  evolution  of  the  shallow  water  organisms  is  at  its  maxi- 
mum.    Clastic  deposits  predominate  and  they  even  encroach  upon 
the  continents.     Climatic  changes  are  toward  a  colder  period,  ow- 
ing to  the  locking  up  of  the  carbon  dioxide  in  land-vegetation,  by 
solution  of  limestones,  and  by  carbonation  of  silicates.    Such  refrig- 
eration may  go  so  far  as  to  result  in  glaciation,  at  least  locally,  the 
evidences  of  such  glaciation  furnishing  an  additional  basis  for  cor- 
relation.    Broad  land  expansions  would  in  general  favor  wide  dis- 
tribution of  animals  and  plants,  unless  the  severity  of  the  climate 
should  enter  in  as  a  deterrent  factor.    Should  climatic  factors  be  less 
in  evidence,  however,  the  wide  expansion  of  the  land  might  favor 
a  wide  distribution  of  land  life.     As  a  result,  the  struggle  for  ex- 
istence would  be  less  intense  and  modifications  would  be  slower, 
and  more  of  the  nature  of  adaptations  to  slowly  changing  environ- 
ment.   The  littoral  region  of  the  sea  being,  however,  much  reduced, 
the  survivors  of  the  once  widespread  marine  littoral  fauna  would 
be  forced  into  a  more  restricted  area  and  hence  a  fierce  struggle 
for  existence  would  be  sure  to  result.    This  would  lead  to  the  rapid 
extinction  of  numerous  types  and  to  the  comparatively  rapid  modi- 
fication of  the  survivors,  and  would  thus  produce  a  comparatively 
sudden  change  in  the  character  of  the  fauna. 

(4)  The  early  stages  of  quiescence  and  base- leveling  which  fol- 
low  and   which    initiate   anew   the    slow   transgressive    movement 
of  the  sea,  will  again  favor  migration  of  marine  faunas.    Owing  to 
the  effect  of  the  previous  restrictions,  however,  the  aspect  of  the 
fauna  will  have  been  changed  to  a  marked  degree,  so  that  the  ex- 
panding fauna  will  have  a  distinct  aspect  of  its  own.     The  great 
expansion  which  followed  the  retreat  of  the  sea  in  the  late  Middle 
or  early  Upper  Cambric  time  in  North  America  brought  with  ^it 
the  spread  of  a  fauna  widely  different  from  that  which  preceded  it. 
The  Middle  and  early  Upper  Ordovicic  expansional  faunas  (Chazy- 


1 144  PRINCIPLES    OF    STRATIGRAPHY 

Trenton)  differed,  likewise,  in  a  marked  degree  from  the  preced- 
ing Beekmantown  faunas.  The  Siluric  fauna  of  North  America, 
also  an  expansional  fauna,  differed  radically  from  that  of  the  preced- 
ing Upper  Ordovicic  (Weller-52),  which  was  largely  exterminated 
by  the  late  Ordovicic  or  early  Siluric  retreat  of  the  sea.  The  com- 
parative uniformity  of  expansional  faunas,  over  wide  areas,  such 
as  that  of  the  Mid-Ordovicic,  the  early  Siluric,  the  Mid-Devonic, 
and  the  later  Jurassic  and  Cretacic,  shows  that  such  periods  are 
eminently  fitted  to  furnish  a  basis  for  practically  worldwide  cor- 
relation. 

Finally,  it  may  here  be  noted  that,  if  the  theory  of  polar  pendu- 
lations,  as  outlined  in  Chapter  XXIII,  should  prove  to  have  a 
sound  basis  in  fact,  we  must  modify  our  conception  of  movements 
of  the  water  body,  to  the  extent  of  recognizing  the  coincident  ris- 
ing of  the  sea-level  in  the  region  approaching  the  Equator,  and  the 
fall  of  the  sea-level  in  the  regions  approaching  the  poles.  Thus 
movements  of  the  water  body  would  not  be  uniform  over  the  earth, 
but  compensatory,  rising  in  the  equatorial  and  falling  in  the  polar 
regions.  For  an  attempt  at  correlation  on  such  a  basis  the  student 
is  referred  to  Simroth's  book  "Die  Pendulations-theorie."  (44.) 


PALuEOGEOGRAPHY  AND    PAI^EOGEOGRAPHIC    MAPS. 

"Palaeogeography,"  says  Dacque,  "may  be  compared  to  a  fire 
which  has  smoldered  long  under  cover,  but  which  has  at  last  broken 
forth  with  all-consuming  energy"  (12).  Attempts  to  restore  the 
outlines  of  continents  and  seas  during  former  geological  periods 
were  essayed  by  geologists  and  palaeontologists  before  the  middle  of 
the  nineteenth  century.  Since  then  the  subject  has  smoldered 
under  cover  of  the  detailed  investigations  carried  on  in  other  fields 
by  the  students  of  the  earth  sciences,  until,  in  recent  years,  it  has 
burst  forth  with  almost  volcanic  violence,  and  palaeogeographic  maps 
and  palaeogeographic  discussions  have  become  the  order  of  the  day. 

The  term  Palao geography  is  credited  to  Robert  Etheridge,  and 
its  birth  is  given  as  in  the  year  1881  (Schuchert-39),*  but  palaeo- 
geographic maps  were  made  much  earlier.  Schuchert  regards  those 
given  by  Dana  in  the  first  edition  of  his  manual  (1863)  as  the  earli- 
est; but  earlier  maps,  though  less  definite  in  character,  had  been 
published,  as,  for  example,  those  by  Goodwin  Austen  for  England 

*Dacque"  mentions  A.  Bou6,  who  in  1875  used  the  terms  palaogeologische  Geo- 
graphic and  geologische  Paldo-Geographie.  (Sitzungsberichte  K.  K.  Akad.  Wiss. 
Wien.  Math.  Nat.  Kl.  Bd.  71,  ite  Abt.,  s.  305-405.) 


PAL^OGEOGRAPHIC   MAPS  1145 

in  1856,  by  B.  Crivelli  for  Italy  in  1853  and  by  Gemmellaro  for 
Sicily  in  1834.  (Dacque-i2:/p^.)  The  most  elaborate  recent  at- 
tempt to  map  the  conditions  of  land  and  water  at  different  geologic 
periods  is  that  of  Schuchert,  who,  in  his  instructive  monograph  on 
the  Palseogeography  of  North  America,  has  published  fifty  separate 
maps  showing  the  changes  in  outlines  of  North  America  from 
Cambric  to  Pliocenic  time. 

TYPES  OF  PALyEOGEOGRApmc  MAPS.  Palseogeographic  maps  may 
be  simple  or  complex,  special  or  generalized.  The  simple  map  aims 
to  show  the  distribution  of  geographic  features,  of  a  particular  pe- 
riod in  the  earth's  history,  over  the  surface  of  the  earth,  much  as  a 
modern  geographic  map  shows  this  distribution  for  the  present  time ; 
a  complex  map,  on  the  other  hand,  attempts  to  show  more  than  this. 
The  simple  map  need  not  be  confined  to  the  depiction  of  the  hypo- 
thetical coastline,  but,  if  the  facts  available  allow  it,  should  repre- 
sent the  ocean  currents,  the  mountains,  the  rivers,  etc.  As  examples 
of  maps  of  this  type,  though  very  incomplete,  especially  in  so  far  as 
the  land  features  are  concerned,  may  be  mentioned  the  Ordovicic 
map  by  Ruedemann  (38)  and  those  for  the  same  time-period  by 
Grabau  (18);  the  older  Devonic  maps  of  Schuchert,  and  many 
others.  The  excellent  maps  by  De  Lapparent  (31)  may  also  be 
classed  here,  though  on  them  the  areas  of  continental  as  well  as 
marine  sedimentation  are  shown.  The  complex  maps  may  show, 
in  addition  to  the  deduced  geographic  conditions,  some  of  the  data 
on  which  this  deduction  is  based,  especially  the  distribution  of  the 
geological  formation  in  question,  or  of  its  outcrops.  Such  a  map^ 
is  in  reality  a  combination  of  a  palseogeographic  and  a  geologic 
map,  and  this  may  prove  highly  useful,  for  the  degree  of  detail  de- 
picted upon  the  map,  and  the  extent  to  which  the  map  is  hypotheti- 
cal, are  at  once  apparent.  Such  are  the  maps  issued  by  Schuchert 
for  North  America.  A  somewhat  more  complicated  type  is  repre- 
sented by  the  Palseogeographic  maps  issued  by  Chamberlin  and 
Salisbury  ( 10)  where  the  attempt  is  made  to  represent  not  only  the 
outcrop,  but  also  the  parts  believed  to  exist  beneath  cover,  and 
the  areas  from  which  the  formations  are  believed  to  be  removed 
by  erosion. 

The  most  complex  and  detailed  maps  of  this  type  published  in 
America  are  those  issued  by  Bailey  Willis  (57;  59).  In  them  the 
attempt  is  made  to  represent  the  oceanic  basins,  the  littoral  and  the 
epicontinental  waters,  the  areas  which  may  have  been  either  sea 
or  land — separating  those  which  were  more  likely  sea  and  those 
which  were  more  likely  land — the  lands  of  the  time,  the  indetermi- 
nate areas,  and  the  ocean  currents,  both  polar  and  equatorial. 


1146 


PRINCIPLES    OF    STRATIGRAPHY 


Maps  of  this  kind  are  more  easily  read  when  colors  instead  of 
symbols  are  used.  Another  type  of  complex  map  is  that  which  at- 
tempts to  show  changes  in  outline  of  the  lands  and  seas  during  the 
period  represented.  Such  are  the  maps  of  Freeh  (13),  in  which 
transgressions  and  regressions  of  the  sea  are  represented  by  differ- 
ences in  color.  Haug,  too  (21),  indicates  the  areas  of  trans- 
gression upon  his  maps,  .  and,  furthermore,  outlines  the  limits 
of  the  geosynclines.  And,  in  addition,  his  maps  are  facies 
maps. 

Special  maps  aim  to  show  the  outlines  of  lands  and  seas  at  a 
definite  time  period,  as  at  the  end  of  the  Lower,  Middle  or  Upper 
Cambric  (Fig.  264  a-c),  or  at  the  beginning  of  a  time  period. 
Such  maps  may  be  either  simple  or  complex.  Examples  of  the 


FIG.  264.  Maps  showing  the  probable  distribution  of  land  and  sea  around 
the  Atlantic  basin  in  Cambric  time.  a.  At  end  of  Lower  Cam- 
bric, b.  At  end  of  Middle  Cambric,  c.  At  end  of  Dictyonema 
ftabelliforme  time.  (A.  W.  Grabau.) 


former  are  the  maps  published  by  Grabau  (19)  for  the  Cambric 
(Fig.  264),  and  for  the  various  stages  of  the  Ordovicic  (18).  The 
maps  published  by  Schuchert,  Chamberlin  and  Salisbury,  Willis, 
Haug,  De  Lapparent,  and,  indeed,  by  most  authors  are  general 
maps  to  cover  a  whole  time  period,  though  in  some  cases  this  period 
may  be  very  small. 

CONSTRUCTION  OF  PAL^EOGEOGRAPHIC  MAPS.  In  the  construction 
of  palseogeographic  maps  it  is  first  of  all  necessary  to  bear  in  mind 
that  modern  geographic  maps  can  at  least  serve  only  as  a  distorted 
base  for  such  depiction.  Thus  the  Appalachian  region  of  North 
America,  and  the  region  of  the  Alps  in  southern  Europe  are  areas 
where  the  earth's  crust  has  been  greatly  foreshortened,  and  where, 
hence,  localities  far  apart  at  an  earlier  time  were  brought  close 
together.  It  is,  of  course,  impossible  to  allow  for  such  foreshorten- 
ing, if  the  localities  where  certain  formations  crop  out  to-day  are 


METHODS    OF   PAL^OGEOGRAPHY  1147 

to  be  brought  into  the  seas  in  which  they  were  deposited.  Thus, 
as  will  be  seen  on  the  maps  for  the  Lower  Cambric  (Fig.  2643.),  the 
New  England  land  barrier  between  the  Atlantic  and  the  Pacific  ex- 
tension in  the  Appalachian  or  Cumberland  trough  is  much  too  nar- 
row, while  the  width  of  that  trough  is  also  too  small.  The  same 
is  true  for  the  land-barrier  in  North  Britain,  between  the  Atlantic 
and  Arctic  oceans.  Since,  however,  the  rocks  carrying  the  faunas 
of  these  two  seas  are  found  so  much  nearer  together  .to-day  than 
was  the  case  at  the  time  of  the  deposition,  such  faulty  construction 
seems  to  be  unavoidable. 

The  overlap  relations  of  marine  strata  are  especially  significant 
as  aids  in  determining  old  shore-lines,  for  such  overlap  of  a  later 
over  an  earlier  formation  indicates,  as  a  rule,  that  the  point  of 
overlap  is  also  a  point  on  the  shore-line  of  the  earlier  formation. 
Due  attention  must  here  be  given  to  the  type  of  overlap  (see  Chap- 
ter XVIII),  and  the  fact  must  be  borne  in  mind  that  minor  over- 
laps may  also  be  developed  upon  an  irregular  sea-bottom,  where 
wave  activity  or  current  scour  is  active. 

Important  factors  that  must  not  be  overlooked  in  the  construc- 
tion of  palaeogeographic  maps  are  the  nature  of  the  sediment  and  its 
source.  Where  coarse  clastic  sediments  abound  in  the  formation, 
a  land  of  sufficient  size  must  have  existed  to  furnish  this  sediment. 
This  is  especially  the  case  when  the  sediment  consists  of  well-as- 
sorted material,  such  as  quartz-sand  or  pebbles,  when  it  must  be 
remembered  that  such  assorted  material  may  represent  only  a  part, 
perhaps  less  than  one-fourth,  of  the  original  rock  which  was  its 
source.  In  general,  it  may  be  said  that  much  closer  discrimination 
between  marine  and  non-marine  sediments  than  has  generally  been 
the  case  is  necessary;  and  the  conditions  of  deposition  must  be 
borne  in  mind,  as  well  as  the  factors  of  marine  and  non-marine  bion- 
omy,  and  the  effects  of  topography  on  currents  and  of  both  on 
deposition,  so  that  we  may  not  again  fall  into  the  error  of  recon- 
structing the  area  of  former  coral-rock  formation  as  an  arm  of  the 
sea,  one-half  or  one-quarter  of  a  mile  in  width,  and  less  than  ten 
fathoms  in  depth. 

When  the  science  of  Stratigraphy  has  developed  so  that  its  basis 
is  no  longer  purely  or  chiefly  pabeontological,  and  when  the  sciences 
of  Lithogenesis,  of  Orogenesis  and  of  Glyptogenesis,  as  well  as  of 
Biogenesis,  are  given  their  due  share  in  the  comprehensive  investi- 
gation of  the  history  of  our  earth,  then  we  may  hope  that  Pabeo- 
geography,  the  youthful  daughter  science  of  Stratigraphy,  will  have 
attained  unto  that  stature  which  will  make  it  the  crowning  attract- 
ion to  the  student  of  earth  history. 


1 148  PRINCIPLES    OF    STRATIGRAPHY 

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INDEX 


(Consult  also  the  table  of  contents.     Names  of  genera  and  species  are,  with  few 

exceptions,  omitted.) 


Aar,   delta  of,  610 

Aarmassive,    308 

Abbe,    C.,    cited,    56 

Abbotsham,   223 

Ablation,    17,    263 

Abrasion,    18 

Abrolhos  Islands,  416 

Abu   Roasch,   856 

Abu    Sir,    355 

Abyssal   district,   983 

Abyssinia,    355 

Abyssinian  Mountains,    rainfall  in,   68 

Abyssolith,    310,    731 

Abysso-pelagic   district,   983 

Acadian,    1128 

Acanthin,    457 

Acaustobioliths,   384 

Acaustophytoliths,   280,  467 

Acceleration,   differential,   964 

,   illustration  of  law  of,  969,  970 

Accordanz,   821 

Accretions,   719 

Achatinellidse,  mutations  of,    1043,    1052 

Acid,  crenic,  37 

,   humic,    37 

,  ulmic,   37 

Actinic   (chemical)   rays,  28 

Adams,   F.    D.,    cited,   92,    747,   773 

Adams,  F.  D.,  and  Coker,  E.  G.,  cited,   773 

Adaptive    radiation,  "  1054 

Adirondacks,   834 

Adour  River,  223,  558 

Adriatic  Sea,   108,  240 

,    Po    delta   in,    584 

,  surface  salinity  of,   153 
n  Sea,  240,  334 

,   temperatures  of,    189 
JQolian  Islands,  volcanoes  of,  861 
^Ethoballism,    749,    765 
Mtna,   radial  dikes  of;  870,  871 
Afghanistan,   habitual  fault  lines  of,  882 
Africa,    coast  of,    235 
African    deserts,    salinas    of,    359 
Agarica,  406 
Agassiz,  A.,  cited,    102,    125,   219,   387,   406, 

408,  414,   416,   461,  462,  469,   470,  471, 

519,    520,    685,    ion,    1021,    1024,    1026, 
1038,    1069 

,  quoted,  519,  680,   1016,   1019,    1020 

Agassiz,  L.,  cited,    143,  462 

Agger,  224 

Agoniatite  limestone,   425,    1131,    1132 

Agra,    26 

Agulhas  banks,  218 

Agulhas  shelf,    103 

Aidin,    54 

Aigon,  earthquake  fissures  in  1861  at,  883 


Air  frost,  63 

Airy,  G.   B.,  cited,  265 

Ajusco  Mountain  group,  new  mountain 
formed  in  1881  in,  863 

Alabama,  coastal  plain  of,   839 

Aland  Islands,  241 

Alands  deep,  temperatures  in,   190 

Alaska,   263 

,  dredging  off  coast  of,  641,  642 

,    glaciers    of,    324 

,  stone  glaciers  from,  544 

,  tundra  of,   507 

Albatross,   dredgings  by,   519,   676 

Albatross,    marine    habitat    of,    985 

Alberta,  pre-Cambric  reefs  of,  418 

Albert  Edward  Nyanza  Lake,  124,  359 

Albert  Lake,    118,    119 

,  composition  of,   157,  158,  159,  160 

,    salinity  of,    155 

,   soda  deposits  of,  361 

Albert  Nyanza  Lake,   124 

Albien,    730 

Albuquerque,   dune  sands  from,    553 

Alcyonaria,    385,    392,    1083 

Aldborough,  church  at,  225 

Alden,   W.   C.,  cited,  92 

Aldrich,    T.   H.,  cited,   916 

Aletschhorn,    308 

,  unconformity  in,  825,  826 

Aleutian   Islands,   basaltic  lava  field  in,   867 

,  submarine  volcanoes  of,  872 

Algae,   935 

,   encrustation  by  silica,  477 

Algal  Lake,  peat  of,  498 

Algeria,  onyx  deposits  of,   345 

,  salt  dome  of,  379,  758 

Algiers,   221,   240 

Alhambra   formation,    591 

,  torrential  deposits  from,   £30 

Allahabad    (Persia),   26 

Allan,    Dr.,    cited,   413 

Allegheny  formation,  thickness  in  Appala- 
chians of,  904 

Allegheny  River,  gravel  terraces  of,    136 

Allen,   H.   S.,  cited,  685 

Allen,    T.  A.,  cited,  921,  956 

Allochthonous,   298,   467,   478 

Allolebod,   355 

Allometrons,   961,   970 

Allotriomorphic  dolomite  crystals,   445 

Alpena,  reefs  at,   427,  428 

Alps,   alluvial   deposits  of,    584 

,   igneous  intrusions  in,   308 

Altenburg,   1086 

Amazon  River,  248 

,   red  mud  opposite  mouth  of,   669 

Amber,    1075 

Amboina  Island,   519 

Ambulacral  areas,   949 


H5I 


1152 


INDEX 


Ames  limestone,    1132 

Amfila  Bay,  355 

Amherstburg,    422 

Ammonites,  945,  978 

,  minerals  in  chambers  of,    1085 

,   naming  of,   913 

,  wide  distribution  of  shells  of,    1022 

Ammonoidea,    945 

Ammonoids,  range  of,  945,  946 
Amu-darja    (Amudaria),    see   Oxus 

Amundsen,  R.,  cited,  327 

Amygdaloidal  structure,   277 

Amygdules,   313 

Anam,  242 

Anamorphism,   zone  of,   747 

Andaman   Islands,    109 

Andaman  Sea,    109,   393 

Anderdon   fauna,    1126 

Anderdon  limestone,  52,  422 

Anderdon,  Ontario,  423 

Anderson,  J.  G.,  cited,  543,  578 

Anderson,   T.,   cited,   878 

Anderson,    W.    S.,    cited,    380 

Andersson,    G.,   cited,   85 

Andersson,  J.   G.,   cited,  92 

Andes,    earthquake    fissures    in,    883 

,  rainfall  on,  67 

,   snow-line  of,    322 

Andesites,   depth  of  formation  of,    15 

Andree,   K.,   cited,   367,    380,   644,   673,   682, 
685,    748,    773,    1069 

Andresen  C.  C.,  cited,  223,  265 

Andrussow,    N.,    cited,    338,    351,    354,    380, 
443,  444,  462,   609,  637,  666,   685 

,    quoted,    354 

Anegada   Straits,    108 

Anemoclasts,   285 

Angara   River,    116 

,Anglesey,  craterlets  of,  885 

,    sandstone    pipes  of,   884 

Anhydrite,  changed  to  gypsum,    537 

Animikie,    385 

,  Archaeocyathidae  of,   417 

Anschutz  quarry,   420 

Antarctic  block,  9 

Antarctic   glacial  clay,    salt  content  of,   367 

Antarctic  Ocean,   manganese  concretions  in, 
718 

Antedon,    development   of,    1032 

Anthracite   coal,    510,    511 

Anthracolithic   period,    511 

Anticosti,   418 

,  peat  beds  of,  508,  509,  514 

Anticyclones,  46 

Antigua    Salines,   onyx   marble   of,    344 

Antilles,  decapods  in  mountains  of,   1027 

Antilles,   Lesser,   233 

,   pteropod  ooze  outside  of,  456 

Apennines,  mud  volcanoes  in,  872 

Aphotic  region,   982,   983 

Apo,    77? 

Apocremc  acid,    173 

Apophyses,  304 

Appalachian    region,    basal    Cambric    sand- 
stones in,  729 

,  overlap  of  marine  strata  in,   732 

Appalachians,    disconformities    in,    823 

,    folding  of,   903 

,    foreshortening  of,   903 

,  revived  topography  of,  845 

,   source  of  Pottsville  conglomerate  in, 

742 

,  spring  line  in,   261 

Aptien,  730,  850 

,  overlapping  of,  850 

Aptychus  beds,   age  of,  459 

,   origin  of,   677 

Aquileja,    153 


Aquitanien,   454 
Arabia,  dune  area  of,  562 
Arabian    Gulf,   temperature   in,    187 
Arabian  Sea,  240 

,  miliolitic  limestone  of,  574 

,   oolite  dunes  of,   472 

,  temperature  of,   187,    190 

Arago,  cited,  72 

Aragon,   Planorbis  of,    1086 

Aragon,  woods  replaced  by  sulphur  at,   1081 

Aragonite,  oolites  of,  473 

,  oolites  changed  to,   469 

,  recrystallization  of,   755 

Aral    Sea,    composition   of,    157 

,   dunes  of,    561 

,  salinity  of,   155 

Arbuckle  Mountains,  Saint  Peter  standstone 

in,    739 

Area,  in  Bermudaite,  573 
Arctic  climatic  period,   506 
Arctic    Ocean,    Lithothamnion   in,    470 

,    mean  temperature  of,    193 

Arenaceous   texture,    285 

Arenig,   315 

Arenytes,   285 

Argentina,    367 

Argentine  basin,   105 

Argon,    25 

Arizona,  onyx  marble  of,  343 

— ,    pre-Cambric   "reefs"   of,    418 
Arizona  desert,  earthquake  fissure  in,  884 
Arkansas,   caverns  of,  346 

,   hot  springs  of,  201 

,  overlap  of  marine  strata  in,  732 

Arkansas  River,   245 

Arkose,   33 

Arldt,   T.,  cited,   1148 

Armenia,    alkaline   lakes   of,    361 

Armorican   Mountains,    71,    373,   375 

,  elevations  of,   374 

Arrhenius,    S.,    cited,    22,    29,    92,    757,    758, 

Arsis,   climatic,  82,  83 
Artemia,    excrements  of,    1093 
Arundel    formation,    632 
Ascutney   Mountain,   302 
Ascension  Island,    105,  215 

,  oolites  of,   336 

,  pteropod  ooze  near,  456 

Aseptata,   943 

Ashkabad,  unbedded  eolian  deposits  at,   554 

,  well-boring  near,   592 

Ashokan  formation,  origin  of,  635 

Asia,   connection  with   America  by   Behring 

Sea,   1 06 1 

Asia  Minor,   240,  334 
Askja,    eruption    of,    866 

Aspen,    dolomitization  of   limestone    at,    761 
Astogeny,  defined,  973 
Astrakhan,    rainfall   at,    65 
Astrakhan  desert,  salt  lakes  of,  357,  358 
Atacama  desert,   32,   364,  365 

,  dunes   in,    563 

,   natural  mummies  in,    1077 

,  soda  niter  deposits  in,   364 

Atlantic  climatic  period,   506 

Atlantic   Ocean,    manganese    concretions   in, 

718 

,    mean  temperature   of,    193 

,    surface   temperature   of,    182 

,    temperatures   in,    185,    187 

Atlantosaurus  beds,  see  Como  beds 
Atmobips,  991,  992 
Atmo-biotic   realm,    982 
Atmoliths,    279 
Atmology,  20 

Atmometamorphism,    749,    767 
Atmoseisma,  88 1 


INDEX 


H53 


Atmosphere,  chemical  work  of,  34 
-    circulation   of,   42 

composition  of,    i,  24 

electrical    phenomena   of,    72 

impurities  of,   24,    27 

mechanical  work  of,  5 1 

optical  characters  of,  28 

temperature  of,   29 

Atmospheric   pressure,    2 
Attawapishkat   River,    reefs  of,   430 
Atwater,    cited,    915 

Aube,   pebble  "rain"  of,  56 
Austen,    G.,   cited,    1144 
Australia,  390 

,   barrier  reefs  of,   387 

,  Cambric  tillites  of,  534,  535 

,  Muree    glacial    formation   of,    536 

Autochthonous,    298,   467 
Autoclasts,  285 
Autophytography,     1082 
Autotype,  919 
Autun,  cannel  coal  of,  481 
Auvergne,  acid  lavas  of,  869 

mineral    springs   of,    179 

petrified   chelonian  eggs   from,    To88 

pustular  lava  cones  in,    870 

volcanic   lake   basins  of,    120 

volcanoes  of,    874 

Aves,    954 

Avon  River,  663 

Ayin  Musa  Springs,  entomostracan  ooze  of, 

456 
Ayrshire,    prismatic    jointing   in    coal    seams 

of,  820 
Azores,    152,   205,   218 

,  pteropod  ooze  near,   456 

,  transported  rocks  off  the,   452 

,  volcanic  cone  in  the,  864,  865. 


Bacteria,    anaerobic,    338 
Baden,  Miocenic  deposits  of,  754 
Bader,   H.,  cited,   352,  380 
Bad  land  topography,    53 
Baffin    Bay,    108,    109,    237 
Baffin  Land,   418 
Bahama    Banks,    233 
Bahama  Islands,  398,  411 

,  foraminiferal  sands  of,  455 

Bahia,   341 

Bahia  Blanca,  360 

Baie,  Bay  of,  volcano  in,  863 

Bain,  F.,  cited,  82,  93 

Bakalsk,    rock   streams   at,    547 

Bakewell  Buxton,  warm  springs  of,  201 

Bala-ischem,   54 

Balbi   lagoon,   401 

Balch,  F.  N.,  cited,   1042,   1069 

Balchash   Sea,   elevation  of,    115 

Bald    Eagle   conglomerate,    636 

Ballingtang  channel,    237 

Baltic,    amber   of,    1075 

Baltic  Provinces,  cuesta  of,  838 

Baltic  Sea,  109,  no 

,  osmotic  pressure  in,  180 

,  salinity  of,  1044,   1045 

,  temperatures  of,    190 

Baltic   stream,    241 

Baltzer,  A.,   cited,   307,   308,   320,  825 
Baluchistan,   desert   areas  of,    562 
•Banda,     Island    of,    Spirula    dredged    near, 

1021  * 

Banda  Sea,    107,   186,  242 
Rinff,    synclinal    fold    near,    796 
Ranks,    104 
Baraboo   ridge,   848 


Barbados,  dust  falls  at,  60  , 

,  radiolarian  ooze  of,  458,  678 

Barbados  earth,  458,   1008,   1082 
Barbour,  E.  H,,  cited,   1092 
Barca,    153,   240 
Barchans,    556,    563 
Bardarson,    G.,   cited,   92 
Baren,  G.  van,  cited,  92 
Barent  shelf,    103 
Barent  Straits,   236 
Barents  Sea,   112,  236 
Barnstable,   1041 
Barnstable  Bay,   waves  in,  222 
Barrande,  J.,   cited,    1126 
Barrell,    J.,    cited,    93,    541,    578,    619,    633, 
634.   635,    637,    662,    709,    721,    740,    744 

,  quoted,    604,    621 

Barren   lands,    133 

Barrows,  W.  L.,  cited,  72,  73,  93 

Barus,  C.,  cited,   15,  22,  685 

Barysphere,    i. 

Basal  bed,  formation  of,  731 

Basalts,  depth  of  formation  or,   15 

Bascom,   F.,  cited,  772,  773 

Basel,   251 

Basin,  Alabama-Mississippi,  810 

Allegheny,   810 

Brazilian,    105 

Illinois,    810 

Iowa,   810 

James  Bay,  810 

Michigan,   810,   846 

New  York,    810 

North    African,    105 

North    Atlantic,    105 

Oklahoma,    810 

Ottawa,   8 10 

Paris,   846 

Quebec,    810 

St.   Lawrence,   810 

Wisconsin,  810 
Baskunchak    Lake,    357 

Bassler,  R.  S.,  cited,   1089,  1095,   1139,  1148 
Bastei,    53 
Batavia,  26 

Bath,    hot    springs    of,    201 
Bather,   F.   A.,   cited,   93 
Batholith,    303 
Bauer,  M.,  cited,   93,  537 
Bauermann,  cited,  469 
Bavaria,  Jurassic  reefs  of,  437 
Bay  of  Bengal,   240 

,   temperature   of,    187 

Bay   of  Biscay,    112,   219 

,  dune  areas  of,   557 

,  salinity  range  of,   152 

Bay  of  Cadiz,  temperatures  of,   189 
Bay  of  Danzig,  salinity  of,    151 

,  delta   in,   614 

Bay  of  Fundy,   112,  649 

,  tides  of,  226 

Bay  of  Morlaix,  peat  of,   514 

Bay  of  Naples,    mud  of,    334 

Bay  of  New  York,  in  Tertiary,   984 

Bayou  la  Fourche,  245 

Beach  cusps,   706 

Beardmore,   cited,   248,   265 

Bear  Island,   solifluction  on,   543,  544 

Bear  Island  stream,   236 

Bear  River,  calcium  carbonate  in,  468 

Beaumont,  Elie  de,  cited,  203 

Beche,   see  de  la  Beche 

Bechilite,    364 

Becker,   G.   F.,   cited,   752,   774,  906,   908 

Beecher,   C.   E.,  cited,    979,    1086 

Beede,   J.   W.,   cited,   624,   637 

Beekite  rings,  formation  of,   1083,  1085 

Behrens,  J.  H.,  cited,  685 


1 154 


INDEX 


Behring  Sea,    108,   242 

Behring   Sea,   pole  migrating  toward,   895 

,  surface  freezing  of,   181 

Behring  shelf,  104 

Behring  Straits,  242 

Belfast,    South    Africa,    glacial    deposit    at, 

Belgica,   185,   187 
Belgium,   dunes  of,   558 

,  Permic  climate  of,   375 

,  reefs  of,  423 

Bell,  R.,  cited,  430,  462 

Belle  Isle,  Cambric  limestone  of,  417 

Belt  of  cementation,    17 

Belt  of  weathering,  17 

Belt  terrane,  334 

,  age  of,    1138,    1139,    1140 

— ,  Cryptozoan  of,  417 
Belvedere  gravels,  595 
Bengal    Gulf,    temperature    in,    187 
Ben  Nevis,  32 

,  wind-blown  pebble  on,   56 

Benthos,  denned,  991,  996 

,  sedentary,   996 

,  vagrant,    996 

Benton  clay,   261 

Berckhemer,   F.,   cited,   438 

Berendt,    G.,    cited,     126,     133,    557 

Bergschrund,    264 

Berkey,    C.    P.,    cited,    206,    223,    265,    637, 

717,  721,  903,    1140,   1148 
Berkey,  C.  P.,  and  Hyde,  J.  E.,  cited,  200 
Berlepsch  salt  shaft,  757 
Bermuda,   390,   397,  411 

calcareous  dunes  of,  573 

calcareous  sand  of,  651 

cementation  of  sands  of,  753 

consolidation   of   sand  of,    750 

eolian   rocks   of,   293,    439 

lime-sand  dunes  of,  343 

Lithothamnion  at,  471 

peat  in,   509 

reefs,  416 
Bermudaite,  573 
Bernard,  F.,  cited,  956,  1095 

quoted,    1073 

Bert  e  waterlime,  376 
Bertin,  cited,  217 

Bertrand,   C.  E.,  cited,  481,  482,  520 
Bessarabia,  443 
Bessel,  cited,  7 
Beyrich,   E.,   cited,    1108 
Biarritz,    103,    558 
Bigelow,  H.  B.,  cited,  520,  685 
Biggs,  Oregon,  53 

Bighorn  Basin,   Eocenic  and   Oligocenic  de- 
posits of,  627 

Big  Pine,   block  movement  of,  88/ 
Bigsby,  J.,  cited,   1122 
Big  Soda  Lake,  analysis  of,  361 
Billings,   E.,  cited,  915 
Bilma  oasis,   359 
Bimana,   956 
Bingerloch,   245 
Binnewater  sandstone,   731,   823 

,  Lorraine  age  of,  823 

Bioclasts,   285 

Biogenesis,   importance   of,    1147 

Bioliths,  384 

Bionomic  realms,   982 

Biometamorphism,   768 

Bioseisma,  88 1 

Biosphere,   i,    16 

Bird  s   Eye   limestone    (see    Lowville),    488, 

1124 

Birma  shelf,   103 
Birsig    River,    251 
Bischof,  G.,  cited,  163,  350,  614,  637,  760 


Bitter  Lakes  of  Suez,  366 

— ,    deposits   of,    352 

,  intercalated  silt  layers  of,  697 

Bitter   Spring  Laa,   sulphate  waters  of,    168 
Bituminous  coal,  510,  511 
Black  Hills,   308 

,  dome   of,    841,    842,    843 

Black  Hills  dome,  dips  in,  808 

Black  Hills,   flanking  monoclines  of,   844 

Black  Lake,  salinity  of,   154 

Black  Prairies,   839 

Black  Rock   Desert,  playa  lake  in,  603 

Black  Sea,  107,   115,  230,  240 

,  black  mud  at  bottom  of,   1046 

,  dwarf  fauna  of,   1067 

evaporation   from,   27 

faunal  conditions  in,  666,  667 

muds  in,   479 

optics  of,  204 

salinity  of,    153 

,  salt  and  gypsum   deposits  on   borders 

of,  348 

,  surface   freezing  of,    181 

Black  shale,  261 

,  Devonic,  origin  of,  636,  637,  850 

Blackwell,  T.  E.,  cited,  248,  249,  265 

Bladderworts,   495 

Blake,   abyssal   deposits  dredged  by,   676 

,  dredging    of    Spirula    by    the,    1021 

,  dredgings  of,  off  West  Indies,  519 

Blake,   T.  F.,  cited,  685 
Blake,   W.   P.,  cited,  637 
Blake   Plateau,    673 
Blanck,  E.,  cited,  578 
Blanckenhorn,  M.,  cited,  92 
Blastoidea,  949 

,  naming  of,   913 

Blattermollasse,  630 

Bludenz,  weather  at,  48 

Blue   Lick  Springs,    Upper,   composition  of, 

1 68 

Blue  Ridge,  monoclines  of,   798 
Blum,  J.   R.,  cited,    1081,    1083,    1085,    1086, 

1087,    1088,    1095 
Blytt,   A.,   cited,    506 
Bodlander,  G.,  cited,  657,  658 
Bogdo   Lake,   salinity  of,    154 
Bohemia,   336 

,  Devonic  reefs  of,  423 

,  overlap   relations   of  Cambric   of,    729 

Bohemian   Mass,   373 

Bokkeveld  series,  Devonic  fossils  in,  536 

Bolivia,   365,   369 

Bolson  plains,  341 

Bolsons,  58 

Bon   Ami,    Cape,    gliding   in   limestones   of, 

782,   783 
Bonney,  T.  C.,   cited,  462,  878 

,  quoted,   400 

Bombay   shelf,    103 
Boracite,   372 
Borax  Lake,   363 

,  composition    of,    158 

,  salinity  of,    154 

Bordeaux,  natural  mummies  from,  1076 

Boreal  climatic  period,   506 

Bornemann,  J.  G.,  cited,  284,  417,  455,  520 

Borneo,  242 

Borneo-Java  shelf,   104 

Bornhardt,  W.,  cited,  58,  93 

Bornholm,   191 

Borocalcite,   364 

Bosnia,  284 

Bosphorus,  240 

Boss,   303 

Boston,   sea-breeze  at,  44 

Boston    Basin,    drumlins  in,    532 

Boston  Harbor,  drumlins  of,   265 


INDEX 


H55 


Bosworth,   T.   O.,   cited,   93 

Botany,   20 

Bothnian  Gulf,  109,  no,  in,  241 

,  salinity  of,   1045 

Boue,  A.,  cited,   1144 

Bound  skerries,  222 

Bourbonne-les-Bains,  petrified  wood  of,   1081 

Bourguignat,  J.  R.,  cited,   1064,   1069 

Bourne,  G.  C.,  cited,  392,  462 

,  quoted,    392 

Bournemouth,   215 

Boussingault  and  Lewy,  cited,  38 

Boussingaultite,   364 

Bowland  shales,  432 

Bowling   Green,    Ohio,    167 

Brachiopoda,   944 

,  bathymetric  distribution  of,  1014 

,  importance  of  growth  lines  of,  911 

Bradygenesis,    defined,    964 
Bradyseisms,  887 
Brahmaputra  delta,   607,   608 

,  thickness  of,  609 

Brahmaputra  River,  alluvial  plain  of,  585 
Branner,   J.   C.,    cited,   32,    34,   38,   93,    341, 

380,   692,   693,   695,   707,   721,   761,   774, 

884,   1092,    1095 

,  quoted,  33,  342,  693,  694 

Brauhauser,  cited,  634 
Brayman  shale,  261,  823 

Salina  age  of,   823 

Upper  Ordovicic  age  of,  823 

Braz  1,  341 

disintegration  of  rocks  in,  33 

fringing   reefs    of,    390 

hydration   of   rocks  of,    38 

lime  sands  of,   416 

rainfall  of,   67 

range  of  temperature  in,   32 
Brazilian  basin,   105 
Breccia,   limestone,  432,  433 

,  limestone  tuff  of  Tyrol,  437 

Breccias,    endolithic,    536 

,  intra-formational,   529,   779 

,  fault,   528 

Breckenridge,  cannel  coal  of,  481 

Breisbach,  250 

Bretonian,    1128 

Brewer,   W.   H.,  cited,   656,   685 

Bridger  beds,  volcanic  dust  in,  572 

— — ,  tuff  of,  526 

Brighton,  force  of  waves  at,  222 

Brisbane    River,    Unio    in,    1015 

British  coast,   force   of   waves  on,   221 

British   Columbia,    305 

,  pre-Cambric  reefs  of,  418 

British   Isles,    mild  temperatures  of,    234 

British  shelf,    103 

Brock,  R.  W.,  cited,  92 

Brocken,    hornstone   of,    766 

Brockmann-Jerosch,  H.,  cited,  92 

Brogger,   W.   C.,   cited,    302 

Brongniart,    A.,    cited,    1099 

Brooks,  W.  K.,  cited,    1017,   1038 

Brown,  T.  C.,  cited,  530,  537,  762,  785,  826 

Brown  coal,  510,   511 

Browne,  W.   R.,   cited,   685 

,  quoted,  663 

Bruckner,  E.,  cited,  71,  92,  93 
Bruckner  cycle,  71 
Brunswick,  salt  domes  of,  758 
Bryozoa,   385 

,  bathymetric  range  of,    1014 

,  growing  on  corals,  428 

Buchanan,  J.  Y.,  cited,  215,  265,  679,  685 
Buchenstein,   435 
Buchensteiner  formation,  434 
Buckley,    E.    R.,    quoted,    140 
Buckmann,  S.  S.,  cited,  957,  976,  979 


Buenos  Ayres,    droughts  in,    593 
Buffalo,  fossil  earthquake  fissure  of,  792 

,  sandstone  dike  at,   885 

Bugula,  growing  on  Laminaria,  995 
Bunsen,   R.    W.,   cited,    164 

— ,  quoted,    169 
Bunter  sandstein,    71,  225,  436 

,  Ceratodus  in,   1034 

,  Limulus  in,   1029 

,  origin  of,  634 

,  Rogensteine   of,   472,   473 

,  tracks  in,    605 

,  transgression  on  Zechstein,  565 

,  windkanter  of,   55 

Burlington  formation,  fossils  in,  732 

Burma  Mountains,  rainfall  in,   69 

Burma  Sea,   109 

Butte,   tepee,   840 

Buttes,   57 

Bysmalith,    303,    304 

Byssus,    attachment  of   Lucina    by,   448 


Cabot  Straits,  113,  235 

Cader   Idris,    lavas  of,   315 

Caithness,   219 

Caithness  flags,  651 

Caithness    Old    Red    sandstone,    Palseospon- 

dylus  in,    1034 
Calabria,    earthquake   in,    883 

,  earthquake  craterlets  in,   886 

,  Pliocenic     foraminiferal     deposits    of, 

454 

,  torrential   deposits   in,    591 

Calamites,   375,    512,    939,    1004,    1082 

Calcaire   de  Givet,  431 

Calcaire  de  Waulsort,   432 

Calcaire  Grossier,  977 

Calciferous,   1124 

Calciferous    series    of    Scotland,    oil    shales 

in,  479 

Calcification,  1079 
Calcutta,    borings    in    alluvial    deposits    at, 

586 

Caliche,    365 
California,    basaltic    plateau    of,    867 

borax    lakes   of,    363 

earthquakes    of,    882,    887 

lava  of,    315 

onyx  marble   of,   344 

sandstone  dike  of,  885 

valley   of,    alluvial    fans   in,    584 

Call,    R.   E.,  cited,    578 

Callao,   tripolite  near,   460 
I    Callunetum,   503 
Calms,   equatorial,  43,   67 
Calumet  and  Hecla  mine,    14 
Calvin,  S.,  cited,   1095 
Cambrian,   origin  of  name,    1112 
Cambric,  breaks  in,  729 
Cambric   salt  deposits,   371 
Camiguin  volcano,  863 
Camillus  shales,  376,  378 
Campanularia,  growing  on  Laminaria,  995 
Campbell,  M.  R.,  cited,  363,  380,  1131,  1148 
Campeche  bank,    104,   335 
Campeche    shelf,    103 
Campo    Bianco    pumice-cone,    863 
Campos,  68 
Canada,  old  land  of,  834 

,   unconformity  in  Siluric  of,   826 

Canadian   shield,    311 
Canary  Islands,  244,  335,  336 
Canary  Islands,   dust  falls  of,  60 

,  passages  between,  680 

,  pteropod  ooze  west  of  the,  456 


1156 


INDEX 


Candolle,   C.   de,  cited,   721 

Caney  shale,  262 

Cannel  coal,  analyses  of,  481 

,  ash  of,  480 

,  Carbonic,    479 

,  organic   remains  in,   481 

,  origin  of,  482 

Canu,  F.,  cited,  1148 

Cape  Ann,   boulders  on,   226 

Bojador,  dunes  on,  558 

Breton,    Etcheminian   at,    729 

Canaveral,  234 

Cod,  234 

apron  plains  of,   54,    598 
difference  of  faunas  on  north  and 

south  side  of,  1125 
dunes  of,   551,   559 
lignite  in  dunes   of,    565 
moraine   of,    265 
old  marshes  on,  491 
sand  plains  of,  600 
strand  dunes  on,  557 
wave  work  on,  223 
wind  kanter  from,  573 

Colony,   238 

tillite  of,  535 

Comorin,  456 

Farewell,    234 

Finisterre,    187 

Gata,    152 

Hatteras,  226,  652 

Hurd,  838 

Leeuwin,    239 

of  Good  Hope,  214,  238 

Palmas,  235 

Pedaran,    242 

Reykyanaes,    865 

St.   Roque,   233 

Skagen,    103 

Teneriffe,    1018 

,  dredging  off,   1024 

trough,  temperatures  in,    187 

Verde,  dunes  on,   558 

Islands,    152,  235 

York,  387 

Capps,  S.  R.,  cited,  544,  578 
Carbonatipn,    17,   30,   38 
Carbon  dioxide,   24,   29 

,  climate   affected  by,   30 

,  sources  of,  25 

Carbonization,  25 
Carcharadon,    teeth   of,   684 
Caribbean  Sea,    107,  239 

,  Spirula  from,   1021 

Carinata-quader  sandstone,  absent  near  Dres- 
den, 681 
Carlsbad    Sprudel,    203 

,  composition  of  waters  of,  168 

,  origin  of  algous  limestone  of,  476 

,  pisoliths  of,   284,   336 

,  travertine   deposits  of,   475 

Carnallite,    368,   371,    372 

Carney,  F.,  cited,  265 

Caroline  Archipelago,  389,  390,  401 

Carpentaria,  394 

Carse  lands,  peat  of,   514 

Carson   River,  tufa  in,   340 

Carter    T.   H.,  cited,   575,   579 

Casa  Colorado,   57 

Cascq  Bay,  relict  fauna  of,  89 

Caspian  Sea,   108,   356,  365,   897 

,  composition  of,  157,  159 

,  dwarf  fauna  of,   1067 

,  elevation  of,    115 

— — ,  salinity  of,    155,    159 
Cassian  formation,  434,  435,  437 
Cataclastic,   746 
Catinga  limestone,   341 


Catskill   formation,   635 

,  alternation  in  colors  of  beds  in,   623 

624 

,  overlap  relations  of,   742 

,  progressive   replacement   in,    743 

,  red    beds   of,    636 

,  variation  in  thickness  of,  683 

Caucasus,  mud  volcanoes  in,  872 
Cauda-galli,    1124 
Caustobioliths,  280,  384 

,  classification  of,  486,  487 

Caustophytoliths,    280,   467,    478 

Cave  Creek,   onyx  marble  of,   344 

Caverns,   aphotic  region  of,  983 

Cavonne  River,   delta  of,   608 

Cayeux,   L.,   cited,   336,   380,    514,  670,   671, 

673,  685 

Cedarburg,  fossil  reefs  of,  419 
Celebes,    392 

Sea,  107 

,  temperature  of,   189 

Cementation,   751,  753 

,  belt  of,    747 

,  substances  causing,   754 

Cenomanien,    730,   1112 

Center  of  the  earth,   density  of,    15 

,  fusion  of  rocks  at,    15 

Centrosphere,    i,    13 

Centrum,  883 

Cephalochorda,  950 

Cephalonia,    Sea  Mills  of,  257 

Cephalopoda,  naming  of,  913 

Ceratopyge  limestone,  53 

Cesena,  wood  replaced  by  sulphur  at,    1081 

Cette,  348 

Cevennes,    133 

,   winds  from,    50 

Ceylon,    390 

Chagos  group,   388,   389,   39O,   392,  393,   399 

,   nullipores  of,   471 

Chaleur,  Bay  of,   1041 

Chalk,  chemical  precipitation  of,   336 

,  Radiolaria  of,  1082 

Challenger   Bank,   nullipores  on,   471 

Challenger,  the,  334,  410 

,  annelids  dredged  by  the,    1024 

Anthozoa  dredged  by  the,    1012 

blue  mud  dredged  by  the,  668 

Cirripedia  dredged  by  the,    1026 

glauconite  dredged  by  the,  671,  672 

Ostracods   dredged  by   the,    1026 

Plumularians  obtained  by  the,  ion 

Radiolaria  dredged  by  the,   1008 

Spirula    dredged   by   the,    1021 

Challenger    Expedition,    147,    184,    451,    452, 

Challenger    Exploration,    in    Marian    deep, 

Challenger  narrative,  cited,  469 

Chama,  in  Bermudaite,   573 

Chamaeliths,   281 

Chamberlin,  R.  T.,  cited,  903,  904,  905,  908 

Chamberlin,  T.  C.,  cited,  29,  93,  107,  265, 
327,  418,  420,  462,  990,  1038,  1148 

,  quoted  876,  1142 

Chamberlin,  T.  C.,  and  Salisbury,  R.  D., 
cited,  2,  4,  22,  59,  93,  148,  206,  263, 
265,  278,  294,  297,  298,  325,  326,  327, 
579,  634,  637,  675,  679,  861,  878,  908, 
1145,  1146,  1148 

,  ^quoted,   698 

Chamisso,  A.  von,  cited,  399,  410 

Champlain  clays,   concretions  in,   763 

Chapeiros,  396 

Chapman,   F.,   cited,   575 

Chara,  426,  471,  475,  495,   935,   1001 

— — ,  analyses  of,  471 

— —  marls,  494 


INDEX 


Charleston,   234 

,  earthquake  craterlets  at,   885 

sandstone,    1131 

Charybdis,    maelstrom   at,    230 
Chatard,   cited,    362 
Chattanooga  shale,   823 

,  complex  nature  of,   549 

,  hiatus  indicated   in,    1130 

,  origin  of,  479,   514 

Cheirotherium,   tracks  in   Bunter   Sandstein, 

605 

Chelonians,   953 
Chelsea,    England,   28 
Chemakha,    earthquake  at,   885 
Chemical    (actinic)    rays,  28 
Chemnitzia,   436 
Chemung,   overlap    relations  of,   742 

,    progressive   overlap    of,    744 

,    Protolimulus  in,    1029 

,  variation  in  thickness  of,   683 

Cherbourg,   221 

Cherry     county,      Nebraska,     dune-enclosed 

lakes  in,  562 

Chesil  Bank,  force  of  waves  on,  222 
Chile,   369 

,  dunes  in,   563 

,  earthquake  in,    888 

,  natural  mummies  from,    1076 

,  nitrate  deposits  of,   364 

,  origin  of  nitrates  of,   370 

Chiltern  Hills,   chalk  cuesta  of,   839 
China,    loess  of,    565 

Sea,  237,  240,  242,  392 

. ,  atolls  and  fringing  reefs  of,  390 

Chin-kiang,    dust   storm  at,    59 
Chirotype,  defined,  919 
Chitin,   composition  of,    1078 
Chlorides,    177 
Chlorinization,    768 
Cholnoky,   E.   de,    cited,    92 
Chonolith,    304,    305,    307,    309 
Chonos  Archipelago,   peat  in,  509 
Chotila  Hill,   miliolite  limestone  on,    575 
Chouteau   limestone,    732 
Christmas  Island,   393 

,   radiolarian  ooze  around,  458 

Chronobios,   922 

Chronofauna,    922,    1043 

Chuar  series,   age   of,    1140 

Chun,   C,   cited,   460,   999,    1038,    1069 

Chunnenugga    Ridge,    839 

Chuquicamata,  natural  mummy  at,   1077 

Cidaroidea,  950 

Cincinnati,   artesian   well  at,    168 

Cincinnati   dome,   808 

Circulus,   978 

Civitavecchia,   221 

Clamshell  cave,  basaltic  jointing  of,   318 

Clapp,   F.  C.,   cited,   143,  600 

Clark,  W.  B.,  cited,  672,  686,  979 

Clarke,   F.  W.,  cited,   39,   93,    157,    168,   206, 

348,   362,    363,    364,   365,   369,    380,   468, 

570,   579,    614,    637,    657,   671,   678 
,   quoted,    154,    156,    161,    162,    163,    166, 

169,  173,  468,  668,  670,  671,  677 
Clarke,  J.  M.,  cited,  456,  462,  479,  520,  667, 

686,  1038,  1069,  1070,  1113,  1119,  1134, 

1148 

,  quoted,   1023,   1123,    1127 

Clarke,   J.    M.,    and   Ruedemann,    R.,    cited, 

1030,    1038 
Clarke  Range,   334 
Clastation,  17 
Clay-galls,  564,  711 
Clay  iron  stones,    719 
Claypole,   E.  W.,  cited,   903,   908 
Cleavage,  769 
Clement,  J.  M.,  cited,  317,  320 


Cleveland  shales,  tissue  of  sharks  in,  1080 
Climate,  desert,  77 

,   interior,   76 

,  littoral,   75 

,   mountain,   77 

,  oceanic,   75 

— ,   physical,    74,   75 

,   solar,   74 

Climatic  belts,  74 

provinces,    77 

•  types,    78 

zones,  Mesozoic,  80 

,  Neumayr's  Jurassic,   79 

— ,  past,  78 
Clino-unconformity,    821 
Clinton  formation,  ballstone  reefs  of,  446 
—  iron  ore,  dwarf  fauna  of,   1045,   1068 

,   origin  of,    762 

Clinunconformity,   821,  824 
Clione,   borings  of,    1092 

Clitheroe    district,     carbonic    limestones    of, 
449 

— ,   limestone,    432 
Closs,  H.,  cited,  93 
Clouds,   cirrus,   63 
• — — ,   cumulus,   63 

,   nimbus,    63 

— - — ,   stratus,   63 

Coal,   oxidation  of,    37 

Coal    measure    limestones,    intraformational 

breccia   in,    530 
Coastal  plain,  830 

— ,   New  York  Palaeozoic,   834 
Cobalt,    Huronian   tillite    from,    534 
Cobequid    Bay,    tides   in,    227 
Coblenz,    245 

Cobleskill  limestone,   continuity  of,    1132 
Coccoliths,    453,   454,   456,    933 

,    in    Severn   muds,    664 

Cochabamba,    365 

Cochin  China,  242 

Cocos  Islands,   gradual   emergence    of,   895 

— ,    radiolarian    ooze    around,    458 
Cocos-Keeling  atoll,   388,   389,  390 
Codden  Hill  beds,  459 
Cohn,  F.,  cited,  476,  520 
Coire    Bog,    peat   in,    505 
Cole,   G.  A.  J.,  and  Crook,  T.,  cited,  686 
Cole,    G.  A.  J.,   and  Gregory,  J.   W.,   cited, 

315,    316,    320 

Coleman,  A.   P.,   cited,  81,   92,   93,   534,   537 
Colemanite,   364 
Colima,  dust  from,  60 
Collet,    L.   W.,   cited,   686 
Collet,  L.  W.,  and  Lee,  G.  W.,  cited,  686 
Colob   formation,    dune  origin   of,    571 
Cologne,   brown-coal   north   of,   513 
Colorado,    291 

,  Cretacic  dwarf  fauna  of,  1069 

,  Palaeozoic   sandstones  of,  310 

delta,   deposits  of  lime  in,   616 

desert,    70 

desert,   dunes  of,   562 

River,   delta,   619 

Springs,     eolian     cross-bedding     near, 

705 

Columbia  River,   dune  area  of,  561 

Columbian  gravels,   cementation  of,  754 

Columbus  limestone,   424 

Commentry  basin,  coal  deposits  of,  518 

Como  beds,    colors  of,    624 

Comoro   Isles,   388 

Concepcion,   earthquake  waves  from,  890 

Harbor,  earthquake  in,  888 

Conchiolin,    1078 
Concretions,  718,  763 
Condore  Islands,  242 
Conduction,   30 


1158 


INDEX 


Coney  Island,  sea-breeze  at,  45 

Confervales,   935 

Conformable  strata,  826 

Congelation,    31,    751 

Conglomerate,  edgewise,   530,   784,  785 

Congo  River,   235,   248 

Congress  Spring,  chloride  waters  of,    168 

Conidae,  poison  fangs  of,   1020 

Conifers,  375 

Conn,    H.   W.,   cited,    1038 

Conneautsvillej  well  at,   168 

Connecticut  River,  131 

1     Valley,     concretions     in     post-glacial 

,  clays   of,    719 

,  trap   of,    313 

Conocoryphidae,   as  index  fossil,    1134 
Conodonts,   947,   951 
Conoplains,    830,   856 
Conrad,  T.,  cited,  915,   1123 
Constantinople,  240 
Contacts,  fault,  309 

,  igneous,   309 

-,  sedimentary,    309 

Continental   block,   7,    100 

deposits,   70,  71,   734 

,  red  color  of,  84 

platform,   8 

slope,   7 

Convection  currents,   30,   31 
Convergence  979 
Conybeare,   W.,   cited,    1108 
Coode,   Sir  J.,  cited,   222,  266 
Cook  Inlet,    in 

Coon   Butte,   86 1 

Cooper  Creek,  dry  delta  of,   584 

Copal,    518 

Cope,  E.  D.,  964,  1040 

Coquina,  260 

Coral  basin,  temperature  in,   187 

Coralline  Crag,   faunas  of,   89 

Corallines,    476 

Coral    Sea,    108 

Corals,   growth  lines  on,    911 

,  naming  of,  913 

Cordonan,   lighthouse  of,   223 

Corndon,    307 

Corniferous  limestone  (see  Onondaga),  424, 
1124' 

Cornish,   V.,   cited,   215,   265,    286 

Corrasion,   eolian,    18 

,  glacial,   1 8 

,  river,    18 

,  wind,   51,   52 

Corrosion,    18 

Corsica,   275 

Coseguina,  volcanic  ash  from,  60 

Cotentin,   peat  at,   514 

Cotidal    lines,    228 

Cotopaxi    dust  from,   60 

Cotswold  Hills,   oolite  cuesta  of,   839 

Cotype,  defined,   919 

Couvin,   Devonic  reef  near,   431 

Covesea,    256 

Crabs,  production  of  alkalinity  by,  331 

Cragin,   F.  W.,  cited,  521 

— ,  quoted,   469 

Craigellachie,    255 

Cramer,  F.,  cited,   753,  774 

Crammer,   H.,   cited,   601,   602,    637 

Crater  Lake,   120 

,  depth  of,   116 

Craven    district,    432 

Credner,  G.  R.,  cited,  609,  613,  618,  637 

Credner,   H.,   cited,    317,   320,   537 

,  quoted,  699 

Credner,  R.,  cited,   1063,   1064,   1070 

Credneiia  beds,  absent  in  vicinity  of  Dres- 
den, 681 


Creep,    541 

"Creeping  Joe"  dune,   560 

Crenic  acid,    173 

Creodontia,    955 

Cretacic  clays,   pyrite  concretions  in,   764 

Crete,    240,    334 

Crinoidea,  421,  949 

,   naming  of,   913 

Crivelli,    B.,    cited,    1145 

Croatia,  lakes  of,    125 

Crocodiles,  marine  habitat  of,  985 

Cromdale,  252 

Crosby,  W.  O.,  cited,  4,  13,    15,   16,  22,  38, 

93,    143,    264,    265,    266,    287,    288,    298, 

310,   315,   320,   412,    462,    533,   537.   600, 

638,    726,    744,    790,    821,    826,    848,    857 

,   quoted,  36,   532,  621 

Crosby,  W.  O.,  and  Ballard,  H.,  cited,  265, 

266 
Crosby,  W.  O.,  and  Crosby,   F.,  cited,   257, 

266 
Cross,  W.,  cited,   58,  82,  93,  638 

,  quoted,  627 

Cross,   W.,    iddings,   J.   P.,   Pirsson,   L.   V., 

and  Washington,  H.  S.,  cited,  273,  277, 

298 
Cross-bedding,   delta  type,  701 

,  eolian,   702,   703 

,  in    Devonic    limestone    of    Michigan, 

429 

,  torrential,   701 

Cross  Fell,  peat  covering,  504 

Croton   reservoir,    salinity  of,    155 

Crozet  Islands,   40 

Crustacea,   destruction  of  limestone  by,  415 

Crustal    block,    lowering    and    elevation    of, 

1141 

,  thickness    of,    905 

Crustal  blocks,   4 

Cruzy,  sulphate  waters  of,   168 

Cryohydrate,   194 

Cuba,  233 

Cuesta,  832,  836 

Cuestas,  Devonic,  838 


,  , 

,  Mesozoic,  838 

,  Palaeozoic,  838 


Culbin,   dunes  of,   256 
Cullis,  G.,  cited,  445,  462 
Culm,   cherts  from,  459 
Culmination  circle,  894 
Cumings,   E.  R.,  cited,  973,  979 
Current  ripples,  712 
Currents,    Agulhas   Stream,   238 

,  Benguelan,  235,   1050 

,  Brazil,   233,   235,    1050 

,  Cabot,   235 

,  California,   237,  239 

,  Canary,  235,    1050 

,  Cape  Horn,  235 

,  East  Australian,    237 

,  East  Greenland,  234 

,  Equatorial   counter,    235,    237,   238 

,  Falkland,  235 

,  Florida,  235 

,  Guiana,   233 

,  Guinea,   235 

,  Irminger,  234 

,  Kuroshiwo  drift,  237,  242,    1049 

,  Labrador,  234,  237 

,  Mozambique,    238 

,  North  Cape,  236 

,  North  Equatorial,  233,   235,  237,    1050 

,  North  Pacific  west-wind  drift,  237 

,  Peruvian,  238,  460,    1050 

,   South   equatorial,   233,   237,   238,    1050 

,  South  Pacific  west-wind  drift,   238 

,  West  Australian,  239 

,  West  Greenland,   237 


INDEX 


H59 


Cutch,  Miliolite  of,   575 

Cuttle-fish,   946 

Cuvier,  G.,   cited,    1099 

Cuxhaven,    229 

Cvijic,  J.,  cited,   133,   143 

Cyatholiths,  457,  933 

Cycle   of   erosion,    137,    829,    849 

Cyclones,  46 

Cypress,    513 

Cypns,   in  playa  lakes,   603 

Cyprus  Island,   153 

Cystoidea,  949 

,  naming  of,  913 


Dacque,  E.,  cited,   1145,   1148 

,  quoted,    1144 

Dadoxylon    wood,    941 
Daemonelix,    1091,    1092 
Dago    Island,    cuesta    of,    838 
Dakota  sandstone,  71,  260,  642 

,  compound   overlap  of,    739 

,  dune   origin   of   parts  of,    570 

,  non-marine,    1101 

Dale,  T.  N.,  cited,  80 1 

Dall,  W.  H.,  cited,  92,    1038,   1070 

,  quoted,   1048 

Dallas,  dunes  at,  561 

Dalmatia,   240 

Dalmatian  coast,  Karst  region  of,  882 

Daly,  R.  A.,  cited,  302,  303,  304,  305,  307, 

309,   320,    331,   333,   334,   338,   380,   719, 

721,    764,    774 

,  quoted,  333,  334 

Dana,   J.    D.,   cited,    16,    38,    143,    314,    320, 

336,   380,   391,   406,  408,   409,  462,   520, 

537,   76i,   774,    799,   878,   900,   902,  908, 

1038,    1055,   1103,    1106,   1119,    1144 
,   quoted,   315,    396,   409,   414,   481,   699, 

720,   890,    1007,    1012 
Danish  coast,   dunes  of,   558 
Danube,   248,   251,   587 

delta,  608 

,  rate  of  growth  of,  609 

,  velocity  of,   245 

Danzig  Bay,  temperatures  in,   190 

Daphnia,   in   playa  lakes,   603 

Darcy,  cited,   257 

Dardanelles,  240 

Darwin,   C.,   cited,   335,   336,   380,   386,   397, 

398,  404,    408,   413,   462,   509,    520,    544, 

579,     638,     693,     694,     695,     908,     1015, 

1018,   1026,    1038,    1055,    1070 
,   quoted,   360,   398,    399,   415,   416,    593, 

594,  888 
Darwin,  G.  H.,  cited,   91,  92,  94,   579,   712, 

713,  721,  897 
Darya,   salinas  of,   358 
Daubree,  A.,  cited,  226,  266,  294,  295,  298, 

686,   789,  790,  826,  906,  907,   1081 
Davenport,  C.  B.,  cited,   1038,   1042,   1070 

,   quoted,    1019 

David,    T.   W.    E.,    cited,    81,    94,    393,   462, 

535,    538 

David    Island,    397 
Davidson,   T.,  cited,    1038 
Davis,  C.  A.,  cited,  471,  491,  495,  496,  498, 

500,   502,    516 

,  quoted,  490,  491,  492 

Davis,    W.    M.,    cited,    22,    40,    43,    54,    94, 

116,    120,    121,   124,    126,    128,    133,   134, 

137,     143,     212,     217,     2l8,     220,     228,     266, 

356,  409,  410,  462,  487,  520,  535,  538, 
573,  579,  626,  638,  816,  826,  839,  842, 
845,  852,  854,  857,  858 


Davis,  W.  M.,  quoted,  90,  215,  229,  410, 
535,  536,  566,  584,  585,  588,  589,  839, 
852,  853,  854,  885 

Davison,  C.,  cited,  693,  695,  908 

Davis  Straits,  186,  234,  237 

Dawson,  Sir  W.,  cited,  515,  520,  621,  638 

,  quoted,   515,  516,  622 

Daylight,  diffusion  of,  28 

Dead  Sea,  897 

composition   of,    157,    159 

coral  from,   1013 

elevation  of,  115 

leached  salt  of,  367 

salinity  of,    154,    159 

Deadwood  Gulch,  308 
Dean,  B.,  cited,  950,   1095 


-,  quoted,    1080 

th  Valley,  Cal.,  27 


Deatl  ...          ,      . 

,  soda  niter  deposits  of,  364 

desert,  364 

De   Candolle,   A.,   cited,   56 

Decapods,   range  of,   948 

Decarbonation,    39 

Deccan  Plateau,  Cretacic  trap  forming,  868 

Decewville   beds,    424 

Decomposition,    17 

Deep,  Nero,    106 

,    Tuscarora,    106 

Deep  sea  platform,  8 
Deflation,    17,   51,   52,   55 
Deformation,   endogenetic,   776,   777 

,  endolithic,    757 

,  exogenetic,    776 

De  Groot,  H.,  cited,   363,   380 

Dehna    Desert,    dune    area    of,    562 

Dehydration,   38 

De  la  Beche,  Sir  Henry  T.,  cited,  269,  299, 

576,   577,  578,  865,  878 

,   quoted,    864 

De    Lapparent,    A.,    cited,    203,    1068,    1070, 

1145,    1146,    1149 

-.  quoted,  6 

De  Laumy,  cited,   203 
Delaware   Bay,   drowned,   832 

River,  tides  in,  227 

Delesse,  A.,  cited,  219,  266,  686 
Delta  beds,  612 

Deltas,   coal  in  fossil,   741 
Delthyris  shale,    1124 
Demorphism,   belt  of,   34 
Dendrites,    791 

Denmark,    Chara  in  lakes  of,  471 
S  coastal   erosion  of,   224 

Straits,    109 

,   ridge,    188,    192 

Density  of  the  earth,   12,  15 
Denudation,    17 
Deposition,    17,    19 
Depressed   oceanic    region,    8 
Depth  of  compensation,    10 
Derby,   O.  A.,   cited,   38 
Desalinification,    748,   763 

De    Saussure,    H.    B.,    cited,    72 
Desert,  Hamada,   57 

'  of  Gobi,  material  brought  from,  566 

varnish,  27,  57 

Deserts,  eolian  ripple  marks  in,   714 

Desmids,    935 

Deuterogenous,   260 

De  Vries,  H.,  cited,  962,  963,  979 

Dew,    26,    62 

point,    62 

D'Halloy,  O.,   cited,   1108 
Diabase,   defined,   278 
Diadematoidea,    950 
Diagenesis,    748 
Diagenetic  processes,  750 


n6o 


INDEX 


Diagenism  of  cinder  cones,  863 

Diastrophism,    12,    16 

Diatomaceous  ooze,   salt  content  of,   367 

Diatom  ooze,  analysis  of,  677 

Diatoms,  983 

Dicotyledons,    941 

Diego  Garcia,  388,  392,  393 

Diener,  C.,  cited,  682 

Diener,    C,    and    Arthaber,    G.,    cited,    435, 

462 

Dietrich,  cited,   397 
Dikes,  clay,   564 

,  composite,    304 

,  multiple,  304 

,  sandstone,   791 

Diller,   J.    S.,    cited,    72,    299,    885,   908 

Dinosauria,   954,    1037 

Dippersdorf,  246 

Disceras  limestone,  438 

Discolith,   457,    933 

Disconformity,  821,  822,  823,  826 

Discordanz,    821,    824 

Disintegration,    17 

Disko    Island,    post-glacial    deposits    of,    87 

Dismal  Swamp,    120,   500 

Distillery  quarry,  419 

Dittmar,    W.,   cited,    147,    148,    194 

Dixon,    E.   E.    L.,    and   Vaughan,   A.,   cited, 

459,  460,  462 

Dnieper  River,   dunes  along,  560 
Dodge,   R.  E.,  cited,   131,   143 
Dogger  Bank,   104,    191,  218,  230 

?er,   459 


Dog's   Bay,    Foraminifera  in,    576 
Doldrums,   67 
Dolerite,    278 

of  Bombay,    39 

.  of  South    Staffordshire,    39 

Dolgeville,    243 
Dolinas,  857 
Dolomitization,    761 
Domes: 

Adirondack,  810 

Black   Hills,    841,    842,    843 

Cincinnati,    810,    843 

Nashville,  810,  843 

North  Ontario,  810 

Ontario,    810 

Ozark,   810 

Wisconsin,    810 

Donetz  Valley,  dunes  in,  561 

Donney   Lake,    361 

D'Ooust,   Virlet,   cited,   336 

D'Orbigny,  A.,  cited,  964,  979,  1088,   1095 

,  quoted,    1074 

Dorpat,  27 
Dorset,  838 
Dover,  228 

Straits,    234 

,  tidal   interference  in,  229 

Drasche,    R.   von,   cited,  462 
Dreikanter,    54 

,   in  basal  Cambric   of  Sweden,   728 

Dresden,    651 

Dresser,  J.  A.,  cited,  92 

Drift,    englacial,    265 

,  subglacial,  265 

,  superglacial,  265 

Drigg,    fulgurites   of,    73 

Drumlins,  material  of  Boston,  532 

Drummond  Island,   corals  of,  420 

Ducie    Island,    390 

Dufour,   L.  cited,    196,  206 

Dundee  limestone,   424,   648 

Dundelbach,   delta  of  the,   610,    613 

Dune    deposits,     reworked    by    encroaching 

Dune  Park,   height  of  dunes  in,   559 


Dunes,    slopes   of,    563,    703 

Dunker,   G.,  cited,   915,  916 

Dunnet  Head,   Lighthouse  of,  219 

Dupont,  E.,  cited,  431,  462,  463 

Durance,    Mont    Genevre,    316 

Durham,  Magnesian  limestone  series  of,  341 

Durham,   W.,   cited,   686 

Durness  limestone,   gaps  in,    684 

Dust  falls,  volume  of,  60 

Dust   fogs,   6 1 

storms,   28 

Dutton,    C.    E.,    cited,    314,    320,    868,    869, 
878,  908 

,  quoted,  869 

Dwyka  conglomerate,   82,    535,   536 
Dybowski,  W.,   cited,    1064,    1070 
Dysodil,  479 
Dysphotic  region,  982 


Earawalla,  Isthmus  of,  foraminiferal  de- 
posit of,  576 

Earth  glacier,  34 

Earth's  axis,  displacement  of,  90 

Earth's  crust,  characters  of,   12 

,  denned,  10 

,  deformation  of,    12 

,  materials  of,    12 

,  specific  gravity,    12 

,  thickness  of,    10,    n,    12 

Earth's  interior,  condition  of,  16 

,  temperature  of,    13,   14,    15 

East  Abyssinian   mountains,   355 

East  China   Sea,   107 

Easter  Ross,  peat  of,  505 

East  Greenland,  post-glacial   fauna  of,  88 

Mediterranean,  salinity  of,    151 

sea,    109 

stream,  temperature  of,    192 

Eastham,  sand  plains  of,   600 

East   Islet,    392 

Eaton,   Amos,    cited,    1122 

Ebro  River,  delta  of,  608 

Ecca   formation,   coals  of,    536 

Eccles,   J.,   cited,   72 

Echinodermata,  949 

Echinoderms,  destruction  of  limestone  by, 
4*5 

Echinoidea,  naming  of,  913 

Echinoids,  burrows  in  limestone  made  by, 
1092 

Ecuador,    earthquake  fissures  in,   883 

,  position    of    oscillation    poles    in,    893 

Edentata,   955 

Eel  grasses,  985 

Egleston,   T.,   cited,    54,   94 

Egmont  Island,  399 

Egypt,   369 

,  alkaline   lakes  of,   361 

,  Foraminifera    in    eastern  desert  of,  576 

,  soda  lakes  of,   362 

Ehlers,   cited,    1024 

Ehrenberg,  C.  G.,  cited,  384,  455,  686 

Eifel,  crinoidal  limestone  of  the,  431 

,  Maare  region   of  the,    860 

,  reefs  of  the,  423,  430,  431 

,  Tertiary  volcanoes  of  the,   874 

Eimer,  T.,  cited,  963,  964,  977,  979 

Einkanter,  54 

Eisenach,   434 

Ekman,   F.  L.,  cited,   191 

Elbe  River,  225,  229 

,  dune  areas  of,  557 

Elbruz  Lake,   120 

Eld  cleft,  lava  from,  866 


INDEX 


1161 


Eldgja,  length  of,  866 

Elgin,   Triassic  reptiles  from,   953 

Elgin   sandstone,    dune    origin  of,    571 

Ellis  Island  group,   388,   389,   393,   394,   401 

El    Late   Mountains,    308 

Elm,   Switzerland,   rock  fall  at,   546,   66 1 

Elton  Lake,  357 

,  composition  of,   157 

,  salinity  of,    154,    156 

Ely  River,   662 
Embryonic  periods,   971 
Emerson,  B.  K.,  cited,  313,  320 
Emmons,    E.,    cited,    1123 
Ems   delta,    607 

Encrinal  limestone,  continuity  of,  684,    1131 
Encyclopaedia  Britannica,   cited,  24,   348 
Endell,   K.,  cited,  463 
.  Endolithic  brecciation,    777 
Endosmosis,    180 
England,   Carbonic   oolites   of,   472 

,  Jurassic  oolites  of,  472 

,  origin    of    chalk   of,    850 

,  transgressing   Cretacic  of,    730 

English  Channel,  112,  218,  219,  234 

,  tides  in,  228 

Enterolithic  structure,   527,  758,   778 

Eolation,    51 

Eolian  cross-bedding,  tangency  of  layers  in, 

704 

Eolian  deposits,  size  of  grains  of,   56,  553 
Eophyton   sandstone,    windkanter    from,    573 
Epeirogenic   movements,    12 
Epembryonic  periods,   971 

stages,   971 

Ephebastic,   973 

Ephebic  stage,  972 

Epicenter,   883 

Epicontinental  sea,  provincial  fauna  of,  984 

Epidote,   177 

Epiphytes,    1-002 

Epiplankton,  994 

Equatorial  currents,   390 

Erdmann,    E.,   cited,   372,    373,   380 

Erongo,    692 

Erosion,    17 

Erosion    cycle,    137,    829,    849 

Eruptions,    explosive,    860 

,  extravasative,  860,  865 

Erzgebirge,   375 

Escambia,  295 

Eschscholtz  Bay,  tundra  at,   508 

Eskers,    133,   257 

Esmeralda    county,    Nev.,    363 

Esopus  grit,   635 

Estheria,  in  playa  lakes,  603 

Esthonia,   838 

Etcheminian,    1128 

,   thickness  of,    729 

Etheridge,  R.,  cited,  1 144 
Etna,  volcanic  gases  from,  203 
Eureka  black  shale,   732 
Euryhalinity,    1045 
Eurypterida,   377,  425,   948,   950 

,   habitat   of,    989,    1029,    1030 

Eurythermal  organisms,   80 
Eustatic   movements,    negative,    3,    4 

,  positive,  4 

Eutraphent,  498 

Evans,  J.  W.,  cited,   574,   577,   579 

Evaporation,  27 

Everding,    H.,   cited,    757,    774 

Everglades,    126,    404,   406,    407 

Ewing,  A.  L.,  cited,  94,   175,  206 

Exaration,    17,    263 

Excretions,    719,    720 

Exfoliation,   concentric,    33 

Exomorphic,  765 

Exosmosis,   180 


Faira  Island,  218 

Fairchild,   H.    L.,   cited,    126,    127,    137,    143, 

264,   266,   297,   299,   652,   686,   707,   708, 

721,  861,  878 
Falb,   R.,   cited,   908 
Falkland   Islands,   glacial  deposits  of,   82 

,  peat  in,    509 

,  "stone  rivers"  of,  544 

Falls  of  the  Ohio,  corals  of,  420 

,   reefs  of,   426 

Farafrah,  chalk  from,   454 
Farlow,  W.  G.,  cited,  979 

,  quoted,  959,  960 

Faroe-Iceland  ridge,    no,    188 
Faroe  Islands,  192,  218,  234 

,  Tertiary  basaltic  flows  in,  867 

Farrington,  O.  C.,  cited,  1088,   1095 

Fault  breccias,    291 

Fault   scarps,   submarine,   890 

Favosites,  worn  heads  of,  428 

Faxon,   W.,   cited,    1059 

Fedden,    F.,    cited,    574,    579 

Feldspar,    clouding  of,    33 

Fenneman,    N.   M.,   cited,   686 

Fenner,  C.  N.,  cited,  312,  320 

Fermor,   L.,   cited,   94 

Ferns,    375,    941 

Ferrara,  height  of  channel  of  Po  in,  617 

Fetlar,    72 

Fife,  lava  flows  of,   313 

Fiji  basin,  temperature  in,   187 

Islands,    388,   411 

,   nullipores   on,    471 

,  pteropod   ooze    around,    456 

,  raised  reefs  of,  436 

,  reefs  of,   393 

Fillmore,  gypsum  deposit  at,   359 
Finckh,   A.   E.,  cited,   394,   463,  471,   520 
Fingal's   Cave,    columnar    structure    of,    318 

,  Tertiary  basaltic  flows  forming,  867 

Finger  Lakes,    123,    127 
Fimstere,  peat  deposits  of,  514 
Finland,   eskers  in,    599 

,  undecomposed  granite  of,   40 

Finlay,   G.    L,   cited,    300 

Finnish  Gulf,   109,   no,   in 

Fire  clay,  517 

Firn,  279 

Fischer,  P.,  cited,  603,    1019,    1038 

Fissility,   769,  794 

Fissures,  gases  active  in,  767 

Fissures,   solution,   857 

Flachsee,  987 

Flamborough   head,   224 

Flammarion,  C.,  cited,  28 

Flanders,   dunes  of,   557 

Fleming,   J.   A.,   cited,    721 

Flints,   764 

Flocculation,    654,   655,   656 

Flores  Sea,    186,  242 

Florida,   233,  405,  411 

,  cypress  swamps  of,   500 

,  deposits  in  lagoons  of,  424 

,  fringing  reefs  of,   386,  390 

,  muds  in  lagoons  of,  479 

,  peat  in  cypress  swamps  of,   509 

,  ripple  marks  off  coast  of,  219 

,  sands  of,   226,   295 

Straits,  233,   244 

Florida-Texas  shelf,    103 
Florissant  Lake,  beds  of,  291 

,  mud  cracks  in,   710 

,  volcanic  ashes  of,   524 

,  volcanic  dust  in,   572 

Flower,  Sir  William,  cited,  989 
Flying  fish,   988 


Il62 


INDEX 


Focus,   earthquake,  883 

Foehn,  explanation  of,  49 

Foerste,  A.  E.,  cited,  843,  858 

Fogs,  63 

Fol   and   Sarasm,   cited,    205 

Folds  section  of  Appalachian,  844 

Foraminifera,   942,    1007 

Forbes,  E.,  cited,  248,  266,  686,    1070,   1125 

Forchhammer,  G.,  cited,   147,    194,  206,  559, 

579,  686,  703,  721 
Foredeep,  defined,  800 
Forel,  F.  A.,  cited,  170,  196,  197,  198,  204, 

205,  206,  244,  266,  721 
Fore-set  beds,  702 
Forestian,  Lower,  506 

,  Upper,  506 

Forest  marble,   cross-bedding  in,   704 

Formaldehyde,  24 

Forres,  413 

Fort  Jefferson,    391 

Fossa  Magna,   882 

Fosters  Flats,   246 

Foureau,  F.,  cited,  604,  638 

Fowey  Rocks,   406 

Fowler,  G.  H.,  cited,  992 

Fox,  H.,  and  Teall,  J.  J.,  cited,  316,  320 

Fraas,   E.,  cited,   442,   634,   635,   638 

Fraas,  O.,  cited,  456,  463,  711,  721 

Fractoconformity,    826 

Fracture,  zone  of,  819 

From,    ijj  i 

Frank,   Canada,  rock  fall  in,   546 

Franken,    Solnhofen    reefs   at,    438 

,  subaquatic  gliding  at,   782 

dolomite,   438,  440 

Frankenwald,  375 

Frantzen,   T.,  cited,   455,   521 

Franzensbad,  volcanic  hill  near,  874 

Franz  Josef  fjord,  post-glacial   fauna  of,  88 

Franz  Josef  Land,  236 

,  post-glacial  fauna  of,  88 

Frasnien   reef,    43 1 

Frauenthal,   stylolites  at,   786 

Freeh,  F.,  cited,  94,  431,  463,   1146,   1148 

Fredericksburg  formation,  Dakota  sand- 
stone on,  739 

Free,  E.  E,  cited,  55,  56,  57,  60,  94,  579 

,  quoted,  59,  60 

Freeman,  W.  B.,  and  Bolster,  R.  H.,  cited, 
356,  380 

Free-stone,    752 

Fresenius,  K.,  cited,  346 

Friendly   Islands,   386 

Friesian   Islands,   dunes  of,   557 

Frische   Haff,    126 

,  strand    dunes   of,    557 

Nehrung,   dunes  of,   559 

Fritsch,  K.  von,  cited,  60,  94,  537 
Fritting,    766 

Frontenac  axis,  810 

Front  Range,  Appalachian,  844 

,   Rocky   Mountain,    260 

,  basal  Palaeozoic  contact 

in,  726 

> ,  hog-backs  of,   841 

,  monoclines  facing,  798, 

844 
,  torrential    deposits    of, 

591 
Frost,  26,  62,  63 

work,   31,   34 

Fuchs,  T.,  cited,  463,  684,   1038,   1068,    1070 

Fiichsel,  cited,   1099 

Fucoids,  936 

Fulgurites,   72 

Fuller,    M.    L.,   cited,    5,   22,    142,    143,    257, 

266 
Fumarolic  action,  768 


Funafuti,  388,  426 

-  atoll,     389,     393,     394,    4«9,    4*2,    4*3, 


4i5 
--  ,  d 


epth  of  lagoon  of,   393 
--  ,  diagenism  in,    761 
--  ,  nullipores    on,    471 
Fungi,  933,   937,    1002,   1003 
Fusulina  limestone,  453 

Fusulina    limestones,    asphaltic    material    in, 
485 


Gagas  River,  jet  deposits  of,  483 
Gagatite,    482 

Gaisa  series,  glacial  deposits  on,  534 
Galapagos   Islands,    237,   239 

,  tripolite  near,   460 

Galicia,  443 

,  Oligocenic  shales  of,  485 

Galveston,   range  of  tide  at,  230 

Ganges,    127,  248 

,  alluvial  plain  of,  585 

delta,  607 

,  lignitized  wood  in,  614 

,  overlap  in.   741 

• ,  remains  of  river  animals  in,  615 

,  thickness  of,  609 

•  flood   plain,    589 

system,   hydrographic  basin  of,   247 

,  sediment   of,    247 

Ganoids,  951,    1034 
Gardiner,  J.   S.,  cited,  463,  471,   520 
Garden  River,  dunes  in  valley  of,  $( 
Garonne  River,  223,  558 

,  alluvial   fan  of,   584 

Gaspe   limestones,    enterolithic   structure    in, 
782 

sandstone,  Bothryolepis  from,    1034 

,  dry  delta  deposit,  635 

Gaub,  F.,  cited,  521 

Gault,   730 

-,  overlapping   of  the,    850 


560 


Gciuss,   185 

Gautier,  A.,  cited,  24,  206 

,  quoted,  203 

Gaylussite,  362 

Gaysum    Island,    calcareous    eolian    deposits 

on,  577 

Gazelle,  observations  on  the,  204 
Gebbing,  J.,  cited,  687 
Geer,   G.  de,  cited,  92 
Geic  acid,   173 
Geikie,   A.,   cited,    175,    206,    266,    304,    318, 

320,   537,  774,  796,  873,  875,  878,   1119, 

1148 
,  quoted,   219,   315,   698,   770,   864,   872, 

1074,    1105,    1106,    1125 
Geikie,  J.,  cited,   505,  506 
Gekrose,    757 
Gekrosekalk,  759,  785 
Gemmellaro,  G.,  cited,    1145 
Genepistasis,  964 
Generation,  alternation  of,  938 
Genesee  glacial  lakes,   126 

River,    137,   837 

shale,  origin  of,  479 

,  Protosalvinia   in,    718 

Valley,  Portage  sandstone  in,   569 

Geneva,  foehn  of,  47 
Genoholotype,   920 

Genolectotype,   920 
Genosyntype,   920 
Genotype,  selection  of,  920 

, ,  elimination    method,    920,    921 

, ,  first  species  method,  920,  921 

Geo-biotic  realm,  982 


INDEX 


1163 


Geologic  genera,  978 
Geological  time  scale,   22 
Geology,  defined,   19 

,  subdivided,  20 

Georgia  Straits,    iti 
Georgian  Bay,  836,  837 
Geosyncline,    799 

,  proposed  by  Dana,  900 

Gephyrean  worms,   destruction  of  corals  by, 

415 

Gerbing,  J.,  cited,  763,   774 
Germersheim,  251  ^ 

Gerontastic,   973 
Gerontic  stage,  defined,  972 
Ghadames,   26 
Giants'    Causeway,    columnar    structure    of, 

3i8 

,  Tertiary  basalt  of,  867 

Gibbsite,    177 

Gibraltar,  limestone  breccias  of,  547 

,   Straits  of,   240 

Gilbert,    G.    K.,    cited,    119,    143,    380,    705, 

706,   707,   709,   721,   861,  878,   908 

,  quoted,    705,    706,    712,    713,   882 

,  and  Gulliver,   F.    B.,  cited,   447,  448, 

463,  840 
,  and  others,  cited,  908 

Islands,  389 

Gironde  River,   223?  231 
Girvan  district,  oolites  of,  471 
Girvanella,  283,  474 
Givetien,  431 

Gjas,  866 
Glabella,  947 
Glacial  grooves,  264 

periods,   30 

Glaciation,  Cambric,  81 

,  Lower  Huronian,   81 

,  Permo-Carbonic,  82 

,  Pleistocenic,   80,  81 

,  pre-Cambric,   81 

Glaciers,  ablation  of,  642 

alpine,  324 

cliff,  324 

continental,   325 

piedmont,  324 

plateau,  325 

ravine,  324 

,  valley,  324 

Glauberite,    363 

Glauconite,  330,  451 

Glen  Roy,  "Parallel  Roads"  of,   125 

Glinka,   K.,  cited,   687 

Globigerina  ooze,    450-453,   675 

,  analysis  of,   677 

,  salt  content  of,   367 

Glossopteris,  481,  967 
Glyptogenesis,   16,  829,   1147 
Glyptoliths,    572 
Gneiss,  279,  771 

,  restriction  of  term,  770 

Gneissoid  structure,  defined,  795 

Goat   Island,    fossiliferous  gravels  of,   89 

Gobi  desert,  strength  of  wind  in,  56 

Goebel,  quoted,  357 

Goethe,   cited,   874 

Goldspie,  650 

Golfe  di  Taranto,    113,  608 

Golfe  du  Lion,   113 

Gollachy    Mill,    Old    Red    conglomerate    of, 

716 
Gondwana   formation,   reptiles  of,   953 

land,   82 

Goniatites,   978 

Goodchild,  J.   G.,  cited,   253,  266 
Goodenough  Lake,   composition  of,   157,    158 

,    salinity   of,    154 

Goppert,  cited,   1081 


Gorjanovic-Kramberger,  K.,  cited,  92 

Gorteen  Bay,   576 

Gossendorf,   246 

Gotan,    S.,   cited,   79,   94 

Gotland,  420,   421,   838 

,  reefs  of,   418,   427 

,  Siluric  oolites  of,  472 

Gotthard  road,  368 

Gotzinger,  G.,  cited,   543,   579 

(Jour,  53 

Gower,  limestones  of,  459 

Grabau,  A.  W.,  cited,  124,  126,  127,  143, 
243,  257,  266,  271,  283,  288,  299,  355, 
366,  377,  380,  381,  418,  419,  424,  425, 
427,  446,  463,  547,  579,  599,  600,  635, 
636,  637,  638,  684,  687,  719,  721,  723, 
732,  739,  744,  749,  758,  774,  821,  827, 
837,  858,  916,  960,  964,  970,  977,  979, 
980,  981,  989,  990,  992,  994,  999,  1043, 
1052,  1066,  1070,  1095,  1097,  1113, 
1119,  1136,  1139,  1145,  1146,  1148 

,  quoted,     273,     282,     792,     793,     1074, 

1075,    1076 
— ,  and   Reed,   M.,   cited,   980 

,  and  Sherzer,    W.    H.,    cited,     52,    94, 

537,    538,    1127,    1148 

,  and  Shimer,   H.  W.,  cited,  956,    1095, 

n  19 

; ,   quoted,    1074,    1076 

Graff,  cited,   1024 

Grafton,   420 

Graham's  Island,   864 

Grampians,  Carex  peat  of,  505 

Gran  Canada,    244,  336 

• ,  oolite    grains   of,    753 

Grand  Banks,  234 

Grand  Canyon,  lava  flows  of,  313 

Grand  Cayman   Island,    108 

Grand  Puy  of  Sarconi,  lava  cone  of,  870 

Granite,   disintegration  of,  32 

Granite,   graphic,    194 

Granulites,   consolidation  of,    751 

Graphite,    510,    511 

Graptolites,  243 

,    wide   distribution   of,    1134 

Gravenzande,    destruction   of   dunes  at,    224 

Graz,  246 

Great  Bahama  Banks,    104 

Great  Banks,  red  algae  on,  470 

Great  Barrier  Reef,  387,  389,  390,  391,  402, 
403,  411,  413,  417 

,  pterppod   ooze   near,   456 

,   Orbitolites  on,   1007 

Great    Basin,    diatomaceous    earth   of,    461 

• ,  rainfall  in,   69 

Great  Fisher  Bank,    191 

Great  Geyser,   siliceous  waters  of,    168 

Great  Lakes,  American,  wave  erosion  on, 
606 

Great   Oolite,    worn   grains  of,    577 

Great  Pamir  Mountains,  sands  brought 
from,  561 

Great  Plains,   260 

Great  Salt  Lake,   70,  338,  360 

,  absence    of    calcium    carbon- 
ate  in,   476 

,  calcium    carbonate   in   tribu- 
taries   of,    468 

,  change    in    salinity   of,    155, 

156    . 

,  composition    of,    159 

,  dune-forming  oolites  of,   550 

,  elevation  of,    115 

,  excrements    of    Artemia    in, 

1093 

,  oolite  dunes  of,  472,   574 

— ,   oolites   of,    467,    468,    473 

,  salinity  of,    154,    159 


1164 


INDEX 


Great  Salt   Lake,   soda  deposits  of,   361 

Great  Syrt,  dunes  on,  559 

Grebenau,    cited,    251 

Greece,  257 

Greenalite,  671 

Greenfield,   Triassic   extrusives  of,    317 

Greenland,    236 

,  Eocenic  climate  of,  29 

,  glaciers  of,   263 

,  ice  cap  of,  325 

,  snow-line  in,  322 

Greenland-Iceland  region,  migration  of  pole 

from,  895 

Sea,  temperatures  in,   192 

Greenly,  cited,  884 

Green  River  Beds,    fossil  mosses  from,   938 

Gregory,  J.   W.,  cited,   22,   81,  94 

Grenada,   1021 

Greylock,  Mount,  799,  80 1 

Griquatown  series,   tillite  of,  535 

Ground   water,   4,    139 

,  depth  of,  4,   5,    142 

Grund,    alteration   of   limestones  of,    767 
Grundy  county.  111.,  concretions  in  carbonic 

shales  of,   764 

Guadalquiver  River,  dunes  on  bank  of,   560 
Guam,   island  of,    2 
Guano,   370,  461 
Guayaquil,   60 

Guelb-el-Zerzour,   erosion-buttes  near,   854 
Guelph .  dolomite,   376,    377 
Guiana  shelf,    103 
Guinea  current,   187 
Gulf  of  Aden,   113 

,  temperatures  of,  190,  192 

Akabah,    113 

Cadiz,    113 

,  salinity  of,    153 

,  temperature   of,    187,    192 

California,    1 12,  356,   652 

Finland,  241,  838 

Guinea,    113,   195,  235 

£:msa,  576 
ion,    113 

Mexico,   107,  230,  233,  239,  247 

Naples,  470 

,  blue  mud  in,  668 

Obi,   in 

Oman,    113 

Panama,    113 

Riga,   dunes  of,   557 

St.  Lawrence,   113 

Sidra,  240 

Suez,    113 

Taranto,  delta  in,  608 

Tartary,   242 
Gulf  Stream,    192,   215,   233,   234,  236,   239, 

335,   390,   405,  406,   407 

,  greensand   under,   673 

,  velocity   of,    680,    1050 

Gulick,  J.  T.,  cited,    1070 

,  quoted,    1043 

Giimbel,    C.    W.    von,    cited,    73,    298,    482, 

687,   748 

Gunnison   River,    131 
Giinther,  A.  C.  L.  G.,  cited,   1056,   1070 
Gunther,   S.,  cited,   13,  22,  23 
Guppy,  H.  B.,  cited,  59,  94,  248,  411,  463 
Giirich,   G.,  cited,  956 
Gypsum,   dehydration  of,   765 
,  recrystallization  of,  756 


H 

Haeckel,  E.,  cited,  993,  996,  999,   1039 
Haecker,   V.,  cited,  463 
Hagg,   R.,  cited,  92 


gro 

Ish 


Hague,  A.    cited,   143,  201,  203,  206 
Hahn,  F.  F.,  cited,   380,  381,  459,  463,  530, 

.  538,  758,   774,  783,  784,  827,   1039 
Haidinger,   cited,    1087 
Hail,  62,  63 
Halimeda,   388,    394,   474,   476,   935 

,  chemical  analysis  of,  469,  470 

Hall,    C.    W.,    and    Sardeson,    F.    W.,    cited, 
687 

,  quoted,   672 

Hall,  J.,  cited,  900,  902,    ion,  1123,   1127 
Halle,   J.,   cited,  82,  94 
Halligan,  G.  *H.,  cited,  463 
Hallock,   W.,   cited,   73 
Halobips,    991,    992 
Halo-biotic  realm,  982 
Halo-pelagic  district,   988 
Hamburg,    cited,    194 
Hamilton   fauna,    1053 
jroup,  426 
land,    397 
-,  locofauna  of,  922 

sandstone,  636 

Hanamann,  J.,  cited,    166,   206 
Handlirsch,   A.,    cited,   949 

Hanford    Brook,    thickness    of    Etcheminian 

at,    729 

Hankow,   dust  storm  at,   59 
Hanksite,   363 
Hann,    J.,    cited,    26,    28,    47,    76,    94,    323, 

328 

,  quoted,   48,    50 

Hanover,  salt  domes  of,   758 

county,  Va.,  Greensand  marls  of,  671, 

672 

Hansen,    H.,    and    Nansen,    F.,    cited,    236, 

266 

Hansen,  H.  J.,  quoted,   181 
Harder,    P.,    cited,    92 
Harding      sandstone,      ostracoderms      from, 

1033 

Hard  war,    127 
Harker,   A.,    cited,    277,   299,   306,    307,    308, 

320 

Harper,   R.  M.,  cited,  521 
Harris,    G.    D.,    cited,    380,    381 

,  G.  F.,  cited,  275,  299 

Harrisburg,  Appalachian  folds  at,  844,  903, 

904 
Harrison,   J.    B.,    and   Jukes-Browne,    cited, 

463 

,  and  Williams,  J.,  cited,  206 

Harrison  beds,   loess-like  origin  of,   568 

Hartland  Point,  222 

Hartsalz,   371 

Hartt,  C.  F.,  cited,  463 

,  quoted,  396 

Harz,    375 

,  Zechstein  reefs  of,  433 

Hatcher,  J.  B.,  cited,  538 

Haug,   E.,    cited,   23,   79,    94,    101,    no,   270, 

299,   643,   687,   873,   901,   902,    907,   908, 

987,   1057,    1146,    1148 
Hawaiian  Islands,  lava  of,  314 

,  marine  erosion  of,  875 

,  origin  of,    679 

,  pteropod   ooze   around,    456 

,  rainfall   of,  67 

,  submarine  cones  of,  872 

Hay,  O.  P.,  cited,  90,  92,  95 

,  R.,  cited,   908 

Hayden,  F.  V.,   cited,  36,  202,  342,   824 

Hayek,  A.  von,  cited,  92 

Hayes,    C.    W.,    cited,    95,    176,    206,    1113, 

1119 

,  and  Ulrich,  E.  O.,  cited,   1113,   1119 

Hayford,  J.  F.,  cited,   10,  11,  23 
Hazen,   A.,   cited,   258,    266,   687 


INDEX 


1165 


Heautotype,   919 

Heawandoo  Pholo,   399 

Hebrides,    234 

Hecker,  O.,  cited,   58,  95 

Hedin,   S.,  cited,  53,  92,  95 

Hedstrom,  H.,  cited,  420,  463 

Heidelberg   Schloss,   erosion   of,    58 

Heiderich,   quoted,   6 

Heilprin,  A.,  cited,   870,  878,    1037,    1070 

Heim,    Albert,    cited,     176,     546,     579,     657, 

687,  798,  800 
,  Arnold,  cited,  657,  660,  661,  687,  780, 

821,    827 

,  F.,  cited,  687 

Helderberg   escarpment,    837,    838 

mountains,   261,    709 

Heleoplankton,   998 

Helgoland,   Island  of,  225 

Helium,   25 

Hellbrun,  Nagelfluh  of,  602 

Hell  Gate,  narrows  at,   229 

Hellmann,    J.    G.    G.,    and    Meinardus,    W., 

cited,  95 

Helman,  C.  H.,  cited,  556,  579 
Helmert,   F.   R.,   cited,    15,  23 
Helmsdale,  651 
Heluan,   594 
Hematite,   35 

Henning,   K.    L.,   cited,   633,    638 
Henry   Mountains,   308 
Hensen,   V.,   cited,   992,   999,    1039 
Herculaneum,    human    bodies    preserved    at, 

525 

,  molds  of  bodies  buried  at,    1089 

Herero     Land,     destruction    of    surface    by 

herds  in,   691 

Hermansville,  peat  deposit  near,   502 
Hernpsand,    no 
Heroppolite  Gulf,  352 
Herrick,   C.  L.,  cited,   578,   579 
Heterepistasis,    964 

,  illustration  of,    1136 

Heterocerci,  951 

Heteroconteae,    934 

Hexaseptata,   943 

Hibbert-Ware,    S.,    cited,    72,    95 

Hieber,   V.,   cited,   443,  463 

Hilgard,    E.    W.,    cited,    140,    369,    381,    611, 

638,    70S 
Hill,    R.    T.,    cited,    58,    95,    575,    579,    870, 

878,    1108 

,  and  Vaughan,  T.  W.,  "cited,   587,   638 

Hill,    W.,    and   Jukes-Browne,    A.    J.,    cited, 

463 

Hilo,  lava  flow  near,  868 
Himalayas,   a  geosyncline,   902 

,   Eocenic  marble  of,  773 

,  Meekoceras  beds  of,    1137 

,  rainfall  in,  69 

,  rock  fall  in,  546 

Hinde  and  Fox,  cited,  459 
Hinds,  R.  B.,  cited,  917 
Hindu  Rush  Mountains,  sands  brought 

from,   561 

Hippopus,  in  Arabian   eolian  limestone,    575 
Hitchcock,   C.   H.,  cited,   314,   317,   320,   878 
Hjort,  J.,  cited,  205,  206 
Hobbs,    W.    H.,    cited,    328,    547,    590,    629, 

630,  638,   816,   827,  861,  886,  878,    881, 

908 

,  quoted,  862,  866,  885 

Hoburgen,  reefs  of,  421 

Hochenburger,   cited,   246,    256 

Hochstetter,  F.  V.,  cited,  336,  381 

Hoernes,  R.,  cited,  595,  638,  882,  1064,  1070 

Hog-backs,  840,  841 

Hogoleu,   402 

Holland,   subsidence  of   coast  of,    224     .  .    . 


Hollick,   A.,  cited,    1070 

Holmboe,  J.,  cited,  86,  92 

Holmia,  index  fossil  of  Lower  Cambric,  912 

fauna,    1052 

Holocenic,  910 
Holocephali,  951 
Holoplankton,  992 
Holoplastotype,   919 
Holothuroidea,  950 
Holotype,   919 
Holyoke,  trap  of,   313 

Holy   Well,  composition  of  water  of,    168 
Holzmaden,  jet  from,  483 

,  Lias  of,    1078 

,  petrifaction   of  Pentacrinites  at,    1087 

Homceomorph,    976,    978,    1061 

Homoeotype,    919 

Homozooidal  belts,  78 

Horgen,     subaqueous    gliding    at,    657,    780, 

784 

Hornblendite,    278 

Horsepen,    brachiopod    fauna   of,    742 
Hoskins,    L.    M.,    cited,   906,   908 
Hot  Lake,   composition  of  water  of,    168 
Hot  Spring,  borate  waters  of,   168 
Housatonic   River,    131 
Houtin,    sea   advance  at,    558 
Hove,    force  of   waves  at,  222 
Hovey,    E.    O.,    cited,    86 1,    870,    878,    883, 

908 

,   quoted,   862,   876 

How,   j.   A.,    cited,    827 

Howchin,  W.,  cited,  81,   535,  538 

Howe,    M.    A.,    cited,    385,    463,    471,    521, 

545,    579 

Huang-hai   (Yellow)   Sea,   m 
Huang-ho,  248 
,  alluvial  fan  of,   584 

delta,    extent   of,    252 

,  overlap    in,    741 

,  rate  of  growth  of,   609 

,  slope  of,   904 

flood  plain,    589 

Hubbard,    L.   L.,   cited,   381 
Hudson   Bay,    109,   241 

• ,  mean    temperature    of,    193 

,  temperatures    in,    191 

furrow,   104 

Highland,   northwest  thrusting  of,  903 

River,  depth  of  channel  of,   662 

• •  beds,   261 

,  drowning  of,   136 

• group,   folding  of,  851 

•  series,  metamorphism  of,   772 

,  tides  in,  227 

Hughes,  T.   McK.,  cited,    1085,    1095 

Hugh    River,    tidal   bore   of,   227 

Hull,   cited,    1149 

Humber   River,   224,   225 

Humboldt,  A.  von,  cited,  72,  322,   1108 

Lake,  composition  of,   i$7>  *58 

• ,    salinity   of,    155 

Hume,  W.  F.,  cited,  92 

Humic   acid,    173,    174 

Humidity,  absolute  and  relative,  26 

Humphreys,    A.    G.,    and    Abbott,     H.     L., 

cited,   247,   267 
Humulith,  281 
Humus,  281 
Hungary,  alkaline  lakes  of,  361 

,  dune  area  of,  562 

Hunt,   A.    R.,   cited,    713,    721 

Hunt,  T.  S.,  cited,  206,  347,  369,  381,  672, 

687 

,  quoted,    174 

Huntington,    E.,   cited,  82,   83,   84,   95,   381, 

555,   579,  623,   638,   703,   722 
,  quoted,  358,  359 


ii66 


INDEX 


Hunton  limestone,  684 

Huronian,    Lower,    tillite    from,    534 

Hurst  castle,   222 

Hussakof,   L.,  cited,  980 

Huxley,  T.,  cited,    1059,   1070,   1125 

Hyatt,    A.,    cited,    913,    964,    965,    966»    97°, 

971,   976,    980,    1136,    1149 
Hyde,   T.   E.,  cited,   530,   538,   777.   827 
Hydration,    17,   37,   765 
Hydrargillite,  39 
Hydroclasts,  285 
Hydrocorallines,  385,  418,  943 
Hydrogen  sulphide,   24 

,  in  peat  beds,   493 

Hydrology,   20 

Hydrometamorphism,  748,  749,  766 
Hydromicas,    177 
Hydroseisma,    88 1 
Hydrosphere,    i 

,  subdivisions  of,   99 

Hydrothecae,  943 
Hydrozoa,  942 

reefs,  439 

Hyolithidae,   946 
Hyphae,   937 

Hypnetum,   486,   487,    500 
Hypocenter,  883 
Hypoplastotype,   919 
Hypsometric  niveau,   444 


Ice,  glacier,  279 

,  snow,   279 

•  caps    Cordilleran,   326 

Keewatin,    326 
Labradoran,   326 
Newfoundland,    326 
Pleistocenic,   325,    326 

floes,   198 

Iceland,  234 

,  earthquake   in,    888 

,  hot  springs  and   geysers  of,   201 

,  sinter  deposits  of7  475 

,  Tertiary  basaltic  flows  in,  867 

,  volcanic  fissures  of,   866 

Iceland-Faroe  shelf,    103 

Icoplastotype,   919 

Idaho,  Archaean   d9lomites  of,  334 

Iddings,    J.    P.,    cited,    277,    299,    303,    304, 
313,   319,   320 

Idiotype,  919 

Ihering,   H.  von,  cited,    1149 

He  Julia,   864 

Illinois  River,  plankton  in,   997 

Illye's  Lake,   salinity  of,    154 

Imatra  stones,  764 

Inclusions,  acicular,   716 

,  irregular,   716 

,  regular,    716 

Incretions,  719,  720 

Indevsk  Lake,   salinity  of,   154 

India,    earthquake   lakes   of,    889 

,  isobars  of,  45,  46 

,  regur  of,  514  „.    , 

,  winds  of,  45,  46  .     . 

Indian   Ocean,    240  .      <    ... 

atolls  of,  388 

evaporation   from,    182,    183  ..  .• 
fringing  reefs  in,   386,.  390 
manganese  concretions  in,   718 
mean  temperature   of,    193 
Permic    position    of    North    Pole 
in,   536 

,  surface  temperature  of,    182,   183 

,  temperatures  of,    185,    187 

Peninsula,   836 


Indo-Gangetic  delta   plain,    584 

flood  plain,   585 

Indus,   248 

,  delta,    607,    608 

— ,  deposits  or   lime   in,    616 

,  overlap  in,  741 

River,   alluvial   plain  of,    585 

• ,  mud  volcanoes  along,  872 

Inner   Lowland,    83 1 

Innsbruck,    fohn  days  of,  47 
Insectivora,   955 
Insects,   marine  habitat  of,  985 
Inselberge,    58,    853 

,  Kalahari,  692 

,  South  Africa,   854,   855 

,  West  Australia,   855 

Insolation,   31,   41 
Intercontinental  seas,    9 
Interactions,   719 
Interformational  sheets,  304,  305 
Interlaken  » delta  at,    127 
Interstrophe,   climatic,   82,   83 
Intervale,  flood  plain  in,  588,  596 
Intracontinental   seas,   9 
Intumescens  fauna,   1023 
Inyo  county,   Cal.,   362 

,  soda  niter  deposits  in,  364 

Ionian  Sea,  230,  240 
Iquique,  guano  of,  461 
Iran,  desert  areas  of,   562 
Ireland,   374 

,  greensands  of  northeast,  850 

,  mild  temperatures  of,   234 

,  origin  of  chalk  of,   850 

,  transgressing  Cretacic  of,   730 

Irish   Sea,    112 

-,  tidal  interference  in,  229 


"Irish   Stream,"  234 

Irondequoit    limestone,    ballstone    reefs    of, 

Iron  Gate,  gorge  of,  cut  by  Danube,   587 
Irvine,  R.,  cited,    194 

,  and    Woodhead,     G.     S.,    cited,     331, 

381,   464 

,  and  Young,  G.,  cited,  381 

Irving,  A.,  cited,  774 
,    quoted,    766 

Island    of    Gran    Canaria,    244,    336 
Island  of  Rhodes,   153 

,  Skye,  306,  308 

,  Staffa,   318 

Isle  of  Man,   229 

of  Wight,   ercsion   of   chalk   cliffs  of, 

225 

Isobars,    4 1 
Isostacy,   9 

,  Penck's   illustration   of,    9 

Isostatic  equilibrium,    10 

readjustment,  900 

Issyk  Kul,  composition  of,    157 

,  salinity   of,    155 

Isthmus  of   Suez,   Bitter  lakes  of,   352 
Italy,   221 

,  cavern  deposits  of,   346 

,  travertine  of,   343 

Ithaca,  salt  well  at,  376 

fauna,   1053 


abor,  lagoon  at,  441 

ackson,   K.  T.,  cited,  980 

acobitti,   E..  cited,   897,  898,  908 

aggar,  T.  A:,  cited,  870-,  872,  878 

ahn,  J.,   cited,   464 

aluit,   lagoon  at,  441 

amaica,    foramini feral   limestone   of,    455 


INDEX 


1167 


James,  E.,  cited,    1122 
James,   U.    P.,   cited,   917 
James   Bay,   430 
Japan,   earthquake  in,  887 

,  explosive  eruption  in,  86 1 

,  New  Mountain  formed  in,  863 

,  Pliocenic   climate   of,    89 

• ,  seismic  periods  observed  in,  891 

Sea,   108,  242 

,  mean  temperature  of,   193 

Jatulian    formation,    anthracite    in,    478 
Java,  390 

•  Sea,    242 

Jaxartes  delta,    608 

— • ,  rate  of  growth  of,   609 

River,  dunes  along,  561 

Jefferson,   M.   W.,  cited,   707 
Jeffersonville  limestone,  426 
Jeffrey,  E.  C.,   cited,  482,  521 
— — ,  quoted,  482 
Jena,    252 

,  Muschelkalk   of,    335 

Jensen,  A.    S.,   cited,  92 

,  and    Harder,    P.,    cited,    87 

Jensen  expedition,    1066 

Jentzsch,  A.,  and  Michael,   R.,  cited,   95 

Jet,  482,  483 

— ,  analysis  of,  483 
Jhelam   River,    587 
Joggins,    South,   section   at,    515 
Johnson,    D.   W.,   cited,    135,    143,   228,   267, 
706,   722,   858,   874,   878,   966,   980 

,  quoted,    707 

,  Willard  D.,  cited,  888,  909 

,  and   Hobbs,  W.  H.,  cited,   909 

Sohnston,  J.,   cited,   753,   774 
ohnston-Layis.   H.  j.,  cited,  879 
ointing,   prismatic,   in   coal,    820 
oints,    compression,    789 

,  tension,    789 

,  widening  of,    791 

Joly,   J.,   cited,   687 

Jordan,   D.   S.,   cited,    1042,   1070 

,  quoted,    1043 

Jordan    River,    Utah,    calcium   carbonate   in, 

468 

orullo,   cinder  cone  formed  in,   863 
osephine  bank,  335 
udith  Mountains,  306 
uglans,   630 

ukes-Browne,  A.  J.,   cited,    104,   387,   464 
ulien,  A.   A.,   cited,   73,   95,    166,    173,    174, 

206 
Jumna    River,    vertebrate    remains   in    clays 

of,  586 
Junagarh  limestone,   455,    574 

,  eolian  cross-bedding  in,   704 

Tuniata  shales,    636 

Jupiter  Serapis,  temple  of,  3,  887 

Jura,  formation,    367 

,  origin  of  oolites  of,   455 

,  White,   of   Swabia,   442 

•  Mountains,     anticlines     and     synclines 

of,  847 

Jurassic  limestone,  Alpine,  breaks  in,  682 
Jutland,  dunes  of,  557 
,  structure  of  dunes  of,  703 


Kainite,  371,  372 

Kalahari,  Inselberge  of,  692 

desert,    123,   124 

,  erosion  in,  58,  70 

,  leveling  of,   854 

,  oolites  of   lakes  in,    469,    473 

,  rainfall  of,  63,  64 


Kalahari  desert,   salinas  of,   359 

Kalala  oasis,  359 

Kalkowsky,  E.,  cited,  469,  472,  473,  521 

Kalmar  Sund,  838 

Kammerbuhl,  volcanic  hill,  874 

Kampar  River,   509,  510 

Kamtchatka,    186 

Kanab  formation,   dune  origin  of,   571 

Kankar,   586,   719 

Kaolin,   37,    177 

Kaolinite,  39,  292,  540,  548 

Kaolinization,  37 

Kapstadt,  452 

Karabugas  Gulf,  366 

,  composition  of,  157 

density  of,    180 

deposits  of,   354 

freezing  of,    181 

map  of,   353 

salinity  of,    154,   351 

sulphate  of  soda  deposits  in,  360 


Kara  Kum,  dunes  of,   551,   561,   565 
Kara  Sea,    in,   241 

Straits,   236 

Karibib,  692 

Karisimbi  Mountain,   125 

,  height  of  crater  rim  of,  866 

Karnic  Alps,   Devonic  reefs  of,   431 
Karnic  limestone,  ammonoid  from,   975 

,  Trachyceras   from,    1136 

Karoo    formation,    Ceratodus   in,    1034 

• ,  glacial   deposits    in,    535 

Karpinsky,  A.,  cited,  82,   1149 
Karst   landscape,    133 

region,    125,  791,  882 

Kashmir,  Vale  of,   587 
Katamorphism,  zone  of,  747 

, ,  depth  of,    747 

Kathiawar    peninsula,    foraminiferal    (Juna- 
garh)  limestone  of,  455,  574 

Kattegat,  241,    1045 

Katwee  Lake,   359 

Katwijk,  224 

Kauar,  oasis  of,  26 

Kayser,   E.,  cited,  247,  267,  434,  442 

,  and  Holzapfel,   E.,  cited,  423,  464 

Kazan   district,    dunes  in,    561 
Keeling   atoll,    397,    398,    399,   416 
Keewatin,   311 

,  Devonic  reefs  of,  430 

Keilhack,  K.,  cited,  252,  267,  287,  299,  805, 

828 

Kelheim,  440 
,  Solnhofen  reefs,  438 

limestone.  438 

Kelley's  Island,  glacial  grooves  of,  264 
Kelvin,   see  Thompson 

Kemp,  J.   F.,  cited,   23,    138,   142,   144,   206, 
277,    279,    299,   874 

,  quoted,  4 

,  and  Knight,  W.   C.,  cited,   879 

Kengott,  cited,  368 

Kenny,    Captain,   cited,    224 

Kent,  pipes  of  sand  in  chalk  at,  698 

Kentucky,   fossil  reefs  of,   420 

Keokuk  anticline,  810 

Kerguelen  Islands,  40 

Kermadec  deep,  3,  896 

,  temperatures  in,    187 

•  Islands,  pteropod  ooze  around,  456 

Kerr,  W.   C.,   cited,   34,   95 
Kertch,   peninsula  of,   443 

,  and  Taman,  mud  volcanoes  in,  872 

Kettle  Point,  concretions  of,   719,   764 

River,   305 

Keuper,  Ceratodus  in,   1034 

marls,  loess-like  origin  of,   568 

— — ,  organic    remains    of,    635 


n68 


INDEX 


Keuper    sandstone,  origin  of,   634 

,  transgression  on  Muschelkalk,   565 

Kew,  28 

Keweenawan,  lava  sheets  of,  868 

sandstone,  cementation  of,   754 

Keyes,  C.  R.,  cited,  58,  95,   579,  858 
"Keys,"  404,  406,  407 
Key  West,   404 

,  diagenism  of  limestone  of,   761 

Khanat  Desert,  sand  ripples  in,  556 

Khasi  Hills,  rainfall  in,  68 

Kielce,  petrifaction  of  crinoids  at,   1087 

Kieserite,   368,   372,    757 

Kiev,  rainfall  at,  65 

Ki  Island,  519 

Kilauea,   138 

,  elevation  of  rim  of,  869 

,  frozen  lava  surface  of,  866,  869 

Kilnsea,  church  at,   225 

Kinderhook  fauna,  732,   1124 

Kindle,  E.  M.,  cited,  641,   687 

King,  C.,  cited.   15,  23,  626,  638 

King,  F.  H.,  cited,   258,  267 

King,  L.  V.,  cited,  747,  774 

King    Charles    Land,    Jurassic    temperature 

of,   79 

— ,  post-glacial  fauna  of,  88 

King  Edward    Island,    volcanoes   of,    877 
King  River,  alluvial   fan  of,    126 
Kingsley,  J.   S.,  cited,    1029 
Kingston,    repetition    by    faulting   near,    817 
'Kiota,   seismic  periods  observed  at,   891 
Kirchoff,   A.,  cited,   1070 
Kirk,  E.,  cited,  449,  464,   1031,    1039 
Kizil  Kum,  dunes  of,  551,  561 
Klintar  of  Gotland,  420,  430 
Knight,  C.  W.,  cited,  534,  538 
Knop,  A.,  cited,  381 
Knorria,    518 

Knowlton,  F.  H.,  cited,  92,   1149 
Knudsen,  cited,   179,    180 
Kochbrunnen,  composition  of  the,    168 
Koken,    E.,   cited,    513,    536,    538,    757,    758, 

759,   774,   784,   785,   827,   897,  909,  956, 

1058,   1070,  1149 

Koko-Nor  Lake,  salinity  of,   159 
Kola,  peninsula  of,  86 
Konjepruss,   423 

limestones,  431 

Koppen,  cited,  45,  46 

Korea,  242 

Kormos,  T.,  cited,  '92 

Kossmat,    F.,   cited,    1149 

Kostritz,  433 

Kota-Maleri  beds,   Ceratodus  in,    1034 

Koto,  B.,  cited,  909 

Kotzebue   Sound,   508 

Krakatoa,  28 

,  ashes  from,  60 

,  dust  from,  59,  550,  572 

,  explosive  eruption  of,  875,  881 

,  secondary   thalassoseisma  from,   890 

Kraus,  E.  H.,  cited,   537,  538 
Kreichgauer,   D.,  cited,   893,   909 
Kriimmel,  O.,  cited,  2,  3,  6,  8,  23,  99,   105, 

106,   107,    144,   145,   147,    149,   150,    151, 

153,    165,    170,   179,   180,    183,    184,    193, 

206,   231,  232,   234,  236,  239,   245,  267, 

453,  458,  464,  644,  657,  687 
,  quoted,    103,    171,    181,    182,    194,   212, 

213,   214,   216 
Krypton,   25 
Ktypeit,  336 

,  oolites  changed  to,  469 

,  recrystallization   of,    755 

Kufra,  oasis  of,  26 

Kiimmel,  H.  B.,  cited,  634,  740,  744 

Kupferschiefer,  372,  375,  434 


Kupferschiefer,   fishes  of,  951 

,  origin  of,  479 

Kurische  Haff,    126,    1063 

,  strand  dunes  of,  557 

Nehrung,   migrating  dunes  on,   559 

Kurland,  dunes  on  coast  of,  557 
Kuroshiwo,  see  currents 
Kymoclastic,  295 


Laacher  Sea,  122,  860 

,  salinity  of,    155 

Labadie-Cockburn  bank,    104 
Labrador,  234 

,  Archaeocyathidae   of,    417 

,  lakes  of,    199 

Labyrinthodonts,    633 

Laccadive  Islands,  389,  390 

Laccoliths,   306,  308 

Lac  de   Brenets,    125 

Lacertilia,  953 

Lachmann,   cited,   758 

Ladakh,  364 

Ladinian,  435 

Ladrone   (Marian)    Islands,  2 

Lady   Elliott    Island,    387 

La  Fayette   formation,    eolian   cross-bedding 

in,   705 

Lagarfljot,   1063 
Laggo    Maggiore,    116,    124 
Lagonite,  364 
Lahore,   26 
Lake  Agassiz,    126 

Agnano,    120 

Akiz,    1 063 

Altai    Beisk,   soda   deposits  of,    361 

Averno,    120 

Baikal,    118 

,  composition   of,    161 

,  depth  of,   116 

. ,  drainage  of,    116 

,  elevation  of,   116 

,  salinity   of,    155 

Balaton,   122 

Biljo,  composition  of,    157,   158 

,  salinity  of,   155 

Bonneville   70,    121 

,  alluvial  fans  in,  83 

,  calcareous  deposits  of,   338 

,  ^former  extent  of,   119 

Bouve,    126 

,  sand  plains  in,   600 

Brienz,    127,  610 

Champlain,  composition  of,  161 

,  fulgurites   of,    73 

— — ,  salinity  of,    155 

Charles,   126 

Chichen-Kanab,   composition  of,    157 

,  gypsum  in,  359 

,  salinity    of,    155 

Como,  depth  of,   116 

Constance,  622 

,  composition  of  silt  in,  616 

,  optics  of,  205 

,  rock  slide  at,   546 

,  shells  in,   631 

Domoshakovo,  composition  of,   157 

,  salinity  of,    154 

,  soda   deposits  of,    361 

Drummond,    120 

,  peat    of,    500 

Erie,   245,   264 

,  composition  of,  161 

,  nature    of   pebbles   on    shores   of, 

595 


INDEX 


1169 


Lake  Erie,   salinity  of,    15 


ic,   salinity  ot,    155 

,  shale   pebbles  of,   650 


Eulalie,   drainage  of,  889' 
Florissant,    125 
Geneva,    196,    197,    198 

,  aphotic  region  of,  983 

,  Characeae  in,  204 

,  subaquatic  glidings  in,   659 

Hachinchama,    363 

Huron,    composition  of,    161 

,  cross-section  of,   838 

,  elevation    of,    116 

,  salinity   of,    155 

Illye's,    122,    154 
Iroquois,   glacial  lake,    753 
Kisil-Kull,   soda  deposits  of,    361 
Kivu,    124,    125 

,   rift-valley    of,    866 

Koko-Nor,  composition  of,  157,  158,  159 

,  salinity  of,    155 

Ladoga,   85 

Lahontan,  calcareous  deposits  of,  338 

,  successors   of,    121 

,  tufa  deposits  of,  340,  341,  347 

Lucerne,    124 

Lucrinus,  863 

Lugern,  delta  in,  610,  613 

Maggiore,  depth  of,    116 

Michigan,   composition  of,    161 

,  dunes  on,  559 

,  elevation  of,   116 

,  glacial  sands  of,   553 

,  limestone  pebbles  of,  650 

,  nature    of    pebbles   on    shores    of, 

595 

,  salinity  of,   155 

,  shore  dunes  of,   557 

,  storm   terraces  on,    606 

,  tides  of,   231 

Nashua,   126 
Nemi,   120 
Nicaragua,    1 18 
Nyassa,    118 

,  drainage  of,    116 

Onega,   478 

Ontario,   118,   124,  218 

,  crystallines  of,   834 

,  elevation  of,    116 

Pangkong,    126 
Passaic,   126 
Pontchartrain,    121,   1063 

,  cypress  swamps  in,  500 

Rukwa,   figured,    119 

St.   Laurent,    127 

Schunett,   soda  deposits  of,   361 

Seyistan,    deposits  in,   84 

Shaler,    126 

Superior,    118 

,  aphotic  region  of,   983 

,  composition  of,    16 1 

,  depth  of,    116 

,  salinity  of,   155 

region,    Keweenawan    lava    sheets 

in,  868 

sandstone,    648 

,  basal  arkose  of,  548 

Tahoe,  depth  of,   116 
Tanganyika,    118,   119,    125 

,  elevation  of,    116,   867 

,  medusa  of,    1009 

,  relict  fauna  of,  «io64 

Thaxter,  23 
Thun,   127 
Tinetz,   351 

,  salinity   of,    154 

Venern,  1064 
Vettern,  1064 
Winnipeg,  837 


Lake    Winnipegasie,    199 

Zurich,  optics  of,  205 
Laki,  volcano  of,  866 
Laminaria,  470,  936,  995,   1001 

-  ,  organisms  growing  on,  995 
Lamination,   planes  of,   699 
Lamplugh,  G.  W.,  cited,  92 
Lamprecht,   cited,   758 
Lampreys,   951,    1034 

Land,   area  of,   6 

-  ,  elevation   of  surface   of,   6 

-  breezes,  45 

Lander,  red  beds  from,  633 
Landes,  223 

-  ,  dunes   of,    558 

Land  lobe,  Alleghany,  807,  809 
--    Cape   Breton,   808,   809 
--    Maine,    808,    809 
--    Mississippi,    807,    809 
--    New    York,    807,    809 
--    Rome,    807,   809 
Landscha,  246 
Lane,  A.  C.,  cited,   138,   139,   144,   167,  326, 

376,   381,   635,    1017,    1020,    1024 
Lang,  A.,   cited,    1039 
Langenbeck,   R.,  cited,  464 
Languedoc,  dunes  in,  560 
Lapilli,  860,  862 
Lapland,   snow-line   in,    322 
La   Plata,    mountains,    308 

-  ,  River  and  Estuary,  248,  66  1,  662 

La  Platte  sandstone,  eolian  cross-bedding  in, 

704 

Lapparent,    A.    de,   see   De    Lapparent 
Lapworth,   C.,   cited,    ion,    1108 

-  ,  and  Watts,  cited,  307,  308,  321 
Laramie    formation,    non-marine,    1101 
La  Soufriere,  dust  from,  60 

Las  Palmas,  336 

Laterite,    39,   292,    540,   548 

Laterization,  39 

Laufer,   E.,   cited,   287,   288 

-  ,   and  Wahnschaffe,  F.,  cited,   299 
Laurentian,   311 

Lava,  pillowy   (pahoehoe),  313,   314,  868 

-  ,  ropy    3/3 

-  ,  rough   (aa),   313,  316 
Le  Chenaillet  Ridge,   316 

Le  Conte,  J.,  cited,  247,  267,  386,  387,  388, 
405,  407,  464,  617,  639,  909,   1119 

-  ,  quoted,  890 
Lecoq  cited,    179 
Lectotype,  919 
Leda,  88 

clays,    1074 


Lehmann,  T.  G.,  cited,  1098,  1119 

Leitersdorf,  246 

Leith,  C.  R.,  cited,  671,  687,  793,  827,  906, 

909 

Lena  delta,  607,  608 
Lendenfeld,  R.  v.,  cited,  ,92 
Lepidodendraceae,  geologic  range  of,  941 
Lepidodendrales,   940 
Lepidodendron,  512,  940,    1004,   1082 
Lepidophytes,    512 
Lesley,   J.   P.,   cited,   903 
Lesquereux,   cited,   708 
Leucite  Hills,  volcanic  necks  of,  874 
Leverett,   F.,  cited,   579 
Lewiston,   Pleistocenic  delta  near,   60  1,   616, 

Lewistown  limestone,  418,  422,  423 

Leythakalk,   474 

Lias  of  Ireland,    730 

Liburnau,  J.  L.  von,  cited,   595,  639 

Libyan    desert,    chalk   from,    454 

--  ,  erosion   needles  in,   856 

--  ,  fossils  in,  642 


1170 


INDEX 


Libyan   desert,    fulgurites  in,   73 

rounding  of  grains  in,   553 

sorting  of  sands  in,  552 

source  of  sands  of,  62 

,  transgressing  dunes   of,    565 

wind  erosion  in,   52 

• windkanter  of,    54 

dunes,  origin  of  sands  of,  551 

Lichens,  937,    1003 

calcicolous,   1003 

calciferous,   1003 

corticolous,   1003 

destruction  of  rocks  by,  695 

epiphyllous,    1003 

muscicolous,    1003 

wind  blown,   56 
Liebenstein,   434 
Life  districts,   983 
Light,  28 
Lightning,   72 
Lignite,    510 
Ligurian  Sea,  240 
Lil,   lagoon  of,   441 
Lille,  France,  24 
Lima,  438,    1016 
Limnaaa,   630,  665,   1018,   1047,   1067 

,  in   Baltic,    1018 

Limno-aphotic   region,    983 

Limnobios,  991,  992 

Limno-biotic  realm,   982 

Limnogenic  deposits,   329 

Limnography,  21 

Limno-littoral   district,    fauna  of,   988 

,  flora  of,   988 

Limnology,  20 

Limonite,  35,  177 

Limulava,    948,    1030 

Linck,    G.,    cited,    332,    337,    381,    464,    469, 

Lincoln,  F.  C.,  cited,   144,  203,  207 

Lincoln,  New  Zealand,  rain  at,   166 

Lindberg,  H.,  cited,  92 

Linnaean  species,  960,   962 

Linth,    foehn   of,   47 

Linton,  organic  remains  in  cannel  coal  of, 

481 

Lipari  group,  317,  863 
Liptobiolith,   281 

Lisbon,    tidal   wave  of,   889,    890 
Lithification,   748,   750 
Lithodomus,   1016 
Lithogenesis,    16,    1147 
Lithographic  beds,  fish  from,  951 
Lithology,  20 
Lithophysae,   277 
Lithoseisma,   88 1 
Lithosphere,    i 
Lithothamnion,  394,  406,  415,  470,  471,  474, 

476,   649,   936 
Little  Ararat,    fulgurites  of,    72 

Prairie,  earthquake  lake  near,  888 

Rocky    Mountains,     igneous    intrusion 

in,  308 

— —  Soda  Lake,  analysis  of,  361 
Littoral  belt,    100 

• belts,   explosive  eruptions  on,   863 

•  district,   646,   647,   983,   987,   988 

districts,   estuarine  facies  of,   987 

zone,    646,    647 

Littorina,  on   mangrove  trees,  Brazil,  986 

Livingston,   David,  cited;   32 

Livonia,    378 

— —  salt  shaft,  376 

Lizard,  greenstone  of  the,  316 

Lizards,   Fimer's  observations  on,   963 

Llanos,   68 

Lobes,  defined,  966 

Lob  (Lake)   Nor,  waste-filled  basin  of,   588 


Loch  Fyne,   concretions  in,   679 
Loch  Lomond,    1063 
Lockport,  New  York,  420  • 
,  ballstone  reefs  of,   44"6 

dolomite,    261 

series,  enterolithic  structure  in,  758 

Locobios,  922 

Locofauna,    922,    1043 
Locoflora,    922 
Loczy,  L.  de,  cited,  92 
Loess,   565 

coloring  agent  of,  622 

concretions  in,  701 

Mississippi    Valley,    origin   of,    566 

Prairie,   origin  of,   566 

vertical  tubes  in,   566 

Loesskindel,    568 

Loessmannchen,   568,    578,   719,   764 
Loesspiippchen     568,    701,    718,   764 
Lofoten   Islands,    whirlpools  of,   230 
Logan,  Sir  W.,  cited,  782,  783,  827 
Loire,  the,  251 

Lomas,    J.,   cited,    569,    579 

Long  Island,  apron  plains  of,  598 

coast  marshes  of,  493 

destruction  of  coast  of,   649 

dunes  on,   557,  559 

old  marshes  of,  491 

wave  work  on,  223 

•  Sound,   229 

,   drowned,   833 

Reef,  406 

Longwood  shales,  377,  636 

Loo  Choo  group,   fringing  reefs  of,   390 
Looking  Glass  Rock,  57 

Loomis,    F.    B.,    cited,    568,    580,    980,    1067, 
1070 

,  quoted,    1045 

Lop,   Great   Salt   Plain   of,   358 
Lossie   River,   252,   256 
Loueche,   spring  at,    175 


Lough  Neagh,   173 
Louisiana,   de 


,      eformed   salt   domes  of,    758 
Louisville,    fossil  reefs  of,   420 

limestone,  418 

Loup  River,  259 

Loven,   S.,  cited,   990,    1062 

,  quoted,  987 

Low  Archipelago,  388,   389,  390,   399,  456 

Lowville  limestone,  origin  of,  488 

Lucknow,   depth  of  alluvial  deposits  at,   582 

Ludlow,  bone  bed,   1034 

Luksch,    J.,    cited,    189 

Lull,  R.   S.,  cited,  980,   1090,   1095,   1149 

Lumfjord,  the,   224 

Lutaceous  texture,  285 

Lu-Tschu  Islands,    108 

Lutytes  defined,   285 

Luzon,   dredgings  off  coast  of,   519 

Lycia,  jet  of,  483 

Lycopods,   940 

Lydekker,    R.,   cited,    1055,    1062,    1070 

Lyell,    Sir    C.,    cited,    3,    23,    343,    381,    475. 

521,    611,    615,    824,    857,     1099,     iioo. 

1108,    1119 

,    quoted,    1074 

Lykens,    Lower,    Naiadites   and    "Spirorbis" 

in,  742 
Lyme  Regis,   black  shale  of,  483 


M 

Maare,    122,  860 
Macclesfield  bank,  391 
Mackenzie  delta,  607,  608 
,  driftwood  in,  614 


INDEX 


1171 


Mackie,  W.,  cited,  252,  253,  254,  255,  256, 
267,  293,  294,  299,  716,  722 

.quoted,  254,  255,  256 

Mackinac,    breccias  of,    547,    548 

Maclear,  Captain,  cited,  399,  400 

Macrophytes,   983 

Madagascar,    195,   386,  390,  413 

Madeira,  235 

Madras,   fish   falls  at,    56 

Maelstrom,    230 

Magdeburg-Halberstadt    region,    371 

Magnesian  limestone  of  England,    571 

,   dwarf  fauna  of,    1069 

Magnet  Cove,  composition  of  spring  near, 
1 68 

Magnetite,    oxidation   of,    35 

Magnolias,   in  brown-coal,    513 

Mahoning  sandstone,  continuity  of,    1131 

Maine  coast,  sea  urchins  on,  103;:,   1033 

Makaroff,  cited,   240 

Makatea  Island,   diagenism  in  reefs  of,   761 

Malaspina  Glacier,  324 

Malaysian  Islands,  volcanic  belt  in,  877 

Maldive  Islands,    186,   388,  389,  390,  399 

,  gradual  submergence  of,  895 

Mallet,   P.,  cited,  909 

Malm,   459 

Malta,    153,   240,   454 

Mammoth  Cave,  organisms  in,   1028 

Mangrove,  494 

,  floating  islands  of,  235 

,  partial  marine  habitat  of,   985 

Creek,  Anthozoa  in,   1013 

Manitou,   310 

— ,  pre-Cambric,  peneplain  of,  848 
Manitoulin  Islands,  836 
Manlius,  Stromatopora  reefs  of,  445 

limestone,  423,  456 

Mannheim,    245 
Manouai,  402 
Manson,  M.,  cited,  95 
Maranhao,    416 
Marcellus    muds,    407,    424 

shale,  origin  of,  479,  484 

Marcou,   J.,   cited,   78 
Marian   depression,   2,   897 

Islands,   diatomes  near,  460 

,  (Ladrone),   2 

trench,    105 

Mariana  Islands,   386 

Marin   county,    315 

Marine  elastics,   negative  characters  of,  642 

littoral  district,   depth  of,  983 

,  life  of,   984 

— ; ,  origin  of,  983 

Marlekor,   719 

Marquesas,  406,  441 

Marquette,  basal  sandstone  at,   726 

— ,  buried  peat  at,   516 

,  Lake  Superior  sandstone  of,  310 

district,   metamorphism  in,   772     • 

Marr,  J.   E.,  cited,  432,  433,  464,    1070 

,  quoted,  432,  699 

Marsh,   O.    C.,    cited,   709,    789,    827 

Marshall  group,  388,  389,  399 

Martha's  Vineyard,  apron  plains  of,   598 

,  deformation  of  Tertiary  beds  of, 

785 

Martin,   L.,   cited,  909 

Martinique,   Island  of,  erosion  on,  875,  876 
Martonne,   E.  de,  cited,  52,  96 
Marzelle,  cited,   149 
Masmarhu,  399,  400,  401 
Massachusetts,    392 

,  peat  deposits  of  coast  of,  514 

,  sea-breeze  of,  44 

Mastodon,  956 

Mather,    W.    W.,    cited,    1123 


Matilda  atoll,  399 

Matthew,  G.  F.,  cited,  92,   1086 

,  W.   D.,  cited,  568,  580 

Matto  Grosso,  ants'  nests  in,  692 
Mauch  Chunk,   635,  636 

shales,   carnotite  in,   365 

Mauna  Loa,  314 

— — ,  elevation  of  rim  of,  869 

Mauritius,  386,  390,  399,  402 

Maurua,  402 

Maury,  M.  F.,  cited,  96 

,  quoted,  44 

Mauth-Eichdorf,    246 

Mazon   Creek,    concretions  of,    764 

McClure,     W.,    cited,     1122 

McConnell,   R.  G.,  cited,  92,   580 

McGee,    W.    J.,    cited,    245,    267,    580,    652, 

687,    909,    1119 
Mead,  C.  W.,  cited,   1095 

,   quoted,    1076,    1077 

Mean  sphere  level,  6,  7 

Mecklenburgian  period,   506 

Medina  sandstone,  beach  cusps  in,  707 

beach  features  of,  652 

eolian  cross-bedding  in,   704,   706 
fucoid  in,   937 
rill  marks  in,   709 
wave  marks  in,   708 
Mediterraneans,    8,    99,    107,    108,    109,    115, 

219,  240,  344,  355 

,  provincial  fauna  of,  984 

,  temperatures  of,    189 

Mediterranean  Sea,  evaporation  from,  27 

,  height    of   waves   of,    210 

,  salinity    of,    152 

,  submarine  volcanic  eruptions  of, 

864 
Medlicott,    H.    B.,    and    Blanford,    W.    T., 

cited,   639 

— ,  quoted,    592 
Medve   Lake,    122 
Meek,    F.    B.,   cited,    917 
Meigen,  W.,  cited,  39,  96 
Melville  Sound,   in 
Menilite  shales,  485 
Mentawie  Islands,  456 
Merced  River,  alluvial   fan  of,   584 
Mer-de-Glace,  glacial  sand  of  the,    532 
Meriden,    earthquake  fissures  at,   885 
Merionthshire,   315 
Merjelen  See,   125 
Meroplankton,   defined,  993 
Merostomata,   948,   950 
Merriam,  J.  C.,  cited,    1071 
Merrill,  G.   P.,  cited,  38,  96,  286,  287,  299, 

344,  38i 

,  quoted,  344,  345 

Merseburg,    1029 

Mesa,  839 

Mesabi  Range,  greenalite  in,  671 

Mesotraphent,  498 

Messina,  earthquake  at,  888 

,  Straits  of,  230 

Metamorphism,   746 

,  contactic,  748 

,  dynamic,  748 

,  regional,  749 

,  static,   748 

Metatype,  919 

Meunier,  S.,  cited,  56,  96 

Meuse  delta,  607 

River,  224 

— ,  capture  of,   134,   136 
Mexican  lagoons,  oolites  of,   336 

Sea,   temperature  of,   190 

Mexico,  341 

,   cinder  cones  of,   863 

,  onyx  marble  of,    344 


1172 


INDEX 


Mfumbiro  Mountains,   124,   125 

,  volcanic  origin  of,  866 

Michael  Sars,   the,   205 

Michalski,  cited,  443,  464 

Michigan,  Devonic  clay  boulders  of,  711 

— ,  reefs   in    Southern    Peninsula   of,    427 
,  salt   deposits  of,    376 

City,  dune  sands  from,  553 

Microphytes,    983 
Microspherulites,   277 
Mid-Atlantic  rise,    105 

Milan,  weather  at,  48 
Miliola,    in    Severn   muds,   664 
Miliolitic  formation,   574 
Mill,   H.   R.,   cited,   7,   23 
Miller,  S.  A.,  cited,  957 

,  W.  J.,  cited,   569,   580,   621,   639,   783, 

827 

Millstone  grit,   composition  of,   596 
Milne,  J.,  cited,  899,  909 
Milne-Edwards  and  Haime,  cited,  1013 
Milwaukee,    419 
Mindanao,    519 

Minnesota,   glauconite  of,   671,  672 
Mississippi   delta,    608,    611 

fine  muds  of,   850 

mud  lumps  of,  615 

passes  of,  610 

thickness  of,  609 
embayment,   984 
River,   248 

back  swamp  of,  497,   589 

load  of,  247 

mud  at  mouth  of,  655 

reversal  of  current  of,   889 

tree  trunks  carried  by,   1051 

velocity   of,    245 

system,   discharge  of  sediment  of,   247 
— ,  hydrographic    basin    of,    247 

Valley,   black  shale  in,   732 

Mississippi    black    shale,    Ordovicic    fossils 

in,  685 
Missouri,    caverns   of,    345 

,  overlap  of  marine  strata  in,   732 

— —  River,  Great  Falls  of,    137 
Mittagong,   chalybeate  waters  of,    168 
Mjodoboren    hills,    443 
Mjosen,   Biri  limestone  of,  784 
Moas,    1038 

,  petrified  eggs  of,   1088 

Moencopie  beds,  84 

,  alternation  of  colors  in,  623 

Mohave    Desert,    70,    364 

,  dunes  of,   562 

Mohn,  PL,  cited,  96 

,  quoted,   51 

Mojsisovics,    E.    von,    cited,    435,    464,    474, 

521 

Mollasse,    591 
,  subaqueous  gliding  of  the,  658 

torrential  deposits,  630 

Mollusca,  importance  of  shells  of,  911 
Molucca   Straits,   237 

Mombas,  404 

Monadnock,  847,  848,  849 

Mona  passage,    108 

Monchsberg,   Nagelfluh  of  the,   602 

Monhegan,  Island  of,  848 

Mono  Lake,  salinity  of,   155    , 

,   soda  deposits  of,    361 

Valley,  extinct  lake  of,  340 

Monongahela  River,  gravel  terraces  of,    136 
Monroe  limestone,    261,   422 

,  endolithic  brecciation  in,   537 

• ,  oolites  of,  472 

Mons,  greensands  near,  673 

Monsoons,  45,   75 

Mont  Blanc,   fulgurites  of,   72 


Mont    Dore   Province,    breached   lava   cones 

of,  871 

Mont  Genevre,   315 
Mont  Pelee,   dust  from,  60 
,  eruption   of,   86 1 

- — ,  spine   of,   870 

Montana,  Belt  terrane  of,  334,  417 
Monte  Nuovo,  cinder  cone  of,   863 
Monte  Somma,  871,  875 
Monte  Viso,   fulgurites  of,   72 
Montessus  de  Ballore,  F.  de,  cited,  909 
Montgomery    county,    O.,    peat   bed    in,    515 
Monticules,   formation  of,  871 
Montreux-Veytaux,    subaquatic    glidings    of, 

659 

Montrose    county,     Col.,    carnotite    of,    365 
Monument  Creek  beds,  cementation  of,   754 

,  dune  origin  of,   570 

,  joints  in,   792 

Park,    53 

,  erosion   features  of,  857 

Moor,   Captain,    227 

Moore,  J.    E.   S.,   cited,    119,    125,    144,   761, 
774,   879,    1064,    1071 

Moraines,   lateral,   265 

,  medial,  265 

Moray,  rivers  of  Eastern,  252 

,  sands  on  eastern  shores  of,  226 

,  Firth,   256,   650 

,  temperatures   of,    191 

Morgan,  T.   H.,  cited,  980 
— ,  W.    C,    and    Tallmon,    M.    C.,    cited, 
1088,    1096 
,  quoted,    1089 

Morlot,   cited,    uoo 

Moros  Valley,  salt  dome  in,   758 

Morphological  equivalents,  976,   1135 

Morrisville,   377 

Morse,  E.  S.,  cited,   1042,   1071 

Morse  Creek  limestone,  684 

Morvern,  Cenomanien  greensands  of,  850 

Moscow    shale,    variation    in    thickness    of, 
683 

Moselle  River,   134 
,  meanders  of,    137 

Mosely,    H.   N.,   cited,    1009,    1071 

Mosken,   230 

Mosquito  bank,  335 

Mottez,   Admiral,  cited,  215 

Mt.  Adams,    32 

Mt.  Everest,  5 

Mt.  Hillers,  308 

Mt.  Holmes,    308 

Mt.  Mar^ellina,  308 

Mt.  Mica,    composition   of   spring  near,    168 

Mt.  Monadnock,   32 

Mt.   Shasta,  fulgurites  of,  72 

Mt.  Sinai,   33 

Mt.   Starr-King,  32 

Mt.  Taylor  region,  volcanic  necks  of,  874 

Mt.  Thielson,  fulgurites  of,   72 

Mt.  Washington,    Arctic   plants   and    butter- 
flies on,   1066 

Mountain    Home,    hot   springs  of,    201 
— ,  limestone    reefs   in,    432 

Mozambique,   386 

channel,    388 

Mud  cracks,    530 

lumps,   611,   615 

Muir  glacier,  263 
Mulder,    cited,    173 

Mull,   Cenomanien  greensands  of,  850 

and    Morvern,    transgressing    Cretacic 

of,  730 

Mullion   Island,  greenstone  of,   316 
Mummies,   Chile,    1076,    1077 
Munthe,  H.,  cited,  420,  464 
Mur  River,  252 


INDEX 


Murchison,   Sir  R.,  cited,  222,   1108 

Muree  glacial   formation,   53$ 

Murgoci,    G.,   cited,   92 

Murray,  Sir  J.,  cited,  7,  23,  63,  65,  96,  165, 
194,  207,  387,  391,  408,  410,  451,  452, 
466,  678,  679,  687,  688,  1071 

,  quoted,   6,  66,    164 

and  Hjort,   J.,  cited,   205,  207 

and  Lee,   G.    V.,   cited,   688 

and  Philippi,   E.,  cited,  688 

and  Renard,    A.    F.,    cited,    451,    453, 

455,  643,   644,  668,  670,   688 

and   Renard,  M.  A.,  cited,  56,  96 

Muschelkalk,  225,  436 

,  cementation  of,  335 

,  origin  of  oolites  of,  455 

,  subaquatic   gliding   in,    782 

Sea,  376 

Muskegon,   dune   near,    559 
Mutation  of  De  Vries,  963 

,  of  Waagen,   912,   960 

Mycelium,  937 
Myxinoids,   951 


N 

Nagasaki,    59 
Nagelfluh,  601,  602,   750 
,  cementation  of,   753 

delta,    616 

Naiadites,  in  Lower  Lykens,   742 

Nairn  River,   252 

Nakkehrod,    719 

Namak,   358      . 

Nansen,   F.,   cited,    no,  267 

Nantasket,  Carbonic  lavas  of,   315 

,  drumlins  of,  532 

Nantucket  Island,  apron  plains  on,  598 

• ,  old  marshes  on,   491 

Naples,   Bay  of,  bradyseisms  in,  887 

,   Gulf  of,   3 

Napoleonite,   275 

Narni,  travertine  deposits  of,  343 
Natissa  River,  salt  water  in,  153 
Natron,  362 

Lake,   salinity  of,    155 

Natterer,  cited,   332 
Nattheim,  reefs  near,  439 
Natuna    Islands,    242 

Naumann,  C.  F.,  cited,  269,  270,  299,  537 
Nautiloidea,   945,    946 
Nautilus,    945,    946,    1022 
Nauset   Lights,   223 

•— — ;  peat  under  sand  dunes  at,  564 

Navahoe  Lake,   125 
Navigator  Islands,  386 
Neanastic  stage,  973 
Neanic   stage,    972 
Nebraska,   259 

— ,   lakes  in   sandhill   region  of,    562,    564 
Nebraska  dunes,   122,  572 

,  lignite  in,    565 

,  origin  of  sands  of, 

Nebular  hypothesis,  92 
Neckar,    velocity   of,    245 

Valley,    enterolithic   structure   in,    758, 

759,  785 

Nefud  desert,  37 

,    red   sands  of,   562 

Nekton,  991,  996 

Neocomien,   greensand  lenses  in,   673 

Neon,   25 

Neotype,    919 

Nepiastic,   973 

Nepionic  stage,  972 

Neritic  zone,  643,   987 

Nero  deep,  2,   105,  897 


551 


Netherlands,   dunes  of,  557 
Neumayr,   M.,   cited,    78,   80,    133,    144,   682, 
1057,   1149 

,  quoted,   79 

,  and  Paul,  C.  M.,  cited,  958,  959,  9«o 

Neutral  level,    u 

Nevada,  borax  lakes  of,  363 

— ; — ,  playa  lakes  in,  603 

Neve,   279 

Newark   sandstone,    arkose   character  of,    84 

• ,   footprints  in,    1090 

,  fucoid  in,  937 

,  non-marine,  noi 

,   origin  of,  633 

,  overlap   relations  in,    740 

,  red  color  of,   625 

Newark  trap  sheets,  312 
Newberry,  J.   S.,  cited,   708 
New  Caledonia,   388 
New  England,  color  of  till  of,   532 

• ,  destruction  of  coast  of,  649 

• ,  eskers  in,  599 

Newfoundland,  215,  234 

,  Archaeocyathidae   of,    417 

,  frost   work  in,   34 

,  peat  beds  of,  508 

banks,   104,  218,  234,  262 

shelf,    103 

New  Guinea,  334 
New  Haven,   1042 

New  Hebrides   Islands,   386 

New  Jersey  coast,  dunes  on,   557,   559 

,  marshes  of,  493 

New  Mexico,  Cretacic  dwarf  fauna  of,  1069 

,  dune  of  gypsum  in,  578 

New  Red  sandstone,  origin  of,  569 

New    Scotland   beds,    overthrust  of,   817 

Newson,  J.  F.,  cited,  885,  909 

New    South   Wales,    medusae   of,    1009,    1010 

New  World  block,   9 

New  York,  beveling  of  Palaeozoic  strata  in 

835 
— — ,  Lower   Cambric   limestones  of,    335 

,  thickness  of  salt  beds  of  Central,  378 

,  type   section   for   the   Palaeozoic,    1127 

,  Western,   disconformity  in   Siluric  of. 

826 

City,    age   of   schists   and   marbles    of, 

1140 

,  Aqueduct   Commission   of,   286 

New  Zealand,   239 

,  sinter   deposits  of,  475 

Niagara    Falls,    amount   of    water    per    min- 
ute,  246 
,  height  of,   246 

escarpment,    261 

gorge,   261 

River,    133 

— — • ,  changes  in  bed  of,  245,   246 

,  consolidated    plains   along,    601 

• ,  old  shore  lines  of,  654 

Niagaran,    former  extent  of  the,   379 
,  reefs  of  the,  431 

Sea,    evaporation  of,   377 

Nicaragua,  335 

,  colors  of  soil  of,  36,  620 

Nicholson,  H.  A.,  cited,  455 

and  Etheridge,    R.,    cited,    472 

,  and   Lydekker,   R.,  cited,  956,    1096 

,  quoted,    1073 

Nicobar  Islands,  109,  386,  390,  456 
Niger  delta,   608 
Nikitinsky,  quoted,  357 
Nile  delta,  252,  607,  608 

,  deposits  of  lime  in,  616 

,  iron  content  of,  622 

,  nature   of   deposits  of,    614 

,  rate  of  growth  of,  609 


1 174 


INDEX 


Nile  delta,   salines  of,   355 

• ,  saline  deposits  on,  617 

,  thickness  of,  609 

River,   248 

,  flood    plain  of,    589 

,  overflow  of,  68 

Nile  Valley,   angular  sands  along,   553 

,     caverns    in    Eocenic    limestones 

of,  346 

Niles,  W.  H.,  cited,  753,  774 
Nitrogen,  24,  25 
Nittany   Valley,    175 
Nodes,  945 

Noel  black  shale,   732 
Nontronite,  39 
Nordmann,   V.,  cited,  92 
Normandy,    dunes   of,    557 
North    Cape,    236 

Germany,    Permic    climate   of,    375 

Pole,    ascertained    migration   of,    899 

,  hypothetical  migration  of,  898 

Sea,  112,  218,  234,  236,  239 

,  height  of  waves  of,  210 

,  submarine   forests  of,    224 

,  subsidence  of  coast  of,   223 

,  temperatures  in,    191 

Siberian  shelf,   103 

Northwest  Australian   shelf,    103 

Norway,  Cambric  glacial  deposits  from,   534 

,  concretions   m   clays  of,    763 

,  dolomites  of,  334 

,  recent  corals  of,   392 

Norwegian  shelf,   103 

Novaculite,  755 

Nova    Scotia,    erosion    stacks    of,    225 

,  peat  bog  of,  515 

,  red  Mississippic   beds  of,   622 

Nova  Zembla,  236 

,  red  algae  at,  470 

Novorssiisk,  winds  from,  49 
Nubian   sandstone,    61,    565 

,  dune  origin  of,   570 

,  Libyan   sands  derived   from,   553 

Nullipore,   385,   470 

Nummulite   limestone,    453 

Nummulites,   942 

Nunatack,  326 

Nunda  sandstone,   see  Portage 

Nyssetum,  487,    500 


O 

Oatka,   377 

Oaxaca,  volcanic  ash  deposit  of,  60 

Obrutschew,   cited,   604 

Ocean,  composition  of,    158,   159 

,  mean    depth   of,    6 

Oceanography,  20,   21 

Oceanology,    20 

Oceans,  areas  of,    100 

Ochsenius,    C.,    cited,    267,    350,    353,    359, 

366,   369,   370,   381,    382 

O'Connell,    M.,    cited,    989,    990,    1029,    1039 
Octapoda,   1021 
Octoseptata,  943 

Odessa,  subaquatic   glidings  at,    659 
Oeningen,  deformations  at,  784 

,  folding  in  Miocenic  marl  of,  780,  781 

,  Miocenic  shell  deposits  of,   631 

Oesel,  Island  of,  cuesta  of,  838 

,  Synxiphosurans  from,    1029 

Ogden  quartzite,   817 

River,  calcium  carbonate  in,  468 

Ogilvie,   I.  H.,   cited,  856,   858 
Ogilvie-Gorden,  M.,   cited,  435,  464 
Ohio,  Devonic  limestones  of,  471 
,  origin  of  black  shale  of,  484 

River,   245 


Oisan  Mountains,   127 
Ojen,   P.  A.,  cited,  92 
Okefenoke  Swamp,   500 
Oken,    LV    cited,    917 
Okhotsk-Sachalin   shelf,    104 

Sea,    1 08 

Oklahoma,   262 

•n ,  basal  Cambric  sandstones  in,  729 

Oland,   Island  of,  cuesta,   838 

Old    Faithful    Geyser,    siliceous    waters    of, 

168 
Oldham,  R.  D.,  cited,  585,  639 

,    quoted,    586 

Old  Red  sandstone,  analyses  of  sand  grains 
of,  716 

,  cliffs  of,   225 

,  deltaic  origin   of,   636 

,  dune  origin  of  parts  of,  571 

,  fishes  in,   951 

— ,   Myriopoda   in,    947 

,  non-marine,   1101 

,  unconformity  below,   824 

Old  World   Block,   9 
Olean    conglomerate,   252 
Olenellus  fauna,    1052 
Olenidae,   as  index  fossils.    1134 
Olenoides    fauna,    1052 
Olenus  limestones,   53 
Oligocenic,   pyroclastics  of,    526 
Oligochaete,     1024 
Oligotraphent,   498 
Olkusz,  fulgurites  in,  73 
Omori,  F.,  cited,  879 
Onchidium,  986 
Oneonta,   see  Portage 

sandstone,  636 

Onondaga    limestone,     261,    407,    423,     424, 

425,  426 
Onto-stages,  971 
Onto  sub-stages,   971 
Oolite,   Great,   472 

•-,   Inferior,  472 

— ,   Superior,  472 
Oolites,   size  of  phytogenic,  468 
Oolitic  sands,  422 
Oozes,   formation  of,   996 
Opercula,   945 
Operculina  limestone,   52 
Oran,   province  of,  345 
Orange   Spring,   composition  of,    168 
Orbitoidal  limestone,   453 
Ordovicic,  black  shale  resting  on,   732 

,  insects  from  graptolite  shales  of,   949 

-,  origin  of  black  shales  of,  674 


,   Upper,    replacing  overlap  of,    744 

sandstone,    marine   progressive   overlap 

of,  728 

Oregon,    basaltic   plateau    of,    867 
Ore   Sound,  241 
Organ  Pipe  Reef,  404 
Orinoco  delta,  608 

River,   tree   trunks  carried  by,    1051 

Oriskany-Esopus,     contact     in     Heldeijaergs, 

823 
Orkney  Islands,   112,  218,  230,  234 

,  Tertiary  dikes  in,  867 

Orogenesis,   16,   776,   1147 

Orogenic  movements,    12 

Orpiksuit  fjord,   87 

Orth,   cited,   287,    299 

Orthoboric  acid,   364 

Orthogenesis,  963 

Ortiz  Mountains,  conoplains  of,  856 

Ortmann,    A.    E.,    cited,    80,    96,    647,    688, 

995»   999.    1022,    1027,    1039,    1059,    1061, 

1062,    1071,    1134,    "49 

,  quoted,   1042,   1055,    1061,  1065 

Orton,  252 


INDEX 


H75 


Osage  River,  boulders  in  loess  on,  567 
Osborn,    H.    F.,    cited,    920,    956,    957,    961, 
970,  980,   981,    1149 

and  Grabau,  A.  W.,  cited,  958 

Oscillation,  circle,  894 

ripples,   712,   713 

Ostrea,  in  Arabian  eolian  limestone,  575 
Ostwald,   quoted,    747 
Oswing,  Neocomien  of,  673 
Ottawa  River,   334 

,   drainage  of,    166 

Otyipatura  River,   692 
Owen,   D.   D.,  cited,  915,    1108 
Owens,  J.   S.,  cited,   688 
Owens  Lake,  362,   369 

,  change  in  salinity  of,    155 

,  composition  of,    157,   158 

,  salinity  of,   154,   155 

,  soda   deposits  of,    361 

Valley,  earthquake  fissures  in,  883 

,  earthquake  of,   887 

Oxford  lowland,  839 

Oxidation,    17,   25,    35 

,  of  organic  compounds,  37 

Oxus   River,    23 

,  delta    of,    608 

,  dunes  along,  561 

Oxygen,   24 

sources  of,   25 

Oysters,    attached    to    roots    of    mangroves, 

986 
Ozark  region,  basal  Cambric  sandstones  in, 

729 
Ozone,  72 


Pacific    Ocean,    manganese    concretions    of, 
330,  718 

,  mean  temperature  of,  193 

,  surface  temperature  of,   182,   183 

,  temperatures  of,    185,   187 

Paenaccordanz,    821,    822 
Pahoehoe,   Hawaiian  Islands,   868 
Palseechinoidea,    950 
Palaeobotany,  20,  gio 
Palseo-Cordillerans,   70 
Palaeohypsometric,  444 
Palaeozoic,  diversity  of  fauna  of,  984 

rocks,  desert  varnish  of,  57 

Palaeozoology,   20,  910 

Palawan  Island,  242 

Palgrave,  W.  G.,   cited,   562,   580 

Palic   Lake,    C9mposition  of,    157,    158 

• ,    salinity  of,    155 

Palisades  trap,  320 

Pallas,   cited,   443 

Pallas  and  Humboldt,  V.,  cited,  1063 

Paludina,   631 

,  in   loess,    568 

series,  960 

Paluxy  sandstone,  729 
Pantelleria,    153 

Paradoxides,    index    fossil    of    Middle    Cam- 
bric, 912 

,  fauna,   1052 

Parallelism,   979 

,  illustration  of,  976,   977 

Parallelkanter,    54 

Parana,  carcasses  of  animals  in,  593 

,  tributary  of  La  Plata,  66 1 

Paratype,   919 

Para-unconformity,  821 

Paris,  Lieutenant,  cited,  214 

Paris  Basin,   Eocenic  locofauna  of,    1043 

,  Eocenic  shales  of,  485 

i 1  prismatic     structure     in     gypsum 

beds  of,  779.  820 


Parks,  W.  A.,  cited,  731,  744 

Parmas,  808 

Parrot  fish,  destruction  of  corals  by,  415 

.  River,    663 

Parry  Archipelago,  237 
Parsons,  A.  L.,  cited,  485,  521 

,  quoted,  486 

Partiot,  cited,  231,  267 
Parunconformity,    821,   822 
Paruschowitz  well,    14 
Pas-de-Calais,   dune   areas  of,   557 

,  peat  of,  514 

Pass  a  1'Outre,  form  of,  610 

,  rate  of  growth  of,  609 

Passarge,   S.,   cited,    58,    196,   359,   382,   580, 

692,    695,   854,   855,   858 
Patagonia,  239 

coast  of,  235 

salinas  of,  360 

salitrales,  329,  360 

shelf,    103 

Tertiary    volcanic    dust    deposits    of, 

572 

Patapsco    formation,    632 

Paterson,  trap  of,  312 

Patten,   W.,  cited,   950,  957 

Patuxent  formation,  632 

Paumota  Archipelago,  see  Low,  456 

Peach,    B.    N.,    and    Home,    J.,    cited,    315, 

321,  867,  879 

Peat  bog,   succession  of  strata  in,   499,    506 
Pebbles,  facetted,  54 
Pechuel-Loesche,   E.,  cited,   32,  695 

,  quoted,   691 

Pedro  bank,    108 

Pei-ho,  248 

Pelagic  district,   101,  983,  988 

organisms,  quantity  of,  451 

Pelew   Islands,    388 

Pelytes,   285 

Penck,  A.,  cited,  2,  3,  5,  6,  7,  8,  9,  23,  100, 
125,  144,  165,  248,  250,  251,  257,  267, 
541,  580,  595,  602,  639,  858,  1063 

,  quoted,   162,  163,  213,  246,  248,  584 

and  Bruckner,  E.,  cited,  328,  639 

and  Supan,  A.,   cited,  23 

Pendleside  limestone,  432 
Peneplain,   defined,  847 

,   transgression   over,   731 

Penhallow,   D.  P.,  cited,  981 

Pennines,  peat  of,  504 

Penrose,  R.  A.  F.,  Jr.,  cited,  370,  382 

Pensauken   gravels,    fulgurite  in,    73 

Pentland  fjord,  230 

Permic,  position  of  North  Pole  in,  897 

Permille,   defined,    147 

Perry,   N.   W.,  cited,   701,   709,   712,   722 

Persia,  onyx  deposits  of,  345 

Persian   Gulf,    in,   242,   390 

,  temperature  of,   193,  373 

Peru,   natural  mummies  from,    1076,    1077 
Peschel,    O.,   cited,    1063,    1071 
Pestalozzi,   cited,   251,   267 
Peterhead,    force    of    waves   at,    221 
Petermann,  A.,  cited,   584,  639 
Petersen,  C.  G.  J.,  92 
Petit   Codiac   River,   tidal  bore   of,    227 
Petoskey,   reefs  of,  429 
Petrascheck,  cited,  682,  688 
Petro-Alexandrovsk,    rainfall    at,    65 
Petten,    height  of   dunes  near,    558 
Pettersson,  S.  O.,  cited,   193,  207 
Pfaff,   F.   W.,  cited,  96,   175,  759,  774 
Phacoliths,    307 
Phanerogams,   941 

,   acquired  marine  habitat  of,  985 

Philippi,  E.,  cited,  82,  92,  96,  332,  334,  335, 
382,  635,  639,  644,  675,  681,  688 


1176 


INDEX 


Philippine  Islands,  204,  237,  242 

,  diatoms    near,    460 

Philippine  Sea,    195 

Phillips,  J.,  cited,  224,  267,   1099 

,  J.  A.,  cited,  37,  96,  294,  299,   639 

Phillipsite,  330 

Phoca,   in   fresh  water,    1063 

Photic  region,  982 

Phragmitetum,   486,   487,    500 

Phyllocarida,  377,  948 

Phylogerontic  stages,  973 

Phylum,  912 

Physa,  in  Florissant  Lake  Basin,  525 

Phytogenic  deposits,  384 

Phytolitharia,    marine,    in    Mississippi    mud, 

615 

Phytoliths,   280 
Phytology,  20 
Phytosphere,    16,   910 
Piedmont  region,   226 
Pierre  shales,  447 
Pike's  Peak,   32,   33,   310 
Pilgrim,  G.  E.,   cited,  92 
Pilot,  fish,  996 
Pine   Creek   Valley   spring,    composition   of, 

168 

Pittsford  shales,  376,  377,   1029 
Planetesimal   hypothesis,    92,   297 
Planetesimals,    907 
Plankton,  denned,  991,  992 
Planoconformity,  826 
Planorbis,    1064 

in  Florissant  Lake  basin,  525 

in  loess,   568 

in  Severn  deposits,  665 

mutations  of,   1043 

shell   replaced   by   sulphur,    1086 

Plants,  chlorophyll-forming,  25 
Plasmodium,  933 

Plasticity,   zone  of,   819 
Plastotype,  919 
Plattenkalke,  438 
Playa  lake,   77,    123,   602 
Playa  surface,  709 
Pleistocenic,  beaches  of,  654 

,  location  of  pole  in,  895,  896 

Pleistocenic  ice  sheet,  344 

Plesiotype,  919 

Plitvicer  seas,    125 

Plucking,   1 8 

Plum  Island,  map  of,  491 

Plymouth,   force  of  waves  at,   221 

Po,  248 

delta,  607,  642 

,  lignitized   wood   in,    614 

,  thickness  of,  609 

River,    alluvial   plain  built  by,    584 

• ,  flood  plain  of,  589 

,  natural  levees  of,  617 

Pocahontas,   Pottsville  conglomerate  at,   742 
Pochutla,  cinder  cone  of,  863 

Pocono   conglomerate,    636 

sandstone,  635 

Podolia,  443 

Point  au  Sable,  838 

Point  Bonita,   basic  lava  of,   315 

Polar   Sea,   temperatures  of,    193 

Pole,  migration  of,   891,  892 

Pole,  shifting  of,   536 

Poles,  wanderings  of,  91,  92 

Polyhalite,  371,  372,  374 

Pomerania,  brackish  ponds  of,  126 

Pompeckj,   J.   F.,   cited,   479,    521,   667,   678, 

688 
Pompeii,  human  bodies  in  volcanic  mud  at, 

525,   1089 
Pool,   R.  J.,  cited,   563,   580 


Porta   do    Mangue,    diagenism   of   reefs   of, 

761 

Portage  beds,  faunas  of,  1053 
Portage  sandstone,   554,  635,  936 
--  ,  loess-like  origin  of,  569 

-  shales,   origin   of,   479 
--  ,  Protosalvinia  in,    718 
Portageyille,    127 

Port  Elizabeth,  sea  wave  at,  875 

Port  Hudson  clays,   611 

Port  Jefferson,  wave  cutting  at,  223 

Portugal,  recent  corals  of,  392 

Posidonia  shale,  jet  from,  483 

--  ,  organic   remains  in,   483,   484 

--  ,  origin  of,  479 

Possneck,  433 

Potamoclastic,  295 

Potamogenic  deposits,  329 

Potamology,    20 

Potamoplankton,  998 

Potomac   formation,    colors   of  beds   of,    624 

--  ,  delta  and  flood  plain  deposits  of, 

631 

--  ,  non-marine,   not 
Potonie,  H.,   cited,  280,   330,   382,  480,  482, 

510,  517,  521,  578 
Potsdam  sandstone,  642,  729,  856 
--  ,  trails  in,   1091 
Pottsville  conglomerate,   635,  742 
--  ,  extent  of,  252,   594 
--  ,  pebbles   from,.  596 
--  ,  thickness  of,  904 

-  series,    westward   overlap   of  members 
of,  741 

Poughkeepsie,    227 

Pouillon-Boblage,  cited,  267 

Pourtales,    L.    F.   von,   cited,   406,   464,   673, 

688 

Pourtales  Plateau,   106,  244,  335,  407,  414 
Pozzuoli,  3 

-  ,  solfatara  at,  168 

Prather,    J.    K.,    cited,    671,    672,    688 
Pre-Cambric  ocean,   lime  of,   331 
Precipitation,  effect  of  latitude  on,   71 
Presque    Isle,    Lake    Superior   sandstone   of, 

726 
Pressure,  areas  of  high  and  low,  41 

-  ,  belts  of,   43 

-  ,  normal  atmospheric,  40 
Prestwich,   J.,    cited,   698 
Primates,  956 

Prince  Edward  Island,   glacial  conglomerate 

of,   82 

Progressive  overlap,  marine,   740 
Prothallus,   938 
Protcecium,   973 
Protogenous,  269 
Protograph,   919 
Protolimulus,    1,029 
Protolog,   919 
Protoplastotype,  919 
Protosalvinia,    718,    1004 
Prouyot,   cited,    188 
Provincetown,  dunes  of,  557,  559 
Provincial   faunas,   984 
Przhevalsky,  N.  M.,  cited,  56,  562,  580 
Psammytes,   285 
Psephytes,  285 
Pseudoplankton,    994 
Psilotales,   940 
Pteropod  ooze,  455,  456 
--  ,   analysis  of,   677 
Pteropoda,  946 
Pueblo,   27 


Pugha.    lake  plain   of,    364 
Pulverites,    consolidation    o,    751 
Pumpelly,    R.    W.,    cited,    56,    96,    580,    655, 


INDEX 


1177 


Punjab  district,  26 

,   salt  range  of,   592 

Punta  Robanal,   218 
Pupa,  in  delta  beds,  613 

,  in  loess,   568 

Purgatory  chasm,  graben  of,  815 

Put,    the,    355 

Pyramid  Lake,    160,  340 

,  composition  of,    157,    158 

,  salinity  of,  155 

Pyrenees  Mountains,   fulgurites  of,   72 
Pyroclasts,    285 
Pyrogeology,   20 
Pyrometamorphism,    749,    765 
Pyrosphere,   i 

,  limits  of,   12 

,   manifestations  of,    13 


juadrumana,  956 

iuahog  Bay,  1065 

Juaquaversal  dip,  808 

Juartz,     secondary    enlargement    of    grains, 

754 

.  jartzite,   755 

Juebradas,   earthquake,  884 
Jueensland  shelf,   104 
jueneau,  A.    L.,  cited,   319,   321 
'uenstedt,   A.,   cited,    438,    1085 
uiriquina    Island,     earthquake     destruction 

of,  888 


Rabaka  River,  volcanic  mud  in,  876 
Radiation,  30,  31 
Radioactivity,  876 
Radiolarian  ooze,   457 

,  analysis  of,   677 

Ragaz,   251 
Ragged    Keys,    406 
Ragged  Top  Mt.,  308 
Ragtown,    361 
Raibler  beds,  437 
Rain,  26,  62,   63 
Rainberg,  Nagelfluh  of,  602 
Rainfall,  amount  of,  63,  64 

,  influence  of  winds  on,   66,   67 

,  influence  of  topography  on,   66,  67 

— — ,  equatorial  type  of,    68 

,  tropical  type  of,  68 

,  periodicity  of,    71 

Rain-prints,   712 

Ramann,  E.,  cited,  499,  503,  521,  689 

• ,   quoted,   486 

Ramsay,  W.,  cited,  175,  689 
Rann,  the,  Miliolite  of,  575 
Rann  of  Cutch,  in,  348 

,  salt  deposits  in,  617 

,  salt  pans  of,  354,  355 

Ransome,  F.  L.,  cited,  315,  321 

Rantum,   223 

Rantum,  advance  of  dunes  in,   558 

Rapakiwi,   275 

Raritan  Bay,  Pleistocenic  gravels,   754 

Raritan  clays,  632 

Raritan    formation,    dune    origin    of,    570 

,  lignitic  sands  of,    365 

Raritan   sands,    fulgurites  in,  .  73 
Rath,   G.  von,  cited,   879 
Rauchwacke,   434 
Ravenser,  225 
Ravenserodd,  225 
Raymond,  P.  E.,  cited,  72 


Reade,    T.    M.,    cited,    175,    244,    248,    267, 

634»  639 

Recklinghausen,  coal  at,  482 
Reclus,  J.  J.  E.,  cited,   127,   144,   175,  879 
Recrystallization,    748,    755 
Rectigradations,   961,   970 
Redbank  sands,  origin  of  color  of,  671 
Red  beds,  70 
Red  River,  lakes  along,   127 

,   rafts  of,    127 

Red  Sea,   107,   109,  334,  352,  393 

barrier  reefs  of,   388 

clay  boulders  from,  711 
clay  galls  from,  711 
fringing  reefs  in,  386,  390 
mean  temperature  of,   193 
oolites  on  shores  of,  468 
osmotic    pressure    in,    180 
salinas  on  borders  of,  355 
salinity  of,    154,    190,    1044 

,  salt  and  gypsum  on  borders  of,  348 

—-,  temperature,  of,    189,    190,   373 
Reed,  F.  R.  C.,  cited,   1071 
Reede  of  Suez,  oolites  of,  336 
Reeds,   C.   A.,    cited,    684,    689,    1119 
Reef    knolls,    449 
Reefs,  atoll,   386 
,  barrier,  386 

bedded,  417 

epicontinental,    389 

fringing,    386 

inter-fringing   of,    422 

neritic,  389 

oceanic,  389 

Reelfoot  Lake,  origin  of,  889 
Regensburg,  Jurassic  of,  667 
Regnard,   P.,  cited,    181,   207 
Regressions,    3 
Regressive  deposits,   734 
Regressive  movements,    1141 
Regressive-transgressive  series,  736,  737 
Reibisch,   P.,  cited,   892,   909 

Reid,   H.   F.,   cited,    263,   267,    328,   810,   8n 

and  others,   cited  on   faults,    827 

Reis,  O.  M.,  cited,  782,  827,  1080,   1096 
Relicts,    1044,    1054 

Renault,   cited,   482 

Renevier,    cited,    643 

Replacement,  metasomatic,  761 

Reptilia,  naming  of,  913 

Retreatal    sandstone,    735,    736 

Reusch,   H.,   cited,    81,   267 

Reuss,  foehn  of,   47 

Revy,  J.  J.,  cited,  661,   689 

Rewa,    Anthozoa   in   harbor   of,    1012 

Reyer,  cited,  203 

Rhabdoliths,   456,   933 

Rhaetic  sandstone,   destruction  of,    247 

Rhang-el-Melah,  379 

Rhine,  foehn  of,  47 

,  Maare  region  of,   860 

Rhine  delta,   607,  642 

,  composition  of  silt  in,  616 

,  lime  content  of,  622 

,  thickness  of,   609 

Rhine  graben,    815 

Rhine   River,    137,   248,   250,   251 

,  velocity  of,   245 

Rhine  Valley,  loess  of,   565 

Rhizocarps,   941 

Rhizopoda,    942 

Rhodes'  Marsh,   363 

Rhombenporphyry,   305 

Rhone,    foehn   of,   47 

Rhone  delta,  cementation  of  deposits  in,  616 

,  inclination   of   strata   in,    610 

,  rate  of  growth  of,  609 

,  thickness  of,   609,   610 


INDEX 


Rhymney    River,    662 

Richmond,   Va.,   diatoms  beneath,   461,   676, 

1002 

Richmond  formation,   reefs  of,  418 
Richthofen,  F.  von,   cited,  40,  96,  435,  465, 

565,    58o 

Richthofen  reef,  434 
Ridge,  Wyville-Thompon,  see  Wyville-Thom- 

son  ridge 

Faroe-Iceland,   106 

Ries,  H.,  cited,   533,   538,  622,   639 

Riga,  salinity  of  Baltic  at,   1045 

Rill  marks,  708 

Ringer,   cited,    194 

Rio  de  la  Plata,  corals  at  mouth  of,   1012 

,  estuary  of,   113 

,  temperatures  of,    195 

Rio  de  los  Papagayos,   367 

Rio  Grande  rise,  105 

Rio  Janeiro,    1015 

Riparia,  dunes  at,  561 

Ripple  marks,   219,   712 

,  greatest  depth  of  formation  of,  713 

in     Devonic     limestone    of     Michigan, 

429 

Rise,  Easter  Island,    106 

,  Kerguelen,  106 

River  Bar,   136 

Findhorn,    252 

Jordan,    salinity    of,    156 

Mur,     246 

Saale,    252 

Spey,    252,    255 
Rivers,  annual  rainfall  in,  66 

,  solids  in,    163,   164 

Riviere  Blanche,   filling  of,   86 1 
Roba-el-Khali   desert,   dune  area  of,    562 
Robertson,   cited,   689 
Robson,   H.,   cited,   689 
Roches   moutonnees,    264,    265 
Rochester  shales,  261 
Rock  city,   joints  in,   791 
Rock  fracture,  zone  of,   142 
Rockwood   clays,    823 
Rogensteine,   283,   336,  472,  473 

,  structure  of,  472,  473 

Rogers,  A.   F.,  cited,    1082,    1087,   1096 

,  A.  W.,  cited.  81,  92,  96,  538 

,  A.    W.,     and     Schwartz,     E.     H.     L., 

cited,   576,  580 

,  H.   D.,   cited,    708 

Rohlfs,  cited,   56 

Rolland,   quoted,    167 

Romanche    deep,    188 

Romieux,  A.,  cited,  7,  23 

Romney  shale,   424 

Rondout    waterlimes,    mud-cracks  in,    709 

Roost,  the,  230 

Rosalind  bank,    108 

Rosenbusch,    H.,    cited,    270,    271,    299,    302, 

771,   775 
Rosendale  cement,  731 

waterlimes,    absent    at    Kingston,    68 1 

Rossi,  M.  S.   de,  cited,   909 

Rotalia,  in  Severn  muds,   664 
Roth,  J.,  cited,   164,  537,   1080,   1096 
Rothes  Burn,   origin  of  sand   of  the,    716 
Rothliegende,   windkanter  of,    55 
Rothliegende   desert,    375 
Rothpletz,    A.,    cited,    337,    338,    465,    468, 
469,  472,  474,  476,   521,    1093 

quoted,   468,    784,   827 

Royal  gorge,  587 
Rudaceous  texture,   285 
Rudolph,  E.,  cited,  879,  909 
Rudytes,  285 

Ruedemann,    R.,    cited,    243,    268,   474,    521, 


808,    823,    827,    928,    981,    ion,    1012, 

1039,   1136,    1145,   ii49 
Kuedemann,  K.,  quoted,  243,  244 
Ruetschi,   G.,   cited,   580 
Rust,   cited,   458,    465 
Russell,    I.    C.,    cited,    36,    38,    40,    96,    119, 

i2i,    144,    159,    161,    163,    164,    200,   201, 

207,   268,    324,    338,    339,    340,    341,   359, 

382,   517,  625,   634,   639,   870,   879 
,   quoted,    154,    159,    160,    162,    163,    199, 

507,  5o8 

Russell,  W.  J.,  cited,  28,  96 
Russia,    unconsolidated    Palaeozoic    sands   of 

750 

,  tchernpzom  of,  514 

Rutot,  A,,  cited,  92,  689,  724,  745 


Saalfeld,   434 

Sabrina  Island,   864,   865 

Saco,    flood   plain   of,    588,    596 

Saddle  Mt.,  313 

Saddles,   defined,   966 

Saginaw  Bay,  837 

Sahara,   359 

,  dune   area  of,    562 

,  migration  of  dunes  from,   558 

,  preservation  of  tracks  in,  604 

,  rainfall  of,  63,  77 

,   spring   water   of,    167 

,   strength  of  wind   in,   56 

St.  Anthony,    falls  of,    m8 
St.  Augustine,  406 
St.    Croix,   dalles,    23,   648 
,   formation,    648 

sandstone,    729 

sandstone,   Aglaspis  in,    1029 

St.  Giles,  ripple  marks  of,   713 
St.  Gotthard  Pass,  weather  in,  48 
St.  Helena,    Island,    105 

,   harbor  of,    215 

St.   Ignace,  brecciated  limestone  of,  547 
St.  Jean-de-Luz,    encroachments    of    sea    at, 

558 
.  John,    absence    of    Lower    Cambric    at, 


72 
.  John's  River,   tides  in,  227 


St 

St 

St.  Lawrence,    furrow,    104 

,  gulf  of,    235,   241 

river,    133 

,  drowning  of,   136 

spring,    175 

St.  Louis  limestone,  cross-bedding  of,  577 
St.  Michaels,   864,   865 

,  humus  layer  at,   507 

St.   Paul,    Island  of,   872,   873,   875 
St.  Peter   sandstone,   642 

disconformity    represented  by,    1101 

dune  origin  of  parts  of,   571 

hiatus  in,    1132 

inclusions  in,    717 

intercalated,   738-,   739 

loess-like  origin  of  portions  of,   569 

slight  cohesion  of,    752 

.  transgression  of,   565,   738 

St.  Vincent,  erosion  on  Island  of,  875,  876 

Salem,    1041 

Salina,    endolithic  brecciation  in,   537 

Salina  group,    376 

Salina    salt,    366,    731,    756 

Salinas,  603 

Salinity,  defined,   145 

,  types  of,    150 

Salisbury,  R.  D.,  cited,  25,  42,  43,  45,  46, 
59,  96,  116,  125,  144,  200,  207,  247, 
268 


INDEX 


1179 


Salitrales,  329 

Salitre,  341 

Salt,  efflorescence  of,  124 

,  Miocenic  deposits  of,  351 

Salt  domes,   758 

Saltenfjord,  230 

Salton  Sink,   355,  356 

Saltstrom,  230 

Salversen,  Captain,  cited,  224 

Salzburg,   foehn  of,  47 

Nagelfluh   of,    601,    616,    750,    753 

Samoan  islands,  40 
Samuelson,  G.,  cited,  521 

,  quoted,  504,  505 

San   Bernardino,   alluvial  fans  of,   83 

,  borax  lakes  in  county  of,  363,  364 

,  pass,    53 

,  soda  niter  deposits  of,  364 

Sandberger,    F.,   cited,    1086 
Sand  grains,   dimming  of,   61 

,  effective  size  of,   258 

,  rounding  and   sorting   of,   61,    715 

Sands,   coating  of,   37 

,  desert  type  of,  37 

Sandwich    Islands,    386 

,  marine  erosion  of,  875 

San  Filippo,  travertine  of,  343 
San   Francisco,    Bay   of,    1 1 1 

,  earthquake    at,    882 

San  Joaquin  River,  126 

San  Juan   Mts.,   rock  streams  in,   545 

San  Juan  River,   section  on,  848 

Sankaty  Head,   599 

Santa  Anna  Island,  411 

Santa  Fe,  27 

Santa  Maria,  dust  from,  60 

San  Vignone,  baths  of,  343 

Sapping,    18 

Saprocollyte,   480 

Saprodillyte,   480 

Sapropel,    281 

Sapropelite,    281,    480 

Sapropeliths,   478,  479,   480 

Sardinia,   Archaeocyathidae  of,   417 

Sargasso    Sea,    187,    236 

,    temperature   of,    187 

Sarle,  C.  J.,  cited,  465 

,    quoted,   446 

Sarmatian  reefs,  443 

Sassolite,    364 

Sault   Ste.    Marie,    1122 

Sava  de  Malha  group,  389,  390 

Saville-Kent,    W.,   cited,   391,   400,   401,  465 

Savu-Savu,  chloride  waters  of,    168 

Scandinavia,  eskers  in,  .599 

Scania,   Cretacic  boulder  bed  of,   651 

Schala,   The,   603 

Schardt,   H.,   cited,    659,   689 

Schiaparelli,  G.  V.,  cited,  96 

Schiefergebirge,    rheinische,    375 

Schimper,  A.   F.   W.,  cited,  982,  990,    1000, 

1039 

Schire  River,  116 
Schist,   279,   770 

,  restriction  of  term,  770 

Schistosity,    769,    794 
Schladebach  bore  hole,    14 
Schlern   dolomite,    435 
Schleswig-Holstein,  223 

,   coastal  dunes  of,   557.    558 

Schmelck,   cited,    194 
Schnaitheim,  quarries  of,  439 
Schneider,   K.,   cited,   203,  207 
Schoenite,    37*,    372 
Schoharie  grit,   424 

Schoharie  region,    disconformities  in,   823 
Schott,   G.,  cited,   149,   150,  207 
Schott-Mel-Rir,    The,    359 


Schramberg,   Bunter  Sandstein  of,  634 

Schuchert,   C.,  cited,  957,    1107,    1119,    1144, 
1145,   1146,   1149 

Schuchert,  C.,  and  Buckmann,   S.   S.,  cited, 
957 

Schucht,  F.,  cited,  689 

Schutt,  F.,  cited,  994,  999 

Schwartz,   E.   H.   F.,  cited,  535,  538 

Scilla,  land  slip  at,  888 

,  maelstrom  at,  230 

Sclater,  P.  L.,  and  W.  L.,  cited,   1056,  1071 

Scotland,   219,   293 

clay  boulders  on  coast  of,  711 
fundamental  gneiss  of,  252 
Ordovicic  rocks  of,  315 
recent  corals  of,   392 
section   of  peat   moor  of,    504 
waves  on   coast  of,   221 

Scorpions,    948,   949 


Screes,    33 

Scrope,   P.,  cited,  879 

Scudder,  S.   H.,  cited, 


,   525,  538,  917,  957 
sculpturing    processes,    16 
Sea,   bathymetric   zones  of,    100 

,  regional  subdivisions  of,  99 

,  salinity  of,    145 

Sea-breezes,    44 

Sea-lobes  of  Appalachians,   807,   809 

Sea  of  Aral,  elevation  of,    115 

Azov,    240 

,  salinity  of,   153 

Marmora,   240 

,   salinity  of,    153 

,  temperature  of,    189 

Okhotsk,  242 

Searles's  Marsh,    363 

,   soda  niter  of,   364 

Seas,   dependent,  99,    107 

epicontinental,   109 

funnel,    112 

independent,   99,    106 

intercontinental,   99,    100 

intracontinental,  99,   106 

marginal,    99 
Sebcha,  the,  603 
Secca  di   Benda  Palumno,  470 
Secca  di   Gajola,    470 
Secretions,   721 

Sedgwick,   A.,    cited,    1099,    1108 
Sedgwick,    A.,    and    Murchison,     R.,    cited, 

1108 

Sedimentation,  eolian,   51 
Seeley,   A.,   cited,    530,    538,    785 
Seiches,   209,  231 
Seidlitz,   N.  von,  cited,   382 
Seine   bank,   no  sediments  on,    680 
Seine-Dacia  bank,   335 
Seine    River,    meanders   of,    137 

,  tidal    bore    of,    227 

Seismic  center,   883 

Seismic   disturbances,  baryseismic,  882 

,   pyroseismic,  882 

Semper,    K.,    cited,    465,    990,    1019,    1025, 
1039,   1047,    1071 

,  quoted,    986,    1047,    1068,     1069 

Semper,   M.,  cited,    1149,    1150 
Senomien,  730  _ 

,  glauconitic  chalk  of,  850 

Sentis  Mts.,    176 

Sepia,    wide   distribution  of   shells   of,    1022 

Septaria,    763 

Sernander,   R,,  cited,  92 

Serpentine,    177,    279 

Sett  Sass,  reef  of,  434 

Severn,  corals  on  wreck  of,  412 

Severn,  estuary  of,  662 

,  tidal  bore  of,   227 

Sevier  lake,  composition   of,    157 


n8o 


INDEX 


Sevier  lake,  salinity  of,  154 

• ,  soda  deposits  of,  361 

Sewell,   middle  Pottsville  at,   742 

Seychelles  Island,   386,   390 

Seyistan,    alternation    of    beds   in    Lake   of, 

623 
Shaler,    N.    S.,   cited,   32,   82,   96,   226,   268, 

448,   473,   485,   487,    489,   491,   494,    52i, 

522,   652,   689,    694,   695,   851,   858 

,  quoted,  488,   652 

Shaliness,   785 

Shan-Tung  Mts.,   585 

Sharon    conglomerate,    252 

Shaw,  E.  W.,  cited,   136,  144 

Shawangunk  conglomerate,  377,  596,  636 

Sheboygan,    167 

Sheik  Zayed,  355 

Shelden,  J.   M.   A.,  cited,   719,   722 

Shelf,    Florida-Carolina,    106 

Sheppard   limestone,    334 

Sherlock,   R.   L.,  cited,   465 

Sherzer,   W.  H.,  and  Grabau,  A.  W.,  cited, 

422,   465,    553,    570,   571,   580 
Shetland   Islands,   219,   236 

,  force  of  waves  on,  222 

Shimek,   B.,  cited^  566,   580 

Shimer,  H.  W.,  cited,  981,   1067,   1068,   1071 

,  quoted,    1066 

,  and  Blodgett,  M.  E.,  cited,  1069,  1071 

,  and  Grabau,  A.  W.,  cited,    1131,   1150 

Shinarump,  playa  surface  in,  709 

Shoonmaker   quarry,   419 

Shore   formations,   intercalated,    736 

Shropshire,    307,    447 

Shunett  Lake,   360 

Siau,  cited,    713 

Siberia,   Archaeocyathidae  of,   417 

,  mammoths  of,   1075 

Siboga  expedition,   68 1 

Siccar  Point,  unconformity  at,  824 

Sicily,   240,   343 

,  mud  volcanoes  in,  872 

,  Pliocenic    foraminifera    of,    454 

Sickenberger,    cited,    369 

Sieberg,  A.,  cited,  909 

Sierra   Nevada,    gold-bearing   slates   of,    773 

,   rivers  from,    584 

Silicification,    1079 

Sills,   304,  305 

Siluric,    abrupt   change  in   sea-level   in,    731 

,  hiatus  in  Appalachians,  823 

,  replacing  overlap  of,   744 

Silver  Pit,  furrow,   104 
Simpson,  C.  T.,  cited,   1071 

,  quoted,    1059 

Simpson   formation,   739 

Simroth,    H.,    cited,    91,    97,    892,    894,    900, 

909,    1019,    1039,    1144,    1150 
Sinai  desert,  quartz  in,  552 

•  peninsula,  hydrometamorphism  on,  767 

,  oolites  on,   336,   468 

Sinclair,    W.    J.,    cited,    538,    539,    572,    580, 

1119 

,  and   Granger,   W.,   cited,   639 

— ,  quoted,    624,    625,    627,    628 

Singapore,  nsh  falls  at,    56 
Sinj,  earthquakes  of,  883 
Sink  holes,    176 
Sirmur  group,   591 
Siwalik  formation,  904 

,  alternation  of  colors  in,  623 

,  thickness   of,    591 

,  torrential  origin  of,   630 

Siwalik  Hills,  591 

Siyeh   limestone,   334 

Skagerak,  224,   1045 

Skaptar  fissure,  lava  from,  866 


Skeat.c,    E.    W.,    cited,    331,    382,    436,    445, 

465,  761,  775 
skerries,    651 
Skerryvore,   221 
Skottsberg,    C.,    cited,    92 
Slate,   restriction  of  term,    770 
Slatiness,   786 
Slaty   cleavage,   793 
Slavonia,  Paludina  beds  of,  958,  959 
Slichter,   C.   S.,  cited,  4,  23,    140,   141,    142, 

144,  258,  259,  260,  268 
Shckensides     formation    of,    768 
Smith,    J.    P.,    cited,    966,    972,    975,    981, 

c       'u71/-   Vr34'TII36J    II3?'    IJ56 
Smyth,   C.    H.,  Jr.,   cited,   763,    775 
Snake   River,   dune  area  of,    561 

,  lava  plains  of,  867 

Snakes,  in  marine  habitat,  985 

Snow,  26,  62,  63 

Snow  line,  322 

Society  Archipelago,  401,  402 

Society   Islands,   barrier   reefs  of,   388 

Soda  Lake,    120,  361 

,  composition  of,    157,    158 

— — ,  salinity  of,    154,    156 
Soil,  colors  of,   36,  621 

Sokolow,    N.    A.,    cited,    97,    552,    555,    556, 
557,    58o 

,  quoted,   56 

Sokotora,  456 

Soldier  Key,   406 

Solent,  222 

Solfataric  action,   768 

Sollas,  W.  J.,  cited,  662,  689 

,  quoted,  662,  663 

Solnhofen,   calcilutytes  of,    336 

deformation   at,    531,    781 

impressions  in  rock  of,    1078 

insects  in  limestone  of,  440 

,  mud  cracks  in   beds  of,   709 

reefs  of,   437 

remains  in  limestone   of,  439 

roofing  slates  of,   786 

solution  of  limestone  of,   175 

Solomon  Islands,  386,  411 
Sombrero,   108 

Somerville,   drumlins  of,    532 
Somersetshire   oolite,    crosa-bedding    in,    704 
Sonora,    gold-bearing   slates   in,    773 
Sorby,  H.  C.,  cited,  250,  268,  455,  474 
Soudan,  rainfall  of,  68 
South  African  trough,    105 

,  temperature   in,    187 

South  Australian  shelf,   103 

South  Brazil  shelf,    103 

South  China  Sea,   107 

South   Dakota,  artesian  basin  of,   260 

South  Pole,  migration  of,  898 

South  Tunis,   359 

Southern  Appalachians,    caves  in,    346 

Spain,    monsoons   of,    46 

,  torrential  deposits  in,  629,  630 

Spanish  Peaks,  radiating  dikes  in,  874 

Species,   912,   962 

Speremberg,  bore  hole,  13 

Sphaerites,  consolidation  of,   751 

Sphenoconformity,   826 

Spirula,    wide  distribution  of  shell  of,    102? 

Spitzbergen,    192,   236 

,  postglacial  fauna  of,  88 

red  algae  at,  470 


_    .   -,  cited,   664,  665,  689 
Squid,   946,    1021 
Stalactites,   346 
Stalagmites,   346 
Stamm,  K.,  cited,  580 
Stanton,  T.  W.,  cited,  1069,  1071 


INDEX 


1181 


Stapff,   F.   M.,   cited,   23 
Stassfurt,    371 

salts,   350,   372,   374 

• — ,  period   of    deposition   of,   373 

- — ,   "ngs  of,    355,    376 

Stedman,    J.    M.,    cited,    1077 

and  Anderson,  J.  T.,  cited,    1096 

Steidtmann,    E.,  cited,    760,   775 
Steinheim,    Planorbis  of,    1043 

,  shells  in  beds  at,  631 

Steinmann,    G.,    cited,    332,    382,    522,    956, 

1074,   1096 

Stemme,  H.,  cited,   522 
Stenohalinity,    1045 
Stenothermal  organisms,  80 
Stephen  shale,  preservation  of  organisms  in, 

1078 
Stevenson,  J.   J.,  cited,    500,    522 

,   quoted,    509,    514,    515,    517,   518 

Stevenson,  T.,  cited,  213,  218,  221,  222,  268 

,  quoted,  221 

Stille,  cited,  758 

Stinkkalk,  485 

Stinkstein,    434 

Stirling  Island,  411 

Stolle,  J.,  cited,  522 

Stone,  W.,  cited,  921,  957 

Stonesfield  slate,   577,    1034 

Stoneworts,  471,  934 

Storm   King,    1067 

Strahan,  A.,  cited,  81,  97,   534,   539 

Straits  of   Bab-el-Mandeb,    190,    241 

Gibraltar,   230,   244 

,    salinity   of,    152 

Kertch,  240 

,  salinity  of,   154 

Korea,    242 
Strand,  647 
Stratification,  700,  701 
Stratified  Rocks,   269 
Stratigraphy     i 

Stratum,  denned,  698,  699,  700 
Stringocephalus  beds,   430 
Stromatoliths,   473 
Stromatopora;   421,   422,    430,    431 

,  asphaltic  material  in,  485 

,  worn  heads  of,  428 

Stromatopora  reefs,  423 

Stromatoporoids,  385,  418 

Stromboli,  volcano  of,  86 1,  871 

Stromer,  cited,  956 

Strophe,   climatic,   82,   83 

Strutt,  cited,  876 

Stuben  sandstein,  origin  of,   635 

,  reptiles  in,  953 

Stuttgart,  weather  at,  48 

Styliolina  limestone,   456,    1023 

Stylolites,  786,  787,  788 

Subaerial  fans,  overlaps  of,  740 

Subatlantic    climatic    period,    506 

Subarctic  climatic  period,  506 

Sub-mutation,  961,  962 

Suchier,   cited,   250,   268 

Suess,  E.,  cited,  3,   138,  201,  202,  203,  207, 

595,  639,   760,   775,  881,  909 
Suez,   Bitter  Lakes  of,  697 

,  Quaternary  oolite   near,   469 

Suez  Canal,  date  of  cutting,  352 

,  migration   through,    1042 

Sugar   Loaf   Mountain    (Brazil),    32 
Sumatra,   390 

,  oscillation  poles  in,  893 

,  peat  swamp  on,  509,  510,  512 

Summer  Lake,    118 

Sunda  Islands,  242 

Sunderland,  coast  of,  225 

Supan,  A.,   cited,   74,   77,   78,   97,   101,    105, 

106,  144,  678,  689 


Surface  features  of  earth,  Compared,   13 
Susquehanna    River,   845 
Sussex,    chalk  from,   454 
Sutherland,   conglomerate  of,   651 
Sutton,   Mass.,   graben  at,  815 
Swabian  Alp,  442 

,  cuestas  of,   838 

,  Jurassic  reefs  of,  438 

Swainson,    T.,    cited,    917,    918 
Sweden,   Cambric  windkanter  of,   573 

,  coast  of,   241 

,  Cretacic  boulder  beds  of,   651 

,  overlap   of  basal   Cambric   of,    728 

Swell,   Crozet,    106 

Swells,  209 

Sylt,  Island  of,  223 

,  dunes  of,  557,  558 

Sylvania   sandstone,    642 

,  cross-bedding  in,    570,    571,    704 

,  dune  origin  of,  571 

,  hiatus  in,    1132 

,  inclusions  in,  717 

,  slight  cohesion  of,  752 

,  trangression  of,  565 

Sylvinite,   371,    372 
Sylvite,   372 
Symphrattism,   749 

Synchroneity,   black  shale  across  planes  of, 
732 

,  sandstone  crossing  planes  of,  736 

Syntype,    919 

Syracuse  salt,   376 

Syr-darja    (Syrdaria),    561,    608 

Syria,   240 

,  coast  of,  218 

,  desert  areas  of,  562 

Szovata,    122 


Tabasco,   volcanic  ash  deposit  of,   60 

Tachygenesis,    964 

Tahiti,  388,  401,  402,  410 

Takyr,  603,  709 

Talbot   formation,   87 

Talc,  177 

Talcot,   Captain,   cited,   609 

Talheim,  stylolites  of,  788 

TaltaJ,  365 

Talus,  32 

Taman,  peninsula  of,  443 

Tamaracks,   498 

,  filling  of  swamps  by,  496 

Tampa  beds,   casts  of  corals  in,    1090 

Tanfiljef,  G.   L,  cited,  92 

Tapachula,  volcanic  ash  deposit  of,  60 

Tapir,   956 

Taramelli,   T.,  cited,  92 

Tarapaca   desert,    365 

,  guano  of,  461 

,  soda  niter  deposits  in,   364 

Tarawera,  eruption  of,   60 
Tarim  River,  588 
Tarr,  R.  S.,  cited,  642,  689 
Tasmania  shelf,    104 
Tasmanian  Sea,   1 12 
Taurida,   Russia,   dunes  of,   560 
Taylor,  F.  B.,  cited,  909 
Tay  River,  peat  of,  514 
Tectonic,  restriction  of  term,  88 1 
Teisseyre,  L.,  cited,  443,  465 
Teleosts,  352 

Temiscammg  syncline,  810 
Temperature      arrangement,      dichothermal, 
183 

,  heterothermal,   183 

. ,  homothermal,    183 


1182 


INDEX 


Temperature  arrangement,  katothermal,    183 

,  mesothermal,   183 

Teneriffe,  244 

Peak,  trade  winds  of,   44 

Tenison- Woods,   cited,    1013 

Tennessee,  Lower  Cambric  limestone  of,  335 

Tentaculite  limestone,   456,    1124 

Tepee  buttes,  447,  448 

Tepetate,  341,   586 

Teredo,    632,    1016 

Terek  delta,  rate  of  growth  of,  609 

Termites,   height  of  nests  of,   694 

Terra  rossa,  40 

Terreild,  cited,    156 

Tetrabranchiata,  946 

Tetragraptus,   978 

Tetraseptata,   913,    943,    1013 

Teuchern,  Limulus  in  brown  coal  of,  1029 

Teutoburger  Wald,  673 

Texas,  deformed  salt  domes  of,   758 

Textularia,  in  Severn  muds,   664 

Thalassic  zone,   987 

Fhalassogenic  deposits,   329 

Thalassoseisma,  88 1 

Thallophytes,  935 

Thalweg,    258 

Thames  River,  248 

,  currents  in,  229 

Thenardite,   363 

Theobold,  cited,  56,  97 

Thermonatrite,   362 

Thesis,  climatic,  82,  83 

Thetis   Sea,    375 

Thompson,  Sir  W.,  cited,  897,  909 

,  quoted,  897,  898 

Thomson,  W.,  cited,  456,   1071 
Thon-gallen,   711 
Thoroddsen,  T.,  cited,  879 
Thorpe,   parish  of,   225 
Thorshaven    (Faroe   Islands),    31 
Thoulet,    J.,    cited,    34,    97,    268,    288,    299, 
452,  679,  689,   879 

,  quoted,   55 

Thuringia,   Kupferschiefer  of,  479 

— — ,  Zechstein  reefs  in,  433 

Thiiringer  Wald,  252 

Thurr,  the,  355 

Thursday  Island,  404 

Tian-Shan  Mountains,   sands  brought    from, 

561 

Tiber,  cuspate  delta  of,  608 
Tibet,    borax   deposits  of,    364 
Tichenor  limestone,  684 
Tidal  bore,   227 
Tidal  race,   229 

Tiddeman,  R.  H.,  cited,  432,  449,  465 
— - : — '-,  quoted,  433 
Tides,   227 

Tile  fish,    destruction  of,    195 
Tillard,   Captain,  864 
Tillers  Ferry,  fish  falls  of,  56 
Tillite,   534 
Timor,    242 
Tirolites  stage,  preserved  in  a  Trachyceras, 

975 

Titanothere,  956 
Tizard  bank,  391 
Todd,   J.    E.,    cited,    719,    722 
Toledo  anticlinals,  810 
Tolman,  C.   F.,   cited,   97,    197,   207 

,  quoted,  147,   148 

Toltry,  443 

Tomboro,  dust  from,  60 

Tonga  deep,   3,   896 

,  temperatures  in,   187 

Tonkin-Hong-Kong  shelf,    104 
Topography,  karren,  176 
,   lapiaz,    176 


Topotype,  919 

Top-set  beds,   702 

Torell,   O.,  cited,  236 

Tornquist,   A.,   cited,   690,    1134,    1150 

Torres   Strait,   387 

Torridon  sandstone,   33,   293 

•• ,  arkose  character  of,  84 

,  windkanter  of,   54,  573 

Tortugas,   391 

— ,   dry,  406 

Toula,  F.,  cited,   1150 
Tournasien,  reefs  of  the,  432 
Toxodontia,   956 
Trachyceras,   retarded,  975 
Trachytes,   depths  of  formation,    15 
Transcaspian   Desert,   see  Kara   Kum 

,   dunes  in,    563,    564 

Transgressions,    3,    725,    738,    1141 
Transportation,    17,   18 

— ,  distance  of  eolian,  58,  59 
Transylvania,   salt  domes  of,   758 
Trap,   278 
Traverse  Bay,  reefs  of,  429 

group,   423,   426 

,    Stromatopora  reefs  of,   444 

Travertine,    343 
Treasury   Island,   411 
Treitz,.  P.,   cited,   92 
Trench,    Japan,    106 

,  Marian,    106 

Trenton     Falls,    deformation    in    limestones 
of,    783,   784 

limestone,   distortion  of,   530 

,  overlapped  by  Utitica  shales,  743, 

744 

Triassic  time,  climatic  conditions  of,  70 
Tricyrtida,  458 

Trigonodus  limestone,   stylolite   from,   786 
Trilobites,  912,   947 
Trinity  formation,  729 
Tripoli,    diatomaceous  earth  of,   461 
Tripolite,  460,  461,  676 
Tristan  da  Cunha,    105,  452 

,  pteropod  ooze  near,  456 

Triumph   reef,    406 
Trona,    362,   363 
Truckee  River,    160 
Truro,  sands  from,  559 

,  sand  plains  of,  600 

Tschermak,   cited,  203 

Tschudi,   cited,   461 

Tsien-Tang  River,  tidal  bore  of,  227 

Tsunamis,   88 1,  889 

Tufa,   calcareous,   342 

•-,  dendritic,   340,   341 

,  lithoid,    339 

,  thinolithic,   339 

Tulare  Lake,  126 

Tule  Arroyo,  onyx  marble  of,  344 

Tully,  pyrite  layer,  fauna  of,    1045,    1065 

Tultenango,   Permic  position   of  North  Pole 

at,  536 

Tumlirz,  O.,  cited,  23 
Tundra,   frozen  soil  of,  200 

,  lakes   of,    121 

Tung  hai   Sea,    107 

shelf,   104 

Tunis,  240 
Turbarian,   506 
Turkestan,  358 

,  earthquake  in,  885 

"Turks'  Heads,"  403 

Turks'  Island,  412 

Turonien,  730,  850 

Turtle  Mountain,  rock  fall  on,  546 

stones,  720 

Tuscany,   343 

,  borate  deposits  of,  364 


INDEX 


1183 


Tuscany,  fumaroles  of,  370 

Tuscarora     Sour     Spring,     composition     of 

water    of,    168 

Tuskegee,    mineralized  body    near,    1077 
Twenhofel,   W.   H.,   cited,   509,   522 

— ,  quoted,  508 
Tyrol,   dolomites  of,  444 

reefs  of,  434,  435 

Tyrone,   423 

,  Appalachian  folds  at,  903,  904 

Tyrrhenian  Sea,  230,  240 

U 

Udden,   J.   A.,   cited,   58,    59,   97,   552,  ,581, 

653,  654,  690 

,  quoted,   56,   59,   552 

Ued  Kir,  the,    359 

Ugi  Island,   411 

Uhlig,    V.,  cited,    1057,    1058,    1072,    1150 

Uinta  sandstone,   855 

,  age  of,   1138,   1140 

Ulexite,    364 

Ulmic  acid,    173 

Ulrich,    E.    O.,   cited,    824,   828,    1107,    1109, 

1113,    1120,    1124,    1150 

and    Schuchert,    C.,    cited,    1150 

Unconformity,  821,  824,   826 

,  inverted,  826 

Unkar  series,   age  of,    1 140 

Unst,   lighthouse  of,   219 

Unter-Mauthdorf,  246 

Unterschwarza,  246 

Upham,  W.,  cited,    126,    144,   373 

Ural    Mountains,    undecomposed   granite   of, 

40 

Urao,  362 

Urmiah  Lake,  salinity  of,   154 
Uruguay   River,    solids  in,    174 

— -    tributary  of  La  Plata,   66 1 
Usiglio,   J.,    cited,    348,    350,    382 
Usk  River,  662 
Utah,  hot  springs,   168 

,   onyx  deposits  of,   344 

Utica  shales,   243 

,   origin   of,   479 

,  overlap     on     Trenton     limestone, 

743 

,  replacement     of     Trenton     lime- 
stone by,  744 


Vaal  River,  glacial  deposit  at,  535 

Vaccinium,    503 

Val  del  Bove,  basaltic  dikes  in  walls  of  the, 

871 

Valdivia,    185 

Valiant,  W.   S.,  cited,   1086 
Valparaiso,   sea-breeze  of,  44 
Valves,   brachial,   944 

— ,   pedicle,   944 
Van   Hise,   C.    R.,    cited,   4,    23,    37,    38,   97, 

138,    139,    140,    141,    M4,    174.    175,    177. 

178,   207,    293,   299,    528,    539,    713,   751, 

752,   754,    755,    76i,   765,    767,    770,    77i, 

775,   794,   819,  820,   828 
— ,   quoted,    528,    529,    747,    752,    772,   790, 

793 

Van  Lake,  salinity  of,  155 
Vanikoro,   401 

Van't  Hoff  and  Weigert,   F.,  cited,  373,  382 
Vanuxem,   L.,   cited,   787,    1123 
Varanger  fjord,  Cambric  glacial  deposits  in 

.81,  534^ 
Variation,  960 


Varieties,   912 

Variplitic,  277 

Varo,   230 

Vater,  cited,  373 

Vaughan,  T.   W.,  cited,  391,  418,  465,  1072 

Veatch,  A.  C.,  cited,   127,   144 

Vegetation,  tundra  type  of,  85 

Veins,  eruptive,  304 

Velain,   C.,  cited,   873 

Venezuela,  alkaline  lakes  of,  361 

Vera  Cruz,  volcanic  ash  deposit  of,  60 

Verawal,   miliolite  limestone  of,   574 

Verbeck,  R.  D.  M.,  cited,  879 

Verdun,   231 

Vermilion  iron-bearing  district,  316 

Vermillion  Creek  beds,  626 

Vernon-Harcourt,  L.  F.,  cited,  690 

Vernon   shales,    376,   377 

,  iron  in,   621 

,  loess-like  origin  of,   569 

,  origin  of  red  color  of,    569,  622 

Verrill,   A.   E.,   cited,   412,   465,   680 

and  Smith,   S.  J.,  cited,    1065,   1072 

Vertebraria,   in   cannel  coal,    481,   484 
Vesuvius,  dust  from,   60 

,  eruption  of,  875 

,  lavas  of,   317 

,  periodic  activity  of,   871 

,  tuffs  of,  290 

,  volcanic  mud   from,    525 

Veta  Park,  rock  streams  in,  545 
Victoria  Land,  volcanoes  of,  877 
Vienna,  245,  251 

•  Basin,  fossil  nullipores  of,  471 

,   Miocenic  boulder  beds  of,   651 

Ville,   M.,  cited,   379 
Vindelician    Mountains,    373 
,   sediments  from,  634 

period,  old  shore  of,  440 

Virgin   Islands,    108 

Virginia,   Lower   Cambric  limestone  of,    335 

Viry,    phosphate   waters   of,    168 

Visby,    Siluric   reefs  near,   427 

Viseen,  reefs  of  the,  432 

Vistula,  velocity  of,  245 

Vistula  delta,  organic  matter  in,  614 

Vitrification,  766 

Vogt,  C.,  cited,  886 

Vogt,  J.  H.  L.,  cited,  382 

Voigt,    F.   S.,   cited,   605,   639 

Volcanoes,   distribution  of,  877 

,  heights  of,   863 

,  mud,    885 

Volga   delta,    608 

,  deposits  of  lime  in,  616 

River,   357 

,  dunes  on  shores  of,  561 

Volhynia,   443 

von  Baer,  K.  E.,  cited,  200 

von  Buch,  L.,  cited,  336 

von  Kotzebu,  cited,  204 

von  Kvassay,  E.,  cited,  369 

von   Richthofen,    see   Richthofen. 

von  Seidlitz,  cited,  353 

von  Tillo,  cited,  39,   183,   566 

Vosges,    1029 

Vulcanello,  erosion  of,   875 

Vulcanian  periods,  861,  871 

Vulcano,    Island  of,   875 

,  eruption   of,    86 1 

,  lava  flows  of,  317 

Vulcanology,  20 

W 

Waagen,  W.,  cited,  960,  963,  981 
Wade,  A.,  cited,  54,  97,  594,  639 


1184 


INDEX 


Wadi  Deheese,  oolites  of,  336 

Wadsworth  Lake,  340 

Wagner,   G.,  cited,   784,   786,   788,  828 

,  H.,  cited,  23,    100 

,  R.,   cited,   335,   382 

Wagon-bed  Spring,  pyroclastic  mud  at,   526 

Wahnschaffe,  F.,   cited,  92,   287,   288,   300 

Walcott,  C.  D.,  cited,  335,  382,  417,  418, 
465,  530,  539.  1078,  1089,  1096,  1103 

Walker  Lake,  salinity  of,    155 

Wallace,  A.   R.,  cited,    1072 

Waltershausen,   S.  von,  cited,   879 

Walther,  Johannes,  cited,  23,  32,  34,  37,  52, 
54,  56,  57,  6p,  61,  97,  120,  138,  140, 
144,  167,  176,  207,  208,  225,  263,  271, 
300,  336,  354,  355,  357,  362,  368,  372, 
373,  382,  383,  397,  40i,  437,  439,  44<>, 
441,  458,  461,  466,  470,  522,  541,  542, 
552,  554,  56i,  573,  58i,  592,  603,  604, 
605,  626,  634,  639,  697,  700,  701,  703, 
704,  711,  712,  714,  718,  722,  748,  749, 
775,  854,  856,  858,  861,  879,  892,  896, 
987,  993,  995,  999,  1008,  ion,  1021, 
1022,  1031,  1039,  1068,  1072,  1134,  1150 

,  quoted,  371 

Walther,  J.,  and  Schirlitz,  R.,  cited,  334, 
383 

Warsaw  limestone,  cross-bedding  of,  704 

Wasatch  formation,  629,   855,  856 

River,   analyses  of  clays  of,   624 

Washington,  basaltic  plateau  of,  867 
Washita  formation,   729,  739 
Waste-lake,  Arkansas,   587 
Waste-stream,  541 

Water,  density  of,  179 

,  heat  capacity  of,   182 

,  heat  conductivity  of,  182 

,  potable,    161 

Waterlime,  1124 
Water  plane,  141 
Water  vapor,  24,  25,  29 

,  amount  of,  26 

,  source  of,  27 

Watson,  T.  L.,  cited,   23 

Wauwatosa    (Wis.),    fossil   reefs  at,    419 

Wave  activity,  depth  of,  647 

Wave  marks,   708 

Weald,   dome  of,  847 

Wealden,  the,   850 

Weathering,   belt    of,    17,    34,    39,    139,    747 

Weber,  C.  A.,  cited,   522 

,  M.,  cited,  68 1,  690 

Weber  River,  calcium  carbonate  in,  468 
Weed,    W.    H.,    cited,    346,    347,    383,    476, 

477,   522 

,  quoted,  346,  476,  477 

Weed,   W.    H.,   and   Pirsson,    L.   V.,    cited, 

306 
Weissliegende,   375 

,  dune  origin  of,  571 

Welding,  751 

Weller,     S.,    cited,     791,    823,     1072,     1124, 

1139,    1144,    1150 
Wellfleet,    sands    from,   559 

,  sand  plains  of,  600 

Wengen   formation,   434,   435 
Wenlock,  ballstone  reefs  of,  446 

Edge,  446,  838 

,  reefs  of,    418 

Werner,  A.  G.,  cited,  874,  1098,  1099,  1122, 

1123 

Wernsee,   246 
Werthausen.  245 

Wesenberg-Lund,   C.,   cited,   471,    522 
West  African  trough,   105 
West  Atlantic,   reefs  in,  411 
West  Elk  Mts.,  308 


West  Indies,  386,  412 

,  dust  falls  at,  60 

,  fringing    reefs    in,    390 

West  Palm  Beach,  226,  293 
Wethered,   E.,   cited,   472,   522 
Wetterstein   Kalk,   471 
Weule,  K.,  cited,   690 
Whale  rise  (ridge),  105 

,  temperatures  on,    188 

Wheeler,   W.   H.,   cited,   225,    268,   656,    690 

,   quoted,   219,    221-225,    231 

Wherry,  E.  T.,  cited,  365,  383 
Whimper,    E.,   cited,    792,   883,   909 
Whirlwinds,   47 
Whitby,  ammonites  of,   1086 

,  jet  from,  483 

White,  C.  H.,  cited,  718,   1082,   1096 
White,  David,  cited,  519,  523,  535,  539,  722, 

1 150 
White   Cliff  sandstone,   dune  origin  of,    571 

— ,  eolian    cross-bedding    in,    704 

White  Mountains,  ice  crystals  on,  62 

,  pebbles  in   streams  of,   596 

,  relicts  in,  1066 

White    River    beds,    cross-bedding    of,    84 

,  loess-like  origin  of,  568 

White  Sea,    in 

,  temperature  of,   193 

Whitney,   M.,   cited,   657,    690,   883 
Whitsunday  Island,  388 
Wick,   harbor  of,   222 
Wieland,   G.   R.,   cited,   761,   775 
Wieliczka,    351 
Wilbur  limestone,   68 1 
Wilckens,  O.t  cited,  459,  466 
Wilckes,   cited,   204 
Wildon,   246 

Williams,  H.  S.,  cited,  1072,  1108,  1118, 
1 1 20,  1124,  1150 

,  quoted,   1125 

Williams  canyon,  310 

,  unconformity  in,   824 

Williamsville,  425,  426 

Willis,  B.,  cited,  81,  97,  534,  539,  654,  661, 
662,  673,  682,  845,  903,  909,  1 1 10, 
1120,  1145,  1146,  1150 

,  quoted,    653,    673,    674,    690 

,  and  Salisbury,  R.  D.,  cited,   1150 

Williston,   S.   W.,  cited,    1072 

,  and  Case,  E.  C.,  cited,  633,  640 

Wills.  L.  J.,  cited,  98 
Wilmington,   soda  beds  at,  361 
Wilson,  A.  W.  G.,  cited,  724,  731,  732,  745, 
838,   858 

,  J.  H.,   cited,   126,   144,  326,   599,  600, 

640 

Wiman,  C.,  cited,  420,  421,  466,  1083,   1096 
Winchell,  A.,  cited,    1108 
Wind,  carrying  power  of,   55 

,  influence  of  mountains  on,  47 

,  rounding  of  sand  grains  by,   61 

,  sorting  power  of,   61 

,  velocities  of,  50,  56 

Windkanter,   54 

Wind   River,   analyses  of  clays  of,   624 
Wind   River   Basin,   Eocenic  and  Oligocenic 
of,  627 

,  tuff   bed    of,    525 

Winds,   easterlies,   43 

mountain  and  valley,    50 

Permic  westerlies,  374 

— i —    planitary,    44 

prevailing,   44 

special  types,  49,   50 

trade,  43,  67 

westerlies,   43,   69,   356,   652 

Windsor  limestone  fauna,    1069 
Winnebago  Lake,  837 


INDEX 


1185 


Winnemucca   Lake,    salinity   of,    155 

Winter   Park,   fish   falls  of,    56 

Wisconsin,  oolitic  iron  ore  of,  283,  473,  762 

,  reefs   of,   419,    420 

Withered,   cited,  455 

Witteberg   series,   536 

Wittecliff,  225 

Witwatersrand  Mines,    14,    15 

Wollny,  E.,  cited,  287 

Wooburn,   greensands  of,   671,   672 

Woods    Hole,    392,     1041 

Woodward,  R.  S.,  cited,  23,  200,  208 
— ,   S.  P.,  cited,    1020,   1039,    1055,   1072    * 

Woodworth,  J.  B.,  cited,  262,  268,  571, 
581,  599,  640,  790,  828,  887,  909,  1090, 
1091,  1096 

,  quoted,  791 

Worcester  lowland,  839 

Worth,    R.    H.,    cited,    690 

Wrangell    and    Spindler,    cited,    153 

Wright,  G.   F.,   cited,   566.   581 

Wiirttemberg,   Bunter   Sandstein  of,    1034 
enterolithic   structure   in,   758,    759 
Ichthyosaurians  in  Lias  of,   1078 
jet    from    Lias    of,    483 
Jurassic  escarpment  of,  838 
Jurassic  lutytes  of,   786 
origin  of  Liassic  black  shales  of,   678 

Wye   River,    227,    662 

Wynne,    A.    B.,   cited,    640 

,  quoted,  592 

Wyoming,    soda   lakes  of,    361 

Wyoming  county,   New   York,   378 

Wyville-Thomson  ridge,  106,  no,  188,  192, 
218 


Yakutat   Bay,    324 

,  earthquake  of,   888 

Yakutsk   (Siberia),    31 

,    frozen   soil  at,   200 

Yang-tse-Kiang,   248,   585 

,  Cambric  glacial  deposits  of,  81,  534 

,  red  mud  of,  669 

Yardangs,   53,   53,  856 

Yavapai  county,  Ariz.,  onyx  marble  of,  344 

Yellow  River,   dissection  of  loess  by,   566 

Yellowstone  Park,    304 

,  columnar   structure   in,    319 


Yellowstone  Park,  hot  springs  of,  201,  202, 
343.    475 

— ,   rhyolite  flows  of,   313 
Yeniseisk    (Siberia),    27 
Yeo   River,   663 
Yokoyama,  M.,   cited,  89,  98,  897 

— ,  quoted,    91 
Yorkshire,   839 

,  erosion  of  chalk  cliffs  of,  225 

,  marine  erosion  in,  224 

Yucatan,  335,  357 

basin,    108 

Sea,  temperature  of,    190 

Yukon,   humus  on  delta  of,   508 
Yuma    (Arizona),   27 


Zacharius,   Q.,  cited,  998 
Zagazig,  boring  at,  594 
Zambesi   delta,    615 

River,    116 

shelf,    103 

Zandt,  quarries  of,  439 

Zante,    earthquake    scarp    near,    890 
Zechstein,  bryozoan  reefs  of,  375,  433 

,  erosion  cliff  of,   225 

,  salt  in,   756 

Sea,    120,  373,   376 

Zeolites,    177 

Zepce,  pisoliths  of,  284 

Ziegler,    V.,    cited,    254,   268,   473,   523,    762, 

775 

Zirkel,   F.  von,  cited,  270,  300,  336,   383 
Zittel,   K.  A.  von,   cited,   98,   454,    552,   562, 

581,   956 

,   quoted,    1073 

Zoarium,    943 
Zooecia,  943 
Zoogenic  deposits,  384 
Zooliths,  280 
Zoology,  20 
Zoosphere,   16,  910 
Zug,  784 

,   subaqueous  gliding  at,   657,   780 

Zug  spitze,   massif  of,   436 
Zuidersee,  223 

,   deepening  of,   558 

Zurich,  Lake  of,  subaqueous  gliding  in,  657, 

780 


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